Main applications of diffusion
At the present time, diffusion imaging is essentially used for brain exploration in clinical practice. Nevertheless, new applications are emerging outside neuroradiology (cancerology, musculoskeletal radiology…).
Diffusion imaging (DW MRI)
Diffusion imaging was used in application to stroke. Indeed, diffusion imaging is the earliest and most sensitive method in diagnosing stroke (< 1 hour). It manifests in the acute phase as a drop in ADC translating an ischemic cytotoxic edema. It is also used to date the stroke event and to distinguish between acute and subacute strokes.
Diffusion imaging also participates in diagnosis in different categories of brain pathology:
- Tumoral: cerebral lymphoma (reduced ADC), epidermoid and cholesteatoma cysts (hypersignal in diffusion).
- Infectious: pyogenic brain abscess (reduced ADC, providing differential diagnosis from a necrotic tumor in which the ADC is increased), herpes encephalitis
- Degenerative: Creutzfeldt-Jakob’s disease (aid to early diagnosis)
- Inflammatory: MS
Diffusion Tensor Imaging (DT-MRI)
Diffusion tensor imaging enables the in-vivo study of tissue microstructure. It gives indications about possible nerve fiber anomalies in white matter or the spinal cord that are not visible in conventional imaging.
Fiber tractography is the only method giving an indirect, in-vivo view of the nerve fiber trajectory (figure 13.12). It can be associated with functional MRI to study the interconnexions between nerve centers, used to analyze brain maturation and development (myelinization), assist in the preoperative check-up for brain tumors (corticospinal bundle) or for medullary compression. Diffusion tensor imaging can also be of interest in exploring Alzheimer’s disease, certain psychiatric affections, inflammatory, tumoral, vascular, traumatic (irreversible comas) pathologies or drug-resistant epilepsies.