MPI Flashcards
what does a MPI do?
looks at the blood flow to the heart muscles
what are the three views that we typically view MPIs in?
- short axis
- vertical long axis
- horizontal long axis
what RPs are used for MPIs?
99mTc-Mibi, 99mTc-Tetrofosmin or Tl-201
what are indications for MPI?
- risk assessment and prognosis for chest pain, MI, unstable angina, family hx of heart disease, abnormal lab results
- detect and eval cad
- assessing efficacy of CABG
CABG
coronary artery bypass graft
attaching the an artery to the aorta, downstream of where build-up is to provide a new route for blood flow
when are 1 day protocols usually done?
for patient convenience or when prompt results are needed
dose and rp for rest studies for 1 day protocols
296-370 MBq of 99mTc-mibi or 99mTc-tetrofosmin
dose for stress test for 1 day protocol?
925-1110 MBq
which drugs administered do not increase HR?
dipy and adenosine
what drug of choice is the first if a patient can’t exercise?
dipy
how do we determine target HR?
target HR = (220-age)*0.85
when do we use dobutamine?
if patients have contraindications for dipy and adenosine + can’t exercise
what is the bruce protocol?
- increasing the speed and inclination every 3 mins till the patient reaches target hr then we inject the patient with the RP
- let patient stay on treadmill for another 1-2 mins to let RP circulate around the body
- let patient off treadmill wait 10-20 mins before imaging
how do you calculate how much dipy to give to a patient?
0.56 mg/kg
what is the max dipy you can admin. to a patient
60 mg
how do you calculate how much adenosine to give to a patient?
0.140 mg/kg/min
how do you calculate how much dobutamine to give to a patient?
5ug/kg/min up to 40ug/kg/min
which protocol is preferred and why?
2 day protocol to eliminate possible interference in 2nd study due to residual myocardial activity
rest is done day 1 of a 2 day protocol. t/f
false
rest is done day 2 of the 2 day protocol
can you gate a MPI study?
yes
pitfall to G-SPECT
- heart beat variances can cause inaccurate EF values
attenuation correction
reduces the influence of variable photon attenuation in the body on the final SPECT images
- but can cause artifacts
how is attenuation correction done?
- addition of low dose CT
- external RN source
ct parameters for attenuation correction
- no contrast + normal tidal breathing
- current: 5-20 mA
- voltage: 80-140 kVp
- x-ray segments: 1
- slice thickness: 2-5 mm
when do we use prone imaging?
when we want to distinguish artifact from real defect when CT is unavailable
*always done in addition to supine imaging
what are the units for CTDI?
mGy
what are the units for DLP?
mGy*cm
what is the key differences between 1 day protocol and 2 day protocol?
1 day - lower dose first for rest images then stress is done afterwards
2 day - stress first then rest images but dose is the same
ST elevation
segment greater than 1mm of normal
ST elevation can mean?
MI
ST depression
decline of greater than 2mm
ST depression can mean?
ischemia
when do you stop exercise stress tests?
- patients want to stop, fatigue - unable to continue
- reached target HR
- moderate to severe chest pain
- dizziness
- diaphoresis
- arrhythmias (atrial fibrillation, ventricular tachycardia)
- drastic increase in BP or drop in BP from baseline
inotropic
making the heart beat with increasing force
chronotropic
increasing heart rate
Name two reasons why cardiac stressing of a patient should be terminated.
Dizziness, fatigue, ST elevation/depression, drastic increase/decrease in BP, reached target HR, if patient asks to stop
What is the mechanism of stress using dipyridamole?
vasodilation
When would aminophylline be used in cardiac imaging?
Antidote to dipy side effects, but 2 mins after RP admin
What dose of RP would you inject for the stress portion of a 2 day protocol?
740-1110 MBq
what is needed to be done for processing before patients leave?
- using cine to check for motion
- check the quality, is the bowel in the way?
- CT registration
what is the steps for processing?
- ac registration
- reconstruction (iterative), reorientation
- display
what does reorientation mean?
aligning with the long axis of the LV
what can we suggest if a patient’s bowels are closer to the heart than it should be due to natural motion?
light exercise
ac registration
attenuation correction - ensuring the heart on the NM study lines up with the CT study
what slices are seen for ac registration?
transverse, sag, coronal
what views have the line drawn through the center of it for reorientation?
transaxial and sagittal
vertical long axis =
oblique sagittal - separating right and left
horizontal long axis =
oblique transaxial = inferior and superior
short axis =
oblique coronal = slicing from apex to base
short axis view is displayed from?
apex to base
vertical long axis view is displayed from?
septal to lateral
horizontal long axis view is displayed from?
inferior to anterior
perfusion quantification
comparing perfusion to a reference population
functional quantification
looking at EF
which wall is seen “hotter” than other walls? why?
lateral - closer to camera
what is unique in the apex between patients?
some have thinner myocardium at apex
- as long as it matches in stress + rest = don’t report as fixed defect
ischemia
defect on stress that fills in rest images
ischemia akas?
reversible or mismatched defect
if we inject before target HR what can happen?
results in us underestimating the extent of ischemia
infarct
defect present in same location on both stress and rest
infarct aka?
non-reversible or fixed
stunned myocardium
delayed perfusion by wall motion should improve over time
hibernating myocardium
presents the same was as an infarcy
- severe chronic ischemia, decreased perfusion, poor contractility
who would benefit from coronary revascularization?
those with hibernating myocardium
what are some ways you can do perfusion quantifications?
1) polar maps
2) summed stress score
3) summed rest score
4) summed difference score
how are polar plots done?
short axis slices are stacked and the center represents the apex and the base is at the periphery
what do polar plots allow us to do?
allows for the perfusion of different segments of the myocardium and it is comparable to a normal sex-matched database
when looking at polar plots, what images are we looking at?
stress, rest, + reversibility
black areas on a polar plot = ?
areas of less perfusion than database
what is summed stress score?
dividing the polar plot into 17-20 segments then assignment a number dependent on its level of reduce uptake in that region (1-4)
numbers in each segment are then added together to get SSS
SSS assignment number
0 =?
normal uptake
SSS assignment number
1 =?
slight reduced uptake
SSS assignment number
2 =?
moderately reduced uptake
SSS assignment number
3=
severe reduction uptake
SSS assignment number
4=
absence of uptake
SSS = < 4
normal
SSS = 4-8
mildly abnormal
SSS = 9-13
moderately abnormal
SSS = >13
severely abnormal
what is summed rest score?
same concept as SSS but using the resting phase polar plot
what is summed differences score?
the difference between the summed stress and summed rest
what does the SDS indicate?
measurement of the degree of reversibility of defects
LVEF in a MPI is (less/more) accurate than one from a MUGA.
LESS accurate than MUGA
when do we use Tl-201 for MPI?
when we want myocardial viability
what contraindications are there for Tl-201for MPI?
specific to stressing agents
half life of Tl-201
73 hours
energy of Tl-201
167 keV (10%), majority is 69-93 keV
how does Tl-201 behave?
like K+, gets actively transported into cells by Na/K pump
where does Tl-201 localize?
4% in heart (5-10 mins post injection)
in proportion to myocardial blood flow + tissue oxygenation
max uptake during rest? stress?
rest = 10-30 mins
stress = 5 mins
Tb of 201Tl-Cl?
10 days
how is 201Tl-Cl excreted?
renal and hepatobiliary excretion
redistribution
continuous exchange between EC and IC compartments
when does equilibrium occur for redistribution?
3-4 hrs later
what are disadvantages of Tl protocol?
- suboptimal imaging characteristics
- more attenuation
- expensive (produced by cyclotron)
- higher patient dose
when are redistribution images supposed to be taken?
3-4 hrs after injection
dose of 201Tl?
74-148 MBq at peak stress
imaging for stress occurs when (thallium protocol)?
~10 mins after injection
how do we obtain a lung:heart ratio?
only with Tl
what view is used to determine lung:heart ratio?
planar ant
two ways to determine viability
1) second injection after redistribution images are done
2) obtain a rest/redistribution study
what shows viability?
an increase in concentration of tracer from initial images to redistribution images
when do we use Tl to improve specificity?
when we see a fixed defect
what shows non-viable myocardium?
fixed defect between initial and reinfection images
what values are considered normal for the Lung:heart ratio?
<0.5
how do you determine the lung to heart ratio?
counts in lung divided by counts in myocardium
How is ischemia identified in myocardial perfusion imaging?
Mismatched defect, ie. Reversible defect
(present on stress but not rest)
How is an infarct identified on myocardial perfusion imaging?
Fixed defect (on both stress and rest)
What is the difference between hibernating and stunned myocardium?
- Hibernating myocardium is chronically underperfused tissue, presents as a fixed defect (needs to be revascularized)
- Stunned is normally perfused but there was an episode of underperfusion – tissue hasn’t fully recovered
–Normal perfusion on imaging, but poor wall motion but just needs time to recover
