A lung scan, also known as a ventilation/perfusion (VQ) scan, is performed for three major purposes:

1. To diagnose and locate pulmonary emboli

2. To detect the percentage of the lung that is functioning normally

3. To assess the pulmonary vascular supply by providing an estimate of regional pulmonary blood flow

Lung imaging in both adults and children is done to assess pneumonia, cystic fibrosis, cyanosis, asthma, airway obstruction, infection, inflammation, and AIDS-related pulmonary diseases. It is a simple method for monitoring the course of embolic disease because an area of ischemia persists after apparent resolution on chest x-rays. In the case of pulmonary embolus, the blood supply beyond an embolus is restricted. Imaging results in poor or no visualization of the affected area. Assessment of the adequacy of pulmonary artery perfusion in areas of known disease can also be done reliably as well as after lung transplantation to detect reperfusion of lung and bronchiolitis obliterans.

There are two parts to the lung scan: the ventilation scan and the perfusion scan. The ventilation scan reveals the movement or lack of air in the lungs. An aerosol of ^99mTc-DTPA or xenon 133 (¹³³Xe) gas demonstrates the ventilation properties of the patient’s lungs. The perfusion scan demonstrates the blood supply to the tissues in the lungs.

For the ventilation scan, the radioactive gas or aerosol is inhaled and follows the same pathway as air with normal breathing. With some pathologic conditions affecting ventilation, there is significant alteration in the normal ventilation process. This is significant in the diagnosis of pulmonary embolism (PE). It is also helpful in diagnosing bronchitis, asthma, inflammatory fibrosis, pneumonia, chronic obstructive pulmonary disease (COPD), and lung cancer.

The perfusion scan can be performed after the ventilation scan. A macroaggregated albumin (MAA) labeled with technetium is injected intravenously, and assessment of the pulmonary vascular supply is achieved by scanning.

A pulmonary arteriogram is necessary before an embolectomy can be attempted. A PE is determined by a mismatch between the ventilation and perfusion scans. In other words, a normal ventilation scan and an abnormal perfusion scan with segmental defects indicate PE.

1. Ask the patient to breathe for approximately 4 minutes through a closed, nonpressurized ventilation system. During this time, administer a small amount of radioactive gas or aerosol. It is important that the patient not swallow the radioactive aerosol during the ventilation portion of the lung scan. Doing so causes radioactive interference with the lower lobes of the lung and makes an accurate diagnostic interpretation difficult. Also, take care that the patient does not aspirate the aerosol.

2. Alert the patient that breath-holding will be required for a brief period at some time during the imaging.

3. The imaging time is 10–15 minutes. When the ventilation scan is performed with a perfusion scan (e.g., in differential diagnosis of PE), the testing time is 30–45 minutes.

4. Perform the perfusion scan immediately after the ventilation scan.

5. For the pediatric patient, reduce the number of particles given in the MAA dose because of the smaller size of the capillary beds. Use caution with MAA in patients with atrial and ventricular septal defects.

6. See Chapter 1 guidelines for safe, effective, informed intratest care.

1. Abnormal ventilation and perfusion patterns indicate possible:

   1. Tumors

   2. Emboli

   3. Pneumonia

   4. Atelectasis

   5. Bronchitis

   6. Asthma

   7. Inflammatory fibrosis

   8. COPD

   9. Lung cancer

2. For pediatric patients, there is an increased incidence of an airway obstruction caused by mucus plugs or foreign bodies. However, PE does not occur in children as often as in adults.

Pretest Patient Care

1. Explain the purpose, procedure, benefits, and risks of the test.

2. Alleviate any fears the patient may have concerning nuclear medicine procedures.

3. Ensure that a recent chest x-ray is available.

4. Remember that the patient must be able to follow directions for breathing and holding the breath, including breathing through a mouthpiece or into a facemask.

5. Refer to standard NMI pretest precautions.

6. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

1. False-positive images occur with vasculitis, mitral stenosis, and pulmonary hypertension and when tumors obstruct a pulmonary artery with airway involvement.

2. During the injection of MAA, care must be taken that the patient’s blood does not mix with the radiopharmaceutical in the syringe. Otherwise, hot spots may be seen in the lungs.

Normal

Normal functioning lung

Normal pulmonary vascular supply

Normal gas exchange