Vassilios Raptopoulos MD, PRESENTER: Nothing to Disclose

Abstract: HTML Purpose: To investigate if with decreasing slice thickness, renal stone conspicuity will improve if scanning with low mA Methods and Materials: We measured the CT attenuation of 30 renal stones of six different types including uric acid, cystine, struvite, calcium oxalate dehydrate and monohydrate and brusite. Each group included five stones, 3 mm to 12 mm in size, suspended in a 2x renal attenuation simulation fluid of diluted play-dough (60 - 80 HU). Stones of each type immersed in simulation were placed in the bore of a CT body dose phantom. Scanning was done with 120 kV at 200, 150, 100, and 50 mA on a multislice 8-retector-row scanner, 1.25 mm collimation, 0.5 sec/rotation. Axial images were reconstructed at 1.25, 2.5 and 5.0 mm slice thickness. The scanning and display filed of view was 50 cm and 36 cm, respectively. Mean HU and SD of region of interest occupying 3/4 of the center of stones and renal simulation the material were. recorded. ANOVA model used to study the effects of mA and slice thickness on density measurements. Multiple t-test of least square means was used to explore effect of slice thickness and stone size on stone conspicuity while adjusting mA and slice thickness. Results: : With varying mA, the mean attenuation of the various stones did not change significantly. However the SD decreased when mA increased from 50 to 100 to 150 but not from 150 to 200. As slice thickness increased there was statistically significant decrease in mean attenuation and a tendency of SD to decrease as well. ANOVA model fit to test global effect of mA and slice thickness on stone density showed that mA does not significantly impact mean HU measurements as opposed to stone type. slice thickness and stone size. All these factors, however were significant source of variation as indicated by changes in SD. Multiple t-tests of the least square means to test the effect of each factor on stone conspicuity showed that stone densitities of all but two stone types (COM and brusite) had significantly different attenuation and the denser stones had greater SD. No mA level provided statistically different stone attenuation or SD, except higher SD with 50 mA. All levels of slice thickness were statistically different with increasing both mean and SD with decreasing slice thickness. All stones were differentiable from renal simulation material by mean attenuation values. Conclusion: In in vitro imaging of small stones, thin collimation of 1.25 mm minimized partial volume effect allowing stone visualization with use of extremely low energies of 25 mAs (V.R. is a consultant for and received a grant from GE Medical Systems. J.B. is an employee of Averion, Inc.) Questions about this event email: vraptopo@bidmc.harvard.edu

Raptopoulos MD, V, Influence of Milliamperage and Slice Thickness on CT Conspicuity of Renal Stones in Vitro.  Radiological Society of North America 2003 Scientific Assembly and Annual Meeting, November 30 - December 5, 2003 ,Chicago IL. http://archive.rsna.org/2003/3108723.html