Hi Hains

Trying to answer your questions:

(1) How efficient is the bodies ability to correct this calcium imbalance, or does calcium just bio-accumulate in brain cells?

Ca2+ is accessible to all body compartments, including the brain. Insoluble Ca2+ rich deposits can form in in the brains of people with Fahr disease, which is extremely rare. More commonly elevated levels of Ca2+ are often a sign of hyperparathyroidism, which usually arises from benign tumours in the parathyroid glands, leading to excess PTH production. Your health care team should be able to arrange for measurements of your blood Ca2+ and PTH levels.

(2) Can neuroimaging (FMRI or SPECT scan) capture these regions of calcium accumulation [...]?

No. This is well-understood physics. A CT scan can be diagnostic of Fahr disease, which is autosomal-dominant.

(3) What reasonable processes can be used to correct intra-/extracellular calcium imbalance?

Do you have any evidence (eg, interpretation of clinical signs by your health care team) that you have an "intra-/extracellular calcium imbalance" - I don't know what you mean by this phrase?

(4) If oxygen is the key to remediating calcium imbalance and inflammation, can rigorous breathing exercises like the Wim Hof method or kundalini yoga be as effective and much more economical than HBOT, or chelation?

Do you have any evidence to suggest that body oxygen levels are "the key" to your hypothetical "calcium imbalance"?