Ting-Yim Lee MSc, PhD, Abstract Co-Author: Research grant, General Electric Company Consultant, General Electric Company

Aaron So, Presenter: Nothing to Disclose

Glenn Stuart Bauman MD, Abstract Co-Author: Nothing to Disclose

Jiang Hsieh PhD, Abstract Co-Author: Employee, General Electric Company

Jean-Baptiste Thibault, Abstract Co-Author: Employee, General Electric Company, Waukesha, WI

Roman I. Kozak MD, Abstract Co-Author: Nothing to Disclose

Radiation dose is a critical limitation in the use of CT Perfusion (CTP) to measure cerebral blood flow (CBF) and blood volume (CBV) in stroke and brain tumor patients. We investigated the use of ASIR (GE Healthcare) to reduce radiation dose from CTP studies.

Four brain tumor patients were studied. Each patient had two CTP brain studies separated by 10 min on a HD 750 CT scanner (GE) with injection of 1ml•kg-1 Omnipaque 300 at a rate of 3 ml•s-1 each time. Both studies used a two phase protocol scanning eight 5 mm thick slices at 80 kVp: 1s images at 0.5 s intervals for 45 s followed by images at 15 s intervals for another 90 s. The x-ray tube current was reduced from 200mA (HD) to 20 mA (LD) between studies. Images in both studies were reconstructed with regular filter backprojection and with ASIR(GE) and CBF, CBV and average maps were generated from them using CT Perfusion 4 software(GE). Grey and white matter were segmented using HU thresholds from the average maps and their pixel masks superimposed on the CBF and CBF maps to determine the mean (Μ) and standard deviation (σ) of each parameter in the respective tissue. A figure of merit (FOM), defined as σ/Μ of the parameter in the tissue, was used to asses the quality of each grey or white matter parametric map: smaller FOM implies better quality and vice versa. Paired t-tests were used to compare FOMs from HD and LD studies reconstructed with and without ASIR.

For white matter CBF, the FOMs for HD, HD+ASIR, LD and LD+ASIR were 0.44±0.03, 0.43±0.05 (NS), 0.63±0.09 (*) and 0.49±0.04 (NS), where NS denotes non-significant and * significant differences from HD; and those for white matter CBV were: 0.37±0.03, 0.36±0.03 (NS), 0.61±0.01(*) and 0.47±0.05 (NS). Similar results were obtained for grey matter CBF and CBV.

This study showed that ASIR can reduce the effective dose of a CT Perfusion brain study by 10 times (5.9 vs 0.59 mSv) relative to the standard technique of 80kVp and 200mAs per image without affecting the quality of CBF and CBV maps in both grey and white matter. The recommended standard technique for CT Perfusion may not be dose limited because ASIR did not improve the quality of parametric maps obtained.

The low effective dose made possible with the application of ASIR will increase the use of CT Perfusion brain studies in stroke and brain tumor patients.

Lee, T, So, A, Bauman, G, Hsieh, J, Thibault, J, Kozak, R, Reducing Effective Dose from CT Perfusion with Adaptive Statistical Iterative Reconstruction (ASIR).  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8006952.html