2. TheUltrasound has become increasingly important in medicine and has taken its place along with
X-ray and nuclear medicine as a diagnostic tool. Its main attraction as an imaging modality lies in
its non-invasive character and ability to distinguish interfaces between soft tissues. In contrast,
X-rays only respond to atomic weight differences and often require the injection of a more dense
contrast medium for visualization of non-bony tissues. Similarly, nuclear medicine techniques
measure the selective uptake of radioactive isotopes in specific organs to produce information
concerning organ function. Radioactive isotopes and X-rays are, thus, clearly invasive. Ultrasound
is not only non-invasive, externally applied and non-traumatic but also apparently safe at the
acoustical intensities and duty cycles presently used in diagnostic equipment.
Diagnostic ultrasound is applied for obtaining images of almost the entire range of internal
organs in the abdomen. These include the kidney, liver, spleen, pancreas, bladder, major blood
vessels and of course, the foetus during pregnancy.
3. It has also been usefully employed to present
pictures of the thyroid gland, the eyes, the breasts and a variety of other superficial structures. In
a number of medically meaningful cases, ultrasonic diagnostics has made possible the detection
of cysts, tumours or cancer in these organs. This is possible in structures where other diagnostic
methods by themselves were found to be either inapplicable, insufficient or unacceptably
hazardous. Ultrasonic studies which do not involve image formation have also been extensively
developed to allow the dynamics of blood flow in the cardiovascular system to be investigated
with a precision not previously possible. The main limitation of ultrasound, however, is that it is
almost completely reflected at boundaries with gas and is a serious restriction in investigation of
and through gas-containing structures.
