COMPARISON OF DOSIMETRY AND IMAGE QUALITY IN COMPUTED AND CONVENTIONAL TOMOGRAPHY

Comparison was made of tomograms of a phantom head and a normal adult cadaver head on GE CT/T, Delta 50, EMI 5005, and CGR Stratomatic units. Image quality was ranked as follows: First, GE CT/T 8800 system; second, EMI; third, GE CT/T 7800 and Delta. The GE CT/T 7800 imaged 3.7 line pairs at high contrast with an exposure to the head phantom of 2.5 R (6.5 x 10-4 C kg-1). The EMI exposure level was 5 R (13 x 10-4 C kg-1) in the fast mode and 12 R (5.2 x 10-4 C kg-1) in the slow mode, while the Delta 50 exposure level was fixed at 2 R (5.2 x 10-4 C kg-1). The GE CT/T 8800 could image 6.1 line pairs/cm in a high-contrast phantom with exposures as low as 100 mR (25.8 μC/kg) but a typical operating exposure would be about 1-2 R (2.58-5.2 x 10-4 C kg-1). Dosimetry ranged from 1.1 to 5.5 R/scan section (2.8-14.2 x 10-4 C kg-1) in the CT units but never increased by a factor of more than 2, irrespective of the number of sections scanned. In conventional tomography, however, exposure increased almost arithmetically with the number of contiguous sections scanned.