PET

Question 1

F-18 FDG half life

Answer 1

fluoro-2-deoxyglucose
110 minutes
cyclotron

Question 2

Rb-82 half life

Answer 2

rubidium-82
75 seconds half life
generator

Question 3

PET

Answer 3

positron emission tomography

511 keV gamma rays emitted when a positron collides with an electron.

emitted photons are nearly collinear, traveling in opposite directions, almost 180 degrees apart.

Question 4

Crystals employed for PET

Answer 4

BGO - highest stopping power but relatively poor energy resolution and timing resolution

Newer crystals: decrease dead time - allow for data acquired at much higher count rates
GSO
LSO - has intrinsic radioactivity
lutetium yttrium orthosixicate (LYSO) - has intrinsic radioactivity

Question 5

CT QC for PET/CT: water phantom QA

Answer 5

daily

Question 6

CT QC for PET/CT: Tube warm-up

Answer 6

daily

Question 7

CT QC for PET/CT: air calibration (“fast QA”)

Answer 7

daily

Question 8

CT QC for PET/CT: water phantom checks: thickness, accuracy, positioning

Answer 8

monthly

Question 9

Rule of thumb for pixel per FWHM of resolution

Answer 9

at lesasat 3 pixels for every FWHM of resolution in the image

Question 10

Rb-82 characteristics

Answer 10

monovalent cationic analog of potassium; extracted by Na+/K+ ATP pump

produced in generator by decay from strontium-82 (Sr-82) attached to an elution column

Generator is replaced q4wks

Question 11

Sr-82 half life

Answer 11

25.5 days

Question 12

Sr-82 mode of decay to:

Answer 12

Rb-82, bu electron capture

Question 13

Rb-82 half life

Answer 13

75 seconds

daughter product is krypton-82, stable

Question 14

Extraction of Rb-82 in blood affected by:

Answer 14

decreased by severe acidosis, hypoxia, and ischemia

also with increasing blood flow –> decreased extraction

Question 15

Scout scanning

Answer 15

use to ensure patient is correctly positioned before injection

Fast transmission image or with a low-dose Rb-82 injection (10-20 mCi)

Question 16

PET imaging parameters

Answer 16

Rest imaging should be performed before stress imaging to reduce the impact of residual stress effects (e.g., stunning and steal). For Rb-82, about 80% of the useful counts are acquired in the first 3 minutes, 95% of the useful counts are obtained in the first 5 minutes, and 97% are obtained in the first 6 minutes. The patient should be infused with Rb-82 for a maximum of 30 seconds.

Question 17

PET imaging time wait

Answer 17

nl LV function, >50%, imaging start 70-90 secs after injection

reduced LV function, 30-50%, imaging begins 90-110 seconds after termination of infusion

<30%, 110-130 seconds

Question 18

N-13 ammonia characteristics

Answer 18

At physiologic pH, ammonia is in its cationic form with a physical half-life of 10 minutes. Its relatively short half- life requires an on-site cyclotron and radiochemistry synthesis capability. The N-13 nitrogen decays by posi- tron emission. The daughter product is C-13 carbon, which is stable.

Ammonia - Passive diffusion
Ammonium ion by active Na/K transport mechanism

Question 19

N-13 ammonia dosimetry

Answer 19

adult: 1.48 mSv total effective dose from 20 mCi

Critical organ is urinary bladder (6 mSv from 20 mCi)

Question 20

Rb-82 dosimetry

Answer 20

1.75-7.5 mSv total effective dose for a maximal allowable activity of 60 mCi at both rest and stress

Question 21

PET glucose metabolism

Answer 21

under fasting and aerobic conditions: long-chain fatty acids are preferred fuel in the heart (65-70%), glucose provides the rest

ischemia - glucose

Question 22

F-18 FDG

Answer 22

produced in a cyclotron - bombardment of O-18 enriched water

decays by emission of positron with half-life ~110 minutes

63r keV kinetic energy window

Enters myocardial cells by same transport mechanism as glucose, in cell phosphorylated by hexokinase to FDG-6-phosphae, once phosphorylated, subsequent metabolism of FDG is minimal.

Question 23

F-18 FDG

Answer 23

Whole body dosimetry from a 10 mCi dose is 7mSV

critical organ is urinary bladder, received 59 mSV

Question 24

Myocardial substrate utilization

Answer 24

For the evaluation of myocardial viability with FDG, the substrate and hormonal levels in the blood need to favor utilization of glucose over fatty acids by the myocardium. This is usually accomplished by loading the patient with glucose after a fasting period of at least 6 hours to induce an endogenous insulin response. The temporary increase in plasma glucose levels stimulates pancreatic insulin pro- duction, which in turn reduces plasma fatty acid levels through its lipogeneic effects of adipocytes and also nor- malizes plasma glucose levels. The most common method of glucose loading is with an oral load of 25-100 g, but IV loading is also used.