rad 265 introduction to digital radiography

The Field of Digital
Radiography

Loren Sachs
Instructor


What is Digital Radiography?
 Historically,

digital radiography referred to
specialized modalities that produced digital
images.
 Examples would include:
–
–
–
–

CT
MRI
Nuclear Medicine
Ultrasound


Digital Radiography Today
 Since

the early 1990s, Digital Radiography
has grown to include Computed
Radiography(CR) and ‘true’ Digital

Radiography(DR) or Direct Radiography.
 Our lecture today will focus on CR and DR.


Digital Terms
 Pixel
– Picture element. This is the basic component of

the digital image, it is what we see. 2
dimensional
 Voxel
– Volume element. This is a 3 dimensional

element that includes depth. The pixel is
essentially the end of the voxel.


 Matrix
– The actual image we see is made up of a series of pixels

in rows and columns called a matrix. Generally, the
larger the matrix the better the spatial resolution of the
image.
 Bit
– The amount of gray scale in the image. The bit is the

exponent to two, ie, a 2 bit image is two to the second
or four. So the image would have 4 shades of gray
possible. Today, most images are 10 or 12 bit.

 FoV
– Field of view. This is how much anatomy is

displayed. A 12 cm FoV will display 12 cm of
anatomy on the screen. The smaller the FoV
the more magnified the anatomy is.


 Window

width

– The gray scale of the digital image. The larger

the width the more grays demonstrated the
lower the contrast of the image.
 Window

level

– The density or brightness of the image. The

higher the number the brighter the image.


Computed Radiography
 The

technical aspects of CR are similar to

what you see in the traditional analog
radiology department, i.e., the technologist
exposes a cassette that is then processed.
 CR differs from analog in that the CR
cassette contains a phosphor plate instead of
a sheet of film.


CR Overview


The Technology of CR
 After

the cassette is exposed by the x-ray
beam, the cassette is loaded into a reader.
 The reader removes the phosphor plate and
exposes it to a laser, stimulating the
phosphors.
 The light emitted from the plate is collected,
quantified, and digitized.


CR Processing


Advantages of CR
 The

major advantage of CR is that existing

radiology rooms can use the technology.
– Consequently, the Radiology department can be

digital at a relatively low cost, between
$100,000-150,000 per reader.
 Also,

due to the similarities with traditional
radiography the learning curve is much
shorter with CR.


Digital Radiography
 DR

uses no cassette. The image capture
device is embedded within the table-top.
 The advantage here is that the steps
involved in processing a ‘cassette’ are
eliminated resulting in a huge increase in
productivity.
 Studies have estimated a 100% increase in
room throughput.


DR Overview


Technology of Digital
Radiography

 There

are two types currently being used

– Direct
– Indirect


Direct Digital Radiography
The photoconductor is made up of
amorphous selenium.


Indirect Digital Radiography
The intensifying screen is made up of
cesium-iodide crystals and the
photodetector is made up of amorphous
silicon.


Which DR Methodology is
Best?
 It

depends entirely on who you listen to.
 Basically, different manufacturers are using
proprietary technology and claiming theirs
is the best.
 Ultimately, it will be decided by end-users.

DR Issues
 The

significant disadvantage for DR is cost.
 Normally, rooms with DR technology have
to be constructed from the ground up.
Today, the average DR room cost is
$400,000-600,000 plus construction costs.
 Construction costs can be overwhelming,
particularly in older buildings that need to
be brought up to code.


How does CR and DR Affect
You the Technologist?
 RSV is

less for both CR and DR when compared
to film/screen combinations. Consequently,
techniques are going to be higher.
 Centering and collimation are REQUIRED.
 You gain a tremendous amount of exposure
latitude.
 Post-processing manipulation allows you to adjust
film quality.


How does CR and DR Affect
You the Technologist? 2

 By

selecting processing algorithms you can
obtain different anatomical information with
one exposure.
– A PA chest film and be reprocessed as a PA rib

film.
 These

methodologies are not a panacea for
being a ‘bad’ technologist.


How does CR and DR Affect
the Patient and Medical Care?
 Patient

dose goes up with these systems for an
individual exam; however, there are fewer repeats.
 Films are available hospital-wide almost
immediately and can be view in multiple locations
simultaneously.
 No films get lost.
 Everyone associated with a patient’s films
becomes more efficient.


Other Considerations
 In

order to gain maximum efficiency with CR and
DR a RIS/PACs systems needs to be deployed.
 RIS, Radiology Information Systems, are used to
manage non-image patient data, i.e. exam number,
dictation status, and billing.
 PACs, Picture Archiving Computer, allows for the
distribution of images over a pre-described area.


Conclusion
 Digital

radiography will change the way
technologists practice radiography.
 However, it will not eliminate the need for a
quality education and an understanding of
radiology principles. In fact, digital
radiography will require additional learning
in order to maximize its usefulness.