Radiographic Imaging

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Chapter 12 Image Receptors
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Digital Receptors

  • A digital image is recorded as a matrix with numerous pixels
  • Each Pixel represents a single brightness level on a display monitor
  • Algorithm - mathematical calculation used for image construction

2 types of digital Receptors

  • Computed Radiography (CR) cassette based, most common
  • Direct Digital Radiography (DR) cassetteless

CR - Computed Radiography

  • The CR IR has a cassette which includes an IP (Imaging Plate)
  • Radiation exiting the patient interacts with the IP and the energy is stored to produce a latent image
  • Never remove the IP by hand!!

The IP consists of...

(Imaging Plate)

  1. Protective layer
  2. Phosphor layer
  3. reflective layer
  4. conductive layer
  5. and support layer

The Phosphor layer is...

(Test question)

The active layer and is made from barium fluorohalide and europium activated.


DR (Digital Radiography) cassetteless

  • DR combines image capture and image readout
  • A detector array replaces the bucky with DR
  • Images are available instantly after exposure
  • Much more fragile and expensive than CR

Acquisition ( How do we acquire the Image?)

  • Histogram - a graphic representation of a data set: represents the number of digital pixel values -vs- the relative prevalence of those values
  • Histogram analysis - the computer analyzes the histogram and compares it to a pre-established histogram specific to that part.
  • Not enough quantity gives off a histogram error


  • CR - the electrons trapped in the IP represent the latent (invisible) image
  • The IP is removed for the cassette in the reader, a laser sweeps over the IP releasing the trapped electrons
  • The electrons release energy as light and the light is directed to a photodetector which is sent to an ADC. (Analog to Digital Converter)
  • The digital signal is then converted to a matrix
  • The IP is erased and ready for the next exposure.

Post Processing

Advantage of digital processing

Preprocessing is an automatic function and occurs before the image is displayed (In the system before it is displayed to us)

  • Histogram analysis
  • Automatic rescaling

Post-processing Functions

  • Windowing - window length is adjusted to adjust contrast; window level is used to adjust brightness.
  • Annotation - allows text to be added; should not be used to replace markers.
  • Image Flip ; used to properly orientate the image.

Image Inversion

allows the inversion of white (bone) to black; some pathologies are better visualized



used to visualize small details


Edge enhancement

increases contrast along the edge of structures



suppresses noise (fog, grainy)



can make overexposed areas lighter and underexposed areas darker; creates a lower contrast (Saturation)


Region of interest

allows for a pixel value to be calculated to characterize disease.


Digital Communication Networks

PACS - Picture Archival and Communication System

To capture, stores and distributes digital images; an electronic network for communication between modalities, display stations and storage.

DICOM - Digital Imaging and Communications in Medicine

This is a common language used for these communication systems to work; allows for the exchange of medical images and information


Tele radiology

Images can be accessed from various workstations in or outside the facility. (If doctor is out of town)


RIS (Radiology Information Systems)

HIS (Hospital Information Systems)

Computer systems that provide medical information.

An important goal of radiology is to provide the physician with the radiology report, patient data, and images in a convenient and timely manner.

  • The software used at each work station differs
  • For non-interpreting workers, (ME) a basic monitor is used allowing minimal adjustments
  • Monitors used by radiologists have more capabilities. (Review techs work quality)