Defined as a frequency above that which humans can hear, or more than 20,000 Hz.

Therapeutic ultrasound creates heat using mechanical sound waves.

Therapeutic ultrasound has lower frequency is then diagnostic ultrasound.

The frequency of diagnostic ultrasound is measured in millions of hertz (MHz).

Lower frequency ultrasound has better penetration with lower resolution.

Higher frequency ultrasound provides clearer imagery, but has poorer visualization of the deep structures.

Trans abdominal or cardiac ultrasound probes have a frequency in the range of 2-5 MHz.

Dermatological ultrasound probes have a frequency as high as 100 MHz.

Ultrasound uses a crystal which maybe quartz, or composite piezoelectric material and generates a sound wave when an electric current is applied.

As the sound wave returns the material, as described above, generates a current, therefore the crystal both transmits and receives sound.

Presently screen images generate a B-mode or grayscale two dimensional image.

The crystal produces a scan line that creates an image or frame, and this process is refreshed multiple times per second producing a moving image on the screen.

Multiple crystals are used across the face of the transducer.

In addition to the B-mode there are three-dimensional, four dimensional, a Doppler and tissue Doppler modes.

Highly operator dependent.

Beam penetration limited by the patient’s body habitus.

Penetrates fluid and solid organs well.

Does not penetrate through bone or air well, and therefore is limited in evaluating the skull, chest and areas of the abdomen where gas obscures the image.

Blood, bile, urine, and ascites fluid are anechoic, and appear black on ultrasound.

Ultrasound is very useful for detecting such fluids and for detecting cystic structures or vascular areas and differentiating from solid structures.

Should be the first diagnostic imaging study done in the workup of renal failure.

More than 95% specific and 60% sensitive in diagnosing bile duct stones.

Is the most widely used diagnostic modality to detect and screen for DVT in trauma patients.

Bilateral whole breast ultrasound performed in patients with dense breast tissue is useful in detecting breast cancer not discovered by mammography or clinical breast examination with a cancer detection rate of 0.3%.

Can distinguish cystic from solid lesions in 97% of patients.

Not as accurate in asymptomatic patients as it is in symptomatic patients for detecting DVT.

Sensitivity 91% and specificity 98% in diagnosing DVT in non-trauma patients compared to venogram in symptomatic patients.

Imaging of the liver may fail to detect up to 50% of liver lesions in colorectal cancer.

Sensitivity to detect liver metastases reduced by the presence of infiltration of fat into the liver.

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