Definition and Overview
A CT scan of the lungs is one of the many imaging procedures used to diagnose and monitor treatment of various lung diseases. CT scans, or computed tomography scans, involve the use of several x-ray images taken from different angles, which are then combined to produce cross-sectional images and three-dimensional images of the internal structures of the lungs.
The main purpose of this imaging procedure is to detect abnormal structures inside the lungs or irregularities that might be contributing to the symptoms experienced by the patient. Aside from diagnosing illnesses or injuries to the lungs, CT scans can also be used to guide certain treatment procedures to ensure accuracy and precision. Many medical professionals use CT scans of the lungs to decide on the best treatment plan for the patient, which typically includes prescribing a course of medication, surgery, or radiation therapy.
CT scans of the lungs usually fall under the chest or thoracic CT scan category. The procedure involves producing various x-ray images, known as “slices,” of the patient’s chest and upper abdomen. These slices are fed into a computer for the final image, which can be viewed in different angles, sides, and planes. Unlike a traditional x-ray procedure, a CT scan provides more details and accurate images that show even minor abnormalities and irregularities.
Also, CT scans of the lungs can be more useful in diagnosing lung tumours when compared to standard x-rays of the chest. That is why it is used to determine the location, size, and shape of the cancerous growths. This imaging procedure can also help identify the presence of enlarged lymph nodes, which can be symptoms of the cancer cells spreading from the lungs.
Who Should Undergo and Expected Results
The procedure is recommended for patients who are suspected of suffering from the following conditions:
- Obstructive lung disease
- Lung cancer
- Conditions afflicting the pleura
- Diffuse interstitial lung disease
- Injury caused by trauma
Normal results mean that the patient has healthy lungs while abnormal results can mean a diagnosis of the suspected lung disease. However, if the images from the CT scan did not yield conclusive results, the doctor might order another round of tests, including more invasive ones, such as biopsies for tumours or suspected cases of cancer.
How is the Procedure Performed?
The procedure can be performed in a hospital or a clinic on an outpatient basis. Before starting the procedure, the doctor or technician performing the CT scan might ask the patient to ingest a contrast agent, a special dye that will make the structures inside the patient’s body more defined on the x-ray images. This contrast agent can also be injected through an intravenous line or a vein in the arm. The patient can expect a warm feeling in his or her face as the contrast agent courses through the body.
After the contrast agent has been introduced into the body, the patient will be directed to wear a paper or hospital gown and remove jewellery or accessories that can prevent the CT scan machine from taking pictures of the chest. The CT scan machine resembles a large donut—it is a large cylindrical machine with an opening (or hole) in the middle. The patient will lie on a table-like surface, which will then be fed into the opening. The hard, cold surface of this table might be uncomfortable to the patient. The patient must lie still for a couple of minutes while the scan is being performed. It is important to note that CT scans last longer than traditional x-rays, mostly because more images are being taken instead of a single one.
After the slices are taken, the patient can leave the CT scan machine. The images taken from the patient’s chest will be fed into a computer, where all the slices taken will be combined to create CT images, which can then be viewed on a computer or printed on film, like traditional x-ray images. Modern computers connected to equally modern CT scan machines can also stack the images together to form a three-dimensional model of the lungs, which is very useful for diagnosis and treatment management.
Some patients might also feel anxious about the cramped space inside the CT scan machine. Patients suffering from intense anxiety or claustrophobia can be prescribed relaxants.
After the procedure, the patient can easily leave for home or resume normal activities. There is no required recovery time, though a patient who has taken relaxants will be asked to stay in the hospital or clinic for a while.
Possible Risks and Complications
If the CT scan procedure requires the use of contrast agents, it is important to note that some patients might experience hives or allergic reactions. Typically, contrast agents contain iodine, which can cause nausea, vomiting, and dizziness in patients allergic to the substance. It is best to inform the doctor performing or ordering the procedure if the patient has experienced allergic reactions to contrast agents in the past.
Since CT scans use the basic principle of x-ray imaging, they emit low levels of ionizing radiation. Research shows that repeated exposure to significant amounts of this kind of radiation can cause different types of cancer and other illnesses. However, CT scan machines are generally safe and emit the lowest amount of ionizing radiation possible.
Patients with kidney disease should also inform their doctor about their condition as the contrast agent used for the procedure could aggravate their condition.
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.