van Velden Floris H P, Kloet Reina W, van Berckel Bart N M, Wolfensberger Saskia P A, Lammertsma Adriaan A, Boellaard Ronald
Department of Nuclear Medicine & PET Research, VU University Medical Centre, PO Box 7057, 1007 MB Amsterdam, The Netherlands.
Phys Med Biol. 2008 Jun 21;53(12):3217-30. doi: 10.1088/0031-9155/53/12/010. Epub 2008 May 27.
The High-Resolution Research Tomograph (HRRT) is a dedicated human brain positron emission tomography (PET) scanner. Recently, a 3D filtered backprojection (3D-FBP) reconstruction method has been implemented to reduce bias in short duration frames, currently observed in 3D ordinary Poisson OSEM (3D-OP-OSEM) reconstructions. Further improvements might be expected using a new method of variance reduction on randoms (VRR) based on coincidence histograms instead of using the delayed window technique (DW) to estimate randoms. The goal of this study was to evaluate VRR in combination with 3D-OP-OSEM and 3D-FBP reconstruction techniques. To this end, several phantom studies and a human brain study were performed. For most phantom studies, 3D-OP-OSEM showed higher accuracy of observed activity concentrations with VRR than with DW. However, both positive and negative deviations in reconstructed activity concentrations and large biases of grey to white matter contrast ratio (up to 88%) were still observed as a function of scan statistics. Moreover 3D-OP-OSEM+VRR also showed bias up to 64% in clinical data, i.e. in some pharmacokinetic parameters as compared with those obtained with 3D-FBP+VRR. In the case of 3D-FBP, VRR showed similar results as DW for both phantom and clinical data, except that VRR showed a better standard deviation of 6-10%. Therefore, VRR should be used to correct for randoms in HRRT PET studies.
高分辨率研究断层扫描仪（HRRT）是一种专门用于人体脑部的正电子发射断层扫描（PET）设备。最近，一种三维滤波反投影（3D-FBP）重建方法已被应用，以减少在短时间帧中出现的偏差，这种偏差目前在三维普通泊松有序子集期望最大化（3D-OP-OSEM）重建中可以观察到。基于符合直方图而不是使用延迟窗技术（DW）来估计随机事件，使用一种新的随机事件方差减少（VRR）方法有望进一步改进。本研究的目的是评估VRR与3D-OP-OSEM和3D-FBP重建技术相结合的效果。为此，进行了多项体模研究和一项人体脑部研究。对于大多数体模研究，与DW相比，3D-OP-OSEM在使用VRR时显示出更高的观察活度浓度准确性。然而，作为扫描统计量的函数，重建活度浓度中仍观察到正偏差和负偏差以及灰质与白质对比度的大偏差（高达88%）。此外，与使用3D-FBP+VRR获得的结果相比，3D-OP-OSEM+VRR在临床数据中，即在一些药代动力学参数中也显示出高达64%的偏差。在3D-FBP的情况下，对于体模和临床数据，VRR显示出与DW相似的结果，只是VRR显示出更好的标准差，为6-10%。因此，在HRRT PET研究中应使用VRR来校正随机事件。
