This is a computer based imaging technique . in this technique use X ray beams to produce cross section images of the body .the ct scan was developed by Godfry Hounsefield in 1972 .he awarded nobel prize for this invention. An Indian biophysicist Gopalasamudram N Ramachandran give the theoretical basis of this technique. The technique used to find dieases of brain , spinal cord , chest , abdomen etc. the tumors such as benigan and malignant tumors can be find out by this technique. Im ct scan a x ray emitting machine is rotated around the body region is to be examined .the x ray beam passed through the body in different angles . at the same time the x ray detector is rotated in opposite direction on the other side of the body .the tissues and body organs are varying thickness , they absorb x rays in different quantity. So the amount of x rays reaching at the detector is varied .the detector output is coupled to a computer where mathematically generates the image of the body parts. The advantage of ct scan is it gives three dimensional images.