Nuclear cardiology uses radiolabeled tracers and imaging techniques to provide functional data on myocardial perfusion and viability. The main types of studies are myocardial perfusion imaging using thallium-201 or technetium-99m sestamibi, blood pool imaging with technetium-99m, and infarct imaging. Myocardial perfusion imaging can detect ischemia and scar tissue and has prognostic value. Newer techniques like SPECT and PET provide higher quality images but some techniques like thallium redistribution imaging remain important clinically.

1. Nuclear
Cardiology
Frank Meissner, MD, FACP, FACC, FACP
Chief of Cardiology

2. General Appoach
●IV administration of radiolabeled
agents
●Scintillation or positron camera
●Computer processing
●Physiologic/functional data, rather
than structural/anatomic
●e.g., Myocardial perfusion imaging is
prognostically more important than
classification by angiography

3. Types of Studies/Agents
●Myocardial Perfusion Thallium-201
(201Tl), technetium-99m sestamibi
●Blood Pool/First Pass Tc 99m
pertechnetate
●Myocardial Infarct
●PET

4. Myocardial Perfusion
-Thallium 201 imaging
●Intracellular transport by passive and
active mechanisms
●Early myocardial uptake directly
proportional to regional myocardial
blood flow and myocardial extraction
fraction

5. Myocardial Perfusion
-Thallium 201 imaging
●After initial phase continuous
exchange of myocardial 201Tl and
extracardiac 201Tl
●This process of continuous
exchange is the basis of 201Tl
redistribution
●Thallium, metallic element group IIIA
- periodic table

6. Thallium Redistribution
●Defined as total or partial resolution
of initial postexercise defects
●Reimaging at 2.5 to 4 hrs after tracer
injection
●Late reimaging is performed when
defects are believed to be due to
severe ischemia

7. Technical Considerations
●2.5 to 3.0 mCi of 201Tl via IV cannula
●End-points: angina , dyspnea,
fatigue, claudication, hypotension
●Exercise 30 to 45 s so that initial
myocardial uptake reflects peak
exercise
●Image within 5 minutes post exercise

8. Thallium TMT interpretation
●Decreased 201Tl uptake ischemia or
scar
●Reversible defects = ischemia
●30% of persistent defects = severe
ischemia rather than scar
●Reinjection protocols reveals
reversibility in 40% of 4 hr ‘defects’
●24 hr redistribution imaging show
reversibility in 20-25% of ‘fixed’ 4

9. Sensitivity/Specificity
Considerations
●Qualitative visual 201Tl using planar
imaging sensitivity and sensitivity of
84 & 87% respectively
●Quantatively analysis (computer
assistance) 90% sensitivity &
specificity
●Spect 201 Tl increased sensitivity
with decreased specificity

10. SPECT ADVANTAGES
●Images free of background
●Lesion contrast higher
●Localization of defects is more
precise and more clearly seen by the
inexperienced eye
●Extent and size of defects better
defined

11. Sensitivity Factors
●Left circumflex lesions difficult to ID
●Branch stenoses of arteries more difficult
●Sensitivity for single vessel disease <<
sensitivity for multivessel disease
●Less sensitive suboptimal exercise
●Not influcenced by antianginal drugs
●NOT a good test post-CABG

12. HIGH RISK Characteristics
●Multiple 201 Tl defects in multiple
vascular regions
●Increased Lung uptake (defined by
lung/heart ratio > .5)
●Exercise induced transient LV
dilatation

13. PROGNOSTIC
Characteristics
●Presence of reversible defects worse
prognosis than fixed defects
●Total number of defects best
prognositic indicator vs Presence of
Lung uptake (reported as POORER
prognosis than total segments)
●Chest Pain + TOTALLY normal 201Tl
scans < 1% yrly risk of sudden death

14. Resting Thallium
●Useful technique for case selection in
patients with depressed LVEF & CAD
●‘Hibernating’ myocardium preserved
201Tl uptake at rest
●IV 201Tl imaged at 20 mins and 4 hours
●Resting hypoperfusion will demonstrate
initial defects that fill with redistribution
●Asynergy with preserved 201Tl uptake
improved systolic function post-Bypass

15. 201Tl Limitations
●Breast tissue attenuates tracer
penetration
●Large RV blood pool overlying inferior
wall on Anterior Projection => artifact
●High left Hemidiaphragm overlying post
wall
●SPECT imaging relatively less than 201Tl
activity in the inferobasilar segments on
short axis images

16. 99mTc sestamibi Imaging I
●Lipophilic cationic 99mTc-complex
whose myocardial uptake
proportional to blood flow
●140 keV photon energy peak is
optimized for gamma camera
imaging
●Produces higher quality images than
those produced by 201Tl

17. 99mTc sestamibi Imaging II
●Shorter half life than 201Tl permits
administration of 10-15 X’s as high a
dose of tracer than 201Tl
●Gated acquisition of SPECT allows for
animation and rgn wall motion
analysis
●First PASS acquisition can yield LVEF
at rest or exercise with animation for
MUGA like scans done prior to

18. 99mTc-sestamibi Technical
Characteristics
●Does NOT redistribute after injection
●Separate injections during stress and resting
states
●Ideal protocol is 24 hours between rest and
stress
●However, current practice is to inject and
image rest followed by Stress images
●Increased photon energy defeats attenuation
& artifacts

19. Sensitivity & Specificity
●Sensitivity is reported at 85-90%
range
●Increased specificity with superior
image quality and decreased image
artifacts
●Some authors report more
individually stenosed arteries are
dected by sestabmibi SPECT than

20. Pharmacologic Stress
Imaging
●Useful for patients UNABLE to exercise to
reasonable double products
●Adenosine vs dipyridamole protocols
●Critical coronary stenosis detected by
reduced flow reserve in stenotic area
●Degree of vasodilatation is less relative to
increase in flow in normal segments
●Sensitivity and specificity is comparable to
that reported with exercise protocols

21. Dipyridamole Stress
Imaging: Cavets/Technique
●NO caffeinated beverages for 12 hrs prior to
the test
●NO use of Theophylline compounds
●0.56 mg/kg dipyridamole infused over 4
minutes
●3.0 mCi 201Tl injected at 9 minutes, with
intial images at 5 mins post injection
●Aminophylline (50-100 mg IV) for systemic
hypertension, chest pain, severe nausea

22. Adenosine Stress Imaging:
Technique
●IV adenosine 140ug/kg/min for 6
minutes
●3 mins after starting infusion inject
with 3.0 mCi dose of 201Tl in
contralateral vein
●Additional 3 minute infusion of
adenosine

23. USEFULNESS of
Pharmacological stress
testing
●Predominately for PreOp eval of
vascular surgical patient
●Preoperative 201Tl defects
experience a 7X > periorperative
ischemic event rate
●PATIENTS WITH RECURRENT
ANGINA AT REST should NOT
receive pharmacological stress

24. Radionuclide angiography
●Blood pool imaging rather than
myocardial avid tracers
●Information obtained is identical to
that of contrast ventriculography
●In vivo labeling with 99mTc
●IV stannous pyrophosphate is
injected 15-20 mins prior to 15-30
mCi of 99mTc

25. Uses I
●Differentiation of ischemic from
nonischemic cardiomyopathy
●Cancer patient monitoring for
doxorubicin by serial estimate of EF
●RV fxn and size with first pass for
suspected RV infarction
●RV dynamics in COPD

26. Uses II
●Bicycle ergometry for detection of
CAD
●Timing of valve replacement in
regurgitant valvular disease - serial
studies
●Post MI risk stratification

27. First Pass Imaging
●Single bolus of 99mTc is injected rapidly via
IV (preferably central line)
●Analysis is limited to intial transit
Multicrystal scintillation camera prefered to
single-crystal Anger Camera, since high
count
●Rates (up to 400,000 counts/sec) can be
obtained with multiple crystal cameras

28. Equilibration Imaging I
●Multiple Gated Acquisition Scan (MUGA)
●Equal subdivisions of the patients
cardiac cycle
●Generally 30-50ms framing interval at
rest or 20-30 ms for exercise study
●200 successive cardiac cycles, with
R-wave gating

29. Equilibration Imaging II
●Several algorithms and methods to
deal with R-R wave variability
●DO NOT SEND A Fib or
Bigemy/Trigemeny patient to MUGA
●Time Activity Curve - Relative volume
curve
●Displayed with activity in LV vs time
●Change in activity is proportional to
change in LV volume

30. Data Obtained
●LVEF
●RVEF
●Peak systolic ejection rate
●Regurgitant fraction
●Diastolic filling time
●Left to right intracardiac shunts
●Phase analysis

31. MUGA Advantages
●Highly reproducible EF
●Able to image patients NOT well seen
with Echo
●NO geometric assumptions are made
in the calculation of EF (MOST
IMPORTANT ADVANTAGE)
●Wall motion analysis is VERY
comparable to ECHO & LV-gram

32. Myocardial infarction
imaging
●Radiopharmaceutical is preferentially
sequestered in necrotic myocardial tissue
●Yields a hot spot on the scan
●99mTc pyrophosphate first agent used
●Scan is abnormal 12-24 hours after MI
●Recent interest in indium-111(111In)
antimyosin antibodies

33. Technique
●Fab fragments of antimyosin
antibodies labeled with 111In
●Images obtained one hour after
injection

34. Clinical Uses
●NOT useful for routine patients
●Late patients (>2 days from Chest
pain with negative enzymes and
equivocal EKG’s)
●Surgical MI’s, i.e., patient felt to have
MI in OR
●Acute Myocarditis
●Acute and chronic allograft rejection

35. PET
●Positron emission tomography
●Imaged with short half life positron
emitors such as carbon-11 (11C),
nitrogen-13 (13N), oxygen-15 (15O),
fluorine-18 (18F), and rubidium-82
(82Rb)
●Generator produced half lifes of 75
seconds to 2 minutes

36. Uses
●Research TOOL ONLY
●For testing purposes the hallmark of
Myocardial Viability in ‘stunned’ or
hibernating myocardium is increased FDG
(18F, 2-fluoro-2-deoxyglucose) activity in
myocardial tissue
●Diminished perfusion with increased FDG
activity is due to glycolysis
●Diminished perfusion with diminished FDG
activity implies NO viability

37. THE
END