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 (ΔR ₂*) and phase-based (Δφ) AIFs were numerically simulated for several doses and baseline MRI noise levels [SNR(I₀)]. 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 (SNR_mean), rather than SNR at the AIF peak (SNR_peak) because, compared to SNR_peak. doses predicted by SNR_mean 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 ΔR₂*. Δφ signal has 4 to 80 times the SNR over all doses and time points, and ∼10-fold SNR_mean at respective optimal doses. Optimal doses induce 85% to 90% signal drop for the ΔR₂* method, and 70% to 75% for Δφ, with two-fold dose errors causing ∼1.7-fold loss in SNR_mean. Increases in SNR(I₀) proportionally increase AIF SNR, but at a cost. Conclusion: AIF SNR is affected most by signal type, then dosing, and lastly, SNR(I₀).