From the time of World War I when ultrasonography was used with the deployment of SONAR for detection of underwater objects, its industrial uses expanded considerably. But the application of ultrasonography in the medical field started only in the early 70s.
image source: uscollegesearch.org
Ultrasonography waves are mechanical pressure waves whose frequency (ranging from 2-10 MHz) is much higher than that of sound (20-16,000 Hz).
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An ultrasonography wave emitted by a transducer, containing a piezoelectric crystal, encounters a target organ and gets either reflected back or refracted.
The waves reflected back reach the transducer and are converted into voltage wave forms, processed and ultimately displayed on a cathode ray tube (TV monitor) in a two-dimensional format.
Apart from cardiology where ultrasonography has been extensively used, the greatest benefit of ultrasonography in diagnostic imaging has been in diagnosing disorders in the abdomen and pelvis.
In most cases, transabdominal sonography (TAS) is used. However, intracavitary ultrasonography or endosonography is widening the scope of ultrasonography.
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Transvaginal ultrasonography (TVS) gives far better resolution and therefore better distinguishes adnexal masses from bowel loops; it also provides greater detail of the internal characteristics of a pelvic mass.
Endosonography of the lumen allows for detection of mucosal abnormality, delineation of the layers of gut wall and definition of surrounding soft tissues to a depth of 8 to 10 cm.
Thus, tumours hidden below normal mucosa, tumour penetration into the layers of gut wall, and tumour involvement of surrounding vital structures and lymph nodes may be well evaluated.
Endosonography of the oesophagus, stomach, duodenum, rectum and anal canal is now possible with use of special probes.
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Small parts ultrasonography of scrotum, thyroid or breast is making the early diagnosis and treatment of small tumours very easy.
Newer trends in ultrasonography involve the development of contrast agents to the lumen of the bowel, veins, arteries, bile ducts and ureters.
Ultrasonography contrast agents may aid in tissue-specific or tumour specific agents. Trials have already been completed with SH U 454 (Schering AG, Germany) which has shown improved detection of liver tumours in rats following hepatic arterial or portal venous injection.
The wider use of this modality is of great benefit in reducing the need for expensive and hazardous diagnostic procedures and, in future will be recommended as a primary method of imaging.
Accuracy of diagnosis improves with increased experience, improved working methods and versatile equipment system. The combination of good sonography image and an examiner with sufficient experience can yield a sensitivity and specificity comparable with CT.
Whereas the cardiac structures and their motion are visualised with 2-D echocardiography, Doppler echocardiography studies the flow of blood within these structures.
To obtain better spatial orientation of flow within the cardiovascular system, real-time colour flow mapping is done by the modern colour flow ultrasound (Doppler) system. Hard copy of the results can be obtained by a choice of devices strip chart recorder, video printer, multiformat camera or colour camera.
Qualitative and quantitative haemodynamic and anatomic information regarding valve defects and cardiac shunts are now possible with these versatile equipments.
Equipment, Physical Facilities and Staffing:
Ultrasonographic diagnosis is entirely dependent on the quality of the ultrasonography machine. The factors that require careful consideration in selection of the machines are
I. Type of work
II. Type of hospital, and
III. Case turnover
There has been a virtual technological explosion in medical electronics field during the last few years. The medical electronics field has now any number of manufacturers and suppliers who have entered the field, not all of them being reliable.
For smooth functioning of the department, the machines and equipments should be selected from renowned and time-tested firms. The equipment should have the backing of an after-sales service capability and provision of stand-by machine.
Accessibility of the service centre is important. For small peripheral hospitals, this becomes a real problem.
The standard size of an ultrasonography room should not be less than 16 m2 which will accommodate the examination bed apart from the equipment. A toilet attached to the room is desirable.
The ultrasonography machines are handled only by a qualified ultrasonologist. Therefore, no additional technical staff is necessary except an attendant. Other administrative staff such as receptionist or clerk, etc. can be pooled from the staff of the radiography department.