MUGA Flashcards
What happens if a patient has a longer than average cardiac cycle?
Framing stops before end diastole which under represents EDV which decreases EF
What happens if a patient has a shorter than average cardiac cycle?
Lack of data to be recorded in the last few frames also resulting in a decrease of EDV = decrease EF
Too much background subtraction: effect on EF?
falsely increased EF = false negative results
Too little background subtraction: effect on EF?
falsely decreased EF = false positive results
what happens to the EF if LA overlaps LV ROI slightly?
overestimate ES which means more vol. at ES which means heart not doing a good job at contracting = underestimate EF
what are some artifacts seen in MUGAs?
- arrhythmias
- improper ROI
- attenuation from ECG leads, pacemakers, other metals in FOV
- poorly tagged RBCs
what are the advantages to MUGA?
- accurate + non-invasive
- reproducible
- simple technique
what are the disadvantages to MUGA?
- RVEF can’t be accurately calculated
what study is best to assess RVEF?
first pass
why is it difficult for us to assess RVEF?
RV can’t be easily separated from RA or an enlarged LV
what are the advantages to a gated equilibrium stress study?
- more sensitive to ischemic changes
- completed in short time period
what are the disadvantages to a gated equilibrium stress study?
- “demanding”
- requires considerable patient compliance
- more patient motion, less statistics/shorter images
- more electrical interference on ECG
- must have qualified physician present during stress
downfall of echocardiography? pros?
-no reproducibility
+noninvasive + accurate at determining EF
downfall of angiography? pros?
-invasive+high radiation dose
+highly accurate
downfall of gated MRI?
-demanding + requires multiple breath holds
downfall of gated CT?
-single breath holds + needs contrast injection
T/F
The purpose of tin when labeling RBC’s is to ensure 99mTc04- is reduced intracellularly.
true
T/F
When performing an LAO view, 5-10 degrees caudal tilt improves separation between the two ventricles.
False
separates LV and LA
T/F
A 3 lead ECG is adequate for gating MUGA studies
true
T/F
500 accepted beats per image provides adequate statistics
true
what is the range for beats per image in a MUGA?
300-600
what is the set time for a MUGA?
10 minutes
what are the counts needed for a MUGA?
3-5M
T/F
Wall motion that is described as dyskinetic means that the area of myocardium is not contracting as vigorously as expected.
false
dyskinetic describes phasing therefore, it would mean that the area is not in phase with what it is supposed to be in phase with (eg. ventricles)
hypokinetic is the proper term
p wave
atrial contraction
on an ECG, which wave indicates ventricular depolarization? repolarization?
QRS - R wave signals for ventricles to contract
depolarization - t wave
indications for a MUGA
- baseline and follow up measurements for Sx or chemotherapy
- assessing valvular heart disease, cardiomyopathies
- eval EF, global and LV regional wall motion, size and volumes
- CAD eval + post MI eval
how is EF calculated?
EF = (EDV-ESV)/(EDV)
what are contraindications for MUGA?
severe arrhythmias (atrial fibrillation, greater than 10% PVCs)
dose for MUGA study
740-1850 MBq
radiopharm used for MUGA
99mTc-RBCs
IV infusion
critical organ of 99mTc-RBCs
Spleen
dosimetry in spleen?
1.1 mGy/37 MBq
excretion of 99mTc-RBCs
predominantly renal (25% in first 24hrs)
breastfeeding guidelines for 99mTc-RBCs (in vivo vs in vitro)
- stop 12 hours if done in vivo
- in vitro = halt feeding for minimum of 4 hrs (pump and discard)
Which of the following is NOT an indication for a gated equilibrium study?
A) Assess blood flow to the heart muscle
B) Screening prior to or after chemotherapy
C) Evaluation of cardiac chamber size
D) Evaluation of the percentage of blood pumped from the heart/beat
A
how do we acquire data for MUGA?
dynamic frame mode that is triggered by R-R intervals
frame mode acquisition
data from each cardiac cycle has counts added to each frame until adequate counts are achieved or an average beat is obtained
what % is typical beat rejection?
+/- 10% to 20%
longer than average cardiac cycle = ?
framing to stop before end diastole
- under represents EDV therefore decreases EF
shorter than average cardiac cycle?
lack of data recorded in last few frames
= decreases EF
patients with infants?
limit contact to <5 hours for the first 24 hrs
how many frames do we choose per cycle?
16-32 frames
heart should occupy __% of FOV
50%
how long do we wait for homogeneous mixing? what does it mean?
10 minutes
mixing with the rest of our blood around the body/heart evenly
what angles do we get images from for a MUGA?
ANT, LAO (30-60d) and LLAT
caudal tilt (10-15d)
what other angles can be done?
LPO, RAO, RLAT
why do we do caudal tilts?
separation of LA/LV
what is best separation?
clearly see separation of right/left ventricles
what are some stop conditions?
- 10 min/image
- 200-250 kcts/frame
- 300-600 heart beats
- 3-7M total counts
why do quantitative blood pool spect?
- isolates r/l ventricles without overlap therefore able to assess LVEF and RVEF
- less time to acquire
- better regional wall motion assessment
views for blood pool spect?
90 degrees
- one detector doing 45d RAO
- other at 45 LPO
T/F
Setting up a MUGA acquisition with 32 frames will have greater temporal resolution than an acquisition with 16 frames.
true
smoothing
spatial
each surrounding pixel around an individual pixel is examined and counts are averages
smoothing
temporal
counts in pixel frame before and after area averaged
best septal view
LAO
where do we draw background ROI?
between 3 and 6 o’clock of LV
what is produced from ROIs?
time activity curve
qualitative analysis
visual
- cine loop: for wall motion, ventricular size + wall thickness
quantitative analysis
time-activity curves, global ejection fraction, regional EF, phase + amplitude
hypokinetic
wall motion - not moving as much
akinetic
wall motion - not moving at all
dyskinetic aka?
paradoxical
wall motion - moving the wrong way
normal LVEF?
50-80%
normal RVEF?
40-60%
time-activity curve
time of blood volume (aka counts) changes in LV during average cardiac cycle
how do we get a time activity curve?
by drawing ROI around the LV on every frame and the counts are then plotted on a graph over time
what can be derived from a time activity curve?
EF, peak ejection rate and peak filling rate
end frame drop off
caused by heart rate variability
the EDV is not the same as it was in the beginning
normal stroke volume?
80-100ml
how do you calculation stroke volume?
EDV-ESV
normal cardiac output?
5-6L
how do you calculate cardiac output?
stroke volume * heart rate
normal EDV?
150ml
phase
comparing the timing of atrial and ventricular contraction
atria and ventricles should be contracting with the phase difference of ____
“180 degrees apart”
phases can be looked at by?
images and histograms
amplitude
degree/force of contraction
- looking at regional wall motion
what area of the heart normally shows the least amount of contraction?
septal area
what areas show less contractility than healthy myocardium?
areas of old infarcts and scarring
what words are used to describe phase?
dissynchronous/synchronous
dyskinetic/paradoxical
what words are used to describe amplitude?
hypokinetic/akinetic
_____ of the LV shows most movement
_____ of the LV shows the least movement
most - lateral wall
least - interventricular septum
for normal results, the septum ______ and moves slightly towards _____ during _____
septum shortens/thickens and moves slightly towards LV during systole
during a gated equilibrium stress study, what are normal results?
- increasing HR
- minimum 5% increase in EF at max exercise
- normal wall motion
what view(s) are acquired for an exercise MUGA?
LAO - multiple, resting and at each stage of exercise
