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PET Study Guide Ed 3 > Chapter 4 > Flashcards

Chapter 4 Flashcards

1
Q

What size of axial FOV do early PET or PET/CT scanners have?

12cm
15cm
18cm
20cm

A

15cm

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2
Q

What size of axial FOV do newer PET or PET/CT scanner systems have?

15-20cm
18-20cm
20-26cm
22-30cm

A

20-26cm

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3
Q

What 4 PET scanner system designs are there besides the full-ring system?

A

Partial Ring
Full Ring
Gamma Camera Coincidence Imaging
Panel RIng

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4
Q

What is the source material that is housed in the scanner for calibration of the detectors?

Ga-68
Cs-137
F-18
Ge-68

A

Ge-68

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5
Q

What should the depth of the crystal be to provide enough thickness to effectively stop the 511keV annihilation photons?

10mm
20mm
15mm
14mm

A

20mm

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6
Q

What detector module have manufactures migrated to create digital systems that have improved speed and short coincidence time resolution (250psec)?

A

SiPM

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7
Q

What is the line along which a the annihilation interaction occurs in the annihilation photon pair is detected by crystals on opposing sides?

A

line of response (LOR)

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8
Q

What is the lead or tungsten plates between each ring of individual crystals?

A

septa

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9
Q

Each ring of detectors have septa in place may only detect photons coming from with in the direct plane.

2D or 3D imaging?

A

2D

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10
Q

When septa are removed or moved out of the way, with no septa to restrict the angel of acceptance of annihilation photons.

2D or 3D imaging?

A

3D

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11
Q

3D imaging sensitivity is ______ times better than 2D imaging.

2 to 3
5 to 12
4 to 10
8 to 10

A

4 to 10

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12
Q

If there is a smaller angle of acceptance , is the sensitivity higher or lower at the center?

A

higher sensitivity

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13
Q

When the annihilation event interaction takes place, the 2 photons are not absorbed in the body, and they arrive directly into opposing detectors.

This is called what?

True event
Random event
Scatter event

A

True Event

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14
Q

When 2 photons from different decaying atoms arrive into opposing crystals with in the coincidence timing window and a false LOR is created.

This is called what?

True event
Scatter event
Random event

A

Random event

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15
Q

Detected when one or both of the photons undergo a scatter interaction, which also creates a false LOR.

This is called what?

True event
Scatter event
Random event

A

Scatter event

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16
Q

The overall effect of detecting false LORs is a substantial (increase or decrease) of the contrast in the image?

A

decrease

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17
Q

Corrections for both _______ and ______ events are absolutely required during the reconstruction process to produce a useful image.

A

random and scatter events

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18
Q

The fraction of detected events that are from scattered photons is called what?

A

Scatter fraction

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19
Q

What is the dominant type of interaction at 511keV?

True event
Scatter event
Compton scattering event
Random event

A

Compton scattering event

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20
Q

What are the ranges of energy windows for old and new scanners?

A

Old 350keV-650keV
New 425keV-600keV

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21
Q

What fraction is dependent on the amount of radioactivity both within the FOV and adjacent to the scanner, where single photons from out the FOV may be detected and contribute as a random event?

Scatter fraction or Randoms fraction

A

Randoms fraction

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22
Q

The noise equivalent count rate (NECR) may be used to measure _________.

A

signal-to-noise ratio

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23
Q

What is the equation for NECR?

A

T^2 / (T+S+R)

T= true count rate
S=scatter coincident count rate
R=randoms count rate

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24
Q

These following factors allow the use of what for PET imaging?

-Use of small crystals
-The creation of an LOR between 2 crystals to record the pathway of the radiation
-The use of coincidence-timing window to record and hopefully capture the data of true events

A

electronic collimation

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25
Q

When LORs are closer to the edge of the detector ring, interactions may take place at different depths with the crystal the will cause a slight mispositioning of the LOR.

What effect is taking place?

A

axial blurring or detector parallax

26
Q

The principle of _____ is based on computing the arrival time difference between 2 annihilation photons that are detected on opposite sides of the ring of crystals.

A

ToF (Time-of-Flight)

27
Q

ToF has greatly improved what contrast aspect in PET?

A

lesion-to-background contrast

28
Q

ToF systems often acquire in what mode?

29
Q

Whole-body scan starts and ends where on the body?

How many beds?

A

eyes to thighs

5 to 6 beds

30
Q

Total-body scan starts and ends where on the body?

How many beds?

A

Tope of the head to the tips of toes

10 to 14 beds

31
Q

Detector sensitivity with __________ over the patient provides more uniform photon-detection sensitivity than the pyramidal sensitivity profile that is achieved with bed overlapped routine PET imaging.

A

continuous motion

32
Q

Cardiac gating uses what interval?

A

R to R interval

33
Q

Respiratory gating is usually performed to provide improved visualization of what?

A

oncology lesions

34
Q

Dynamic acquisition is PET is used to image for what?

A

The brain, heart, or limited tumor area

35
Q

__________ is used to create a map of attenuation correction values for each pixel in the image.

A

Transmission scan

36
Q

What is the advantage of transmission scanners over CT?

A

the use of radioactive sources is a very low radiation exposure compared to CT

37
Q

__________ are created from raw data and list-mode data.

Represents the activity across the detector (horizontal axis) at each projection angle (vertical axis) over 180 degrees.

38
Q

______ creates an initial estimate of the image, and projections from the estimated image are computed.

A

Iterative reconstruction

39
Q

What is the original iterative technique?

A

Maximum likelihood expectation maximization (MLEM)

40
Q

The iterative technique that uses a subset of data and is the most commonly used reconstruction method is what?

A

ordered subset expectation maximization (OSEM)

41
Q

The higher the number of subsets and iterations, the finer the resolution and detail in the resultant images, however the noise in the image may also be _________.

42
Q

What algorithm is very similar to OSEM and used on Philips systems?

A

Row-Action Maximization-Likelihood Algorithm (RAMLA)

43
Q

What are the 3 ways to use the 3D angle sinograms?

A

-single slice rebinning (SSRB)
-fourier rebinning (FORE)
-full 3D reconstruction

44
Q

Oldest and simplest method and forces the 3D sinograms back into 2D planes.

Which one is this?

-fourier rebinning (FORE)
-single slice rebinning (SSRB)
-full 3D reconstruction

A

single slice rebinning (SSRB)

45
Q

Most commonly used technique for processing 3D sinograms is ________. 3D sinogram info is mathematically transformed into frequency space and using a frequency-distance principle, the info is placed back into an appropriate slice with in the volume space.

Which one is this?

-fourier rebinning (FORE)
-single slice rebinning (SSRB)
-full 3D reconstruction

A

fourier rebinning (FORE)

46
Q

New and improved computer speeds allow a much more mathematically intense reconstruction of the full 3D volume.

Which one is this?

-fourier rebinning (FORE)
-single slice rebinning (SSRB)
-full 3D reconstruction

A

full 3D reconstruction

47
Q

Slices are most commonly smoothed using what filter?

A

Gaussian filter

48
Q

The blur or spreading out of a point source by an imaging system describes what?

A

point spread function (PSF)

49
Q

PSF correction refocuses the counts to their correct location but may ______ SUV(max) while improving image quality.

increase or decrease?

50
Q

The oldest and simplest attenuation correction method is to assume that the body is elliptical, and to draw an ellipse outside the body and assign an attenuation coefficient to all pixels inside that ellipse.
(should not be used in area of the chest)

What technique of attenuation correction is this?

A

Chang technique

51
Q

Measured attenuation correction techniques in the chest may be preformed using either a _______ or __________.

A

transmission radioactive source or CT scan

52
Q

The CT scan first before the PET imaging creates what?

A

attenuation-correction CT map

53
Q

A method called ________ is commonly used to remove noise within the transmission scan.

A

image segmentation

54
Q

ROI tracer concentration (mCi/cc) divided by tracer dose(mCi)/patient weight(kg)

This equation calculates what?

55
Q

For repeat PET/CT scans the _____ is important to monitor effectiveness of therapy.

56
Q

What other formulas can be used besides SUV based on body weight?

A

body surface area (BSA) or lean body mass (LBM)

57
Q

____________ is the apparent loss of density or concentration of a small object in an imaging system and occurs in PET, SPECT, CT, and MRI. The ___________ arises when more than one tissue concentration occurs in an individual pixel or voxel, such as near the edge of an organ or tumor.

Both blanks are the same answer…..

A

Partial volume effect

58
Q

What helps correct the partial volume effect?

A

recovery coefficient curve

59
Q

Small objects have only part of their area seen by a pixel, and the pixel value will be falsely _______.

Low or High?

60
Q

PET scan of the ________ demonstrates that the small rods are seen with lower intensity due to the partial volume effect.

A

Jaszczak phantom

PET Study Guide Ed 3 (19 decks)

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