COMPUTED TOMOGRAPHY
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Introduction
Many imaging techniques exist to help in diagnosing medical conditions. The most frequently used modalities are ultrasonography, computed tomography, and MRI. The technologies have similar applications but different advantages and disadvantages. Also, the various systems can complement each other when one cannot be used due to some reasons, and an alternative is chosen instead to provide the same information while minimizing the risks to patients. Computed Tomography has emerged as one of the best methods to diagnose different medical conditions and with minimal adverse effects. This research paper discusses CT and its use.
Computed Tomography (CT)
CT is a diagnostic technique where information from X-rays beams passes through an area of a person’s body is processed using a computer. CT became available in the 1970s, after being developed by Godfrey Newbold and Allan MacLeod.
How CT System Operates
When high-speed electrons are hit a metal target, X-rays are produced, with the kinetic energy of the moving electrons being transformed into electromagnetic energy. In a CT system, the filaments contained in the X-ray tube provides the electrons that create x-ray photons (Romans, 2011). The heating of the filament produces the electrons that hover around the filament, creating a space cloud (Romans, 2011). A high voltage generator transmits the voltage to the X-ray tube, moving the electrons from the filament to the rotating anode, producing heat and X-ray photons. The target rotates to spread the heat over a large area. An increase in voltage increases the energy of the electrons striking the target, causing the intensity of the X-ray beam to increase.
The X-ray photons produced irradiates the section of the body under investigation (Figure 1). The X-ray photons that pass the human body strike a detector, with the detector cells converted to a digital format by data acquisition system (DAS). Each sample is called a view, which is used by the reconstruction processor that reconstructs the densities within a slice (Romans, 2011). The information from DAS is transmitted into a matrix that assigns a density number to the image pixels. The data is then passed to a display processor that displays the information on a computer monitor in a human-readable format. The CT process is thus broken into three phases: data acquisition, image reconstruction, and image display.
Figure 1. CT system operation
Reasons for CT on the Body
CT is used to study different parts of the body due to various reasons. Some of the applications discussed below.
Head CT. It is used in the evaluation of patients with head injuries, mostly in the emergency department. Head CT is also used in cases of patients suspected of stroke, altered mental status, headache, and other neurological abnormalities (Fox, 2017).
CT of the Spine. It is used for trauma patients and other spinal pathologies. Back pain with osteoporosis or a history of cancer requires a CT of the spine (Fox, 2017). Also, spinal stenosis, perispinal infection, and cancer metastasis require a CT of the spine. CT of the spine is used instead of MRI due to its sensitivity to many pathogens, faster, and less expensive than MRI, and readily available (Fox, 2017). Also, when a patient has pacemaker or steel implants, a CT of the spine is used instead of MRI (Fox, 2017).
CT of the chest. It is used and included in the imaging of trauma patients due to its sensitivity for detecting intrathoracic pathology after trauma. Also, the chest CT detects many injuries that chest radiograph misses (Fox, 2017). It is used in assessing chest injuries to the airway, chest wall, diaphragm, lung parenchyma, pleura, and aorta. Chest CT is also used in the diagnosis of pneumonia, especially when radiographic results are not reliable.
CT of the Abdomen and Pelvis. It is used for the diagnosis of patients with pelvic or abdominal pain. Delayed diagnosis of the abdomen increases mortality and mobility rates, and laboratory findings are usually not conclusive to offer a diagnosis (Fox, 2017). CT is the best method for examining abdominal injuries. CT is also used in evaluating bowel obstruction.
Benefit of CT
CT is noninvasive and thus preferred over surgical methods. CT can image the soft tissues, blood vessels, and the bones all at the same time. Also, CT imaging is real-time, and thus it can be used in invasive procedures such as needle aspirations and biopsies of the lungs, abdomen, pelvis, or bones. CT can be used on a patient with medical implants that make it impossible to use MRI. In addition, CT examinations are fast and straightforward, making them useful in emergency settings where they reveal internal injuries quickly for medics to take action immediately. Effective use of CT can eliminate the need for surgical procedures.
Effects of CT on the Body
Just like X-rays, CT scans expose a person to ionized radiation, which the main component in creating the body structures seen on the computer monitor. CT is more effective than X-rays in evaluating medical conditions. However, the dose of radiation from CT is so small that the risk of cancer from the radiation is minimal.
Children are more sensitive to radiation since their body is growing. Also, due to their age, children have a longer life expectancy, widening the time for cancer from radiation to develop. A single CT scan has minimal chances of causing cancer. However, multiple CT scans increases risks of brain tumor, leukemia, and other cancers later in life (Pearce et al., 2012). It is therefore advised to use CT only when it is crucial.
When not to use CT
There are cases and periods in a person’s life that make it dangerous and risky for them to go through a CT scan. For instance, pregnant mothers are discouraged from CT usage. The radiation can affect the fetus causing developmental problems.
Patients with allergies to intravenous contrast media (IVCM) should not use CT when IVCM is used to achieve a diagnosis. Abdominal and chest CTs require IVCM, and CT is not advisable, especially when the allergy is a major issue (RadiologyInfo, n.d.). Renal impairment makes it impossible for a patient to use IVCM and, thus, CT requiring IVCM use.
Conclusion
There are many benefits of CT from its low radiation, to its effectiveness in diagnosing different conditions. Also, CTs are beneficial in many situations that other methods, such as X-rays and lab procedures shortfall. Availability and speed of CT make them the best tools for emergencies. Also, MRI has its limitations, and CT is of significant support to patients. CT is thus, invaluable to diagnosing many medical conditions. The adverse effects of CTs are few and occur in a tiny percent of people who have used CTs, making the safe.
References
Fox, J.C. (2017). Clinical Emergency Radiology (2nd Ed.). Cambridge University Press.
Pearce, M.S., et al. (2012). Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: a retrospective cohort study. Lancent, 380 (9840), 499-505. https://dx.doi.org/10.1016%2FS0140-6736(12)60815-0
RadiologyInfo. (n.d.). Computed Tomography (CT) – Chest. RadiographyInfo.org. https://www.radiologyinfo.org/en/info.cfm?pg=chestct
Romans, L.E. (2011). Computed Tomography for Technologists: A Comprehensive Text. Wolters Kluwer Health.