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Cone beam breast CT with a high pitch (75 μ m), thick (500 μ m) scintillator CMOS flat panel detector: Visibility of simulated microcalcifications
Author(s) -
Shen Youtao,
Zhong Yuncheng,
Lai ChaoJen,
Wang Tianpeng,
Shaw Chris C.
Publication year - 2013
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4820440
Subject(s) - scintillator , detector , flat panel detector , optics , dot pitch , optical transfer function , materials science , microcalcification , visibility , physics , beam (structure) , detective quantum efficiency , nuclear medicine , mammography , pixel , image quality , medicine , breast cancer , cancer , artificial intelligence , computer science , image (mathematics)
Purpose: To measure and investigate the improvement of microcalcification (MC) visibility in cone beam breast CT with a high pitch (75 μ m), thick (500 μ m) scintillator CMOS/CsI flat panel detector (Dexela 2923, Perkin Elmer).Methods: Aluminum wires and calcium carbonate grains of various sizes were embedded in a paraffin cylinder to simulate imaging of calcifications in a breast. Phantoms were imaged with a benchtop experimental cone beam CT system at various exposure levels. In addition to the Dexela detector, a high pitch (50 μ m), thin (150 μ m) scintillator CMOS/CsI flat panel detector (C7921CA‐09, Hamamatsu Corporation, Hamamatsu City, Japan) and a widely used low pitch (194 μ m), thick (600 μ m) scintillator aSi/CsI flat panel detector (PaxScan 4030CB, Varian Medical Systems) were also used in scanning for comparison. The images were independently reviewed by six readers (imaging physicists). The MC visibility was quantified as the fraction of visible MCs and measured as a function of the estimated mean glandular dose (MGD) level for various MC sizes and detectors. The modulation transfer functions (MTFs) and detective quantum efficiencies (DQEs) were also measured and compared for the three detectors used.Results: The authors have demonstrated that the use of a high pitch (75 μ m) CMOS detector coupled with a thick (500 μ m) CsI scintillator helped make the smaller 150–160, 160–180, and 180–200 μ m MC groups more visible at MGDs up to 10.8, 9, and 10.8 mGy, respectively. It also made the larger 200–212 and 212–224 μ m MC groups more visible at MGDs up to 7.2 mGy. No performance improvement was observed for 224–250 μ m or larger size groups. With the higher spatial resolution of the Dexela detector based system, the apparent dimensions and shapes of MCs were more accurately rendered. The results show that with the aforementioned detector, a 73% visibility could be achieved in imaging 160–180 μm MCs as compared to 28% visibility achieved by the low pitch (194 μ m) aSi/CsI flat panel detector. The measurements confirm that the Hamamatsu detector has the highest MTF, followed by the Dexel detector, and then the Varian detector. However, the Dexela detector, with its thick (500 μ m) CsI scintillator and low noise level, has the highest DQE at all frequencies, followed by the Varian detector, and then the Hamamatsu detector. The findings on the MC visibility correlated well with the differences in MTFs, noise power spectra, and DQEs measured for these three detectors.Conclusions: The authors have demonstrated that the use of the CMOS type Dexela detector with its high pitch (75 μ m) and thick (500 μ m) CsI scintillator could help improve the MC visibility. However, the improvement depended on the exposure level and the MC size. For imaging larger MCs or scanning at high exposure levels, there was little advantage in using the Dexela detector as compared to the aSi type Varian detector. These findings correlate well with the higher measured DQEs of the Dexela detector, especially at higher frequencies.