Comparing dual energy CT and subtraction CT on a phantom: which one provides the best contrast in iodine maps for sub-centimetre details?

ObjectivesTo compare contrast-to-noise ratios (CNRs) and iodine discrimination thresholds on iodine maps derived from dual energy CT (DECT) and subtraction CT (SCT).MethodsA contrast-detail phantom experiment was performed with 2 to 15 mm diameter tubes containing water or iodinated contrast concentrations ranging from 0.5 mg/mL to 20 mg/mL. DECT scans were acquired at 100 kVp and at 140 kVp+Sn filtration. SCT scans were acquired at 100 kVp. Iodine maps were created by material decomposition (DECT) or by subtraction of water scans from iodine scans (SCT). Matched exposure levels varied from 8 to 15 mGy. Iodine discrimination thresholds (C-r) and response times were determined by eight observers.ResultsThe adjusted mean CNR was 1.9 times higher for SCT than for DECT. Exposure level had no effect on CNR. All observers discriminated all details 10 mm at 12 and 15 mGy. For sub-centimetre details, the lowest calculated C-r was 0.50 mg/mL for SCT and 0.64 mg/mL for DECT. The smallest detail was discriminated at 4.4 mg/mL with SCT and at 7.4 mg/mL with DECT. Response times were lower for SCT than DECT.ConclusionsSCT results in higher CNR and reduced iodine discrimination thresholds compared to DECT for sub-centimetre details.Key Points center dot Subtraction CT iodine maps exhibit higher CNR than dual-energy iodine maps center dot Lower iodine concentrations can be discriminated for sub-cm details with SCT center dot Response times are lower using SCT compared to dual-energy CT