A Computed Tomography (CT) scan uses a series of X-ray beams taken from multiple angles around the body. A computer processes these measurements to create detailed cross-sectional images, often referred to as “slices,” of internal structures. This process allows for a much clearer view of soft tissues, bones, and blood vessels compared to a standard X-ray. When focused on the chest, a CT scan provides an exceptionally high-resolution look inside the thoracic cavity. This technology helps physicians identify various lung conditions.
Understanding the CT Scan Procedure
The CT scan procedure begins with the patient removing metal objects, such as jewelry or belts, as these can interfere with the X-ray beams. The patient then changes into a medical gown and lies down on a motorized table. This table slides into the center of the CT scanner, which is a large, donut-shaped machine that houses the X-ray tube and detectors.
For many lung examinations, an intravenous (IV) contrast material, often called a dye, is used to enhance the visibility of blood vessels or certain masses. This iodine-based material is injected through an IV line, and patients frequently report a temporary sensation of warmth or a metallic taste. During the scan, the technologist provides instructions, often asking the patient to hold their breath for a short period to ensure the lungs are still for image capture.
How CT Scans Visualize Lung Tissues
A standard chest X-ray produces a single, two-dimensional image, causing overlapping structures to obscure fine detail within the lungs. The CT scan overcomes this limitation by using a rotating X-ray source and a row of detectors to capture multiple projections, which the computer then reconstructs into clear cross-sectional images or “slices.” This technique allows radiologists to look at the chest one thin section at a time.
CT imaging relies on its ability to measure subtle differences in tissue density, referred to as attenuation. Air-filled spaces, like healthy lung parenchyma, appear black because they are low-density, while bone or active tissue masses appear white due to their high density. Pathological changes, such as fluid buildup or scarring, alter the normal air-to-tissue ratio, creating distinct visual patterns like “ground-glass opacity” or solid “consolidation.” Advanced reconstruction algorithms can process these slices to create detailed three-dimensional models of the lung anatomy.
Conditions Detected by Lung CT
Abnormal Growths and Infections
The high-resolution detail of lung CT scans makes them a powerful tool for detecting and characterizing pulmonary diseases. A primary use is the identification and monitoring of abnormal growths. A small, round lesion measuring up to 3 centimeters is defined as a pulmonary nodule, while anything larger is classified as a mass. CT is routinely used to track the growth or change in morphology of these nodules over time, helping to differentiate between benign scars from old infections and potentially cancerous tumors or metastatic disease.
The scan is also effective at diagnosing and assessing the extent of infections and inflammatory processes. Pneumonia appears as areas of consolidation, where the air sacs are filled with fluid or inflammatory material, sometimes showing a telltale pattern called an air bronchogram. Chronic conditions, such as emphysema associated with Chronic Obstructive Pulmonary Disease, are visualized as areas of decreased lung density due to the destruction of air sac walls. Specialized expiratory scans, taken after the patient breathes out, can reveal air trapping, a sign of small airway obstruction.
Vascular and Interstitial Diseases
CT angiography, which involves timing the scan to capture the contrast material as it flows through the pulmonary arteries, is the definitive method for diagnosing vascular problems. This technique is used to clearly identify a pulmonary embolism, a life-threatening blood clot that has traveled to the lungs, appearing as a filling defect within the bright, contrast-filled vessels. The size and shape of the main pulmonary artery can be assessed to look for signs of pulmonary hypertension, a condition involving high blood pressure in the lung arteries.
Interstitial Lung Diseases (ILDs), disorders involving inflammation and scarring of the lung tissue, produce distinctive patterns on CT. These patterns include reticular opacities, which look like a fine net or mesh, and “honeycombing,” which describes clustered cystic airspaces indicating advanced fibrosis or scarring. Other ILDs, such as sarcoidosis or hypersensitivity pneumonitis, may present with a specific distribution of small, clustered nodules, providing specific clues that guide the final diagnosis.