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VetRad Boards prep > Nuc Med - Physics > Flashcards

Nuc Med - Physics Flashcards

1
Q

What is the minimum energy required for positron decay?

A

1.022 MeV

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2
Q

What are examples of cyclotron-produced radionuclides?

A

1-123, Indium-111, Gallium-67, Cobalt-57, Thallium-201, Flourine-18, N-13, O-15, C-11

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3
Q

What is the typical decay pathway for radionuclides produced in nuclear reactors?

A

Beta minus decay (neutron rich)

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4
Q

Which radionuclides are produced via fission reactions?

A

Mo-99, 1-131, Xe-133

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5
Q

Which radionuclides are produced via neutron activation?

A

P-32, Chromium-51, I-125

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6
Q

In 99mTc generation, when is elution performed? What solution is used?

A

NaCl used at 23 hours when transient equilibrium occurs

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7
Q

What is the half-life of 99mTc?

A

6 hours

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8
Q

What is the activity ratio of daughter:parent at transient equilibrium in Ci?

A

66:60

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9
Q

In gamma cameras, what is the rate-limiting step?

A

The ADC ->longest dead time

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10
Q

How is spatial resolution improved at the level of the photomultiplier?

A

incr number of PMTs and decreasing size of individual PMTs

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11
Q

What is the trade off between high resolution cameras and high sensitivity cameras?

A

High-resolution cameras have thicker septa and smaller holes, thus increased resolution but reduced counts (e.g. bone scans). High sensitivity cameras have thinner septa and wider holes, thus reduced resolution but higher counts.

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12
Q

Which isotopes require low-energy collimators?

A

99m-Technetium (Tc), 201-thallium (Tl), 123-iodine

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13
Q

Which isotopes require medium energy collimators?

A

131-iodine, 111-Indium(In)

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14
Q

Which isotopes require high-energy collimators?

A

67-Ga, 18-F

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15
Q

What is the advantage of diverging collimators?

A

can use a larger field of view -> minifies the image

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16
Q

What is the advantage of converging collimators?

A

increased spatial resolution - > magnifies the image with incr distance, focal point in front of the camera

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17
Q

What is a major difference between pin-hole and parallel collimators?

A

-pin-hole collimators, the sensitivity dramatically decreases with increasing distance - WIth parallel collimators, increasing distance does not decrease sensitivity

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18
Q

What is the photopeak of 99mTc?

A

140 keV

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19
Q

1 photon is emitted by the NaI crystal per how many eV deposited by gamma rays?

A

1 photon per 25 eV

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20
Q

How do you calculate pixel size?

A

pixel size= FOV/matrix size

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21
Q

To avoid loss of resolution from digitization, the crystal should be

A

<1/3rd

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22
Q

How can you increase count density?

A
  • Increase acquisition time - use a smaller matrix (e.g. 128x128) - Use a larger dose of radiopharmaceutical - use a general-purpose, low-energy collimator - Use image filters, such as medium smooth or Metz
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23
Q

Equine: If early bone uptake is expected, what radiopharmaceutical can be used?

A

99mTc-DTPA or 99mTc-mebrofenin - use for vascular and soft tissues phase because rapidly excreted from kidneys, then bone scan be performed later

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24
Q

Which has better bone uptake, 99mTC-MDP or HDP?

A

HDP has best bone uptake and faster renal excretion

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25
What acquisition parameters are necessary for small animal bone scintigraphy?
- LEAP collimator - peak at 140keV w/20% window - incr acq times 20-30% - static frame mode - matrix 256 x 256 x 16 - lateral and dorsal images, +/- obl
26
DDX for pulmonary uptake during bone phase?
- Cushing's - osteomata - pulmonary metastasis - previous lung scan
27
DDX for hepatic uptake during bone scan?
- mineralized granulomas - metastatic disease - parasitic disease - hematoma - radiochemical iniquities - previous sulfur colloid scan
28
How does perineural anesthesia or intraarticular anesthesia effect interpretation?
there will be a positive soft tissue uptake up to 17 days post perineural/14 days post intraarticular injection; there will be no bone uptake
29
Where are sites of normal nonskeletal IRU?
- urinary system - naso/oropharynx - breast tissue (esp during lacation) - blood pool activity
30
Which type of metastatic neoplasia may have poor uptake and why?
multiple myeloma, purely osteoclastic
31
Why is scintigraphy not useful for determining presence of active osteomyelitis?
uptake can be seen for weeks to months after infection has resolved
32
What is the progression of uptake pattern for fracture healing?
- 5 to 7 day - diffuse, intense uptake - 1-4 weeks - focal, intense linear uptake - 6-12 months - gradual decrease in uptake
33
Which radiopharmaceutical is used in R to L shunts?
99mTc- MAA
34
Which radiopharmaceutical is most commonly used for first pass angiography?
99mTcO4
35
What is normal QP:QS?
\<1.2
36
What will QP:QS be in L to R shunts?
\>1.2
37
How do you differentiate between an intracardiac or extracardiac R-\>L shunt?
- Reverse PDA - blood with go to head, neck or forelimbs - VSD w/Eisenmenger's - blood goes to whole body, w/radio uptake concentrating in the brain and kidneys
38
How do you calculate shunt fraction?
%R to L shunt = (total body counts - lung counts) / total body counts x 100
39
Which radiopharmaceuticals are used in GE scintigraphy for liquid and solid phase?
Liquid phase - 99mTc-DTPA Solid - 99mTc-mebrofenin or desofenin (cats)
40
How do you calculate ejection fraction?
EF = [(End-diastolic counts - end systolic counts) / (end-diastolic counts - background counts)] x 100
41
What radiopharmaceutical is used for determination of myocardial perfusion and viability?
99mTc - Sestamibi
42
What competes with 99mTc-mebrofenin in bidning to hepatocytes?
bilirubin -\> will have reduced HEF in hyperbilirubinemia
43
What is the normal GB ejection fraction?
60% (+/- 18%) @ rate of 10% per min
44
In regard to hepatic excretion, what is the normal half-time clearance in dogs?
19 minutes
45
During hepatobiliary scintigraphy, when does normal cardiac wash out occur?
5 min
46
What is the normal hepatic time to peak?
6-8 minutes
47
Which radionuclides are at least partially clear by the RES?
99mTc- MAA and HMPAO
48
How do you calculate hepatic perfusion index?
HPI = aterial slope ÷ portal slope
49
What is the normal HPI?
\< 2:1 (should be about 1:1)
50
What HPI indicates a shunt and what does the slope look like?
HPI \> 2:1; flattening of the slope
51
What is the perrectal absorbtion amount of 99mTcO4-?
15% @ 2 min, the remaider is passed in the feces
52
What is the normal liver to heart transit time in PRPS?
8-12s
53
How do you calculate shunt fraction?
SF = [(ΣHeart ROI)/(ΣHeart ROI + ΣLiver ROI)] x 100
54
How will the PRPS appear in dogs with microvascular dysplasia?
normal
55
What is the PRPS shunt fraction in dogs with a shunt?
\>60%
56
What are advantages of Trans-splenic portal scintigraphy over trans rectal?
* increased count stats * better anatomic detail * better absorption from spleen (53%) * smaller radionuclide dose
57
What is tha half life of 99mTc-mebrofenin?
19 minutes
58
In TSPS, what is the normal shunt fraction for pertechnetate and mebrofenin?
pertechnetate - 2.6% mebrofenin - 0.8%
59
What is the first pass hepatic extraction rate for 99mTc-mebrofenin?
95%
60
What is this image depicting
Normal transsplenic scinigraphic study
61
What is this image depicting?
Left divisional IHPSS
62
What is this image depicting?
portoazygous shunt
63
What is this image depicting?
Splenocaval shunt
64
What is this image depicting?
Multiple acquired PSS and single internal thoracic shunt
65
What isotopes are used for ventilation and perfusion scans?
Perfusion - 99mTc-MAA Ventilation - 99mTc-DTPA
66
Why is 99mTc-DTPA better for GFR determination than the other isotopes?
No tubular secretion - 100% GFR clearance
67
What is the soft tissue linear absorption coefficient for 99mTc y-rays?
0.153/cm
68
When is normal peak renal radioactivity?
2.5-3.5 minutes
69
what would a GFR of 1.2-2.5 ml/min/kg indicate?
subclinical renal insufficiency
70
What is the normal GFR in a dogs and cat?
Dogs \>/= 3 ml/kg/hr Cats \>/= 2.5 ml/kg/hr
71
How do you calculate global GFR in dogs?
GFR = 0.194(%ID RK +%ID LK) - 0.37 In cats it is GFR = 0.284(%ID RK +%ID LK) - 0.164
72
In normal cats treated with methimaxzole, how long will there be enhanced I trapping?
15 days post withdrawal
73
In dogs and cats, when is peak uptake of sodium pertechnetate and when do you image?
Dogs: peak uptake @ 2-3 hours, start imaging at 20 min or 1 hour Cats: peak uptake @ 45 min-1 hr (or 4 hours in one study), image at 20 min
74
In cats, what is the normal T:S ratio?
\<1:1 (0.87:1)
75
What is the physical half life of 131I?
8.1 days
76
what is the NRC release criteria for 131I cats?
\<0.5 mR/hr @ 1 meter at day 3
77
What is the rad to Roentgen conversion?
1R = 1 rad
78
What is the Gray to rad conversion?
1 Gy = 100 rad
79

VetRad Boards prep (11 decks)

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