Ch. 31 Computed Radiography

Question 1

PSL

Answer 1

Photostimulable Luminescence

Question 2

PSP

Answer 2

Photostimulable Phosphor

Question 3

SPS

Answer 3

Storage Phosphor Screen

Question 4

IP

Answer 4

Imaging Plate

Question 5

SP

Answer 5

Storage Phosphor

Question 6

PMT

Answer 6

Photomultiplier Tube

Question 7

PD

Answer 7

Photodiode

Question 8

Computed Radiography was developed in the early 80s by?

Answer 8

Fuji

Question 9

What are the 5 layers of the PSP plate?

Answer 9

1. Protective Layer
2. Phosphor Layer
3. Support Layer
4. Conductor Layer
5. Light Shielding Layer
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Question 10

What are the 2 types of phosphor layers and which one is more effective?

Answer 10

Conventional Powder PSP and Needle PSP.

Needle PSP is better

Question 11

X-ray interaction with a photostimulable phosphor results in excitation of electrons into what state?

Answer 11

Metastable State

Question 12

When metastable electrons return to their ground state this is emitted.

Answer 12

Visible Light

Question 13

When fluorohalides luminesce they do not release all the energy absorbed in the incident beam. Some light is emitted with the interaction, but the phosphor retains energy in the form of what?

Answer 13

Latent Image

Question 14

The latent image is created by energy transfers during what interactions?

Answer 14

Photoelectric

Question 15

Photoelectrons produced, excite low energy electrons to create holes in the crystal phosphor these holes are what?

Answer 15

The latent image

Question 16

Trapped signal will occur exponentially overtime through spontaneous phosphorescence, this is called?

Answer 16

Fading

Question 17

A typical imaging plate will lost about ____ of the stored signal between 10 minutes to 8 hours after an exposure and more slowly afterwards.

Answer 17

25%

Question 18

A computed Radiography Reader is comprised of what modules?

Answer 18

Mechanical, optical and computer modules.

Question 19

What are the 2 main mechanical features of the CR?

Answer 19

1. Drive Mechanism

2. Oscillating Mirror

Question 20

This is a mechanical feature of CR readers that moves the IP along the long axis of the plate and is a slow scan.

Answer 20

Drive mechanism

Question 21

This is a mechanical feature of CR readers that deflects the laser back and forth across the IP and is a fast scan.

Answer 21

Oscillating Mirror

Question 22

After the imaging plate has been inserted into the cassette reader it is opened and the imaging plate is removed and advanced between the roller drive system. A laser beam that has been directed through a focusing lens scans the plate in a raster pattern. When the laser strikes the surface of the plate, light is emitted and channeled up to the Photo Multiplier tube. The PMT sends the analog signal to the analog to digital convertor ADC , which sends the digital signal to the computer for processing and display. This is what process?

Answer 22

Readout Process

Question 23

What is a raster pattern?

Answer 23

A scan of horizontal scanning lines traced by the electron beam. Scans reading across back and forth line by line.

Question 24

What are the 5 optical features of CR reader?

Answer 24

1. Laser
2. Beam Shaping Optics
3. Light Collecting Optics
4. Optical Filters
5. Photodetector

Question 25

This is a source of stimulating light in a CR reader that spreads as it travels and is focused onto the reflector by a lens that keeps beam diameter small at less than 100um.

Answer 25

Laser beam

Question 26

The laser beam size in a CR reader is critical for ensuring what?

Answer 26

High spatial resolution.

Question 27

The laser light in a CR reader frees trapped electrons which return to lower energy states releasing what color photons?

Answer 27

blue-purple light photons

Question 28

What are the 2 techniques to speed up a readout with the laser in a CR reader?

Answer 28

1. Read light from PSP line by line to increase data acquisition
2. Use dual sided PSP that is scanned on both sides which creates increased spatial resolution.

Question 29

This type of tube performs a point by point readout along the laser line.

Answer 29

PMT

Question 30

Each line laser scanned is equal to what?

Answer 30

One line spacing or pixel dimension

Question 31

ADC converts infinite ranges of values into discrete values stored as what?

Answer 31

Digital Code

Question 32

PIxel depth is equal to what?

Answer 32

Number of density values

Question 33

Proper filtering improves signal to noise ratio. Why is this important?

Answer 33

The lower the signal to noise ratio then there is more noise present and the information needed in an image is not present. A high signal to noise ratio is what is desired.

Question 34

A computer control is an output analog signal from PMT that is processed for what 3 things?

Answer 34

1. Amplitude
2. Scale
3. Compression

Question 35

What does the ADC do to the analog signal?

Answer 35

It is digitized or sampled and quantized.

Question 36

This determines the location and size of the of the PSL signal from a specific area of the detector and measures the light intensity.

Answer 36

Sampling

Question 37

This determines that average value rounding the grey scale up or down of the signal amplitude within the sample area. You end up with an image full of numbers.

Answer 37

Quantizing