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| Fig. 1: Example of a computed tomography scanner. (Source: Wikimedia Commons) |
Computed tomography (CT), also known as computerized tomography or computed axial tomography, is a non-invasive medical technique in which specialized X-rays scan cross-sectional images of the body (refer to Fig. 1). [1] These cross-sectional images present targeted segments, or "slices", of the body, which is useful for diagnostic or therapeutic examination of bones, soft tissues, and blood vessels. The procedure of CT scanning is very similar to that of normal X-rays. The patient lies down on a motorized table, usually facing up, and the table moves into a circular-shaped CT imaging system. Once the patient is underneath the tunnel-like structure, an X-ray source and a detector assembly within the structure rotate around the body. A single rotation normally takes less than a second. During this rotation, the X-ray source projects a beam of X-rays that scans the target slice of the body. Detectors are located below the motorized table, which register the X-rays that pass through the body. The detectors assemble the collected information into visual snapshots at many angles. Finally, all the detected snapshots are delivered to a connected computer, which is reconstructed into cross-sectional images of the internal organs and tissues. [1]
CT scan is used for a variety of reasons. CT scan can examine bone-related health issues such as inspecting serious bone injuries, diagnosing spinal problems and skeletal injuries, and detecting osteoporosis (the deterioration of bones due to diminishing bone mass or bone tissue). CT scan is used most widely for detecting many different types of cancers as well as tracking the spread of tumors. Physicians can also locate infections and examine injuries, clots that cause strokes, hemorrhaging, and other health problems occurring inside the head. CT is used for imaging the lungs to identify blood clots in the vessels, excess fluid, pneumonia, and chronic pulmonary obstructive disease (COPD). Moreover, the causes of chest or abdominal pain, difficulty breathing, and other similar symptoms can be determined through CT. In more severe cases, lethal vascular disease can be diagnosed which could cause stroke, kidney failure, or even death. [2]
Computed tomography has minimal risks, so medical benefits seem to outweigh the consequences. As aforementioned, physicians are able to identify, analyze, diagnose, and prevent diseases through detailed cross-sectional images of the human body. However, the X-ray emits very little amount of ionizing radiation, which could increase the risk of adapting cancer in the future. [2] Exposure to radiation in CT scans is measured in millisieverts (mSv), which is the total sum of the negative health risks multiplied by absorbed doses in affected tissues or organs. Humans are exposed to a small amount of ionizing radiation from natural sources in everyday life, and the average amount is 3 mSv per year. A common chest x-ray emits 0.1 mSv on average, while a chest CT emits 7 mSv, which is 70 times as much. [3] Patients of younger age are less immune to the exposure of radiation and the risk of radiation developing into cancer is more probable for patients with longer lifetime. [1] Therefore, testing CT especially on children requires thorough pre-consideration of appropriate exposure factors and checkup on health implications.
The UC Davis Public Health and Sciences department conducted a study with the HMO Research Network to examine trends and risks in CT usage of children below the age of 15 who were registered at 6 specific health care systems. [4] The use of CT within this identified group increased between 1996 and 2005. The rate remained relatively stable from 2005 to 2007, and, decreased between 2007 and 2010. The majority of CT scans was performed on the head, followed by abdomen and pelvis, chest, and spine. Effective doses varied from 0.03 to 69.2 mSv per scan. Doses above 20 mSv, which is considered detrimental to health, were mostly conducted in abdomen and pelvis scans. Therefore, the projected lifetime attributable risk of solid cancer was highest for abdomen and pelvis scans and girls were more prone (25.8 to 33.9 cases per 10,000 scans) compared to boys (13.1 to 14.8 cases per 10,000 scans). Solid risk of leukemia was highest for head CT scans (with 0.5 to 1.9 cases per 10,000 scans), which is still significantly lower than the average risk of cancer. [4]
Computed tomography is an indispensable medical examination that is applicable to a plethora of diagnostic as well as therapeutic purposes. The risk of developing cancer or leukemia through ionizing radiation emitted from the structure is extremely minimal in adults, and the benefits certainly override the negligible risks. However, the implementation of CT in pediatrics tend to be more cautious as patients of younger age are more vulnerable to the potential risks. Therefore, thorough consultation with physicians and ample examination of young patients is necessary when deciding upon CT scanning.
© Hannah Park. 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] M. K. Kalra, A. D. Sodickson, W. W. Mayo-Smith, "CT Radiation: Key Concepts for Gentle and Wise Use," Radiographics 35, 1706 (2015).
[2] D. Fleischmann and F. E. Boas, "Computed Tomography - Old Ideas and New Technology", Eur. Radiol. 21, 510 (2011).
[3] F. V. Coakley et al., "CT Radiation Dose: What Can You Do Right Now in Your Practice?" Am. J. Roentgenol. 196, 619 (2011).
[4] D. L. Miglioretti et al., "The Use of Computed Tomography in Pediatrics and the Associated Radiation Exposure and Estimated Cancer Risk," J. Am. Med. Assoc. Pediatr. 167, 700 (2013).
