Fundamentals Flashcards Preview

Bio-Med > Fundamentals > Flashcards

Flashcards in Fundamentals Deck (26):
1

ROC definition

Receiver Operating Curve

2

What is the ROC?

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

3

Accuracy Defintion

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

4

Sensitivity Definition

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

5

Specificity

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

6

Shape of ROC curve is directly influenced by....

.... image quality

7

Metrics of Image Quality (3)

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

8

Types of Diagnosis and Actual Situation

Q image thumb

(Ans in image)

A image thumb
9

Spatial Resolution Definition

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

10

What is LSF?

Line Spread Function

11

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

12

What is the FWHM & what does it do?

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

A image thumb
13

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.

14

Ideal Imaging System for a PSF

delta function in all three directions

15

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

16

CNR Equation

CAB = |SA - SB|

  • CAB is the contrast between tissue A & B
  • SA & SB are the signals from tissues A & B respectively

17

Difference between active & passive imaging system

Active system produces it's own source of energy

18

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

... proportional to energy readiated by a physical source

0 < f(x,y) < infinity

19

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

... source illumination incident on the scene being viewed

20

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

... reflected by the objects in the scene

21

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

... reflectivity is replaced by some transmissivity

22

Sampling Definition

Digitising image co-ordinate values

23

Quantisation Definition

Digitsing image amplitude values

24

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.

25

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)

26