Reproducibility of liver iron concentration estimates in MRI through R2* measurement determined by least‐squares curve fitting

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.

Multisite reproducibility of quantitative susceptibility mapping and effective transverse relaxation rate in deep gray matter at 3 T using locally optimized sequences in 24 traveling heads

“…Data would then typically contain local sequence variations, which influence reconstructed R 2 * and susceptibility maps. [34][35][36] Moreover, although previous largescale multisite studies included up to 10 sites, the number of subjects to test reproducibility (traveling heads) was only one or two healthy subjects. [28][29][30] The largest previous study with respect to the number of traveling heads included 10 subjects scanned in five sites at 7 T. 26 This study aimed to (1) assess QSM and R 2 * reproducibility in 24 traveling heads at three sites (all at 3 T) with two vendors (and three scanner models) using locally optimized nonharmonized data from the same 24 subjects collected using three independently optimized sequences, and…”

“…However, it is also beneficial to be able to pool multisite data acquired without the same standardized protocol retrospectively to form larger datasets of wider pathological and/or demographical coverage, such as maximizing age/demographical coverage in lifespan studies, or increasing the statistical power of specific under‐represented cohorts of a disorder, effect, or demographic. Data would then typically contain local sequence variations, which influence reconstructed R 2 * and susceptibility maps 34–36 . Moreover, although previous large‐scale multisite studies included up to 10 sites, the number of subjects to test reproducibility (traveling heads) was only one or two healthy subjects 28–30 .…”