9. Digital imaging part 2

Question 1

What is dynamic range?

Answer 1

• Number of brightness values (grey shades) that can be represented.

Question 2

What is the dynamic range identified by?

Answer 2

-Identified by the bit depth of each pixel (associated with each individual pixel)

Question 3

As you increase dynamic range, what does it does it do to Contrast resolution and bit depth?

Answer 3

Increases it

Question 4

How many shades does a 2 bit system have the capability of showing?

Answer 4

four shades

Question 5

What is the range in mAs for optimal dynamic range?

Answer 5

Between 4 different values

Question 6

What is automatic rescaling in DDR

Answer 6

During processing, the system recognizes an inconsistency and automatically rescales the pixel values to a proper contrast/brightness value through pre programmed algorithms

Question 7

What is spatial resolution?

Answer 7

Is the ability to image small objects

Question 8

What is more important in DDR, SR, or CR?

Answer 8

CR

Question 9

What controls SR?

Answer 9

Acquisition pixel size

Question 10

As you decrease the pixel size, does the SR increase or decrease?

Answer 10

It increases

Question 11

What are 3 ways to describe pixel size?

Answer 11

1. Matrix size/FOV (3 by 3)
2. Pixel Pitch (the distance between the middle of one pixel to another)
3. Pixel Density (For the same FOV, the greater the pixel density-numbers of pixels)

Question 12

How does the matrix size affect SR?

Answer 12

• For the same field of view (FOV) (size of IR), spatial resolution increases with a larger matrix
• Matrix size by itself doesn’t effect SR, however to fit more pixels in a smaller field of view, we have to decrease the size of the pixels which increases the SR

Question 13

Describe the general process of how the CR captures an image:

General

Answer 13

1. Excite electrons to a higher energy level and traps them in that level
2. Produces latent image
3. During processing, the e- drop down and release the energy in the form of light
4. We turn the light into an electric signal

Question 14

What does the PSP do?

Answer 14

1. Captures the latent image

Question 15

What is the PSP composed of?

General

Answer 15

Composed of extremely small particles (pixels) which store and release energy

Question 16

What captures and stores the image in the PSP?

Answer 16

F centers trap and store the electrons

Question 17

What is the relationship between the e- in the PSP to the photons?

Answer 17

excited electrons trapped is proportional to the # x-ray photons

Question 18

What is the image called before it is processed in CR

Answer 18

Latent image

Question 19

When is the PSL used?

Answer 19

Happens when scanning CR cassette

Question 20

What is PSL in terms of the e- in the PSP?

Answer 20

-Causes e- to drop down to their ground state
-Electrons return to ground state and release energy in form of light
-Emits light when exposed to a infrared (lazer light)

Question 21

What happens during the read process in CR?

Answer 21

-The PMT(photomultiplier tube) converts the varying light intensities into varying electrical signals.
-Electrical signals are amplified & sent to an A/D converter. A/D converter produces the binary values for the brightness of each pixel

Question 22

In DDR, how does direct digital acquisition work?

Answer 22

1. X-rays interact with the photoconductor (amprphous se)
   Creates an electronic signal (charge)
2. Storage capacitors in the DEL’s collect the charge
3. The charge is released to the ADC -analog to digital converter
4. ADC converts the charge to a digital signal which is used to produce the digital image

Question 23

What is the advantage of direct digital acquisition?

Answer 23

Better SR

Question 24

What is the disadvantage of DD acquisition?

Answer 24

More expensive to purchase and repair

Question 25

In DDR, how does indirect digital acquisition work?

Answer 25

1. X rays hit Sinsilatior
2. Scintillation layer is ‘coupled’ to each CCD chip (pixel) by lenses or fiber optics
3. Converts x-rays to light and causes blur from light spread
4. CCD chips convert the light photons to an electronic signal
5. ADC converts the charge to a digital signal which is used to produce the digital image during processing

Question 26

What is the Scintillation layer made of?

Answer 26

Scintillation layer – cesium iodide

Question 27

How does the scintillation layer help light focus?

Answer 27

Cesium iodide can be formed into small needles like columns to helps to focus the light

Question 28

What is advantage and disadvantage of indirect digital acquisition?

Answer 28

A: Better contrast resolution compared to direct acquisition

D: Less spatial resolution compared to direct acquisition

Question 29

How does Indirect Acquisition-Thin film Transistor (TFT) work?

Answer 29

1. Has Scintillation layer
2. Converts x-rays to light
3. Photodiode layer converts the light into an electronic signal 4.Transferred to the TFT array
4. TFT sends the signal to the ADC
5. ADC converts the charge to a digital signal which is used to produce image

Question 30

What is TFT used for?

Answer 30

TFT used for angiography and fluoroscopy and general radiography