What MRI protocol is recommended for quantifying iron concentration in the liver and heart using T2 mapping?

MRI Protocol for Quantifying Iron Concentration in Liver and Heart

For iron quantification in both liver and heart, order R2-based relaxometry (T2 mapping) as the first-line method, performed at either 1.5T or 3T field strength, with specific protocol optimization including short echo times (<1 msec), short echo spacing (<1 msec), 6-12 echo times, and noise correction.** 1

Liver Iron Quantification Protocol

Primary Recommendation: R2*-Based Relaxometry

R2 relaxometry is the gold standard first-line method for liver iron concentration (LIC) quantification with high-level evidence supporting its use.* 1 This method has been extensively validated through multicenter, multivendor studies and has widespread regulatory approval. 1

Technical Specifications for Liver R2* Protocol:

• Field strength: Both 1.5T and 3T are acceptable 1

  • For severe iron overload (suspected LIC >26-40 mg/g): Prefer 1.5T due to better dynamic range 1
  • 1.5T maximum reliable LIC: ~40 mg/g (700 μmol/g) 1
  • 3T maximum reliable LIC: ~26 mg/g (466 μmol/g) 1

• Protocol parameters (high-level evidence): 1

  • Short TEs: <1 msec
  • Short echo spacing: <1 msec
  • Number of echoes: 6-12 TEs
  • Noise correction: Required
  • Fat correction: Use methods that avoid fat- and noise-related biases 1

Alternative Methods for Liver (if R2* unavailable):

1. R2-based relaxometry (FerriScan): Second-line option with regulatory approval 1

   • Requires 1.5T field strength 1
   • Longer acquisition time (10-20 minutes) 1
   • Requires external processing service 1

2. Signal Intensity Ratio (SIR): Third-line alternative 1

   • Well validated at 1.5T (high evidence), moderate evidence at 3T 1
   • Limited to LIC <19.5 mg/g (350 μmol/g) 1
   • No regulatory approval 1

Cardiac Iron Quantification Protocol

Cardiac T2* Mapping Specifications:

Use T2 relaxometry for myocardial iron assessment, noting that cardiac T2 values differ significantly between field strengths.** 2

• Field strength considerations: 2

  • Myocardial T2* at 3T is approximately 1.75 times shorter than at 1.5T
  • Myocardial T2* (1.5T): ~35.9 ms (range 31.4-39.5 ms) in iron-overloaded patients 2
  • Myocardial T2* (3T): ~20.5 ms (range 18.4-25.9 ms) in iron-overloaded patients 2

• Clinical thresholds for cardiac siderosis: 3

  • Normal: T2* ≥20 ms
  • Cardiac iron overload: T2* <20 ms
  • Severe cardiac siderosis: T2* <10 ms

Important Cardiac-Specific Considerations:

• Myocardial T2 values remain relatively stable between field strengths (60.3 ms at 1.5T vs 55 ms at 3T), but T2* shows significant field-dependent variation 2
• Cardiac T2* correlates inversely with serum ferritin (r = -0.34) 4
• ROI placement should be at mid-left ventricular level 2

Combined Liver and Heart Protocol Order

Recommended Order Details:

"MRI liver and cardiac iron quantification with R2 relaxometry (T2 mapping)"**

Specify the following technical requirements:

1. Sequence type: Multi-echo gradient echo with fat saturation 5, 6
2. Field strength: 1.5T (preferred for suspected severe overload) or 3T 1
3. Echo parameters: 1
   • First TE <1 msec
   • Echo spacing <1 msec
   • 6-12 echo times
4. Corrections: Noise and fat correction required 1
5. Coverage: 2
   • Liver: Mid-hepatic slice with ROI analysis (ideally one large ROI per Couinaud segment) 1
   • Heart: Mid-left ventricular slice 2

Critical Pitfalls to Avoid

• Do not rely on serum ferritin alone: Ferritin levels do not predict organ-specific iron overload as measured by T2* MRI 3
• No correlation between organs: Liver, pancreas, and cardiac iron overload do not correlate with each other 3
• Field strength matters for severe overload: At 3T, R2* may fail to quantify LIC >26 mg/g due to dynamic range limitations 1
• Ensure proper corrections: Uncorrected methods for fat and noise introduce significant bias 1
• Review source images: Always review echo images or ancillary sequences (T2-weighted, in/opposed-phase) to validate measurements 1

Reporting Requirements

The radiology report must include: 1

• The specific MRI method used
• Literature citation describing the calibration method
• Laboratory reference values used for LIC calibration
• Quantitative values in both mg/g and μmol/g