A bench‐top megavoltage fan‐beam CT using ‐photodiode detectors. II. Image performance evaluation

Monajemi, T; Tu, Dongsheng; Fallone, B. G.; Rathee, S

doi:10.1118/1.2181291

Cited by 25 publications

(22 citation statements)

References 39 publications

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“…1,2 The wide-gap semiconductors magnesium, zinc, and cadmium tungstate (MgWO 4 , ZnWO 4 , CdWO 4 ) are remarkable members of this family of compounds and their properties have been extensively studied during the past decade. In particular, their scintillating efficiency and radiation hardness make them prototypic scintillators for rare-event searches.…”

Section: Introductionmentioning

confidence: 99%

Pressure effects on the electronic and optical properties ofAWO4wolframites (A =

et al. 2012

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The electronic band-structure and band-gap dependence on the d character of A 2+ cation in AWO 4 wolframitetype oxides is investigated for different compounds (A = Mg, Zn, Cd, and Mn) by means of optical-absorption spectroscopy and first-principles density-functional calculations. High pressure is used to tune their properties up to 10 GPa by changing the bonding distances establishing electronic to structural correlations. The effect of unfilled d levels is found to produce changes in the nature of the band gap as well as its pressure dependence without structural changes. Thus, whereas Mg, Zn, and Cd, with empty or filled d electron shells, give rise to direct and wide band gaps, Mn, with a half-filled d shell, is found to have an indirect band gap that is more than 1.6 eV smaller than for the other wolframites. In addition, the band gaps of MgWO 4 , ZnWO 4 , and CdWO 4 blue-shift linearly with pressure, with a pressure coefficient of approximately 13 eV/GPa. However, the band gap of multiferroic MnWO 4 red-shifts at −22 meV/GPa. Finally, in MnWO 4 , absorption bands are observed at lower energy than the band gap and followed with pressure based on the Tanabe-Sugano diagram. This study allows us to estimate the crystal-field variation with pressure for the MnO 6 complexes and how it affects their band-gap closure.

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Section: Introductionmentioning

confidence: 99%

Pressure effects on the electronic and optical properties ofAWO4wolframites (A =

et al. 2012

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“…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. [26][27][28][29][30][31][32][33][34] A series of theoretical and empirical studies has been previously reported on 2D segmented crystalline scintillators, which consists of matrices of scintillating crystals separated by septal walls to limit the lateral spread of optical photons. 25,[35][36][37][38][39][40] Monte Carlo simulations of radiation and optical transport have suggested that EPIDs employing segmented CsI:Tl and Bi 4 Ge 3 O 12 ͑BGO͒ detectors up to 40 mm thick can offer DQE values of up to 29% and 42%, respectively.…”

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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“…These detectors are based on concepts involving high pressure gas ͑e.g., xenon͒ chambers employing tungsten walls, [10][11][12] thick optical fibers detecting Cerenkov radiation, 13 thick HgI 2 photoconductors, 14 segmented phosphors based on photopolymer matrices, 15 and segmented crystalline scintillators which consist of 2D matrices ͑or 1D arrays͒ of scintillator crystals separated by optically opaque septal walls. 7,[16][17][18][19] Among these approaches, segmented crystalline scintillators offer significantly improved QE, with only limited loss in spatial resolution, and possibly no substantial increase in noise compared to conventional AMFPIs. In order to examine this strategy, 1D segmented arrays incorporating zinc tungstate ͑ZnWO 4 ͒ and cadmium tungstate ͑CdWO 4 ͒ scintillators, [17][18][19] as well as 2D segmented matrices employing bismuth germanate ͑BGO͒, thallium-doped cesium iodide ͑CsI:Tl͒ and CdWO 4 scintillators, 7,[20][21][22] have been investigated by different research groups.…”

Section: Introductionmentioning

confidence: 99%

“…7,[16][17][18][19] Among these approaches, segmented crystalline scintillators offer significantly improved QE, with only limited loss in spatial resolution, and possibly no substantial increase in noise compared to conventional AMFPIs. In order to examine this strategy, 1D segmented arrays incorporating zinc tungstate ͑ZnWO 4 ͒ and cadmium tungstate ͑CdWO 4 ͒ scintillators, [17][18][19] as well as 2D segmented matrices employing bismuth germanate ͑BGO͒, thallium-doped cesium iodide ͑CsI:Tl͒ and CdWO 4 scintillators, 7,[20][21][22] have been investigated by different research groups. Recently, a 40 mm thick segmented CsI:Tl detector, with an element-toelement pitch of 1.016 mm and an area of 16.25 ϫ 16.25 cm 2 , has been developed and evaluated by our group.…”

Section: Introductionmentioning

confidence: 99%

A Monte Carlo investigation of Swank noise for thick, segmented, crystalline scintillators for radiotherapy imaging

et al. 2009

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Thick, segmented scintillating detectors, consisting of 2D matrices of scintillator crystals separated by optically opaque septal walls, hold considerable potential for significantly improving the performance of megavoltage ͑MV͒ active matrix, flat-panel imagers ͑AMFPIs͒. Initial simulation studies of the radiation transport properties of segmented detectors have indicated the possibility of significant improvement in DQE compared to conventional MV AMFPIs based on phosphor screen detectors. It is therefore interesting to investigate how the generation and transport of secondary optical photons affect the DQE performance of such segmented detectors. One effect that can degrade DQE performance is optical Swank noise ͑quantified by the optical Swank factor I opt ͒, which is induced by depth-dependent variations in optical gain. In this study, Monte Carlo simulations of radiation and optical transport have been used to examine I opt and zero-frequency DQE for segmented CsI:Tl and BGO detectors at different thicknesses and element-to-element pitches. For these detectors, I opt and DQE were studied as a function of various optical parameters, including absorption and scattering in the scintillator, absorption at the top reflector and septal walls, as well as scattering at the side surfaces of the scintillator crystals. The results indicate that I opt and DQE are only weakly affected by absorption and scattering in the scintillator, as well as by absorption at the top reflector. However, in some cases, these metrics were found to be significantly degraded by absorption at the septal walls and scattering at the scintillator side surfaces. Moreover, such degradations are more significant for detectors with greater thickness or smaller element pitch. At 1.016 mm pitch and with optimized optical properties, 40 mm thick segmented CsI:Tl and BGO detectors are predicted to provide DQE values of ϳ29% and 42%, corresponding to improvement by factors of ϳ29 and 42, respectively, compared to that of conventional MV AMFPIs.

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A bench‐top megavoltage fan‐beam CT using ‐photodiode detectors. II. Image performance evaluation

Cited by 25 publications

References 39 publications

Pressure effects on the electronic and optical properties ofAWO4wolframites (A =

Pressure effects on the electronic and optical properties ofAWO4wolframites (A =

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

A Monte Carlo investigation of Swank noise for thick, segmented, crystalline scintillators for radiotherapy imaging

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