Thrombus imaging in acute ischaemic stroke using thin-slice unenhanced CT: comparison of conventional sequential CT and helical CT.

OBJECTIVES: Thin-slice helical unenhanced CT can be used for thrombus imaging but increases radiation exposure. Conventional sequential images obtained by multidetector CT can be reconstructed into thin-slice images. The purpose of this study was to evaluate if conventional sequential unenhanced CT images can replace helical unenhanced CT for thrombus imaging.
METHODS: Fifty consecutive patients with acute ischaemic stroke underwent both 5-mm conventional sequential unenhanced CT and helical unenhanced CT. Each of the sequential and helical unenhanced CT images was subsequently reconstructed into four 1.25-mm images. Thrombus volumes and HU were measured semi-automatically using both types of unenhanced CT. Thrombus HU ratio (rHU) was calculated using the HU of the contralateral segment. The intraclass correlation coefficient (ICC) and Bland-Altman plots were used to assess measurement agreement.
RESULTS: The mean rHUs were 1.47 ± 0.17 for sequential unenhanced CT and 1.47 ± 0.18 helical unenhanced CT (P = 0.542). The mean thrombus volumes were 124.25 ± 125.65 mm(3) and 117.84 ± 124.32 mm(3) on sequential and helical unenhanced CT images, respectively (P = 0.063). Measurement agreement between thrombus volumes from the two unenhanced CT images was high (ICC = 0.981).
CONCLUSIONS: Thin-slice unenhanced CT images reconstructed from 5-mm sequential images can replace helical unenhanced CT for thrombus imaging in acute ischaemic stroke. KEY POINTS : • Unenhanced CT is used to evaluate intra-arterial thrombus. • Thrombus HU and volume measurements using sequential or helical CT are comparable. • Conventional sequential images can replace helical CT for thrombus imaging. • Radiation dose for thrombus imaging can be reduced using sequential CT.