Purpose or Case Report: High T1 and T2 relaxivity macrocyclic gadolinium-based contrast agents (GBCAs), including gadopiclenol, have the potential to improve contrast-enhanced MRI while minimizing Gd dose. However, administered at low volumes in pediatric joint arthrography, the in vivo concentration of GBCA is variable due to pathological and anatomical volume differences. Concentration variations in conjunction with rapid T2 decay inherent to highly relaxive GBCAs can result in variable signal. To determine optimal dosages, we tested concentration-dependent signal changes in phantom studies with T1-weighted (T1w) and T2-weighted (T2w) sequences commonly used in clinical arthrogram studies.
Methods & Materials: Phantoms with gadobutrol (GB) and gadopiclenol (GP) concentrations ranging from 0.03 mM – 3 mM were imaged using T1w and T2w Turbo Spin Echo (TSE) sequences on a 3T MRI scanner. This range was chosen to bracket potential in vivo concentrations. Experimental results were compared with simulated signal curves generated with published relaxivity data. GP results were compared with pediatric joint arthrography using GP doses of 1 mM (n=1 shoulder) and 0.3 mM (n=2 shoulder, n=1 hip) at a volume of ~18mL. An arthrogram protocol using GB at 2.25 mM was first adapted to a 1 mM GP dose to account for the higher relaxivity of GP. Contrast-to-noise ratios (CNR) were generated for enhanced regions in the joint relative to non-enhancing deltoid and quadricep muscles.
Results: A maximum relative value was taken as the highest measured signal of GP (T1w: 0.3 mM; T2w: 0.06 mM). In T1w TSE, GP exhibited ≥65% max signal from 0.06 mM-1.2 mM, while GB exhibited ≥65% max signal from 0.45 mM-3 mM. In T2w TSE, these ranges were 0.06 mM-0.6 mM for GP and 0.3 mM-1 mM for GB. Simulations indicated a T1 peak at ~0.3 mM for GP and faster signal drop-off compared to GB. Clinical joint arthrography administered at a concentration of 0.3 mM of GP demonstrated high signal post contrast administration relative to 1 mM. 0.3 mM: T1w CNR = 223 ± 55.5; T2w CNR = 143.2 ± 34.6. 1.0 mM: T1 CNR = 214.3; T2w CNR = 1.4.
Conclusions: GP-enhanced imaging generates higher MR signal at lower concentrations than GB; however, GP demonstrates greater signal decline at higher concentrations. While T1w CNR remains similar for both GP doses, T2w CNR decreases substantially at 1 mM due to GP’s high T2 relaxivity. While an optimal dose of GP is achievable, changes in injection and intra-articular volume paired with strong T2 effect can lead to unexpected signal outcomes.