Simulation system for understanding the lag effect in fluoroscopic images
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Simulation system for understanding the lag effect in fluoroscopic images Rie Tanaka • Hiroki Kawashima • Katsuhiro Ichikawa Kosuke Matsubara • Hiroji Iida • Shigeru Sanada
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Received: 17 July 2012 / Revised: 11 December 2012 / Accepted: 11 December 2012 / Published online: 29 December 2012 Ó Japanese Society of Radiological Technology and Japan Society of Medical Physics 2012
Abstract Real-time tumor tracking in external radiotherapy can be achieved by diagnostic (kV) X-ray imaging with a dynamic flat-panel detector (FPD). It is crucial to understand the effects of image lag for real-time tumor tracking. Our purpose in this study was to develop a lag simulation system based on the image lag properties of an FPD system. Image lag properties were measured on flatfield images both in direct- and indirect-conversion dynamic FPDs. A moving target with image lag was simulated based on the lag properties in all combinations of FPD types, imaging rates, exposure doses, and target speeds, and then compared with actual moving targets for investigation of the reproducibility of image lag. Image lag was simulated successfully and agreed well with the actual lag as well as with the predicted effect. In the indirectconversion FPD, a higher dose caused greater image lag on images. In contrast, there were no significant differences among dose levels in a direct-conversion FPD. There were no relationships between target speed and amount of image blurring in either type of FPD. The maximum contour blurring and the rate of increase in pixel value due to image
R. Tanaka (&) K. Ichikawa K. Matsubara S. Sanada Department of Radiological Technology, School of Health Sciences, College of Medical, Pharmaceutical and Health Sciences, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa 920-0942, Japan e-mail: [email protected] H. Kawashima Division of Health Sciences, Graduate School of Medical Science, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa 920-0942, Japan H. Kawashima H. Iida Department of Radiological Technology, Kanazawa University Hospital, 13-1 Takara-machi, Kanazawa 920-8641, Japan
lag were 1.1 mm and 10.0 %, respectively, in all combinations of imaging parameters examined in this study. Blurred boundaries and changes in pixel value due to image lag were estimated under various imaging conditions with use of the simulation system. Our system would be helpful for a better understanding of the effects of image lag in fluoroscopic images. Keywords Image lag Simulation Target tracking Image-guided radiotherapy Flat-panel detector (FPD)
1 Introduction Real-time tumor tracking has been facilitated by the use of diagnostic (kV) X-ray imaging with a dynamic flat-panel detector (FPD) in external radiotherapy [1–3]. Kilovoltage X-ray imaging is expected to solve the problems of low image contrast and poor image quality seen in megavoltage imaging. However, several factors remain that could reduce the accuracy of target tracking in external radiation therapy. In terms of image quality, it is thought that i
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