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Core > Nuclear: Pulmonary > Flashcards

Nuclear: Pulmonary Flashcards

1
Q

What are the usual reasons a V/Q scan is done instead of a CTPA?

A
  • Contrast allergy
  • Very low GFR
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2
Q

What radiotracer is used for the perfusion portion of a V/Q scan?

A

Tc-99m MAA (macro aggregated albumin)

Note: This is made by heat denaturation of human serum albumin and selecting a particular particle size to keep the particles trapped in pulmonary capillaries (MAA does not enter systemic circulation until it breaks down).

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3
Q

What is the biologic half life of Tc-99m MAA?

A

~4 hours

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4
Q

What radio tracers are used for the ventilation portion of a V/Q scan?

A
  • Xenon 133 (radioactive gas)
  • Tc-99m DTPA (radioactive aerosol)
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5
Q

Which portion of the V/Q scan needs to be performed first?

A

Ventilation

Note: This is because the radio tracers used for ventilation (Xe/DTPA) have lower energy and would be drowned out by the perfusion radiotracer (MAA).

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6
Q

What is the half life of Xenon-133?

A
  • 30 seconds (biological half-life because you breath it out)
  • 5.3 days (physical half life)
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7
Q

What are the 3 phases of the ventilation portion of a V/Q scan?

A
  • Wash in (single maximum inspiration breath hold)
  • Equilibrium (normal breathing with room air/xenon mix)
  • Wash out (breathing normal air)
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8
Q

What radiotracers are used for a quantitative perfusion study prior to lung resection?

A

Xenon-133 and Tc-99m MAA

Note: You can not use Tc-99m DTPA for the ventilation portion of a quantitative perfusion scan because it will interfere with the Tc from the MAA.

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9
Q

V/Q scan

A

Right-to-left shunt (e.g. ASV, VSD, pulmonary AVM)

Note: Uptake in brain, kidneys, spleen, etc. indicated that radiotracer made it into systemic circulation via a shunt.

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10
Q

How big should Tc-99m MAA particles be?

A

10-100 micrometers

Note: If smaller than 10, the MAA won’t be trapped in pulmonary circulation and will escape to systemic circulation. If larger than 100, the particles may block arterioles.

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11
Q

Why might you reduce the number of Tc-99m MAA particles you use for a V/Q scan?

A
  • Pt has fewer than normal pulmonary capillaries (e.g. pt is a child or only has 1 lung; you don’t want to block more than 0.1% of pulmonary capillaries)
  • Known right-to-left shunt (to minimize blocking capillaries in the brain)
  • Pulmonary hypertension
  • Pregnant pt

Note: The Tc dose will be the same, just added to fewer particles.

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12
Q

V/Q scan

A

Right-to-left shunt

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13
Q

V/Q scan

A

Clumped MAA (due to inadvertent drawing of blood into the MAA syringe before injection)

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14
Q

V/Q scan

A

Normal perfusion

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15
Q
A

Prominence of the pulmonary fissures (“fissure sign”):

  • Pleural effusion
  • Pleural scarring/thickening
  • COPD
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16
Q

V/Q scan

A

Normal ventilation study

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17
Q

V/Q scan

A

Xenon-133 uptake in the liver, suggestive of hepatic steatosis (xenon is fat soluble)

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18
Q

Which radiotracer is this?

A

Tc-99m DTPA

Note: V/Q scan with clumping in the mouth, central airways, and stomach (due to swallowing/aspirating DTPA in saliva).

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19
Q

How can you tell whether Xenon or DTPA was used for the ventilation portion of a V/Q scan?

A

DTPA will have multiple projections (xenon has a very fast washout so there is usually only time for 1 or 2 projections)

DTPA may show “clumping” in the mouth, central airways, and stomach (due to swallowed/aspirated DTPA in saliva)

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20
Q

You see thyroid and/or stomach on a VQ scan…

A
  • Free technetium contamination
  • Right-to-left shunt (will also have uptake in the brain)
21
Q

How should you alter a V/Q scan protocol if the pt has a known right-to-left shunt?

A

Decrease the number of MAA particles given to the pt (from 500,000 to about 100,000)

Note: This is to minimize MAA blocking capillaries in the brain.

22
Q

How should you alter a V/Q scan protocol if the pt has pulmonary hypertension?

A

Decrease the number of MAA particles given to the pt

23
Q

How should you alter a V/Q scan protocol if the pt is a neonate?

A

Decrease the number of MAA particles given to the pt (from 500,000 to about 10,000-50,000)

Note: You don’t want to block more than 0.1% of pulmonary capillaries.

24
Q
A

Suspicious for central obstructing mass (cancer, fibrosis mediastinitis, central PE), recommend a chest CT

Note: Unilateral whole lung perfusion defect with normal ventilation.

25
Q

What is the grade for this V/Q scan?

A

Low probability for PE

Note: But recommend CT chest to look for a central obstructing mass (e.g. bronchogenic carcinoma, central PE, fibrosis mediastinitis).

26
Q

How does gallium-67 localize?

A

It acts as an iron analog: gallium binds to lactoferrin and concentrated in areas of inflammation, infection, and rapid cell division

Note: Gallium can bind to neutrophil membranes even when those cells are dead (giving gallium some advantages over In-111 WBCs in identifying chronic infections).

27
Q

How is gallium-67 produced?

A

In a cyclotron, by the bombardment of Zinc-68

28
Q

What is the half-life of gallium-67?

A

3 days

29
Q

What are the photopeaks for gallium-67?

A
  • 93 keV (40%)
  • 184 keV (20%)
  • 300 keV (17%)
  • 393 keV (5%)
30
Q

Why are gallium scans usually done after 24 hours post injection?

A

Before 24 hours, there is usually to much background noise

31
Q

What is the critical organ for gallium-67?

A

Colon

32
Q

What is the normal distribution for gallium-67?

A
  • Liver (highest uptake)
  • Bone marrow (“poor mans bone scan”)
  • Spleen
  • Salivary/lacrimal glands
33
Q

What scan is this?

A

Gallium-67

Note: Bone uptake AND liver > spleen.

34
Q

Is faint breast uptake normal for gallium-67?

A

Yes, especially if pregnant or lactating

35
Q

Is faint lung uptake normal for gallium-67?

A

Usually no

Note: Only normal during the first 24 hours after injection (most pts are imaged more than 24 hours after injection).

36
Q

Is bowel uptake normal for gallium-67?

A

Yes, after 24 hours

37
Q

Is bone uptake normal for gallium-67?

A

Yes (uptake in both the cortex and marrow)

Note: “Poor mans bone scan.”

38
Q

Differential for lung uptake on a gallium-67 scan

A
  • Infection (i.e. pneumonia)
  • Atelectasis
  • ARDS
  • Heart failure
39
Q

Why are gallium-67 scans used to evaluate for sarcoidosis?

A
  • Helps identify active disease (scans are negative in inactive disease)
  • Helps guide biopsy/lavage (if looking to prove diagnosis)
40
Q
A

Sarcoidosis

Note: “Lambda sign.”

41
Q

Gallium-67

A

Sarcoidosis or Sjogrens

Note: “Panda sign” can also be seen in treated lymphoma.

42
Q

Gallium-67 scan in pt on chemotherapy

A

Pulmonary fibrosis (drug reaction to bleomycin)

43
Q

Gallium-67 scan in pt taking amiodarone

A

Amiodarone pneumonitis

Note: Lung uptake of gallium-67.

44
Q

Gallium-67 scan in pt with HIV

A

Think PCP (pneumocystis jirovecii pneumonia)

Note: Diffuse bilaterala pulmonary uptake.

45
Q

Thallium (C) and gallium (E) scans in a pt with HIV

A

Kaposi sarcoma

Note: Thallium positive and gallium negative.

46
Q

Gallium-67

A

Pneumonia

Note: Focal pulmonary uptake without parotid or nodal uptake to suggest sarcoidosis.

47
Q
A

Malignant otitis externa

48
Q

IV drug user

A

Think spinal osteomyelitis

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