X-ray films are taken of the part of the body under investigation. Some dense tissues like bones, absorb more of these X-rays than others such as the lungs. As a result, in the X-ray picture of the part, we see some areas white indicating more density and some areas dark, indicating less density. Knowledge of how a normal structure looks like, helps in finding out where the fault lies in the X-ray picture of the patient.
X-ray examination involves exposure of a part of the body to X-rays. This should not be done in a pregnant woman. X-ray examination can be divided into two categories:
a) Plain
b) With contrast
Plain X-ray films are taken without any prior preparation. Usual X-rays of the chest and bones, etc. fall under this category. Removal of the clothing which may obstruct the X-rays partly or wholly, is necessary.
Contrast films are taken when a particular hollow organ, like intestines, urinary or gall-bladder or blood vessels are to be delineated.
Tomogram: The usual plain X-ray, as for example, of the chest shows in one plane, all the structures present from back to front, and it becomes difficult to gaze the exact situation of the abnormality.
Tomogram is a series of X-rays taken at different distances from the back, for example, 3 cm, 7 cm, 10 cm, 15 cm or 20 cm or so. This helps in seeing and placing the abnormality more sharply, for follow up or for surgical operation.
CT Scan: It is computerized tomogram, also called CAT scan (computerized axial tomography). In CT scanning, the X-ray source rotates round the part of the body under examination, and the X-ray detector receives information of the density of the body at a particular point of the body. When the scanner and the detector have rotated around the body, the information obtained from all angles is processed by a computer, which produces a picture on the television screen, showing the density of all the body’s structures in the area about which it has rotated. This picture is of a slice of the body as thin as 1/2 cm or more, as required. An X-ray record of each slice can be taken, and thus a composite picture emerges.
Herein we have plain X-ray, not of the part of the body collectively seen from back to front (posterior to anterior), but a slice of the body part under examination. We can see that part, just as we see the section of a thin potato wafer. We can visualize the slices of the body, one after the other, so that we can estimate the extent of the lesion and its exact location.
The usual tomogram shows less resolution, so that the visibility of the part is poor. But in CT scan, the visualization is very clear.
Radioisotope Tests: A very small quantity of a particular radioactive material is injected intravenously in a patient. This particular material has the property to get concentrated in a particular organ, as for example, radioactive iodine in thyroid. The total quantity of radioactivity and its dimension in an organ is scanned by a camera called gamma camera. This tells whether the whole or part of the organ has taken the radioactive material and also whether the organ has taken more or less than the normal, thereby indicating the disease affecting the organ.
Ultrasonic Tests: Sound waves of very high frequency which a human ear cannot hear from a fine source called the ‘probe’ are pressed against a part of the body through which they pass and strike internal organs of various densities and are then bounced back and recorded. This record compared with the normal, gives an indication of the size of an organ or part of an organ and any abnormality indicated therefrom.
This can be seen on the television screen and recorded on an X-ray film No special preparation is necessary and it causes no discomfort or after effect to the patient.