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Medical ultrasonography


Ultrasound Machines

Medical ultrasonography

Diagnostic applications

Typical diagnostic sonographic scanners operate in the frequency range of 2 to 18 megahertz, though frequencies up to 50每100 megahertz have been used experimentally in a technique known as biomicroscopy in special regions, such as the anterior chamber of the eye. The choice of frequency is a trade-off between spatial resolution of the image and imaging depth: lower frequencies produce less resolution but image deeper into the body. Higher frequency sound waves have a smaller wavelength and thus are capable of reflecting or scattering from smaller structures. Higher frequency sound waves also have a larger attenuation coefficient and thus are more readily absorbed in tissue, limiting the depth of penetration of the sound wave into the body (for details, see Acoustic attenuation.)

Sonography (ultrasonography) is widely used in medicine. It is possible to perform both diagnosis and therapeutic procedures, using ultrasound to guide interventional procedures (for instance biopsies or drainage of fluid collections). Sonographers are medical professionals who perform scans which are then typically interpreted by radiologists, physicians who specialize in the application and interpretation of a wide variety of medical imaging modalities, or by cardiologists in the case of cardiac ultrasonography (echocardiography). Sonographers typically use a hand-held probe (called a transducer) that is placed directly on and moved over the patient. Increasingly, clinicians (physicians and other healthcare professionals who provide direct patient care) are using ultrasound in their office and hospital practices, for efficient, low-cost, dynamic diagnostic imaging that facilitates treatment planning while avoiding any ionising radiation exposure.

Sonography is effective for imaging soft tissues of the body. Superficial structures such as muscles, tendons, testes, breast, thyroid and parathyroid glands, and the neonatal brain are imaged at a higher frequency (7每18 MHz), which provides better axial and lateral resolution. Deeper structures such as liver and kidney are imaged at a lower frequency 1每6 MHz with lower axial and lateral resolution but greater penetration.

Medical sonography is used in the study of many different systems:

System/

Specialty

Description

See also

Anesthesiology

Ultrasound is commonly used by anesthesiologists (Anaesthetists) to guide injecting needles when placing local anaesthetic solutions near nerves

Cardiology

Echocardiography is an essential tool in cardiology, to diagnose e.g. dilatation of parts of the heart and function of heart ventricles and valves

echocardiography

Emergency Medicine

Point of care ultrasound has many applications in the Emergency Department, including the Focused Assessment with Sonography for Trauma (FAST) exam for assessing significanthemoperitoneum or pericardial tamponade after trauma. Ultrasound is routinely used in the Emergency Department to expedite the care of patients with right upper quadrant abdominal pain who may have gallstones or cholecystitis.

 FAST exam,Emergency ultrasound.

Gastroenterology/Colorectal surgery

In abdominal sonography, the solid organs of the abdomen such as the pancreas, aorta, inferior vena cava, liver, gall bladder, bile ducts, kidneys, and spleen are imaged. Sound waves are blocked by gas in the bowel and attenuated in different degree by fat, therefore there are limited diagnostic capabilities in this area. The appendix can sometimes be seen when inflamed (as in e.g.: appendicitis). Endoanal ultrasound is used particularly in the investigation of anorectal symptoms such as fecal incontinence or obstructed defecation. It images the immediate perianal anatomy and is able to detect occult defects such as tearing of the anal sphincter.

abdominal ultrasonography,Endoanal ultrasound

Gynecology

see gynecologic ultrasonography

Head and Neck Surgery/Otolaryngology

Most structures of the neck, including the thyroid and parathryoid glands, lymph nodes, and salivary glands, are well-visualized by high-frequency ultrasound with exceptional anatomic detail. Ultrasound is the preferred imaging modality for thryoid tumors and lesions, and ultrasonography is critical in the evaluation, preoperative planning, and postoperative surveillance of patients with thyroid cancer. Many other benign and malignant conditions in the head and neck can be evaluated and managed with the help of diagnostic ultrasound and ultrasound-guided procedures.

Neonatology

for basic assessment of intracerebral structural abnormalities, bleeds, ventriculomegaly or hydrocephalus and anoxic insults (Periventricular leukomalacia). The ultrasound can be performed through the soft spots in the skull of a newborn infant (Fontanelle) until these completely close at about 1 year of age and form a virtually impenetrable acoustic barrier for the ultrasound. The most common site for cranial ultrasound is the anterior fontanelle. The smaller the fontanelle, the poorer the quality of the picture.

Intracerebral: seeTranscranial Doppler

Neurology

for assessing blood flow and stenoses in the carotid arteries (Carotid ultrasonography) and the big intracerebral arteries

see Carotid ultrasonography. Intracerebral: seeTranscranial Doppler

Obstetrics

Obstetrical sonography is commonly used during pregnancy to check on the development of the fetus.

see obstetric ultrasonography

Ophthalmology

Ultrasound images of the eyes, also known as ocular ultrasonography

see A-scan ultrasonography,B-scan ultrasonography

Pulmonology

Endobronchial Ultrasound (EBUS) probes are applied to standard flexible endoscopic probes and used by pulmonologists to allow for direct visualization of endobronchial lesions and lymph nodes prior to transbronchial needle aspiration. Among its many uses, EBUS aids in lung cancer staging by allowing for lymph node sampling without the need for major surgery.

Urology

to determine, for example, the amount of fluid retained in a patient*s bladder. In a pelvic sonogram, organs of the pelvic region are imaged. This includes the uterus and ovaries or urinary bladder. Males are sometimes given a pelvic sonogram to check on the health of their bladder, the prostate, or their testicles (for example to distinguish epididymitis from testicular torsion). In young males, it is used to distinguish more benign testicular masses (varicocele or hydrocele) from testicular cancer, which is highly curable but which must be treated to preserve health and fertility. There are two methods of performing a pelvic sonography 每 externally or internally. The internal pelvic sonogram is performed either transvaginally (in a woman) or transrectally (in a man). Sonographic imaging of the pelvic floor can produce important diagnostic information regarding the precise relationship of abnormal structures with other pelvic organs and it represents a useful hint to treat patients with symptoms related to pelvic prolapse, double incontinence and obstructed defecation. It is used to diagnose and, at higher frequencies, to treat (break up) kidney stones or kidney crystals (nephrolithiasis).

Musculoskeletal

tendons, muscles, nerves, ligaments, soft tissue masses, and bone surfaces

Cardiovascular system

To assess patency and possible obstruction of arteries Arterial sonography, diagnose deep vein thrombosis (Thrombosonography) and determine extent and severity of venous insufficiency (venosonography)

Intravascular ultrasound

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