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Reproducibility of liver iron concentration estimates in MRI through R2* measurement determined by least-squares
Andrew M Headley1, Jared V Grice1, David R Pickens1
1Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, USA.
Abstract:
Measuring transverse relaxation rate (R2* = 1/T2*) via MRI allows for noninvasive evaluation of multiple clinical parameters, including liver iron concentration (LIC) and fat fraction. Both fat and iron contribute to diffuse liver disease when stored in excess in the liver. This liver damage leads to fibrosis and cirrhosis with an increased risk of developing hepatocellular carcinoma. Liver iron concentration is linearly related to R2* measurements using MRI. A phantom was constructed to assess R2* quantification variability on 1.5 and 3 T MRI systems. Quantification was executed using least-squares curve fitting techniques. The phantom was created using readily available, low-cost materials. It contains four vials with R2* values that cover a clinically relevant range (100 to 420 Hz at 1.5 T). Iron content was achieved using ferric chloride solutions contained in glass vials, each affixed in a three-dimensional (3D)-printed polylactide (PLA) structure, surrounded by distilled water, all housed in a sealed acrylic cylinder. Multiple phantom stands were also 3D-printed using PLA for precise orientation of the phantom with respect to the direction of the static magnetic field. Acquisitions at different phantom angles, across multiple MRI systems, and with different pulse sequence parameters were evaluated. The variability between any two R2* measurements, taken in the same vial under these various acquisition conditions, on a 1.5 T MRI system, was <7% for each of the four vials. For 3 T MRI systems, variability was less than 14% in all cases. Variability was <6% for both 1.5 and 3 T acquisitions when unchanged pulse sequence parameters were used. The phantom can be used to mimic a range of clinically relevant levels of R2* relaxation rates, as measured using MRI. These measurements were found to be reproducible relative to the gold-standard method, liver biopsy, across several different image acquisition conditions.
Insights
A novel, low-cost MRI phantom accurately quantifies liver iron concentration (LIC) and fat fraction. This reproducible phantom aids in assessing diffuse liver disease across various MRI systems and conditions.
Area of Science:
- Medical Imaging
- Biophysics
- Materials Science
Background:
- Magnetic Resonance Imaging (MRI) enables noninvasive assessment of liver iron concentration (LIC) and fat fraction, crucial for evaluating diffuse liver disease.
- Excessive iron and fat in the liver can lead to fibrosis, cirrhosis, and increased hepatocellular carcinoma risk.
- Liver iron concentration (LIC) demonstrates a linear relationship with R2* (1/T2*) measurements obtained via MRI.
Purpose of the Study:
- To develop and validate a cost-effective MRI phantom for assessing R2* quantification variability.
- To evaluate the phantom's performance across different magnetic field strengths (1.5 T and 3 T) and acquisition parameters.
- To ensure the phantom's R2* measurements are reproducible and comparable to the gold standard of liver biopsy.
Main Methods:
- A phantom was constructed using low-cost materials, including ferric chloride solutions in vials embedded in 3D-printed polylactide (PLA) structures.
- The phantom featured four vials with R2* values spanning a clinically relevant range (100-420 Hz at 1.5 T).
- MRI acquisitions were performed at 1.5 T and 3 T with varying phantom orientations and pulse sequence parameters to assess R2* quantification variability.
Main Results:
- Variability in R2* measurements on a 1.5 T MRI system was less than 7% across different acquisition conditions for all four vials.
- On 3 T MRI systems, R2* measurement variability was consistently below 14%.
- When pulse sequence parameters remained unchanged, variability was less than 6% for both 1.5 T and 3 T acquisitions, indicating high reproducibility.
Conclusions:
- The developed MRI phantom effectively mimics clinically relevant R2* relaxation rates.
- The phantom provides reproducible R2* measurements across various imaging conditions and MRI systems.
- This low-cost phantom offers a reliable tool for noninvasive assessment of liver iron and fat, supporting clinical evaluation of diffuse liver disease.
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