Digital Imaging Ch 4

Question 1

ambient lighting

Answer 1

Level of light in a room or environment -

Question 2

automatic rescaling

Answer 2

When an exposure is greater or less than what is needed to produce an image - images are produced with uniform density and contrast regardless of amount of exposure
Basically the system is trying to “fix” an image with too much or too little exposure

Histogram analysis is employed to maintain a consistent brightness (despite the under or over exposure

Question 3

bit

Answer 3

Each 0 and 1 is called a BIT and refers to the computer’s basic unit of information.

A digital transistor can be operated in two states: off (0) or on (1).

Question 4

Bit depth

Answer 4

number of bits
Determines the amount of precision in digitizing the analog signal and therefore the number of shades of gray that can be displayed in the image.

bit depth is expressed as 2 to the power of n, or the number of bits (2n)

Question 5

brightness

Answer 5

Level of intensity of a digital image on a display monitor

Question 6

byte

Answer 6

8 bits (2 bytes form a word)

Question 7

contrast resolution

Answer 7

The ability of the imaging system to distinguish between objects that exhibit similar densities because they attenuate the x-ray beam similarly.

I.e. the ability of a digital system display changes in grayscale values

Question 8

CNR

Answer 8

Contrast-to-noise resolution

contrast resolution compared with the amount of noise apparent in a digital image.

Question 9

DQE

Answer 9

Measurement of the efficiency of an image receptor in converting the x-ray exposure it receives to a quality radiographic image

(i.e. measures how efficient a system converts the x-ray input signal into a useful output signal

Question 10

DI

Answer 10

Deviation Index

Value that reflects the difference between the desired or target exposure to the IR and the actual exposure to the IR

Question 11

DICOM

Answer 11

Digital Imaging Communication In Medicine

A standard that allows imaging modalities and PACS to communicate in the same “language”

Question 12

dynamic range

Answer 12

ability of a detector to accurately capture the range of photon intensities that exit the patient

Question 13

electronic masking

Answer 13

shuttering
regions of the image view can be altered

(i.e. blackens our the white collimation borders to eliminate veil glare – should NOT be used due to poor collimation practices)

Question 14

fill factor

Answer 14

percentage of the pixel faces that is sensitive to x-rays
If the Fill factor is approximately 80%, how much of the x-ray beam would NOT contribute to the image?

pixel is smaller than the DEL

Question 15

FPD

Answer 15

Flat Panel Detector
solid-state IRs employing a large-area active matrix array of electronic components ranging in size from 43 × 35 cm to 43 × 43 cm (17 × 14 in to 17 × 17 in).

Question 16

gray scale

Answer 16

number of different shades of gray that can be stored and displayed by a computer system

Question 17

histogram analysis

Answer 17

image-processing technique commonly used to identify the edges of an image and assess the raw data prior to image display.

System finds the useful signal by locating the minimum & maximum signal within an anatomic region of interest an plots it on a graph

X-axis represents the amount of exposure
Y-axis represents the incidence of pixels for each exposure level.

Question 18

Imaging Plate

Answer 18

Used with CR system - it is housed in a cassette

```
Layers of the PSP plate -
top to bottom
Protective
PSP
Reflective
Base
Backing
~~~

Question 19

Latent Image

Answer 19

stored as digital data and must be processed by a computer for viewing on a display monitor

Question 20

LUT

Answer 20

Look-up Table

method of altering the image to change the DISPLAY of the digital image in various ways

FOLLOWS HISTOGRAM ANALYSIS
CR

Question 21

Matrix

Answer 21

combination of rows and columns (array)
(comprised of usually square pixels)

512 x 512
1024 x 1024 = 1,048,576 pixels
2048 x 2048

Question 22

MTF

Answer 22

Modulation Transfer Function

measure of the imaging system’s ability to display the contrast of anatomic objects varying in size, and the value will be between 0 (no difference in brightness levels) and 1.0 (maximum difference in brightness levels)

Question 23

photostimulable luminescence

Answer 23

visible light when stimulate by high-intensity laser beam

Question 24

PSP

Answer 24

Photostimulable Phosphor

IP phosphor layer made up of barium platinocynanide crystals dope w/europium

Question 25

PACS

Answer 25

Picture Archival Computer System

computer system designed for digital imaging that can receive, store, distribute, and display digital images

Question 26

pixel density

Answer 26

number of pixels per unit area

Question 27

pixel pitch

Answer 27

pixel spacing or distance measured from the center of a pixel to an adjacent pixel

Question 28

pixel

Answer 28

2D picture element

Each pixel is recorded as a single numerical value, which is represented as a single brightness level on a display monitor

Question 29

sampling frequency

Answer 29

determines how often the analog signal is reproduced in its discrete digitized form

Question 30

sampling pitch

Answer 30

determines how often the analog signal is reproduced in its discrete digitized form

Question 31

scintillator

Answer 31

Used in Indirect DR
cesium iodide (CsI) or gadolinium oxysulfide (Gd2O2S) to convert the exit radiation into visible light

Wikipedia:material that exhibits scintillation — the property of luminescence,[1] when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate, (i.e. re-emit the absorbed energy in the form of light).[a] Sometimes, the excited state is metastable, so the relaxation back down from the excited state to lower states is delayed (necessitating anywhere from a few nanoseconds to hours depending on the material): the process then corresponds to either one of two phenomena, depending on the type of transition and hence the wavelength of the emitted optical photon: delayed fluorescence or phosphorescence, also called after-glow.

Question 32

SNR

Answer 32

Signal-to-Noise Ratio
method of describing the strength of the radiation exposure compared with the amount of noise apparent in a digital image

Question 33

spatial frequency

Answer 33

unit of line pairs per millimeter (lp/mm)

• can be expressed as cm or mm
• does not refer to size but line pair = black line on a light background - one pair consists of the line and interspace of the same width as the line

Question 34

window level

Answer 34

sets the midpoint of the RANGE OF BRIGHTNESS visible in the image (i.e. the type of tissue or structure you are trying to visualize)

• Changing the window level on the display monitor allows the image brightness to be increased or decreased throughout the entire range
• may see on PACS as “center” number

Question 35

window width

Answer 35

Specific number of gray levels or digital image numbers assigned to an image. It determines the gray scale rendition of the imaged tissue - IMAGE CONTRAST (RADIOGRAPHIC)

Because the digital image can display shades of gray ranging from black to white, the display monitor can vary the range or number of shades of gray visible on the image to show the desired anatomY