Nuclear Cardiology Lecture to Housestaff

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