Quantitative computed tomography liver perfusion imaging using dynamic spiral scanning with variable pitch: feasibility and initial results in patients with cancer metastases.

PURPOSE: To assess the feasibility and image quality of computed tomography (CT) liver perfusion imaging using an adaptive 4D spiral-mode, developed to extend the z-axis coverage, and to report initial qualitative and quantitative results in patients with cancer metastases.
MATERIALS AND METHODS: A total of 21 patients with liver metastases of various origins underwent CT perfusion imaging (100 kV and 150 mAs/rot) using a 4D spiral-mode with single-source 64-slice CT (n = 7) with a scan range of 6.7 cm (protocol A: 16 cycles, 46.5 seconds examination time), or dual-source 128-slice CT with a scan range of 14.8 cm (protocol B: 16 cycles, 46.5 seconds examination time, n = 7; protocol C: 12 cycles, 51.0 seconds examination time, n = 7). Ability to suspend respiration during perfusion imaging was monitored. Two independent readers assessed image quality on a 4-point scale, both before and after motion correction, and performed a qualitative (ie, arterial enhancement pattern and enhancement change over time) and quantitative perfusion (ie, arterial liver perfusion [ALP]; portal-venous perfusion [PVP]; hepatic perfusion index [HPI]) analysis.
RESULTS: Of 21 patients, 7 (33%) could suspend respiration throughout the perfusion study and 14 (67%) resumed shallow breathing during the perfusion scan. The 21 patients had a total of 88 metastases. The scan range of protocol A covered at least 1 metastasis in all patients (total 20/34 [58.8%] metastases). The scan range of protocol B and C covered 53 of 54 (98.1%) metastases, whereas one metastasis in segment VIII was only partially imaged. Image quality was diagnostic both before and after motion correction, whereas being significantly better after motion correction (P < 0.001). Qualitative perfusion analysis of 67 metastases revealed diffuse arterial enhancement in 3 (4.5%), sparse enhancement in 11 (16.4%), peripheral-nodular enhancement in 9 (13.4%), rim-like enhancement in 15 (22.4%), and none in 29 (43.3%) metastases. Enhancement over time of 67 metastases showed a centripetal progression in 6 (8.9%), sustained portal phase in 16 (23.9%), wash-out in 16 (23.9%), and none in 29 (43.3%) metastases. Quantitative perfusion analysis revealed significantly higher arterial liver perfusion and HPI in metastases and metastasis borders than in adjacent normal liver tissue (P < 0.001 each). Portal-venous perfusion was significantly lower in metastases and metastasis borders than in normal liver tissue (P < 0.001). There were no significant differences in image quality and qualitative perfusion analysis between the 3 protocols (P = n.s.). Calculated effective radiation doses were 13.4 mSv for protocol A, 30.7 mSv for protocol B, and 23.0 mSv for protocol C.
CONCLUSION: CT perfusion imaging of the liver using the 4D spiral-mode is feasible with diagnostic image quality, and enables the reliable qualitative and quantitative analysis of the normal and metastatic liver parenchyma. Radiation dose issues must be considered when determining the scan range, number of cycles, and scan duration of the perfusion CT protocol.