Computed Tomography or CT is an exceptional tool used in diagnostic radiography. It is an innovative diagnostic and imaging modality that employs the use of complex computer hardware components and an enclosed x-ray tube along with detector that take a 360˚ image in the body to produce cross-sectional images. (MIC, The CT CrossTrainer, 2nd ed., p.1 ). It differs from plain film radiography in that it provides more detailed anatomy that is not superimposed and further differentiates between organs and tissues that plain film x-rays cannot provide. This is a major benefit for physicians that need to see the contrast between the different organs within the body to make a diagnosis. Another benefit of CT is that it can aid in determining if and when surgery is necessary, it reduces exploratory surgery, improves cancer diagnosis and treatment, and reduces hospitalization time. (Benefits of CT Scans, 2018). It has been noted in the clinical setting that CT is also painless, precise, shows internal bleeding and other traumas, and provides examinations that are very swift which is extremely useful in emergencies.
When having a CT exam performed, the physician can order the study with or without contrast to highlight the areas to be examined. A contrast agent is usually a pharmaceutical compound which when administered to a patient may improve the specificity and sensitivity of the clinical diagnosis (The CT CrossTrainer, module 6, p. 22). As an illustration, the following photo was taken from the Journal of Radiology Case Reports, Vol 3, No 6 (2009); a case of acute appendicitis that shows the contrast versus non contrast image of a transverse slice through the abdomen. The first photo is a non-contrast study and the second is a contrast study. Notice the arrows pointing to the highlighted area that is better seen with contrast showing the diseased appendix.
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Fig. 1 Photo from Maki Kitagawa, Tatsuya Kotani, Yuji Miyamoto, Yoshiaki Kuriu, Hideaki Tsurudome, Hiroshi Nishi, Masaharu Yabe, Eigo Otsuji. Journal of radiology Case Report 2009. Indian Journal of Radiology. http://www.radiologycases.com/index.php/radiologycases/article/view/101. Accessed 4 Feb 2020.
Patients may be asked to take contrast media either orally, by intravenous injection or rectally in order to highlight specific areas within the anatomy. (Stanford Health Care, 2018). When having intravenous contrast injected a 20 gauge or larger needle is placed preferably into the antecubital space on either arm but can also be placed in the back of the hand. Once in place, the vein is flushed with a saline solution to make sure it is viable and able to handle the pressure of the power injection of the contrast. Once this is established, the contrast which is loaded in to a power injector, is attached to the IV to be injected prior to the exam. The contrast is then circulated through the heart, the arteries, into the capillaries, the veins, and back to the heart. The CT’s x-ray beam is offset or attenuated as they pass through the vessels and show up white on CT images. (Rawson, 2013).
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The next contrast route is orally and either barium sulfate or Gastrografin is often used in performing a CT of the pelvis and of the abdomen. The patient is instructed to drink at least 1000 to 1500 cc to fill the stomach and intestines sufficiently for the exam. (Imaginis, 2020)
The final contrast route mentioned is rectally. This is often used to improve visibility of the large intestines and other pelvic organs. Barium sulfate and Gastrografin is also used in this exam but with a different concentration. Rectal contrast is often given in the form of an enema with the patient laying on their side with the bag of contrast raised above the head in order to allow the contrast to fill the lower intestines. (Imaginis, 2020)
Though the benefits of contrast enhanced CT combines these multiple advantages into one session there can be some adverse effects to using contrast in patients. In the clinical experience it has been noted that prior to contrast administration the technologist must make sure the tests to determine renal function such as the Glomerular filtration rate (GFR) and the Creatinine test is within normal range and to ask the correct questions to see if the patient has had an allergic reaction to iodinated contrast before. The patient must be monitored closely during the exam to be sure they are not showing signs of an adverse reaction. According to the Dr. Jason W. Stephenson in his article entitled Adverse Reactions to Contrast: A Review, (2018), some of the mild reactions to contrast media include facial flushing, headache, nausea, itchy throat, mild hypertension, warm sensation, and hives. Dr. Stephenson goes on to describe moderate reactions such as anaphylactic (diffuse hives and throat tightness), hypertensive emergency and chest pain. The more severe responses include anaphylactic shock, seizure,
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hypertensive emergency and bradycardia. The moderate reactions require direct medical therapy and necessitate acquiring or retaining IV access, applying oxygen, and suction if necessary. The more severe reactions could be life threatening without proper intervention.
CT has been a wonderful and innovative addition to the world of diagnostic radiography. Advances in technology has brought it from the first CT of the brain that took about 9 hours to shoot and about 2 hours to reconstruct to a state of the art CT machine that takes about 1 second per image and reconstructs at amazing speed. Using this tool with contrast enhancement is generally considered safe and advantageous but, it should be noted that as a technologist it is imperative that every patient is screened thoroughly and monitored closely to be sure none of the adverse reactions to contrast occur. If they do occur, technologists and Radiologists need to be familiar with the proper steps to take to avert acute reactions that may escalate to life threatening events.
