Introduction to Myocardial Perfusion Imaging (MPI)

  1. The literature will states that Myocardial Perfusion Imaging (MPI) contributes significantly to the diagnosing of coronary artery disease (CAD). MPI is able to assess
    1. Myocardial wall perfusion
    2. Tissue viability
    3. LV function via contractility and ejection fraction
    4. Has a role in determining patient outcome and predicting future cardiac events
  2. Radionuclides used in Nuclear Cardiology
    1. 82Rubidium infusion generator Imaging for the Detection of Coronary Artery (for more information on a Rb-82 generator)
      1. This is one of two positron agent approved by HCFA for reimbursement
      2. It can be used for stress and rest imaging with some limitation
      3. 13NH3 is the other approved agent
    2. 18FDG is another imaging agent that can be used to image the myocardium
      1. Not used with stressing a patient, but is applied in myocardial viability studies
      2. May actually be preferred over 201Tl (also used for viability)
    3. Isonitriles
      1. 99mTc-sestamibi (Cardiolite)
      2. Extract Fraction approximately ~65%
      3. Used in conjunction with stress testing
    4. BATO Compounds - 99mTc-teborosxine
      1. Extraction Fraction is greater than 90%
      2. T1/2 = 10 to 11 minutes with most of the activity gone within 21 minutes
      3. Used in conjunction with stress testing, however, it is currently unavailable
    5. Diphosphines
      1. 99mTc-tetrofosmin (Myoview)
      2. Extraction fraction approximately 54%
      3. Similar imaging characteristics when compared to sestamibi
      4. Used in conjunction with stress testing
    6. 201Tl
      1. Analog to K+ and becomes incorporated with the Sodium Potassium Pump of the heart
      2. Extraction fraction is approximately 87%
      3. Redistributes at rest
      4. Has greater attenuation when compared to the 99mTc agent. Why?
      5. Can be used in conjunction with stress imaging and/or for myocardial viability
  3. Comparing 201Tl to 99mTc-sestamibi and 99mTc-tetrofosmin

    4.  

    201Tl

    99mTc-sestamibi/99mTc-tetrofosmin

    Energy

    69 keV and 83 keV

    140 keV

    Dose

    < 4.0 mCi

    No > than 30 mCi

    Extraction Fraction

    87%

    58%

    Wall Motion

    Not recommended - low counting statistics

    Yes

    Protocol

    1 day

    1 or 2 day

    Injections

    1, however, a second dose prevents a 24 hr scan

    2

    Redistribution

    Yes

    Minor distribution post 2 hrs administration

    Dose and Count rate Low/Low High/High

    Attenuation Correction

    Gd-153 or CT

    Co-57 or CT

  4. How much Thallium reaches the heart?
    1. Only 5% of the dose goes to the myocardium
    2. 4 mCi is injected
    3. 87% is extracted
    4. Only 174 μCi reaches the myocardial tissue
    5. Question - If 30 mCi of sestamibi was injected, how much activity reaches the heart?
  5. How is Thallium-201 created
    1. 203Tl (p,3n) 203Pb
    2. 203 Pb decays for one T1/2 at 9.4 hours with 201Tl being the daughter product
    3. 201Tl is then chemically extracted
  6. Sodium-potassium pump
    1. 201Tl is thought to be K
    2. 201Tl is extracted
    3. 201Tl then washes out
  7. What are the advantages of 99mTc over 201Tl (apply the following concepts)
    1. Count density - statistics and noise
    2. Attenuation
    3. Extraction Fraction
    4. Gamma camera's crystal thickness
    5. Time to complete the study

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