DMI 50b digital radiography modified

Computed Radiography A cassette is used  Contains a photostimulable phosphor imaging plate • Looks like an intensifying screen • Contains a layer of europium-doped barium fluorohalide

Digital Radiography

DMI 50B Kyle Thornton

What Does That Mean?

 Digital has a higher dynamic range than film

 The response is linear v sigmoidal

 It provides more information at the low and high exposure levels

Computed Radiography

 A cassette is used

 Contains a photostimulable phosphor

imaging plate

• Looks like an intensifying screen

• Contains a layer of europium-doped barium fluorohalide crystals

• When struck with x-rays, a new semistable state is produced

• The latent image is stored on this plate

The Imaging Plate

 Made up of multiple layers

 A polyester support layer

 The phosphor layer

 A clear protective layer

 Reflective layer

 Conductive layer

 Support layer

 Backing layer

 Bar code label on the bottom

• Contains a number assigned to the image plate

The Imaging Plate

 Very flexible

 Can maintain a latent image for

about 24 hours

 Can be exposed to light

 Some image degradation may occur with extended storage time and light exposure

The Image Reader

 Converts the analog information from the latent image to a digital format

 The image plate is scanned by laser

 The portion of the plate struck by laser

emits light

 The light is directed to photomultiplier

tubes that convert it to digital electric

signals

 Most modern readers can process 110 –

140 plates per hour

 Rotation/inversion

 The ability to change the image presentation,

or turn the image from a negative to positive

 Anatomic measurements

 The ability to measure certain areas of

interest

 Short-term database functions

 Allows user to locate images, create lists of images, image interpretation, and maintain teaching files

 Dynamic Range Control

 Provides a wide diagnostic field

• Allows for visualization of bone and soft tissue in a single image display

Even More Terminology

 Magnification

 Allows enlargement of a specific area to enhance viewing and diagnosis

 Subtraction

 Allows the user to enhance certain

areas of interest while fading other

areas from view

• Enhancing from vascular detail while fading superimposing bony detail

Image Storage

 Magnetic tape and optical disk

 Each CR image contains app 8 megabytes of data

CR Image Characteristics

 Image resolution

 Dimension of the crystals in the

imaging plate

 Size of the laser beam in the reader

 The image reading matrix

• CR images average 2 – 5 lp/mm

• Standard film demonstrates 3 – 6 lp/mm

Digital Radiography

 X-ray tubes for DR have a high heat capacity

 In excess of 1 MHU

 DR does not use cassettes

 A radiation detector array is used

 These detectors are gas-filled

 The more detectors, the better the

spatial resolution

Direct Capture Radiography

 Image forming x-rays interact with cesium iodide phosphors

 Patient dose is less with this approach

 Or

 They interact with a thin layer of

selenium

 There is no spreading of light and

spatial resolution is improved

 One monitor displays the image

 The operating console is more

complex

 Allows for the input of patient data

 The electron beam of the of the TV

camera tube sweeps the target assembly continuously from top to bottom in 33 ms

 There is no interlace of fields

 The image is sharper with less flicker

Digital Fluoroscopy and

Dose

 Static images are made with a lower dose rate than with 105mm spot

film cameras

 Most DF x-ray beams are pulsed

 The dose to the patient is about half that of conventional image

intensified fluoroscopy

The Three Components of a PACS

 Display System

 Network

 Storage System

Display System

 This is a cathode ray tube monitor

 Provides a workstation for the operator

 Must be very high resolution

 Ranges from 256 X 256 – 1024 X 1024

 This is lower than the spatial resolution of film

• The operator is able to subtract, use edge enhancement, window-level, highlight, pan, scroll and zoom on the monitor

The Image Matrix

 A layout of cells in rows and columns

 Each cell is a specific location in the

matrix

 Each cell is called a pixel

 Each digital image consists of a matrix of cells

 The matrix has various brightness levels

 The level of brightness depends upon the

atomic number and mass density of the tissue that has received x-rays

 A number of computers connected to one another

 In a PACS, many people have access to

an image for different purposes

 Data from one unit to another is first

digitized

 Images can be transferred to another

workstation for interpretation

 This is known as teleradiology

Storage System

 PACS is able to archive

 Images are not lost

 The file room is replaced by a

magnetic or optical memory device

 Electronically, images can be

recalled to any workstation in

seconds

Pitfalls and Acceptance of

CR and DR

 The acceptance of the system is increasing

 This is the future and in many imaging

departments, the future is now!

 Department efficiency is increased

 It does not provide a traditional format

 Some resolution is lost

 Edge enhancement artifacts may actually create pathology

 Due to the increased latitude in image

production, the patient may be exposed to too much radiation

CR – DR and Patient Dose

 If used correctly patient dose can be decreased