or less of a typical scan and views are acquired through one half revolution of the gantry 12 plus the fan beam angle the x ray dose is thus considerably less than a normal image scan but nevertheless a slice image may be reconstructed this reconstructed slice image 104 is displayed on the crt 32 as shown in fig4 the operator may then select from one to three measurement regions a b and c by moving three elliptical cursors 106 108 and 110 to locations in the baseline image 104 these regions will be quantitatively monitored for changes in contrast enhancement in a liver scan as illustrated in fig4 for example the cursor 106 may be located over the aorta artery the cursor 108 may be located over the portal vein in the liver and the cursor 110 may be located over the liver tissue containing the suspected abnormality the mean value of the ct numbers in each of these regions a b and c is then calculated and these form baseline contrast enhancement values c a c b and c c referring again to fig3 the system then waits for the patient to be injected with the contrast agent as indicated at decision block 116 when the operator signals that this event has occurred a real time clock not shown is started and the system branches to a prescribed delay period indicated at process block 118 this is manually selected from 3 to 90 seconds to allow time for the contrast agent to begin reaching the monitored region of interest when this delay time expires a loop is entered in which a monitor scan is performed and a monitor image reconstructed as indicated at process block 120 the monitor scan is virtually identical to the baseline.