Fig. 5.

Detection and localization of metastatic masses by SPECT-CT imaging after the systemic administration of pPEG-HSV1tk. (a–j) Systemic metastatic sites were detected based on the whole body SPECT-CT images in three representative mice, Mel-2 (a,b), Mel-3 (c–h) and BCa-1 (i,j). (a,c,e,g) Transverse, coronal and sagittal views of co-registered SPECT-CT images of Mel-2 (a) and Mel-3 (c,e,g). All images were obtained at 24 h after [¹²⁵I]FIAU injection. (b,d,f,h) Gross anatomical details of the metastatic masses that were located on the basis of the SPECT-CT images (a,c,e,g). Multiple metastatic sites were detected by imaging in Mel-2 (a, dotted circle). Necropsy of the corresponding area revealed melanoma masses under the brown adipose tissue in the upper dorsal area (b, dotted circle). (c) Accumulated radioactivity was detected adjacent to the thoracic mid-spine (arrow), which corresponded to a tumor at this location (d, arrow). Additional metastatic sites demonstrated by SPECT-CT imaging (e,g, arrow and dotted circle) correlated with melanoma masses uncovered immediately above the diaphragm (f, dotted circle) and in the left inguinal lymph node (h, arrow), respectively. (i,j) Cross-comparison of PEG-3 promoter–mediated imaging and FDG-PET in a breast cancer metastasis model, BCa-1. Two nodules (Tu-1 and Tu-2) were detected by [¹²⁵I]FIAU-SPECT near the heart (i) and were confirmed by necropsy (j). Although Tu-1 was also detected by [¹⁸F]FDG-PET, Tu-2, a smaller nodule attached to the heart, was not obvious in the PET image. SPECT images were acquired 48 h after injection of [¹²⁵I]FIAU. The PET and SPECT images were acquired on the same day (i). (Tu, tumor; Ht, heart; Bf, brown fat.) Scale bars, 10 mm. From Bhang et al. (37), Nature Medicine, 2011.