**2.7 Diffusion-weighted MRI**

These methods are based on the diffusive anisotropy of water molecules along nerve axons and plexus, where axial motion takes precedence [41, 54]. Here, we can find techniques such as diffusion tensor imaging (DTI), diffusion spectrum imaging (DSI), and high angular resolution diffusion imaging (HARDI). These more recent techniques serve as a valuable non-invasive pre-operative and preradiosurgery tool to evaluate the involvement and proximity of cerebral AVMs to white matter tracts [41]. Using these methods, it provides clinicians with strong risk assessment capabilities, particularly regarding the microsurgery approach and track planning [55]. dwMRI can be used with other technologies for presenting a combined vascular and neuroanatomical image [55]. It might also enable very early identification of ischemic areas [46]. dwMRI is limited mainly to white matter tracts and presents high sensitivity to protocol operation parameters (e.g., TR/TE/ spatial resolution) and artifacts from inadvertent sources.

#### **Figure 4.**

*(A) PC-MRA original image of right temporal AVM, with (B) velocity, (C) whole brain, and (D) feeding arteries shear stresses data [22].*

#### **2.8 Summary**

AVM analysis is based on the findings of multiple modalities—vascular anatomy of nidus and feeders, acute/chronic brain matter pathological presentations, flow and velocity rates, and surrounding tissue anatomical and functional attributes (e.g., connectometractography). Each modality presents specific strengths and weaknesses. CT is extremely sensitive to hematomas and offers several AVM anatomical finding capabilities. CTA is used to diagnose AVM in patients with acute hematomas. MRI presents improved topography and the detection of subacute and chronic hematomas and surrounding brain tissue pathologies. PC-MRA is used for high-resolution vascular imaging and provides biomechanical data (e.g., shear stresses), that is, highly beneficial in clinical assessment. Functional-anatomical relations data are effectively gathered using fMRI and dwMRI which provide strong clinical decision-making tools. Finally, DSA remains the gold standard for both diagnostic and procedural purposes due to its high-resolution real-time imaging of cerebral angioarchitecture. To conclude, brain imaging is a prolific field constantly presenting the development of promising improved and new modalities.
