Digital x-ray

Question 1

what is beneficial about using digital x-rays?

Answer 1

increased safety since they allow for a decreased number of repeat exposures and removal of toxic processing chemicals, software programs can also correct most exposure problems

Question 2

what are the two types of digital x-rays?

Answer 2

computerized/ computed radiography (CR), or digital radiography (DR)

Question 3

what factors impact the quality on a digital x-ray?

Answer 3

resolution, image noise, pixel size/ number, and field of view

Question 4

how do digital x-rays record images?

Answer 4

as a combination of rows and columns called a matrix

Question 5

voxel

Answer 5

an area within a 3D volume of tissue which is shown by a pixel

Question 6

what determines how many shades of gray there are in a digital x-ray?

Answer 6

grayscale bit depth

Question 7

how is resolution related to pixels?

Answer 7

directly related
increased matrix size = increased number of small pixels

Question 8

image noise

Answer 8

unwanted random variations in shades of gray produced on a radiograph
inversely related to image contrast

Question 9

how does electronic noise interfere with digital x-rays?

Answer 9

it interferes with the passage of electrons and photons throughout the process of obtaining, processing, and displaying an image

Question 10

what causes quantum noise?

Answer 10

it is caused by a random distribution of electrons striking the image receptor

Question 11

how can you minimize quantum noise?

Answer 11

by increasing mAs or kVp

Question 12

dose creep

Answer 12

increase in exposure factors made in an attempt to decrease the amount of image noise

Question 13

what are some characteristics of CR imaging?

Answer 13

requires a cassette with intensifying screen
screen composed of photostimulable phosphors referred to as the photostimulable storage phosphor imaging plate (PSP)

Question 14

what layers make up the imaging plates needed for CR imaging?

Answer 14

from outermost to innermost:
1. protective layer
2. phosphor layer (contains stimulable phosphors)
3. conductor layer (helps minimize electrostatic interference with image formation)
4. light-shielding layer (protects plate from light damage)

Question 15

how is an image formulated in digital x-rays?

Answer 15

electrons in the IP become excited when they interact with the x-rays
some electrons are elevated into a high energy state that leaves gaps in the phosphate layer, these gaps produce the latent image

Question 16

how is the imaging plate processed for CR imaging?

Answer 16

by loading the cassette into the image reader

Question 17

how long after exposure should the imaging plate be processed in CR imagining?

Answer 17

must be processed shortly after exposure because the electrons are only latent for a few hours

Question 18

how does the image reader work in CR imaging?

Answer 18

1. it uses a red focused laser beam to release high-energy electrons which causes an additional release of light
2. released light is directed to a photodetector that converts visible light into an electronic signal which is then converted to a digital signal
3. the plate is exposed to a bright flash of white light that returns electrons to their stable state, fully erasing the image and making the IP ready to reuse

Question 19

what are the IP plates most prone to?

Answer 19

wear and ghosting (prior image can’t be fully erased)

Question 20

how does DR imaging work?

Answer 20

the image receptor is built into the x-ray table so it doesn’t require the use of cassettes and separate imagining processing units

Question 21

what are the different system types for DR imaging?

Answer 21

direct detector systems and indirect detector systems

Question 22

detective quantum efficiency (DQE)

Answer 22

describes sensitivity and accuracy of system
expressed as a % of the x-ray energy that strikes the detector and is converted to the final image, most digital systems have a DQE of 80% with the other 20% being filled in by the computer

Question 23

how does the direct detector system work?

Answer 23

it utilizes a thin film transistor (TFT) device to detect and display image
the imaging plate contains amorphous selenium which releases electrons when they interact with the x-ray beam
TFT collects electrons and directly converts that electronic signal to digital image

Question 24

what are the different types of indirect detector systems?

Answer 24

one uses TFT detector and the other uses a charge-coupled device (CCD)
both types use a scintillator (material that fluoresces when exposed to the x-ray beam)

Question 25

how do the indirect detector systems work?

Answer 25

1. light emitted is detected by the TFT or CCD
2. TFT or CCD convert light energy to electrical energy which is processed by the computer to display the digital image

Question 26

how is digital image processing done on the computer?

Answer 26

the software converts the signal and optimizes the image while minimizing artifacts
1. system generates a histogram (graphical representation of signal intensity of each of the pixel values)
2. system analyzes histogram data and compares pixel values to an internal standard that is specific for that body part

Question 27

how can the software optimize the intensity of pixels?

Answer 27

if exposure factors differ from comparison standards, it can rescale the image to correct overexposure/ underexposure

Question 28

after optimizing the intensity of the pixels in the digital image, what does the software program do?

Answer 28

uses another internal operation called look-up table to adjust contrast to the most desirable amount for the body part
then:
windowing and leveling operations are performed

Question 29

windowing

Answer 29

controls the range of densities displayed

Question 30

leveling

Answer 30

controls the brightness of the image

Question 31

what is the best monitor for viewing digital radiographs?

Answer 31

medical grade monochrome LCD monitor

Question 32

picture archiving and communication system (PACS)

Answer 32

processes, procedures, and technology needed for creating, distributing, and archiving images
includes imaging device and any associated readers as well as computer servers and workstations that store/ retrieve images

Question 33

what is an important digital artifact to know?

Answer 33

ghost images