Ch 18. - Instrumentation II

Positron Emission Tomography

PET

what kind of imaging only uses positron emitting radionuclides

annihilation-coincidence

PET systems take advantage with special ______ detector systems

less than 200-250

what range is a patients glucose supposed to be for PET imaging

1. obtain blood sugar

2. start IV

3. allow to rest for an hour

4. use the restroom

5. image with arms up, unless it’s a whole-body scan then arms down

PET Process

negative electron

when a positron undergoes mutual annihilation with a _____ _____, their masses are converted into a pair annihilation photons

annihilation coincidence detection

this allows nearly simultaneous detection of the two annihilation photons which allows PET to localize their origin along a line between the two detectors

Coincidence logic

this is employed to analyze the signals from the opposing detectors

the electronics attach a digital time stamp to the record for each detected event

how does coincidence logic work

coincidence timing

due to ____ other events may not be detecte3d if they are not actually 180 degrees

Annihilation Coincidence detection

this allows nearly simultaneous detection of the two annihilation photons which allows PET to localize their origin along a lone between two detectors

Electronic collimation

refers to the ability of the ACD to localize events on the basis of coincidence timing, without the need for absorptive collimation

collimators

Due to the lack of ______ on PET systems, they are able to increase the sensitivity much higher than general NM due to the increased unit of activity in the patient

increase

Due to the lack of collimators on PET systems, they are able to _____ the sensitivity much higher than general NM due to the increased unit of activity in the patient

sensitivity

Due to the lack of collimators on PET systems, they are able to increase the ____ much higher than general NM due to the increased unit of activity in the patient

simultaneous

Due to the configuration of multiple detectors in a ring (or other variations) around the patient, multiple projection angels can be acquired _____

time of flight

In theory it is possible to determine the location along a line between the two detectors. This technique, which would allow the formation of tomographic images without mathematical reconstruction algorithms, known as

sensitivity

this is determined primarily by the absorption efficiency of the detector system and its solid angle of coverage for the imaged object

smaller

For PET due to the need for the 180 degree annihilation event registration. The Field of View (FOV) will always be _____ than the actual imaging area

0.34 per cm

NaI(Tl) linear attenuation coefficient is

0.95 per cm

BGO linear attenuation coefficient is

0.88 per cm

LSO, LYSO linear attenuation coefficient is

prompt coincidence

ACD produces an output whenever two events are recorded within a specified coincidence timing window. Generally any such event is called a

True coincidences

are from actual annihilation events that travel through the patient and to the detectors uninhibited or scattered within its timing window

scatter coincidences

Are from an annihilation reaction that occurs and scatters through the patients body resulting in a coincidence event to be registered, although it is a false positive

random coincidence

occur when annihilation photons from two unrelated positron annihilation events are detected in two different detectors, within the coincidence timing window

random coincidence

This can happen when one photon from each annihilation event is detected in each detector element

yes

are random coincidences rare?

the delayed window

allows for the camera acquisition window to be modified from the 4-12 nanoseconds to 64-76 nanoseconds to acquire the “random coincidence” # that are acquired this value is subtracted from the activity of the detector

the single method

Even though they are not added to the image, stand alone “single” events are counted and subtracted from the total events in the image.

the delayed window and the singles method

two methods to help reduce random coincidences in the image

Fluorodeoxyglucose

FDG

F-18

most common radiotracer used in PET

82-RbCl

used for PET myocardial viability studies, with the 75 sec half life, patients must be injected on the scan table without any delay

NaF-18

used for PET bone scans, can provide great info, as well as allow for faster scanning time compared to a general nuclear medicine MDP bone scan

Axumin F-18

Used for prostate cancer patients, must be inject into the right arm, due to a lymph node in the left potentially picking up tracer activity

Ga-68 DOTATATE

neuroendocrine tumor imaging prior to Lu177 Treatment

Cu-64

a common PET tracer that can be used for imaging trials for patients.