ROC definition

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

Accuracy Defintion

The number of **correct diagnoses **divided by the total number of diagnoses

Sensitivity Definition

The number of **true positives** divided by the sum of the true positives and false negatives

Specificity

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)

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- Spatial Resolution - refers to the number of pixels utilised in the construction of the image
- SNR
- 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)

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- 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**

**signal averaging****coherent**CNR Equation

C_{AB} = |S_{A} - S_{B}|

- C
_{AB}is the contrast between tissue A & B - S
_{A}& S_{B}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**

Sampling Definition

Digitising image co-ordinate values

Quantisation Definition

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)