Efficacy of Whole-Blood Model of Gadolinium-Based Contrast Agent Relaxivity in Predicting Vascular MR Signal Intensity In Vivo.

BACKGROUND

Previous in vitro studies have described sub-linear longitudinal and heightened transverse H2O relaxivities of gadolinium-based contrast agents (GBCAs) in blood due to their extracellular nature. However, in vivo validation is lacking.

PURPOSE: Validate theory describing blood behavior of R1 and R2* in an animal model.

STUDY TYPE: Prospective, animal.

ANIMAL MODEL: Seven swine (54-65 kg).

FIELD STRENGTH/SEQUENCE: 1.5 T; time-resolved 3D spoiled gradient-recalled echo (SPGR) and quantitative Look-Locker and multi-echo fast field echo sequences.

ASSESSMENT: Seven swine were each injected three times with 0.1 mmol/kg intravenous doses of one of three GBCAs: gadoteridol, gadobutrol, and gadobenate dimeglumine. Injections were randomized for rate (1, 2, and 3 mL/s) and order, during which time-resolved aortic 3D SPGR imaging was performed concurrently with aortic blood sampling via an indwelling catheter. Time-varying [GBCA] was measured by mass spectrometry of sampled blood. Predicted signal intensity (SI) was determined from a model incorporating sub-linear R1 and R2* effects (whole-blood model) and simpler models incorporating linear R1, with and without R2* effects. Predicted SIs were compared to measured aortic SI.

STATISTICAL TESTS: Linear correlation (coefficient of determination, R2) and mean errors were compared across the SI prediction models.

RESULTS

There was an excellent correlation between predicted and measured SI across all injections and swine when accounting for the non-linear dependence of R1 and high blood R2* (regression slopes 0.91-1.04, R2 ≥ 0.91). Simplified models (linear R1 with and without R2* effects) showed poorer correlation (slopes 0.67-0.85 and 0.54-0.64 respectively, both R2 ≥ 0.89) and higher averaged mean absolute and mean square errors (128.4 and 177.4 vs. 42.0, respectively, and 5506 and 11,419 vs. 699, respectively).

DATA

CONCLUSION

Incorporating sub-linear R1 and high first-pass R2* effects in arterial blood models allows accurate SPGR SI prediction in an in vivo animal model, and might be utilized when modeling MR blood SI.

LEVEL OF EVIDENCE: 1 TECHNICAL EFFICACY: Stage 1.