Ventilation/Perfusion Lung Imaging

Purpose:
  1. Primary reason - to determine if the patient has pulmonary embolism/i (PE)
  2. Can evaluate Chronic Obstruction Pulmonary Disease (COPD)
  3. Can evaluate lung function for the purpose of pneumonectomy (covered next semester)

To evaluate PE, it requires two lung procedures: Ventilation and Perfusion

  1. Ventilation - 133Xe (gas) - Covered next semester
    1. Dose - 10 to 20 mCi
    2. 5.3 day T1/2
    3. 80 keV gamma
    4. Nobel gas
    5. Allows for separation of peaks when imaging with 99mTcMAA

  2. Ventilation - 99mTcDTPA (aerosol)
    1. Dose
      1. 35 mCi if dose before perfusion (preferred method)
      2. 50 - 60 mCi if dosed after perfusion
    2. 6.02 hr T1/2
    3. 140 keV gamma
    4. Nebulized droplets that are less than 2.0 μm reach the alveoli
    5. It does not allow for separation of peak when imaging the perfusion study
  3. Ventilation can be done with radioactive gas - 81mKr or 133Xe and will be discussed next semester

  4. Perfusion - 99mTcMAA - see previous lecture
    1. Dose - 4 to 6 mCi
    2. Small particles used and is trapped by capillary blockage
    3. Size 10 - 90 microns at 90% with nothing greater than 150 microns at 10%
    4. Trapped in the arterioles of the lung
    5. Fewer than one arteriole is blocked for every 1000

Disease

  1. Pulmonary Embolism (PE)
    1. Originates from deep vein thrombi (DVT's) found in legs
    2. DVT's break off, move through the venous system and become trapped in the lungs
    3. When injecting MAA particles, the particles cannot pass the area that has a PE
    4. Results in a cold defect when imaged with MAA
    5. Ventilation shows normal uptake since the activity is in the bronchioles (PE does not trap the airway)
    6. Key point - PE appears cold in perfusion and hot in ventilation (mismatched defect)
    7. Symptoms of PE
      1. Shortness of breath/air (SOA)
      2. Sudden onset of chest pain
      3. Dyspnea
      4. Cardiac arrhythmias
      5. Drop in the patient's PO2 level (normal 90-110)
  2. Aerosol Ventilation


    1. Aerosol system
      1. Approximately 35 mCi of 99mTcDTPA is injected into the nebulizer (refer to diagram)
      2. O2 enters the nebulizer converting liquid (99m TcDTPA) into small liquid droplets
      3. The patient inhales and droplets coating the inside of the lungs
      4. The patient exhales and the remaining droplets and water vapor are trapped by the filter
      5. Note the one-way value in the diagram
      6. The system is shielded in a blue bucket
      7. Example of another aerosol system
      8. Below is a display of how a patient is dosed if he/she is on a ventilator. Extra tubing is added at the end of the system referred to as the "tail"

        9. Radio-aerosol administratoin with pateint on a ventilator


    2. Dosing the aerosol
      1. Usually, the patient breaths on this system five minutes
      2. After the ventilation process images are then taken at 150k counts per view or five minutes

    3. View may include: ANT, POST, LPO, RPO, LAO, RAO, LLAT, and RLAT

    4. This procedure is usually done before the Perfusion images (99mTcMAA)
      1. All images that are taken must match all the perfusion images taken (at the exact same angle)
      2. PE will show a mismatch defect(s) - hot in ventilation and cold in perfusion
      3. Usually, PE defects are segmental or subsegmental
      4. Usually, PE is multiple in occurrence
      5. COPD will show matched defect(s) - cold in ventilation and cold in perfusion
      6. Severe COPD will show clumping of the droplets in the lungs - "hot grapes" and may cause the study to be mis-read

      Aerosol Ventilation Procedure
      Xenon Ventilation Procedure
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