PET scanners -- SNR versus NECR....

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Discussion Overview

The discussion revolves around the relationship between signal-to-noise ratio (SNR) and noise-equivalent count rate (NECR) in PET scanners, specifically comparing 2D and 3D systems. Participants explore the implications of these metrics on image quality and the confusion arising from their interactions.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants assert that 2D PET scanners have a superior SNR compared to 3D PET scanners due to reduced scatter and random events.
  • Others note that NECR is higher in 3D PET scanners, which seems contradictory to the SNR observations.
  • There is a claim that NECR is linearly proportional to SNR, while another participant questions this by suggesting it should be inversely proportional.
  • A participant relates NECR to the concept of Noise-Equivalent Temperature and questions whether it represents the number of signal counts needed to match sensor noise.
  • One participant proposes that the noisier real images from 3D PET require more integration time to achieve the same SNR as 2D PET images, providing numerical examples to illustrate this point.
  • Confusion arises regarding the relationship between SNR and NECR, with some participants stating they are essentially the same, while others disagree and suggest further clarification is needed.

Areas of Agreement / Disagreement

Participants express conflicting views regarding the relationship between SNR and NECR, with no consensus reached on whether they are directly or inversely related. The discussion remains unresolved on this point, as different interpretations are presented.

Contextual Notes

Some participants reference their lecturers' opinions, indicating that definitions and interpretations may vary. The discussion includes assumptions about the definitions of SNR and NECR that are not universally agreed upon.

BobP
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In PET, 2D PET scanners have a superior SNR to 3D PET scanners as the influence of scatter and random events is lowered by the septa between detector rings. However, the NECR (noise-equivalent count rate), which is linearly proportional to SNR, is higher in 3D PET scanners. These two facts seem to contradict each other and I am therefore slightly confused.

Please can someone clarify the situation for me
 
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BobP said:
...the NECR (noise-equivalent count rate), which is linearly proportional to SNR...
Shouldn't that be '...inversely proportional to SNR...' ?
 
Tom.G said:
Shouldn't that be '...inversely proportional to SNR...' ?
Not according to my lecturer...
 
BobP said:
However, the NECR (noise-equivalent count rate), which is linearly proportional to SNR, is higher in 3D PET scanners. These two facts seem to contradict each other and I am therefore slightly confused.

That sounds similar to Noise-Equivalent Temperature. Is NECR the number of signal counts needed to match the internal noise of the sensors?
 
Drakkith said:
That sounds similar to Noise-Equivalent Temperature. Is NECR the number of signal counts needed to match the internal noise of the sensors?
The NEC is the true count rate of a theoretical image without any scatter or random events which would give the same statistical quality image as a real image which includes scatter and randoms.
 
Okay. So it seems to me that the NECR for 3D PET is higher than that of 2D PET because the 3D PET real images are noisier and require more integration time to reach the same SNR as a 2D PET image.

In other words:

Real 2D PET
Signal: 100
Noise: 20
SNR: 5

Ideal 2D PET
Signal: 50
Noise: 10
SNR: 5
NECR: 50

Real 3D PET
Signal: 200
Noise: 40
SNR: 5

Ideal 3D PET
Signal: 100
Noise: 20
SNR: 5
NECR: 100I hope my terminology is okay, I'm used to talking about digital camera sensors and images, not PET sensors.
 
Drakkith said:
Okay. So it seems to me that the NECR for 3D PET is higher than that of 2D PET because the 3D PET real images are noisier and require more integration time to reach the same SNR as a 2D PET image.

In other words:

Real 2D PET
Signal: 100
Noise: 20
SNR: 5

Ideal 2D PET
Signal: 50
Noise: 10
SNR: 5
NECR: 50

Real 3D PET
Signal: 200
Noise: 40
SNR: 5

Ideal 3D PET
Signal: 100
Noise: 20
SNR: 5
NECR: 100I hope my terminology is okay, I'm used to talking about digital camera sensors and images, not PET sensors.
Well my lecturer said that SNR is basically the same as NECR. So it have a lower SNR and a higher NECR :)
 
BobP said:
Well my lecturer said that SNR is basically the same as NECR. So it have a lower SNR and a higher NECR :)

They certainly aren't the same, but you'll probably need to talk to your lecturer about this. Right now I'm mostly guessing at what all this means.
 
Ref post #2
Tom.G said:
Shouldn't that be '...inversely proportional to SNR...' ?
Ref post #3
BobP said:
Not according to my lecturer...
Ref post #7
BobP said:
Well my lecturer said that SNR is basically the same as NECR. So it have a lower SNR and a higher NECR :)

Posts #3 and #7 seem to conflict with each other. Please clarify.
 
  • #10
Tom.G said:
Ref post #2

Posts #3 and #7 seem to conflict with each other. Please clarify.
Sorry. When I say "basically the same" I mean a high SNR = high NECR...
so they are linearly related...but I clarified this issue with my lecturer..

He said PET has a higher SNR and a higher NECR :)
 

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