PET CT REVIEW QUESTIONS AND
ANSWERS 100% CORRECT
How do you correct for attenuation? - ANSWER-CT AC Map
Cs137/Ge68 Transmisson
Why is CT better for attenuation correction in PET? - ANSWER-Decrease noise on
attenuation map
Decrease acquisition time
Better anatomic info.
How are x-rays produced? - ANSWER-Bremsstrahlung radiation - (braking radiation) A
charged particle interacts with an atom by entering the electron shell, slowing down, and
changing direction before exiting the electron shell. The atom emits the Brems Ray in
the form of an x- ray to get rid of the excess energy.
Characteristic radiation - electron ejected from inner shell, energy released as
characterisic x-rays as outer shell electrons drop into vacancies.
How are x-rays produced in an x-ray tube - ANSWER-Current is applied to the filament
of the cathode (-), this produces an electron cloud (and increases mAs). The electron
cloud is accelerated towards anode (+) when voltage is applied to the anode (increasing
kVp). The electrons strike the anode on the target producing x-rays.
When you increase kVp = - ANSWER-Increase x-ray energy
Increase penetration of object
Decrease noise
Decrease beam hardening
Increase pt. dose
Decrease contrast
When you increase mA = - ANSWER-Increase # of x-rays
Decrease noise
Increase contrast
Increast pt. dose
Hounsfield unit for water? - ANSWER-0
Hounsfield unit for air? - ANSWER--1000
Hounsfield unit for bone? - ANSWER-1000
, What is reconstruction kernel? - ANSWER-An algorithm applied to raw data that
determines the amount of smoothing during reconstruction process. It is necessary to
use more than one reconstruction kernel because of the different densities in the body.
What is the window width and level? - ANSWER-It controls how the image is displayed.
The gray scale and filter is set by the operator to help differentiate tissue densities like
soft tissue or bone.
What is the DAILY QC for CT? - ANSWER-Tube warmup
Air calibration
CT # accuracy
Image noise at clinical parameters
Eval of tomo uniformity
What is Line of Response? - ANSWER-Uses the detection of a pair of two 511 KeV
photons on two opposite detectors to recreate the line where the annihilation interaction
took place.
What is Time of Flight? - ANSWER-Uses the detection of a pair of two 511 KeV photons
on two opposite detectors to pinpoint the exact location of the annihilation event on the
LOR.
What is the typical coincidence timing used to detect true coincidences? What is the
typical coincidence timing used to detect randoms? - ANSWER-Coincidence timing
window: 4-12 nano seconds
Randoms Rate: 60-100 nanoseconds
What pitch does diagnostic CT imaging use? - ANSWER-Uses a lower pitch to increase
spatial resolution
What pitch does CT use for AC? - ANSWER-Uses higher pitch (1 or higher)
From which part of the atom is the positron emitted? - ANSWER-Nucleus
From which part of the atom is the x- ray emitted? - ANSWER-electron shell
2. Define the following: Prompt coincidence - ANSWER-total number of events detected
by the coincidence circuit
2. Define the following: True coincidence: - ANSWER-A pair of annihilation photons,
from a single event, striking 2 detectors at the same time
2. Define the following: Random coincidence - ANSWER-A false event, when 2
annihilation photons reach 2 detectors at the same time, but originate from 2 different
atoms/events. ↑ with ↑ activity and when 3D mode is used.
ANSWERS 100% CORRECT
How do you correct for attenuation? - ANSWER-CT AC Map
Cs137/Ge68 Transmisson
Why is CT better for attenuation correction in PET? - ANSWER-Decrease noise on
attenuation map
Decrease acquisition time
Better anatomic info.
How are x-rays produced? - ANSWER-Bremsstrahlung radiation - (braking radiation) A
charged particle interacts with an atom by entering the electron shell, slowing down, and
changing direction before exiting the electron shell. The atom emits the Brems Ray in
the form of an x- ray to get rid of the excess energy.
Characteristic radiation - electron ejected from inner shell, energy released as
characterisic x-rays as outer shell electrons drop into vacancies.
How are x-rays produced in an x-ray tube - ANSWER-Current is applied to the filament
of the cathode (-), this produces an electron cloud (and increases mAs). The electron
cloud is accelerated towards anode (+) when voltage is applied to the anode (increasing
kVp). The electrons strike the anode on the target producing x-rays.
When you increase kVp = - ANSWER-Increase x-ray energy
Increase penetration of object
Decrease noise
Decrease beam hardening
Increase pt. dose
Decrease contrast
When you increase mA = - ANSWER-Increase # of x-rays
Decrease noise
Increase contrast
Increast pt. dose
Hounsfield unit for water? - ANSWER-0
Hounsfield unit for air? - ANSWER--1000
Hounsfield unit for bone? - ANSWER-1000
, What is reconstruction kernel? - ANSWER-An algorithm applied to raw data that
determines the amount of smoothing during reconstruction process. It is necessary to
use more than one reconstruction kernel because of the different densities in the body.
What is the window width and level? - ANSWER-It controls how the image is displayed.
The gray scale and filter is set by the operator to help differentiate tissue densities like
soft tissue or bone.
What is the DAILY QC for CT? - ANSWER-Tube warmup
Air calibration
CT # accuracy
Image noise at clinical parameters
Eval of tomo uniformity
What is Line of Response? - ANSWER-Uses the detection of a pair of two 511 KeV
photons on two opposite detectors to recreate the line where the annihilation interaction
took place.
What is Time of Flight? - ANSWER-Uses the detection of a pair of two 511 KeV photons
on two opposite detectors to pinpoint the exact location of the annihilation event on the
LOR.
What is the typical coincidence timing used to detect true coincidences? What is the
typical coincidence timing used to detect randoms? - ANSWER-Coincidence timing
window: 4-12 nano seconds
Randoms Rate: 60-100 nanoseconds
What pitch does diagnostic CT imaging use? - ANSWER-Uses a lower pitch to increase
spatial resolution
What pitch does CT use for AC? - ANSWER-Uses higher pitch (1 or higher)
From which part of the atom is the positron emitted? - ANSWER-Nucleus
From which part of the atom is the x- ray emitted? - ANSWER-electron shell
2. Define the following: Prompt coincidence - ANSWER-total number of events detected
by the coincidence circuit
2. Define the following: True coincidence: - ANSWER-A pair of annihilation photons,
from a single event, striking 2 detectors at the same time
2. Define the following: Random coincidence - ANSWER-A false event, when 2
annihilation photons reach 2 detectors at the same time, but originate from 2 different
atoms/events. ↑ with ↑ activity and when 3D mode is used.
