Nukes Cardiac

Question 1

In pts with a Bundle branch block, should you do exercise or pharmacologic stress test?

Answer 1

pharmacologic

Question 2

What pharmacologic agent do you use in a pt with BBB for a stress test?

Answer 2

vasodilator - (dipridamole, adenosine, regadenoson)

Question 3

MOA of dipridamole

Answer 3

adenosoine deaminase inhibitor. allows endogenous adenosine to accumulate

Question 4

MOA of regadenoson

Answer 4

adenosine receptor agonist with a 2-3 min half life

Question 5

Contra-indications for adenosine

Answer 5

severe asthma, COPD, recent caffeine

Question 6

how do you reverse dipryridamole and regadenoson?

Answer 6

caffeine and theophylline

Question 7

Indications for a MUGA scan

Answer 7

before chemotherapy or after chemotherapy cycles (to evaluate cardiotoxicity); EF in pt with CHF; CAD in pts with COPD

Question 8

When is dobutamine indicated in a stress test?

Answer 8

when adenosine is contraindicated (severe asthma, COPD, recent caffeine).

Question 9

Dobutamine MOA

Answer 9

beta-1 agonist

Question 10

Radionuclides used in nuclear cardiology

Answer 10

thallium-201, Tc-99m Sestamibi, Rubidium-82, Nitrogen-13 ammonia, F-18 FDG

Question 11

half life of thallium

Answer 11

73 hours

Question 12

THallium-201 Characteristic xrays

Answer 12

69-81 keV

Question 13

MOA of Thallium-201

Answer 13

potassium analog - crosses into the cell via active transport through ATP dependent Na-K pump

Question 14

Does thallium-201 or Tc-99m sestamibi undergo redistribution?

Answer 14

Thallium-201 - ischemic myocardium progressively extracts thallium but washes out more slowly than normal myocardium. Post-redistribution images will show normalization of defects in ischemic myocardium. Mibi is fixed in the myocardium

Question 15

MOA of Tc-99m-sestamibi

Answer 15

binds to mitochondrial membrane proteins

Question 16

PET perfusion agents used in nuclear cards

Answer 16

Rubidium-82 and Nitrogen-13 ammonia

Question 17

Rubidium-82 MOA

Answer 17

potassium analog like Thallium

Question 18

Half life of rubidium-82

Answer 18

76s

Question 19

Do you perform exercise or pharmacologic stress test when using Rubidium-82?

Answer 19

pharmacologic stress test only. The super short half life of 76s precludes using an exercise stress

Question 20

How can you tell there is motion artifact on nuclear cardiology scans?

Answer 20

sinogram or linogram https://pubs.rsna.org/doi/pdf/10.1148/rg.317115090

Question 21

What should you look for on the sinogram outside of the heart?

Answer 21

look for the breast cancer

Question 22

What does it mean to see significant right ventricular uptake on the sinogram?

Answer 22

implies right heart disease or pulmonary hypertension

Question 23

If there is pulmonary uptake on the sinogram what does this mean?

Answer 23

LV dysfunction

Question 24

What is the advantage to doing a stress-rest protocol as opposed to rest-stress

Answer 24

if stress is first, and normal, then the rest does not need to be completed

Question 25

Prior to a nuclear cardiac myocardial perfusion exam, what are key patient preparation steps that improve the subsequent imaging?

Answer 25

Patients should be instructed to fast for something like 4 hours to reduce uptake in the GI system/liver. If possible, have patient refrain from taking certain medications to include longacting nitrates, caffeine, calcium channel and beta blockers as these will reduce sensitivity for detection of a perfusion defect/coronary artery stenosis.

Question 26

Is Tc-sestamibi or Tc-tetrofosmin more likely to show liver and bowel uptake on a cardiac imaging study?

Answer 26

Tc-tetrofosmin has more rapid liver and bowel clearance compared to sestamibi and therefore will have less competing /adjacent activity in the liver and bowel on a cardiac imaging study.

Question 27

What is the purpose of adding physiologic or pharmacologic stress to a nuclear cardiac exam?

Answer 27

Stressing the patient with exercise (physiologic) or pharmacologic stress increases the sensitivity for detection of coronary artery stenosis. Without stress, nuclear cardiac imaging can detect something like stenosis >90%. With stress sensitivity improves to be able to detect a stenosis >50%.

Question 28

Name some common pharmacologic vasodilators used for myocardial perfusion imaging?

Answer 28

Adenosine, dipyridamole and regadenoson are common pharmacologic vasodilators used for myocardial perfusion imaging.

Question 29

What pharmacologic stress agent is a specific adenosine receptor agonist with a lower risk of inducing bronchospasm?

Answer 29

Regadenoson is a specific A2A adenosine receptor agonist with a lower risk of inducing bronchospasm compared to adenosine or dipyridamole. Note that adenosine typically is associated with the highest risk of side-effects, including a risk of AV block. Dipyridamole inhibits the breakdown of adenosine, thus raising adenosine levels to cause vasodilation.

Question 30

What drug is typically associated with the highest risk of side-effects, including a risk of AV block

Answer 30

Adenosine

Question 31

Which agent has a longer half-life: regadenoson or adenosine?

Answer 31

Regadenoson has a half-life of 2-3 minutes and therefore may be given as a single IV bolus. Adenosine has a half-life of only 10 seconds and therefore is given as an IV drip.

Question 32

half life of adenosine

Answer 32

10 seconds

Question 33

what must be avoided prior to myocardial perfusion imaging when using any of the pharmacologic vasodilators

Answer 33

caffeine must be avoided prior to myocardial perfusion imaging when using any of the pharmacologic vasodilators in order to obtain adequate pharmacologic vasodilation/stress

Question 34

Which agent has a longer half-life: aminophylline or dipyridamole?

Answer 34

Aminophylline has a shorter half-life than dipyridamole. Therefore, when giving aminophylline to reverse the effects of dipyridamole, breakthrough symptoms can occur so you must continue to monitor for breakthrough when using aminophylline as a reversal agent.

Question 35

why do you have to monitor the patient when reversing dipyridamole with aminophylline?

Answer 35

Aminophylline has a short half-life. Therefore, when giving aminophylline to reverse the effects of dipyridamole, breakthrough symptoms can occur so you must continue to monitor for breakthrough when using aminophylline as a reversal agent.

Question 36

Which pharmacologic agent increases stress by increasing heart rate and myocardial contraction as opposed to vasodilation?

Answer 36

Dobutamine is a beta 1 agonist that can be used to induce stress for myocardial perfusion imaging. This essentially causes a similar increase in heart rate and contractility to exercise instead of causing direct coronary vasodilation as with adenosine, dipyridamole and regadenoson.

Question 37

Which patients may be best suited for pharmacologic stress with dobutamine?

Answer 37

Dobutamine may be considered for myocardial perfusion stress imaging in patients who cannot tolerate exercise for stress imaging who also have COPD and/or asthma to avoid the risk of bronchospasm that exists with the vasodilatory agents. Dobutamine can also be used in patients who have had caffeine intake within the past 12 hours. Note that dobutamine should not be used in patients on beta blockers as this would prevent the beta-1 induced increase in heart rate and contractility that is necessary to induce stress.

Question 38

During a 1-day myocardial perfusion scan, is a higher dose of radiotracer administered during the stress or during the rest portion of the study?

Answer 38

higher dose during the stress portion for a 1 day protocol, you would start with a rest portion of the study at lower dose. Subsequently, a much higher dose would be given to overwhelm the rest counts and now provide perfusion information under stress.

Question 39

is stress or rest performed first with a two day myocardial perfusion scan?

Answer 39

2-day protocols often would do stress first, and then rest the following day, only if stress is abnormal. Note that a normal stress study effectively rules-out significant coronary artery stenosis, so if stress is performed first and is normal the rest portion of the study would not be necessary.

Question 40

how many half lives between stress and rest imaging

Answer 40

4 half lives, or administer a dose something like 3-4 times higher for the second portion of the study to overwhelm and diminish residual counts that may be hanging around from the initial imaging

Question 41

By which mechanism does Thallium enter into a cell?

Answer 41

Thallium enters a cell using a Na/K pump in a manner related to blood flow

Question 42

What happens after Thallium enters into a cell?

Answer 42

Unlike Tc-sestamibi and Tc-tetrofosmin, Thallium is able to redistribute among viable cells in the myocardium. So initial Thallium imaging provides information about blood flow to the myocardium and delayed imaging evaluates for redistribution.

Question 43

How does Thallium distinguish between normally perfused, ischemic, and dead (infarcted/scarred) myocardium?

Answer 43

Thallium can show areas of ischemic but viable myocardium. Ischemia: perfusion defect on initial imaging but uptake is seen on delayed imaging as Thallium redistributes into the viable but hibernating myocardium. Scar/prior infarct: perfusion defect on initial imaging that persists on delayed imaging (redistribution requires functional Na/K pumps—which won’t be functioning in case of myocardial scarring). Normal perfusion: No defect on initial imaging.

Question 44

Is delayed imaging performed with Tl-201 viability studies?

Answer 44

No Delayed imaging would typically not be performed as ischemia and/or scar is already excluded if initial imaging is normal.

Question 45

On a myocardial perfusion study with Tc-sestamibi or Tc-tetrofosmin, how does imaging distinguish between scar/prior infarct and ischemia?

Answer 45

A fixed defect on both stress and rest is consistent with scar from prior infarct. A reversible defect, meaning a defect seen on stress imaging only, with no defect on rest imaging, is a manifestation of stress induced ischemia. Sometime a fixed defect is seen with reversible components around the fixed defect (in other words the defect is distinctly larger on stress images and smaller on rest images) and this suggests a component of scar with peri-infarct ischemia.

Question 46

True or false: A thallium lung to heart ratio study with decreased lung uptake suggests multivessel coronary artery disease.

Answer 46

False. Multi-vessel coronary artery disease would show increased uptake in lungs as the reduced blood flow through the lungs due to cardiac disease is not sufficient to clear the tracer from the lungs.

Question 47

What are imaging manifestations and clinical implications of transient ischemic dilation?

Answer 47

Transient ischemic dilation (TID) is identified on a myocardial perfusion scan when the left ventricular cavity appears larger on stress imaging compared to rest imaging. Note that perfusion can appear otherwise normal—the finding of interest is simply apparent left ventricular enlargement on stress imaging that is not seen on rest imaging. The significance of this finding is that this correlates with left main and/or 3-vessel coronary artery disease that causes diffuse subendocardial hypoperfusion. This diffuse subendocardial hypoperfusion means that less radiotracer is delivered to the subendocardial myocardium, therefore causing a diffuse subendocardial perfusion defect on stress imaging that causes the appearance of left ventricular enlargement on stress imaging, not seen on rest imaging (therefore transient dilation as in the name), thus showing diffuse reversible subendocardial ischemia related to left main and/or 3-vessel coronary artery disease.

Question 48

How might dilated cardiomyopathy without ischemia manifest on a myocardial perfusion scan?

Answer 48

In comparison to transient ischemic dilation, dilated cardiomyopathy would be expected to present with left ventricular dilation that is fixed on both stress and rest images.

Question 49

What is the significance of seeing increased right ventricular activity (right ventricle uptake similar to left ventricle uptake) on rest imaging?

Answer 49

If the right ventricle shows higher than normal uptake on rest imaging which would manifest as right ventricle uptake similar to left ventricle uptake this is a sign of right ventricular hypertrophy.

Question 50

What is the difference between stunned and hibernating myocardium?

Answer 50

Stunned myocardium is seen in the acute phase following ischemia that resolves with reperfusion injury but not frank myocardial infarction/scarring and manifests as normal perfusion with impaired contractility of the heart. As the name suggests this stunning is temporary and typically resolves within a few weeks. Hibernating myocardium results from chronic decreased perfusion to the heart from chronic severe coronary artery disease and manifests as areas of decreased perfusion and decreased contractility in myocardium that is not infarcted and is still viable. A key to remember for board exams is that hibernating myocardium is viable heart tissue that is chronically hypoperfused, and therefore poorly contractile but if the perfusion is improved through intervention such as coronary stenting or angioplasty, cardiac contractility can recover to normal or else be significantly improved.

Question 51

protocol for Tl-201

Answer 51

Although a 2-day protocol with separate rest and stress injections has been used in the past, Tl-201 redistribution allows for assessment of both stress and rest perfusion after a single injection on the same day. After stress, initial images are obtained at 10 to 15 minutes and delayed images acquired at 3 hours

Question 52

perfusion defect on initial imaging but uptake is seen on delayed imaging as Thallium redistributes into the viable but hibernating myocardium.

Answer 52

Ischemia

Question 53

Tl-201 scan with perfusion defect on initial imaging that persists on delayed imaging

Answer 53

scar/prior infarct:

perfusion defect on initial imaging that persists on delayed imaging (redistribution requires functional Na/K pumps—which won’t be functioning in case of myocardial scarring).

Question 54

stress acquisition must begin in what time of Tl-201 injection

Answer 54

within 10 min

Thallium-201 (Tl-201) is a potassium analog, which is transported across the myocardial membrane via the Na+-K+ ATPase pump into the myocardial cytosol. It has a very high first-pass extraction rate of approximately 85% compared to about 60% for the Tc-99m–labeled myocardial perfusion imaging agents (sestamibi or tetrofosmin). Unlike Tc-99m–labeled myocardial perfusion imaging agents, Tl-201 quickly undergoes redistribution, which is a dynamic exchange of Tl-201 between the myocardial cytosol and the vascular blood pool. Because of redistribution, poststress images with Tl-201 must be performed quickly after its injection (<10 minutes). Redistribution is also the basis for the use of Tl-201 in the evaluation of myocardial viability with delayed 24-hour imaging. Either exercise or pharmacologic stress protocol can be used with Tl-201

Question 55

Which is a higher dose in myocardial perfusion imaging, Tl-201 or Tc-99m sestamibi

Answer 55

Tc-99m

due to its longer half-life of 3 days, the injected dose of the Tl-201 is lower than the Tc-99m–labeled myocardial perfusion agents.

Question 56

which has less soft tissue attenuation in myocardial perfusion imaging? Tl-201 or Tc-99m sestamibi?

Answer 56

Since Tc-99m photon has higher energy (140 keV) than mercury daughter x-rays from Tl-201 (69 to 81 keV), less soft tissue attenuation would be seen with Tc-99m–labeled agents compared to Tl-201.

Question 57

What is the major difference between the PET myocardial perfusion images acquired with N-13 ammonia when compared to rubidium-82?

Answer 57

better resolution

N-13 ammonia positron has less energy than the positron emitted by the decay of rubidium-82 (Rb-82). As such, it travels shorter distance before undergoing annihilation.

Question 58

what has better resolution, N-13 or rubidium-82?

Answer 58

N-13

N-13 ammonia positron has less energy than the positron emitted by the decay of rubidium-82 (Rb-82). As such, it travels shorter distance before undergoing annihilation.

This decreased range is responsible for the better image resolution (smaller full width at half-maximum) of N-13 ammonia myocardial perfusion images compared to that acquired with Rb-82.

Question 59

A 47-year-old gentleman with clinical history of chest pain and shortness of breath presents for evaluation of coronary artery disease. His resting ECG showed left bundle branch block. What is the most appropriate next step?

Answer 59

Regadenoson myocardial perfusion study

A patient with a left bundle branch block (LBBB) or ventricular paced rhythm should undergo vasodilator myocardial perfusion study.

Question 60

A patient who is undergoing pharmacologic stress test with adenosine develops an atrioventricular block (shown below). What is the most appropriate next step?

Answer 60

turn off adenosine

Question 61

Name the labeling method where the red blood cells are separated via centrifugation, washed, incubated with Sn2+, incubated with 99m-TcO4−, and reinjected?

Answer 61

In vitro

all steps involved in the labeling of the RBCs with in vitro labeling are performed outside the patient. It has the highest labeling efficiency (>97%) of the three labeling methods.

Question 62

formula for calculating the percentage of the right-to-left shunt

Answer 62

% R-L shunt = systemic circulation counts/whole-body counts × 100%

systemic counts = whole-body counts − lung counts

right-to-left shunt can be estimated by using intravenous injection of Tc-99m macroaggregated albumin (MAA) and calculating counts in the regions of interest placed over the whole body and lungs. Cardiac MRI is usually done for this indication because in addition to accurately quantifying shunts, cardiac MRI can detect associated anomalies, evaluate pulmonary vasculature, and quantify ventricular size/function.

Question 63

What are key features of a positive Tc 99m pyrophosphate scan for ATTR cardiac amyloidosis?

Answer 63

An uptake ratio of 1.5 or higher of the heart to contralateral chest on a planar view is positive for ATTR deposition in the heart. Semi-quantitative measures are also used (0-absent cardiac uptake, 1 uptake less than bone, 2 uptake equal to bone, 3 uptake greater than bone) but for board purposes I think remembering the 1.5 cutoff of heart to contralateral lung uptake is the most important measure to remember.

Question 64

What is the preferred agent for nuclear cardiac imaging of amyloidosis?

Answer 64

Tc 99m pyrophosphate (PYP) is the main agent used in the US for nuclear imaging of ATTR amyloidosis. Tc 99m pyrophosphate binds to deposited amyloid transthyretin protein (ATTR) in the myocardium

Question 65

True or false: patients being evaluated for cardiac sarcoidosis typically complete a myocardial perfusion scan in addition to an FDG-PET/CT study?

Answer 65

True. FDG images for inflammation related to sarcoidosis but this does not give information about perfusion of the heart. Comparing information regarding inflammation from FDG and perfusion from a nuclear perfusion agent such as Rubidium on PET or a Technetium agent allows differentiation of normal tissue from scar tissue or areas of active sarcoidosis. This is also important for staging as sarcoid progresses from normal (perfusion and FDG both normal) to early stage (mild perfusion defect, mild increased FDG uptake) and progressive stages wherein perfusion defects worsen, and FDG uptake progressively gets more pronounced.

Finally, end stage fibrosis from sarcoidosis would show a severe perfusion defect with minimal to no FDG uptake.

Question 66

end stage fibrosis in cardiac sarcoid appearance on FDG PET

Answer 66

end stage fibrosis from sarcoidosis would show a severe perfusion defect with minimal to no FDG uptake.

Question 67

What patient preparation steps need to take place in order to prepare for FDG-PET/CT imaging for cardiac sarcoidosis?

Answer 67

Dietary modifications in which patients follow a high fat and low carbohydrate diet the day prior to imaging, with an overnight fast, is necessary.

This switches myocardial metabolism away from glucose metabolism to free fatty acid metabolism. The purpose is to decrease the physiologic uptake of glucose in the heart with the rationale that areas of cardiac sarcoidosis will not switch their metabolism away from glucose uptake, thus allowing maximal signal to noise with areas of cardiac sarcoidosis taking up the FDG while areas of normal myocardium will take up less FDG as normal myocardium has preferentially switched to fatty acid metabolism. This is termed myocardial suppression and you need good myocardial suppression in order to get a high quality FDG-PET/CT scan for cardiac sarcoidosis. Some protocols also use IV heparin prior to imaging that can further suppress myocardial FDG uptake.

Question 68

for myocardial suppression, in addition to fasting what other pharmacologic method can be used

Answer 68

Some protocols also use IV heparin prior to imaging that can further suppress myocardial FDG uptake.

Question 69

What is the most commonly used nuclear medicine agent for evaluation of cardiac sarcoidosis?

Answer 69

FDG is the agent most commonly used in nuclear medicine to evaluate for cardiac sarcoidosis. On an FDG-PET/CT study active cardiac sarcoidosis shows heterogeneous myocardial uptake. Note that unlike amyloidosis and other infiltrative diseases of the heart, myocardial sarcoidosis is typically patchy and this patchy involvement accounts for the heterogeneous, slightly patchy uptake seen on a positive FDG-PET/CT study. A negative scan shows no increased myocardial uptake of FDG.

Question 70

What is the calculation for maximal heart rate used to determine whether somebody has reached sufficient cardiac stress for a Bruce treadmill protocol?

Answer 70

220 minus the patient’s age.

Question 71

In general, it is desired to reach _____% of this maximal heart rate value for the stress portion of myocardial perfusion imaging.

Answer 71

In general, it is desired to reach 85% of this maximal heart rate value for the stress portion of myocardial perfusion imaging.

Question 72

What is the top cause of reconstruction artifact on a myocardial perfusion scan?

Answer 72

Bowel or liver uptake “stealing” counts from the heart causes reconstruction artifact.

Question 73

What is the leading cause of attenuation artifact on nuclear cardiac imaging?

Answer 73

Breast tissue overlying the heart is likely the top cause of attenuation artifact.

Question 74

What is the primary purpose of a MUGA scan?

Answer 74

The primary purpose of a MUGA scan is to provide an ejection fraction calculation. MUGA stands for multi-gated acquisition scan and uses gating to provide evaluation of cardiac function and contractility after equilibration of radiotracer in the intravascular space.

Question 75

What radiotracer is classically used for a MUGA exam?

Answer 75

MUGA classically uses a Tc-99m tagged red blood cell technique.

Question 76

If you see a photopenic halo around the cardiac blood pool what does this suggest on a MUGA scan?

Answer 76

A photopenic halo around cardiac blood pool is a potential manifestation of a pericardial effusion.

Question 77

If structures such as the pulmonary artery, thoracic aorta, left atrium, or right ventricle overlap the left ventricle on a MUGA acquisition will this falsely lower or falsely increase estimation of ejection fraction on a MUGA scan?

Answer 77

Vascular structures that overlap the left ventricle on a MUGA scan, whether great vessels or other cardiac chambers, will give the false appearance that tracer is not exiting the left ventricle and this will therefore lower the estimated ejection fraction. If you are asked this question, simply think it through and realize that in this scenario of vascular overlap, tracer will not be clearing the left ventricle as it should and this would therefore allow for underestimation of left ventricle ejection fraction.

Question 78

If the background region of interest is erroneously placed over the spleen will this falsely lower or falsely increase estimation of ejection fraction on a MUGA scan?

Answer 78

Erroneously placing the background region of interest over the spleen will falsely increase ejection fraction calculation. The reason for this false increase in calculated ejection fraction is that there will be over-subtraction of background that is in the denominator of the ejection fraction equation, therefore this will lower the denominator and increase the calculated ejection fraction. The equation is (end diastolic counts – background) – (end systolic counts – background)/ (end diastolic counts – background).

Question 79

Is tagging of Tc to red blood cells for a MUGA scan typically performed using in vivo or in vitro labeling?

Answer 79

For MUGA one can get by with in vivo labeling of red blood cells to Tc. This is different from a tagged red blood cell scan performed for a GI bleed which requires a higher labeling efficiency and requires in vitro labeling.

Question 80

Stunned myocardium:

Answer 80

myocardial perfusion imaging will show normal perfusion but decreased contractility. This is temporary and is the result of a recent, transient ischemic insult to the heart but not frank infarction.

Question 81

*R

MPS with fixed defects anterior and inferior, and dilated LV. Prior MI with cardiomyopathy, next step?

Answer 81

asked for gated SPECT to assess motion and EF. There was hypo or akinesis anterior and inferior, and EF was 37%.

Question 82

first pass portion of a MUGA exam demonstrates