Receiver Operating Curve
What is the ROC?
a plot of test sensitivity along the y-axis vs it's (1-specificity) along the x-axis
The number of correct diagnoses divided by the total number of diagnoses
The number of true positives divided by the sum of the true positives and false negatives
The number of true negatives dvided by the sum of the number of the true negatives and false positives.
Shape of ROC curve is directly influenced by....
.... image quality
Metrics of Image Quality (3)
- Spatial Resolution - refers to the number of pixels utilised in the construction of the image
- CNR - Contrast to Noise ratio
Types of Diagnosis and Actual Situation
(Ans in image)
Spatial Resolution Definition
The smallest distance between two features such that they can be individually resolved rather than appearing as a single structure
What is LSF?
Line Spread Function
What is the LSF?
The sum of the spatial distribution of illuminance in the fron and back emulsion caused by a beam of x-rays which pass through a narow slit
What is the FWHM & what does it do?
- Full-Width at Half-Maximum
- Determines whether two structures can be resolved
What is the Point Spread Function?
It describes the response of an imaging system to a point source/object. It is focussed on a 3D environment, where as the LSF is based on 2D.
Ideal Imaging System for a PSF
A delta function in all three directions
Factors affecting SNR (3)
- Depends on the image formation process for each modality
- Truly random noise can be mitigated by signal averaging
- In ultrasound, situation is more complicated as speckle noise is coherent
CAB = |SA - SB|
- CAB is the contrast between tissue A & B
- SA & SB are the signals from tissues A & B respectively
Difference between active & passive imaging system
Active system produces it's own source of energy
Intensity values of an image generated by a physical process are.....
... proportional to energy readiated by a physical source
0 < f(x,y) < infinity
Illumination, i(x,y) is the amount of ...
... source illumination incident on the scene being viewed
Reflectance, r(x,y) is the amount of illumination...
... reflected by the objects in the scene
Imagesformed via transmission of illumination through a medium, the previous expression are still true but ...
... reflectivity is replaced by some transmissivity
Digitising image co-ordinate values
Digitsing image amplitude values
When using a sensor array for image acquisition, what is considered?
The number of sensors in the array determines the limits of sampling in both directions.
A pixel, p, at co-ordinates (x,y) has how many horizontal and vertical neighbours?
And how many diagonal neighbours?
4 - Co-ordinates (x+1,y), (x-1,y), (x,y+1), (x, y-1)
4 - Co-ordinates (x+1,y+1), (x+1,y-1), (x-1,y+1), (x-1,y-1)