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Behöver Plugga > Ct Perfusion > Flashcards

Ct Perfusion Flashcards

1
Q

What is the recommended scan duration for CTP?

A

60-90 seconds

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2
Q

Why is a 60-90 second scan duration important in CTP?

A

Shorter durations may lead to truncation artifacts. Minskad CBV (most affected, AUC truncated), ökad MTT, CBF ospecifikt.

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3
Q

What is the ideal temporal resolution for CTP and why?

A

1-2 seconds per phase. Accurate characterization of the arterial input function (AIF) and tissue time-density curves.

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4
Q

What should be the minimum z-axis coverage for CTP?

A

At least basal ganglia to vertex, ideally whole brain

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5
Q

Where should the AIF be located in CTP?

A

Contralateral MCA or ACA

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6
Q

Where should the VOF be located in CTP?

A

Superior sagittal sinus or transverse sinus

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7
Q

What characteristics should an ideal AIF peak have in CTP?

A

Sharp, high (>250 HU), and early

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8
Q

Why is a well-defined, high-amplitude AIF crucial in CTP?

A

It’s necessary for accurate deconvolution. Low or broad peaks can lead to overestimation of CBF and underestimation of MTT.

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9
Q

How should the VOF peak compare to the AIF peak in CTP?

A

Broader, slightly delayed, and higher than AIF

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10
Q

Why should the VOF peak be higher than the AIF peak in CTP?

A

Due to contrast accumulation in the venous system.

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11
Q

What should you look for in motion plots during CTP analysis?

A

Significant spikes or shifts in the motion plots

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12
Q

What percentage of patients with acute ischemic stroke experience moderate to severe head motion during CTP?

A

Almost 25%

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13
Q

Why is assessing motion important in CTP analysis?

A

Severe motion can lead to misregistration between time points and errors in time-density curves, potentially affecting the accuracy of perfusion maps.

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14
Q

What is the threshold for core infarct on a CBF map?

A

Relative CBF <30% of contralateral side

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15
Q

Why is a relative threshold used for core infarct on CBF maps instead of an absolute value?

A

Relative thresholds are more robust across different scanners and software.

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16
Q

In what situations might the CBF threshold overestimate core infarct (10 reasons)?

A
  1. Ultra-early imaging (< 1h):
    Severely hypoperfused tissue may not have progressed to irreversible infarction yet
  2. Rapid reperfusion:
    Tissue may recover if blood flow is quickly restored
  3. Good collaterals on angiography
  4. “Ghost infarct core”:
    A combination of ultra-early imaging and good collaterals
  5. Chronic hypoperfusion:
    Caortid stenosis fx, tissue may have adapted to chronically low blood flow
  6. Luxury perfusion:
    CTP in subacute phase shows areas of increased perfusion but they’re actually infarcted
  7. Technical factors:
    CTP with incorrect AIF shows large area with rCBF <30%
  8. Posterior circulation strokes:
    CTP shows large areas in posterior fossa with rCBF <30%, CBF threshold may not apply in this region
  9. Small vessel disease:
    Multiple areas with rCBF <30% in white matter. Chronic changes can lead to overestimation of IC
  10. Vasospasm:
    Severe vasospasm can cause CBF reduction that mimics core infarct

Evaluating CBV in addition to CBF can help (preserved CBV in areas of low CBF might indicate potential overestimation).

Being aware that overestimation is more likely in ultra-early imaging or after recent reperfusion

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17
Q

What is the “ghost infarct core” phenomenon in CTP?

A

Appears as core infarct on initial CTP but shows no infarction on follow-up. Ultra early imaging or after successful reperfusion och excellent collaterals.

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18
Q

How does CBV typically appear in core infarct areas?

A

Reduced

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19
Q

Why is CBV less commonly used for core delineation than CBF?

A

Due to its lower accuracy

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20
Q

How might CBV appear in the penumbra?

A

Preserved or elevated

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21
Q

Why might CBV be preserved or elevated in the penumbra despite reduced CBF?

A

Due to autoregulatory vasodilation, which is a key feature of potentially salvageable tissue

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22
Q

What is the threshold for penumbra on a Tmax map?

A

Tmax >6 seconds

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23
Q

What does a region with Tmax >10 seconds indicate?

A

Severe hypoperfusion with higher risk of progressing to infarction

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24
Q

What is the hypoperfusion intensity ratio (HIR)?

A

The volume of Tmax >10s tissue relative to Tmax >6s tissue

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25
Q

What does the HIR provide information about?

A

Collateral status and the severity of hypoperfusion

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26
Q

What is the maximum core infarct volume for late window treatment eligibility?

A

<70 mL

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27
Q

What is the minimum mismatch ratio for late window treatment eligibility?

A

> 1.8

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28
Q

How is the mismatch ratio calculated?

A

(Volume of critically hypoperfused tissue) / (core infarct volume)

29
Q

What is the minimum penumbra volume considered clinically meaningful?

A

15 mL

30
Q

How is HIR (hypoperfusion intensity ratio) calculated?

A

HIR = Volume of Tmax >10s / Volume of Tmax >6s

31
Q

What does a lower HIR suggest?

A

Good collaterals and slower infarct growth

32
Q

What HIR value is associated with good collaterals and slower infarct growth?

A

HIR <0.4

33
Q

How can chronic infarcts affect CTP interpretation?

A

They may mimic acute core infarcts

34
Q

How can delayed contrast arrival affect CTP interpretation?

A

It can overestimate penumbra, especially in cases of carotid stenosis

35
Q

Why might small infarcts be missed on CTP?

A

Due to limited sensitivity for small infarcts (<15mm), lower spatial resolution, and artifacts at the skull base

36
Q

What is the “ghost infarct core” phenomenon and when does it occur?

A

It occurs in ultra-early imaging or rapid reperfusion, showing falsely large core infarcts on CTP

37
Q

What conditions can mimic perfusion deficits on CTP?

A

Seizures, migraines, and PRES (Posterior Reversible Encephalopathy Syndrome)

38
Q

What constitutes a target mismatch profile?

A

Core <70 mL, mismatch ratio >1.8, and mismatch volume >15 mL

39
Q

What does CBF measure in CTP?

A

Cerebral Blood Flow - the volume of blood passing through a given amount of brain tissue per unit time

40
Q

What are the typical units for CBF?

A

mL/100g/min

41
Q

What is a normal CBF value for gray matter?

A

50-60 mL/100g/min

42
Q

What is a normal CBF value for white matter?

A

20-25 mL/100g/min

43
Q

What does CBV measure in CTP?

A

Cerebral Blood Volume - the total volume of blood in a given amount of brain tissue

44
Q

What are the typical units for CBV?

A

mL/100g

45
Q

What is a normal CBV value for gray matter?

A

4-5 mL/100g

46
Q

What is a normal CBV value for white matter?

A

2-3 mL/100g

47
Q

What does MTT measure in CTP?

A

Mean Transit Time - the average time it takes for blood to pass through the brain tissue

48
Q

What is a normal MTT value?

A

4-6 seconds

49
Q

What does Tmax measure in CTP?

A

Time to maximum of the residue function - a measure of delay in bolus arrival

50
Q

What Tmax threshold is commonly used to define critically hypoperfused tissue?

A

> 6 seconds

51
Q

What does TTP measure in CTP?

A

Time to Peak - the time from the start of contrast injection to the peak enhancement in the tissue

52
Q

How does TTP differ from Tmax?

A

TTP is more sensitive to delayed contrast arrival but less specific for tissue at risk

53
Q

What does TTD measure in CTP?

A

Time to Drain - the time it takes for contrast to clear from the tissue

54
Q

How can TTD be useful in CTP interpretation?

A

It can help assess venous outflow and collateral circulation

55
Q

In a typical MCA stroke, how might the perfusion parameters appear in the core?

A

Decreased CBF, decreased CBV, increased MTT, increased Tmax

56
Q

In a typical MCA stroke, how might the perfusion parameters appear in the penumbra?

A

Decreased CBF, normal or increased CBV, increased MTT, increased Tmax

57
Q

What perfusion pattern might you see in a patient with chronic carotid stenosis?

A

Delayed TTP and increased MTT in the affected hemisphere, but possibly normal CBF due to collaterals

58
Q

In a case of luxury perfusion after recanalization, what perfusion pattern might you see?

A

Increased CBF and CBV in the affected area

59
Q

What perfusion pattern might suggest reperfusion injury?

A

Very high CBF and CBV in the previously ischemic area, possibly with contrast extravasation

60
Q

How might perfusion parameters appear in a patient with seizures?

A

Increased CBF and CBV in the seizure focus during the ictal phase

61
Q

What perfusion pattern might you see in a case of reversible cerebral vasoconstriction syndrome (RCVS)?

A

Patchy areas of decreased CBF and prolonged MTT, often with watershed distribution

62
Q

In a case of cerebral venous thrombosis, what perfusion abnormalities might you expect?

A

Increased CBV and MTT, with variable CBF depending on the stage and severity

63
Q

How might a subacute infarct appear different from an acute infarct on CTP?

A

Subacute infarcts may show luxury perfusion with increased CBF and CBV, unlike the decreased CBF and CBV seen in acute infarcts

64
Q

What perfusion pattern might suggest misery perfusion in chronic cerebrovascular disease?

A

Increased MTT and decreased CBF, but preserved CBV due to autoregulatory vasodilation

65
Q

How can vascular stenosis affect CTP interpretation?

A

It can cause delay and dispersion of the contrast bolus, potentially overestimating the extent of hypoperfusion

66
Q

What pitfall might occur when interpreting CTP in a patient with a vascular malformation?

A

High-flow arteriovenous malformations can lead to early venous filling and errors in AIF selection

67
Q

What pitfall might occur when interpreting CTP in a patient with severe leukoaraiosis?

A

Chronic white matter changes can have low CBF, potentially being misinterpreted as acute ischemia

68
Q

What pitfall might occur when interpreting CTP in a patient with intracranial hemorrhage?

A

Beam hardening artifacts from acute blood can mimic perfusion deficits

69
Q

How can selection of an AIF in a partially occluded vessel affect CTP interpretation?

A

It can lead to overestimation of perfusion deficits in the affected territory

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