Timmins Rachel, Klein Ran, Petryk Julia, Marvin Brian, Wei Lihui, deKemp Robert A, Ruddy Terrence D, Wells R Glenn
Division of Cardiology, University of Ottawa Heart Institute, Ottawa, Ontario K1Y4W7, Canada.
Nordion, Inc., Ottawa, Ontario K2K 1X8, Canada.
Med Phys. 2015 Sep;42(9):5075-83. doi: 10.1118/1.4927723.
Absolute myocardial blood flow (MBF) and myocardial flow reserve (MFR) measurements provide important additional information over traditional relative perfusion imaging. Recent advances in camera technology have made this possible with single-photon emission tomography (SPECT). Low dose protocols are desirable to reduce the patient radiation risk; however, increased noise may reduce the accuracy of MBF measurements. The authors studied the effect of reducing dose on the accuracy of dynamic SPECT MBF measurements.
Nineteen 30-40 kg pigs were injected with 370 + 1110 MBq of Tc-99m sestamibi or tetrofosmin or 37 + 111 MBq of Tl-201 at rest + stress. Microspheres were injected simultaneously to measure MBF. The pigs were imaged in list-mode for 11 min starting at the time of injection using a Discovery NM 530c camera (GE Healthcare). Each list file was modified so that 3/4, 1/2, 1/4, 1/8, 1/16, and 1/32 of the original counts were included in the projections. Modified projections were reconstructed with CT-based attenuation correction and an energy window-based scatter correction and analyzed with FlowQuant kinetic modeling software using a 1-compartment model. A modified Renkin-Crone extraction function was used to convert the tracer uptake rate K1 to MBF values. The SPECT results were compared to those from microspheres.
Correlation between SPECT and microsphere MBF values for the full injected activity was r ≥ 0.75 for all 3 tracers and did not significantly degrade over all count levels. The mean MBF and MFR and the standard errors in the estimates were not significantly worse than the full-count data at 1/4-counts (Tc99m-tracers) and 1/2-counts (Tl-201).
Dynamic SPECT measurement of MBF and MFR in pigs can be performed with 1/4 (Tc99m-tracers) or 1/2 (Tl-201) of the standard injected activity without significantly reducing accuracy and precision.
与传统的相对灌注成像相比，绝对心肌血流量（MBF）和心肌血流储备（MFR）测量可提供重要的额外信息。相机技术的最新进展使得通过单光子发射断层扫描（SPECT）实现这一点成为可能。低剂量方案有助于降低患者的辐射风险；然而，噪声增加可能会降低MBF测量的准确性。作者研究了降低剂量对动态SPECT测量MBF准确性的影响。
19头体重30 - 40千克的猪在静息和负荷状态下分别注射370 + 1110 MBq的锝-99m甲氧基异丁基异腈或替曲膦，或37 + 111 MBq的铊-201。同时注射微球以测量MBF。使用Discovery NM 530c相机（GE医疗）从注射时开始以列表模式对猪进行11分钟成像。修改每个列表文件，使原始计数的3/4、1/2、1/4、1/8、1/16和1/32包含在投影中。使用基于CT的衰减校正和基于能量窗的散射校正对修改后的投影进行重建，并使用FlowQuant动力学建模软件通过单室模型进行分析。使用修改后的Renkin - Crone提取函数将示踪剂摄取率K1转换为MBF值。将SPECT结果与微球测量结果进行比较。
对于所有3种示踪剂，全注射活度下SPECT与微球MBF值之间的相关性r≥0.75，并且在所有计数水平上均未显著下降。在1/4计数（锝-99m示踪剂）和1/2计数（铊-201）时，平均MBF和MFR以及估计值的标准误差并不比全计数数据差很多。
猪的MBF和MFR的动态SPECT测量可以使用标准注射活度的1/4（锝-99m示踪剂）或1/2（铊-201）进行，而不会显著降低准确性和精密度。
