Iwanishi Katsuhiro, Watabe Hiroshi, Hayashi Takuya, Miyake Yoshinori, Minato Kotaro, Iida Hidehiro
Department of Investigative Radiology, National Cardiovascular Center Research Institute, 5-7-1 Fujishirodai, Suita, Osaka, 565-8565, Japan.
Ann Nucl Med. 2009 Jun;23(4):363-71. doi: 10.1007/s12149-009-0243-7. Epub 2009 Apr 10.
Cerebral blood flow (CBF), cerebral metabolic rate of oxygen (CMRO(2)), oxygen extraction fraction (OEF), and cerebral blood volume (CBV) are quantitatively measured with PET with (15)O gases. Kudomi et al. developed a dual tracer autoradiographic (DARG) protocol that enables the duration of a PET study to be shortened by sequentially administrating (15)O(2) and C(15)O(2) gases. In this protocol, before the sequential PET scan with (15)O(2) and C(15)O(2) gases ((15)O(2)-C(15)O(2) PET scan), a PET scan with C(15)O should be preceded to obtain CBV image. C(15)O has a high affinity for red blood cells and a very slow washout rate, and residual radioactivity from C(15)O might exist during a (15)O(2)-C(15)O(2) PET scan. As the current DARG method assumes no residual C(15)O radioactivity before scanning, we performed computer simulations to evaluate the influence of the residual C(15)O radioactivity on the accuracy of measured CBF and OEF values with DARG method and also proposed a subtraction technique to minimize the error due to the residual C(15)O radioactivity.
In the simulation, normal and ischemic conditions were considered. The (15)O(2) and C(15)O(2) PET count curves with the residual C(15)O PET counts were generated by the arterial input function with the residual C(15)O radioactivity. The amounts of residual C(15)O radioactivity were varied by changing the interval between the C(15)O PET scan and (15)O(2)-C(15)O(2) PET scan, and the absolute inhaled radioactivity of the C(15)O gas. Using the simulated input functions and the PET counts, the CBF and OEF were computed by the DARG method. Furthermore, we evaluated a subtraction method that subtracts the influence of the C(15)O gas in the input function and PET counts.
Our simulations revealed that the CBF and OEF values were underestimated by the residual C(15)O radioactivity. The magnitude of this underestimation depended on the amount of C(15)O radioactivity and the physiological conditions. This underestimation was corrected by the subtraction method.
This study showed the influence of C(15)O radioactivity in DARG protocol, and the magnitude of the influence was affected by several factors, such as the radioactivity of C(15)O, and the physiological condition.
采用含（15）O气体的正电子发射断层扫描（PET）定量测量脑血流量（CBF）、脑氧代谢率（CMRO₂）、氧摄取分数（OEF）和脑血容量（CBV）。Kudomi等人开发了一种双示踪剂放射自显影（DARG）方案，通过依次给予（15）O₂和C（15）O₂气体，能够缩短PET研究的时长。在该方案中，在用（15）O₂和C（15）O₂气体进行连续PET扫描（（15）O₂ - C（15）O₂ PET扫描）之前，应先进行一次C（15）O的PET扫描以获取CBV图像。C（15）O对红细胞具有高亲和力且洗脱速率非常缓慢，在（15）O₂ - C（15）O₂ PET扫描期间可能存在来自C（15）O的残留放射性。由于当前的DARG方法假定扫描前不存在残留的C（15）O放射性，我们进行了计算机模拟，以评估残留C（15）O放射性对使用DARG方法测量的CBF和OEF值准确性的影响，并提出一种减法技术以最小化因残留C（15）O放射性导致的误差。
在模拟中，考虑了正常和缺血条件。带有残留C（15）O PET计数的（15）O₂和C（15）O₂ PET计数曲线由具有残留C（15）O放射性的动脉输入函数生成。通过改变C（15）O PET扫描与（15）O₂ - C（15）O₂ PET扫描之间的间隔以及C（15）O气体的绝对吸入放射性来改变残留C（15）O放射性的量。使用模拟的输入函数和PET计数，通过DARG方法计算CBF和OEF。此外，我们评估了一种减法方法，该方法可减去输入函数和PET计数中C（15）O气体的影响。
我们的模拟表明，残留的C（15）O放射性会低估CBF和OEF值。这种低估的程度取决于C（15）O放射性的量和生理条件。通过减法方法可校正这种低估。
本研究显示了DARG方案中C（15）O放射性的影响，且影响程度受多种因素影响，如C（15）O的放射性和生理条件。
