Clarify behavioral factor of X-ray scatter in MDCT scanners based on evaluation data by a wide variety of MDCT scanners

Transcription

1 Clarify behavioral factor of X-ray scatter in MDCT scanners based on evaluation data by a wide variety of MDCT scanners Poster No.: C-1748 Congress: ECR 2012 Type: Educational Exhibit Authors: S. Miyashita 1, S. Tokuyasu 2 ; 1 Sapporo/JP, 2 Tokyo/JP Keywords: Artifacts, Physics, Image compression, CT, Education DOI: /ecr2012/C-1748 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 11

2 Learning objectives Review Image quality effects of scattered radiation. Review anti-scatter grids and its impact on overcoming x-ray scatter. Demonstrate the difference effects of X-ray scatter by a wide variety of MDCT scanners. (7models of 5 vendors) Background CT scanner is rapidly developing to wide coverage. It is possible to be different behavior of X-ray scatter because it has different specification of MDCT. However, there are no reports which evaluate with the behavioral factor of X-ray scatter in MDCT on detail. Conventional anti-scatter grids with in-plane axis (1D) remove the impact of X-ray scatter. Therefore CT value and repeatability of image keep correctly. A lot of CT scanner removes the impact of X-ray scatter by conventional anti-scatter grid (1D) even increasing longitudinal coverage of CT scanner. On the other hands, a CT scanner with 2D anti-scatter grid which removes the impact of X-ray scatter of longitudinal axis turns up in the market. (Fig. 1) Images for this section: Page 2 of 11

3 Fig. 1: 2D-Anti Scatter Grid It is possible the effect of X-ray scatter removal for X and Z-direction. Page 3 of 11

4 Imaging findings OR Procedure details Phantom design: We designed our phantom by combining water phantom (internal diameter##300mm, internal length#275mm) with a pair of lead rings (Pb ring) (internal diameter##320mm, width#300mm, Tickness#3mm). (Fig.2) CT scans were performed to control beam width by adjusting distance of a pair of Pb ring that passes through the water section the phantom. (Fig.3) We define the distance of a pair of Pb ring as slit. Slit center of Pb ring is placed on the center row of machine. Scan parameters are as follows; tube voltage 120kV, tube current 500mA, rotation time 1.0sec/rot, slice thickness 5mm, conventional scan. We estimated Scatter-to-Primary Ratio (SPR)for evaluating of the impact of scatter Specifically, SPR set up from the subtraction between CT value with Pb ring to CT value without Pb ring. We measured SPR on a variety of MDCT scanners. (7 models of 5 vendors) Brilliance 64 (Philips Healthcare, Cleveland, OH, USA) (Vender1 1D ASG) Brilliance ict (Philips Healthcare, Cleveland, OH, USA) (Vender1 2D ASG) LightSpeed VCT(GE Healthcare, Milwaukee, WI, USA) (Vender2 1D ASG) Aquilion 64 (Toshiba Medical Systems, Otawara, Japan) (Vender3-1 1D ASG) Aquilion ONE (Toshiba Medical Systems, Otawara, Japan) (Vender3-2 1D ASG) SOMATOM Definition AS+ (Siemens Healthcare, Forchheim, Germany) (Vender4 1D ASG) SCENARIA (Hitachi Medical Systems, Kashiwa, Japan) (Vender 2D ASG) Brilliance ict(philips Healthcare) and SCENARIA(Hitachi Medical Systems) are equipped with 2D anti-scatter. Result: CT value changed in all vendors CT machine. CT value without Pb ring was higher than CT value with Pb ringalso, when the distance of Pb ring keeps same, CT values is higher when beam width is wider in all vendors CT machine. Minimum distance of Pb ring is 10mm in this demonstration. Setting beam width and raising CT value were as follows. (fig.4) Vender1(1D ASG) ;CT value raises 12.9HU in 40mm beam width. (collimation mm) Vender1(2D ASG) ; CT value raises 5.5HU in 40mm beam width. (collimation mm) Page 4 of 11

5 Also CT value raises 7.5HU in 80mm beam width. (collimation mm) Vender2(1D ASG) ; CT value raises 13.1HU in 40mm beam width. (collimation mm) Vender3-1(1D ASG) ; CT value raises 6.8HU in 32mm beam width. (collimation mm) Vender3-2(1D ASG) ; CT value raises 9.33HU in 40mm beam width. (collimation mm) Also CT value raises 14.24HU in 80mm beam width. (collimation mm) and raises 26.77HU in160mm beam width (collimation mm) Vender4 (1D ASG) ; CT value raises 12.7HU in 38mm beam width. (collimation mm) Vender5 (2D ASG) ; CT value raises 12.0HU in 40mm beam width. (collimation mm) The result of calculation as raising CT value divided by beam width (fig.5) Vender1 1D ASG#Vender2 1D ASG#Vender4 1D ASG has almost same value. Vender3-1 1D ASG and Vender3-2 1D ASG has slightly lower value compared as other three venders. Vender5 2D ASG has almost same value as 1D ASG machines of other vendors. However, vender1 2D ASG has the lowest value in all vendors MDCT scanners. Images for this section: Page 5 of 11

6 Fig. 1: 2D-Anti Scatter Grid It is possible the effect of X-ray scatter removal for X and Z-direction. Page 6 of 11

7 Fig. 2: Water phantom with lead rings. This phantom make from water phantom and a pair of lead rings, The detail of water phantom as follows; internal diameter : 300mm. Internal length: 275mm, The detail of a pair of lead rings as follows ; internal diameter : 320mm. Width : 300mm, thickness : 3mm Page 7 of 11

8 Fig. 3: Water phantom with lead rings. CT scan target to slit which made by adjusting the distance a pair of lead ring. Page 8 of 11

9 Fig. 4: Raising CT value in case of slit width :10mm Raising CT value due to impact of X-ray scatter in each machine. Page 9 of 11

10 Fig. 5: Calculate scatter factor on each scanner model. Scatter factor calculate as raising CT value in 10mm beam divided beam width on each machine. Scatter factor means specific raising CT value on each machine ignoring beam width. Page 10 of 11

11 Conclusion The shifting of CT value caused by scatter occurred in all vendors MDCT scanners. It is possible that distance of Pb ring and beam width are the main factors for the shifting of CT value. 2D ASG is also possible to be important factor of shifting CT value. Vender 1(2D-ASG) can reduce shifting volume of CT value effectively. On the other hands, Vender 5(2D-ASG) is not so different shifting volume of CT value compared as other machines with 1D-ASG. We gather from above result that both 2D-ASG has different grid-ratio and Vender 1 has higher grid-ratio as compared Vender 5. X-ray scatter increased with increasing longitudinal coverage of CT scanners as a result of Vender 3-2 machine. It is considered that 2D-ASG influence removing X-ray scatter regularly even though expecting X-ray correction in software. This study is very useful for verifying the problem of CT scanners with wide longitudinal coverage. Personal Information References Joseph PM, Spital RD. The effects of scatter in x-ray computed tomography. Med Phys Jul-Aug;9(4): Chan HP, Lam KL, Wu YZ. Studies of performance of antiscatter grids in digital radiography: effect on signal-to-noise ratio. Med Phys Jul- Aug;17(4): Ning R, Tang X, Conover D. X-ray scatter correction algorithm for cone beam CT imaging. Medical Physics. 2004;31(5):1195. Endo M, Mori S, Tsunoo T, Miyazaki H. Magnitude and effects of x-ray scatter in a 256-slice CT scanner. Medical Physics. 2006;33(9):3359. Engel KJ, Herrmann C, Zeitler Gn. X-ray scattering in single- and dualsource CT. Medical Physics. 2008;35(1):318. Page 11 of 11