Chest Tomography

Also called laminagraphy, planigraphy, stratigraphy, or body section roentgenography, chest tomography provides clearly focused radiographic images of selected body sections otherwise obscured by shadows of overlying or underlying structures. In this procedure, the X-ray tube and film move around the patient in opposite directions (a motion called the linear tube sweep), producing exposures in which a selected body plane appears sharply defined and the areas above and below it are blurred. Because tomography emits high radiation levels, it's used only for evaluation of chest lesions.

Purpose

• To demonstrate pulmonary densities (for cavitation, calcification, and presence of fat), tumors (especially those obstructing the bronchial lumen), or lesions (especially those located deep within the mediastinum, such as at lymph nodes at the hilum).

Patient Preparation

• Explain to the patient that this test helps evaluate lesions inside the chest.
• Describe the test, including who will perform it, where it will take place, and its duration (30 to 60 minutes).
• Tell him that he needn't restrict food or fluids before the test.
• Warn the patient that the equipment is noisy because of rapidly moving metal-on-metal parts and that the X-ray tube swings overhead.
• Advise him to breathe normally during the test but to remain immobile; tell him that foam wedges will be used to help him maintain a comfortable, motionless position.
• Suggest that he close his eyes to prevent invohmtary movement.
• Instruct him to remove all jewelry within the X-ray field.

Procedure And Posttest Care

• The patient is placed in a supine position or in different degrees of lateral rotation on the X-ray table. The X-ray tube then swings over the patient, taking numerous films from different angles.
• For lung tomography, the X-ray tube is usually moved in a linear direction but may be moved in a hypocycloid, circular, elliptic, trispiral, or figure­eight pattern. Multidirectional films aid diagnosis of mediastinal lesions or tumors.

Precautions

• Tomography is contraindicated during pregnancy.
• To avoid exposure to radiation, leave the room or the immediate area during the test; if you must stay in the area, wear a lead-lined apron.

Normal Findings

A normal chest tomogram shows structures equivalent to those seen on a normal chest X-ray film.

Abnormal Findings

Central calcification in a nodule suggests a benign lesion; an irregularly bordered tumor suggests malignancy; a sharply defined tumor suggests granuloma or nonmalignancy. Evaluation of the hilum can help differentiate blood vessels from nodes, detect tumor extension into the hilar lung area, and identify bronchial dilation, stenosis, and endobronchial lesions. Tomography can also identify extension of a mediastinal lesion to the ribs or spine.

Interfering Factors

• Failure to remove all metal objects within the X-ray field (possible poor imaging)
• Uncooperative patient