Renal T(*)(2) perfusion using an iron oxide nanoparticle contrast agent--influence of T(1) relaxation on the first-pass response.

Quantitative perfusion measurements require accurate knowledge of the correlation between first-pass signal changes and the corresponding tracer concentration in tissue. In the present study, a detailed analysis of first-pass renal cortical changes in T(1) and T()(2) following bolus injection of the iron oxide nanoparticle NC100150 Injection was investigated in a pig model using a double-echo gradient-echo sequence. The estimated change in 1/T()(2) during first pass calculated from single-echo sequences was compared to the true double-echo-derived 1/T()(2) curves. Using a single-echo (TE = 6 ms) spoiled gradient-echo sequence, the first-pass 1/T()(2) response following a bolus injection of 1 mg Fe/kg of NC100150 Injection was significantly underestimated due to counteracting T(1) effects. Signal response simulations showed that the relative error in the first-pass response decreased with increasing TE and contrast agent dose. However, both the maximum TE and the maximum dose are limited by excessive cortical signal loss, and the maximum TE is further limited by high temporal resolution requirements. The problem of T(1) contamination can effectively be overcome by using a double-echo gradient-echo sequence. This yields a first-pass response that truly reflects the tissue tracer concentration, which is a critical requirement for quantitative renal perfusion assessment.