J Comput Assist Tomogr, Volume 33, Number 4, July/August 2009
Jenny K. Hoang, MBBS, FRANZCR, Lynne M. Hurwitz, MD, and Daniel T. Boll, MD
Abstract: 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, radio¬graph 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 ialculated. 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); cir¬cumferences based on scouts adequately reflected body weight (co¬efficients, 0.86maie/0.87ftma|e). 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 cor-onaty enhancement can be used for future coronary CT angiography optimization of tube current based on scout imaging.