Functional Magnetic Resonance Imaging (fMRI) Introduction Structural imaging reveals the static physical characteristics of the brain. It makes it useful in diagnosing disease. Functional imaging reveals dynamic changes in brain physiology that might correlate with cognitive functioning, for example. Neural activity consumes oxygen from the blood. This triggers an increase in blood flow to that region and a change for deoxyhemoglobin in that region. As the brain is always physiologically active, functional imaging needs to measure relative changes in physiological activity. The most basic experimental design in functional imaging research is to subtract the activity in each part of the brain whilst doing one task away from the activity in each part of the brain whilst doing a slightly unfamiliar task.  We call this cognitive subtraction . Other methods, including parametric and factorial designs, can minimize many of the problems associated with cognitive subtraction. There is no foolp

Positron Emission Tomography (PET) Positron Emission Tomography is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in metabolic processes, and in other physiological activities including blood flow, regional chemical composition, and absorption. They use different tracers for different imaging, depending on the target process within the body. We inject a radiopharmaceutical—a radioisotope attached to a drug—into the body as a tracer. Gamma cameras emit and detect Gamma rays to form a three-dimensional image, similar to that of an X-ray image. Positron-emission tomography scanners can incorporate a computerized tomography scanner, and we call them positron-emission tomography-computerized tomography scanners. One disadvantage of a positron-emission tomography scanner is its high initial cost and ongoing operating costs. Applications Positron-emission tomography can give information about: Metabolic changes Regional c

Single-photon Emission Tomography SPET Principle uses single-photon (gamma-ray) emitting isotopes given IV or inhaled the resolution is lower than PET Uses SPET can give information about: regional cerebral blood flow ligand binding Clinical uses include: Alzheimer’s disease When the symptomatology (e.g. hallucinations, epilepsy) occurs when the patient is not near a scanner; we can give a suitable ligand at the material time and the patient scanned afterward Schizophrenia reduced rCBF in frontal regions—‘hypofrontality’ Affective disorders as that in schizophrenia, with reversal after antidepressant therapy Alzheimer’s disease decreased rCBF in posterior parietal and temporal regions Xenon inhalation Shows the failure of activation of frontal lobes in schizophrenics performing the Wisconsin Card Sorting Test