Tuesday, 26 July 2011

Scope of Ultrasonography

Published in Panorama

Why Ultrasonography

Ultrasound scan is a procedure which enables specialists in the field to visualize the internal parts of the body, or a fetus within the uterus, using sound waves which bounce these waves off of tissues and structures and uses the pattern of echoes to form an image, the sonogram. The wide spectrum of ultrasound specialties include ultrasound in surgery, ultrasound-guided biopsies and diagnostic ultrasound for the abdomen, breast, thyroid, in obstetrics and gynecology and vascular system, explains Dr.Joseph Cherian, Specialist Radiologist and Head of Radiology & Imaging, Welcare Hospital, Dubai.

The appeal of the ultrasound as a major diagnostic tool lies in the fact that it is safe, painless, easy and quick, involving no radiation at all and can be done without any particular patient preparation in an emergency. Since it involves real time imaging, it can be used to guide invasive procedures and also allows us to visualize breathing, bowel movements and blood flow anywhere in the body. It is highly operator dependant. The diagnostic yeild is directly proportional to tthe skill and experience of the operator.

Dr.Cherian explains, "In several non gynaecological areas, ultrasound has now become a routine screening method to determine the causes of pain, swelling, bleeding, or infection -- stones, tumor, cyst, inflammations, injury, congenital anomalies, particularly in the abdominal cavity, both upper and lower. It is very useful in diagnosing appendicitis and pancreatitis. The big advantage of the ultrasound is in detecting gall stones, majority (at least 95%) of which are cholesterol stones which are not revealed by an X Ray. This investigative tool is particularly important since gall bladder stones today are seen in younger individuals, even in adolescents, of both sexes, unlike the fat, fertile, female of forty, as classically believed!"

Elaborating the benefits of an ultrasound scan, Dr.Cherian continues, "It is used to examine blood flow and discover blockages -- atherosclerotic plaque, blood clots in the arteries and veins of extremities, abdomen, pelvis, and neck. The importance here is from the viewpoint of starting immediate treatment once the problem and its area of location is diagnosed. For instance, once a vein thrombus is picked up and you don't thin the blood immediately, the clot can travel in an upward direction and reach the lungs, causing pulmonary embolism which is catastrophic."

Cysts, fibroids, polyps and cancers in the pelvic region, bladder tumour and other conditions of the urinary system and genitals, prostate cancer, fibrocystic breast condition, goiter, cysts, tumour or cancer of the thyroid, tendon and muscular tears, masses, tumours, bleeding or other fluid collections within the muscles and joints, can all be picked up on an ultrasound investigation, says Dr.Cherian.

The usefulness of ultrasound cannot be overemphasized in guiding invasive procedures such as needle biopsy as in breast cancer, sampling or withdrawal of fluid as in amniocentesis, amoebic liver abscess. Dr.Cherian emphasizes, "There is no radiation involved; we don't even give an injection as part of the preparation procedure. Ultrasound, I believe, would be the starting point of a radiological investigation which is least invasive with maximum yield."

How is a patient prepared for an ultrasound examination and what does the procedure itself involve? The procedure may be trans-abdominal or intra cavitry, explains Dr.Cherian. While the former mode is completely non-invasive, intra-cavitry ultrasound is a very minimally invasive technique with much better results in terms of clarity, by comparison to the trans-abdominal mode. In the non invasive procedure, a hand-held device called a "transducer" or "probe", is placed on the area being examined and moved around. This probe generates ultrasound and sends it through the body. It also detects the returning echoes and transmits them as electrical signals. Because one probe continuously generates many ultrasound waves while detecting echoes, a real time image can be produced on a viewing monitor. These images can be recorded on videotape, or images can be frozen and recorded on to film.

As for patient preparation prior to the procedure, Dr.Cherian explains, "For instance, if we need to diagnose gall bladder stones, we ask the patient to come on empty stomach, six hours fasting prior to the procedure. This is because if the person has a full breakfast, the moment food, particularly fat, comes into the stomach, the gall bladder contracts and the bile comes out to digest the fat. So we see an empty gallbladder. And in an empty gall bladder, the stones can be hidden and not seen in an ultrasound. Secondly, Ultrasound yields best results in a liquid medium since sound waves cannot penetrate gas or bones. Therefore, sometimes we give the patient some gas tablets - charcoal tablets- to absorb the unnecessary gas, to get a clear abdomen. For the pelvic scan, an appendix scan, the urinary bladder should be full, because we use the full bladder as a window to scan to the left, right and to the interior aspect of the bladder. Similarly, prostate in men, uterus and ovaries in women can be easily seen in this manner. Also, if there is any fluid secondary to the rupture of an ovarian cyst, twisted ovarian cyst or ectopic pregnancy, all these can be seen with a full bladder."

"Now there is a big role for intra-cavitry probe, as the rectal probe, which is a long probe which we put into the rectum after applying some gel, to study the rectal wall, rectal tumours and prostate. Along with the vaginal probe, these are the only slightly invasive ultrasound procedures, but they do not cause any trauma to the patient. While going in for the rectal probe, we ask the patients to take a deep breath so as not to feel pain when it passes through the rectal sphincter," explains Dr.Cherian.

Depending on the area to be scanned, the procedure may take between 10 to 30 minutes, says Dr.Cherian.

What are the limitations of ultrasound scan as it exists today? Dr.Cherian responds: "Ultrasound does not penetrate air or bone. So if the abnormality to be seen is behind bowel gas, ribs or calcified rib cartilage, ultrasound may not reveal it. Since ultrasound is absorbed and reflected inside the body, only some of the waves reach deep places farthest from the probe. So the ability to look deep into the body may be restricted. The probes themselves are of three different types in terms of their range: 3-5 megahertz; 5-7 megahertz and 7-12 megahertz. The first type is used for scanning internal abdominal organs; the second probe type is used to scan superficial organs like thyroid, testes, et al. The third one also scans thyroid, breast in addition to superficial sub-cutaneous areas like muscles, tendons, etc. Higher the frequency, lesser the penetration and vice-versa."

Dr.Ulrich Honemeyer, Specialist in Gynaecology and Obstetrics at Welcare, adds, "Breast ultrasound scan is very potent in diagnosing the rather dense breast tissue of younger women below the age of 40. Also, it can do the differentiation of cystic lesions in the breast, which a mammography will not show. Yet, the ultrasound has its limitations and cannot totally replace mammography because the latter can show us micro-calcification which are difficult to see un ultrasound. And these are very important tracer or market in breast cancer."

Dr.Cherian continues, "Also, ultrasound may not pick up kidney stones measuring 3mm and less. Similarly in guided surgery and biopsy, if the mass to be probed is between 1 and 2 cm, CT scan is preferred to an ultrasound. Again, if we want to do an aspiration of a liver abscess, either ultrasound or CT scan may be used with the CT scan having a slight edge over the ultrasound scan, especially if the fluid collection is small.'

"For the lungs, there is not enough role for ultrasound except when there is infection (pneumonia) or pleural fluid or pericardial effusion because the lungs are full of air and they will get reflected upon ultrasound scanning", adds Dr.Cherian.


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