DynaTOF: Time-Resolved Noncontrast Cerebral MR Angiography Using Spatially Modulated RF Saturation

To develop a time-resolved extension of three-dimensional time-of-flight MR angiography, termed Dynamic TOF (DynaTOF), that exploits intrinsic RF saturation behavior to enable noncontrast visualization of cerebrovascular hemodynamics.

DynaTOF was implemented by varying flip angle, repetition time (TR), and slab-selective RF excitation profile to modulate longitudinal magnetization saturation and encode relative inflow timing. Data were acquired using a short-TR protocol combined with deep-learning reconstruction to ensure scan efficiency. Five healthy volunteers underwent DynaTOF and pulsed arterial spin labeling (PASL) MRA. Five patients with intracranial arteriovenous malformations (AVMs) were scanned to evaluate clinical feasibility and compare temporal patterns with digital subtraction angiography (DSA). Analyses included inflow-time characterization, cross-correlation with PASL, region-of-interest assessment of arterial, nidus, and venous structures, as well as apparent SNR and contrast-to-noise ratio (CNR) quantification.

In healthy volunteers, DynaTOF exhibited predictable parameter-dependent inflow behavior and qualitative agreement with PASL-derived inversion-time dynamics. Apparent arterial SNR and CNR maxima were slice-position dependent, shifting from higher flip angles (20°-30°) at the slab entrance to lower angles (7°-15°) distally. In AVM patients, DynaTOF delineated arterial-to-nidus-to-early-venous transitions consistent with DSA, while venous depiction was attenuated for horizontal or curved-flow vessels due to the directional dependence of TOF-based inflow contrast. Short-TR acquisition with deep-learning reconstruction enabled single-slab imaging with a voxel size of 0.5 × 0.7 × 0.8 mm³ in approximately 1 min, supporting flexible parameter sweeps within routine clinical time constraints.

DynaTOF offers a noninvasive approach for time-resolved characterization of cerebrovascular flow while preserving TOF-like spatial resolution.