About this MRI Scan Time
MRI scan time is purely a function of the sequence parameters. Technologists balance image quality (SNR/Resolution) against patient comfort (Scan Time). This calculator determines the duration of 2D acquisitions like Spin Echo (SE) or Fast Spin Echo (FSE/TSE).
Who this calculator is for
- MRI technologists, trainees, and protocol builders reviewing sequence timing.
- People who already know the TR, phase matrix, NEX, and echo train length for a sequence.
- Learners studying how image-quality choices translate into longer or shorter acquisitions.
When to use it
- Use this calculator when estimating how a parameter change will affect sequence duration.
- Use it to compare a conventional spin-echo setup with a faster turbo or fast spin-echo approach.
- Use it in teaching when explaining why NEX, TR, and ETL materially affect room time.
How to use this calculator
- Enter TR in milliseconds.
- Enter Phase Encoding Steps (matrix size in the phase direction).
- Enter NEX (Number of Excitations/Averages).
- Enter ETL (Echo Train Length). Use 1 for standard Spin Echo.
Key assumptions
- The calculation is a simplified sequence-time estimate for 2D-style acquisitions and does not model every vendor-specific timing factor.
- Parallel imaging, partial Fourier, calibration scans, respiratory gating, and 3D sequence behavior can change real exam time substantially.
- This tool is best used for planning and education rather than predicting exact scanner console times.
Accuracy and testing
Review formula sources, default test cases, assumptions, unit handling, rounding rules, and changelog for this calculator.
How this calculator works
Inputs explained
TR (Repetition Time)
The time between consecutive excitation pulses. Long TR increases scan time but provides T2 weighting.
Phase Steps
The resolution in the phase encoding direction (e.g., 256 or 192).
NEX / NSA
Number of Excitations / Number of Signal Averages. Increasing this improves SNR but directly multiplies scan time.
ETL / Turbo Factor
Echo Train Length. Used in Fast Spin Echo sequences to speed up acquisition by collecting multiple echoes per TR.
Understanding your results
Example scenarios
T1 Spin Echo
TR 500ms, Phase 256, NEX 1, ETL 1. Time = 128 seconds (2m 8s).
T2 Fast Spin Echo
TR 3000ms, Phase 256, NEX 2, ETL 16. Time = (3000*256*2)/16 = 96,000ms = 96s (1m 36s).
Key Features
- Supports SE and FSE
- Instant Minute/Second conversion
- Physics-based logic
Tips & Best Practices
- Doubling NEX doubles scan time but increases SNR by only √2 (approx 1.4x).
- Increasing ETL reduces scan time but can introduce blurring or reduce the number of available slices.
Glossary of Terms
- K-Space
- The raw data matrix filled during an MRI scan.
- Sequence
- A pre-defined set of pulses and gradients used to generate specific image contrast.