Precision, signal-to-noise ratio, and dose optimization of magnitude and phase arterial input functions in dynamic susceptibility contrast MRI

Purpose: To determine optimal conditions for precise measurement of arterial input function (AIFs) in dynamic susceptibility contrast (DSC) perfusion MRI. Materials and Methods: Magnitude-based (Delta R-2* and phase-based (Delta(phi)) AIFs were numerically simulated for several doses and baseline MRI noise levels [SNR(I-0)]. Random noise (1000 realizations) was added to real/imaginary MRI signals (derived from an internal carotid AIF), and AIF signal, noise, and signal-to-noise ratio (SNR) were determined. The optimal dose was defined as the dose that maximizes mean AIF SNR over the first-pass (SNRmean), rather than SNR at the AIF peak (SNRpeak) because, compared to SNRpeak, doses predicted by SNRmean reduced the AIF-induced variability in cerebral blood flow (CBF) by 24% to 40%. Results: The AIF SNR is most influenced by choice of AIF signal, then optimal dosing, each with little penalty. Compared to Delta R-2*, Delta(phi) signal has 4 to 80 times the SNR over all doses and time points, and -10-fold SNRmean at respective optimal doses. Optimal doses induce 85% to 90% signal drop for the Delta R-2* method, and 70% to 75% for Delta(phi), with two-fold dose errors causing similar to 1.7-fold loss in SNRmean. Increases in SNR(I-0) proportionally increase AIF SNR, but at a cost. Conclusion: AIF SNR is affected most by signal type, then dosing, and lastly, SNR(I-0).