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Geisinger Medical Center
School of Radiologic Technology
Radiologic Procedures
Unit #8: Radiographic Equipment
Objectives: Upon completion of the lesson the student will be able to:
1.
2.
3.
4.
5.
6.
7.
8.
9.
Describe the following types of radiographic imaging
processes:
a. Diagnostic (conventional)
b. Digital imaging (DI)
1. Computed Radiography (CR)
2. Direct-Read Radiography (DR)
3. Digital Fluoroscopy (DF)
4. Computed tomography (CT)
c. PACS
Describe and identify the main components of an x-ray tube.
Describe the tube housing by its function and contents.
Describe types of beam restriction devices.
1. Aperture diaphragm
2. Cones and Cylinders
3. Collimator
Describe collimator in terms of use and function.
a. Controls
1. Directional
i. Longitudinal
ii. Vertical
iii. Angle
2. Centering lock (detector)
3. Light field
4. Field size (beam restriction)
b. Indicators
1. Field size
2. Angle
c. External components
Identify types of support systems.
Define image receptor.
Describe a cassette.
Describe a grid.
1. Purpose
2. Types
3. Interspace materials
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10.
11.
12.
13.
14.
15.
16.
17.
Identify types of grids.
1. Parallel grid
2. Crossed grid
3. focused grid
Describe the Bucky device.
Describe radiographic tables
1. Types
2. Table top
Describe radiographic procedures devices in terms of use
and function.
a. Calipers
b. Lead strips
c. Sponges
List immobilization devices and state appropriate uses.
a. Pig-O-Stat
b. “Brat”-board
c. Compression bands
d. Sheets
e. Sandbags
f. Tape
Describe basic exposure terminology.
a. mA
b. Time
c. mAs
d. kVp
e. Distance (SID, OID)
f. Focal Spot
Describe basic control panel controls in terms of use and
function.
a. mA
b. mAs
c. kVp
d. On/Off
e. AEC
f. Exposure switch
Given an image of a generic control panel the student will be
able to identify the following controls:
a.
mA
b.
mAs
c.
kVp
d.
On/Off
e.
AEC
f.
Exposure switch
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References:
1.
2.
3.
4.
5.
Merrill’s, 10th ed., Vol. 1, Chapter 1, page 33 - 35
Merrill’s, 10th ed., Vol. 3, Chapter 34, page 357 – 359
(Image Acquisition Functions)
Bushong, 8th ed.,
a. Pages 105 - 107
b. Pages 123 - 135
c. Pages 241 – 249 (2008)
d. Pages 225 - 230
e. Chapter 27, Digital Radiography
Bontrager, 5th ed., pages 48 – 51
Carlton, 3rd ed., Chap. 5 (X-ray Equipment), pg 86 - 92;
Chap. 6 (X-ray Tube), pg 110 – 116; Chap. 18 (Grid) pg 265
- 261
6.
Lesson Plan(s):
1.
2.
Determine to what extent to cover film handling (possibly drop from the
discussion).
Might make sense to review small equipment, then work up to the
table, since there is a need to identify the grid before Bucky,
Instructor Notes:
Objective 1:
Describe the following types of radiographic imaging processes:
a. Diagnostic (conventional)
b. Digital imaging
1. Computed Radiography
2. Direct-Read (direct-capture) Radiography
3. Digital Fluoroscopy
4. Computed Tomography
a. PACS
new
Instructional Strategies:
Ref:
1.
Merrill’s, 10th ed., Vol. 1, Chapter 1, page 33 – 35
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2.
3.
4.
Merrill’s, 10th ed., Vol. 3, page
Bushong, 9th ed., Chapters 25 & 26
Bontrager, 7th ed., pages 47 - 58
Lesson Content:
INTROUDCTION
Computed Tomography: (limited discussion for class)
CT, one of the early forms of computed radiography, uses digital technology
to produce images, as slices of tissue, some as thin as a millimeter (mm)
This discussion will be directed towards the process used in diagnostic
radiography.
Regardless of the type of the radiography performed there are basics that
are constant.
Radiation: X-rays, the source, the tube has not changed.
Physics: radiation
Anatomy
Patient care
The difference between the current processes is the manner by which the
“shadow” of the anatomy is captured as an image.
DIAGNOSTIC (CONVENTIONAL) RADIOGRAPHY
Conventional radiography uses a film/screen combination to capture the
image (latent), and a chemical process to produce a visible image
(manifest).
A cassette is used to hold the film, and screens (which are part of the
cassette) are used to enhance amount of radiation used to produce the
image.
A processor passes the film through the various stages of processing; from
chemical to chemical, to a drying section.
DIGITAL IMAGING (RADIOGRAPHY) INTRODUCTION
There are four processes
1. CT (Computed Tomography)
2. Computed Radiography
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3.
4.
Direct Digital (Read) Radiography
Digital Fluoroscopy
A conventional radiographic image is made like a shadowgraph, an image
after transmission of x-rays through a patient is recorded on an receptor
(film).
The source of x-ray radiation has remained the same. The difference is how
the image is captured.
Currently there are two ways the image is captured in digital radiography
general diagnostic procedures; one is through the use of detectors or by a
photostimulable phosphor.
Computed Radiography (CR):
CR is a process where the cassette/film combination is replaced by a
cassette/image plate combination. The image plate is the IR.
Just as with conventional radiography, there has to be a means to convert
the invisible (latent) image held in the image plate to a visible image
(manifest).
To accomplish this conversion an image plate reader is used. The image
place is removed from the cassette and scanned by a laser beam. The laser
light causes the stored energy in the phosphors to be released. After the
plate is read it is erased and replaced in the cassette.
Computer workstation: Includes a bar code reader (optional), a monitor for
image display, and a keyboard and mouse. Images are reviewed and
adjusted as needed before sending the PACS.
Exposure Factors: Is similar to conventional radiography, except that the
computer provides exposure compensation. Exposure compensation occurs
after the image is read.
CR has the advantage of allowing approximately 500% over exposure and
80% under exposure when the automatic exposure control (AEC) is used.
The result is fewer repeats, especially for mobile and ER work.
However this can allow for increased exposure to the patient so care must
be exercised to select the appropriate technique as if no compensation is
possible.
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Direct Read (DR):
May also be known as Direct-Capture, or Direct Digital. A system where an
IR is not used, instead the direct conversion of the image to digital form is
used. Digital detectors both captures, and converts the image to a digital
format. A technologist can adjust the image quality post exposure.
Flat panel receptor replaces the image plate cassette and image reader.
Automatic exposure control provides accurate patient exposure. Post
exposure adjustments may be made.
Digital Fluoroscopy:
Conventional fluoro uses an image intensifier, optic and conversion to a
video image.
In DF a direct capture/conversion detector is used.
Image quality is improved because the multiple image manipulations that
occur with conventional fluoro are not used.
Computed Tomography: (CT):
Define: Tomography – images that show a specific level of anatomy, known
as body sectioning.
CT used digital technology to produce images, as slices of tissue, some as
thin as a millimeter (mm)
PACS (Picture
Archiving &
Communication
Systems)
Ref: Bontrager,
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pg 48
Picture: digital medical images
Archiving: storage
Communication: retrieval / sending of images
System: network that manages the complete system
Instead of using film and storing it, with digital radiography the
image acquisition and storage is digital (electronic). Film would
be used when a hard copy was needed (example: a patient
needs to take the exam to a physician with no access to the
PACS system).
Objective 2:
Describe and identify the main components of an x-ray tube.
A. Glass enclosure
B. Cathode
1. Filament
2. Focusing cup
3. Term: Thermionic emission
4. Charge: negative
C. Anode
1. Charge: positive
2. Types: Stationary & rotating
3. Target
4. Target area
5. Induction motor: stator and rotor
D. Protective housing (objective #3)
new
Instructional Strategies:
1.
2.
Ref:
Be sure to stress that the filament alone is not the cathode.
Bring the tube for display.
1. Bushong, 9th ed., pages 120 – 128, Figure 7.25 (pg 133)
Lesson Content:
Introduction:
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Envelope
An x-ray tube is an electronic vacuum tube containing two
electrodes.
The components of a tube are contained in a glass or metal
envelope, glass being the most common material used. A thinner
part of the envelope is the window that allows the maximum
emission of x-rays with minimal absorption in the window.
Cathode:
The
negative
side of the
tube.
●
The function of the cathode is to produce a thermionic cloud,
conduct the high voltage to the gap between the cathode and
anode, and focus the electric stream as it heads towards the
anode. The cathode is a complex device that can be referred
to as the cathode assembly. (Ref: Carlton)
● Filament – A coil of wire similar to that in a kitchen toaster.
When heated it emits electrons. The process of ejecting
electrons from the filament is called thermionic emission.
Filaments are usually made of tungsten.
Most diagnostic x-ray tubes have dual filaments called a dual
focus arrangement. (Ref: Carlton)
Filaments of dual focus cathodes are typically of two different
lengths. The shorter filament produces a smaller source of
emitted x-rays (from the anode) that results in finer image
detail. A technologist who understands this concept can select
a filament appropriate for the desired detail.
●
Focusing cup – a filament is (or filaments are) located in a
metal cup whose purpose is to keep the electrons confined.
(see Figs 10-6 & 10-7 of Bushong)
Electrons possess negatives charges, therefore have a
tendency to diverge rather than travel in straight lines. In order
to counteract that tendency the low negative charge of the
focusing cup along with it geometry focuses the electrons
toward one another in a convergence pattern.
Typical cathodes have two filaments, of different lengths.
Anode: The
positive side
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of the tube.
Functions:
● Electrical conductor receives electrons emitted by the cathode
to conduct them through the tube back to the high-voltage
generator.
● Provides mechanical support for the target
● Thermal radiator – 99% of the electron’s kinetic energy is
converted to heat (the rest forms of x-rays). The heat must be
quickly conducted away to prevent damaging the anode.
Types
● stationary
● rotating
●
Target
The area of the anode struck by the electrons from the cathode.
Objective 3:
Describe the tube (protective) housing by its function and
contents.
NEW
Instructional Strategies:
1.
Ref:
1.
Bushong, 9th ed., pages 121 - 122
Lesson Content:
A x-ray tube
is enclosed
in a
protective
housing that
provides
electrical
safety for
the
technologist,
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radiation
protection
and a
means to
support the
x-ray tube
Electrical
safety
To prevent accidental electric shock high-voltage receptacles are
incorporated in the tube housing. Some housings contain oil that
serves as an insulator to prevent electric shock.
Radiation
protection
When x-rays are produced they are emitted isotropically, that is
with equal intensity in all directions. The housing contains the
radiation allowing only rays to be emitted through a special section
called a window. The emitted rays are considered the useful
beam.
Mechanical
support
The housing provides a mechanical means of support and
protects it from damage that could be caused by rough handling.
Oil
Besides preventing electrical shock the oil provides a thermal
cushion by dissipating heat generated during the production of xrays.
Objective 4:
Describe types of beam restriction devices.
1. Aperture diaphragm
2. Cones and Cylinders
3. Collimator
NEW
Instructional Strategies:
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Ref:
Bushong, 9th ed., pages 229 - 232
Lesson Content:
Introduction:
Radiation protection and image quality depend on the restriction of
the beam. Maintaining the beam to the correct size helps to reduce
scattered radiation and thereby improving image quality.
There are three types.
Aperture
diaphragm
This is simplest of all beam-restricting devices. It is basically a lead
or lead-lined metal diaphragm that is attached to the x-ray tube
head. An aperture must be used at specified distance to match the
size of the cassette it is designed for.
Cones &
Cylinders
Cones confine the beam to a prescribed size for a given distance.
Cylinders can telescope which will allow changing the size of the
beam to a limited degree.
Collimator
(variableaperture)
A collimator is a light-localizing variable-aperture device. Lead
shutters are adjusted to vary the size of the emitted beam. A
collimator can be used for distances.
Objective 5: Describe collimator in terms of use and function.
NEW
Instructional Strategies:
Ref:
Bushong, 9th ed., 231 - 232
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Lesson Content:
Introduction
A collimator provides a means to vary the size of the beam and to
see the size of the field via a light that mimics the x-ray beam.
Collimator
Controls
1. Directional
a. Longitudinal
b. Vertical
c. Angle
2. Centering lock (detector)
3. Light field
Field size
(beam
restriction)
●
●
●
Collimator
Cone
Diaphragm
External
components
Support mechanisms are required so that the tube can be
positioned.
Types:
● Ceiling support system
● Floor-to-ceiling support system
Objective 6: Identify types of support systems.
NEW
Instructional Strategies:
Ref:
Lesson Content:
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Definition:
Objective 7: Define image receptor.
NEW
Instructional Strategies:
Ref:
Lesson Content:
Definition:
Used for computed radiography the plate is coated with
photostimulable phosphor (europium-activated barium fluorohalide
compounds) which are energized when exposed to x-rays.
The plate can be used repeatedly, and for a short time exposed to
light
The latent image is made manifest by exposure to a very narrow
beam from a high-intensity laser. The laser beam causes the trapped
electrons to return the valence band with the emission of blue light.
The blue light is converted to a digitized image.
Objective 8: Describe a cassette.
NEW
Instructional Strategies:
Ref:
Lesson Content:
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Definition:
A rigid holder that contains the film and radiographic intensifying
screens for conventional radiography, and the image plate for digital
imaging.
Objective 9: Describe a grid.
NEW
Instructional Strategies:
Ref:
Lesson Content:
Objective 10:
Describe a grid.
new
Instructional Strategies:
Ref:
Bushong, 9th ed., pages 232 - 238
Lesson Content:
Objective 11: Describe the Bucky device.
new
Instructional Strategies:
Can use the wall-mounted grid holder to show what it looks like.
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Ref:
Lesson Content:
Introduction
In 1913, Gustave Bucky designed a method of reducing scatter
radiation, a grid of carefully fabricated series of radiopawue
materials (grid lines) alternating with sections of radiolucent
material (interspace material). The device that contains a grid is
often called the Bucky Device.
A Bucky is the component in a table that contains a grid, and a
holder for the cassette. The bucky is moved to place the cassette
(IR) in line with the beam.
Bucky
Device
(tray)
This is the device that holds the cassette or IR
Components
● Grid
● Tray – holds the cassette
Objective 12:
Describe the radiographic table in terms of use and function.
A. Types
B. Tops
NEW
Instructional Strategies:
1.
Ref:
1.
2.
Bushong, 9th ed., pages 105 – 107
Bushong, 8th ed., page 233
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Lesson Content:
A
radiographic
table is
supports the
patient
during the
examination.
Types
●
●
●
Stationary
Pedestal
Fluoroscopic – allow tilt, and identified by the degree of tilt.
ex: 90/30 - 90º to the foot, and 30º to the head.
Table top
Top: Either flat or curved.
Must be uniform in thickness and transparent to x-rays.
Floating – most common. Have a range of motion to allow moving
the patient without physically moving the patient.
Bucky
device
In 1913, Gustave Bucky designed a method of reducing scatter
radiation, a grid of carefully fabricated series of radiopawue materials
(grid lines) alternating with sections of radiolucent material (interspace
material). The device that contains a grid is often called the Bucky
Device.
A Bucky is the component in a table that contains a grid, and a holder
for the cassette. The bucky is moved to place the cassette (IR) in line
with the beam.
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(template page)
Objective x:
Describe a grid.
Instructional Strategies:
Ref:
Lesson Content:
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