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NMED 251 - Clinical Procedures > MPI > Flashcards

MPI Flashcards

1
Q

what does a MPI do?

A

looks at the blood flow to the heart muscles

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2
Q

what are the three views that we typically view MPIs in?

A
  1. short axis
  2. vertical long axis
  3. horizontal long axis
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3
Q

what RPs are used for MPIs?

A

99mTc-Mibi, 99mTc-Tetrofosmin or Tl-201

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4
Q

what are indications for MPI?

A
  • 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
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5
Q

CABG

A

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

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6
Q

when are 1 day protocols usually done?

A

for patient convenience or when prompt results are needed

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7
Q

dose and rp for rest studies for 1 day protocols

A

296-370 MBq of 99mTc-mibi or 99mTc-tetrofosmin

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8
Q

dose for stress test for 1 day protocol?

A

925-1110 MBq

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9
Q

which drugs administered do not increase HR?

A

dipy and adenosine

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10
Q

what drug of choice is the first if a patient can’t exercise?

A

dipy

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11
Q

how do we determine target HR?

A

target HR = (220-age)*0.85

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12
Q

when do we use dobutamine?

A

if patients have contraindications for dipy and adenosine + can’t exercise

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13
Q

what is the bruce protocol?

A
  • 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
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14
Q

how do you calculate how much dipy to give to a patient?

A

0.56 mg/kg

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15
Q

what is the max dipy you can admin. to a patient

A

60 mg

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16
Q

how do you calculate how much adenosine to give to a patient?

A

0.140 mg/kg/min

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17
Q

how do you calculate how much dobutamine to give to a patient?

A

5ug/kg/min up to 40ug/kg/min

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18
Q

which protocol is preferred and why?

A

2 day protocol to eliminate possible interference in 2nd study due to residual myocardial activity

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19
Q

rest is done day 1 of a 2 day protocol. t/f

A

false
rest is done day 2 of the 2 day protocol

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20
Q

can you gate a MPI study?

A

yes

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21
Q

pitfall to G-SPECT

A
  • heart beat variances can cause inaccurate EF values
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22
Q

attenuation correction

A

reduces the influence of variable photon attenuation in the body on the final SPECT images
- but can cause artifacts

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23
Q

how is attenuation correction done?

A
  • addition of low dose CT
  • external RN source
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24
Q

ct parameters for attenuation correction

A
  • no contrast + normal tidal breathing
  • current: 5-20 mA
  • voltage: 80-140 kVp
  • x-ray segments: 1
  • slice thickness: 2-5 mm
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25
Q

when do we use prone imaging?

A

when we want to distinguish artifact from real defect when CT is unavailable
*always done in addition to supine imaging

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26
Q

what are the units for CTDI?

A

mGy

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27
Q

what are the units for DLP?

A

mGy*cm

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28
Q

what is the key differences between 1 day protocol and 2 day protocol?

A

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

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29
Q

ST elevation

A

segment greater than 1mm of normal

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30
Q

ST elevation can mean?

A

MI

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31
Q

ST depression

A

decline of greater than 2mm

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32
Q

ST depression can mean?

A

ischemia

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33
Q

when do you stop exercise stress tests?

A
  • 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
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34
Q

inotropic

A

making the heart beat with increasing force

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35
Q

chronotropic

A

increasing heart rate

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36
Q

Name two reasons why cardiac stressing of a patient should be terminated.

A

Dizziness, fatigue, ST elevation/depression, drastic increase/decrease in BP, reached target HR, if patient asks to stop

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37
Q

What is the mechanism of stress using dipyridamole?

A

vasodilation

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38
Q

When would aminophylline be used in cardiac imaging?

A

Antidote to dipy side effects, but 2 mins after RP admin

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39
Q

What dose of RP would you inject for the stress portion of a 2 day protocol?

A

740-1110 MBq

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40
Q

what is needed to be done for processing before patients leave?

A
  • using cine to check for motion
  • check the quality, is the bowel in the way?
  • CT registration
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41
Q

what is the steps for processing?

A
  1. ac registration
  2. reconstruction (iterative), reorientation
  3. display
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42
Q

what does reorientation mean?

A

aligning with the long axis of the LV

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43
Q

what can we suggest if a patient’s bowels are closer to the heart than it should be due to natural motion?

A

light exercise

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44
Q

ac registration

A

attenuation correction - ensuring the heart on the NM study lines up with the CT study

45
Q

what slices are seen for ac registration?

A

transverse, sag, coronal

46
Q

what views have the line drawn through the center of it for reorientation?

A

transaxial and sagittal

47
Q

vertical long axis =

A

oblique sagittal - separating right and left

48
Q

horizontal long axis =

A

oblique transaxial = inferior and superior

49
Q

short axis =

A

oblique coronal = slicing from apex to base

50
Q

short axis view is displayed from?

A

apex to base

51
Q

vertical long axis view is displayed from?

A

septal to lateral

52
Q

horizontal long axis view is displayed from?

A

inferior to anterior

53
Q

perfusion quantification

A

comparing perfusion to a reference population

54
Q

functional quantification

A

looking at EF

55
Q

which wall is seen “hotter” than other walls? why?

A

lateral - closer to camera

56
Q

what is unique in the apex between patients?

A

some have thinner myocardium at apex
- as long as it matches in stress + rest = don’t report as fixed defect

57
Q

ischemia

A

defect on stress that fills in rest images

58
Q

ischemia akas?

A

reversible or mismatched defect

59
Q

if we inject before target HR what can happen?

A

results in us underestimating the extent of ischemia

60
Q

infarct

A

defect present in same location on both stress and rest

61
Q

infarct aka?

A

non-reversible or fixed

62
Q

stunned myocardium

A

delayed perfusion by wall motion should improve over time

63
Q

hibernating myocardium

A

presents the same was as an infarcy
- severe chronic ischemia, decreased perfusion, poor contractility

64
Q

who would benefit from coronary revascularization?

A

those with hibernating myocardium

65
Q

what are some ways you can do perfusion quantifications?

A

1) polar maps
2) summed stress score
3) summed rest score
4) summed difference score

66
Q

how are polar plots done?

A

short axis slices are stacked and the center represents the apex and the base is at the periphery

67
Q

what do polar plots allow us to do?

A

allows for the perfusion of different segments of the myocardium and it is comparable to a normal sex-matched database

68
Q

when looking at polar plots, what images are we looking at?

A

stress, rest, + reversibility

69
Q

black areas on a polar plot = ?

A

areas of less perfusion than database

70
Q

what is summed stress score?

A

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

71
Q

SSS assignment number
0 =?

A

normal uptake

72
Q

SSS assignment number
1 =?

A

slight reduced uptake

73
Q

SSS assignment number
2 =?

A

moderately reduced uptake

74
Q

SSS assignment number
3=

A

severe reduction uptake

75
Q

SSS assignment number
4=

A

absence of uptake

76
Q

SSS = < 4

A

normal

77
Q

SSS = 4-8

A

mildly abnormal

78
Q

SSS = 9-13

A

moderately abnormal

79
Q

SSS = >13

A

severely abnormal

80
Q

what is summed rest score?

A

same concept as SSS but using the resting phase polar plot

81
Q

what is summed differences score?

A

the difference between the summed stress and summed rest

82
Q

what does the SDS indicate?

A

measurement of the degree of reversibility of defects

83
Q

LVEF in a MPI is (less/more) accurate than one from a MUGA.

A

LESS accurate than MUGA

84
Q

when do we use Tl-201 for MPI?

A

when we want myocardial viability

85
Q

what contraindications are there for Tl-201for MPI?

A

specific to stressing agents

86
Q

half life of Tl-201

A

73 hours

87
Q

energy of Tl-201

A

167 keV (10%), majority is 69-93 keV

88
Q

how does Tl-201 behave?

A

like K+, gets actively transported into cells by Na/K pump

89
Q

where does Tl-201 localize?

A

4% in heart (5-10 mins post injection)
in proportion to myocardial blood flow + tissue oxygenation

90
Q

max uptake during rest? stress?

A

rest = 10-30 mins
stress = 5 mins

91
Q

Tb of 201Tl-Cl?

A

10 days

92
Q

how is 201Tl-Cl excreted?

A

renal and hepatobiliary excretion

93
Q

redistribution

A

continuous exchange between EC and IC compartments

94
Q

when does equilibrium occur for redistribution?

A

3-4 hrs later

95
Q

what are disadvantages of Tl protocol?

A
  • suboptimal imaging characteristics
  • more attenuation
  • expensive (produced by cyclotron)
  • higher patient dose
96
Q

when are redistribution images supposed to be taken?

A

3-4 hrs after injection

97
Q

dose of 201Tl?

A

74-148 MBq at peak stress

98
Q

imaging for stress occurs when (thallium protocol)?

A

~10 mins after injection

99
Q

how do we obtain a lung:heart ratio?

A

only with Tl

100
Q

what view is used to determine lung:heart ratio?

A

planar ant

101
Q

two ways to determine viability

A

1) second injection after redistribution images are done
2) obtain a rest/redistribution study

102
Q

what shows viability?

A

an increase in concentration of tracer from initial images to redistribution images

103
Q

when do we use Tl to improve specificity?

A

when we see a fixed defect

104
Q

what shows non-viable myocardium?

A

fixed defect between initial and reinfection images

105
Q

what values are considered normal for the Lung:heart ratio?

A

<0.5

106
Q

how do you determine the lung to heart ratio?

A

counts in lung divided by counts in myocardium

107
Q

How is ischemia identified in myocardial perfusion imaging?

A

Mismatched defect, ie. Reversible defect
(present on stress but not rest)

108
Q

How is an infarct identified on myocardial perfusion imaging?

A

Fixed defect (on both stress and rest)

109
Q

What is the difference between hibernating and stunned myocardium?

A
  • 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

NMED 251 - Clinical Procedures (11 decks)

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