Balanced
Make modest changes without heavily prioritizing one outcome.
Resolution
Favor smaller voxels and finer spatial detail.
SNR
Favor stronger signal and a less noisy appearance.
Scan Time
Favor a shorter acquisition while preserving coverage.
Field strength changes available SNR, relaxation timing, susceptibility, chemical shift, SAR behavior, and inversion null points.
Enter TR and TE to identify the most likely sequence. Add TI for STIR or FLAIR.
How Parameters Optimize Images
Field strength
Higher field strength often provides more available SNR that may be used for resolution or speed, but can increase susceptibility, chemical shift, B1 variation, and SAR constraints.
FOV
Sets anatomy coverage. Reducing FOV with the same matrix makes smaller pixels, but can cause wrap if anatomy lies outside the selected area.
Matrix
Increasing matrix improves spatial resolution. Frequency matrix has less scan-time impact; phase matrix directly adds phase-encoding steps and time.
Slice thickness
Thinner slices improve through-plane detail and reduce partial volume, but reduce SNR and may require more slices for coverage.
NEX
More averages reduce random noise. SNR rises only with the square root of NEX, while scan time rises approximately in direct proportion.
ETL
A longer echo train shortens fast/turbo spin-echo acquisition, but may increase blurring and alter contrast.
TR
TR affects scan time and image weighting. It should not be shortened solely for speed if doing so changes the intended tissue contrast.
Receiver bandwidth
Lower bandwidth can improve SNR but increases chemical-shift and distortion sensitivity. Higher bandwidth does the opposite and may permit shorter readouts.
TI
TI selects which tissue is nulled in inversion recovery. STIR and FLAIR require scanner- and field-strength-specific TI values, so TI should not be optimized like a speed control.
Common Sequence Timing Reference
Educational starting ranges for conventional spin-echo or fast/turbo spin-echo-style imaging. They are not universal best settings; confirm the anatomy-, vendor-, and sequence-specific protocol on the scanner.
T1-weighted spin echo
Anatomic detail and pre/post-contrast comparison
Short TR with the shortest practical TE below 15 ms emphasizes T1 differences while limiting T2 influence.
T2-weighted FSE/TSE
Fluid-sensitive pathology assessment
Long TR reduces T1 influence; long effective TE adds T2 weighting.
Proton density FSE/TSE
High-SNR structural and musculoskeletal detail
Long TR and short TE minimize T1 and T2 weighting.
STIR at 1.5T
Uniform fat suppression and edema visibility
TI is selected to null fat and must be verified for the scanner and field strength.
T2 FLAIR
T2-sensitive brain imaging with CSF suppression
Long TI is selected to null CSF; 3D and vendor implementations may differ substantially.
These ranges do not cover gradient echo, balanced SSFP, EPI, diffusion, perfusion, spectroscopy, vendor-specific 3D sequences, or contrast- and anatomy-specific protocol requirements.