Download RELATIONSHIP OF SNR – SRb – CNR and QUANTA of DOSE to

RELATIONSHIP OF SNR – SRb –
CNR and QUANTA of DOSE
to
DETECTION
TVA/VMI ADVANCED TECHNOLOGY CONFERENCE
SAN ANTONIO, TX
AUGUST 10, 2016
What is SNR
Signal-to-Noise Ratio (CR) is defined as:
quotient of mean linear pixel value and standard deviation of mean
linear pixel values (noise) for a defined detector area-of-interest in
a digital image.
—Notwithstanding extraneous sources of digital image noise, SNR
will normally increase as exposure dose is increased.
What is Basic Spatial Resolution
- terminology used to describe the smallest degree of visible detail within a
digital image that is considered the effective pixel size.
The concept of basic spatial resolution involves the ability to separate two
distinctly different image features from being perceived as a single image
feature. When two identical image features are determined minimally distinct,
the single image feature is considered the effective pixel size. If the physical
sizes of the two distinct features are known, for example, widths of two
parallel lines or bars with an included space equal to one line or bar, then the
effec ve pixel size is considered 1⁄2 of their sums. Example: A digital image is
determined to resolve five line pairs per mm or a width of line equivalent to
five distinct lines within a millimetre. The basic spatial resolution is
determined as 1/ [2 × 5 LP/ mm] or 0.100 mm.
What is CNR
quotient of the digital image contrast (pixel value difference between any two
areas of interest within a computed radiograph. Digital contrast = PV2 – PV1
where PV2 is the pixel value of area of interest “2” and PV1 is the pixel value
of area of interest “1” on a computed radiograph. ) and the averaged standard
deviation of the linear pixel values.
—CNR is a measure of image quality that is dependent upon both digital
image contrast and signal- to-noise ratio (SNR) components. In addition to
CNR, a digital radiograph must also possess adequate sharpness or basic
spatial resolution to adequately detect desired features.
Quanta of Dose
Quanta or “Amount” of radiation exposure to the imaging plate (IP).
- Is there a minimum dose?
- Is there a maximum dose?
- Is there a relationship between dose and discontinuity detection?
- Is it possible to achieve “normal” image quality metrics at low doses?
The Latent Image
- What is a Latent Image?
- Could we say “Latent Signals”?
- Is there a difference / why should I care?
- It’s the same as film – right?
“It’s the Physics “
says Dr. PHD
- What is “the Signal”?
- What does it represent?
- What’s the “Noise”?
- I’m a Radiographer – not a UT head!!!!
The Contrast – It’s all about the
Contrast
- The Contrast of What – to What
- Grey Levels or Pixel Intensities – right
- Wait – don’t GV/PI begin as “signals”
Targets
- What are these Targets
- Do reference target orientation/shape have relevance to signal
generation
- Let’s think UT for a moment
Dose aka Incident Engergy
- Remember – it’s all about contrast
- Thinner the material, smaller the allowable flaw size
- Thinner the material, smaller the potential incident energy target
- What does that mean to Dose required
Theory/Physics Aside
Let’s Talk About the
REAL WORLD