Download PRINCIPLES OF NUCLEAR CARDIOLOGY.ppsx

Principles of nuclear cardiology
History
• Hermann blumgart-1927-injected radon to
measure circulation time
• Liljestrand-1939-normal blood volume
• Myron prinzmetal-1948- radiolabelled
albumin
• Hal anger-1952-gamma camera-beginning of
clinical nuclear cardiology
• 1976-thallium201-two dimensional planar
imaging
• 1980s-SPECT using rotating anger camera
• 1990-technetium99m based agents and gated
SPECT
• 90% of SPECT in U.S use technetium and 90%
are gated SPECT
SPECT
single photon emission computed tomography
Basic concept
• Intravenously injected radiotracer distributes
to myocardium proportional to blood flow
• Gamma camera captures the photons,
converts to digital data and displays it as a
scintillation event
• Parallel hole collimator-better localisation of
source
• Photomultiplier tubes-conversion of signals
• Final result-multiple tomograms of radiotracer
distribution
SPECT image display
• Short axis images-perpendicular to long axis of
the heart,displayed from apex to base
• Vertical long axis-parallel to long axis of heart
and parallel to long axis of body
• Horizontal long axis-parallel to long axis of
heart,perpendicular to VLA slice
SPECT
SPECT perfusion tracers
• Thallium 201
• Technetium–99m
– Sestamibi (Cardiolyte)
– Tetrafosmin (Myoview)
– Teboroxime
• Dual Isotope
– Thallium injected for resting images
– Tech -99m injected at peak stress
Thallium-201
• Monovalent cation,property similar to
potassium
• Half life 73 hours,emits 80keV photons,t½
73hrs,85% first pass extraction
• Peak myocardial concentration in 5 min, rapid
clearance from intravascular compartment
• Redistribution of thallium-begins 10-15
min.after ,related to conc.gradient of thallium
between myocyte and blood
• Differential washout-clearance is more rapid
from normal myocardium
• Hyperinsulinemic states reduce blood
conc.&slow redistribution.so fasting
recommended
• Thallium protocols– Stress protocols-injected at peak stress and
images taken at peak stress and at 4 hrs,24hrs
– Reversal of a thallium defect marker of reversible
ischemia
– Rest protocols-thallium defect reversibility from
initial rest images to delayed redistribution images
reflect viable myocardium with resting
hypoperfusion
– Initial defect persists-irreversible defect
• Stress/redistribution/reinjection method
commonly used
• Reinjection if fixed defects seen at 4 hrs
• Timing of stress image-early
• Rest redistribution image for resting
ischemia/viability
Technetium-99m labelled tracers
• Half life 6 hrs,140keV photons,60% extraction
• Uptake by passive distribution by gradient
• Minimal redistribution-require two separate
injections-one at peak stress and one at rest
• Single day study-first injected dose is low
• Two day study-higher doses injected both rest
and stress-optimise myocardial count ratelarger body habitus
• Tc99m tracers bound by mitochondria.limiyed
washout occurs.so imaging can commence
later and can be repeated
• 2 day image protocol better for image quality
• Most common-same day low dose rest/high
dose stress-disadvantage is reduction in stress
defect contrast.
• Viability assessment improved by NTG prior to
rest study
Dual isotope protocol
• Anger camera can collect image in different
energy windows
• Thallium at rest followed by Tc 99m tracer at
peak stress
• If there is rest perfusion defect,redistribution
imaging taken either 4 hrs prior or 24hrs after
Tc99m injection
Radionuclide Properties
Property
Thallous Chloride
Tc-Sestamibi
Chemistry
+1 cation, hydrophilic
+1 cation, lipophilic
half life
73 hrs
6 hours
Photon energy
68-80 keV
140 keV
Uptake
Active: Na-K ATPase
pump
Passive diffusion (if
intact membrane
potentials)
Extraction fraction
85%
66%
Heart uptake
4%
1.2%
Redistribution
Redistributes
Fixed
Stress protocols
• Dipyridamole infusion for 4 min-isotope
injection 3 min after infusion
• Adenosine infusion for 6 min-isotope given 3
min into infusion
Interpretation and reporting
• Myocardium devided into 17 segments on the
basis of 3 short axis and a long axis slice
• Perfusion graded from 0(normal perfusion) to
4(no uptake)
• SSS-summed stress score-stress perfusion
abnormality
• SRS –summed rest score-extent of infarction
• SDS-summed difference score-stress induced
ischemia
Visual Analysis of Perfusion SPECT
•
•
•
•
•
0-normal uptake,
1-mildly reduced uptake,
2-moderately reduced uptake,
3-severely reduced uptake, and
4-no uptake
• bulls̒ eye polar plot-two dimensional
compilation of all three dimensional short axis
perfusion data
Normal
Ant
Stress
Apex
Inf
Rest
Septum  Lateral
Stress
Apex
Lat
Sep
Rest
Inferior  Anterior
Ant
Stress
Lat
Sep
Rest
Inf
Apex  Base
Ant
Stress
Apex
Rest
Inf
Septum  Lateral
Stress
Apex
Lat
Sep
Rest
Inferior  Anterior
Ant
Stress
Lat
Sep
Rest
Inf
Reversible Ischeamia, defect
appears
at stress and disappears during rest
Apex  Base
Ant
Stress
Apex
Rest
Inf
Septum  Lateral
Stress
Apex
Lat
Sep
Rest
Inferior  Anterior
Ant
Stress
Lat
Sep
Rest
Inf
Apex  Base
Fixed Scar, defect is seen in both stress and rest
Interpretation of the Findings-SPECT
Stress
• No defects
• Defect
Rest
Interpretation
No defects
Normal
No defect
Ischemia
• Defect
Defect
Scar/
hibernating
(Stress-induced
ischemia)
• Defect location (anterior, posterior, lateral, or septal wall),
size (small, medium, or big), severity (mild, moderate,
absent), degree of reversibility at rest (completely
reversible, partially reversible, irreversible)
• Regional wall motion, EDV, ESV, EF
Additional signs
• Lung uptake of thallium
• Transient ischemic dilatation of left ventricle
Thallium-201 Lung Uptake
• ↑ lung uptake of thallium following stress -marker of severe
CAD,elevation of PCWP,↓EF
• ↑PCWP-slow pulmonary transit-more extraction
• Minimal splanchnic uptake,early image after stress-lung
uptake more apparent in thallium
• More liver uptake,delayed imaging-lung uptake missed with
Tc99m
TID: transit Ischemic Dilation (Stress
induced LV Cavity Dilation)
• Severe, extensive CAD (usually with classic ischemic defect)
Left Main
Prox LAD
MVD
diffuse subendocardial ischemia
Variations
•
•
•
•
Dropout of the upper septum
Apical thinning
Lateral wall may appear brighter than septum
Minimised by review of series of normal
volunteers
Technical artifacts
• Breast attenuation– Minimised by Tc99m agents,ecg gated SPECT
– Presence of preserved wall motion and thickening
• Inferior wall attenuation
– Diaphragm overlapping inferior wall
– Minimised by gated SPECT,prone position
• Extracardiac tracer uptake
– Repeat imaging,drink cold water to clear tracer
from visceral organs
• LBBB– isolated reversible perfusion defects of septum
– Heterogeneity of flow b/w LAD &LCx due to
delayed septal relaxation
– Reduced O2 demand due to late septal
contraction,when wall stress is less
• HCM– due to ASH,appearance of lateral perfusion defect
• Combined SPECT/CT or PET/CT scannerscomplementary anatomical and functional
information
Gated SPECT
• Simultaneous assessment of LV function and
perfusion
• Each R-R interval is devided into prespecified
number of frames
• Frame one represent end diastole,middle
frames end systole
• An average of several hundred beats of a
particular cycle length acquired over 8-15 min.
• Normal regional systolic function-brightening
of wall during systole
• Quantitative analysis of LV function-three
dimensional display representing global LV
function created by information from all
tomographic slices-EF and LV volumes
calculated
Radionuclide ventriculography
• MUGA scanning-multiple gated acquisition
– Tc 99m labelled r.b.c or albumin
– Image constructed over an average cardiac cycle
by e.c.g gating,16-32 frames /cycle
– Image acquired in antr.,LAO, left lateral
projections
– Size of chambers,RWMA,LV function
– Time activity curve-LV volumes
• First pass RVG-i.v injected radioactive tracer
passes through rt.chambers-lungs-lt.chambers
• Tc99m DTPA preferred
• RAO projection
• 2-5 cycles summed for RV phase,5-7 for LV
phase
• Time activity curves generated-quantitative
analysis
PET
• Radiotracers labelled with positron emitting
isotopes
• Perfusion tracers-Rb82 and n13 ammonia
• Metabolic tracer-F18 FDG
• Beta decay-positron emission
• Annihilation-collide with electron-give two
gamma rays of 511keV-travel in opp.direction
• PET scanner detects opposing photons in
coincidence-spatial and temporal resolution
Perfusion tracers
• Diffusible tracers-O-15-accumulate and wash
out.
• Non diffusible-Rb82,N13ammonia
• Rb82-generator produced,t½76s.
Advantage of PET
• Higher spatial resolution
• Improved attenuation correction
• Quantification regional blood flow
– SPECT may fail to detect balanced ischemia in multivessel
CAD
– ↓blood flow reserve by PET –early identification of CAD
• Higher sensitivity and specificity(95%)for detection
of CAD
Limitations
• High cost
• Requirement of cyclotron
• Short half life-pharmacological stress only
Metabolic tracers
• C-11 palmitate
• I-123 BMIPP-Ischemic memory-fatty acid
metabolism suppressed for longer time after
an ischemic event
• F18 FDG-imaging myocardial glucose
utilisation with PET
– Phosphorylated and trapped in myocardium
– Uptake may be increased in hibernating but viable
myocardium
• FDG uptake in regions with reduced blood
flow at rest –marker of hibernation
• FDG studies performed after 50 to 75 gm
glucose loading 1-2 hrs prior to injection
– ↑glucose metabolism,FDG uptake and improves
image quality
• Enhanced FDG uptake relative to blood flow
referred to as PET mismatch pattern indicative
of viable myocardium
Viability PET Study
• Traditionally the gold standard
• Two sets of resting images to detect viable and
hibernating myocardium:
– Perfusion image (usually with N-13 ammonia or
rubidium-82)
– Glucose metabolic image (with F-18
fluorodeoxyglucose = FDG)
*
PET Viability
Scan Patterns
Normal
Stunning
Hibernation
Scar
Contractility
N
Perfusion
N
-N
Metabolism
N
N-
Guidelines
• Acute syndromes
– Assessment of patients presenting to ED with
chest pain
– Diagnosis of AMI when other measures non
diagnostic-Tc99m
– Risk assessment,prognosis in AMI
– Risk assessment,prognosis in NSTEMI/UA
Chronic syndromesrecommendations
Class1• Exercise SPECT for identifying location ,severity of
ischemia in pts without baseline ECG
abnormalities that interfere with ST seg.analysis
• Adenosine SPECT for LBBB,paced rhythem,unable
to exercise
• To assess functional significance of an
intermediate coronary lesion(25-75%)
• Intermediate duke TMT score
• Rpt.MPI for recent change of symptoms
• Class 2a– 3-5 yrs after revascularisation in asymptomatic
patients
– As initial test in high risk patients(>20% 10yr risk)
• Class 2 b– Pts with cor.calcium score more than 75 percentile
– Asymptomatic pts.high risk occupation
Indications for PET for risk stratification of patients
with intermediate likelihood of CAD
CLASS1– SPECT study equivocal
• Class 2a– As initial test in patients unable to exercise
– As initial test in pts. With baseline ECG
abnormalities
Risk Stratification
• Normal perfusion imaging after adequate
stress: very low cardiac event rate < 1%
• Small fixed defect with normal global LV
function: good prognosis
• High risk: (reversible defects) more than
one territory, LAD (most important coronary
artery), post-stress LV (left ventricular)
dysfunction (LV dilatation, abnormal wall
motion, decreased LVEF, lung uptake)