Optimization of tube current in coronary multidetector computed tomography angiography: assessment of a standardized method to individualize current selection based on body habitus.
UNLABELLED: This study sought to extract information on individual patient habitus from scout imaging and to correlate radiograph tube current settings with enhancement of the coronaries as a function of patient profiles for coronary multidetector computed tomography. MATERIALS AND METHODS: Fifty patients underwent coronary 64-slice multidetector computed tomography consisting of 2-plane scouts and electrocardiography-gated coronary studies at 64 x 0.625 mm, radiograph voltage of 120 kVp, and radiograph currents of 295 to 788 mA, which were reconstructed during 65%, 75%, and 85% R-R intervals. Patients' weight was recorded. On scout imaging, chest diameters were determined, and circumferences were calculated. To determine whether body weight showed sex-specific characteristics, t test was used. Pearson correlation determined whether cross-sectional measurements reflected female/male body habitus. On coronary imaging, contrast-to-noise ratios (CNRs) of the aorta and the coronaries were calculated. To assess whether CNRs differed throughout the diastolic phase, t test was used. Data triplets of CNRs and the corresponding current and circumference were plotted; CNRs less than 250 Hounsfield unit (HU) were discarded, dissecting lines as 95th percentiles correlating radiograph currents and patients' circumferences were calculated. RESULTS: Female/male weights differed significantly (P = 0.0006); circumferences based on scouts adequately reflected body weight (coefficients, 0.86 male/0.87 female). Homogenous vascular enhancement of the aorta (mean +/- SD, 344.4 +/- 81.8 HU) and the right (292.3 +/- 82.8 HU) and left (285.8 +/- 81.3 HU) coronaries was achieved (P > 0.005). Ninety-fifth percentile cutoffs identified linear relationships between patient's circumference and the minimal adequate radiograph current achieving CNR less than or equal to 250 HU. CONCLUSION: Scout imaging can be used to determine individual patient habitus; habitus-adjusted minimal radiograph tube current cutoff levels identified in this study ensuring clinically required levels of coronary enhancement can be used for future coronary CT angiography optimization of tube current based on scout imaging.
Hoang, JK; Hurwitz, LM; Boll, DT
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