Department of Radiology University of California Davis Medical Center, 4860 Y Street, Suite 3100 Sacramento, California 95817, USA.
Med Phys. 2011 Feb;38(2):646-55. doi: 10.1118/1.3537077.
The current study aimed to experimentally identify the optimal technique factors (x-ray tube potential and added filtration material/thickness) to maximize soft-tissue contrast, microcalcification contrast, and iodine contrast enhancement using cadaveric breast specimens imaged with dedicated breast computed tomography (bCT). Secondarily, the study aimed to evaluate the accuracy of phantom materials as tissue surrogates and to characterize the change in accuracy with varying bCT technique factors.
A cadaveric breast specimen was acquired under appropriate approval and scanned using a prototype bCT scanner. Inserted into the specimen were cylindrical inserts of polyethylene, water, iodine contrast medium (iodixanol, 2.5 mg/ml), and calcium hydroxyapatite (100 mg/ml). Six x-ray tube potentials (50, 60, 70, 80, 90, and 100 kVp) and three different filters (0.2 mm Cu, 1.5 mm Al, and 0.2 mm Sn) were tested. For each set of technique factors, the intensity (linear attenuation coefficient) and noise were measured within six regions of interest (ROIs): Glandular tissue, adipose tissue, polyethylene, water, iodine contrast medium, and calcium hydroxyapatite. Dose-normalized contrast to noise ratio (CNRD) was measured for pairwise comparisons among the six ROIs. Regression models were used to estimate the effect of tube potential and added filtration on intensity, noise, and CNRD.
Iodine contrast enhancement was maximized using 60 kVp and 0.2 mm Cu. Microcalcification contrast and soft-tissue contrast were maximized at 60 kVp. The 0.2 mm Cu filter achieved significantly higher CNRD for iodine contrast enhancement than the other two filters (p = 0.01), but microcalcification contrast and soft-tissue contrast were similar using the copper and aluminum filters. The average percent difference in linear attenuation coefficient, across all tube potentials, for polyethylene versus adipose tissue was 1.8%, 1.7%, and 1.3% for 0.2 mm Cu, 1.5 mm Al, and 0.2 mm Sn, respectively. For water versus glandular tissue, the average percent difference was 2.7%, 3.9%, and 4.2% for the three filter types.
Contrast-enhanced bCT, using injected iodine contrast medium, may be optimized for maximum contrast of enhancing lesions at 60 kVp with 0.2 mm Cu filtration. Soft-tissue contrast and microcalcification contrast may also benefit from lower tube potentials (60 kVp). The linear attenuation coefficients of water and polyethylene slightly overestimate the values of their corresponding tissues, but the reported differences may serve as guidance for dosimetry and quality assurance using tissue equivalent phantoms.
本研究旨在使用专用乳腺计算机断层扫描（bCT）对尸体乳腺标本进行成像，通过实验确定最佳的技术因素（管电压和附加滤过材料/厚度），以最大限度地提高软组织对比度、微钙化对比度和碘对比增强。其次，本研究旨在评估体模材料作为组织替代物的准确性，并描述随着 bCT 技术因素的变化，准确性的变化。
在适当的批准下获取尸体乳腺标本，并使用原型 bCT 扫描仪进行扫描。标本中插入了聚乙烯、水、碘对比剂（碘昔醇，2.5mg/ml）和钙羟磷灰石（100mg/ml）的圆柱形插入物。测试了六种管电压（50、60、70、80、90 和 100kVp）和三种不同的滤过片（0.2mmCu、1.5mmAl 和 0.2mmSn）。对于每一组技术因素，在六个感兴趣区域（ROI）内测量强度（线性衰减系数）和噪声：腺体组织、脂肪组织、聚乙烯、水、碘对比剂和钙羟磷灰石。测量了六个 ROI 之间的对比噪声比（CNRD）的剂量归一化值。使用回归模型估计管电压和附加滤过对强度、噪声和 CNRD 的影响。
使用 60kVp 和 0.2mmCu 可实现最大的碘对比增强。60kVp 时微钙化对比度和软组织对比度最大。0.2mmCu 滤过片在碘对比增强方面的 CNRD 明显高于其他两种滤过片（p=0.01），但铜和铝滤过片的微钙化对比度和软组织对比度相似。在所有管电压下，聚乙烯与脂肪组织的线性衰减系数平均百分比差异分别为 0.2mmCu、1.5mmAl 和 0.2mmSn 时为 1.8%、1.7%和 1.3%。水与腺体组织的平均百分比差异分别为 0.2mmCu、1.5mmAl 和 0.2mmSn 时为 2.7%、3.9%和 4.2%。
使用注射碘对比剂的对比增强 bCT 可优化增强病变的最大对比度，60kVp 时采用 0.2mmCu 滤过片。软组织对比度和微钙化对比度也可能受益于较低的管电压（60kVp）。水和聚乙烯的线性衰减系数略高于其相应组织的测量值，但报告的差异可作为使用组织等效体模进行剂量学和质量保证的指导。
