Watson Charles C, Casey Michael E, Bendriem Bernard, Carney Jonathan P, Townsend David W, Eberl Stefan, Meikle Steve, Difilippo Frank P
Siemens Medical Solutions Molecular Imaging, Knoxville, Tennessee, USA.
J Nucl Med. 2005 Nov;46(11):1825-34.
To optimize the injected dose of radiopharmaceutical in PET, one needs to know its relationship to some metric of data quality for individual patient scans, such as noise-equivalent counting rate (NECR). In this paper, we show how one may accurately model the clinical NECR response corresponding to specific patient scans much as if a counting-rate test had been performed on each patient. We apply this technique to patient data and show how it can lead to improved clinical scanning protocols.
True and random coincidence rates expressed as functions of an appropriate measurable system parameter such as the detector single-event rate have functional forms that are largely independent of the object being scanned. Thus, reference true and random response functions may be scaled directly to the specific counting rates measured on a clinical scan, thereby yielding a curve of NECR versus injected dose. We have applied this technique to 2 groups of 163 clinical (18)F-FDG scans each. One of the groups was obtained on a lutetium oxyorthosilicate PET/CT scanner with conventional front-end electronics, and the other was obtained on a lutetium oxyorthosilicate PET/CT scanner with a new digital data processing system (Pico-3D).
At 90%-95% of maximum signal-to-noise ratio (SNR), the mean optimal dose for a 60-min uptake period ranged from 366 to 717 MBq depending on the electronics and randoms processing method. There was only a slight (1 MBq/kg) dependence of optimal dose on patient weight but a larger dependence on position in the body. Pico-3D electronics improved optimal data SNR by 35% for a 70-kg person, but in both cases NECR fell rapidly with increasing weight (1.4%/kg). For an equivalent data SNR, a 120-kg person would have to be scanned 2.3 times longer than a 60-kg person. Over this range of weight, the mean scatter fraction increased by 12% whereas the ratio of mean randoms to trues increased by 48%.
The methodology developed here allows one to directly estimate the optimal dose to inject for specific clinical scans and permits a detailed analysis of the sources of noise in PET data and of their variation with parameters such as patient weight.
为了优化正电子发射断层扫描（PET）中放射性药物的注射剂量，需要了解其与个体患者扫描数据质量的某种度量指标的关系，例如噪声等效计数率（NECR）。在本文中，我们展示了如何能够准确地对与特定患者扫描相对应的临床NECR响应进行建模，就好像对每个患者都进行了计数率测试一样。我们将此技术应用于患者数据，并展示了它如何能够带来改进的临床扫描方案。
以适当的可测量系统参数（如探测器单事件率）的函数形式表示的真符合率和随机符合率，其函数形式在很大程度上与被扫描的物体无关。因此，可以将参考真响应函数和随机响应函数直接按临床扫描中测量的特定计数率进行缩放，从而得到NECR与注射剂量的曲线。我们已将此技术应用于两组各163例临床（18）F - FDG扫描。其中一组是在配备传统前端电子设备的正硅酸镥PET/CT扫描仪上获得的，另一组是在配备新数字数据处理系统（Pico - 3D）的正硅酸镥PET/CT扫描仪上获得的。
在最大信噪比（SNR）的90% - 95%时，根据电子设备和随机处理方法的不同，60分钟摄取期的平均最佳剂量范围为366至717 MBq。最佳剂量对患者体重的依赖性很小（1 MBq/kg），但对身体部位的依赖性较大。对于一个70千克的人，Pico - 3D电子设备将最佳数据SNR提高了35%，但在两种情况下，NECR都随着体重增加而迅速下降（1.4%/kg）。对于等效的数据SNR，一个120千克的人扫描时间要比一个60千克的人长2.3倍。在这个体重范围内，平均散射分数增加了12%，而平均随机事件与真事件的比率增加了48%。
本文开发的方法允许直接估计特定临床扫描的最佳注射剂量，并允许对PET数据中的噪声源及其随患者体重等参数的变化进行详细分析。
