Neuroimaging and Magnetic Resonance Imaging - Essay Example

Neuroimaging Neuroimaging is the given to the techniques used for imaging the structureand characteristics of the brain and diagnosing brain diseases. The term can be divided into two categories: structural imaging and functional imaging. The structural imaging deals with imaging of the structure of the brain and it helps in diagnosing large scale (gross) intracranial diseases and injuries like tumors in the brain. Functional imaging is helps in diagnosing disease on finer scale like it is used to detect fine scale lesions in Alzheimer disease. Functional imaging is also used for psychological and neurological research on the brain. Among the many brain imaging techniques, computed tomography scan or CT scan is quite popular. Allan M Cormack and Godfrey N Hounsfield introduced CT scanning in the 1970s. They also won Nobel Prize in medicine in 1979 for their work. This scanning technique uses a number of x rays of the head taken from different directions. A computer program than performs a number of calculations on those x ray series to calculate of how much of the x ray beam has been absorbed by a small volume of brain (Jeeves, p21). CT scanning is primarily used for evaluation of swelling from tissue damage of the brain. This technique is used when brain injuries are required to be viewed quickly, as CT scanning can produce good brain images in a matter of minutes. Magnetic resonance imaging (MRI) is another popular brain imaging technique. MRI was first introduced by Paul Lauterbur and Peter Mansfield. They were both awarded Nobel Prize for their work in medicine in 2003. The MRI technique uses radio waves and magnetic fields to produce high quality pictures of the brain structure. During MRI process, the head of the patient is placed in a large cylindrical magnet that creates magnetic field around the head through which radio waves are sent. When magnetic field is created, each point in the space has a unique radio frequency at which the signal is transmitted and received (Filler AG). Sensors detect these signals and a computer then use these signals to create an image. The mechanism for detection of signals is so precise that changes in brain structure over time can be detected through MRI. Images of the brain with great anatomical details of both subsurface and surface structures can be created using MRI. With this technique cross sectional images of the brain in any direction like from top to bottom or front to back or side to side can be made. The original MRI technique was able to provide detailed information about the physical appearance and derangements like bleeding and inflammation of the structure of the brain, but it did not provide any information like how actively the brain is functioning at the time of imaging. The 'functional magnetic resonance imaging', a new type of MRI recently introduced, provides both the structural as well as the functional information about the brain. Positron emission tomography (PET) is another type of neuroimaging technique in which radioactively labeled chemicals are injected into the blood streams and emissions from it are measured. The data of the emissions is the then computer processed to create a three or two dimensional picture of the distributions of the chemicals around the brain (Nilsson, pg 57). The PET scanning helps to show the blood flow, glucose metabolism and oxygen in the tissues of the brain. It helps in calculating the amount of activity in different parts of the brain and it helps to learn more about the working of the brain. But because the radioactive chemical used in PET decay rapidly, PET scanning is limited to monitoring short tasks (Nilsson pg 60). This technique is used in diagnosing brain diseases like strokes, tumors and diseases that cause dementia like Alzheimer disease and Pick's disease. All these diseases cause changes in brain metabolism and are thus detectable in PET scans. Single photon emission computed tomography (SPECT) is a neuroimaging technique that is similar to PET scanning. This technique uses gamma rays emitting radioisotopes and a gamma rays detecting camera. The camera records data and a computer uses that data to create 2 or 3 D images of the active brain regions (Philip Ball). Using the SPECT technique a radioactive tracer is injected into the blood stream that is rapidly taken up by the brain but is not redistributed. The uptake of the tracer is nearly hundred per cent complete within half a second to one second, depicting the cerebral blood flow at the minute when tracer was injected. These characteristics of SPECT imaging makes it particularly useful for epilepsy imaging, which is difficult to undertake because of problems with movements of patients and because of different seizure types. SPECT provides snapshots of cerebral blood flow at the time of seizure (if the radio active tracer has been injected at the time of seizure). SPECT like PET is primarily used to differentiate between the different kinds of diseases that cause dementia. Neuroimaging is seen as a major tool that will be used in future for evaluating and treating major depressive disorder patients. MRI is used in psychiatry for measuring different levels of neurochemicals like GABA and glutamate. MRI studies have showed decreased levels of GABA and glutamate in major depressive disorder patients. Magnetic imaging spectroscopy (MRS) studies have also revealed deficits of energy metabolism of brain in depression which may be due to dysfunction of mitochondria in the brain. Experiments have revealed recently that the anti depressant treatment is associated with renormalization of bioenergetics metabolism (Iosifescu, p1127). These metabolic measures through MRS can help differentiate between patients that respond to the anti depressants and those patients who do not respond to the antidepressants and can help suggest new uses for antidepressant treatment. Magnetic imaging spectroscopy can be used in the future to target specific biological markers to predict the treatment responses for major depressive disorder patients. MRS may also be used in future to identify placebo responders to the antidepressant drug who might not need treatment at all. Thus neuroimaging techniques promise to show practical use in clinic for treating brain disorders in future. References 1. Malcom Jeeves. Mind Fields: Reflections on the Science of Mind and Brain. Grand Rapids, MI: Baker Books. 1994 2. Filler, AG: The history, development, and impact of computed imaging in neurological diagnosis and neurosurgery: CT, MRI, DTI: Nature Precedings DOI: 10.1038/npre.2009.3267.5.Neurosurgical Focus (in press) 3. Lars-Goran Nilsson and Hans J. Markowitsch. Cognitive Neuroscience of Memory. Seattle: Hogrefe & Huber Publishers 1999 4. Philip Ball. Brain Imaging Explained. 5. Iosifescu DV, Bolo NR, Nierenberg AA, et al. Brain bioenergetics and response to T3 augmentation in major depressive disorder. Biol Psychiatry. 2008;63(12):1127-1134 Read More