Non-invasive diagnostic procedures: MRI and CT scans

Both Magnetic Resonance Images (MRIs) and Computed Tomography (CT) are used as noninvasive diagnostic techniques to understand what may be happening in the brain of a patient.  Because both techniques provide a visual representation of a patient's brain, they can detect brain tumors, degeneration in the brain, and other structural malformations that are identified as characteristics of disease.  These images are frequently used along with neurological tests to help produce a proper diagnosis.

MRIs, technically known as Nuclear Magnetic Resonance Imaging, utilizes the electromagnetic properties of protons to generate tissue images which form an important tool in diagnosing neurological conditions and diseases.  MRI machines emit a pulse in the radio-frequency range which cause [nuclear] protons, primarily within the body's water molecules, to align to the pulse's magnetic field.  When the pulse completes, the protons "relax" to their original alignment, releasing weak electromagnetic energy that is detected to form the image.  Careful calibration of these fields across a gradient (varying the field strength at known points) allows the resulting emissions to be located in three-dimensional space, so that cross-sectional images can be produced (Nave, 2004).

Computed Tomography (CT), sometimes called Computerized Axial Tomography (CAT) is a development of radiography that uses data from a series of X-ray exposures at different angles to calculate a three-dimensional image.  X-rays are high-frequency photons that attenuate (partially reflect or get absorbed) to a different extent depending on the substances that passes through.  Dense materials, such as bone, attenuate the X-ray beam more strongly than fatty tissue, for example.  The strength of the beam received by the detector, on the opposite side of the target from the emitter, is used to determine the radio-opaqueness (represented with shades of color) of matter from each angle. Because each of these exposures lack information about the depth of the attenuating matter, they are computer-processed together to extrapolate a three-dimensional model (Knipe, n.d.).  CT scans are particularly good at detecting abnormalities, including hemorrhaging, tumors, and fractures, but do, on their own, have difficulty displaying soft tissues in good detail, and do involve exposure to small amounts of ionizing radiation (Athale, 2012).  Use of a contrast agent such as iodine, which strongly attenuates X-rays, can show organs and particularly abnormalities clearly (Kennedy, 2015).

 

Athale, S. (2012). A tale of two scans: Which is better - a CT scan or an MRI? The Hanford Sentinel. Retrieved November 28, 2015 from http://hanfordsentinel.com/news/local/a-tale-of-two-scans-which-is-better--/article_82dce24a-0d87-11e2-bb76-0019bb2963f4.html

Kennedy, T., et al. (2015). Neuroradiology Learning Module: Contrast. Department of Radiology, University of Wisconsin School of Medicine and Public Health. Retrieved November 28, 2015 from https://sites.google.com/a/wisc.edu/neuroradiology/image-acquisition/contrast

Knipe, H., Nadrljanski M., et al. (n.d.) Computed Tomography. Radiopaedia.org. Retrieved November 28, 2015 from http://radiopaedia.org/articles/computed-tomography

Nave, R. (2004). Magnetic Resonance Imaging. Hyper Physics. Retrieved November 29, 2015 from http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/mri.html