ULTRASONOGRAPHY
Typical diagnostic sonographic scanners operate in the frequency range of 2 to 18 megahertz, though frequencies up to 50–100 megahertz has been used experimentally in a technique known as biomicroscopy in special regions, such as the anterior chamber of eye.[citation needed] 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.
Sonography (ultrasonography) is widely used in medicine. It is possible to perform both diagnosisand therapeutic procedures, using ultrasound to guide interventional procedures (for instancebiopsies 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.
Sonography is effective for imaging soft tissues of the body. Superficial structures such asmuscles, tendons, testes, breast and the neonatal brain are imaged at a higher frequency (7–18 MHz), which provides better axial and lateral resolution. Deeper structures such as liver and kidney are imaged at a lower frequency 1–6 MHz with lower axial and lateral resolution but greater penetration.
Medical sonography is used in the study of many different systems:
| System | Description | See also |
| Ultrasound is commonly used by anesthesiologists (Anaesthetists) to guide injecting needles when placing local anaesthetic solutions near nerves | | |
| Echocardiography is an essential tool in cardiology, to diagnose e.g. dilatation of parts of the heart and function of heart ventricles and valves | ||
| Point of care ultrasound has many applications in the Emergency Department, including the Focused Assessment with Sonography for Trauma (FAST) exam for assessing significant hemoperitoneum 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. | see FAST exam | |
| 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 appendixcan sometimes be seen when inflamed (as in e.g.:appendicitis). | | |
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| for basic assessment of intracerebral structural abnormalities, bleeds, ventriculomegaly or hydrocephalusand 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 | |
| for assessing blood flow and stenoses in the carotid arteries (Carotid ultrasonography) and the big intracerebral arteries | see Carotid ultrasonography. Intracerebral: seeTranscranial Doppler | |
| Obstetrical sonography is commonly used duringpregnancy to check on the development of the fetus. | ||
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| 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 orurinary bladder. Males are sometimes given a pelvic sonogram to check on the health of their bladder, theprostate, or their testicles (for example to distinguishepididymitis from testicular torsion). In young males, it is used to distinguish more benign testicular masses (varicocele or hydrocele) from testicular cancer, which is still very highly curable but which must be treated to preserve health and fertility. There are two methods of performing a pelvic sonography – 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).[3] | | |
| tendons, muscles, nerves, ligaments, soft tissue masses, and bone surfaces | | |
| To assess patency and possible obstruction of arteriesArterial sonography, diagnose DVT (Thrombosonography) and determine extent and severity of venous insufficiency (venosonography | |
