背景:定量CT成像,特别是碘和钙的定量,是一种重要的基于CT的生物标志物。
目的:本研究量化了单能量和能谱CT定量CT成像中的误差来源。
方法:这项工作检查了CT数之间的理论关系,线性衰减系数,和物质量化。我们得出四个理解:(1)CT数与体内元素质量不成比例,(2)只有当包含在纯水的体素中时,CT数与元素质量成正比,(3)碘-水物质在体内分解永远不准确,和(4)对于无误差材料分解,体素必须仅由基本分解向量组成。使用国家标准与技术研究所(NIST)XCOM数据库计算基于误解的错误:组织化学成分,羟基磷灰石(HAP)的临床浓度,和碘。还使用幻影通过实验证明了定量误差。
结果:在单能量CT中,对脂肪中HAP密度的误解引起的错误,肌肉,肺,软组织,血液在0-132%之间,即,质量误差为0-749mg/cm3。在光谱CT中,碘在相同组织中的误差导致<0.1-33%的误差范围,导致质量误差<0.1-1.2mg/mL。
结论:我们的工作表明,由于测量条件与假设不同,因此在体内测量时,材料定量从根本上受到限制,并且误差处于或高于骨矿物质密度(BMD)和光谱碘定量的检测限。要定义CT衍生的生物标志物,我们证明的错误应该避免或建立在不确定性界限中。
结论:改善定量CT生物标志物的误差范围,特别是在碘和BMD定量中,可能会导致基于定量CT的临床护理方面的改善。
结论:仅当包含在纯水的体素中时,CT数仅与元素质量成正比,因此碘-水物质在体内的分解是不准确的。错误解释引起的错误范围为HAP密度的0-132%,而在碘的能谱CT中<0.1-33%。对于无错误的材料分解,体素必须仅由基本分解向量组成。
BACKGROUND: Quantitative CT imaging, particularly iodine and calcium quantification, is an important CT-based biomarker.
OBJECTIVE: This study quantifies sources of errors in quantitative CT imaging in both single-energy and spectral CT.
METHODS: This work examines the theoretical relationship between CT numbers, linear attenuation coefficient, and material quantification. We derive four understandings: (1) CT numbers are not proportional with element mass in vivo, (2) CT numbers are proportional with element mass only when contained in a voxel of pure water, (3) iodine-water material decomposition is never accurate in vivo, and (4) for error-free material decomposition a voxel must only consist of the basis decomposition vectors. Misinterpretation-based errors are calculated using the National Institute of Standards and Technology (NIST) XCOM database for: tissue chemical compositions, clinical concentrations of hydroxyapatite (HAP), and iodine. Quantification errors are also demonstrated experimentally using phantoms.
RESULTS: In single-energy CT, misinterpretation-induced errors for HAP density in adipose, muscle, lung, soft tissue, and blood ranged from 0-132%, i.e., a mass error of 0-749 mg/cm3. In spectral CT, errors with iodine in the same tissues resulted in a range of < 0.1-33% error, resulting in a mass error of < 0.1-1.2 mg/mL.
CONCLUSIONS: Our work demonstrates material quantification is fundamentally limited when measured in vivo due to measurement conditions differing from assumed and the errors are at or above detection limits for bone mineral density (BMD) and spectral iodine quantification. To define CT-derived biomarkers, the errors we demonstrate should either be avoided or built into uncertainty bounds.
CONCLUSIONS: Improving error bounds in quantitative CT biomarkers, specifically in iodine and BMD quantification, could lead to improvements in clinical care aspects based on quantitative CT.
CONCLUSIONS: CT numbers are only proportional with element mass only when contained in a voxel of pure water, therefore iodine-water material decomposition is never accurate in vivo. Misinterpretation-induced errors ranged from 0-132% for HAP density and < 0.1-33% in spectral CT with iodine. For error-free material decomposition, a voxel must only consist of the basis decomposition vectors.