Lung Perfusion

Overview

The macro-aggregated albumin perfusion nuclear medicine exam is very useful as an adjunct for evaluating regional pulmonary blood flow. The particles that are greater than 10 micrometers in size are trapped in the pulmonary alveolar capillary bed by a purely mechanical process. Areas of reduced perfusion are revealed by decreased photon density. The aggregated albumin particles are sufficiently fragile for erosion and fragmentation to reduce the particle size, thus allowing passage through the pulmonary alveolar capillary bed.

The fragments are then taken up by the reticuloendothelial system. Elimination from the lung occurs with a half-life of about five hours. This test is used in conjunction with the inhalation exam to rule out pulmonary emboli. If a defect is noted on the perfusion exam and is not seen on the same view in the aerosol study then an emboli is a high probability diagnosis. The aerosol will also show defects in the studies such as pneumonia, tumor, bronchiectasis and sometimes asthma.

Other conditions that might cause a defect in both studies are vasculitis, enlarged lymph nodes, COPD and neoplasm. All of these may cause a false positive perfusion exam, if it is interpreted without accompanying aerosol study and a chest x-ray. A chest x-ray must be obtained within 24 hours of the lung perfusion/aerosol study.

Indications

  • Diagnosis of pulmonary embolism.
  • Evaluation of regional pulmonary perfusion prior to lung reduction surgery.

Study Description

The patient will be injected intravenously with a radiopharmaceutical and asked to take deep breaths during infusion. Images will be taken shortly after. Injection should be done with the patient supine. Images will be taken from a variety of projections as the patient condition permits and will require 30-45 minutes. This test is used in conjunction with the aerosol inhalation exam.

Examination Time

  • 30-45 Minutes
  • 1 ½ hours if in conjunction with “Lung Aerosol/Ventilation” (normal protocol majority of the time)

Patient Preparation

  • Ensure the patient is not pregnant or breastfeeding.
  • A chest x-ray must be taken within 24 hours of the lung scan for comparison.
  • Contraindication: Patient with severe pulmonary hypertension, right to left shunt, pneumonectomy, and poor respiratory function.