肺部肿瘤PET/CT同机图像融合精度研究

Accuracy of image coregistration of pulmonary carcinoma using integrated PET/CT system

目的探讨肺部肿瘤PETCT图像融合的精度及其影响因素,以及不同方法测定融合精度的差异。方法肺部肿瘤患者24例,行18F脱氧葡萄糖(FDG)PETCT检查,共31个病灶。分别采用几何中心(COG)法及体积法测定PETCT同机图像融合精度,COG法测定病灶PET图像的COG与CT图像COG的距离,体积法测定病灶PET与CT图像融合部分体积占总体积的百分比(PPETCT),并按病灶的部位(左肺与右肺,上肺与下肺,肺顶区、周围区、中央区与肺底区)、体积(≤2cm3,21～99cm3,≥10cm3)进行分组比较。结果用COG法测定所有病灶的融合误差为(439±233)mm(100～868mm),用体积法测定融合精度为(3618±2266)%(0%～8053%)。按病灶部位分组,用COG法和体积法测量融合精度各组间差异均无显著性(P>005)。按病灶大小分组,用COG法测定融合精度各组间差异无显著性(P>005);用体积法测定,≤2cm3组最差,PPETCT为(1411±1064)%(P<001)。结论肺部病灶同机PETCT融合的偏差较小,但小病灶融合误差较大。测定融合精度宜联合应用COG法和体积法。

Objective To evaluate the accuracy of coregistration of PET/CT images in patients with pulmonary carcinoma and the affecting factors, and to investigate the difference between two methods for measuring coregistration accuracy. Methods Twenty-four patients with well-circumscribed pulmonary carcinoma were examined by integrated PET/CT. Thirty-one lesions with the diameter of 1.0～5.0 cm were analyzed. The registration accuracy of PET/CT was measured with two methods, volume measure and center of geometry (COG) measure. The volume of interest of each lesion was defined separately on PET, CT and the images were fused (V_~PET , V_~CT , V_~PET+CT ). The overlap volume of PET and CT images was calculated with the formula: V_~PET/CT =V_~PET +V_~CT -V_~PET+CT . The percentage of V_~PET/CT on V_~PET+CT , P_~PET/CT , was used to assess the fusion accuracy of PET and CT images. The COG was assessed. The distance of COGs between the PET image and the CT image, D_~COG , was measured. The coregistration accuracy was compared between lesions classified according to the lesion location and volume. Results The mean D_~COG was (4.39±2.33) mm (range, 1.00～8.68 mm). P_~PET/CT was (36.18±22.66)% (range, 0%～80.53%). Misregistration tended to be profounder in the lower lungs [D_~COG =(4.63±2.37)mm, P_~PET/CT =(32.25±18.40)%] than in the upper lungs [D_~COG =(4.11±2.36) mm, P_~PET/CT =(40.95±26.91)%, P=0.30]. Misregistration also tended to be slightly profounder in the left lung [D_~COG =(5.18±3.08) mm, P_~PET/CT =(33.01±20.21)%] than in the right lung [D_~COG =(4.02±1.87) mm, P_~PET/CT =(37.68±24.07)%, P=0.78]. There was no statistical difference among lesions located at different lung regions (the apex, peripheral, central, and base of lung) while using two indexes. As for the lesions with different volumes as ≤2 cm3, 2.1～9.9 cm3 or ≥10 cm3, the P_~PET/CT were (14.11±10.64)%, (41.64±16.22)% and (53.77±17.71)%, respectively (P<0.01). Conclusions The registration of the pulmonary lesion in PET/CT images is usually accurate, but spatial misregistration does occur, especially for the smaller lesions. The combination of different methods for measuring coregistration accuracy may be more valuable in defining this kind of misregistration.