Adrenal MRI Chemical Shift Calculator
Enter lesion signal intensities from in-phase and out-of-phase images to estimate lipid-rich adenoma likelihood using common radiology cutoffs.
What this MRI adrenal calculator does
This tool helps you quickly compute two widely used chemical-shift MRI metrics for adrenal lesions:
- Signal Intensity Index (SII)
- Adrenal-to-Spleen Ratio (ASR) (optional, if spleen references are available)
These metrics are commonly used to assess whether an adrenal mass behaves like a lipid-rich adenoma, which usually shows a drop in signal on out-of-phase imaging.
Core formulas used
1) Signal Intensity Index (SII)
SII = ((SI in-phase − SI out-of-phase) / SI in-phase) × 100
Higher percentages generally indicate greater intracellular lipid content.
2) Adrenal-to-Spleen Ratio (ASR)
ASR = (Lesion out-of-phase / Spleen out-of-phase) ÷ (Lesion in-phase / Spleen in-phase)
Lower values support lipid-rich adenoma behavior.
Typical interpretation ranges (common, not universal)
- SII ≥ 20%: strongly supportive of lipid-rich adenoma.
- SII 16.5% to 19.9%: borderline/intermediate zone.
- SII < 16.5%: less supportive for lipid-rich adenoma.
- ASR ≤ 0.71: supportive of adenoma in many protocols.
Thresholds vary by scanner, sequence parameters, ROI method, and institutional protocol. Always use local radiology standards when available.
How to measure correctly before using the calculator
ROI best practices
- Use identical ROI placement as much as possible between in-phase and out-of-phase images.
- Avoid necrosis, calcification, hemorrhage, and partial-volume edges.
- Prefer a reasonably large ROI over tiny spot measurements to reduce noise sensitivity.
- If using spleen normalization, place ROI in homogeneous splenic parenchyma and avoid vessels.
Common pitfalls
- Misregistration between in-phase and out-of-phase slices.
- Very small lesions where accurate ROI placement is difficult.
- Heterogeneous lesions with mixed tissue composition.
- Protocol differences (TE, sequence type) that shift expected cutoffs.
When MRI metrics are especially useful
Chemical-shift metrics are particularly helpful for incidentally found adrenal lesions where prior imaging is limited and CT washout characterization is unavailable or undesirable. They can provide fast, quantitative support for benign adenoma patterns in the right clinical context.
When caution is needed
Indeterminate or discordant results should not be overcalled. Lesions without meaningful out-of-phase drop may still be benign, and some malignant lesions can occasionally complicate interpretation. If features are atypical, guidelines may recommend additional imaging follow-up, dedicated adrenal protocol studies, endocrine testing, or multidisciplinary discussion.
Quick practical workflow
- Measure lesion SI on in-phase and out-of-phase images.
- Optionally measure spleen SI on both phases.
- Run this calculator to compute SII (and ASR if available).
- Compare values with your institution’s accepted thresholds.
- Integrate findings with full report context, not as a stand-alone diagnosis.
FAQ
Is this the same as CT adrenal washout?
No. CT washout and MRI chemical-shift characterization are different techniques with different formulas and thresholds.
Can one value alone confirm diagnosis?
Usually no. Quantitative metrics are supportive, but final interpretation should remain clinical and radiologic, not purely numeric.
Do all centers use the same cutoff?
No. Published cutoffs are similar but not identical. Local protocol validation is ideal.