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| Fig. 1: The above is an example of a SPECT scan before and after common medical treatment used for a wide variety of treatments known as Hyperbaric Oxygen Treatment. The different colors represent the difference of perfusion before and after treatment. (Source: Wikimedia Commons) |
Traumatic brain injuries (TBIs) occur as a result of blunt force to the head or trauma and can range from mild concussions to severe and prolonged loss of consciousness. [1] TBIs like Post Traumatic Stress Disorder both leave one a greater risk for developing depression, anxiety, or drug addiction. [1] It is difficult to differentiate whether such symptoms are the result of physical trauma to the head or of psychological stress from the event. This distinction is particularly difficult to make in treating military men after a traumatic accident. [1] The treatment for TBIs is also expensive estimated at $11,700 a year for a patient with a TBI the first year out of the military versus $2,400 a year for a military person without a TBI. [1] In addition, the long term repercussions of not treating even a mild TBI can lead to increased risk of depression and suicide. [1] Clinically, it is important to distinguish PTSD from a traumatic brain injury, or to determine whether a patient suffers from both diagnoses to explore treatment options. Imaging studies such as MRI and CT scans can detect TBIs, but recent research suggest SPECT scanning might be a more sensitive imaging alternative. [2]
SPECT, which stands for single photon emission computed tomography, scans are able to give a three-dimensional picture of organs such as the brain by utilizing both a computer tomography (CT) and a radioactive tracer that is injected into the bloodstream. [3] Depending on what the scan is for, different radioactive isotopes such as I-123, Tc-99, or In-111, can be used, because they all give off gamma rays. Brain scans typically use Tc-99 as it has a half life sufficient for viewing the metabolic activity of the brain. [4] Special cameras then detect the gamma rays from the tracers and a 3D image is configured. This scan is commonly used to allow doctors to see how blood flows throughout the organs and tissues, and shows a differentiation and often lack of blood flow to injured areas. [3]
An example of a SPECT scan is shown in Fig. 1 - both before and after a common treatment used to enhance healing in many different scenarios. This SPECT scan of the brain demonstrates the increased blood flow after Hyperbaric Oxygen Treatment as shown by the increase in red and orange colors to many regions of the brain. The colors are intended to denote ranges of blood flow with red being the most blood flow and violet the least. Though each subsequent color after red denotes a 10% decrease in blood flow to the area, the scale adjacent to the image measuring from 0-2000 has unclear meaning. [5] Despite the unknown representation of the scale and, thus, unknown amount of blood flow to each area, the colors are meant to visually represent an increase in blood flow to specific regions in the brain post treatment as compared to pre-treatment. Physicians use SPECT scans like the one shown to detect areas of the brain that might have traumatic injuries as demonstrated by reduced blood flow. The scans are also useful in detecting whether treatment is effective.
In a PET scan, tracers can be dissolved into the tissues surrounding blood, while SPECT tracers remain only in the blood, allowing doctors to look specifically at blood flow to potentially injured areas. SPECT scans are also relatively inexpensive and accessible which makes them a good option as compared to PET scans. [3]
Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) scans are currently the most commonly used diagnostic imaging technologies for detecting signs of head trauma. However, in a systemic review of 71 studies by Cyrus et al. SPECT was found to outperform both MRI and CT scans in detecting TBIs. [2] The better diagnostic capabilities of SPECT were even more pronounced in cases where brain trauma was mild. In addition to finding cases of TBIs that both MRI and CT scans had missed, SPECT also had a 100% negative predictive value meaning that subjects that test negative on the scan actually do not have brain trauma. [4]
Nonetheless, CT scans and MRI scans are still important, in that unlike SPECT scans that reveal metabolic activity in the brain, CT and MRI scans are able to show anatomical structure. Thus, SPECT scans may be most effectively used as a secondary diagnostic scan when MRI and/or CT scans fail to reveal a TBI in a symptomatic patient, because of their higher specificity. [2]
SPECT scans are important tests in detecting evidence of traumatic brain injury, especially in cases where the injury is mild and unable to be detected on either an MRI or CT scan. Because there are many long term effects, of even mild TBIs, such as depression, progressive brain damage, and other psychiatric symptoms, it is important to detect TBIs early. [2] Nuclear medicine techniques such as SPECT scans show promising ways to distinguish between symptoms from psychological responses to a traumatic event versus symptoms from physical trauma to the brain. [1] Thus, in knowing whether symptoms come primarily from TBIs of PTSD, doctors can personalize treatment for a more effective recovery for their patients. Therefore, SPECT and other nuclear imaging scans demonstrate future potentials for more personalized medicine. [6]
© Kaitlyn Merritt. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] D. G. Amen et al. , "Functional Neuroimaging Distinguishes Posttraumatic Stress Disorder from Traumatic Brain Injury in Focused and Large Community Datasets," PLoS One 10, 30129659 (2015).
[2] C. A. Raji et al., "Clinical Utility of SPECT Neuroimaging in the Diagnosis and Treatment of Traumatic Brain Injury: A Systematic Review," PLoS One 9, e91088 (2014).
[3] C. Stewart, "SPECT (Single Photon Emission Computed Tomography) Scan," Mayfield Clinic, April 2016.
[4] J. Uang, "SPECT Instrumentation and Radionuclides," Physics 241, Stanford University, Winter 2016.
[5] P. G. Harch et al., "Low pressure Hyperbaric Oxygen Therapy and SPECT Brain Imaging in the Treatment of Blast-Induced Chronic Traumatic Brain Injury (Post-Concussion Syndrome) and Post Traumatic Stress Sisorder: a Case Report," Cases J. 2, 6538 (2009).
[6] G. Klaris, "The Future of Nuclear Medicine," Physics 241, Stanford University, Spring 2016.