What Is Neuroimaging?

Neuroimaging is a collection of techniques used to visualize the structure, function, and connectivity of the nervous system, particularly the brain. It encompasses both anatomical methods, which map the physical architecture of neural tissue, and functional methods, which track physiological correlates of neural activity such as blood flow, glucose metabolism, and oxygenation. Neuroimaging emerged as a clinical and research discipline in the 1970s with the introduction of computed tomography (CT) and was substantially transformed in the 1980s and 1990s by magnetic resonance imaging (MRI) and positron emission tomography (PET). The field now supports a wide range of activities from pre-surgical planning to the study of cognitive processes in healthy volunteers.

Neuroimaging draws on physics, engineering, computational science, and medicine. Its development has been shaped by advances in detector technology, radio-frequency engineering, signal processing, and statistical inference, making it a field where engineering and clinical neuroscience interact closely.

Structural and Functional MRI

MRI produces high-resolution images of brain anatomy by exploiting the magnetic properties of hydrogen nuclei in tissue. Structural MRI identifies tumor location, atrophy patterns, white matter lesions, and congenital malformations. Functional MRI (fMRI) extends this capability by detecting changes in the blood-oxygen-level-dependent (BOLD) signal, discovered by Seiji Ogawa in 1990, which tracks local increases in oxygenated hemoglobin that follow neural activation with a lag of one to several seconds. Resting-state fMRI measures spontaneous BOLD fluctuations to map functional connectivity networks, including the default mode network, the salience network, and sensorimotor networks, without requiring task performance. An exploration of recent advances in neuroimaging including fMRI and PET surveys how these techniques are being applied across neuroscience and clinical settings.

Functional Near-Infrared Spectroscopy

Functional near-infrared spectroscopy (fNIRS) measures cortical hemodynamic responses by passing near-infrared light through the scalp and skull and detecting differential absorption by oxygenated and deoxygenated hemoglobin. Like fMRI it measures the neurovascular coupling signal, but it is portable, relatively inexpensive, and tolerates movement, making it suitable for studying infants, children, patients in naturalistic environments, and individuals who cannot tolerate MRI. Its spatial resolution is coarser than fMRI and its depth penetration is limited to the cortical surface, but the practical advantages make it widely used in developmental neuroscience, brain-computer interface research, and bedside monitoring. Research from Frontiers in Neuroscience on fNIRS clinical applications and future directions covers the state of the field across neurological and psychiatric applications.

Neuroradiology

Neuroradiology is the clinical subspecialty that applies neuroimaging to the diagnosis and treatment planning of nervous system disorders. Neuroradiologists interpret CT, MRI, PET, and conventional angiographic studies in patients presenting with stroke, brain tumors, epilepsy, traumatic injury, multiple sclerosis, and spinal pathology. Interventional neuroradiology extends the role to endovascular procedures including mechanical thrombectomy for acute ischemic stroke, aneurysm coiling, and arteriovenous malformation embolization. The accuracy of neuroradiological diagnosis has improved substantially with diffusion-weighted MRI for acute stroke, perfusion imaging for penumbra estimation, and spectroscopy for tumor characterization. Standards for imaging protocols and reporting are governed by the American College of Radiology and international bodies including the European Society of Neuroradiology.

Applications

Neuroimaging has applications in a range of fields, including:

• Presurgical planning for brain tumor resection and epilepsy surgery
• Acute stroke management, guiding thrombolysis and thrombectomy decisions
• Psychiatric research, characterizing structural and functional differences in depression, schizophrenia, and autism spectrum disorder
• Alzheimer's disease diagnosis and clinical trial outcome measurement
• Cognitive neuroscience, mapping the neural correlates of attention, language, memory, and decision-making