Lecture 6-7

Question 1

What is noise characterized by?

Answer 1

1)Randomness in data
2) Different data with the same experiment
3) Poisson distribution

Question 2

What is background?

Answer 2

1)Signal that is not of interest.
2)Reduces contrast

Question 3

What is contrast?

Answer 3

1.The ability to distinguish between different intensities.
2.Ratio of Signal to Background

Question 4

What is projection?

Answer 4

The 2D image of a 3D anatomy

Question 5

What are we measuring in X-Ray Imaging?

Answer 5

1) Attenuation along the line connecting to the focal spot
2) Counts proportional to e^-mu*x(when mu is constant and when mu is varying)

Question 6

What is the formula for magnification?

Answer 6

Ideal Focal Spot:
M=I/O or Image over object
M= SID/SOD
SID= distance from the source to the image
SOD= distrance from the source to the object being observed
Looks like a triangle

Question 7

What happens in the case of imperfect focal spot?

Answer 7

The focal spot is dependent on multiple different points rather than just Aa,Bb,Ff as the triangles are no longer similar.
The geometric structure results in possible blurring.
Decreasing OID can result in reduced blurring but also can result in reduced magnification.
Best is to reduce the f/I = don’t know what that is
Good to minimize OID

Question 8

Which condition is for breast imaging?

Answer 8

1)Small focal spot, small F(means small blurring)
2)High resolution

Question 9

What is the function of a scintillator?

Answer 9

1. Phtoelectric/compton effect is at work: results in optical photons
2. High absorption and high conversion efficiency
3. X ray photons become processed into optical photons which results in more energy for the system

Question 10

Absorption Efficiency

Answer 10

QDE(Quantum Detection Effiency)
Amount of X rays that interact with the detector
Measures how efficiently the screen detects x-ray photons
Proportional to 1- e^-mux

Question 11

What is radiographic speed?

Answer 11

How long radiation exposure is needed
High speed=high absorption efficiency=short exposure time

Question 12

Conversion Efficiency

Answer 12

Fraction of energy deposited by z ray absorption that is converted into optical photons
Depednent on phosphor
Conversion efficiency of GD2o2S: 15%
Emits green light