Definition and Overview
A chest CT scan, or a computed tomography scan of the chest, is a non-invasive and painless test that is conducted to obtain a precise image of a person’s chest. It is non-invasive because there is no surgery involved and there are no instruments that are inserted into the patient’s body. The scan uses an enhanced form of x-ray technology that is capable of giving a more detailed images of the chest than a standard x-ray can. A CT scan produces images that include the bones, muscles, fats, and organs, giving doctors a better view that is crucial in making accurate diagnoses.
There are two kinds of chest CT scan, namely the high-resolution and spiral chest CT scan. The high-resolution chest CT scan provides more than a slice (or image) in a single rotation of the x-ray tube. The spiral chest CT scan, on the other hand, makes use of a table that continuously moves through a tunnel-like hole while the x-ray tube follows a spiral path. The advantage of the latter is that it is capable of producing a three-dimensional image of the lungs.
Who Should Undergo and Expected Results
The people who are advised or required to undergo the test are those who are experiencing symptoms related to chest and lung problems, such as:
- Shortness of breath
- Excess fluid around the lungs
- Pulmonary embolism
- Chest pain
After undergoing a chest CT scan, a detailed image of the structures of the lungs including the bones, muscles, fats, and other organs nearby is produced and used by the requesting physician to diagnose certain conditions related to the lungs.
A chest CT scan is also normally requested as a follow-up procedure when there are abnormal findings from a previously performed standard chest x-ray. It can help find the cause of certain lung symptoms, such as chest pain, lesions, intrathoracic bleeding, and shortness of breath, and can provide further information for the investigation of any abnormalities suspected in the chest.
How Does the Procedure Work?
X-rays work with the use of ionizing radiation, which is a form of energy that enables x-ray to take pictures of the inside of the chest. A chest CT scan, like a standard x-ray, also uses this same energy. However, the scan is sometimes accompanied by the use of a contrast dye material, which enhances the images and makes the organs appear clearer on the test results. A contrast dye is a substance that may either be taken by mouth or injected into an IV line prior to the scan. However, due to the use of the dye material, patients who have to take a chest CT scan using this method are asked to refrain from eating or to avoid certain kinds of food prior to the scan.
The CT scanner used in a chest CT scan is a huge machine resembling a tunnel. During a chest CT scan, the patient is asked to lie on a table that moves through the scanner’s hole. While the patient is lying down on the table, an x-ray beam rotates around the body as the table moves through the tunnel-like machine. A computer is then used to receive the data gathered by the x-ray beams and these are then interpreted as a series of images called slices. The results are then forwarded to the requesting physician for analysis and diagnosis.
Possible Complications and Risks
Possibly the biggest risk associated with a chest CT scan is related to its use of radiation. Exposure to radiation exposes a person to the risk of certain health issues, the worst of which is cancer. Young children are more vulnerable to the negative effects of radiation, and pregnant women are advised to avoid radiation exposure where there is a possibility that radiation can cause birth defects. Pregnant women are only given the clearance to undergo a CT scan in matters of life and death wherein the expected benefits outweigh the risks. In cases where a CT scan cannot be avoided or where there is a lack of alternatives, doctors can adjust the amount of radiation to minimize the risk to the patient. Regardless of the case, however, all chest scans only use the approved amount of radiation.
Another possible complication is an allergic reaction to the contrast dye material, if it is used. However, such allergic reactions are very rare and can easily be resolved with anti-allergy medications.
Also, patients who have problems with their kidneys must tell their doctor about their condition prior to a CT scan. There is a small chance that the contrast dye will cause kidney failure in patients who have existing issues with their kidneys. Patients who have diabetes and are taking diabetes medications, such as metformin (Glucophage) or any medication of the same type, must also notify their attending doctor. This is because the medication, when combined with the contrast dye material, may trigger a condition known as metabolic acidosis.
Gotway MB, Elicker BM. Radiographic techniques. In: Mason RJ, Broaddus CV, Martin TR, et al, eds. Murray &Nadel's Textbook of Respiratory Medicine. 5th ed. Philadelphia, PA: Elsevier Saunders; 2010:chap 19
Stark P. Imaging in pulmonary disease. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 84