Development of high quantum efficiency, flat panel, thick detectors for megavoltage x‐ray imaging: A novel direct‐conversion design and its feasibility

Pang, G.; Rowlands, J. A.

doi:10.1118/1.1803771

Cited by 34 publications

(45 citation statements)

References 32 publications

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“…Attaching a standard X-ray tube and an FD to a rotating linear accelerator allows for CT imaging of the patient on the therapy couch [9,43,44]. It is the same rationale as in C-arm CT: the practical advantages of real-time control of patient positioning and tumour control and the option of real-time therapy planning outweigh potential disadvantages in image quality, which are to be acknowledged (Fig.…”

Section: Fd-ct In Combination With Radiation Therapy Unitsmentioning

confidence: 99%

Flat-detector computed tomography (FD-CT)

2007

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Flat-panel detectors or, synonymously, flat detectors (FDs) have been developed for use in radiography and fluoroscopy with the defined goal to replace standard X-ray film, filmscreen combinations and image intensifiers by an advanced sensor system. FD technology in comparison to X-ray film and image intensifiers offers higher dynamic range, dose reduction, fast digital readout and the possibility for dynamic acquisitions of image series, yet keeping to a compact design. It appeared logical to employ FD designs also for computed tomography (CT) imaging. Respective efforts date back a few years only, but FD-CT has meanwhile become widely accepted for interventional and intraoperative imaging using C-arm systems. FD-CT provides a very efficient way of combining two-dimensional (2D) radiographic or fluoroscopic and 3D CT imaging. In addition, FD technology made its way into a number of dedicated CT scanner developments, such as scanners for the maxillo-facial region or for micro-CT applications. This review focuses on technical and performance issues of FD technology and its full range of applications for CT imaging. A comparison with standard clinical CT is of primary interest. It reveals that FD-CT provides higher spatial resolution, but encompasses a number of disadvantages, such as lower dose efficiency, smaller field of view and lower temporal resolution. FD-CT is not aimed at challenging standard clinical CT as regards to the typical diagnostic examinations; but it has already proven unique for a number of dedicated CT applications, offering distinct practical advantages, above all the availability of immediate CT imaging in the interventional suite or the operating room.

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Section: Fd-ct In Combination With Radiation Therapy Unitsmentioning

confidence: 99%

Flat-detector computed tomography (FD-CT)

2007

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“…20 For this reason, high-efficiency x-ray detectors have been widely examined. Those detectors that directly detect MV X rays include a 1D arc array of tungsten cavities filled with high-pressure xenon gas, 21 2D gas chambers formed by microstructured tungsten spacer plates 22 and thick HgI 2 photoconductors. 23 For indirect detection, some of the detectors considered include thick optical fibers detecting Cerenkov radiation, 24 2D polymer matrices filled with Gd 2 O 2 S : Tb phosphor, 25 as well as 1D and 2D crystalline scintillators ͑e.g., CsI:Tl, Bi 4 Ge 3 O 12 , CdWO 4 , and ZnWO 4 ͒, employing the concept of segmentation.…”

Section: Introductionmentioning

confidence: 99%

High‐DQE EPIDs based on thick, segmented BGO and CsI:Tl scintillators: Performance evaluation at extremely low dose

et al. 2009

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Purpose: Electronic portal imaging devices ͑EPIDs͒ based on active matrix, flat-panel imagers ͑AMFPIs͒ have become the gold standard for portal imaging and are currently being investigated for megavoltage cone-beam computed tomography ͑CBCT͒ and cone-beam digital tomosynthesis ͑CBDT͒. However, the practical realization of such volumetric imaging techniques is constrained by the relatively low detective quantum efficiency ͑DQE͒ of AMFPI-based EPIDs at radiotherapy energies, ϳ1% at 6 MV. In order to significantly improve DQE, the authors are investigating thick, segmented scintillators, consisting of 2D matrices of scintillating crystals separated by septal walls. Methods: A newly constructed segmented BGO scintillator ͑11.3 mm thick͒ and three segmented CsI:Tl scintillators ͑11.4, 25.6, and 40.0 mm thick͒ were evaluated using a 6 MV photon beam. X-ray sensitivity, modulation transfer function, noise power spectrum, DQE, and phantom images were obtained using prototype EPIDs based on the four scintillators. Results: The BGO and CsI:Tl prototypes were found to exhibit improvement in DQE ranging from ϳ12 to 25 times that of a conventional AMFPI-based EPID at zero spatial frequency. All four prototype EPIDs provide significantly improved contrast resolution at extremely low doses, extending down to a single beam pulse. In particular, the BGO prototype provides contrast resolution comparable to that of the conventional EPID, but at 20 times less dose, with spatial resolution sufficient for identifying the boundaries of low-contrast objects. For this prototype, however, the BGO scintillator exhibited an undesirable radiation-induced variation in x-ray sensitivity. Conclusions: Prototype EPIDs based on thick, segmented BGO and CsI:Tl scintillators provide significantly improved portal imaging performance at extremely low dose ͑i.e., down to 1 beam pulse corresponding to ϳ0.022 cGy͒, creating the possibility of soft-tissue visualization using MV CBCT and CBDT at clinically practical dose.

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“…29,30 In addition, 2D detectors that have been investigated include a 12 mm thick CsI:Tl scintillator coupled to a video camera, 31 a 10 mm thick segmented CsI:Tl scintillator coupled to a lens and CCD camera, 32,33 a Cerenkov radiation detection EPID incorporating an ϳ30 cm thick taper consisting of a matrix of optical fibers, 34 and a xenon gas detector with tungsten walls consisting of microstructured plates packed together and aligned with the incident x-ray beam. 35 Furthermore, 2D scintillators integrated into MV AMFPIs include a 0.8 mm thick CsI:Tl needle scintillator, 36 a 2 mm thick segmented phosphor scintillator, 22 and several segmented CsI:Tl and BGO scintillators with thicknesses ranging from 8 to 40 mm. 18,19,37,38 An alternative approach for improving DQE performance involves the development of direct detection MV AMFPIs incorporating thick films of polycrystalline mercuric iodide ͑HgI 2 ͒ photoconductor.…”

Section: Introductionmentioning

confidence: 99%

Performance evaluation of polycrystalline photoconductors for radiation therapy imaging

et al. 2010

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Purpose: Electronic portal imaging devices based on megavoltage ͑MV͒, active matrix, flat-panel imagers ͑AMFPIs͒ are presently regarded as the gold standard in portal imaging for external beam radiation therapy. These devices, employing indirect detection of incident radiation by means of a metal plate plus phosphor screen combination, offer a quantum efficiency of only ϳ2% at 6 MV, leading to a detective quantum efficiency ͑DQE͒ of only ϳ1%. In order to significantly improve the DQE performance of MV AMFPIs, a strategy based on the development of direct detection imagers incorporating thick films of polycrystalline mercuric iodide ͑HgI 2 ͒ photoconductor was undertaken and is reported. Methods: Two MV AMFPI prototypes, one incorporating an ϳ300 m thick HgI 2 layer created through physical vapor deposition ͑PVD͒ and a second incorporating an ϳ460 m thick HgI 2 layer created through screen-printing of particle-in-binder ͑PIB͒ material, were quantitatively evaluated using a 6 MV photon beam. The reported measurements include empirical determination of x-ray sensitivity, lag, modulation transfer function ͑MTF͒, noise power spectrum, and DQE. Results: For both prototypes, MTF and DQE results were found to be consistent with theoretical expectations and the MTFs were also found to be higher than that measured from a conventional MV AMFPI. In addition, the DQE results exhibit input-quantum-limited behavior, even at extremely low doses. Compared to PVD, the PIB prototype exhibits much lower dark current, slightly higher lag, and similar DQE. Finally, the challenges associated with this approach, as well as strategies for achieving considerably higher DQE through thicker HgI 2 layers, are discussed. Conclusions:The DQE of each of the prototypes is found to be comparable to that of conventional MV AMFPIs, commensurate with the modest photoconductor thicknesses of these early samples. It is anticipated that thicker layers of HgI 2 based on PIB deposition can provide higher DQE while maintaining good material properties.

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Development of high quantum efficiency, flat panel, thick detectors for megavoltage x‐ray imaging: A novel direct‐conversion design and its feasibility

Cited by 34 publications

References 32 publications

Flat-detector computed tomography (FD-CT)

Flat-detector computed tomography (FD-CT)

High‐DQE EPIDs based on thick, segmented BGO and CsI:Tl scintillators: Performance evaluation at extremely low dose

Performance evaluation of polycrystalline photoconductors for radiation therapy imaging

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