Shen Y, Zhong Y, Lai C, Wang T, Shaw C
UT MD Anderson Cancer Center, Houston, TX.
Med Phys. 2012 Jun;39(6Part24):3915. doi: 10.1118/1.4735978.
To investigate the advantage of a high resolution flat panel detector for improving the visibility of microcalcifications (MCs) in cone beam breast CT Methods: A paraffin cylinder was used to simulate a 100% adipose breast. Calcium carbonate grains, ranging from 125-140 μm to 224 - 250 μm in size, were used to simulate the MCs. Groups of 25 same size MCs were embedded at the phantom center. The phantom was scanned with a bench-top CBCT system at various exposure levels. A 75μm pitch flat panel detector (Dexela 2923, Perkin Elmer) with 500μm thick CsI scintillator plate was used as the high resolution detector. A 194 μm pitch detector (Paxscan 4030CB, Varian Medical Systems) was used for reference. 300 projection images were acquired over 360° and reconstructed. The images were reviewed by 6 readers. The MC visibility was quantified as the fraction of visible MCs and averaged for comparison. The visibility was plotted as a function of the estimated dose level for various MC sizes and detectors. The MTFs and DQEs were measured and compared.
For imaging small (200 μm and smaller) MCs, the visibility achieved with the 75μm pitch detector was found to be significantly higher than those achieved with the 194μm pitch detector. For imaging larger MCs, there was little advantage in using the 75μm pitch detector. Using the 75μm pitch detector, MCs as small as 180 μm could be imaged to achieve a visibility of 78% with an isocenter tissue dose of ∼20 mGys versus 62% achieved with the 194 μm pitch detector at the same dose level.
It was found that a high pitch flat panel detector had the advantages of extending its imaging capability to higher frequencies thus helping improve the visibility when used to image small MCs. This work was supported in part by grants CA104759, CA13852 and CA124585 from NIH-NCI, a grant EB00117 from NIH-NIBIB, and a subcontract from NIST-ATP.
研究高分辨率平板探测器在锥束乳腺CT中提高微钙化（MCs）可见性的优势。方法：用石蜡圆柱体模拟100%脂肪乳腺。使用尺寸范围为125 - 140μm至224 - 250μm的碳酸钙颗粒模拟MCs。将25个相同尺寸的MCs组嵌入体模中心。使用台式CBCT系统在不同曝光水平下对体模进行扫描。使用具有500μm厚碘化铯闪烁体板的75μm间距平板探测器（Dexela 2923，珀金埃尔默公司）作为高分辨率探测器。使用194μm间距探测器（Paxscan 4030CB，瓦里安医疗系统公司）作为参考。在360°范围内采集300幅投影图像并重建。由6名阅片者对图像进行评估。将MCs可见性量化为可见MCs的比例，并进行平均以作比较。将可见性绘制为不同MC尺寸和探测器的估计剂量水平的函数。测量并比较调制传递函数（MTFs）和量子探测效率（DQEs）。结果：对于成像小尺寸（200μm及更小）的MCs，发现75μm间距探测器获得的可见性显著高于194μm间距探测器。对于成像较大尺寸的MCs，使用75μm间距探测器几乎没有优势。使用75μm间距探测器时，对于小至180μm的MCs，在等中心组织剂量约为20 mGys时可成像达到78%的可见性，而在相同剂量水平下，194μm间距探测器达到的可见性为62%。结论：发现高间距平板探测器具有将其成像能力扩展到更高频率的优势，因此在用于成像小尺寸MCs时有助于提高可见性。本研究部分得到了美国国立卫生研究院 - 国家癌症研究所（NIH - NCI）的CA104759、CA13852和CA124585资助，美国国立卫生研究院 - 国家生物医学成像和生物工程研究所（NIH - NIBIB）的EB00117资助，以及美国国家标准与技术研究院 - 先进技术计划（NIST - ATP）的分包合同支持。
