cardiac scanning

NUCLEAR CARDIAC SCANNING

BY /DR.MAHRAN MOHAMMED

2. Ventricular Function

1. Myocardial Perfusion

3. Cardiac Metabolism and Myocardial Viability

4. Myocardial Innervation

Nuclear medicine methods in Cardiology are available for the evaluation of :

5. Infarct Imaging

MYOCARDIAL PERFUSION SCINTIGRAPHY

This test is designed to evaluate regional myocardial perfusion under rest and stress condition in order to define regional myocardial perfusion reserve.


It involves the injecton of a radiolabelled substance which is extracted by the myocardium and accumulates in proportion to myocardial blood flow.Such radipharmaceuticals are injected under stress as well as resting conditions, and images are obtained to define the regional distribution of radioactivity within the myocardium.


The main indication is the detection and localization

of myocardial ischaemia or scar.

MYOCARDIAL PERFUSION IMAGING

Clinical Indications

•Diagnosis of coronary artery disease - presence - location (coronary territory) -extent (number of vascular territories involved)•Determine prognosis•Determination of the significancof anatomic lesions detected by angiography.

•Monitoring treatment effect after coronary revascularization.


Determine prognosis risk stratification

*Patients with normal perfusion imaging after adequate stress have a very low cardiac event rate independently of the presence or absence of angiographic CAD (yearly rate of myocardial infarction or death of less than 1%).

*A benign prognosis is asociated with a small fixed defectand a normal global left ventricle function.


Determine prognosis risk stratification

* The risk of cardiac event can be suspected in all patients with the reversible perfusion defect.

* A higher risk can be expected in patients with a large perfusion defect, when more territories are affected, if the anterior wall is affected or if signs of postress dysfunction appear (transient ischemic dilation, deterioration of postress EF, increased uptake 201Tl in the lungs).


Myocardial ischaemia is defined as a perfusion defect present during stress but not resting conditions.Scar tissue is associated with a relative perfusion defect at rest as well as under stress.


RADIOPHARMACEUTICALS

99mTc-Labeled Myocardial Perfusion Agents

•99mTc-SESTAMIBI (MIBI, 2-methoxy-isobutyl-isonitril, Cardiolite, CardioSPECT…)• 99mTc-Tetrofosmin (Myoview)• 99mTc-Teboroxim (cardioTec)

201Thallium


99mTc-SESTAMIBI

•Is a lipophilic cationic Tc-99m complex - it enteres pasivelly into the cells and binds at the intracells membranes, especially of mitochondrials. - it does not wash out of the myocardium in 3-4 hours

Tc-99m-Labeled Myocardial Perfusion Agents

99mTc - gamma rays of energy 140 keV - half life T1/2 = 6 hours


201Thallium

- is an analog of potassium- it is actively transported into cardiac muscle via the sodium-potassium ATPase pump

- physical half-life is 73 h

- is a cyclotron-produced radiopharmaceutical

- emits x-rays of energy 69- to 83 keV - also emits gamma rays 167 kev 10%

Imaging protocol

• Single day protocol the patient receive a lower dose of radiopharmaceuticals

for the initial study (8-10 mCi ) and several fold higher dose (25-30 mCi )for the second study , which commences approximately 1.5 hour later to allow time for background activity ,biological clearance and decay.

• Tow day protocol The patient receive maximum dose (25-30mCi)for both

studies on separate days.Most commonly used on obese patients .

Exercise Stress

* is performed by cardiologist * graded stress is usually performed with bicycle ergometr * it is necessary to reach the gender and age predicted 85% maximal heart rate * suboptimal stress level reduce sensitivity of this procedure for detection of CAD * the radiopharmaceutical is injected 1-2 minut before end of exercise

Pharmacologic Stress

Patients who are unable to exercisefor non cardiac reasons - e.g.arthritis, amputation, neurologic diseases or cardiac reasons - with LBBBmay be stress pharmacologically .

Pharmacologic Stress

* vasodilators : adenosine dipyridamole* inotropic : dobutamine

Pharmacologic Stress using dipyridamole

* mechanism of action different from exercise* directly tests flow reserve* dipyridamol causes vasodilatation* normal vessel vasodilate, increasing flow five times* stenotic vessels are already maximally vasodilatated, cannot increase flow* results in heterogenity on scan * does not depend on induction of ischemia* Heart rate increases 13 beats per minute (20%)* Blood pressure decreases 6 mm Hg (2 ti 8%)* Contraindication: bronchial Asthma .

Pharmacologic Stress produced by dobutamine

* similar to exercise* indirectly tests flow reserve* increases myocardial oxygen consumption1) chronotropic effects2) ionotropic effects

Acquisition SPECT study Dual head gamma camera moves around the patient viewing the object in 180 degrees in 64 steps for 25 seconds

45 deg.RAO

135 deg. LPO

Initial Displayof selected study-Reconstruction

With ellipse we selectregion of the heartin anterior viewin left lateral view.

The selected data setsare processed.

We must alignment axes of heartfor creation of the vertical long and short axis tomograms

Summed image-added multiple projec-tion images

99m Tc-MIBI

slices in the short axis

slices in the long axis vertical

slices in the long axis horisontal

MYOCARDIAL ISCHEMIA

Can be identified by comparingthe results of exercise-injected studies and rest images .

As narrowing of coronary vessel approaches 70%lesion is hemodynamically significant during exercise.

99m-Tc-MIBI

Polar maps

Short axis slices are sequentially diplayed frombase to apex.

Conical myocardium is transformed into a disk.


INTERPRETATION CRITERIA

1. NORMAL FINDINGS

2. REVERSIBILE DEFECT - lesion is seen at stress and improves on the rest - is usually due to ischemia

3. NONREVERSIBILE DEFECT - lesion at rest is usually associated with myocardial scar or with severe ischemia.

NORMAL FINDING

57 yo MALE

REVERSIBILE DEFECT

NONREVERSIBILE DEFECT

GATED SPECT study

• ECG is acquired at the time of the SPECT acquisition • for simultaneous assessment of perfusion and function of the left ventricle in one examination evaluation of regional wall motion ejection fraction systolic thickening of the walls

GATED SPECT study

We obtain myocardial perfusion images within one representative cardiac cycle : from end-diastole through end-systole to end-diastole of next cardiac cycle

MYOCARDIAL VIABILITY

detection of myocardial viability has clinical importance for

- patients with chronic ischaemic left ventricular dysfunction and low left ventricle ejection fraction it is necessary to know, if defect of myocardial perfusion is

- ischemia vs. scar - predict improvement in function following revascularization

REQUIREMENTS FOR CELLULAR VIABILITY

-adequate myocardial blood flow-sarcolemmal metabolic integrity-preserved metabolic activity


The gold standard method

evaluation of myocardial glucose utilisation with fluorine-18 fluorodeoxyglucose (FDG)and positron emission tomography (PET)


Principle Under fasting conditions the normal myocardium primarily utilises free fatty acids. In ischaemic myocardium glucose becomes an important energy substrate, FDG uptake will be enhanced.

VIABLE MYOCARDIUMis characteristic in

NONREVERSIBILE PERFUSION DEFECT ( 99m-Tc MIBI) vs. PRESERVED MYOCARDIAL METABOLISM (18-FDG) = mismatch

99mTc MIBI

18FDG

non viable

match

viable

mismatch

- we can expect improvement in function following revascularization

SCARis characteristic in

NONREVERSIBILE PERFUSION DEFECT ( 99m-Tc MIBI) vs. NO PRESERVED MYOCARDIAL METABOLISM (18-FDG )

= match

99mTc MIBI

18FDG

nonviable

match

viable

mismatch

- we can´t expect improvement in function following revascularization

cardiac scanning

Health & Medicine

myocardial perfusion

myocardial viability

normal perfusion imaging

myocardial blood flow

exercise stress

relative perfusion defect

large perfusion defect

perfusion defect present