Mismatched Ventilation- Perfusion (V/Q) Scan
Multiple Bilateral Pulmonary Emboli

• A Ventilation-Perfusion (V/Q) scan is a
• diagnostic imaging test used to evaluate the
  • blood blow and
  • ventilation – air flow.
• It is commonly used for the diagnosis of
  • pulmonary embolism,

The V/Q scan involves two components:

• Ventilation
  • evaluates the airflow
    • patient inhales a radioactive gas or aerosol, and a
    • gamma camera detects the
      • distribution of this radioactive material  in the lungs.
      • helps assess the distribution or lack of distribution of
      • air in the lungs.
• Perfusion (Q):
  • evaluates the blood flow in the lungs.
    • radioactive material is injected into the bloodstream,
    • the camera captures images of the blood flow in the lungs.
    • helps assess the
    • distribution or
    • lack of distribution of
    • blood in the lungs
• The comparison of the ventilation and perfusion images
  • allows the identification of matched or mismatched perfusion and ventilation
    • mismatched areas
    • suggest the presence of a pulmonary embolism or other lung diseases.
    • Certainly, here’s an overview of Ventilation-Perfusion (V/Q) scans with information on indications, contraindications, advantages, disadvantages, aim, method, patient preparation, equipment, technique, results, and potential complications:Indications:
      1. Pulmonary embolism:
      2. Assessment of lung function: To evaluate ventilation and perfusion in patients with lung diseases such as chronic obstructive pulmonary disease (COPD).
      3. Preoperative evaluation: Especially in cases where lung surgery is planned.
      4. Assessment of lung transplant viability.
      5. Evaluation of pulmonary vascular diseases.

      Contraindications:

      1. Pregnancy: Radiation exposure may pose risks to the developing fetus.
      2. Known allergies: For patients allergic to the radioactive materials used.
      3. Severe respiratory distress: In some cases, the patient’s condition may make it challenging to perform the test safely.

      Advantages:

      1. Sensitivity: Can detect pulmonary embolism and other lung abnormalities.
      2. Non-invasive:
      3. Functional information: Provides information on both ventilation and perfusion in the lungs.

      Disadvantages:

      1. Exposure to radiation: Though the radiation levels are typically low,
      2. Limited anatomical detail: Compared to other imaging modalities like CT scans.
      3. Potential for false positives or negatives: Interpretation may be influenced by various factors.

      Aim: To assess and diagnose pulmonary embolism, evaluate lung function, and identify abnormalities in ventilation and perfusion.

      Method:

      1. Ventilation (V): Patient inhales a radioactive gas or aerosol, and a gamma camera captures images of the distribution of the inhaled substance in the lungs.
      2. Perfusion (Q): Patient receives an injection of a radioactive substance into the bloodstream, and the gamma camera captures images of the blood flow in the lungs.

      Patient Preparation:

      1. No special preparation: Usually, patients can eat and drink normally before the test.
      2. Avoidance of certain medications: Some medications may need to be stopped temporarily, depending on the specific protocol.

      Equipment: Gamma cameras, radioactive tracers (commonly technetium-99m), inhalation devices for ventilation component.

      Technique:

      1. Ventilation (V): Patient inhales the radioactive substance.
      2. Perfusion (Q): Patient receives an injection of the radioactive substance.

      Results: Comparison of ventilation and perfusion images to identify areas of mismatch, helping to diagnose pulmonary embolism or other lung conditions.

      Complications:

      1. Allergic reactions: Rare, but possible reactions to the radioactive substances.
      2. Radiation exposure: Minimal, but considerations for pregnant women.

V/Q scans are particularly useful when other imaging modalities, such as CT scans, are not feasible or contraindicated. However, advancements in imaging technology, including the widespread use of computed tomography pulmonary angiography (CTPA), have  reduced the frequency of V/Q scans in the diagnosis of pulmonary embolism. The choice of imaging modality depends on the specific clinical situation and the patient’s individual circumstances.

Prior to V/Q Scan CXR is Needed to Ensure there are No Other Reasons that Could Account for Perfusion or Ventilation Abnormalities

The Procedure

The Report

Correlation with CTPA