Comparison of Dosimetry and Image Quality in Computed and Conventional Tomography

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Abstract
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: 1st, GE CT/T 8800 system; 2nd, EMI; 3rd, 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 .times. 10-4 C/kg). The EMI exposure level was 5 R (13 .times. 10-4 C/kg) in the fast mode and 12 R (31 .times. 10-4 C/kg) in the slow mode, while the Delta 50 exposure level was fixed at 2 R (5.2 .times. 10-4 C/kg). 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 .mu.C/kg) but a typical operating exposure would be about 1-2 R (2.58-5.2 .times. 10-4 C/kg). Dosimetry was 1.1-5.5 R/scan section (2.8-14.2 .times. 10-4 C/kg) 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.

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