Cluster for Molecular Imaging, Faculty of Health Sciences & Department of Clinical Physiology, Nuclear Medicine & PET, Rigshospitalet, University of Copenhagen, Blegdamsvej 3, Copenhagen DK-2200, Denmark.
Diagnostics (Basel). 2012 Oct 9;2(4):42-51. doi: 10.3390/diagnostics2040042.
The purpose of this study was to investigate whether a correction for annihilation photon attenuation in small objects such as mice is necessary. The attenuation recovery for specific organs and subcutaneous tumors was investigated. A comparison between different attenuation correction methods was performed.
Ten NMRI nude mice with subcutaneous implantation of human breast cancer cells (MCF-7) were scanned consecutively in small animal PET and CT scanners (MicroPET(TM) Focus 120 and ImTek's MicroCAT(TM) II). CT-based AC, PET-based AC and uniform AC methods were compared.
The activity concentration in the same organ with and without AC revealed an overall attenuation recovery of 9-21% for MAP reconstructed images, i.e., SUV without AC could underestimate the true activity at this level. For subcutaneous tumors, the attenuation was 13 ± 4% (9-17%), for kidneys 20 ± 1% (19-21%), and for bladder 18 ± 3% (15-21%). The FBP reconstructed images showed almost the same attenuation levels as the MAP reconstructed images for all organs.
The annihilation photons are suffering attenuation even in small subjects. Both PET-based and CT-based are adequate as AC methods. The amplitude of the AC recovery could be overestimated using the uniform map. Therefore, application of a global attenuation factor on PET data might not be accurate for attenuation correction.
本研究旨在探讨是否需要对小鼠等小物体的湮没光子衰减进行校正。研究了特定器官和皮下肿瘤的衰减恢复。比较了不同衰减校正方法。
连续在小动物 PET 和 CT 扫描仪（MicroPET（TM）Focus 120 和 ImTek 的 MicroCAT（TM）II）上对 10 只皮下植入人乳腺癌细胞（MCF-7）的 NMRI 裸鼠进行扫描。比较了基于 CT 的 AC、基于 PET 的 AC 和均匀 AC 方法。
有和没有 AC 的同一器官的活性浓度显示 MAP 重建图像的整体衰减恢复为 9-21%，即无 AC 的 SUV 可能会低估该水平的真实活性。对于皮下肿瘤，衰减为 13 ± 4%（9-17%），对于肾脏为 20 ± 1%（19-21%），对于膀胱为 18 ± 3%（15-21%）。FBP 重建图像显示所有器官的衰减水平与 MAP 重建图像几乎相同。
湮没光子即使在小物体中也会受到衰减。基于 PET 和 CT 的方法都可以作为 AC 方法。使用均匀图可能会高估 AC 恢复的幅度。因此，在 PET 数据上应用全局衰减因子可能无法准确进行衰减校正。
