O'Brien T J, O'Connor M K, Mullan B P, Brinkmann B H, Hanson D, Jack C R, So E L
Department of Neurology, The Mayo Clinic, Rochester, MN 55905, USA.
Nucl Med Commun. 1998 Jan;19(1):31-45. doi: 10.1097/00006231-199801000-00006.
Computer-aided subtraction of the co-registered and normalized interictal from the ictal single photon emission tomography (SPET) scan, followed by co-registration to the magnetic resonance image, may improve the utility of ictal SPET in the localization of partial epilepsy. This paper describes and technically validates our method. The SPET to SPET co-registration was tested using six sequential 99Tc(m) brain phantom SPET images of different known positions (15 matches). The registration error was determined by multiplying the calculated match transformation matrix by the inverse of the known transformation matrix. The 'worst case' co-registration error was less that one voxel diameter in all cases (median 3.2 mm, range 1.2-4.8 mm). For interictal to ictal SPET registrations in 10 consecutive intractable partial epilepsy patients, a similar root mean square distance (RMSD) between corresponding points on the matched scans was found as for the phantom studies (median 2.2 vs 2.6 mm). The appropriateness of our normalization was studied by comparing the pixel intensity distributions between the matched scans, and by analysing the subtraction pixel intensity distribution. The pixel intensity distribution for both the normalized phantom, and paired normalized patient studies, were closely matched to each other except for the extreme values, which in clinical situations likely represent regions of ictal activation or depression. The subtraction image intensity distributions were symmetrically centred on zero for all values up to at least within the 5th to 95th centile range, confirming good normalization for the 'non-activated' pixels. Also, a linear relationship was demonstrated between the measured pixel intensity on the phantom scans and the true changes in 99Tc(m) activity based on its decay constant. The results of this study demonstrate that our method produces accurate SPET to SPET co-registration, and appropriate SPET normalization, thereby allowing a valid ictal subtraction image to be derived.
在发作期单光子发射断层扫描（SPET）扫描中，通过计算机辅助从共配准且归一化的发作间期图像中减去发作期图像，随后将其与磁共振图像进行配准，可能会提高发作期SPET在部分性癫痫定位中的效用。本文描述并从技术上验证了我们的方法。使用六个不同已知位置的连续99Tc（m）脑模体SPET图像（15次匹配）对SPET到SPET的配准进行了测试。通过将计算出的匹配变换矩阵乘以已知变换矩阵的逆来确定配准误差。在所有情况下，“最坏情况”下的配准误差均小于一个体素直径（中位数为3.2毫米，范围为1.2 - 4.8毫米）。对于10例连续的难治性部分性癫痫患者的发作间期到发作期SPET配准，在匹配扫描上对应点之间发现了与模体研究相似的均方根距离（RMSD）（中位数分别为2.2毫米和2.6毫米）。通过比较匹配扫描之间的像素强度分布以及分析减法像素强度分布，研究了我们归一化方法的适用性。除了极值外，归一化模体以及配对的归一化患者研究的像素强度分布彼此紧密匹配，在临床情况下，这些极值可能代表发作期激活或抑制区域。对于所有值，至少在第5至95百分位数范围内，减法图像强度分布以零为中心对称，证实了“未激活”像素的良好归一化。此外，基于模体扫描上测量的像素强度与基于99Tc（m）衰变常数的真实活性变化之间显示出线性关系。本研究结果表明，我们的方法能够实现准确的SPET到SPET配准以及适当的SPET归一化，从而能够得出有效的发作期减法图像。
