MEG and MRI scan

With the delivery of CMP's first MEG due within the next 2 months, it is good to know exactly what MEG does and how it supplement or competes with existing scan. Refer to the two sources below, the take-away for me is that
Both MEG and MRI will be needed.
MEG measures the brain activities (functional scan) e.g. brain signals
MRI measures the brain structure (anatomic scan) e.g. brain structure

Traditionally, MRI is commonly used, due to its ability to identify damages or abnormal structure in brain. But, increasingly, MEG is used to measure seizures and mental illness, which do not cause visible changes to brain structure but can be measured by looking at brain signals.

By having MRI and MEG, doctors can more clearly understand how patients' brain functions, in terms of its structure and neuro signals. To sum up, MRI is important for brain surgery, because it shows the structure of a brain, and MEG is important to identify less visible mental/brain illness, because it shows the signals of a brain. MRI and MEG can complement each other by "create a map, or magnetic source image (MSI), that shows areas of normal and abnormal activity in the brain" , in another word, basically mapping brain signals to the structure of a brain.
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From https://www.ucsfbenioffchildrens.org/education/magnetoencephalography_meg_scan/
Magnetoencephalography, or MEG scan, is an imaging technique that identifies brain activity and measures small magnetic fields produced in the brain. The scan is used to produce a magnetic source image (MSI) to pinpoint the source of seizures.

The MEG scan can provide valuable information used by doctors to locate your child's seizure focus and determine if he or she is a candidate for seizure surgery. Results from the MEG test are matched up with a magnetic resonance image (MRI), which is an anatomical picture of the brain.
The MEG and MRI create a "map," or magnetic source image (MSI), that shows areas of normal and abnormal activity in the brain.
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From https://my.clevelandclinic.org/health/diagnostics/17218-meg-test

Diagnostic methods for imaging the brain generally divide between two categories: anatomic and functional. CT and MRI are most common for anatomic imaging, while PET and fMRI are examples of functional imaging. Like EEG, MEG records the electrophysiological effect of neuronal activity over time; however, with its higher sensor count and simpler modeling physics, MEG has a higher source resolution.

Additionally, recordings with MEG are reference-free; its signals are not attenuated by bone and multichannel, whole-head, high spatial-density recordings are easily obtained. By its very nature, MEG shows areas of function: It localizes the signals generated by neurons as they are activated, as they communicate and as activity spreads through them.

MEG is sometimes called a functional imaging test, but it differs in significant ways from other such tests:

• The functional tests available at most centers are indirect measurements, dependent on changes in oxygen consumption (fMRI), glucose uptake (PET) and blood flow (SPECT). Conversely, MEG measures neuronal activity directly.
• While PET and fMRI measure changes in metabolism and blood flow, respectively, over many seconds, MEG measures electrical activity millisecond by millisecond.

Localizing the entire sequence of activation as it evolves over time is what MEG does superbly. Hence, the activity of the whole chorus of neurons required for everyday actions (pressing on the accelerator) or abnormal episodes (an epileptic aura) — not just the maximally involved area — can be mapped in space chronologically as it changes.
Like PET and fMRI, MEG “lights up” brain areas activated by a task. In epilepsy, MEG can show the propagation of activity from one brain region over a few milliseconds or during the onset of a seizure; in fact, ictal MEGs constitute approximately 15 percent of MEG scans performed at Cleveland Clinic Epilepsy Center. MEG results are coregistered with anatomic images from MRI and are reconstructed three-dimensionally to show the exact areas of activity.
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