Brain Imaging and Behavior: Progress and Opportunities

The emergence of advanced noninvasive medical imaging directed toward the in vivo investigation of the human brain has revolutionized the study of brain behavior relationships in healthy individuals as well as in those with illnesses affecting neural structure and function. Computer-assisted tomography (CT), magnetic resonance imaging (MRI) and positron emission tomography (PET) are landmark technical advances that forever changed the clinical neuroscience disciplines of neurology, neurosurgery, psychiatry and neuropsychology, as well as radiology itself, as they entered widespread use during the 1970s (CT) and 1980s (PET and MRI). These tools were rapidly applied to clinical research studies of major brain disorders from strokes and tumors to dementia and schizophrenia. In the post-millennial era, high field MRI now yields unprecedented information about brain morphology with spatial resolution at the millimeter or sub-millimeter scale. Numerous MR techniques can be tuned to reveal particular normal or lesional tissue contrast. T2-weighted and fluidattenuated inversion recovery MR scans have become an accepted surrogate marker for quantifying demyelinating lesion burden in patients with multiple sclerosis in clinical trials and are also widely used to quantify microvascular lesion burden. These techniques have also been used to study cognitive correlates of specific brain disorders. MR and PET are moving toward becoming accepted biomarkers for detection and treatment monitoring in Alzheimer’s disease and other dementias. Fluorodeoxyglucose PET assessment of metabolism was recently approved by Medicare for use in the differential diagnosis of dementia in complex or ambiguous cases. Advanced molecular imaging probes targeting specific receptors, transporters or pathophysiological features of disease also show great promise for early diagnosis and as a biomarker for treatment response. These and other related tools will play a major role in the new era of personalized medicine. A remarkable recent example is the advent of ligands for in vivo labeling of brain amyloid, a key molecular hallmark of Alzheimer’s disease involved in plaque formation. Use of blood oxygen level dependent contrast functional MRI (fMRI) to assess brain activation patterns has been enormously successful as a research tool since the milestone studies in the early 1990s. Arterial spin labeling fMRI techniques now permit quantitative determination of cerebral blood flow without ionizing radiation. Evidence of fMRI’s maturity is the recent provision of a current procedural terminology code for reimbursement when used as a clinically indicated mapping procedure for neurosurgical planning. Clinical fMRI continues to advance, for example, in combination with transient disruption approaches such as repetitive transcranial magnetic stimulation and intraoperative stimulation mapping. MR spectroscopy and spectroscopic imaging address the neurochemical composition of brain tissue. Magnetic resonance spectroscopic imaging is now capable of rapidly generating quantitative maps of major metabolites that serve as markers for neuronal integrity and also yield information regarding metabolism, membrane breakdown and inflammation. Another remarkable MR technique, diffusion weighted imaging, can reveal acute strokes as they are evolving and influence treatment strategy in near real time. A related technique, diffusion tensor imaging (DTI), permits visualization of fiber tracts indicating the location and integrity of connectivity patterns within major neural circuits subserving Brain Imaging and Behavior (2007) 1:1–2 DOI 10.1007/s11682-007-9005-0