Here is an interesting upcoming study that came out of the one you sharedI'm not sure MRI is used that much in the diagnosis of ME/CFS, other than looking at craniocervical instability. You are ruling out things like MS that can show on MRI.
As far as I can tell, MRI isn't that useful for ME/CFS. But I'm not really up on the research in this area.
Here's a recent review article: https://translational-medicine.biomedcentral.com/articles/10.1186/s12967-020-02506-6
it's testing the hypothesis that "abnormal neurovascular coupling (NVC) may be the neurobiological origin of ME/CFS. NVC is a critical process for normal brain function, in which glutamate from an active neuron stimulates Ca2+ influx in adjacent neurons and astrocytes. In turn, increased Ca2+concentrations in both astrocytes and neurons trigger the synthesis of vascular dilator factors to increase local blood flow assuring activated neurons are supplied with their energy needs."