Improving Patient to Patient CT Value Uniformity in Coronary CT Angiography with an Individualized Contrast Injection Protocol Tailored to Fat Free Mass and kVp.

PURPOSE To achieve a consistent enhancement in coronary CT angiography (CCTA) by implementing a contrast injection protocol with adjusted iodine concentration based on patient habitus and kVp. METHOD AND MATERIALS Retrospective data from 80 consecutive patients (group 1) scanned on a Revolution CT (GE Healthcare) with one-heartbeat automated triggering, 100 kVp (N=74) or 120 kVp (N = 6), noise index = 25 and standard iodine dose (70 ml of 370 mg I / ml, 350 mg I / ml or 320 mg I / ml) was collected, using DoseWatch (GE Healthcare). The optimal correlation between arterial enhancement (HU) and body habitus normalized to total iodine dose (TID) was determined by considering following parameters: weight, Body Mass Index (BMI), Body Surface Area (BSA), Lean Body Mass (LBM) and Fat Free Mass (FFM). From the parameter giving the best correlation, a model for optimal contrast concentration to achieve a target enhancement value of 550 HUtarget was determined and prospectively applied to 62 patients (N=1 at 80 kVp, N=55 at 100 kVp and N=6 at 120 kVp) undergoing a CCTA exam (group 2). Personalized iodine concentration was administered by parallel mixing of iodine with saline on a dual-head power injector (Nemoto-Kyorindo, Japan). Enhancement was compared between group 1 and 2 (Mann-Whitney U- test) and homogeneity of variances was tested (Levene’s test). RESULTS Compared to other body habitus parameters (R² range 0.1 – 0.5), Free Mass (FFM) showed the strongest correlation (R² = 0.5) with enhancement. Following contrast injection model was established for 100 kVp: TID = (HUtarget - 237)*FFM/946; for 120 and 80 kVp TID should be scaled by 1.22 and 0.77 respectively. With the modified protocol, variance (standard deviation) reduced from 102 HU to 67 HU (p < 0.01). The mean enhancement 506 HU was lower than the target 550 HU (p <0.01). CONCLUSION An injection protocol with contrast concentration adapted to body habitus, iodine concentration and kVp improves patient-to-patient CT value uniformity. CLINICAL RELEVANCE/APPLICATION Personalizing the iodine injection protocol for CCTA homogenizes image quality in terms of contrast enhancement for an easier interpretation and correlation of images.