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Assessing Cortical Cerebral Microinfarcts on High Resolution MR Images
Published on: November 20, 2015
In vivo diffusion-weighted MRS using semi-LASER in the human brain at 3 T: Methodological aspects and clinical
Guglielmo Genovese1,2, Małgorzata Marjańska3, Edward J Auerbach3
1Centre de NeuroImagerie de Recherche (CENIR), Institut du Cerveau et de la Moelle épinère (ICM), Paris, France.
Abstract:
Diffusion-weighted (DW-) MRS investigates non-invasively microstructural properties of tissue by probing metabolite diffusion in vivo. Despite the growing interest in DW-MRS for clinical applications, little has been published on the reproducibility of this technique. In this study, we explored the optimization of a single-voxel DW-semi-LASER sequence for clinical applications at 3 T, and evaluated the reproducibility of the method under different experimental conditions. DW-MRS measurements were carried out in 10 healthy participants and repeated across three sessions. Metabolite apparent diffusion coefficients (ADCs) were calculated from mono-exponential fits (ADCexp ) up to b = 3300 s/mm2 , and from the diffusional kurtosis approach (ADCK ) up to b = 7300 s/mm2 . The inter-subject variabilities of ADCs of N-acetylaspartate + N-acetylaspartylglutamate (tNAA), creatine + phosphocreatine, choline containing compounds, and myo-inositol were calculated in the posterior cingulate cortex (PCC) and in the corona radiata (CR). We explored the effect of physiological motion on the DW-MRS signal and the importance of cardiac gating and peak thresholding to account for signal amplitude fluctuations. Additionally, we investigated the dependence of the intra-subject variability on the acquisition scheme using a bootstrapping resampling method. Coefficients of variation were lower in PCC than CR, likely due to the different sensitivities to motion artifacts of the two regions. Finally, we computed coefficients of repeatability for ADCexp and performed power calculations needed for designing clinical studies. The power calculation for ADCexp of tNAA showed that in the PCC seven subjects per group are sufficient to detect a difference of 5% between two groups with an acquisition time of 4 min, suggesting that ADCexp of tNAA is a suitable marker for disease-related intracellular alteration even in small case-control studies. In the CR, further work is needed to evaluate the voxel size and location that minimize the motion artifacts and variability of the ADC measurements.
Insights
This study optimized diffusion-weighted magnetic resonance spectroscopy (DW-MRS) for clinical use, finding N-acetylaspartate (NAA) apparent diffusion coefficients (ADCs) in the posterior cingulate cortex are reproducible and suitable for detecting disease-related changes.
Area of Science:
- Neuroimaging
- Biophysics
- Metabolomics
Background:
- Diffusion-weighted magnetic resonance spectroscopy (DW-MRS) non-invasively probes tissue microstructure by measuring metabolite diffusion in vivo.
- Reproducibility of DW-MRS is crucial for clinical translation, yet limited data exists.
- Optimization of DW-MRS sequences is needed for robust clinical applications.
Purpose of the Study:
- To optimize a single-voxel DW-semi-LASER sequence at 3 Tesla for clinical applications.
- To evaluate the reproducibility of metabolite apparent diffusion coefficients (ADCs) under various experimental conditions.
- To assess the impact of motion and explore acquisition parameters for improved reliability.
Main Methods:
- DW-MRS measurements were performed on 10 healthy participants across three sessions using a 3T scanner.
- Apparent diffusion coefficients (ADCs) were calculated using mono-exponential (ADCexp) and diffusional kurtosis (ADCK) models.
- Inter-subject variability, motion effects (cardiac gating, peak thresholding), and intra-subject variability (bootstrapping) were analyzed in the posterior cingulate cortex (PCC) and corona radiata (CR).
Main Results:
- Coefficients of variation were lower in the PCC compared to the CR, indicating better reproducibility in the PCC.
- Cardiac gating and peak thresholding were important for managing signal fluctuations due to physiological motion.
- Power calculations demonstrated that 7 subjects are sufficient to detect a 5% difference in tNAA ADCexp in the PCC with 4-minute acquisition, suggesting its utility in small studies.
Conclusions:
- The optimized DW-MRS sequence shows good reproducibility for N-acetylaspartate + N-acetylaspartylglutamate (tNAA) apparent diffusion coefficients in the posterior cingulate cortex.
- tNAA ADCexp is a promising marker for detecting disease-related intracellular alterations, even in small case-control studies.
- Further optimization is needed for the corona radiata to minimize motion artifacts and improve ADC variability.
