연세대 / 최성훈, 김희중*
그림1. 개발된 영상장치의 하드웨어 모식도와 사진
그림2. 총 3가지 촬영 세트에 적용된 기존 FBP, SART 기술과 제안된 CS 알고리즘의 폐결절 확대영상
그림3. 저선량 흉부촬영 단층영상합성영상의 임상적 가치를 확인하기 위해 같은 팬텀의 일반촬영 (a, b, f, g)과 흉부 CT (e, j)를 제시하였고, 이를 단층영상합성영상의 기존 알고리즘 (c, h)과 제안된 알고리즘 (d, i)와 비교하였다.
Abstract
PURPOSE:
This work describes the hardware and software developments of a prototype chest digital tomosynthesis (CDT) R/F system. The purpose of this study was to validate the developed system for its possible clinical application on low-dose chest tomosynthesis imaging.
METHODS:
The prototype CDT R/F system was operated by carefully controlling the electromechanical subsystems through a synchronized interface. Once a command signal was delivered by the user, a tomosynthesis sweep started to acquire 81 projection views (PVs) in a limited angular range of ±20°. Among the full projection dataset of 81 images, several sets of 21 (quarter view) and 41 (half view) images with equally spaced angle steps were selected to represent a sparse view condition. GPU-accelerated and total-variation (TV) regularization strategy-based compressed sensing (CS) image reconstruction was implemented. The imaged objects were a flat-field using a copper filter to measure the noise power spectrum (NPS), a Catphan® CTP682 quality assurance (QA) phantom to measure a task-based modulation transfer function (MTFTask ) of three different cylinders' edge, and an anthropomorphic chest phantom with inserted lung nodules. The authors also verified the accelerated computing power over CPU programming by checking the elapsed time required for the CS method. The resultant absorbed and effective doses that were delivered to the chest phantom from two-view digital radiographic projections, helical computed tomography (CT), and the prototype CDT system were compared.
RESULTS:
The prototype CDT system was successfully operated, showing little geometric error with fast rise and fall times of R/F x-ray pulse less than 2 and 10 ms, respectively. The in-plane NPS presented essential symmetric patterns as predicted by the central slice theorem. The NPS images from 21 PVs were provided quite different pattern against 41 and 81 PVs due to aliased noise. The voxel variance values which summed all NPS intensities were inversely proportional to the number of PVs, and the CS method gave much lower voxel variance by the factors of 3.97-6.43 and 2.28-3.36 compared to filtered backprojection (FBP) and 20 iterations of simultaneous algebraic reconstruction technique (SART). The spatial frequencies of the f50 at which the MTFTask reduced to 50% were 1.50, 1.55, and 1.67 cycles/mm for FBP, SART, and CS methods, respectively, in the case of Bone 20% cylinder using 41 views. A variety of ranges of TV reconstruction parameters were implemented during the CS method and we could observe that the NPS and MTFTask preserved best when the regularization and TV smoothing parameters α and τ were in a range of 0.001-0.1. For the chest phantom data, the signal difference to noise ratios (SDNRs) were higher in the proposed CS scheme images than in the FBP and SART, showing the enhanced rate of 1.05-1.43 for half view imaging. The total averaged reconstruction time during 20 iterations of the CS scheme was 124.68 s, which could match-up a clinically feasible time (<3 min). This computing time represented an enhanced speed 386 times greater than CPU programming. The total amounts of estimated effective doses were 0.12, 0.53 (half view), and 2.56 mSv for two-view radiographs, the prototype CDT system, and helical CT, respectively, showing 4.49 times higher than conventional radiography and 4.83 times lower than a CT exam, respectively.
CONCLUSIONS:
The current work describes the development and performance assessment of both hardware and software for tomosynthesis applications. The authors observed reasonable outcomes by showing a potential for low-dose application in CDT imaging using GPU acceleration.
Author information
Choi S1, Lee H1, Lee D2, Choi S2, Lee CL1, Kwon W3, Shin J4, Seo CW1, Kim HJ1,2.
1
Department of Radiological Science, Yonsei University, 1 Yonseidae-gil, Wonju, 26493, Korea.
2
Department of Radiation Convergence Engineering, Yonsei University, 1 Yonseidae-gil, Wonju, 26493, Korea.
3
Department of Radiology, Wonju Severance Christian Hospital, 20 Ilsan-ro, Wonju, 26426, Korea.
4
LISTEM Corporation, 94 Donghwagongdan-ro, Munmak-eup, Wonju, Korea.
편집위원
저 선량 일지라도 광여 피폭에 의해 발생 가능한 방사선 폐렴의 가능성을 감소시키기 위한 연구이므로 임상적으로 의미가 있으며 또한 GPU를 사용하여 계산속도를 300배 이상 증가 시킨 점이 흥미로웠습니다.
2018-04-17 11:05:36