Nukes Cardiac Flashcards
(82 cards)
1
Q
In pts with a Bundle branch block, should you do exercise or pharmacologic stress test?
A
pharmacologic
2
Q
What pharmacologic agent do you use in a pt with BBB for a stress test?
A
vasodilator - (dipridamole, adenosine, regadenoson)
3
Q
MOA of dipridamole
A
adenosoine deaminase inhibitor. allows endogenous adenosine to accumulate
4
Q
MOA of regadenoson
A
adenosine receptor agonist with a 2-3 min half life
5
Q
Contra-indications for adenosine
A
severe asthma, COPD, recent caffeine
6
Q
how do you reverse dipryridamole and regadenoson?
A
caffeine and theophylline
7
Q
Indications for a MUGA scan
A
before chemotherapy or after chemotherapy cycles (to evaluate cardiotoxicity); EF in pt with CHF; CAD in pts with COPD
8
Q
When is dobutamine indicated in a stress test?
A
when adenosine is contraindicated (severe asthma, COPD, recent caffeine).
9
Q
Dobutamine MOA
A
beta-1 agonist
10
Q
Radionuclides used in nuclear cardiology
A
thallium-201, Tc-99m Sestamibi, Rubidium-82, Nitrogen-13 ammonia, F-18 FDG
11
Q
half life of thallium
A
73 hours
12
Q
THallium-201 Characteristic xrays
A
69-81 keV
13
Q
MOA of Thallium-201
A
potassium analog - crosses into the cell via active transport through ATP dependent Na-K pump
14
Q
Does thallium-201 or Tc-99m sestamibi undergo redistribution?
A
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
15
Q
MOA of Tc-99m-sestamibi
A
binds to mitochondrial membrane proteins
16
Q
PET perfusion agents used in nuclear cards
A
Rubidium-82 and Nitrogen-13 ammonia
17
Q
Rubidium-82 MOA
A
potassium analog like Thallium
18
Q
Half life of rubidium-82
A
76s
19
Q
Do you perform exercise or pharmacologic stress test when using Rubidium-82?
A
pharmacologic stress test only. The super short half life of 76s precludes using an exercise stress
20
Q
How can you tell there is motion artifact on nuclear cardiology scans?
A
sinogram or linogram https://pubs.rsna.org/doi/pdf/10.1148/rg.317115090
21
Q
What should you look for on the sinogram outside of the heart?
A
look for the breast cancer
22
Q
What does it mean to see significant right ventricular uptake on the sinogram?
A
implies right heart disease or pulmonary hypertension
23
Q
If there is pulmonary uptake on the sinogram what does this mean?
A
LV dysfunction
24
Q
What is the advantage to doing a stress-rest protocol as opposed to rest-stress
A
if stress is first, and normal, then the rest does not need to be completed
25
Prior to a nuclear cardiac myocardial perfusion exam, what are key patient preparation steps that improve the subsequent imaging?
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.
26
Is Tc-sestamibi or Tc-tetrofosmin more likely to show liver and bowel uptake on a cardiac imaging study?
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.
27
What is the purpose of adding physiologic or pharmacologic stress to a nuclear cardiac exam?
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%.
28
Name some common pharmacologic vasodilators used for myocardial perfusion imaging?
Adenosine, dipyridamole and regadenoson are common pharmacologic vasodilators used for myocardial perfusion imaging.
29
What pharmacologic stress agent is a specific adenosine receptor agonist with a lower risk of inducing bronchospasm?
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.
30
What drug is typically associated with the highest risk of side-effects, including a risk of AV block
Adenosine
31
Which agent has a longer half-life: regadenoson or adenosine?
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.
32
half life of adenosine
10 seconds
33
what must be avoided prior to myocardial perfusion imaging when using any of the pharmacologic vasodilators
caffeine must be avoided prior to myocardial perfusion imaging when using any of the pharmacologic vasodilators in order to obtain adequate pharmacologic vasodilation/stress
34
Which agent has a longer half-life: aminophylline or dipyridamole?
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.
35
why do you have to monitor the patient when reversing dipyridamole with aminophylline?
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.
36
Which pharmacologic agent increases stress by increasing heart rate and myocardial contraction as opposed to vasodilation?
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.
37
Which patients may be best suited for pharmacologic stress with dobutamine?
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.
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?
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.
39
is stress or rest performed first with a two day myocardial perfusion scan?
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.
40
how many half lives between stress and rest imaging
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
41
By which mechanism does Thallium enter into a cell?
Thallium enters a cell using a Na/K pump in a manner related to blood flow
42
What happens after Thallium enters into a cell?
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.
43
How does Thallium distinguish between normally perfused, ischemic, and dead (infarcted/scarred) myocardium?
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.
44
Is delayed imaging performed with Tl-201 viability studies?
No Delayed imaging would typically not be performed as ischemia and/or scar is already excluded if initial imaging is normal.
45
On a myocardial perfusion study with Tc-sestamibi or Tc-tetrofosmin, how does imaging distinguish between scar/prior infarct and ischemia?
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.
46
True or false: A thallium lung to heart ratio study with decreased lung uptake suggests multivessel coronary artery disease.
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.
47
What are imaging manifestations and clinical implications of transient ischemic dilation?
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.
48
How might dilated cardiomyopathy without ischemia manifest on a myocardial perfusion scan?
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.
49
What is the significance of seeing increased right ventricular activity (right ventricle uptake similar to left ventricle uptake) on rest imaging?
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.
50
What is the difference between stunned and hibernating myocardium?
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.
51
protocol for Tl-201
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
52
perfusion defect on initial imaging but uptake is seen on delayed imaging as Thallium redistributes into the viable but hibernating myocardium.
Ischemia
53
Tl-201 scan with perfusion defect on initial imaging that persists on delayed imaging
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).
54
stress acquisition must begin in what time of Tl-201 injection
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
55
Which is a higher dose in myocardial perfusion imaging, Tl-201 or Tc-99m sestamibi
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.
56
which has less soft tissue attenuation in myocardial perfusion imaging? Tl-201 or Tc-99m sestamibi?
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.
57
What is the major difference between the PET myocardial perfusion images acquired with N-13 ammonia when compared to rubidium-82?
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.
58
what has better resolution, N-13 or rubidium-82?
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.
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?
Regadenoson myocardial perfusion study
A patient with a left bundle branch block (LBBB) or ventricular paced rhythm should undergo vasodilator myocardial perfusion study.
60
A patient who is undergoing pharmacologic stress test with adenosine develops an atrioventricular block (shown below). What is the most appropriate next step?
turn off adenosine
61
Name the labeling method where the red blood cells are separated via centrifugation, washed, incubated with Sn2+, incubated with 99m-TcO4−, and reinjected?
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.
62
formula for calculating the percentage of the right-to-left shunt
% 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.
63
What are key features of a positive Tc 99m pyrophosphate scan for ATTR cardiac amyloidosis?
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.
64
What is the preferred agent for nuclear cardiac imaging of amyloidosis?
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
65
True or false: patients being evaluated for cardiac sarcoidosis typically complete a myocardial perfusion scan in addition to an FDG-PET/CT study?
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.
66
end stage fibrosis in cardiac sarcoid appearance on FDG PET
end stage fibrosis from sarcoidosis would show a **severe perfusion defect with minimal to no FDG uptake.**
67
What patient preparation steps need to take place in order to prepare for FDG-PET/CT imaging for cardiac sarcoidosis?
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.
68
for myocardial suppression, in addition to fasting what other pharmacologic method can be used
Some protocols also use IV heparin prior to imaging that can further suppress myocardial FDG uptake.
69
What is the most commonly used nuclear medicine agent for evaluation of cardiac sarcoidosis?
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.
70
What is the calculation for maximal heart rate used to determine whether somebody has reached sufficient cardiac stress for a Bruce treadmill protocol?
220 minus the patient’s age.
71
In general, it is desired to reach \_\_\_\_\_% of this maximal heart rate value for the stress portion of myocardial perfusion imaging.
In general, it is desired to reach 85% of this maximal heart rate value for the stress portion of myocardial perfusion imaging.
72
What is the top cause of reconstruction artifact on a myocardial perfusion scan?
Bowel or liver uptake “stealing” counts from the heart causes reconstruction artifact.
73
What is the leading cause of attenuation artifact on nuclear cardiac imaging?
Breast tissue overlying the heart is likely the top cause of attenuation artifact.
74
What is the primary purpose of a MUGA scan?
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.
75
What radiotracer is classically used for a MUGA exam?
MUGA classically uses a Tc-99m tagged red blood cell technique.
76
If you see a photopenic halo around the cardiac blood pool what does this suggest on a MUGA scan?
A photopenic halo around cardiac blood pool is a potential manifestation of a pericardial effusion.
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?
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._**
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?
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).
79
Is tagging of Tc to red blood cells for a MUGA scan typically performed using in vivo or in vitro labeling?
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.
80
Stunned myocardium:
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.
81
\*R
MPS with fixed defects anterior and inferior, and dilated LV. Prior MI with cardiomyopathy, next step?
**asked for gated SPECT to assess motion and EF**. There was hypo or akinesis anterior and inferior, and EF was 37%.
82
first pass portion of a MUGA exam demonstrates
