SAR
Specific Absorption Rate — RF power deposited in tissue per unit mass, measured in W/kg. Regulatory limit protects against tissue heating from MR RF transmission. IEC 60601-2-33 defines normal-mode and first-level-controlled-mode SAR limits; the scanner enforces them in real time.
Why it matters to buyers: SAR limits effectively cap how fast you can drive certain sequences. Particularly limiting at 3T (RF power scales with B0²) on high-flip-angle sequences (turbo-spin echo, T2-weighted) and on heavy-habitus patients. Acceleration features (Compressed SENSE, parallel imaging) help recoup throughput within SAR ceilings.
Why it matters to engineers: Scanner monitors SAR in real time and throttles sequences that exceed limits. Patient weight is a key input — incorrect weight entry produces incorrect SAR estimation. SAR is also the gating constraint for some implants with conditional MR-safe labeling.