A nuclear lung scan, also known as a ventilation-perfusion (V/Q) scan, is a medical imaging procedure used to evaluate lung function. This non-invasive test assesses how effectively air moves into and out of the lungs, a process called ventilation. It also examines how well blood flows through the lung tissue, known as perfusion. By providing insights into air distribution and blood circulation, the V/Q scan helps identify various respiratory conditions.
How the Scan Operates
A nuclear lung scan involves two distinct parts: a ventilation scan and a perfusion scan. During the ventilation phase, a patient inhales a small, safe amount of radioactive gas or aerosol through a mouthpiece or mask. This tracer travels with the air into the lungs, allowing images to be captured that show how air is distributed throughout the airways.
For the perfusion phase, a different radioactive tracer is injected into a vein in the arm. This tracer travels through the bloodstream to the lungs, where it momentarily lodges in the tiny blood vessels. A specialized camera, known as a gamma camera, then detects the radiation emitted by these tracers. The camera creates detailed images that illustrate blood flow patterns within the lung tissue. Comparing the images from both the ventilation and perfusion scans provides a comprehensive view of lung function, highlighting areas where air and blood flow might be unbalanced.
Key Conditions Identified
The nuclear lung scan identifies medical conditions by revealing imbalances in air and blood flow. One of its most frequent applications is in the assessment of pulmonary embolism (PE). A PE occurs when a blood clot blocks an artery in the lung. The scan helps detect these clots by showing areas where air distribution (ventilation) is normal, but blood flow (perfusion) is significantly reduced or absent, indicating a “mismatched defect.” This specific pattern is a strong indicator of a blood clot obstructing blood supply to a part of the lung.
The V/Q scan can also provide information about chronic obstructive pulmonary disease (COPD), including emphysema. These conditions involve damage to the lung tissue that affects both airflow and blood supply. The scan can reveal uneven patterns of air distribution and blood flow, often showing “matched defects” where both ventilation and perfusion are reduced in the same areas. This helps clinicians assess the extent and distribution of lung damage caused by these progressive diseases.
Before certain lung surgeries, such as those for lung cancer or lung reduction, a nuclear lung scan is used to evaluate regional lung function. By determining how much healthy lung tissue will remain post-operation, the scan assists surgeons in planning procedures to ensure sufficient lung capacity for the patient. This pre-surgical assessment is important for predicting outcomes and minimizing risks. The scan also plays a role in detecting shunts, which are abnormal connections that allow blood to bypass the lungs, indicating issues with the normal circulatory pathway.
Understanding the Scan Images
Interpreting the images from a nuclear lung scan involves a careful comparison between the ventilation and perfusion studies. A nuclear medicine physician or radiologist analyzes these two sets of images to identify any discrepancies. A normal scan shows a uniform distribution of both inhaled air and injected blood flow throughout the lungs.
Abnormal findings deviate from this uniform distribution. A “mismatched defect” is where an area of the lung has normal ventilation but reduced or absent perfusion. This pattern strongly suggests a pulmonary embolism, as air can enter the lung tissue, but blood flow is blocked.
Conversely, a “matched defect” occurs when both ventilation and perfusion are reduced in the same region of the lung. This pattern typically points to other lung conditions, such as COPD or pneumonia, where an underlying disease process affects both air movement and blood flow in that specific area. The interpretation relies on these distinct patterns to pinpoint the nature of the lung issue.