Boellaard R, van Lingen A, van Balen S C M, Lammertsma A A
Clinical PET center, VU University Medical Centre, De Boelelaan 1117, 1081 HV Amsterdam, The Netherlands.
Phys Med Biol. 2004 Feb 21;49(4):N31-8. doi: 10.1088/0031-9155/49/4/n01.
The quality of thorax and pelvis transmission scans and therefore of attenuation correction in PET depends on patient thickness and transmission rod source strength. The purpose of the present study was to assess the feasibility of using count-based transmission scans, thereby guaranteeing more consistent image quality and more precise quantification than with fixed transmission scan duration. First, the relation between noise equivalent counts (NEC) of 10 min calibration transmission scans and rod source activity was determined over a period of 1.5 years. Second, the relation between transmission scan counts and uniform phantom diameter was studied numerically, determining the relative contribution of counts from lines of response passing through the phantom as compared with the total number of counts. Finally, the relation between patient weight and transmission scan duration was determined for 35 patients, who were scanned at the level of thorax or pelvis. After installation of new rod sources, the NEC of transmission scans first increased slightly (5%) with decreasing rod source activity and after 3 months decreased with a rate of 2-3% per month. The numerical simulation showed that the number of transmission scan counts from lines of response passing through the phantom increased with phantom diameter up to 7 cm. For phantoms larger than 7 cm, the number of these counts decreased at approximately the same rate as the total number of transmission scan counts. Patient data confirmed that the total number of transmission scan counts decreased with increasing patient weight with about 0.5% kg(-1). It can be concluded that count-based transmission scans compensate for radioactive decay of the rod sources. With count-based transmission scans, rod sources can be used for up to 1.5 years at the cost of a 50% increased transmission scan duration. For phantoms with diameters of more than 7 cm and for patients scanned at the level of thorax or pelvis, use of count-based transmission scans is feasible and results in statistically more consistent transmission scans as compared with fixed transmission scan duration.
胸部和骨盆的透射扫描质量以及正电子发射断层扫描（PET）中的衰减校正质量取决于患者的厚度和透射棒源的强度。本研究的目的是评估使用基于计数的透射扫描的可行性，从而保证图像质量更加一致，定量比固定透射扫描持续时间更精确。首先，在1.5年的时间里确定了10分钟校准透射扫描的噪声等效计数（NEC）与棒源活性之间的关系。其次，通过数值研究了透射扫描计数与均匀体模直径之间的关系，确定了穿过体模的响应线计数相对于总计数的相对贡献。最后，确定了35名在胸部或骨盆水平进行扫描的患者的体重与透射扫描持续时间之间的关系。安装新的棒源后，透射扫描的NEC首先随着棒源活性的降低而略有增加（5%），3个月后以每月2-3%的速率下降。数值模拟表明，穿过体模的响应线的透射扫描计数数量随着体模直径增加到7厘米而增加。对于直径大于7厘米的体模，这些计数的数量以与透射扫描总计数数量大致相同的速率下降。患者数据证实，透射扫描的总计数数量随着患者体重增加而减少，约为0.5%kg-1。可以得出结论，基于计数的透射扫描可以补偿棒源的放射性衰变。使用基于计数的透射扫描，棒源可以使用长达1.5年，代价是透射扫描持续时间增加50%。对于直径大于7厘米的体模以及在胸部或骨盆水平进行扫描的患者，使用基于计数的透射扫描是可行的，并且与固定透射扫描持续时间相比，在统计学上可以得到更一致的透射扫描结果。
