The in vivo relationship between cross-sectional area and CT dose index in abdominal multidetector CT with automatic exposure control.
The relationship between patient cross-sectional area and both volume CT dose index (CTDI) and dose length product was explored for abdominal CT in vivo, using a 16 multidetector row CT (MDCT) scanner with automatic exposure control. During a year-long retrospective survey of patients with MDCT for symptoms of abdominal sepsis, cross-sectional areas were estimated using customised ellipses at the level of the middle of vertebra L3. The relationship between cross-sectional area and the exposure parameters was explored. Scans were performed using a LightSpeed 16 (GE Healthcare Medical Systems, Milwaukee, WI) operated with tube current modulation. From a survey of 94 patients it was found that the CTDI increased with the increase in patient cross-sectional area. The relationship was logarithmic rather than linear, with a least-squares fit to the data (R(2) = 0.80). For abdominal CT the cross-sectional area gave a measure of patient size based on the region of the body to be exposed. Exposure parameters increased with increasing cross-sectional area and the greater radiation exposure of larger patients was partly a consequence of their size. Given increasing obesity levels we believe that cross-sectional area and scan length should be added to future dose surveys, allowing patient size to be considered as a factor of relevance when examining population doses.
Radiology Group, Nuffield Department of Surgery, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DU, UK. stuart.meeson@nds.ox.ac.uk
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Meeson
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Alvey
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Golding
D000005:Abdomen / Q000033:anatomy & histology*; D001822:Body Burden; D049628:Body Size; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009929:Organ Size; D011829:Radiation Dosage; D011860:Radiography, Abdominal / Q000706:statistics & numerical data*; D018570:Risk Assessment; D013223:Statistics as Topic; D014057:Tomography, X-Ray Computed / Q000706:statistics & numerical data*; D006113:United Kingdom / Q000453:epidemiology