Department of Imaging Physics, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030.
Med Phys. 2013 Oct;40(10):101915. doi: 10.1118/1.4820440.
To measure and investigate the improvement of microcalcification (MC) visibility in cone beam breast CT with a high pitch (75 μm), thick (500 μm) scintillator CMOS/CsI flat panel detector (Dexela 2923, Perkin Elmer).
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 μm), thin (150 μm) scintillator CMOS/CsI flat panel detector (C7921CA-09, Hamamatsu Corporation, Hamamatsu City, Japan) and a widely used low pitch (194 μm), thick (600 μm) 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.
The authors have demonstrated that the use of a high pitch (75 μm) CMOS detector coupled with a thick (500 μm) CsI scintillator helped make the smaller 150-160, 160-180, and 180-200 μm 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 μm MC groups more visible at MGDs up to 7.2 mGy. No performance improvement was observed for 224-250 μm 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 μm) 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 μm) 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.
The authors have demonstrated that the use of the CMOS type Dexela detector with its high pitch (75 μm) and thick (500 μm) 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.
使用高螺距（75μm）、厚（500μm）闪烁体 CMOS/CsI 平板探测器（Dexela 2923，Perkin Elmer）测量并研究锥形束乳腺 CT 中微钙化（MC）可见度的改善。
将不同大小的铝丝和碳酸钙颗粒嵌入石蜡圆柱中，模拟乳腺中钙化的成像。使用台式实验锥形束 CT 系统在不同曝光水平下对体模进行成像。除 Dexela 探测器外，还使用高螺距（50μm）、薄（150μm）闪烁体 CMOS/CsI 平板探测器（C7921CA-09，Hamamatsu Corporation，日本滨松市）和广泛使用的低螺距（194μm）、厚（600μm）闪烁体 aSi/CsI 平板探测器（PaxScan 4030CB，Varian Medical Systems）进行扫描比较。图像由六名读者（影像物理学家）独立评估。MC 可见度作为可见 MC 的分数进行量化，并作为各种 MC 大小和探测器的估计平均腺体剂量（MGD）水平的函数进行测量。还测量和比较了三种探测器的调制传递函数（MTFs）和探测量子效率（DQEs）。
作者证明，使用高螺距（75μm）CMOS 探测器结合厚（500μm）CsI 闪烁体有助于在高达 10.8、9 和 10.8 mGy 的 MGD 下使较小的 150-160、160-180 和 180-200μm MC 组更可见。它还使更大的 200-212 和 212-224μm MC 组在高达 7.2 mGy 的 MGD 下更可见。对于 224-250μm 或更大尺寸的组，未观察到性能提高。凭借 Dexela 探测器的更高空间分辨率，MC 的明显尺寸和形状被更准确地呈现。结果表明，与低螺距（194μm）aSi/CsI 平板探测器相比，使用上述探测器可实现 160-180μm MC 73%的可见度，而低螺距（194μm）aSi/CsI 平板探测器的可见度为 28%。测量结果证实，Hamamatsu 探测器具有最高的 MTF，其次是 Dexel 探测器，然后是 Varian 探测器。然而，Dexela 探测器凭借其厚（500μm）CsI 闪烁体和低噪声水平，在所有频率下都具有最高的 DQE，其次是 Varian 探测器，然后是 Hamamatsu 探测器。MC 可见度的研究结果与这三种探测器的 MTF、噪声功率谱和 DQE 的差异测量结果一致。
作者证明，使用高螺距（75μm）和厚（500μm）CsI 闪烁体的 CMOS 型 Dexela 探测器有助于提高 MC 可见度。然而，改进取决于曝光水平和 MC 尺寸。对于较大 MC 的成像或在高曝光水平下扫描，与 aSi 型 Varian 探测器相比，使用 Dexela 探测器几乎没有优势。这些发现与 Dexela 探测器的更高测量 DQE 相关，特别是在更高的频率下。
