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Purpose: The planar average equilibrium dose of CT is measured using the methodology suggested by AAPM report No. 111, and compared with the traditional weighted average estimate and the new proposed equal weighted average estimate. Methods: The study used a 320 slices Toshiba Aquilion ONE scanner, three CTDI body phantoms with total length of 46.5 cm (two of them are nested 3 piece CTDI phantoms with diameters of 10, 16, and 32 cm for each piece), a Radcal Accu‐Pro electrometer, and a Radcal 0.6 cc farmer chamber. In the helical mode (120 kVp, 200 mAs, nominal beam width 0.5×16 mm, pitch 0.938), we measured the cumulative dose DL(z=0) at the center of the phantoms and 12 clock position at radius of 4, 7, and 15 cm from the center, for scan length L=100, 200, 300, and 400 mm. The procedure was repeated for pitch setting of 0.641 and 1.438 and nominal beam width of 0.5×160 mm and 0.5×64 mm at L=400 mm. Results: The data obtained at four scan lengths were fit to estimate the equilibrium Dose (Deq) at radius of 0, 4, 7 and 15 cm from the phantom center. Three models (linear, quadratic, and exponential) were then used to fit DL(z=0) and Deq as a function of radius to phantom center for various scan length, pitch, and beam width combinations. We calculated the planar average cumulative (and equilibrium) dose using the above models and compared the results with the traditional weighted average estimate (Dcenter/3+2Dedge/3) and the new proposed equal weighted average estimate (Dcenter/2+Dedge/2). The planar average dose differs from the traditional weighted estimate within 2%, and equal weighted estimate within 10%. Conclusion: The traditional weighted average method provides a more accurate estimate to the CT planar average equilibrium dose than the proposed equal weighted average method.

Objectives To predict the chronic kidney disease (CKD) state for pediatric patients based on scaled renal cortical echogenicity. Methods Sonograms from a cohort of 26 patients, half of whom had stage 4 or 5 CKD, whereas the other half had normal renal function, were analyzed. For each patient image, a region of interest (ROI) was drawn around the renal cortex for comparison with an ROI drawn around the hepatic parenchyma. The latter ROI was shifted spatially to normalize the signal attenuations and time‐gain compensations of the two organs’ ROIs. Then the average pixel intensity of the renal ROI was divided by the corresponding hepatic value, resulting in scaled renal cortical echogenicity. Results The average scaled renal cortical echogenicity was higher for diseased than healthy kidneys by roughly a factor of 2 (2.01 [95% confidence interval, 1.62–2.40] versus 1.05 [95% confidence interval, 0.88–1.23] for normal kidneys). This difference was statistically significant (P < .001). Conclusions Our results show that the pediatric CKD state correlates with rigorously calculated scaled renal cortical echogenicity.

Purpose:To investigate the kVp dependence of the transmitted exposure for a radiography x‐ray unit.Methods:The study used a GE DiscoveryTM XR656 DR unit, a 30 (L) × 30 (W) × 25 cm thick Lucite phantom, two anthropomorphic phantoms (an Alderson RS‐310 chest phantom and a 3M skull phantom), an Unfors detector, and a Radcal 10×9‐6 ion chamber. We measured the entrance exposure and transmitted exposure of each phantom at 60, 70, 80, 90, 100, 110, 120 kVp for mAs range from 2.5 to 200 mAs, without any additional filter. The FOV is 30×30 cm for the Lucite and chest phantom (AP view), and 20×20 cm for skull phantom (Lateral view). The transmitted exposure was measured at the phantom center of the x‐ray exit side. For chest phantom, the transmitted exposures at 3 inch upper right and upper left from the center were also measured. We also checked the reproducibility and accuracy of the DR unit.Results:For each phantom, at every kVp and mAs setting, the transmitted exposure per mAs was calculated and normalized by the relative entrance exposure; the averaged transmitted exposure per mAs at each specific kVp was then determined. For chest phantom, the mean transmitted exposure per mAs was the average of three exit locations. The averaged transmitted exposure per mAs was fit as a power function of kVp. The result showed the transmitted exposure per mAs was approximately proportional to third power of the kVp for two anthropomorphic phantoms and forth power of the kVp for the Lucite phantom.Conclusion:The traditional assumption of fifth power kVp dependence to the transmitted exposure is inaccurate. At the normal radiography kVp range, the transmitted exposure is approximately proportional to third power of the kVp for a typical patient and up to forth power of the kVp for a large patient.