Positioning - Ch. 1 - Digital Imaging/CR


computed radiography


- the smallest unit in the image
- a single shade of gray

Many pixels make up the _____


Digital processing uses mathematical formulas called what?


In digital, contrast is controlled by what two things?

kVp and LUT


look up table

As kVp increases, the beam penetrability ______, and patient dose _______

increases, decreases


the intensity of light that represents individual pixels in the image on the computer monitor

Does a change in mAs have an effect on the brightness of an image?



picture archiving communication system

Post Processing

altering the image before it is sent to PACS

Contrast resolution

the different between light and dark areas of an image

What controls contrast in post processing?

LUT (look up tables)

Bit depth

determined by the manunfacturer

Spatial Resolution

- the recorded sharpness of detail of structures on the image
- factors: focal spot size, motion, geometric factors, and acquisition pixel size
- measured in line pairs per millimeter (lp/mm)

The smaller the pixel, the ______ the spatial resolution


Spatial Resolution for eyes, CR/DR, and hardfilm

Eyes- 3 lp/mm
CR/DR- 4 lp/mm
Hardfilm- 15 lp/mm

Exposure Indicator

- Exposure value or S#
- a number value given to an image to tell you whether or not you are in range


- Exposure value
- direct relationship

Fuji and Konica

- S#
- indirect relationship

Is the technologist monitor of diagnostic quality?



- random disturbances or occurrences that reduce clarity
- looks grainy


signal to noise ratio

High SNR

- want a high SNR to show low contrast, soft structures
- need enough mAs to obtain
- less noise - better picture


- bad, looks grainy
- not enough mAs

Range for Kodak


How to increase or decrease exposure value for Kodak

- to increase by 300 points, add 1/2 of your mAs
- to decrease by 300 points, cut 1/2 of your mAs

Konica Range


Fuji Range

- Different for every exam
- Extremities usually between 75-150
- Chest usually between 200-600

How to increase or decrease S# for Konica and Fuji

- double your mAs, cuts S# in half
- halving your mAs, doubles S#

Rules for CR

1. One body part per film
2. Needs at leave 60 kVp for algorithms to work (up to 120kVp)
3. Need to be in the middle of the IR
4. Grids are needed for any body part over 10cm
5. Every hospital has a different protocol

Brightness is to CR as ______ is to hardfilm


Increase kVp, _______ radiographic exposure


kVp Range

about 48-130

mAs Range

about .5-630

Increase mAs, _____ radiographic exposure



- user can adjust image contrast and brightness on the monitor
- can adjust window width (contrast) and window level (brightness)


reduces the display of noise in an image


all or part of an image can be magnified

Edge Enhancement

- makes the edges of structures appear more prominent
- spatial resolution of the image does not change


- presents a more uniform image appearance
- makes low brightness brighter and high brightness dimmer


- background anatomy can be removed to allow visualization of contrast media-filled vessels
- used in angiography

Image Reversal

the dark and light pixel values of an image are reversed, x-ray image reverses from a negative to a positive


text can be added to images

Digital archive

a digital storage and image management system, stores patient files and images

Display matrix

series of "boxes" that give form to the image

Display pixel size

pixel size of the monitor, related to the display matrix

Exposure latitude

range of exposure intensities that will produce an acceptable image

Exposure level

a term used by certain equipment manufacturers to indicate exposure indicator

Flat-panel detector with thin-film transistor (FPD-TFT)

- a method of acquiring radiographic images digitally
- replaces the film-screen system
- made with amorphous selenium or silicon
- cassette-based or cassette-less

Photostimulable phosphor (PSP) plate

- a method of acquiring radiographic images digitally
- main components include a PSP image plate, an image plate reader, and a workstation
- cassette-based or cassette-less

Parallel grid

- more absorbed on the outside
- image darker in center
- don't want this

Focus grid

- more even
- focuses towards the center

Grid cutoff

- if grid isn't angled properly
- want angle to go with the lines on the grid

Off-focus grid

using the wrong grid 40 vs. 72in

Upside down grid

black in middle, white on sides