  In the human brain, essential iron molecules for proper neurological
functioning exist in transferrin (tf) and ferritin (Fe3) forms. However, its
unusual increment manifests iron overload, which reacts with hydrogen peroxide.
This reaction will generate hydroxyl radicals, and irons higher oxidation
states. Further, this reaction causes tissue damage or cognitive decline in the
brain and also leads to neurodegenerative diseases. The susceptibility
difference due to iron overload within the volume of interest (VOI) responsible
for field perturbation of MRI and can benefit in estimating the neural
disorder. The quantitative susceptibility mapping (QSM) technique can estimate
susceptibility alteration and assist in quantifying the local tissue
susceptibility differences. It has attracted many researchers and clinicians to
diagnose and detect neural disorders such as Parkinsons, Alzheimers, Multiple
Sclerosis, and aging. The paper presents a systematic review illustrating QSM
fundamentals and its processing steps, including phase unwrapping, background
field removal, and susceptibility inversion. Using QSM, the present work
delivers novel predictive biomarkers for various neural disorders. It can
strengthen new researchers fundamental knowledge and provides insight into its
applicability for cognitive decline disclosure. The paper discusses the future
scope of QSM processing stages and their applications in identifying new
biomarkers for neural disorders.
