The added value of dual-time-point 18F-FDG PET/CT imaging in the diagnosis of colorectal cancer liver metastases

To investigate the added value of dual-time-point ¹⁸F-FDG PET/CT imaging in the diagnosis of colorectal cancer liver metastases (CRLM).

One hundred and eight patients with CRLM preoperatively underwent a dual-time-point ¹⁸F-FDG PET/CT scan. All hepatic lesions were diagnosed by histopathology. The diagnostic sensitivity of ¹⁸F-FDG PET/CT for CRLM was calculated on early scan and delayed scan, respectively. The McNemar test was used to test the differences of the sensitivity and the specificity between early scan and delayed scan.

On a per-patient basis, no significant difference in sensitivity was found between early scan and delayed scan (92.93% vs. 96.97%, P = 0.125). The per-patient specificity of early and delayed scans was 77.78%. On a per-lesion basis, overall sensitivity of delayed scan was significantly higher than that of early scan (83.49% vs. 76.61%, P < 0.001). The per-lesion specificity of early and delayed scans was 69.23%. For the lesion size of CRLM ≤ 10 mm, delayed imaging had significantly higher sensitivity than early imaging (47.17% vs. 26.42%, P < 0.001). However, for CRLM > 10 mm, there was no significant difference in sensitivity between early and delayed scans (92.73% vs. 95.15%, P = 0.125). Of the detected 182 liver metastatic lesions on delayed scan, the SUV_max on delayed scan was significantly higher than that on early scan (12.13 ± 7.13 vs. 9.16 ± 4.74, P < 0.001). The SUVmean of the normal liver on delayed scan was significantly lower than that on early scan (1.91 ± 0.29 vs. 2.33 ± 0.31, P < 0.001). The tumor to normal background ratio on delayed scan was significantly higher than that on early scan (6.59 ± 4.43 vs. 4.02 ± 2.23, P < 0.001).

The dual-time-point ¹⁸F-FDG PET/CT imaging might detect more CRLM lesions compared with single-time-point imaging, especially for small (< 10 mm) lesions.