Molecular Imaging Research Group, Medical Imaging Department, Centre hospitalier universitaire de Québec and Laval University, Quebec City, Canada.
Cancer Imaging. 2011 Jun 15;11(1):56-66. doi: 10.1102/1470-7330.2011.0012.
The combination of single photon emission computed tomography (SPECT) and computer tomography (CT) that incorporates iterative reconstruction algorithms with attenuation and scatter correction should facilitate accurate non-invasive quantitative imaging. Quantitative SPECT (QSPECT) may improve diagnostic ability and could be useful for many applications including dosimetry assessment. Using (177)Lu, we developed a QSPECT method using a commercially available SPECT/CT system.
Serial SPECT of (177)Lu sources (89-12,400 MBq) were acquired with multiple contiguous energy windows along with a co-registered CT, and were reconstructed using an iterative algorithm with attenuation and scatter correction. Camera sensitivity (based on reconstructed SPECT count rate) and dead-time (based on wide-energy spectrum count rate) were resolved by non-linear curve fit. Utilizing these parameters, a SPECT dataset can be converted to a QSPECT dataset allowing quantitation in Becquerels per cubic centimetre or standardized uptake value (SUV). Validation QSPECT/CT studies were performed on a (177)Lu cylindrical phantom (7 studies) and on 5 patients (6 studies) who were administered a therapeutic dose of [(177)Lu]octreotate.
The QSPECT sensitivity was 1.08 x 10(-5) ± 0.02 x 10(-5) s(-1) Bq(-1). The paralyzing dead-time constant was 0.78 ± 0.03 µs. The measured total activity with QSPECT deviated from the calibrated activity by 5.6 ± 1.9% and 2.6 ± 1.8%, respectively, in phantom and patients. Dead-time count loss up to 11.7% was observed in patient studies.
QSPECT has high accuracy both in our phantom model and in clinical practice following [(177)Lu]octreotate therapy. This has the potential to yield more accurate dosimetry estimates than planar imaging and facilitate therapeutic response assessment. Validating this method with other radionuclides could open the way for many other research and clinical applications.
将单光子发射计算机断层扫描（SPECT）与计算机断层扫描（CT）相结合，采用迭代重建算法进行衰减和散射校正，应有助于实现准确的无创定量成像。定量 SPECT（QSPECT）可提高诊断能力，并且在包括剂量评估在内的许多应用中可能有用。我们使用（177）Lu 开发了一种使用市售 SPECT/CT 系统的 QSPECT 方法。
使用多个连续的能量窗口获取（177）Lu 源（89-12400MBq）的 SPECT 序列，并与共配准的 CT 一起重建，使用具有衰减和散射校正的迭代算法进行重建。通过非线性曲线拟合解决相机灵敏度（基于重建 SPECT 计数率）和死时间（基于宽能谱计数率）。利用这些参数，可以将 SPECT 数据集转换为 QSPECT 数据集，从而以贝克勒尔/立方厘米或标准化摄取值（SUV）进行定量。在（177）Lu 圆柱形体模（7 项研究）和接受治疗剂量[（177）Lu]奥曲肽治疗的 5 名患者（6 项研究）上进行了验证性 QSPECT/CT 研究。
QSPECT 灵敏度为 1.08×10(-5)±0.02×10(-5)s(-1)Bq(-1)。瘫痪的死时间常数为 0.78±0.03µs。用 QSPECT 测量的总活性与校准活性的偏差分别为 5.6±1.9%和 2.6±1.8%，在体模和患者中。在患者研究中观察到高达 11.7%的死时间计数损失。
QSPECT 在我们的体模模型和临床实践中都具有很高的准确性，可用于（177）Lu 奥曲肽治疗后的治疗效果评估。这有可能比平面成像产生更准确的剂量估计，并有助于治疗反应评估。用其他放射性核素验证这种方法可能为许多其他研究和临床应用开辟道路。
