Fundamentals

Question 1

ROC definition

Answer 1

Receiver Operating Curve

Question 2

What is the ROC?

Answer 2

a plot of test sensitivity along the y-axis vs it’s (1-specificity) along the x-axis

Question 3

Accuracy Defintion

Answer 3

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

Question 4

Sensitivity Definition

Answer 4

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

Question 5

Specificity

Answer 5

The number of true negatives dvided by the sum of the number of the true negatives and false positives.

Question 6

Shape of ROC curve is directly influenced by….

Answer 6

…. image quality

Question 7

Metrics of Image Quality (3)

Answer 7

• Spatial Resolution - refers to the number of pixels utilised in the construction of the image
• SNR
• CNR - Contrast to Noise ratio

Question 8

Types of Diagnosis and Actual Situation

Answer 8

(Ans in image)

Question 9

Spatial Resolution Definition

Answer 9

The smallest distance between two features such that they can be individually resolved rather than appearing as a single structure

Question 10

What is LSF?

Answer 10

Line Spread Function

Question 11

What is the LSF?

Answer 11

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

Question 12

What is the FWHM & what does it do?

Answer 12

• Full-Width at Half-Maximum
• Determines whether two structures can be resolved

Question 13

What is the Point Spread Function?

Answer 13

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.

Question 14

Ideal Imaging System for a PSF

Answer 14

A delta function in all three directions

Question 15

Factors affecting SNR (3)

Answer 15

• 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​

Question 16

CNR Equation

Answer 16

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

Question 17

Difference between active & passive imaging system

Answer 17

Active system produces it’s own source of energy

Question 18

Intensity values of an image generated by a physical process are…..

Answer 18

… proportional to energy readiated by a physical source

0 < f(x,y) < infinity

Question 19

Illumination, i(x,y) is the amount of …

Answer 19

… source illumination incident on the scene being viewed

Question 20

Reflectance, r(x,y) is the amount of illumination…

Answer 20

… reflected by the objects in the scene

Question 21

Imagesformed via transmission of illumination through a medium, the previous expression are still true but …

Answer 21

… reflectivity is replaced by some transmissivity

Question 22

Sampling Definition

Answer 22

Digitising image co-ordinate values

Question 23

Quantisation Definition

Answer 23

Digitsing image amplitude values

Question 24

When using a sensor array for image acquisition, what is considered?

Answer 24

The number of sensors in the array determines the limits of sampling in both directions.

Question 25

A pixel, p, at co-ordinates (x,y) has how many horizontal and vertical neighbours?

And how many diagonal neighbours?

Answer 25

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)