Medical ultrasound

Medical ultrasound includes diagnostic techniques (mainly imaging) using ultrasound, as well as therapeutic applications of ultrasound. In diagnosis, it is…

Medical ultrasound encompasses both diagnostic methodologies, primarily imaging, and therapeutic applications of ultrasonic technology. Diagnostically, it facilitates the visualization of internal anatomical structures, including tendons, muscles, joints, blood vessels, and organs. Furthermore, it enables the quantification of specific parameters, such as distances and velocities, or the generation of discernible acoustic signals. The application of ultrasound for generating visual medical images is termed medical ultrasonography, often abbreviated as sonography. When sonography relies on ultrasound reflection, it is specifically referred to as echography. Additionally, transmission-based techniques exist, exemplified by ultrasound transmission tomography. The examination of pregnant individuals via ultrasound is known as obstetric ultrasonography, representing a foundational advancement in clinical ultrasonography. The instrumentation employed for this purpose is variously designated as an ultrasound machine, a sonograph, or an echograph. The resulting visual representation generated by this technique is termed an ultrasonogram, a sonogram, or an echogram.

Medical ultrasound includes diagnostic techniques (mainly imaging) using ultrasound, as well as therapeutic applications of ultrasound. In diagnosis, it is used to create an image of internal body structures such as tendons, muscles, joints, blood vessels, and internal organs, to measure some characteristics (e.g., distances and velocities) or to generate an informative audible sound. The usage of ultrasound to produce visual images for medicine is called medical ultrasonography or simply sonography. Sonography using ultrasound reflection is called echography. There are also transmission methods, such as ultrasound transmission tomography. The practice of examining pregnant women using ultrasound is called obstetric ultrasonography, and was an early development of clinical ultrasonography. The machine used is called an ultrasound machine, a sonograph or an echograph. The visual image formed using this technique is called an ultrasonogram, a sonogram or an echogram.

Ultrasound consists of sound waves possessing frequencies exceeding 20,000 Hz, which approximates the upper limit of human auditory perception. Ultrasonic images, alternatively known as sonograms, are generated through the emission of ultrasound pulses into biological tissue via a specialized probe. These ultrasound pulses reflect from tissues exhibiting varying acoustic impedance, subsequently returning to the probe, which then records and renders them as a visual image.

While a general-purpose ultrasonic transducer suffices for the majority of imaging applications, certain scenarios necessitate the deployment of specialized transducers. The predominant method for ultrasound examination involves positioning a transducer on the body's external surface; however, superior visualization can frequently be achieved by placing a transducer internally. Consequently, specialized transducers, such as transvaginal, endorectal, and transesophageal types, are routinely utilized for internal imaging. In advanced applications, exceptionally miniature transducers can be integrated onto small-diameter catheters and inserted into blood vessels to facilitate imaging of vascular walls and associated pathologies.

Uses

Sonography (ultrasonography) is extensively employed within the medical field, facilitating both diagnostic and therapeutic procedures. Ultrasound can guide interventional procedures, such as biopsies or the drainage of fluid collections, serving both diagnostic and therapeutic purposes. Sonographers are medical professionals who conduct these scans, which are traditionally interpreted by radiologists—physicians specializing in the application and interpretation of medical imaging modalities—or by cardiologists for cardiac ultrasonography (echocardiography). Sonography proves effective for imaging the body's soft tissues. Superficial structures, including muscle, tendon, testis, breast, thyroid and parathyroid glands, and the neonatal brain, are imaged at higher frequencies (7–18 MHz), yielding superior linear (axial) and horizontal (lateral) resolution. Conversely, deeper structures like the liver and kidney are imaged at lower frequencies (1–6 MHz), resulting in reduced axial and lateral resolution in exchange for greater tissue penetration.

Anesthesiology

In anesthesiology, ultrasound is routinely employed to guide needle placement for injecting local anesthetic solutions near nerves identified via ultrasound imaging (nerve block). It also facilitates vascular access, including the cannulation of large central veins and challenging arterial cannulations. Neuro-anesthesiologists frequently utilize transcranial Doppler to acquire data regarding flow velocity within the basal cerebral vessels.

Angiology (Vascular Medicine)

In angiology or vascular medicine, duplex ultrasound—which combines B-mode imaging with Doppler flow measurement—is utilized for diagnosing arterial and venous disease. This application holds particular significance in cases of potential neurological issues, where carotid ultrasound is routinely employed to assess blood flow and identify potential or suspected stenosis in the carotid arteries, while transcranial Doppler is applied for imaging flow in the intracerebral arteries.

Intravascular ultrasound (IVUS) employs a specially designed catheter with a miniaturized ultrasound probe affixed to its distal end, which is subsequently advanced into a blood vessel. The catheter's proximal end connects to computerized ultrasound equipment, enabling the application of ultrasound technology, such as a piezoelectric transducer or capacitive micromachined ultrasonic transducer, for visualizing the endothelium of blood vessels in vivo.

For the prevalent and potentially serious issue of blood clots in the deep veins of the leg, ultrasound assumes a pivotal diagnostic role. Concurrently, ultrasonography of chronic venous insufficiency in the legs concentrates on more superficial veins to aid in planning appropriate interventions for symptom relief or cosmetic enhancement.

Cardiology (Heart)

Echocardiography is an essential tool in cardiology, assisting in the evaluation of heart valve function, including stenosis or insufficiency, cardiac muscle contractility, and hypertrophy or dilatation of the main cardiac chambers (ventricle and atrium).

Emergency Medicine

Point-of-care ultrasonography offers numerous applications within emergency medicine. These encompass the differentiation of cardiac versus pulmonary etiologies of acute dyspnea, as well as the Focused Assessment with Sonography for Trauma (FAST) examination, which is often extended to the Extended Focused Assessment with Sonography for Trauma (EFAST) to evaluate for substantial hemoperitoneum or pericardial tamponade following traumatic injury. Furthermore, ultrasonography aids in distinguishing various causes of abdominal pain, such as cholelithiasis and nephrolithiasis. Emergency Medicine Residency Programs have a well-established history of advocating for the integration of bedside ultrasonography into physician training curricula.

Gastroenterology and Colorectal Surgery

Both abdominal and endoanal ultrasonography are commonly employed in gastroenterology and colorectal surgery. In abdominal sonography, the principal abdominal organs, including the pancreas, aorta, inferior vena cava, liver, gallbladder, bile ducts, kidneys, and spleen, can be visualized. Nevertheless, the presence of intestinal gas can obstruct sound waves, and adipose tissue can attenuate them to varying extents, occasionally impeding diagnostic efficacy. When inflamed, the appendix may be visualized (e.g., in cases of appendicitis), and ultrasonography serves as the preferred initial imaging modality to minimize radiation exposure, although it often necessitates subsequent corroboration with other imaging techniques, such as computed tomography (CT). Endoanal ultrasonography is particularly valuable for investigating anorectal symptoms, including fecal incontinence or obstructed defecation. This technique provides imaging of the immediate perianal anatomy and can identify concealed defects, such as anal sphincter tears.

Hepatology

Ultrasonography of liver tumors facilitates both their detection and characterization. Ultrasonographic imaging is frequently utilized during the assessment of fatty liver disease. This modality typically demonstrates a "bright" liver, indicative of increased echogenicity. Furthermore, portable, pocket-sized ultrasound devices may serve as point-of-care screening instruments for the diagnosis of hepatic steatosis.

Gynecology and Obstetrics

Gynecologic ultrasonography involves the examination of female pelvic organs, notably the uterus, ovaries, and fallopian tubes, in addition to the bladder, adnexa, and the Pouch of Douglas. This modality employs transducers engineered for lower abdominal wall approaches, including curvilinear and sector types, alongside specialized transducers such as those used for transvaginal ultrasonography.

Obstetrical sonography originated in the late 1950s and 1960s through the pioneering work of Sir Ian Donald, and it is routinely employed during pregnancy to monitor fetal development and presentation. This technique can identify numerous conditions potentially detrimental to the mother and/or fetus that might otherwise remain undiagnosed or experience delayed diagnosis without sonographic assessment. Presently, the consensus suggests that the risks associated with delayed diagnosis outweigh any minimal risks, if present, linked to undergoing an ultrasound examination. Nevertheless, its application for non-medical purposes, such as creating fetal "keepsake" videos and photographs, is not recommended.

Obstetric ultrasonography serves several primary functions, including:

Determining gestational age.
Confirming fetal viability.
Ascertaining fetal location, distinguishing between intrauterine and ectopic pregnancies.
Assessing placental location relative to the cervix.
Identifying the number of fetuses (e.g., in multiple pregnancies).
Screening for major physical abnormalities.
Evaluating fetal growth, particularly for indicators of intrauterine growth restriction (IUGR).
Monitoring fetal movement and cardiac activity.
Determining fetal sex.

According to the European Committee of Medical Ultrasound Safety (ECMUS):

Ultrasonic examinations must only be conducted by qualified personnel who possess current training and expertise in safety protocols. Ultrasound generates thermal effects, pressure fluctuations, and mechanical disturbances within biological tissues. Diagnostic ultrasound levels are capable of inducing temperature elevations that pose risks to sensitive organs, as well as to the embryo or fetus. While non-thermal biological effects have been documented in animal studies, no comparable effects have been observed in humans to date, with the exception of instances involving micro-bubble contrast agents.

Consequently, it is imperative to employ low power settings and to refrain from pulsed wave scanning of the fetal brain, unless explicitly indicated in high-risk pregnancies.

Data published by the UK Government's Department of Health for the 2005–2006 period indicate that non-obstetric ultrasound examinations accounted for over 65% of all ultrasound scans performed.

Hemodynamics (Blood Circulation)

The velocity of blood flow can be assessed in diverse vascular structures, including the middle cerebral artery and descending aorta, utilizing relatively affordable and low-risk ultrasound Doppler probes connected to portable monitoring devices. This methodology facilitates non-invasive or transcutaneous (non-piercing) minimally invasive evaluation of blood flow. Prominent applications include transcranial Doppler, esophageal Doppler, and suprasternal Doppler.

Otolaryngology (Head and Neck Applications)

High-frequency ultrasound offers excellent visualization of most cervical structures, encompassing the thyroid and parathyroid glands, lymph nodes, and salivary glands, providing exceptional anatomical detail. For thyroid tumors and lesions, ultrasound is the imaging modality of choice, playing a crucial role in the assessment, preoperative strategizing, and postoperative monitoring of individuals diagnosed with thyroid cancer. Furthermore, diagnostic ultrasound and ultrasound-guided interventions facilitate the differentiation, evaluation, and management of numerous other benign and malignant conditions affecting the head and neck region.

Neonatology Applications

Within neonatology, transcranial Doppler is employed for the fundamental assessment of intracerebral structural anomalies, suspected hemorrhages, ventriculomegaly or hydrocephalus, and anoxic injuries such as periventricular leukomalacia. This procedure can be conducted through the fontanelles, the soft spots in a newborn infant's skull, until their complete closure around one year of age, at which point they present an almost impenetrable acoustic barrier to ultrasound waves. The anterior fontanelle serves as the most frequently utilized site for cranial ultrasound; however, a smaller fontanelle size correlates with increased image degradation.

Lung ultrasound has demonstrated utility in diagnosing prevalent neonatal respiratory conditions, including transient tachypnea of the newborn, respiratory distress syndrome, congenital pneumonia, meconium aspiration syndrome, and pneumothorax. A neonatal lung ultrasound score, initially delineated by Brat et al., exhibits a strong correlation with oxygenation levels in neonates.

Ophthalmology (eyes)

Ophthalmology and optometry utilize two primary modalities of ocular examination involving ultrasound:

A-scan ultrasound biometry, frequently termed an A-scan (amplitude scan), operates in A-mode to furnish data regarding the axial length of the eye. This measurement is a critical determinant in prevalent visual disorders, particularly for calculating the appropriate power of an intraocular lens following cataract extraction.
B-scan ultrasonography, also known as a B-scan-Brightness scan, employs B-mode to generate a cross-sectional visualization of the eye and its orbit. This non-invasive technique, operating at frequencies between 10–15 MHz, serves as an indispensable ophthalmological instrument for diagnosing and managing a broad spectrum of conditions impacting the posterior ocular segment. It is frequently integrated with other imaging modalities, such as Optical Coherence Tomography (OCT) or fluorescein angiography, to facilitate a more exhaustive assessment of ophthalmic pathologies.

Pulmonology (Lungs)

Ultrasound serves as a diagnostic tool for pulmonary assessment across diverse clinical environments, including critical care, emergency medicine, trauma surgery, general medicine, and nursing. This imaging modality is deployed at the patient's bedside or examination table to evaluate various lung abnormalities, guide respiratory therapy, inform mechanical ventilation strategies, and facilitate procedures such as thoracentesis (pleural fluid drainage), needle aspiration biopsy, and catheter insertion. While the presence of air within the lungs impedes optimal penetration of ultrasound waves, the analysis of specific artifacts generated on the lung surface enables the detection of pathological conditions.

Pulmonary ultrasound, rather than directly visualizing the lung parenchyma, primarily assesses the tissue-air interface at the pleural line. The critical reliance on artifact interpretation distinguishes lung ultrasound from imaging modalities designed to depict solid organs. This fundamental difference carries significant mechanical implications for interpreting artifactual patterns. While contemporary sonography often employs software filters and acoustic harmonics to improve the visualization of organs like the heart or liver, these enhancements can distort the specific patterns crucial for lung ultrasound analysis. Consequently, a software preset devoid of imaging filters, harmonic imaging, and beam compounding is generally favored for pulmonary examinations.

Fundamentals of Lung Ultrasound

The Normal Lung Surface: The pulmonary surface comprises both visceral and parietal pleura. These two pleural layers are typically apposed, forming the pleural line, which constitutes the fundamental element of lung (or pleural) ultrasonography. In the majority of adults, this line is discernible less than one centimeter beneath the costal margin. When imaged ultrasonographically, it appears as a hyperechoic (bright white) horizontal demarcation, provided the ultrasound transducer is positioned orthogonally to the integument.
Artifacts: Pulmonary ultrasonography fundamentally utilizes artifacts, which in other imaging modalities would typically be regarded as impediments. Given that air obstructs ultrasound propagation, direct visualization of healthy pulmonary parenchyma via this imaging technique is impractical. Consequently, clinicians and sonographers have developed expertise in identifying characteristic patterns generated by ultrasound beams when differentiating between healthy and pathological lung tissue. Three frequently observed and diagnostically significant artifacts in lung ultrasonography are lung sliding, A-lines, and B-lines.
- § Lung Sliding: The manifestation of lung sliding, characterized by a shimmering effect of the pleural line resulting from the reciprocal movement of the visceral and parietal pleura during respiration (occasionally likened to 'ants marching'), represents the most critical indicator of normally aerated lung. This phenomenon signifies both the apposition of the lung to the thoracic wall and its functional integrity.
- § A-lines: Upon impingement of the ultrasound beam on the pleural line, a reflection occurs, manifesting as a prominent hyperechoic horizontal line. The resultant reverberation artifacts, observed as equidistant horizontal lines deep to the pleura, are termed A-lines. Fundamentally, A-lines represent reflections of the ultrasound beam originating from the pleura, with the interval between successive A-lines correlating to the distance between the parietal pleura and the cutaneous surface. The presence of A-lines signifies the existence of air, implying that these artifacts may be observed in healthy pulmonary tissue, as well as in individuals presenting with pneumothorax.
- § B-lines: B-lines similarly constitute reverberation artifacts. They are ultrasonographically depicted as hyperechoic vertical lines originating from the pleura and extending to the periphery of the ultrasound display. These demarcations are characterized by their sharp definition and laser-like appearance, generally maintaining their intensity as they traverse the screen. A limited number of B-lines, exhibiting movement synchronous with the sliding pleura, may be observed in healthy lungs, attributable to variations in acoustic impedance between water and air. Conversely, an abundance of B-lines (defined as three or more) is considered pathological and generally signifies an underlying pulmonary disorder.

Pulmonary Pathologies Evaluated by Ultrasonography

Pulmonary edema: Pulmonary ultrasonography has demonstrated high sensitivity in identifying pulmonary edema. This modality facilitates enhanced diagnostic accuracy and management strategies for critically ill patients, especially when integrated with echocardiography. The characteristic sonographic finding in pulmonary edema is the presence of multiple B-lines. While B-lines may occasionally be observed in healthy lungs, the detection of three or more in the anterior or lateral pulmonary fields consistently indicates an abnormal condition. In the context of pulmonary edema, B-lines signify an elevated extravascular lung water content. Furthermore, B-lines may manifest in various other pathologies, such as pneumonia, pulmonary contusion, and lung infarction. It is crucial to recognize that diverse interactions between the pleural surface and the ultrasound wave can produce artifacts superficially resembling B-lines, yet lacking pathological relevance.
Atelectasis: In contrast to artifactual patterns, pulmonary consolidations are directly visualized through lung ultrasonography. The characterization of intrapulmonary consolidations can be achieved using qualitative criteria, including the identification of dynamic or static air bronchograms, which represent air entrapped within smaller airways embedded within the consolidated tissue. Consequently, pathognomonic alterations associated with resorptive and compressive atelectasis can be differentiated.
Pneumothorax: In clinical scenarios where pneumothorax is suspected, lung ultrasound serves as a valuable diagnostic tool. The presence of air between the pleural layers in pneumothorax results in the absence of lung sliding during an ultrasound examination. The reported negative predictive value for lung sliding on ultrasound ranges from 99.2% to 100%, indicating that the presence of lung sliding effectively excludes a pneumothorax. However, the absence of lung sliding is not exclusively indicative of pneumothorax, as other conditions such as acute respiratory distress syndrome, lung consolidations, pleural adhesions, and pulmonary fibrosis can also manifest this finding.
Pleural effusion: Lung ultrasound offers a cost-effective, safe, and non-invasive imaging modality for the rapid visualization and diagnosis of pleural effusions. While effusions can be identified through physical examination, percussion, and chest auscultation, the sensitivity of these traditional methods can be compromised by factors such as mechanical ventilation, obesity, or specific patient positioning. Therefore, lung ultrasound serves as a valuable supplementary diagnostic instrument, complementing plain chest X-rays and chest computed tomography. On ultrasound, pleural effusions manifest as distinct structural images within the thorax, rather than artifacts, typically exhibiting four defined borders: the pleural line, two rib shadows, and a deep border. For critically ill patients presenting with pleural effusion, ultrasound can also facilitate procedural guidance for interventions like needle insertion, thoracentesis, and chest-tube placement.
Lung cancer staging: In pulmonology, endobronchial ultrasound (EBUS) probes are integrated with standard flexible endoscopic probes, enabling pulmonologists to directly visualize endobronchial lesions and lymph nodes before performing transbronchial needle aspiration. Among its diverse applications, EBUS significantly contributes to lung cancer staging by facilitating lymph node sampling, thereby obviating the necessity for major surgical intervention.
COVID-19: Lung ultrasound has demonstrated utility in the diagnosis of COVID-19, particularly in situations where other diagnostic modalities are inaccessible.

Urinary Tract

Ultrasound is routinely employed in urology to quantify residual fluid within a patient's bladder. Pelvic sonography provides detailed images, encompassing the uterus, ovaries, or urinary bladder in female patients. For male patients, sonographic examinations yield information concerning the bladder, prostate, or testicles, enabling urgent differentiation between conditions such as epididymitis and testicular torsion. In younger males, ultrasound is instrumental in distinguishing benign testicular masses, such as varicoceles or hydroceles, from testicular cancer, which, while curable, necessitates timely treatment to safeguard health and fertility. Pelvic sonography can be performed via two primary methods: externally or internally. Internal pelvic sonography is conducted either transvaginally in women or transrectally in men. Sonographic imaging of the pelvic floor offers crucial diagnostic insights into the precise anatomical relationships between abnormal structures and other pelvic organs, providing valuable guidance for managing patients experiencing symptoms related to pelvic prolapse, double incontinence, and obstructed defecation. Furthermore, ultrasound is utilized for diagnosing and, at higher frequencies, for treating (fragmenting) kidney stones or kidney crystals, a condition known as nephrolithiasis.

Penis and Scrotum

Scrotal ultrasonography is employed for evaluating testicular pain and for identifying solid masses within the scrotum.

Ultrasound represents an excellent modality for examining the penis, particularly in cases involving trauma, priapism, erectile dysfunction, or suspected Peyronie's disease.

Musculoskeletal System

Musculoskeletal ultrasound is utilized for the examination of tendons, muscles, nerves, ligaments, soft tissue masses, and bone surfaces. It proves beneficial in diagnosing ligament sprains, muscle strains, and various joint pathologies. For pediatric patients up to 12 years of age, it serves as an alternative or supplementary imaging technique to X-ray for detecting fractures of the wrist, elbow, and shoulder, a practice known as fracture sonography.

Quantitative ultrasound functions as an adjunctive musculoskeletal assessment for diagnosing myopathic disease in children, estimating lean body mass in adults, and providing proxy measures of muscle quality (i.e., tissue composition) in older adults afflicted with sarcopenia.

Furthermore, ultrasound can facilitate needle guidance for muscle or joint injections, exemplified by ultrasound-guided hip joint injections.

Kidneys

Renal ultrasonography is indispensable for the diagnosis and management of nephrological conditions. This imaging modality facilitates straightforward examination of the kidneys, enabling the identification of most pathological alterations. Its accessibility, versatility, cost-effectiveness, and rapid application make it a valuable tool for clinical decision-making in patients presenting with renal symptoms and for guiding renal interventions. B-mode imaging readily permits the assessment of renal anatomy, and ultrasound is frequently employed for image guidance during renal procedures. Recent advancements include the integration of contrast-enhanced ultrasound (CEUS), elastography, and fusion imaging into renal ultrasonography. Nevertheless, renal ultrasonography possesses inherent limitations, necessitating the consideration of complementary imaging techniques, such as computed tomography (CECT) and magnetic resonance imaging (MRI), for comprehensive renal disease assessment.

Venous Access Procedures

Intravenous access constitutes a routine medical procedure, essential for purposes such as collecting blood samples for diagnostic or laboratory investigations, including blood cultures, and for administering intravenous fluids for hydration, replacement therapy, or blood transfusions in critically ill patients. This requirement extends across various clinical settings, including outpatient laboratories, inpatient hospital wards, and, most critically, emergency departments and intensive care units. Frequently, intravenous access is needed recurrently or for extended durations. In such prolonged scenarios, a needle encased within a catheter is initially introduced into the vein; the catheter is then advanced securely, and the needle subsequently retracted. While veins in the arm are typically preferred, challenging cases may necessitate accessing deeper veins, such as the external jugular vein in the neck or the subclavian vein in the upper arm. Numerous factors can complicate the selection of an appropriate vein. These factors encompass, but are not restricted to, obesity, prior venous injury resulting from inflammatory reactions to previous venipunctures, and damage sustained from recreational drug use.

In such difficult scenarios, ultrasound guidance has significantly facilitated the successful insertion of venous catheters. The ultrasound equipment can be either cart-mounted or handheld, typically employing a linear transducer operating at a frequency range of 10 to 15 megahertz. Generally, vein selection is constrained by the necessity for the vessel to be located within 1.5 centimeters of the skin surface. The transducer can be positioned either longitudinally or transversely over the target vein. Training in ultrasound-guided intravenous cannulation is a standard component of most ultrasound education curricula.

Operational Mechanism

The process of generating an image from sound waves involves three distinct stages: transmitting a sound wave, receiving the resultant echoes, and subsequently interpreting these echoes.

Sound Wave Generation

Sound waves are generally generated by a piezoelectric transducer, which is encapsulated within a plastic housing. The transducer is activated by powerful, brief electrical pulses emitted from the ultrasound machine, operating at a predetermined frequency. While typical operating frequencies range from 1 to 18 MHz, experimental applications, such as biomicroscopy in specialized anatomical areas like the anterior chamber of the eye, have utilized frequencies as high as 50–100 megahertz.

Earlier transducer technologies employed physical lenses for beam focusing. Modern transducers, however, utilize digital antenna array techniques, where piezoelectric elements within the transducer generate echoes at varying times, allowing the ultrasound machine to dynamically adjust the beam's direction and focal depth. Proximal to the transducer, the ultrasound beam's width approximates that of the transducer itself. Upon reaching a specific distance, termed the near zone length or Fresnel zone, the beam narrows to half its initial width. Beyond this point, in the far zone length or Fraunhofer's zone, the beam diverges, leading to a reduction in lateral resolution. Consequently, a wider transducer and a higher ultrasound frequency extend the Fresnel zone, thereby preserving lateral resolution at increased depths from the transducer. Ultrasound waves propagate as discrete pulses. Accordingly, a shorter pulse length necessitates a broader bandwidth, implying a greater range of frequencies, to form the ultrasound pulse.

As previously indicated, acoustic energy is focused through several mechanisms: the intrinsic design of the transducer, the integration of a lens positioned anterior to the transducer, or the application of intricate control pulses generated by the ultrasound scanner, employing techniques such as beamforming or spatial filtering. This focusing action generates an arc-shaped sound wave emanating from the transducer's surface. Subsequently, this wave propagates into the biological tissue, converging at a predetermined depth.

Specialized materials integrated into the transducer's face facilitate the efficient transmission of acoustic energy into the body, frequently comprising a rubbery coating that functions as an impedance matching layer. Furthermore, a water-based gel is applied between the patient's epidermis and the probe to enhance ultrasound propagation into the biological medium. This practice is necessitated by the fact that air induces total reflection of ultrasound, thereby obstructing its effective transmission into the body.

The propagating sound wave undergoes partial reflection at interfaces between dissimilar tissues or is scattered by minute anatomical structures. Specifically, acoustic energy is reflected wherever variations in acoustic impedance occur within the body, such as between blood cells and blood plasma, or within small structures embedded in organs. A portion of these reflections subsequently returns to the transducer.

Reception of Echoes

The return of the acoustic wave to the transducer initiates a process that mirrors the transmission phase, albeit in reverse. The incident reflected sound wave causes the transducer to vibrate, and these mechanical vibrations are subsequently converted by the transducer into electrical pulses. These pulses are then transmitted to the ultrasonic scanner for processing and transformation into a digital image.

Image Formation

For image generation, the ultrasound scanner is required to ascertain two distinct characteristics from each received echo:

The temporal interval between the transmission of the sound pulse and the reception of its corresponding echo. (It is important to note that time and distance are directly proportional in this context.)
The amplitude or intensity of the received echo.

Upon determining these two parameters, the ultrasonic scanner can precisely identify the corresponding pixel within the image matrix to be illuminated and specify its appropriate intensity.

The conversion of the received ultrasonic signal into a digital image can be elucidated through an analogy involving a blank spreadsheet. Initially, one might conceptualize a linear, planar transducer positioned at the apex of this sheet. Acoustic pulses are then transmitted sequentially down the 'columns' of the spreadsheet (e.g., A, B, C). For each column, the system monitors for returning echoes. Upon detection of an echo, the duration of its return journey is recorded. A longer temporal delay corresponds to a greater depth within the 'rows' (e.g., 1, 2, 3). The intensity of the echo dictates the brightness assigned to the respective cell, with strong echoes represented by white, weak echoes by black, and intermediate intensities by various shades of grey. Once all echoes have been systematically recorded across the sheet, a complete grayscale image is rendered.

In contemporary ultrasound systems, image generation relies upon the collective reception of echoes by an array of multiple transducer elements, rather than a singular element. These individual elements within the transducer array operate synergistically to acquire signals, a mechanism critical for optimizing the ultrasonic beam's focal properties and generating high-resolution images. A prominent technique employed for this purpose is "delay-and-sum" beamforming. The precise time delay applied to each element is computed based on the geometric interrelationship among the imaging point, the transducer, and the receiver locations. Through the integration of these temporally adjusted signals, the system achieves precise focusing on specific tissue regions, thereby augmenting image resolution and clarity. The combined application of multi-element reception and delay-and-sum principles forms the fundamental basis for the superior image quality observed in modern ultrasonography.

Image Display

Images generated by the ultrasound scanner are transmitted and rendered utilizing the DICOM standard. Typically, minimal post-processing is subsequently applied.

Acoustic Propagation within Biological Tissues

Ultrasonography, also known as sonography, employs a probe equipped with multiple acoustic transducers to emit pulses of sound into a medium. When an acoustic wave encounters a material possessing a distinct density, characterized by a differing acoustical impedance, a portion of the sound wave is scattered, while another segment is reflected back towards the probe and subsequently detected as an echo. The temporal interval required for the echo to return to the probe is precisely measured and utilized to compute the depth of the tissue interface responsible for generating the echo. A greater disparity in acoustic impedances correlates with an increased amplitude of the echo. Should the ultrasonic pulse encounter gases or solids, the substantial density difference results in the reflection of the majority of the acoustic energy, thereby precluding further penetration.

Frequencies employed in diagnostic medical imaging typically range from 1 to 18 MHz. Higher frequencies result in shorter wavelengths, which facilitate the acquisition of higher-resolution sonographic images. However, acoustic attenuation intensifies at higher frequencies, necessitating the application of lower frequencies (3–5 MHz) for effective penetration into deeper tissues.

Achieving deep tissue penetration using sonography presents significant challenges. A portion of acoustic energy dissipates with each echo formation, but the predominant energy loss (approximately $\textstyle 0.5{\frac {\mbox{dB}}{{\mbox{cm depth}}\cdot {\mbox{MHz}}}}$ ) results from acoustic absorption.

Acoustic wave propagation velocity fluctuates across diverse biological tissues and is contingent upon the material's acoustical impedance. However, sonographic instrumentation operates under the premise of a constant acoustic velocity, typically standardized at 1540 m/s. This inherent assumption leads to beam defocusing and a consequent reduction in image resolution when imaging heterogeneous biological structures.

The creation of a two-dimensional (2-D) sonographic image necessitates the sweeping of an ultrasonic beam. This sweeping action can be achieved mechanically, through transducer rotation or oscillation, or electronically, utilizing a one-dimensional (1-D) phased array transducer. Subsequently, the acquired data undergoes processing to reconstruct the image. The resulting image constitutes a 2-D depiction of the anatomical cross-section.

Three-dimensional (3-D) images are constructed by compiling a sequence of contiguous 2-D sonographic acquisitions. Typically, this involves a specialized probe that mechanically scans a conventional 2-D imaging transducer. Nevertheless, the inherent slowness of mechanical scanning impedes the effective generation of 3-D images for dynamic tissues. Recent advancements include the development of 2-D phased array transducers capable of volumetric (3-D) beam sweeping. Such transducers enable more rapid imaging and facilitate the acquisition of real-time 3-D visualizations, even for structures like a beating heart.

Doppler ultrasonography serves as a diagnostic tool for analyzing blood flow dynamics and muscular movement. Variations in detected velocities are typically rendered in color to enhance interpretability; for instance, a regurgitant jet from a leaky heart valve manifests as a distinct color flash. Alternatively, color mapping can signify the amplitudes of the received acoustic echoes.

Advanced Ultrasonography Techniques

A notable advancement in ultrasonography is bi-planar ultrasound, characterized by a probe incorporating two perpendicular 2D imaging planes, which enhances localization and detection efficiency. Moreover, an omniplane probe offers the capability to rotate 180°, thereby acquiring a multitude of images. For 3D ultrasound, numerous 2D planes are digitally synthesized to construct a comprehensive three-dimensional representation of the target object.

Principles of Doppler Ultrasonography

Doppler ultrasonography leverages the Doppler effect to ascertain the directional movement (towards or away from the transducer) and relative velocity of structures, predominantly blood. Through the computation of frequency shifts within a specific sample volume, parameters such as the speed and direction of arterial blood flow or valvular regurgitant jets can be precisely determined and visually represented. Color Doppler imaging quantifies velocity using a color-coded scale. Typically, Color Doppler images are integrated with grayscale (B-mode) images to produce duplex ultrasonography displays. Clinical applications encompass:

Doppler echocardiography employs Doppler ultrasonography for cardiac examination. An echocardiogram enables precise evaluation, within defined parameters, of blood flow direction and the velocity of blood and cardiac tissue at specific locations, utilizing the Doppler effect. These velocity measurements facilitate the assessment of cardiac valve areas and function, abnormal intracardiac communications, valvular insufficiency (regurgitation), and the calculation of cardiac output and the E/A ratio, an indicator of diastolic dysfunction. Contrast-enhanced ultrasound, utilizing gas-filled microbubble contrast media, may enhance velocity or other flow-related measurements of interest.
Transcranial Doppler (TCD) and transcranial color Doppler (TCCD) assess the velocity of blood flow within intracranial vessels through the cranium. These techniques are instrumental in diagnosing emboli, stenosis, vasospasm secondary to subarachnoid hemorrhage (resulting from a ruptured aneurysm), and various other cerebrovascular pathologies.
Doppler fetal monitors employ the Doppler effect for detecting the fetal heartbeat during antenatal examinations. These devices are typically handheld, with certain versions also providing a digital display of the heart rate in beats per minute (BPM). The application of this monitor is occasionally termed Doppler auscultation. The Doppler fetal monitor is frequently abbreviated to simply a Doppler or fetal Doppler and offers comparable diagnostic data to that obtained via a fetal stethoscope.

Contrast Ultrasonography (Ultrasound Contrast Imaging)

A contrast medium for medical ultrasonography comprises encapsulated gaseous microbubbles designed to augment blood echogenicity, a phenomenon initially identified by Dr. Raymond Gramiak in 1968 and later designated as contrast-enhanced ultrasound. This diagnostic imaging technique is globally employed, with a notable prevalence in echocardiography within the United States, and in ultrasound radiology across Europe and Asia.

Microbubble-based contrast media are intravenously introduced into the patient's bloodstream during the ultrasonographic procedure. Their dimensions ensure that microbubbles are retained within the vascular lumen, preventing extravasation into the interstitial space. Consequently, ultrasound contrast agents are exclusively intravascular, rendering them optimal for imaging organ microvasculature in diagnostic contexts. A common clinical application of contrast ultrasonography involves identifying hypervascular metastatic tumors, which demonstrate a more rapid contrast uptake (reflecting microbubble concentration kinetics in circulation) compared to adjacent healthy biological tissue. Additional clinical utility includes enhancing left ventricular delineation in echocardiography to assess myocardial contractility post-myocardial infarction. Furthermore, quantitative perfusion applications (involving relative blood flow measurement) have developed, facilitating the early detection of patient responses to anti-cancer therapies (as demonstrated by Dr. Nathalie Lassau's methodology and clinical study in 2011), thereby informing optimal oncological treatment strategies.

Within the oncological application of medical contrast ultrasonography, clinicians employ 'parametric imaging of vascular signatures,' a technique developed by Dr. Nicolas Rognin in 2010. This methodology functions as a computer-aided diagnostic instrument for cancer, aiding in the differentiation of suspicious lesions (malignant versus benign) within an organ. The approach leverages medical computational science to analyze a temporal sequence of ultrasound contrast images, essentially a real-time digital video acquired during patient assessment. Subsequently, two sequential signal processing stages are applied to each pixel within the tumor region:

The initial step involves calculating a vascular signature, defined as the contrast uptake differential relative to the healthy peritumoral tissue;
The subsequent step entails the automatic classification of this vascular signature into a distinct parameter, which is then color-coded using one of four categories:
- Green, indicating continuous hyper-enhancement (where contrast uptake surpasses that of healthy tissue);
- Blue, signifying continuous hypo-enhancement (characterized by contrast uptake inferior to that of healthy tissue);
- Red, denoting rapid hyper-enhancement (where contrast uptake precedes that of healthy tissue); or
- Yellow, representing rapid hypo-enhancement (with contrast uptake occurring subsequent to that of healthy tissue).

Upon completion of signal processing within each pixel, a color spatial map of the parameter, known as a parametric image, is displayed on a computer monitor, consolidating all vascular information pertaining to the tumor. Clinicians interpret this parametric image based on the tumor's predominant colorization: red typically signifies a suspicion of malignancy, while green or yellow suggests a high probability of benignity. For suspected malignant tumors, clinicians commonly recommend a biopsy for diagnostic confirmation or a CT scan for a second opinion. Conversely, in cases where a benign tumor is highly probable, a follow-up contrast ultrasonography examination is typically scheduled several months later. Key clinical advantages include mitigating the need for systemic biopsies of benign tumors, which carry inherent risks associated with invasive procedures, and reducing patient exposure to X-ray radiation from CT scans. The parametric imaging method, utilizing vascular signatures, has demonstrated efficacy in humans for characterizing liver tumors. Within a cancer screening framework, this methodology holds potential applicability for other organs, including the breast and prostate.

Molecular Ultrasonography (Ultrasound Molecular Imaging)

The evolving landscape of contrast ultrasonography points towards molecular imaging, with anticipated clinical applications in cancer screening for the early detection of malignant tumors. Molecular ultrasonography, also known as ultrasound molecular imaging, employs targeted microbubbles initially developed by Dr. Alexander Klibanov in 1997. These targeted microbubbles specifically bind or adhere to tumoral microvessels by targeting biomolecular expressions associated with cancer, such as the overexpression of certain biomolecules during neo-angiogenesis or inflammation in malignant tumors. Consequently, within minutes of intravenous injection, these targeted microbubbles accumulate within malignant tumors, thereby facilitating their localization in a distinct ultrasound contrast image. The inaugural exploratory clinical trial in humans for prostate cancer, utilizing this technique, was concluded in Amsterdam, Netherlands, in 2013 by Dr. Hessel Wijkstra.

Within molecular ultrasonography, the acoustic radiation force technique, also employed in shear wave elastography, is utilized to propel targeted microbubbles towards microvessel walls, a principle first demonstrated by Dr. Paul Dayton in 1999. This mechanism enhances binding to malignant tumors by increasing the direct contact between targeted microbubbles and cancerous biomolecules expressed on the inner surface of tumoral microvessels. During preclinical research, the acoustic radiation force technique was integrated as a prototype into clinical ultrasound systems and validated in vivo across both 2D and 3D imaging modalities.

Elastography (Ultrasound Elasticity Imaging)

Ultrasound technology is additionally applied in elastography, a relatively nascent imaging modality designed to map the elastic properties of soft tissues. This technique has gained prominence over the past two decades. Elastography proves valuable in medical diagnostics by enabling the differentiation between healthy and pathological tissues within specific organs or growths. For instance, malignant tumors frequently exhibit greater stiffness than surrounding healthy tissue, and diseased livers are typically more rigid than healthy ones.

Numerous ultrasound elastography techniques exist.

Interventional Ultrasonography

Interventional ultrasonography encompasses procedures such as biopsy, fluid aspiration, and intrauterine blood transfusion for conditions like hemolytic disease of the newborn.

For thyroid cysts, high-frequency thyroid ultrasound (HFUS) offers a therapeutic approach for various glandular conditions. Recurrent thyroid cysts, historically managed surgically, can now be effectively treated using percutaneous ethanol injection (PEI). This procedure involves the ultrasound-guided placement of a 25-gauge needle into the cyst; following fluid evacuation, approximately 50% of the cyst's original volume is reinjected into the cavity, with the operator maintaining precise visualization of the needle tip. This technique demonstrates an 80% success rate in significantly reducing cyst volume.
High-frequency ultrasound (HFUS) also serves as a therapeutic option for metastatic thyroid cancer affecting cervical lymph nodes in patients who decline surgical intervention or are deemed unsuitable candidates for such procedures. This involves the ultrasound-guided injection of minimal ethanol quantities. Prior to injection, a Power Doppler blood flow assessment is conducted. This intervention can ablate the blood supply, thereby inactivating the lymph node. The eradication of Power Doppler-visualized blood flow may lead to a reduction in the cancer biomarker thyroglobulin (TG) as the node loses its functionality. Furthermore, HFUS facilitates the preoperative marking of cancerous nodes to assist surgeons in localizing node clusters during surgical procedures. This process entails the precise ultrasound-guided injection of a minute quantity of methylene dye onto the anterior surface, external to the node. The dye's presence subsequently aids the thyroid surgeon in identifying the target area during cervical exploration. An analogous localization technique utilizing methylene blue can also be employed for identifying parathyroid adenomas.
Medical ultrasound provides guidance for various joint injections, including those administered into the hip joint.

Compression Ultrasonography

Compression ultrasonography involves applying pressure with the ultrasound probe against the skin surface. This technique can reduce the distance between the target structure and the probe, thereby enhancing spatial resolution. Diagnostic insights can be gained by comparing the morphology of the target structure before and after compression.

This method is employed in the ultrasonographic assessment of deep venous thrombosis (DVT), where the lack of vein compressibility serves as a robust indicator of thrombosis. Compression ultrasonography demonstrates high sensitivity and specificity for identifying proximal DVT in symptomatic individuals. However, its diagnostic reliability diminishes in asymptomatic patients, such as high-risk postoperative orthopedic patients.

Panoramic Ultrasonography

Panoramic ultrasonography involves the digital concatenation of multiple ultrasound images to create a single, broader composite image. This technique enables the visualization of an entire abnormality and its spatial relationship to adjacent anatomical structures within a unified display.

Multiparametric Ultrasonography

Multiparametric ultrasonography (mpUSS) integrates various ultrasound techniques to generate a comprehensive diagnostic outcome. For instance, a particular investigation combined B-mode imaging, color Doppler, real-time elastography, and contrast-enhanced ultrasound, yielding an accuracy comparable to that of multiparametric MRI.

Speed-of-Sound Imaging

Speed-of-sound (SoS) imaging endeavors to ascertain the spatial distribution of SoS within biological tissues. The underlying principle involves determining relative delay measurements across various transmission events and subsequently resolving the limited-angle tomographic reconstruction problem by utilizing these delay measurements and the transmission geometry. In comparison to shear-wave elastography, SoS imaging demonstrates superior ex-vivo tissue differentiation capabilities for distinguishing between benign and malignant tumors.

Attributes

Similar to other imaging modalities, ultrasonography possesses distinct advantages and disadvantages.

Strengths

Ultrasonography provides excellent visualization of muscle, soft tissue, and bone surfaces, including precise delineation of interfaces between solid and fluid-filled anatomical compartments.
Real-time, dynamic images can be acquired, facilitating rapid diagnosis and documentation. These live images also enable ultrasound-guided biopsies or injections, procedures that may be more challenging with alternative imaging techniques.
Imaging data is presented instantaneously.
The cost associated with ultrasonography is considerably lower compared to other diagnostic imaging modalities.
The structural morphology of organs can be effectively visualized.
When utilized in accordance with established guidelines, ultrasonography is not associated with any known long-term adverse effects, and patient discomfort is typically minimal.
It offers the capability to image localized variations in the mechanical properties of soft tissues.
Ultrasonography equipment is broadly accessible and offers considerable operational flexibility.
Compact, portable scanners are readily available, enabling point-of-care examinations.
Ultrasound transducers have become relatively cost-effective when contrasted with components of other investigative modalities, including computed X-ray tomography, DEXA, or magnetic resonance imaging.
High-frequency ultrasound transducers provide superior spatial resolution compared to the majority of other imaging modalities.
Employing an ultrasound research interface presents a relatively economical, real-time, and adaptable methodology for acquiring data pertinent to specific research objectives, such as tissue characterization and the advancement of novel image processing techniques.

Weaknesses

Sonographic devices exhibit limited penetration capabilities through bone, which significantly restricts the application of sonography for imaging the adult brain.
The efficacy of sonography is substantially diminished by the presence of gas between the transducer and the target organ, primarily due to significant disparities in acoustic impedance. For instance, gas within the gastrointestinal tract frequently impedes effective ultrasound examination of the pancreas. Similarly, subcutaneous emphysema poses challenges for lung imaging; however, sonography remains valuable for identifying pleural effusions, diagnosing heart failure, and detecting pneumonia.
Even without the presence of bone or air, the depth penetration of ultrasound can be constrained by the imaging frequency employed. This limitation can hinder the visualization of deep-seated anatomical structures, particularly in obese individuals.
In obese patients, both image quality and diagnostic accuracy are compromised because overlying subcutaneous fat attenuates the ultrasound beam. This necessitates the use of a lower-frequency transducer, which inherently results in reduced image resolution.
This diagnostic methodology requires active patient cooperation.
The diagnostic utility of this method is highly operator-dependent, requiring substantial skill and experience to obtain high-quality images and formulate accurate diagnoses.
Unlike computed tomography (CT) and magnetic resonance imaging (MRI), sonography does not generate a scout image, making it challenging to precisely identify the anatomical region depicted in an acquired image.
A significant proportion, specifically 80%, of sonographers report experiencing Repetitive Strain Injuries (RSI) or Work-Related Musculoskeletal Disorders (WMSD), often attributed to suboptimal ergonomic postures during examinations.

Risks and Adverse Effects

Ultrasonography is widely regarded as a safe imaging modality, as affirmed by the World Health Organization, which states:

"Diagnostic ultrasound is recognized as a safe, effective, and highly flexible imaging modality capable of providing clinically relevant information about most parts of the body in a rapid and cost-effective fashion."

Fetal diagnostic ultrasound examinations are generally considered safe throughout pregnancy. Nevertheless, such procedures should only be conducted when a clear medical indication exists, and the lowest possible ultrasonic exposure settings must be utilized to acquire the requisite diagnostic information, adhering to the "as low as reasonably practicable" (ALARP) principle.

Despite the absence of definitive evidence indicating harm to the fetus from ultrasound, medical authorities generally advise against the promotion, sale, or lease of ultrasound equipment for the creation of "keepsake fetal videos."

Research on Ultrasound Safety

A meta-analysis of multiple ultrasonography studies, published in 2000, concluded that there were no statistically significant adverse effects attributable to ultrasonography. However, the analysis also highlighted a paucity of data concerning long-term substantive outcomes, particularly neurodevelopmental impacts.
Research conducted at the Yale School of Medicine and published in 2006 identified a minor yet statistically significant correlation between extended and frequent ultrasound exposure and abnormal neuronal migration in murine models.
A 2001 study conducted in Sweden suggested subtle neurological damage linked to ultrasound, evidenced by an elevated incidence of left-handedness in boys (a non-hereditary indicator of cerebral issues) and speech delays.
- However, these findings were not corroborated in a subsequent follow-up investigation.
- Nevertheless, a subsequent study involving a larger cohort of 8,865 children established a statistically significant, though weak, association between ultrasonography exposure and the development of non-right-handedness later in life.

Regulatory Framework

In the United States, diagnostic and therapeutic ultrasound equipment is regulated by the Food and Drug Administration (FDA), while other national regulatory bodies oversee its use globally. The FDA imposes limits on acoustic output through various metrics, and these established guidelines are generally adopted by other international agencies.

Presently, New Mexico, Oregon, and North Dakota are the sole U.S. states that regulate diagnostic medical sonographers. In the United States, certification examinations for sonographers are administered by three distinct organizations: the American Registry for Diagnostic Medical Sonography, Cardiovascular Credentialing International, and the American Registry of Radiologic Technologists.

The principal regulated parameters include the Mechanical Index (MI), which correlates with the cavitation bio-effect, and the Thermal Index (TI), associated with the bio-effect of tissue heating. The FDA mandates that devices adhere to established, conservatively set limits to ensure diagnostic ultrasound remains a secure imaging modality. This necessitates manufacturers' self-regulation regarding machine calibration.

Ultrasound-based prenatal care and sex screening technologies were introduced in India during the 1980s. Prompted by concerns regarding their misuse for sex-selective abortion, the Government of India enacted the Pre-natal Diagnostic Techniques Act (PNDT) in 1994 to differentiate and govern the permissible and prohibited applications of ultrasound equipment. This legislation was subsequently amended in 2004 as the Pre-Conception and Pre-natal Diagnostic Techniques (Regulation and Prevention of Misuse) (PCPNDT) Act, aiming to discourage and penalize prenatal sex screening and sex-selective abortion. In India, determining or disclosing the sex of a fetus using ultrasound equipment is presently prohibited and constitutes a punishable offense.

Applications in Veterinary Medicine

Ultrasound also serves as a significant instrument in veterinary medicine, providing comparable non-invasive imaging capabilities instrumental in the diagnosis and monitoring of animal health conditions.

Historical Development

The discovery of piezoelectricity by French physicist Pierre Curie in 1880 enabled the deliberate generation of ultrasonic waves for industrial applications. In 1940, American acoustical physicist Floyd Firestone developed the inaugural ultrasonic echo imaging device, the Supersonic Reflectoscope, designed to detect internal flaws in metal castings. The following year, in 1941, Austrian neurologist Karl Theo Dussik, collaborating with his physicist brother Friedrich, is widely considered the first to ultrasonically image the human body, specifically delineating the ventricles of a human brain. Dr. George Ludwig at the Naval Medical Research Institute in Bethesda, Maryland, initially utilized ultrasonic energy on the human body for medical applications in the late 1940s. English-born physicist John Wild (1914–2009) first employed ultrasound to evaluate bowel tissue thickness as early as 1949, earning him recognition as the "father of medical ultrasound." While subsequent advancements occurred simultaneously across multiple nations, it was not until 1961 that research by David Robinson and George Kossoff at the Australian Department of Health yielded the first commercially viable water bath ultrasonic scanner. In 1963, Meyerdirk & Wright commenced production of the first commercial, hand-held, articulated arm, compound contact B-mode scanner, thereby making ultrasound broadly accessible for medical applications.

Developments in France

Léandre Pourcelot, a researcher and educator at INSA (Institut National des Sciences Appliquées) in Lyon, co-authored a report in 1965 for the Académie des sciences, titled "Effet Doppler et mesure du débit sanguin" ("Doppler effect and measurement of blood flow"), which formed the foundation for his 1967 design of a Doppler flow meter.

Developments in Scotland

Concurrently, Professor Ian Donald and his colleagues at the Glasgow Royal Maternity Hospital (GRMH) in Glasgow, Scotland, pioneered the initial diagnostic applications of this technique. Donald, an obstetrician, openly acknowledged a "childish interest in machines, electronic and otherwise." Following his treatment of a company director's wife, he received an invitation to He subsequently adapted their industrial ultrasound equipment to conduct experiments on diverse anatomical specimens and evaluate their ultrasonic characteristics. Collaborating with medical physicist Tom Brown and fellow obstetrician John MacVicar, Donald refined the apparatus to facilitate the differentiation of pathology in live volunteer patients. These findings were published in The Lancet on June 7, 1958, under the title "Investigation of Abdominal Masses by Pulsed Ultrasound," a publication considered among the most significant in the domain of diagnostic medical imaging.

Professors Donald and James Willocks at GRMH advanced their techniques for obstetric applications, specifically developing fetal head measurement to evaluate fetal size and growth. The inauguration of the new Queen Mother's Hospital in Yorkhill in 1964 facilitated further enhancements to these methodologies. Stuart Campbell's seminal research on fetal cephalometry subsequently established it as the definitive long-term method for assessing fetal growth. Progressive improvements in scan technical quality enabled comprehensive pregnancy monitoring from inception to term, allowing for the diagnosis of numerous complications, including multiple pregnancies, fetal abnormalities, and placenta praevia. Since then, diagnostic ultrasound has been adopted across nearly all other medical specialties.

Sweden

In 1953, medical ultrasonography was first employed at Lund University by cardiologist Inge Edler and Carl Hellmuth Hertz, then a graduate student in the university's nuclear physics department and son of Gustav Ludwig Hertz.

Edler initially inquired whether radar could be utilized for internal body examination, a possibility Hertz dismissed. However, Hertz proposed the potential application of ultrasonography. Drawing upon his familiarity with ultrasonic reflectoscopes, an invention by American acoustical physicist Floyd Firestone used for nondestructive materials testing, Hertz collaborated with Edler to adapt this methodology for medical use.

The inaugural successful measurement of cardiac activity occurred on October 29, 1953, employing equipment loaned from the Kockums shipbuilding company in Malmö. By December 16 of the same year, the technique was extended to produce an echo-encephalogram, an ultrasonic examination of the brain. Edler and Hertz subsequently published their research findings in 1954.

United States

Following approximately two years of development, Joseph Holmes, William Wright, and Ralph Meyerdirk introduced the pioneering compound contact B-mode scanner in 1962. This endeavor received funding from the U.S. Public Health Services and the University of Colorado. Subsequently, Wright and Meyerdirk departed the university to establish Physionic Engineering Inc., which commercialized the first hand-held articulated arm compound contact B-mode scanner in 1963, initiating what would become the most prevalent design in ultrasound scanner history.

During the late 1960s, Gene Strandness and the bioengineering team at the University of Washington investigated Doppler ultrasound as a diagnostic instrument for vascular pathologies. Their research ultimately led to the development of duplex imaging technologies, integrating Doppler with B-mode scanning to enable real-time visualization of vascular structures alongside the acquisition of hemodynamic data.

Geoff Stevenson, a key figure in the nascent stages of Doppler-shifted ultrasonic energy development and its medical applications, performed the initial demonstration of color Doppler.

Manufacturers

Prominent manufacturers of medical ultrasound devices and equipment include:

Canon Medical Systems Corporation
Esaote
GE Healthcare
Fujifilm
Mindray Medical International Limited
Koninklijke Philips N.V.
Samsung Medison
Siemens Healthineers

Medical ultrasound