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

Evelinda Baerends,Monique Brink,Mathias Prokop,Luuk J Oostveen,Marco Das,Frank De Lange,Ioannis Sechopoulos,Casper T Smit

doi:10.1007/s00330-018-5496-x

Abstract

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 (Cr) 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 Cr 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• Subtraction CT iodine maps exhibit higher CNR than dual-energy iodine maps• Lower iodine concentrations can be discriminated for sub-cm details with SCT• Response times are lower using SCT compared to dual-energy CT

Highlights

Materials and methodsIodine mapping is among the most frequently reported clinical applications of dual energy computed tomography (DECT) [1,2,3,4,5,6]
Median response times for all details above the concentrations required (Cr) for both techniques were significantly lower for Subtraction CT (SCT) (1.9 s) than DECT (2.3 s), p
Both the 10 and 15 mm diameter details were discriminated in DECT and SCT for all concentrations at 12 mGy and 15 mGy exposures

Summary

Introduction

Materials and methodsIodine mapping is among the most frequently reported clinical applications of dual energy computed tomography (DECT) [1,2,3,4,5,6]. SCT provides an attractive alternative to DECT in the context of iodine mapping because it does not require the special hardware necessary for dual energy CT. For the successful implementation of SCT, only software for accurate registration and subtraction are prerequisites. Both techniques are quantitative in that the signal intensity of the iodine maps is proportional to the iodine uptake [12, 21]. Some vendors implemented this proportionality to allow the user to assess the local iodine concentration [21]

Objectives

Results

Conclusion