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Thoracic Computed Tomography
Thoracic computed tomography (CT) provides cross-sectional views of the chest by passing an X-ray beam from a computerized scanner through the body at different angles. CT scanning may be done with or without an injected contrast medium, which is primarily used to highlight blood vessels and to allow greater visual discrimination. This test provides a three-dimensional image and is especially useful in detecting small differences in tissue
density. The thoracic CT scan may replace mediastinoscopy in diagnosis of mediastinal masses and Hodgkin's disease; its value in the evaluation of pulmonary pathology is proven.
Purpose
- To locate suspected neoplasms (such as in Hodgkin's disease), especially with mediastinal involvement
- To differentiate coinsized calcified lesions (indicating tuberculosis) from tumors
- To distinguish tumors adjacent to the aorta from aortic aneurysms
- To detect the invasion of a neck mass in the thorax
- To evaluate primary malignancy that may metastasize to the lungs, especially in patients with primary bone tumors, soft-tissue sarcomas, and melanomas
- To evaluate the mediastinal lymph nodes
Patient Preparation
- Explain to the patient that this test provides cross-sectional views of the chest and distinguishes small differences in tissue density.
- If a contrast medium will not be used, inform him that he needn't restrict food or fluids. If the test is to be performed with contrast enhancement, instruct the patient to fast for 4 hours before the test.
- Tell him who will perform the test and where and that the procedure usually takes 90 minutes and won't cause him any discomfort.
- Inform him that he'll be positioned on an X-ray table that moves into the center of a large ring-shaped piece of X-ray equipment and that the equipment may be noisy.
- Inform him that a contrast medium may be injected into a vein in his arm.
- If so, he may experience nausea, warmth, flushing of the face, and a salty or metallic taste. Reassure him that these symptoms are normal and that radiation exposure is minimal.
- Tell him not to move during the test, but to breathe normally until told to follow specific breathing instructions. Instruct him to remove all jewelry and metal in the X-ray field.
- Check the patient's history for hypersensitivity to iodine, shellfish, or contrast media.
Procedure And Posttest Care
- After the patient is placed in a supine position on the X-ray table and the contrast medium has been injected, the machine scans the patient at different angles while the computer calculates small differences in the densities of various tissues, water, fat, bone, and air.
- This information is displayed as a printout of numerical values and as a projection on a monitor. Images may be recorded for further study.
- Watch for signs of delayed hypersensitivity to the contrast medium (itching, hypotension or hypertension, or respiratory distress).
- Following the test, encourage the patient to drink lots of fluids.
Precautions
- Thoracic CT scanning is contraindicated during pregnancy and, if a contrast medium is used, in persons who have a history of hypersensitivity reactions to iodine, shellfish, or contrast media.
Normal Findings
Black and white areas on a thoracic CT scan refer, respectively, to air and bone densities. Shades of gray correspond to water, fat, and soft-tissue densities.
Abnormal Findings
Abnormal thoracic CT findings include tumors, nodules ,cysts, aortic aneurysms, enlarged lymph nodes, pleural effusion, and accumulations of blood, fluid, or fat.
Interfering Factors
- Failure to remove all metallic objects from scanning field(possible poor imaging)
- Patient's inability to remain still during the procedure
- Obese patient(may be too heavy for scanning table)
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