Yasuhiro Imai MS, Presenter: Employee, General Electric Company

Takanori Tsunoo PhD, Abstract Co-Author: Employee, General Electric Company

Junko Sekiguchi, Abstract Co-Author: Employee, General Electric Company

Masaru Seto, Abstract Co-Author: Employee, General Electric Company

Hisanori Tsunemine, Abstract Co-Author: Employee, General Electric Company

Masatake Nukui MS, Abstract Co-Author: Employee, General Electric Company

Ryosuke Fujimoto MS, Abstract Co-Author: Employee, General Electric Company

00030490-DMT et al, Abstract Co-Author: Nothing to Disclose

Bismuth shielding is effective method to reduce breast dose on the CT examination, however, it brings beam hardening artifact from the bismuth, and is not so easy to estimate optimum tube current including the attenuation of the bismuth. The purpose of this study was to develop a sensitive organ targeted angular tube current modulation and evaluate its dose reduction effectiveness.

We developed the sensitive organ targeted angular tube current modulation by graphically setting virtual bismuth on the scout view image on the CT. This feature has a rapid tube current modulation to change to half tube current (less than 50 msec), for instance, 200 to 100 mA. And it has capabilities to optimize tube current angular range and tube current reduction rate for the breast. We retrospectively measured an angular range of mammary gland using 40 female chest CT images, and optimized the modulation angle. We also made a dose distribution simulation environment based on the BEAMnrc (NRC, Canada) included x-ray spectrum, bowtie filter absorption, scattered radiation, tube currents for each view and object information. The accuracy of the simulation environment was verified by measured CT Dose Index (CTDI) values on the 64-slice (LightSpeed VCT, GE Healthcare, WI). After that, a human body phantom for the radiotherapy was scanned on the 64-slice CT, and its radiation dose reduction rate at the breast was simulated.

Measured angle range to cover mammary gland was 154.2±19.8 deg, and the tube current angular range was optimized. An error value between measured and simulated dose values using the CTDI phantom was 3.4±3.3%. The simulated dose reduction rate was up to 40% at the breast area by 50% tube current reduction with optimum modulation angle range.

The proposed sensitive organ targeted angular tube current modulation showed possibility to reduce radiation dose up to 40% at breast area with maintaining image quality without the bismuth shield. This method utilizes the full reconstruction algorithm, so it has a possibility to reduce more radiation dose by combined with new image reconstruction algorithm.

The sensitive organ targeted angular tube current modulation has possibility to enable same level dose reduction as bismuth shielding at the breast with keeping image quality on the CT scan.

Imai, Y, Tsunoo, T, Sekiguchi, J, Seto, M, Tsunemine, H, Nukui, M, Fujimoto, R, et al, 0, Breast Dose Reduction Using A Novel Sensitive Organ Targeted Angular Tube Current Modulation on CT.  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8013511.html