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MRI Sequence Parameter Calculator

Calculate scan time, resolution, SNR, and SAR for MRI pulse sequences with clinical and research presets.

NMR & MRI SystemsSequence PlanningClient-Side
Tool details, related tools, and citation

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Sequence Preset

Scanner

Geometry

Timing Parameters

Acquisition

  • Plan MRI acquisition protocols for clinical or research studies
  • Estimate scan time before booking scanner time slots
  • Evaluate resolution and SNR trade-offs when optimizing protocols
  • Check SAR safety margins for high-flip-angle sequences at 3T or 7T
  • Generate standardized methods text for publications and grant applications
  • Compare different sequence configurations (e.g., parallel imaging vs. averaging)

Don't use for

  • For exact SAR values — use your scanner vendor’s SAR monitor for regulatory compliance
  • For absolute SNR — the calculator provides relative units for comparison, not calibrated measurements
  • As a substitute for sequence simulation software (e.g., Bloch equation simulators) for contrast optimization

MRI Sequence Parameter Fundamentals

MRI acquisition parameters control three interdependent properties: image quality, scan time, and patient safety.

Spatial Resolution is determined by FOV / matrix size. Smaller voxels provide finer anatomical detail but reduce SNR proportionally to voxel volume.
Signal-to-Noise Ratio (SNR) scales with voxel volume, the square root of averages (NEX), and field strength. Doubling field strength from 1.5T to 3T doubles SNR.
Scan Time depends on the sequence type. For spin-echo sequences, time = TR ×\times phase steps / (ETL ×\times parallel factor). Turbo spin echo (TSE) sequences use echo trains to acquire multiple phase-encode lines per TR, dramatically reducing scan time.
SAR (Specific Absorption Rate) increases with the square of both flip angle and field strength. At 3T with refocusing pulses (150°), SAR limits become a practical constraint on sequence design.

Common Pitfalls in MRI Protocol Design

Several factors can compromise MRI protocol quality:

• SAR limits at 3T: Spin-echo sequences with 180° refocusing pulses may exceed SAR limits at short TR. Use variable flip angle refocusing or lower parallel factors • Partial volume effects: Thick slices (>5 mm) mix signals from different tissues, reducing diagnostic sensitivity for small lesions • Motion artifacts in long scans: Scan times >8 minutes significantly increase motion artifact risk. Consider parallel imaging or partial Fourier to reduce time • EPI distortion: fMRI and DWI use EPI readouts that are sensitive to B0 inhomogeneity, causing geometric distortion near air-tissue interfaces • Parallel imaging noise: GRAPPA/SENSE acceleration >3 introduces significant g-factor noise penalty. Acceleration of 2 is the typical sweet spot • Inadequate averages: Single average (NEX=1) may be insufficient for small-FOV or high-resolution protocols. SNR increases with sqrt(NEX) but scan time increases linearly

Frequently Asked Questions

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