|ECR 2019 / C-1060||
|A New Iterative Reconstruction CT Technique of Forward Projected Model-based IR Solution (FIRST): Evaluation of Image Quality at Head CT using a Cerebral Stroke Phantom Model|
1. FIRST images
Fig. 6 , Fig. 7 , and Fig. 8 shows the simulation results of each Forward projected model-based Iterative Reconstruction Solution images. Both FIRST Brain and FIRST Brain LCD can observe a significant reduction in noise as the intensity of image reconstruction increases. Furthermore, this tendency appeared remarkably in FIRST Brain LCD rather than FIRST Brain. Focusing on the difference in slice thickness, The slice thickness of 1 mm had less image blur than the slice thickness of 5 mm, and the affected part was clearly drawn.
Fig. 9 , Fig. 10 , and Fig. 11 shows the simulation results of CNRLO in each Forward projected model-based Iterative Reconstruction Solution images. CNRLO showed higher FIRST Brain LCD than FIRST Brain. Both FIRST Brain and FIRST Brain LCD showed higher values as mA was higher, and strong showed the highest value. Compared to FBP, strong in FIRST Brain and all FIRST Brain LCDs got higher, FIRST Brain LCD showed approximately 2.3 times higher value. Focusing on the difference in slice thickness, the value of CNRLO also increased as the slice thickness rose.
The important point here is that guidelines and others have recommended that slice thickness of about 8 mm be used for detection of acute cerebral infarction, However, from the results of this study, it is the point that use of slice thickness of 1 mm is sufficiently conceivable. In other words, the effect of using thin slice thickness revealed the possibility of clarification of lesion area of infarction and detection of microinfarct like lacunar infarction.
Fig. 12 , Fig. 13 , and Fig. 14 shows the simulation results of FOM in each Forward projected model-based Iterative Reconstruction Solution images. FOM showed higher FIRST Brain LCD than FIRST Brain. Both FIRST Brain and FIRST Brain LCD showed higher values as mA was higher, and strong showed the highest value. The FOM was 17 times faster than FBP at 200 mA , 28 times at 400 mA , and 55 times at 600 mAs in reconstruction of strong, obtained of slice thickness of 1 mm. At 200 mA, there is not much difference, but significant difference was seen in FOM under photography conditions (FIRST Brain LCD；standard and strong) of 400 mA or more. That is, it turned out that a certain dose was required.
FIRST revealed that the degree of image quality improvement per patient's exposure dose will be higher. Moreover, the image quality improvement degree increases at a low dose and images with high image quality can be acquired by reconstructing with FIRST.
4. FIRST optimization
Fig. 15 shows FBP and optimized FIRST images. Compared with 120 kV, 400 and 600 mA (mild, standard, and strong images), CNRLO increase between 121 % and 252 % at 400 mA, between 165 % and 309 % at 600 mA. Also, FOM increase approximately 1900 %, and the absorbed dose may be reduced by 50 % or more at 120 kV, 400 mA, FIRST Brain LCD of strong.