Norm of Perfusion and Ventilation (V/Q Scan) Lung Scan
Low probability for emboli or thrombus.
Perfusion scan: Uniform uptake of particles within the entire lung vasculature.
Ventilation scan: Equal gas distribution in the pulmonary airways.
Usage of Perfusion and Ventilation (V/Q Scan) Lung Scan
Diagnosis of pulmonary embolism or thrombosis; determination of the percentage of lungs functioning normally; assessment of pulmonary vasculature supply by providing an estimate of regional pulmonary blood flow and identifying areas of shunting and areas where capillaries are absent (that is, emphysema); and diagnosis of atelectasis, asthma, bronchitis, chronic obstructive pulmonary disease, inflammatory fibrosis, lung cancer or tumors, and pneumonia.
Description of Perfusion and Ventilation (V/Q Scan) Lung Scan
This is a nuclear medicine procedure. There are three types of lung scans: (1) the perfusion scan, (2) the ventilation scan, and (3) the inhalation scan. In the perfusion scan, blood flow to the lungs is evaluated by use of an intravenous injection of macroaggregated albumin (MAA) tagged with technetium (99mTc). The radiolabeled particles become temporarily lodged in the pulmonary vasculature because their diameter is larger than that of the pulmonary capillaries. A gamma-ray detector scans the client, and a scintillation camera records the distribution of particles within the pulmonary vascular supply. “Hot spots” are areas of normal blood flow. “Cold spots” are areas of low radioactivity uptake and indicate poor perfusion and emboli. Although the lung perfusion scan is sensitive, it is not specific because a variety of pathologic conditions can cause the same abnormal results. Therefore lung perfusion scans should be performed with a lung ventilation scan. This scan determines the patency of the pulmonary airways and detects abnormalities in ventilation (such as pneumonia, pleural fluid, emphysema). Ventilation scans will show a normal wash-in and wash-out of radioactivity from the embolized lung area in embolic disorders. Conversely, the wash-in and wash-out will be abnormal in parenchymal disease (such as pneumonia). Finally, a normal inhalation scan looks much like a perfusion scan, except that the trachea and major airways are more visible. Results are interpreted as high, indeterminate, or low probability of embolus or thrombus.
Professional Considerations of Perfusion and Ventilation (V/Q Scan) Lung Scan
Consent form IS required.
Allergic reaction to iodine-131 if use is planned (itching, hives, rash, tight feeling in the throat, shortness of breath, bronchospasm, anaphylaxis, death).
Lung perfusion scanning is contraindicated in clients with primary pulmonary hypertension or right-to-left heart shunts. During pregnancy or breast-feeding. Previous history of allergy to iodine, eggs, or shellfish if iodine-131 will be used.
In pregnant or lactating women; Chan et al. (2002) conclude that pediatric risks are low when this procedure is performed during pregnancy.
- A chest radiograph should be obtained before or after a lung perfusion scan. Comparison of the perfusion scan with a chest radiograph can detect infiltrating disease.
- Have emergency equipment readily available.
- If iodine-131 is to be given (though this is rarely the case), give the client 10 drops of Lugol's solution several hours before the test. This will prevent iodine uptake by the thyroid gland.
- Sedation may be prescribed for very young children or those who are unable to lie still for the scan.
- Establish intravenous access.
- Breathing methods are reviewed with the client before injection and imaging.
- See Client and Family Teaching.
- Just before beginning the procedure, take a “time out” to verify the correct client, procedure, and site.
- Transport the client to the nuclear medicine department.
- In a perfusion scan, a radionuclide-tagged MAA is injected slowly intravenously over several respiratory cycles. Half is injected while the client is sitting up, and the other half while lying down. The client is placed in the supine, prone, and various lateral positions on the nuclear medicine table under the camera. Scanning with a gamma-ray detector is begun immediately. The scintillation camera takes several single stationary images of the anterior, posterior, and lateral areas of the chest. Perfusion imaging lasts about 45 minutes.
- In a ventilation scan, the client inhales a mixture of air and radioactive gas (xenon-133, krypton-85, krypton-81m, or 99mTc-diethylenetriaminepentaacetic acid [99mTc-DTPA]) through the mouthpiece of a face mask. The radioactive gas follows the same pathway as the air in normal breathing. A nuclear scan is performed at three phases: during the buildup of gas, after the client rebreathes from a bag and the radioactivity reaches a steady level, and after removal of the radioactive gas from the lungs. Ventilation imaging lasts about 30 minutes.
- In an inhalation scan, droplets of radioactive material can be administered by a positive-pressure ventilator. The aerosol is then inhaled through the mouthpiece of a face mask.
- Observe the client carefully for up to 60 minutes after the study for a possible (anaphylactic) reaction to the radionuclide.
- When urine is being discarded, rubber gloves should be worn for 24 hours after the procedure. Wash the gloved hands with soap and water before removing the gloves. Wash the ungloved hands after the gloves have been removed.
Client and Family Teaching
- Peripheral venipuncture is the only discomfort associated with this test.
- A physician trained in diagnostic nuclear medicine interprets the results.
- The total time for the procedure is approximately 2 hours.
- No fasting or premedication is required.
- The client will not be exposed to large amounts of radioactivity because only tracer doses of isotopes are used.
- Remove jewelry around the chest area.
- Meticulously wash your hands with soap and water after each void for 24 hours after procedure.
- Family members must wear rubber gloves when discarding the client's urine for 24 hours after the procedure if the family will be providing this care.
Factors That Affect Results
- Jewelry or metal objects in the x-ray field distort the results.
- The client must lie motionless throughout the scan for the most accurate results.
- Ventilation scans with 99mTc-DTPA require client cooperation with deep breathing and appropriate use of breathing equipment to prevent contamination with the radioactive gases.
- The scan results of clients with pulmonary parenchymal disease (such as pneumonia, emphysema, pleural effusion, tumors) will appear to demonstrate perfusion defect and simulate pulmonary embolism. Ventilation scans are hard to interpret in obstructive airway disease that interferes with the distribution of the radioactive gases.
- False-positive scan results occur in vasculitis, mitral stenosis, and pulmonary hypertension and when tumors obstruct a pulmonary artery with airway involvement.
- In pulmonary emboli, perfusion is decreased but ventilation is maintained. Diagnosis of pulmonary embolus cannot be made on the basis of a lung perfusion scan alone.
- In pneumonia, ventilation is absent.
- The perfusion scan immediately follows the ventilation scan. However, ventilation scans using krypton can be performed before, during, or after perfusion scans.
- Health care professionals working in a nuclear medicine area must follow federal standards set by the Nuclear Regulatory Commission. These standards include precautions for handling the radioactive material and monitoring of potential radiation exposure.
- Technetium half-life is 6 hours.
- See also Gas ventilation lung scan.