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Principles of nuclear cardiology

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1 Principles of nuclear cardiology

2 History Hermann blumgart-1927-injected radon to measure circulation time Liljestrand-1939-normal blood volume Myron prinzmetal radiolabelled albumin Hal anger-1952-gamma camera-beginning of clinical nuclear cardiology 1976-thallium201-two dimensional planar imaging

3 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

4 SPECT single photon emission computed tomography

5 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



8 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




12 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

13 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 min.after ,related to conc.gradient of thallium between myocyte and blood

14 Differential washout-clearance is more rapid from normal myocardium
Hyperinsulinemic states reduce blood conc.&slow fasting recommended



17 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

18 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


20 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 rate-larger body habitus

21 Tc99m tracers bound by mitochondria. limiyed washout occurs
Tc99m tracers bound by mitochondria.limiyed washout imaging can commence later and can be repeated


23 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

24 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


26 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



29 Stress protocols



32 Dipyridamole infusion for 4 min-isotope injection 3 min after infusion
Adenosine infusion for 6 min-isotope given 3 min into infusion

33 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

34 Visual Analysis of Perfusion SPECT
0-normal uptake, 1-mildly reduced uptake, 2-moderately reduced uptake, 3-severely reduced uptake, and 4-no uptake



37 bull̒s eye polar plot-two dimensional compilation of all three dimensional short axis perfusion data



40 Normal Apex Septum  Lateral Stress Rest Inferior  Anterior Ant Lat
Apex  Base Apex Septum  Lateral Inferior  Anterior Stress Rest

41 at stress and disappears during rest
Ant Inf Lat Sep Apex  Base Apex Septum  Lateral Inferior  Anterior Stress Rest Reversible Ischeamia, defect appears at stress and disappears during rest

42 Fixed Scar, defect is seen in both stress and rest
Ant Inf Lat Sep Apex  Base Apex Septum  Lateral Inferior  Anterior Stress Rest Fixed Scar, defect is seen in both stress and rest

43 Interpretation of the Findings-SPECT
Stress Rest Interpretation No defects No defects Normal Defect No defect Ischemia Defect Defect Scar/ hibernating 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 (Stress-induced ischemia)

44 Additional signs Lung uptake of thallium
Transient ischemic dilatation of left ventricle

45 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

46 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

47 Variations Dropout of the upper septum Apical thinning
Lateral wall may appear brighter than septum Minimised by review of series of normal volunteers

48 Technical artifacts Breast attenuation- Inferior wall 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


50 LBBB- HCM- 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

51 Combined SPECT/CT or PET/CT scanners-complementary anatomical and functional information

52 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.

53 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




57 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




61 First pass RVG-i. v injected radioactive tracer passes through rt
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

62 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


64 Perfusion tracers Diffusible tracers-O-15-accumulate and wash out.
Non diffusible-Rb82,N13ammonia Rb82-generator produced,t½76s.

65 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

66 Limitations High cost Requirement of cyclotron
Short half life-pharmacological stress only

67 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

68 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

69 Enhanced FDG uptake relative to blood flow referred to as PET mismatch pattern indicative of viable myocardium



72 Cellular membrance integrity
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) Cellular membrance integrity Glucose metabolism

73 * PET with 13N-ammonia and 18F-FDG to assess
myocardial viability (26). Regional myocardial 18F-FDG uptake is disproportionately enhanced compared with regional myocardial blood flow; this pattern is termed perfusion–metabolism mismatch and is indicative of hibernating myocardium

74 PET Viability Scan Patterns
Contractility Perfusion Metabolism Normal N N N Stunning - N N - Hibernation Scar





79 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




83 Chronic syndromes-recommendations
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

84 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

85 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




89 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)

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