ABSTRACT
ObjectiveTo investigate the CT number linearity of the cone-beam CT (CBCT) images at the different spatial locations in the scanning area.MethodsThe CatphanS04 phantom at the different locations are scanned repeatcdly using the CBCT on the Varian 23EX linear accelerator.The phantom is located the isocenter point,eccentric 3 cm,eccentric 6 cm,and different points on the z-axis successively on the accelerator.The scanned mode is the standard head mode.The reconstructive thickness is 2.5 cm.The different densities inserts of CTP404 module on the different locations are measured via Eclips treatment planning system (TPS) and computed by Matlab 7.0 and the CT linear fitting are then processed.In order to understand better the linear distribution along with the value of CT in the spatial distribution the results are compared with the fan-beam CT.ResultsPhantom studies show that:CBCT has good linearity performance not only under the standard header (body) of the scanning conditions,but also on such locations including the cross-sectional,the sagittal,the coronal plane and the eccentric position ( R2 ＞ 0.953 ).Bowtie filtration device does not change the CT finearity but changes the value of CT.ConclusionsThe linearity of X-ray CBCT on the Varian linear accelerator is favorable.CBCT will be used in the TPS dose calculation via further correction of the CT value.
ABSTRACT
Objective To assess the single-exponential and dual-exponential fitting methods of MR T2-Map, and to get T2 value of each pixel. Methods Single and dual-exponential methods with linear fitting and non-linear regression fitting techniques were used for a series images with different TE; then T2-Map images were achieved. T2-Map software was realized on MATLAB and it had the function of compute, display, save and so on. Results T2-Map software with single-exponential and dual-exponential fitting methods was achieved, able to calculate T2 value of tissues everywhere and form the T2-Map image. Conclusion Single-exponential T2-Map method is convenient, having obvious merit-high speed, but can not show the area with obvious different contents very well. However, dual-exponential fitting method can deal with this question with providing different T2 values, thus is accurate with the sacrifice of costing too much time. Dual-exponential fitting method of T2-Map is a beneficial supplement to single-exponential method.