Brain Imaging and Substance Use Disorders: Focus on White Matter Microstructural Integrity

Measuring white matter microstructure in 1,457 cannabis users and 1,441 controls: A systematic review of diffusion-weighted MRI studies

“…However, studies did not consistently control for these in analyses, or match participants on these variables (i.e., studies may have controlled for/matched many, one, or none of these and other variables). These are variables that are themselves frequently associated with differences in white matter microstructure, such as age and sex (Grace et al, 2021 ; López-Vicente et al, 2021 ; Rossetti et al, 2021b ), alcohol (Rossetti et al, 2022 ), nicotine (Gogliettino et al, 2016 ), IQ (Suprano et al, 2020 ), and other substance use (Hampton et al, 2019 ; Rossetti et al, 2022 ). In order to limit the confounding effects of these variables, it is important they are systematically controlled for or at least measured if not feasible to match, to allow for greater comparability of results.…”

“…Second, while a review of diffusion-MRI studies of cannabis users was undertaken more recently, it examined general substance using populations, which prevented a detailed summary and discussion of findings in relation to cannabis users specifically (Hampton et al, 2019). Third, other recent syntheses of the literature were not systematic but narrative (Bloomfield et al, 2019;Blest-Hopley et al, 2020;Chye et al, 2020a;Rossetti et al, 2022). Therefore, it is unclear whether cannabis users show systematic differences in the location, direction, and diffusion-MRI metric of white matter microstructural differences.…”

“…Diffusion tensor imaging (DTI) is a tensor-based metric derived from diffusion-MRI, it measures white matter microstructural organization of white matter fibres in the brain (Basser et al, 1994 ). Recent emerging evidence from DTI studies, shows that cannabis users compared to non-cannabis using controls (henceforth termed controls) have mostly lower Fractional Anisotropy (FA) of white matter fibre tracts in multiple pathways (Bloomfield et al, 2019 ; Hampton et al, 2019 ; Chye et al, 2020a ; Rossetti et al, 2022 ). These include: commissural tracts that connect the hemispheres bilaterally (e.g., corpus callosum), tracts connecting frontal regions of the brain (e.g., forceps minor), as well as other association fibres that connect ipsilateral cortical regions.…”

“…These include: commissural tracts that connect the hemispheres bilaterally (e.g., corpus callosum), tracts connecting frontal regions of the brain (e.g., forceps minor), as well as other association fibres that connect ipsilateral cortical regions. Yet, the group differences were inconsistent, with both higher or lower white matter integrity diffusion-MRI metrics in cannabis users than controls, and lack of significant group differences in some studies (Hampton et al, 2019 ; Chye et al, 2020a ; Rossetti et al, 2022 ). Such inconsistent findings highlight a lack of consensus regarding white matter changes in cannabis users compared to controls using diffusion-MRI metrics [e.g., FA, Mean Diffusivity (MD), Radial Diffusivity (RD), and Axial Diffusivity (AD)].…”

“…Furthermore, emerging literature suggests that white matter integrity in cannabis users is associated with cannabis exposure metrics (e.g., age of cannabis use onset, cannabis dosage, and duration) in a subset of white matter tracts [e.g., corpus callosum and superior longitudinal fasciculus (SLF)] (Hampton et al, 2019 ; Chye et al, 2020a ; Rossetti et al, 2022 ). However, the nature of such associations were somewhat inconsistent (e.g., location, direction, and the type of diffusion-MRI metric).…”