SPECT／CT图像配准不良对心肌灌注显像CT衰减校正的影响

目的探讨CT与SPECT图像配准不良对MPICT衰减校正（CTAC）的影响。方法99Tcm-MIBIMPI受检者19名，均为行健康体格检查者，其中男11名，女8名，年龄（65．3±9．6）岁。对MPI图像进行CTAC。利用仪器自带的软件对CT图像进行模拟位移：相对心脏位置进行上、下、左、右、前、后6个方向的移动，移动幅度分别为0．5、1．0、1．5、2．0、2．5、3．0、3．5、4．0和4．5em。重建不同位移状态的CTAC心肌断层图像，利用靶心图获得左心室各壁段的放射性计数百分比，比较位移前后左心室各壁段放射性计数的差异和图像差异。采用SPSS13．0软件对数据进行配对t检验。结果当CT图像的移动距离为0．5cm时，所有位移方向的CTAC图像均未见明显可识别的图像伪影。当CT图像的移动距离≥1．0CITI时，左心室各壁段出现不同程度的图像伪影以及放射性计数的改变；CT图像向上、下、左、右、前、后方向位移时，分别对心尖部，前壁和心尖部，间壁，前壁、心尖部和侧壁，侧壁和下后壁，前壁、心尖部和间壁放射性计数的影响最为显著。向下位移时左心室各壁段放射性计数的改变大于向上位移（-9．68±8．06）％和（-2．04±1．83）％；f=6．573，P〈0．01]，向右位移的改变大于向左位移（-9．02±8．47）％和（-4．38±3．67）％；t=1．987，P〈0．05]。在左心室各壁段中，前壁、心尖部和侧壁的伪影程度明显较下后壁和间壁显著。结论CT与SPECT图像配准不良可使MPICTAC图像出现不同程度的伪影，其伪影出现的部位和严重程度与配准不良的方向和幅度密切相关。

Impact of misregistration between SPECT and CT on attenuation correction of myocardial perfusion imaging

Objective To evaluate the effects of misregistration with different directions and magni tudes between SPECT and CT on image quality and semi-quantification of MPI. Methods The data of 19 healthy volunteers （ 11 males, 8 females ; mean age ： （ 65.3 ± 9.6） years） were retrospectively analyzed. They all had a low pretest likelihood of coronary artery disease according to exercise and rest 99Tcm-MIBI MPI. The CT attenuation correction （CTAC） was performed on a SPECT/CT system. The CT images were manually shifted by 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 cm distance along the up/down, left/ right, and anterior/posterior axes respectively by using the system built-in software. The counts of the left ventricle were measured using myocardial Bull＇s eye generated from the reconstructed CTAC images. The im age quality and semi-quantification of the CTAC images reconstructed from the raw data with and without shifting were compared and analyzed. Paired t test was used to analyze the data. Results There was no visi ble artifact with 0.5 cm shifting. The image quality was deteriorated significantly and the counting difference was significant with shifting distance greater than or equal to 1.0 cm. The image artifact of apex wall was mainly due to the upward shift, anterior and apex wall due to the downward shift, septal wall due to the left ward shift, anterior, apex and lateral wall due to the rightward shift, lateral and infero-posterior wall due to the forward shift, anterior, apex and septal wall due to backward shift. The counting difference caused by the downward shift was significantly more severe than that caused by the upward shift （ （-9.68±8.06） % and （-2.04±1.83）%, t=6.573, P〈0.01） ; and the rightward shift was more severe than the leftward shift （ （ -9.02± 8.47） % and （-4.38±3.67）%; t= 1.987, P〈0.05）. The image artifacts in anterior, apex and lateral walls were more severe than those in the infero-posterior and septal walls. Conclusions CTAC image artifacts in myo cardial perfusion SPECT/CT studies could be caused by misregistration I〉 1.0 cm. Different directions and magni tudes of shift could result in different degrees of attenuation artifacts at different locations on the original images.