Introduction

Since its introduction for human study in the early 1980s, magnetic resonance (MR) has proven itself an extremely versatile technique for evaluation of many different parameters of anatomic, physiologic, and metabolic interest. The number of phenomena amenable to analysis using magnetic resonance (MR) techniques is increasing every year. This versatility arises from the many different sources of magnetic contrast that can be generated using either endogenous or exogenous contrast, from the versatility of the techniques for manipulation of the nuclear spins that generate the observed signals, and from the extremely safe nature of MR that lends itself well to longitudinal studies and large patient populations.

MR techniques can now evaluate tissue parameters relevant to TCA cycle metabolism, anaerobic glycolysis, ATP levels, blood–brain barrier permeability, macrophage infiltration, cytotoxic edema, spreading depression, cerebral blood flow and volume, and neurotransmitter function. The paramagnetic nature of certain oxidation states of iron leads to the ability to map out brain function using deoxyhemoglobin as an endogenous contrast agent, and also allows for mapping of local tissue iron concentrations. In addition to these metabolic parameters, the number of ways to generate anatomic contrast using MR is also expanding, and in addition to conventional anatomic scans, mapping of axonal fiber tracts can also be performed using the anisotropy of water diffusion. A selective, non-exhaustive, summary of the various parameters of relevance to neurodegeneration (ND) that can be measured using MR techniques is presented in Table 21.1.

Neurodegenerative diseases are becoming increasingly prevalent with the aging of the general population. The twentieth century witnessed a significant demographic change in the human population of the industrialized world that is currently followed by a similar shift of life expectancy to upper age ranges in Asia, Africa, and Middle and South America. Quality of life of the aging population of the world is, to a great extent, determined by the normal aging process of neurons in the central nervous system and especially by the occurrence of diseases characterized by accelerated neuronal loss: diseases which are traditionally designated as being neurodegenerative. They are presently amongst the major contributors to disability and disease in human populations.

Alzheimer's disease is the most prevalent of the neurodegenerative diseases followed by Parkinson's disease. Amyotrophic lateral sclerosis and Huntington's disease affect smaller numbers of patients but have devastating consequences. A large number of other rarer neurodegenerative diseases have similar profound effects on the patients and families who are afflicted by these illnesses. Research into the pathogenesis and treatment for these disorders is exploding exponentially. To a great extent this has been fostered by major advances in genetics, since we now know mutations that are associated with a large number of these illnesses. This includes familial forms of Alzheimer's disease, Parkinson's disease, fronto-temporal dementia, ALS, Huntington's disease and a variety of ataxias.