Stuart Lance Cohen MD, Presenter: Nothing to Disclose

Thomas J. Ward MD, Abstract Co-Author: Nothing to Disclose

Mary Margaret Salvatore MD, Abstract Co-Author: Nothing to Disclose

Adam Jacobi MD, Abstract Co-Author: Nothing to Disclose

Matthew D. Cham MD, Abstract Co-Author: Nothing to Disclose

To determine the impact of CT Scanner capabilities on excess Z-axis scan length and radiation dose.

Noncontrast chest CTs performed between February and July 2012 were evaluated for excess Z-axis scan length (ES). ES was defined as the scanned distance superior or inferior to the lung parenchyma and was compared across different CT scanners. Analysis was performed with ANOVA, F-test, and t-tests. Technologists were instructed to use the minimum scan length needed to include the entire lung during chest CT. These exams were performed with 4 different CT scanners: Siemens Somatom 40 slice (CT1); GE Light Speed 8 slice (CT2); GE VCT 64 slice (CT3); and GE HD750 64 slice (CT4). CT1 provides real-time visualization of the scan and a mouse-driven scan stop capability. CT2 provides real-time visualization of the scan and a keyboard-driven scan stop capability. CT3 and CT4 do not allow real-time visualization or scan stop capability.  

1287 consecutive noncontrast CT scans were evaluated: 475 on CT1, 237 on CT2, 279 on CT3, and 296 on CT4. Mean total excess Z-axis scan length (EST) was 47 mm. CT scanner was a significant predictor EST (p<.001), independent of technologist. CT2 EST was 23% (p<.001) greater than CT1 (48 mm to 39 mm). CT3 EST was 33% (p<.001) greater than CT1 (52 mm to 39 mm). CT4 EST was 34% (p<.001) greater than CT1 (53 mm to 39 mm). Mean excess Z-axis scan length inferior to the lung (ESI) was 28.0 mm. CT scanner was a significant predictor ESI, (p<.001), independent of technologist. CT2 ESI was 36.0% greater (p<.001) than CT1 (29 mm to 22 mm). CT3 ESI was 48.6% greater (p<.001) than CT1 (32 mm to 22 mm). CT4 ESI was 55.7% greater (p<.001) than CT1 (34 mm to 22 mm) and 14 % greater (p<.05) than CT2 (34 mm to 29 mm).  

Real-time visualization of CT scans with mouse-driven scan stop capability significantly reduces ES (p<.001) and thus excess radiation dose. This excess scan length reduction addresses the lack of concordance between the position of the costophrenic angle on the scout film and during the CT acquisition which makes it impossible to predict the minimum scan length needed to include the entire lung.

Real-time visualization of CT scans with mouse-driven scan stop capability should be an essential feature of CT scanners to minimize Z-axis scan length and to reduce patient dose. 

Cohen, S, Ward, T, Salvatore, M, Jacobi, A, Cham, M, Impact of CT Scanner Capabilities on Excess Z-Axis Scan Length and Its Associated Radiation Dose.  Radiological Society of North America 2013 Scientific Assembly and Annual Meeting, December 1 - December 6, 2013 ,Chicago IL. http://archive.rsna.org/2013/13012869.html