ULTRASOUND SCANNING
Medical ultrasonography (sonography) is an ultrasound-based
diagnostic imaging technique used to visualize muscles and internal
organs, their size, structures and possible pathologies or lesions.
Obstetric sonography is commonly used during pregnancy and is widely recognized by the public. There are a plethora of diagnostic and therapeutic applications practiced in medicine.
In physics the term "ultrasound" applies to all acoustic energy with a frequency above human hearing (20,000 hertz or 20 kilohertz).
Typical diagnostic sonography scanners operate in the frequency range of 2 to 15 megahertz, hundreds of times greater than this limit.
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.
Diagnostic applications
Sonography (ultrasonography) is widely utilized in medicine.
It is possible to perform diagnosis or therapeutic procedures with the
guidance of sonography (for instance biopsies or drainage of fluid
collections). Sonographers are medical professionals who perform
scans for diagnostic purposes; they work with specialized doctors called
sonologists who provide reports of the images obtained.
Sonographers typically use a hand-held probe (called a transducer) that
is placed directly on and moved over the patient. A water-based gel is used to couple the ultrasound between the probe and patient.
Ultrasound is effective for imaging soft tissues of the body. Superficial
structures such as muscles, tendons, testes, breast and the neonatal
brain are imaged at a higher frequency (7-15 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, for example:
* Cardiology; see echocardiography
* Endocrinology
* Gastroenterology
* Gynaecology; see gynecologic ultrasonography
* Obstetrics; see obstetric ultrasonography
* Ophthalmology; see A-scan ultrasonography, B-scan ultrasonography
* Urology
* Musculoskeletaltendons, muscles nerves
* Vascular, arteries and veins
* Intravascular ultrasound (eg. ultrasound guided fluid aspiration, fine needle aspiration, guided injections)
* Intervenional
* Contrast-enhanced ultrasound
A general-purpose ultrasound machine may be able to be used for most imaging purposes. Usually specialty applications may be served only by use of a specialty transducer.
Echocardiography is a major sub-specialty of diagnostic ultrasound
that is different.
The dynamic nature of cardiac studies generally requires specialized features in an ultrasound machine for it to be effective.
Obstetrical ultrasound is commonly used during pregnancy to check on the development of the fetus.
In a pelvic ultrasound, organs of the pelvic region are imaged.
This includes the uterus and ovaries or urinary bladder.
Men are sometimes given a pelvic ultrasound to check on the health of their bladder and prostate.
There are two methods of performing a pelvic ultrasound - externally or internally. The internal pelvic ultrasound is performed either transvaginally (in a woman) or transrectally (in a man).
In an abdominal ultrasound, 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, therefore there are limited diagnostic capabilities in this
area.
The appendix can sometimes be seen when inflamed eg: appendicitis.
Therapeutic applications
the body. Therefore much higher energies are used than in diagnostic
ultrasound
Therapeutic applications use ultrasound to bring heat or agitation into
In many cases the range of frequencies used are also very different.
* Ultrasound may be used to clean teeth in dental hygiene.
* Ultrasound sources may be used to generate regional heating in biological tissue, eg. in occupational therapy, physical therapy and cancer treatment.
* Focused ultrasound may be used to generate highly localized heating to treat cysts and tumours (benign or malignant), This is known as Focused Ultrasound Surgery (FUS) or High Intensity Focused Ultrasound (HIFU). These procedures generally use lower frequencies than medical diagnostic ultrasound (from 250 kHz to 2000 kHz), but significantly higher energies. HIFU treatment is often guided by MRI.
* Focused ultrasound may be used to break up kidney stones by lithotripsy.
* Ultrasound may be used for cataract treatment by phacoemulsification
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