CARDIAC NUCLEAR MEDICINE

MYOCARDIAL PERFUSION IMAGING

INDICATIONS:

This study can be done with exercise stress and delayed (resting) views, at rest only, or with drug-simulated stress (dipyridamole = DPM, adenosine = ADN) in those unable to perform treadmill exercise for the assessment of myocardial perfusion in a variety of clinical settings:

  1. Suspected coronary artery disease (CAD) in patients with an abnormal ECG.
  2. Suspected CAD in asymptomatic patients with positive exercise ECG.
  3. Suspected myocardial infarction (Resting Thallium).
  4. Thallium-201 DPM/ADN study: for evaluation of myocardial perfusion in patients unable to exercise.
  5. In others requiring assessment of coronary perfusion (pre-op evaluation, evaluation of viability for by-pass, etc.).
  6. Unexplained chest pain.
  7. Detection of viable myocardial tissues.

PATIENT PREPARATION:

  1. Patient is kept NPO at least 2 hours prior to examination.
  2. For stress exams:

i) Indwelling angiocatheter in arm.

ii) Between stress and delayed views very light food intake (e.g. chicken broth) and minimal physical exertion are allowed.

3. For DIPYRIDAMOLE/ADENOSINE Examinations:

i) The patient should not receive a dose of Theophylline for at least 48 hours prior to DPM thallium stress test.

ii) Caffeineated food and liquids should be avoided for 6 hours before and during the study.

RADIOPHARMACEUTICAL:

Thallium-201 chloride is given I.V. either with patient at rest or after treadmill stress or DPM infusion. Dose = 2.5 mCi. Critical Organ = kidneys 0.4 - 0.9 rad/mCi.

SCANNING TIMES:

RESTING (ONLY) THALLIUM: Imaging is begun 20 to 30 minutes after thallium injection and takes approximately 30 minutes.

EXERCISE (STRESS) THALLIUM: During the final stage of treadmill exercise (peak stress) the patient is injected with Thallium-201 chloride. Planar and SPECT imaging are obtained 10 minutes and 3 hours after the I.V. administration of thallium.

DIPYRIDAMOLE (DPM) THALLIUM: Patient is given DPM I.V. as a coronary vasodilator and carefully monitored for 20 minutes. Thallium-201 is then injected intravenously and scanning is performed the same as for exercise thallium.

Once images are acquired, the information must be computer processed. In general, the examinations are scheduled for early morning and the scans are ready for interpretation by mid-to-late afternoon the same day.

OTHER CONSIDERATIONS:

  1. Cardiology and Nuclear Medicine can be of great assistance in planning your patients' studies. Please feel free to contact the department for any questions
  2. The DPM/ADN Tl-201 study is useful for patients who cannot perform or tolerate treadmill exercise and should be arranged through the Nuclear Medicine Department.
  3. A resting-only thallium is useful for detection of infarction and is positive within the first 24 hours of injury.
  4. Failure to obtain adequate stress or administration of beta blockers can limit the examination's usefulness. Other drugs which cause decreased thallium uptake include Adriamycin, Digitalis, Lasix, Lidocaine, Nifedepine, and Ouabain.
  5. Tissues that fail to show significant wall motion can be checked for viability using a special protocol. Please be sure to request this protocol on patients where myocardial viability is an issue.

RATIONALE:

Thallium is a potassium analog and is taken up by viable myocardial cells via active transport (Na/K pump). This uptake depends on a adequate coronary blood flow; in fact, thallium distribution is linearly related to regional coronary perfusion. This is the basis for imaging. Since resting-state flow may be adequate in the presence of severe stenotic disease, the increased myocardial oxygen demand of exercise-testing is necessary to adequately assess the true state of the coronary circulation. DPM is a non-nitrate vasodilator that is used to simulate the physiologic effects of exercise. It causes increased flow in normal vessels but not stenotic vessels (these are already maximally dilated). Possible side effects of DPM include angina (although there is no increase in myocardial 02 demand), headaches and dizziness. Intravenous aminophylline will rapidly reverse these effects.