Nuclear - Essentials of Cardiac PET, Perfusion, Viability Flashcards

Question

Describe the steps in a Rest/Stress-FDG Viability: PET-CT Protocol

Answer 1

* Rest and/or Stress Perfusion * Glucose manipulation - 60-90 minutes * Trutol (oral glucose) * Based on BG levels --\> IV insulin to drive glucose intracelluarly * Blood glucose \< 150 --\> proceed to next step * 10-15 mCi FDG injection * Cellular uptake - 60 minutes allowed * FDG imaing - 15 minutes

Answer 2

Fixed defects on MPI * **Perfusion/Metabolism mismatch --\>** Hibernating myocardium * Perfusion/Metabolism match --\> Scarred myocardium

Answer 3

**Stress study (dobutamine)** * normal resting perfusion = viable myocardium **Myocardial stunning - severe CAD** * Severe defect of LAD territory - completely reversible at rest * may be cause of CHF

Answer 4

* Perfusion * more sensitive * less specific * Contractile function * more specific * less sensitive

Answer 5

* Sensitivity * Perfusion techniques \> contractile assessments * Most sensitive: **FDG PET** * Most specific: **DSE**

Answer 6

* myocardial blood flow cannot distinguish viable from non-viable segments * among segments classificed as non-viable in the thallium study, 23-35% (R-R, or R-R-RI) are classified as viable by FDG PET

Answer 7

* Hypoxia, ischemia, insulin --\> **overexpression of GLUT 4 receptors** * causes increased uptake of glucose / FDG-F18 * hibernating cells consume more glucose/FDG-F18 than normal cells * Fatty acid metabolism (β-oxidation) extremely sensitive to hypoxia * Hibernating myocytes do not utilize fatty acids --\> **selective overuse of glucose**

Answer 8

**GLUT 4 translocation/overexpression** * hypoxia * ischemia * insulin

Answer 9

**to improve uptake in normal segments that serve as reference**

Answer 10

* Baseline LVEF (lower is worse) * Magnitude of myocardial scar (larger is worse) * Degree of remodeling of the LV (larger is worse) * Time to revascularization (delay \> 42 days is worse)

Answer 11

**\> 10% viable myocardium**

Answer 12

* Identify microvascular dysfunction * Improve assessment of balanced ishcemia and extensive CAD * Assess response to therapy

Answer 13

FDG F18 PET

Answer 14

**the first sample of the day eluted from the Rb-82 generator is examined for "breakthrough" of radionuclide contaminants** * Strontium 82 and Strontium 85 can both be found as contaminants

Answer 15

* small portable generator * contains Strontium-82 ("parent" radionuclide) * absorbed onto a SnO2 column * washed (eluted) off the column using normal saline

Answer 16

* radioactive analog of potassium * relies upon Na-K ATPase transporter for cellular uptake

Answer 17

**C11-acetate** * marker of myocardial oxidative substrate metabolism * in clinical studies of patients with CAD * rates of C11-acetate clearance have proven useful for identifying dysfunctional myocardial segments * which will exhibit an improvement in function followin revascularization * Because C11-acetate has a high first pass myocardial extraction fraction * images obtained early following tracer injection can also be used to measure regional tissue blood flow, in mL/min/g tissue

Answer 18

used to depict sympathetic innervation of the myocardium

Answer 19

tracer of myocardial fatty acid utilization

Answer 20

**Oxygen-15 water** * freely diffusible tracer of myocardial blood flow whose net tissue uptake is near unity even at hyperemic blood flows * Other tracers (Tl201, N13, Tc99m) - net tissue uptake gets progressively smaller for each unit increase in tissue blood flow

Answer 21

**Tc 99m tracers** * ****greater problem with this tracer * especially when performed in conjunction with pharmacologic stress * greater increase in coronary blood flow relative to exercise

Answer 22

* **Prior MI / Scar or Fibrosis** * ****severe matching perfusion and metabolic defects in the anteroapical and basal inferior regions * **Delayed-gadolinium enhancement** * consistent with fibrosis / scar on PET

Answer 23

* Post-PVC: * Postextrasystolic potentiation of regiona function * Tl 201 * redistribution * Cardiac MR * end-disastolic wall thickness of 8.0 - 8.5 mm

Answer 24

**25-50%** * Ca score \> 400 - \< 1000 ---\> almost 50% chance of ischemia in patients with intermediate likelihood of CAD

Answer 25

* **Small fixed perfusion defect** * **Basal, anterior wall - Diagonal distribution** * ****corresponds to the loss ("jailing") of a small 1st diagonal branch a the time of intervention

Answer 26

* 2D PET - **contain septa** * lead or tungsten septa interposed between the detector rings * serve to reduce coincidence events between detectors in a given ring and the adjacent rings, decreasing the number of scatter events * 3D PET - **"septa out"** * ****permits a greater number of coincidence events between detectors in differing rings * serving to increase the sensitivity of the device as well as the number of scatter events

Answer 27

**Bismuth germanate (BGO)** * energy and timing resolution are not as favorable

Answer 28

* Lutetium oxyorthosilicate (LSO) * Gadolinium oxyorthosilicate (GSO) * Lutetium yttrium orthosilicate (LYSO) * reduction in dead times and higher count rates

Answer 29

**cold pressor test** * cold water stimulates **release of norepinephrine from cardiac sympathetic nerve terminals**, which in turn results in **vasodilation of the coronary circulation via endothelium-mediated release of nitrous oxide (NO)** * vasodilation induced by dipyridamole, adenosine, and regadenoson is largeley indepndent of endothelial function

Answer 30

* involves immersion of a hand or foot into ice water (2C) for 2 minutes * stress perfusion tracer typically injected at 1 minute --\> with imaging for an additional minute while the hand or foot remains immersed in the cold water * cold water stimulates **release of norepinephrine from cardiac sympathetic nerve terminals**, which in turn results in **vasodilation of the coronary circulation via endothelium-mediated release of nitrous oxide (NO)** * vasodilation induced by dipyridamole, adenosine, and regadenoson is largeley indepndent of endothelial function

Answer 31

* System Sensitivity * Intrinsic scatter fraction * Accuracy of attenuation correction

Answer 32

**center of rotation** * assesses performance of rotating SPECT MPI cameras

Answer 33

**ICD with RV lead** * objects with very high density (such as defibrillator coil) may not be adequately characterized by CT transmission images * XR CT transmission images overcompensate for the density of the object, resulting in hot spots on the attenuation-corrected images

Answer 34

**Same for each isotope** * the energy of annihilation photons emitted by each of the isotopes --\> **511 keV** * the masses of the positron and electron are fixed, and the speed of light is a constant * therefore, E = mc2

Answer 35

**Urinary bladder** * for a 10-mCi dose of FDG --\> urinary bladder receives **~59 mSv** * can minimize radiation exposure by emptying their bladder frequently after the study

Answer 36

**The time difference between two annihilation photons reaching their corresponding detectors** * when two 511-keV photons are generated by the annihilation of a positron and an electron, they travel in opposite directions until each photon reaches its corresponding detector

Answer 37

slight differences in timing of the scintillation events in paired opposite detectors

Answer 38

**Kidneys** * potassium analong * 5.8 microGy/MBq is absorbed * myocardium is the second largest dose

Answer 39

**protective effect of exposure to low amounts of ionizing radiation** * possibly on the basis of up-regulation of molecular cell repair mechanisms

Answer 40

* effect in which the dose is related to severity of effect * usually characterized by a minimal dose for the effect to be observed

Answer 41

* effect in which the **probability of occurrence** ( as opposed to severity of effect) is **determined by the dose** * stochastic effects may not have an apparent threshold dose * example: late development of a radiation-induced malignant neoplasm

Answer 42

late development of a radiation-induced malignant neoplasm

Answer 43

**Following a low-carbohydrate, high-fat meal** * low-carbohydrate, high-fat meal --\> favors myocardial utilization of free fatty acids --\> reduces myocardial FDG uptake --\> decreases background activity --\> maximize FDG uptake and increased probability of visualizng the plaque * visualization of a coronary arterial plaque on FDG PET can be impaired by high background activity --\> due to myocardial uptake of tracer * use of glucose load, glucose or insulin clamps will increase myocardial substrate utilzation and thus increase FDG background activity

Answer 44

**High background activity** * visualization of a coronary arterial plaque on FDG PET can be impaired by high background activity --\> due to myocardial uptake of tracer * use of glucose load, glucose or insulin clamps will increase myocardial substrate utilzation and thus increase FDG background activity

Answer 45

**Activated macrophages exhibit an up-regulation of hexokinase, increasing the metabolic trapping of FDG within the plaque** * FDG transported across the cell membrane via GLUT transport proteins (GLUT 1 and GLUT 3 in macrophages) * phosphorylated by the enzyme hexokinase to FDG-6-phosphate which becomes largely trapped in a phosphate moeity * poor substrate for further glycolytic or glycogen pathways * "reverse reaction" very slow under hypoxic conditions --\> FDG becomes "trapped"

Answer 46

**2 hours following tracer injection** * most of background activity occurs from the arterial blood iteself * allowing for clearance of this background activity improves imaging of unstable plaques

Answer 47

**Extensive ischemia involving the LAD, CFx and RCA distributions - and scar involving the RCA** * reversible defects of the LAD, CFx and RCA --\> stress-induced ischemia * small fixed defect of RCA distribution --\> scar

Answer 48

**Average kinetic energy of the RB-82 positron is greater than that of the Fluorine-18 positron** * higher kinetic energy --\> longer positron range --\> lower image resolution * Kinetic energy of positrons: Rb-82 positrons \>\>\> Fluorine-18

Answer 49

* Oral glusoe load with 50g of dextrose prior to FDG injection * IV glucose loading with D50W to which 20mg of hydrocortisone has been added to administra a total of 25g dextrose * "Priming" the patient with 50 mL of 20% dextrose and 5units of regular insulin * Acipimox, 250mg orally prior to FDG injection

Answer 50

**Normal variant of myocardial uptake of N-13 ammonia** * may see a decrease in N-13 ammonia uptake in the **inferolateral region** of the ventricle * quantification of MBF and segmental wall motion is normal

Answer 51

**retention of Rb-82 activity on PET images obtained 3-7 minutes following IV tracer injection** * on the premise that nonviable tissue would not be capable of transmembranous uptake and retention of the tracer

Answer 52

**Diffuse preclinical atherosclerotic disease of the coronary arteries** * parallels findings oibtained in invasive studies using doppler flow and pressure probes

Answer 53

**Reversible perfusion defect of RCA** **With transmission-emission mismatch on rest images** * Rest perfusion images * modest reduction in tracer activity of the basal anterolateral area of the LV * Rest images fused with CT for AC * misalignment between the image sets is noted * spurious decrease in tracer activity in the basal anterolateral area on stress study

Answer 54

**N-13 Ammonia passively crosses the cell membrane and mitochondrial membrane; the tracer is then trapped within mitochondria as N13 NH₄+** * N13-NH3 is lipophilic and crosses the cell membrane * once inside the cell, NH3 is metabollically trapped * predominantly as glutamine via the glutamine synthase reaction

Answer 55

**C-11-hydroxyephedrine** * largely reflects the uptake 1-mechanism * also subject to monoamine oxidase degredation and storage within vesicles within the neuron

Answer 56

**C - coronary angiography and possible revascularization** * high risk stress test + large defect + abnormal systolic function --\> **Class I** * fixed defect on rest/stress myocardial perfusion imaging does not necessarily indicate scarring. Fixed defect can indicate: * scar * hibernating myocardium * attenuation artifact (significant) * Regional wall motion abnormalities + perfusion defect --\> **excludes attenuation** * Presence of chest pain --\> hibernating myocardium *

Answer 57

* scar * hibernating myocardium * attenuation artifact (significant) * Perfusion defect + regional wall motion abnormalities --\> rules out attenuation

Answer 58

* Stunning * Hibernation \*\*\*both may be improved with revascularization

Answer 59

* reversible state of regional contractile dysfunction that occurs after transient ischemia * despite the absence of necrosis * (believed to) play an important role in the **persistent contractile dysfunction seen in patients after reperfusion** of acute MI and following attacks of UA * **Perfusion/metabolism match (with positive stress perfusion)**

Answer 60

* refers to a state of persistent LV dysfunction that results from chronically reduced blood flow without infarction and necrosis * chronic downregulation in contractile function at rest is thought to represent a protective mechanism --\> heart reduces oxygen requirements to ensure myocyte survival * protective mechanism may also decrease myocardial contractility --\> LV dysfunction * **Perfusion - Metabolism mismatch** * Revascularization --\> improves contractile function significantly * depends on: * chronicity of hibernation * degree of ventricular remodeling * other factors

Answer 61

**C - Surgical revascularization of the LAD and LCx arteries** * Viability study demonstrates * normal Rb82 rest perfusion and thus viability in nearly the entire distribution of the LAD artery with the exception of the apex * mismatch between the Rb82 rest perfusion and F18-FDG metabolism images in the basal LCx distribution --\> hibernating myocardium * modest mismatch in the remainder of the LCx distribution --\> admixture of infarction and hibernating myocardium *

Answer 62

**A - nearly the entire myocardium is viable** * under resting conditions, the myocardium generally will oxidize free fatty acids to produce ATP * ischemia --\> up-regulation of glucose transporters * in some cases (particularly insulin resistance) --\> F18-FDG uptake in normal regions may remain less than that of ischemic or hibernating regions **\*\*\*\*pattern seen in current study**

Answer 63

* PET matched defect * decreased N13 rest perfusion and decreased F18-FDG uptake * transmural LGE * delayed clearance of gadolinium based contrast agent (GBCA) from affected myocardium * infusion of GBCA --\> wait 10 minutes before T1-weight imaging is performed ("LGE")

Answer 64

* Transmural LGE --\> Non-viable * **\> 75% thickness involvement** * No LGE or subendocardial LGE --\> viability and functional recovery after revascularization

Answer 65

**B - cancel F18-FDG uptake imaging and proceed with CABG** * normal resting perfusion --\> viable myocardium

Answer 66

**more than 12 months** * complete recovery of hibernating myocardium may take more than 12 months * prior ischemia may have resulted in: * sarcomere loss * glycogen accumulation * disarray of mitochondria * fibrosis

Answer 67

**If FDG PET is performed, then PET recommendations should be followed** * at 1 year --\> no significant difference in composite event rate in PET arm vs. Standard arm * However, patients that adhered to PET recommendations for revascularization, revascularization work-up, or neither, **PET guided strategy --\> lower event rate** * Bottom line: * no significant reduction in cardiac events in patients with LV dysfunction and suspected CAD for FDG PET-assisted management vs. standard care * Benefits observed * those without recent angiography * PET recommendations

Answer 68

**Administer SL NTG 400mcg, 5 minutes before injection of Tc99m sestamibi** * NTG improves ability to detect viable myocardium * improves flow to peri-infarct regions and enhances tracer delivery * Nitrate studies have been shown to be superior predictors of recovery of function after revascularization

Answer 69

* Stress, 4-hour redistribution, reinjection * Rest, 24-hour redistribution * Rest, 4-hour redistribution, reinjection

Answer 70

shows uptake in as many as **54% of the segments** without uptake at 3-4 hours \*\*\*\*aditional waiting for redistribution after reinjection has not been found to be helpful --\> less than 5% of persistent defects after reinjection showing viability

Nuclear - Essentials of Cardiac PET, Perfusion, Viability Flashcards

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