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Improved T2* assessment in liver iron overload by magnetic resonance imaging
Vincenzo Positano1, Benedetta Salani, Alessia Pepe
1MRI Laboratory, Gabriele Monasterio Foundation, Via Moruzzi, 1 56124 Pisa, Italy. positano@ifc.cnr.it
Abstract:
In the clinical MRI practice, it is common to assess liver iron overload by T2* multi-echo gradient-echo images. However, there is no full consensus about the best image analysis approach for the T2* measurements. The currently used methods involve manual drawing of a region of interest (ROI) within MR images of the liver. Evaluation of a representative liver T2* value is done by fitting an appropriate model to the signal decay within the ROIs vs. the echo time. The resulting T2* value may depend on both ROI placement and choice of the signal decay model. The aim of this study was to understand how the choice of the analysis methodology may affect the accuracy of T2* measurements. A software model of the iron overloaded liver was inferred from MR images acquired from 40 thalassemia major patients. Different image analysis methods were compared exploiting the developed software model. Moreover, a method for global semiautomatic T2* measurement involving the whole liver was developed. The global method included automatic segmentation of parenchyma by an adaptive fuzzy-clustering algorithm able to compensate for signal inhomogeneities. Global liver T2* value was evaluated using a pixel-wise technique and an optimized signal decay model. The global approach was compared with the ROI-based approach used in the clinical practice. For the ROI-based approach, the intra-observer and inter-observer coefficients of variation (CoVs) were 3.7% and 5.6%, respectively. For the global analysis, the CoVs for intra-observers and inter-observers reproducibility were 0.85% and 2.87%, respectively. The variability shown by the ROI-based approach was acceptable for use in the clinical practice; however, the developed global method increased the accuracy in T2* assessment and significantly reduced the operator dependence and sampling errors. This global approach could be useful in the clinical arena for patients with borderline liver iron overload and/or requiring follow-up studies.
Insights
A new global analysis method for liver T2* measurements significantly reduces variability and operator dependence compared to traditional region of interest (ROI) methods. This enhances accuracy in assessing liver iron overload using MRI.
Area of Science:
- Magnetic Resonance Imaging (MRI)
- Medical Imaging Analysis
- Radiology
Background:
- Clinical MRI practice commonly assesses liver iron overload using T2* multi-echo gradient-echo images.
- Current T2* measurement methods rely on manual region of interest (ROI) placement, leading to potential variability based on placement and signal decay model choice.
Purpose of the Study:
- To investigate how different T2* measurement methodologies impact the accuracy of liver iron overload assessment.
- To develop and validate a novel global, semi-automatic T2* measurement method for improved accuracy and reduced operator dependence.
Main Methods:
- A software model of iron-overloaded liver was created from MRI data of 40 thalassemia major patients.
- A global semi-automatic T2* measurement method was developed, incorporating automatic liver parenchyma segmentation and pixel-wise analysis with an optimized signal decay model.
- The global method was compared against the conventional ROI-based approach.
Main Results:
- The ROI-based approach showed intra-observer and inter-observer coefficients of variation (CoVs) of 3.7% and 5.6%, respectively.
- The global analysis method demonstrated significantly lower CoVs for intra-observer (0.85%) and inter-observer (2.87%) reproducibility.
- The global method substantially reduced operator dependence and sampling errors compared to the ROI-based approach.
Conclusions:
- While the ROI-based approach is acceptable in clinical practice, the developed global method offers superior accuracy and reproducibility for T2* measurements.
- The global T2* assessment method is a valuable tool for clinical settings, particularly for patients with borderline liver iron overload or those requiring follow-up studies.
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