Subtraction-multiphase-CT unbeneficial for early detection of colorectal liver metastases

PurposeTo assess the value of multiphase-subtraction-CT for early detection of colorectal-liver-metastases (CRLM).Methods and materialsIn 50 patients suspected of CRLM a routine pre-operative 4-phase-CT-scan of the upper abdomen was obtained. All 12 possible image subtractions between two different phases were constructed applying 3D-image-registration to decrease distortion artefacts induced by differences in inspiration volume. Two experienced radiologists initially reviewed the conventional 4-phase-CT for malignant and/or benign appearing lesions and at least 1-month hereafter the same 4-phase-CT now including the subtracted images. The results were compared to histology reports or to a combination of surgical exploration and intraoperative ultrasound together with results from pre-operative PET and follow-up examinations.ResultsAlthough an additional number of 31 malignant appearing lesions were detected on the subtraction images, none proved to represent a true CRLM. Interobserver agreement (κ) decreased from 0.627 (good) to 0.418 (fair).ConclusionAdding linearly co-registered subtraction-CT images to a conventional 4-phase-CT protocol does not improve detection of CRLM.