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Updated: Jun 19, 2025
Registered Bioimaging of Nanomaterials for Diagnostic and Therapeutic Monitoring
Published on: December 9, 2010
An Improved Postprocessing Method to Mitigate the Macroscopic Cross-Slice B0 Field Effect on R2* Measurements in the
Chu-Yu Lee1, Daniel R Thedens1, Olivia Lullmann2,3
1Department of Radiology, University of Iowa, Iowa City, IA 52242, USA.
Abstract:
The MR transverse relaxation rate, R2*, has been widely used to detect iron and myelin content in tissue. However, it is also sensitive to macroscopic B0 inhomogeneities. One approach to correct for the B0 effect is to fit gradient-echo signals with the three-parameter model, a sinc function-weighted monoexponential decay. However, such three-parameter models are subject to increased noise sensitivity. To address this issue, this study presents a two-stage fitting procedure based on the three-parameter model to mitigate the B0 effect and reduce the noise sensitivity of R2* measurement in the mouse brain at 7T. MRI scans were performed on eight healthy mice. The gradient-echo signals were fitted with the two-stage fitting procedure to generate R2corr_t*. The signals were also fitted with the monoexponential and three-parameter models to generate R2nocorr* and R2corr*, respectively. Regions of interest (ROIs), including the corpus callosum, internal capsule, somatosensory cortex, caudo-putamen, thalamus, and lateral ventricle, were selected to evaluate the within-ROI mean and standard deviation (SD) of the R2* measurements. The results showed that the Akaike information criterion of the monoexponential model was significantly reduced by using the three-parameter model in the selected ROIs (p = 0.0039-0.0078). However, the within-ROI SD of R2corr* using the three-parameter model was significantly higher than that of the R2nocorr* in the internal capsule, caudo-putamen, and thalamus regions (p = 0.0039), a consequence partially due to the increased noise sensitivity of the three-parameter model. With the two-stage fitting procedure, the within-ROI SD of R2corr* was significantly reduced by 7.7-30.2% in all ROIs, except for the somatosensory cortex region with a fast in-plane variation of the B0 gradient field (p = 0.0039-0.0078). These results support the utilization of the two-stage fitting procedure to mitigate the B0 effect and reduce noise sensitivity for R2* measurement in the mouse brain.
Insights
A new two-stage fitting procedure effectively reduces magnetic field (B0) inhomogeneities and noise in R2* measurements for mouse brain MRI. This method improves accuracy for detecting iron and myelin content, crucial for understanding brain tissue composition.
Area of Science:
- Magnetic Resonance Imaging (MRI)
- Neuroscience
- Biophysics
Background:
- R2* is a key MRI metric for assessing iron and myelin in tissues.
- R2* is highly sensitive to macroscopic B0 inhomogeneities, complicating accurate measurements.
- Existing three-parameter models to correct for B0 effects increase noise sensitivity.
Purpose of the Study:
- To present and validate a novel two-stage fitting procedure for R2* measurement in the mouse brain at 7T.
- To mitigate B0 effects and reduce noise sensitivity in R2* quantification.
- To compare the performance of the new method against traditional monoexponential and three-parameter models.
Main Methods:
- Developed a two-stage fitting procedure based on a three-parameter model for gradient-echo signals.
- Acquired 7T MRI data from eight healthy mice.
- Applied monoexponential, three-parameter, and the novel two-stage fitting procedures to generate R2nocorr*, R2corr*, and R2corr_t* values, respectively.
- Analyzed within-ROI mean and standard deviation (SD) in selected brain regions.
Main Results:
- The three-parameter model significantly improved the Akaike information criterion compared to the monoexponential model.
- The standard three-parameter model showed increased within-ROI SD in certain regions due to noise sensitivity.
- The novel two-stage fitting procedure significantly reduced within-ROI SD by 7.7-30.2% across most ROIs, except where B0 gradients varied rapidly.
Conclusions:
- The two-stage fitting procedure effectively mitigates B0 inhomogeneities and reduces noise sensitivity in R2* measurements.
- This method offers improved accuracy for R2* quantification in the mouse brain at 7T.
- The findings support the adoption of this two-stage approach for more reliable R2* analysis in neuroimaging research.
