Principles of nuclear cardiology
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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

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Principles of nuclear cardiology

Principles of nuclear cardiology


History

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


Principles of nuclear cardiology

  • 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

SPECT single photon emission computed tomography


Basic concept

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

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


Spect perfusion tracers

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

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


Principles of nuclear cardiology

  • Differential washout-clearance is more rapid from normal myocardium

  • Hyperinsulinemic states reduce blood conc.&slow redistribution.so fasting recommended


Principles of nuclear cardiology

  • 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


Principles of nuclear cardiology

  • 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

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


Principles of nuclear cardiology

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


Principles of nuclear cardiology

  • 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

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

Radionuclide Properties


Stress protocols

Stress protocols


Principles of nuclear cardiology

  • 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

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

Visual Analysis of Perfusion SPECT

  • 0-normal uptake,

  • 1-mildly reduced uptake,

  • 2-moderately reduced uptake,

  • 3-severely reduced uptake, and

  • 4-no uptake


Principles of nuclear cardiology

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


Principles of nuclear cardiology

Ant

Stress

Apex

Inf

Rest

Septum  Lateral

Stress

Apex

Rest

Lat

Inferior  Anterior

Sep

Ant

Stress

Lat

Sep

Rest

Inf

Apex  Base

Normal


Principles of nuclear cardiology

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


Principles of nuclear cardiology

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


Interpretation of the findings spect

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)


Additional signs

Additional signs

  • Lung uptake of thallium

  • Transient ischemic dilatation of left ventricle


Thallium 201 lung uptake

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

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

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

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


Principles of nuclear cardiology

  • 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


Principles of nuclear cardiology

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


Gated spect

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.


Principles of nuclear cardiology

  • 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

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


Principles of nuclear cardiology

  • 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


Principles of nuclear cardiology

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

Perfusion tracers

  • Diffusible tracers-O-15-accumulate and wash out.

  • Non diffusible-Rb82,N13ammonia

  • Rb82-generator produced,t½76s.


Advantage of pet

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

Limitations

  • High cost

  • Requirement of cyclotron

  • Short half life-pharmacological stress only


Metabolic tracers

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


Principles of nuclear cardiology

  • 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


Principles of nuclear cardiology

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


Viability pet study

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


Principles of nuclear cardiology

*


Pet viability scan patterns

PET ViabilityScan Patterns

ContractilityPerfusionMetabolism

Normal NNN

Stunning- NN -

Hibernation

Scar


Guidelines

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 syndromes recommendations

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


Principles of nuclear cardiology

  • 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

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

    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 coronaryartery), post-stress LV (left ventricular) dysfunction (LV dilatation, abnormal wall motion, decreased LVEF, lung uptake)


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