Principles of nuclear cardiology

1. Principles of nuclear cardiology

2. 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

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

9. SPECT

10. 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

11. 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

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

15. 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

16. 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

18. 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

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

21. 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

22. 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

24. Radionuclide Properties

27. Stress protocols

30. Dipyridamole infusion for 4 min-isotope injection 3 min after infusion • Adenosine infusion for 6 min-isotope given 3 min into infusion

31. 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

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

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

38. Ant Stress Apex Inf Rest Septum  Lateral Stress Apex Rest Lat Inferior  Anterior Sep Ant Stress Lat Sep Rest Inf Apex  Base Normal

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

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

41. 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 septalwall), 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)

42. Additional signs • Lung uptake of thallium • Transient ischemic dilatation of left ventricle

43. 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

44. 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

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

46. 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

48. 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

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

50. 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.