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CHAPTER 11 Equipment Design for Radiation Protection
217
Fluoroscopic Exposure Control Switch. According to
state and federal regulations, the fluoroscopic exposure
control switch (e.g., the foot pedal) must be of the dead-
man type, meaning that only continuous pressure applied by the operator can keep the switch activated and
the fluoroscopic tube emitting x-radiation. This clearly
implies that the exposure automatically terminates if
the person operating the switch becomes incapacitated
(e.g., has a medical emergency) or, for any reason, removes his or her foot from the pedal.
Mobile Fluoroscopic Systems
Radiation Safety Features of Mobile C-arm Fluoroscopy.
portable x-ray unit that has a C-shaped multiorientable gantry arm. An x-ray tube is attached to one end
of its curved arm and an II attached to the other end.
C-arm fluoroscopes (Fig. 11.20) are frequently used in
the operating room for orthopedic procedures (e.g.,
pinning of a fractured hip). They are also employed
quite commonly for:
• Cardiac imaging
• Interventional procedures
A mobile C-arm fluoroscopic unit is a
The use of C-arm fluoroscopy in interventional procedures carries the potential for a relatively large patient
radiation dose. C-arm fluoroscope operators, if standing close to the patient, could also receive a significant
increase in occupational exposure from patient scatter
radiation during such cases. For these reasons, equipment operators, including attending physicians, must
have appropriate education and training to ensure that
they will be able to follow guidelines for safe C-arm
operation and also meet radiation safety protocols essential to patient and personnel safety. A necessary
component of this is the wearing of wrap-around lead
aprons and thyroid shields by all involved personnel
throughout each procedure.
Mobile fluoroscopic units are required to have a
minimal source-to-end of collimator assembly distance
of 30 cm (12 inches). Some type of spacer or collimator
extension is customarily installed to prevent any part
of the patient from coming closer than 30 cm (12 inches)
to the tube target. During C-arm fluoroscopy procedures,
the patient-II distance should be as short as possible
(Fig. 11.21). This reduces patient entrance dose. For fur-
ther dose-reduction purposes it is preferable to position
the C-arm so that the x-ray tube is under the patient.
With the x-ray tube in this position, scatter radiation is
attenuated (Fig. 11.22) toward personnel above the knee
level. However, when the x-ray tube is positioned over the
patient, scatter radiation is not attenuated by the table,
and therefore it is more intense, and radiation exposure
of personnel increases correspondingly.
Fig. 11.20 C-arm fluoroscope and monitor.
RADIATION SAFETY FEATURES OF DIGITAL FLUOROSCOPIC EQUIPMENT
Digital Fluoroscopy (DF)
Pulsed Progressive Systems. Various methods are
used to obtain digital images in fluoroscopic equipment.
The electrical signal from the video camera attached to
the output phosphor may be digitized. In newer equipment, the analog TV camera may be replaced by a digital
device such as a CCD camera or other digital detector. In
whatever manner the digital image is acquired, the use of
digital technology offers the possibility of several methods of dose reduction. One such method utilizes a brief
high-intensity pulse of radiation to create an entire image on the output phosphor. The lines composing the
image are progressively scanned (i.e., from left to right
218
CHAPTER 11 Equipment Design for Radiation Protection
TELEVISION CAMERA
IMAGE INTENSIFIER
PATIENT
TABLE
SPACER CONE
X-RAY TUBE
Fig. 11.21 To reduce the patient’s entrance dose during C-arm fluoroscopy, the patient–image intensifier
distance should be as short as possible. (Courtesy Mark Rzeszotarski.)
WEAK
SCATTER
REGION
C-ARM ASSEMBLY
CONTROL
UNIT
IMAGE INTENSIFIER
STRONG
BACKSCATTER
REGION
INTENSE
PRIMARY
BEAM
Fig. 11.22 To reduce scatter radiation during C-arm fluoroscopy, position the C-arm so that the x-ray tube is
under the patient whenever possible. (Courtesy Mark Rzeszotarski.)
followed by right to left and so on, usually referred to as
raster scanning, from top to bottom) to provide the image that appears on a monitor during a brief period
(one-sixtieth of a second). The x-ray beam is deactivated
while the image is being scanned, thereby decreasing
patient dose, and then pulsed back on for the next image.
These systems are known as pulsed progressive systems
and are commonly used to lower patient dose.
SPACER
X-RAY
TUBE
CONE
Last Image Hold. Another dose-reduction technique
that is particularly effective in DF systems is the last image hold feature. For this feature, the image formed
when the x-ray tube was last energized remains on the
monitor so that no further radiation exposure is needed
to regenerate it. In a digital system, using embedded
processing software, this retained image could also be
composed of several frames of information that have
CHAPTER 11 Equipment Design for Radiation Protection
219
been added together to reduce the effect of quantum or
random noise that would be particularly apparent in a
single frame.
Digital Subtraction Angiography (DSA) and Interventional Systems
Interventional Procedures. Digital techniques have
had a major impact on interventional fluoroscopy. The
goal in interventional procedures is to locate highcontrast, small objects such as catheters, stents,* or
electrical leads for electronic implants. Not only are
these devices in the millimeter-size range, but they are
also moved within the patient as part of the procedure
to implant the devices or to inject liquids such as
glues,** steroids, or anesthetics. Contrast material is
sometimes injected to improve the visibility of the devices or the leading edge of catheters. The visualization
of high-contrast, small objects with a digital imaging
system requires that the pixel elements reveal very small
regions of the patient. In addition, images must be updated at a reasonable rate to reveal the location of objects in the patient as the objects are moved. In the latest
DF systems, the II has been replaced by a “flat-panel”
detector that is similar to those used in DR. A flat-panel
digital detector for fluoroscopy meets the same technical requirements as previously described (direct or indirect conversion of x-ray energy to stored electronic values) but is also capable of recording images rapidly, as
many images or “frames” as are required per second to
be perceived as motion and presented in a live digital
video format. The advent of these techniques has allowed the performance of more complicated procedures that are sometimes associated with much longer
exposure times for patients. Some of the data related to
these lengthy irradiations are provided in Chapter 2. It
is still the responsibility of the imaging team to make
sure that acceptable risk versus benefit principles are
applied. While the radiation risk may be increased compared to other imaging techniques, the benefit of repair
of life-threatening conditions must also be considered.
*A stent is a tubular support that can be placed inside a blood
vessel, canal, or duct to create a pathway or relieve an obstruction.
**Injection of glues or glue embolization is an interventional
technique that uses a chemical called n-butyl cyanoacrylate,
which is usually shortened to NBCA, to block problematic
arteries.
Digital Subtraction Angiography. One of the most sig-
nificant advances in digital imaging in vascular and interventional fluoroscopy over the past 50 years has been
Digital Subtraction Angiography (DSA). In vascular flu-
oroscopy, the objective is the visualization of blood vessels.
This may be necessary to complete an interventional procedure, or it may be used to reveal vascular problems such
as occlusion (blockage), stenosis (narrowing), or aneurysms (abnormal bulging). It usually includes the injection of contrast material to enhance vascular appearance.
DSA implies the performance of arithmetic operations on
the pixel values of digital images. Since the individual images or frames of the digital video are available as a matrix
of signal (voltage) values that are stored in a computer,
pairs of images may be subtracted. In image subtraction,
the digital values recorded for each corresponding pixel of
an image pair are subtracted from each other. This process
produces a resultant image that “only” consists of features
that have changed between the initial two images.
In DSA, a “mask” image (simply a reference image of
the same area before the contrast is administered) is
obtained prior to the injection of contrast material.
Subsequent images may be subtracted from the initial
mask so that the main difference between pairs of images (the movement of contrast material) is emphasized. Therefore, the contrast material that lines the
vessels of interest enhances the appearance of the vessels
revealing features such as narrowing, or stenosis. Interventional procedures may use this information to guide
the insertion of stents to open occluded blood vessel.
For complex interventional procedures, this increased
vascular contrast allows visualization of small vessels
surrounding arteriovenous malformations.* Additional
clarity may be obtained by remasking (redefining the
image from which subsequent images are subtracted)
when catheters approach the malformation.
Roadmapping. In situations where the vasculature is
complex or overlying structures provide a confusing
background, the location of the catheter may be difficult
to determine visually. More contrast material could be
injected to improve visibility, but the image would still
be cluttered, and there are limits to the amount of contrast material that can safely be injected into the patient
*An abnormal tangle of blood vessels connecting arteries
and veins, which disrupts normal blood flow and oxygen
circulation.
220
CHAPTER 11 Equipment Design for Radiation Protection
Fig. 11.23 Roadmapping: First, the digital subtraction angiography (DSA) of the vascular structure is per-
formed. The postcontrast frame associated with maximum vessel opacification becomes the roadmap mask;
subsequent digital fluoroscopic (Fluoro) images are subtracted from the roadmap mask. The result in live
fluoroscopic images of the inserted catheter or wire overlaid on a static image of the vasculature (with distracting underlying tissue removed). (From Pooley RA, McKinney JM, Miller DA, The AAPM/RSNA physics
tutorial for residents: digital fluoroscopy, Radiographics 21(2): 521–534, 2001).
so as to avoid potential kidney damage. A technique
known as roadmapping is useful in this situation. If the
patient is not moving and the FOV is not altered, a static
image of the vasculature may be obtained through subtraction, pre- and postcontrast injection, as in standard
DSA. This static image may be preserved as a lowercontrast “ghost” image or as a reversed-contrast lighter
image. In either case, it serves the function of a stationary map over which the outline of the catheter can be
shown as it advances to the position where it is needed.
Fig. 11.23 illustrates a roadmap procedure used for a
catheter approaching an aneurism.
RADIATION SAFETY FOR HIGH-LEVEL CONTROL INTERVENTIONAL PROCEDURES
Justification for Use of High-Level Control
(HLC) Interventional Procedures
As mentioned previously, interventional procedures are
invasive actions performed by a physician with the aid of
fluoroscopic imaging. The interventional physician, usually a radiologist or a cardiologist, inserts catheters into
vessels or directly into patient tissues for the purpose of:
• Drainage
• Biopsy
• Alteration of vascular occlusions (obstructions) or
malformations
For these procedures, high-level control fluoros-
copy (HLCF) is often employed. HLCF is an operating
mode for state-of-the-art fluoroscopic equipment in
which entrance radiation levels are substantially higher
than those normally employed in routine procedures.
The higher entrance exposure rate or entrance dose
rates allows the examination of smaller and lowercontrast objects that are not ordinarily discerned during
standard fluoroscopy. HLCF therefore is used for those
interventional procedures in which visualization of fine
catheters or other not easily seen structures is crucial.
An audible signal constantly reminds personnel that the
HLC is engaged. It is strongly recommended that pulsed
mode and frequent last image hold be the standard methods of operation when HLCF is being used.
CHAPTER 11 Equipment Design for Radiation Protection
221
Public Health Advisory About the Dangers of Overexposure of Patients and Exposure Rate Limits
Many of the fluoroscopically guided therapeutic interventional procedures have the potential for substantial
patient exposure. On September 30, 1974, the US Food
and Drug Administration (FDA) issued a public health
advisory to alert health care workers to the probability
and dangers of overexposure of patients through the use
of high-level fluoroscopy. The FDA x-ray equipment
standards, issued in 1994, limited the tabletop exposure
rate of fluoroscopic equipment for routine procedures
to a maximum of 10 R/min unless an HLC was present,
in which case routine fluoroscopy maximum tabletop
exposure rates were set at 5 R/min when the system was
not in HLC mode and unlimited when it was in HCL
mode.11 The authors of these 1994 standards believed
that the unrestricted high-level capability was necessary
for certain vital situations involving therapeutic interventional procedures in which the potential risks to the
patient of much increased radiation exposure would
be subordinate to a successful medical outcome of an
intervention. As a safeguard, however, HCL was required to have manual continuous positive pressure on a
special high-level foot pedal, accompanied by a steady
audible signal to remind personnel that the high-level
fluoroscopic mode was in use. In this operational mode,
patient entrance exposure rates have been estimated to
range from 20 to 120 R/min (176 to 1056 mGya/min
entrance or skin dose rates). When the rule was issued,
total patient irradiation was limited by the heat-loading
capabilities of the x-ray tube. Amazingly, the thinking or
belief at that time was that the tube would reach its heat
limit before any detectable patient early tissue reactions
could occur. By the early 1990s, however, advances
in x-ray tube heat dissipation technology and the increased frequency of vascular interventional procedures
that require long fluoroscopic times (Box 11.5) had
created a situation in which very serious skin reactions
had been reported in some patients. Radiogenic skin
injuries such as erythema (diffuse reddening) and des-
quamation (sloughing off of skin cells) are early tissue
reactions in which the severity of the disorder increases
with radiation dose. As the data in Table 11.2 demonstrate, a half-hour of total high-level beam-on time at
one location on a patient’s skin is sufficient to produce
BOX 11.5 Procedures Involving
Extended Fluoroscopic Time
• Percutaneous transluminal angioplasty
• Radiofrequency cardiac catheter ablation
• Vascular embolization
• Stent and filter placement
• Thrombolytic and fibrinolytic procedures
• Percutaneous transhepatic cholangiography
• Endoscopic retrograde cholangiopancreatography
• Transjugular intrahepatic portosystemic shunt
• Percutaneous nephrostomy
• Biliary drainage
• Urinary or biliary stone removal
From the US Food and Drug Administration (FDA): Public
health advisory: avoidance of serious x-ray-induced skin
injuries to patients during fluoroscopically guided procedures,
Rockville, MD, September 30, 1994, FDA.
erythema. In this case, the skin injury does not usually
appear for approximately 10 days. Because manifestations of skin injury are delayed, a radiologist would not
typically be the first person to observe the onset of the
symptoms. Therefore, patient monitoring, radiation
dosimetry, and accurate record-keeping are essential for
the future medical management of adverse reactions.
The FDA has recommended that a notation be placed
in the patient’s record if a skin dose in the range of 1 to
2 Gy
is received. The location of the area of the patient’s
t
skin that received the absorbed dose should also be
noted using:
• A diagram
• Annotated photograph
• Narrative description
Since 2000, however, alarmed state regulatory agencies
have imposed a restriction on high-level radiation
entrance rates. With the II at a distance of 30 cm (≈12
inches) above the tabletop, the maximum continuous
fluoroscopic entrance exposure rate permitted is 20 R/min
(176 mGya/min entrance dose rate). This is not true,
though, for pulsed mode for which the instantaneous
exposure rates values can be very much higher.
Use of Fluoroscopic Equipment by Non-radiologist Physicians
Fluoroscopic devices are capable of subjecting the
patient, the physician, and other personnel close to
the fluoroscopic equipment to substantial amounts of
222
TABLE 11.2 Radiation-Induced Skin Injuries
Effect
Early transient erythema 2 1.7 0.17 Hours
Temporary epilation 3 2.5 0.25 3 weeks
Main erythema 6 5.0 0.50 10 days
Permanent epilation 7 5.8 0.58 3 weeks
Dry desquamation 10 8.3 0.83 4 weeks
Dermal atrophy 11 9.2 0.92 0.14 weeks
Telangiectasias 12 10.0 1.00 0.52 weeks
Moist desquamation 15 12.5 1.25 4 weeks
Late erythema 15 12.5 1.25 6–10 weeks
Dermal necrosis 18 15.0 1.50 0.10 weeks
Secondary ulceration 20 16.7 1.67 0.6 weeks
*Time required to deliver the typical threshold dose at the specified dose rate.
†
The unit for absorbed dose is the gray (Gyt) in the International System of Units.
‡Time after single irradiation to observation of effect.
Modified from Wagner LK, Eifel PJ, Geise RA: Potential biological effects following high x-ray dose interventional procedures, J
Vasc Interv Radiol 5:71, 1994.
CHAPTER 11 Equipment Design for Radiation Protection
HOURS OF FLUOROSCOPIC “ON TIME” TO REACH THRESHOLD*
Typical Threshold
Absorbed Dose
(Gy
†
)
t
Usual Fluoroscopic
Dose Rate of
0.02 Gy
/min
a
High-Level
Dose Rate of
0.2 Gya/min
Time to
Onset of
‡
Effect
direct and/or indirect ionizing radiation. These devices
include:
• C-arm fluoroscopes
• Fluoroscopes on stationary equipment with HCL
mode used for interventional procedures
• Biplane (dual x-ray tubes) interventional fluoro-
scopic systems*
Ongoing education and training in the safe use of
fluoroscopic equipment should be mandatory for nonradiologist physicians and equipment operators. Many
institutions have therefore established through their
RSOs radiation safety accreditation programs that must
be taken and passed before non-radiologist physicians
are permitted to use such devices.
Some of the causes of elevated radiation exposures to
personnel during interventional procedures include:
• Operation of the fluoroscopic tube for long periods
in continuous mode in place of pulsed mode
• Failure to use the protective curtain or floating
shields on the stationary fluoroscopic equipment’s II
as a means of protection
*Biplane x-ray fluoroscopy systems consist of a double c-arm
independent configuration with each c-arm having its own
x-ray source and corresponding detector panel. The two
c-arms are in the mechanical arrangement that allows them to
generate multiple oblique dual-angle projections.
Monitoring and documenting procedural fluoroscopic time are essential. The responsibility for
this documentation has generally belonged to the
radiographer assisting with the procedure. With
newer systems, the computer software automatically
produces a record of both accumulated continuous
and pulsed radiation time, as well as estimates of delivered dose and dose area product. In addition, if a
physician loses track of how long a procedure is taking and how much radiation is being delivered to a
localized area of the patient’s body, it becomes the
radiographer’s ethical responsibility to call this to the
physician’s attention in the interest of the safety of all
concerned. In the event of a critical situation in
which there is markedly excessive fluoroscopic irradiation time, the radiographer is responsible for notifying an appropriate supervisor, who should then
implement the imaging facility’s relevant established
protocol.
The National Cancer Institute and the Society of
Interventional Radiology have conjointly designed
guidelines to assist physicians in developing strategies
that will enable them to fulfill their interventional
clinical objectives while controlling patient radiation
dose and minimizing exposure to occupationally
exposed personnel. These strategies are listed in
Box 11.6.
CHAPTER 11 Equipment Design for Radiation Protection
223
BOX 11.6 Strategies to Manage Radiation Dose to Patients, Operators, and Staff During
Interventional Fluoroscopy
Immediate Long-Term
Optimize Dose to Patient
Use proper radiologic technique:
• Maximize distance between x-ray tube and patient
• Minimize distance between patient and image receptor
• Limit use of electronic magnification
Control fluoroscopic time:
• Limit use to necessary evaluation of moving structures
• Employ last image hold function to review findings
Control images:
• Limit acquisition to essential diagnostic and documenta-
tion purposes
Reduce dose:
• Reduce field size (collimate) and minimize field overlap
• Use pulsed fluoroscopy and low frame rate
Minimize Dose to Operators and Staff
Keep hands out of the beam
Use movable shields
Maintain awareness of body position relative to the x-ray
beam:
• Horizontal x-ray beam: operator and staff should stand on
the side of the image receptor
• Vertical x-ray beam: the image receptor should be above
the table
Wear adequate protection:
• Protective, well-fitted lead apron
• Leaded glasses
From the National Cancer Institute, Division of Cancer Epidemiology and Genetics, Radiation Epidemiology Branch: Interventional
fluoroscopy: reducing radiation risks for patients and staff, NIH Publication No. 05-5286, Rockville, MD, 2005, National Institutes
of Health.
Include medical physicist in decisions:
• Machine selection and maintenance
Incorporate dose-reduction technologies and dose-
measurement devices in equipment
Establish a facility quality improvement program that
includes an appropriate x-ray equipment quality
assurance program, overseen by a medical physicist,
which includes equipment evaluation/inspection at
appropriate intervals
Improve ergonomics of operations and staff:
• Train operators and staff in ergonomically good position-
ing for use of fluoroscopy equipment; periodically assess
their practice
• Identify and provide the ergonomically best personal
protective gear for operators and staff
• Urge manufacturers to develop ergonomically improved
personal protective gear
• Recommend research to improve ergonomics for per-
sonal protective gear
S U M M A R Y
• A diagnostic-type tube housing protects the patient
and imaging personnel from off-focus, or leakage,
radiation by restricting the emission of the x-rays to
the area of the useful, or primary, beam.
• Leakage radiation from the tube housing measured
at 1 m from the x-ray source must not exceed 0.88
mGya/h (100 mR/h) when the tube is operated at its
highest kilovoltage at the highest current (mA) that
allows continuous operation.
• The control panel, or console, must be located behind a suitable protective barrier that has a radiation-absorbent window that permits satisfactory
observation of the patient during any procedure.
This panel must indicate the conditions of exposure
and provide indication when the x-ray tube is ener-
1
gized.
• The radiographic examination tabletop must be of
uniform thickness, and for under-table tubes as used
in fluoroscopy, the patient support surface also
should be as radiolucent as possible, which will lead
to reducing the patient’s radiation dose.
• Radiographic equipment must have an sourceto-image receptor distance (SID) indicator.
• X-ray beam limitation devices must be used to confine the useful beam before it enters the anatomic
area of clinical interest.
224
CHAPTER 11 Equipment Design for Radiation Protection
• The patient’s skin surface should always be at least
15 cm below the collimator to minimize exposure to
the epidermis.
• Good coincidence between the x-ray beam and the
light-localizing beam of the collimator is necessary;
both alignment and length and width dimensions
of the two beams must correspond to within 2% of
the SID.
• Exposure to the patient’s skin may be reduced
through proper filtration of the radiographic beam.
• Compensating filters are used in radiography to
provide uniform imaging of body parts when considerable variation in thickness or tissue composition exists.
• Diagnostic x-ray units must have consistent exposure reproducibility, that is, the ability to duplicate
specific radiographic exposures for any given combination of kVp, mA, and time.
• Exposure linearity is essential. When a change is
made from one mA station to a neighboring mA station, the most that linearity can vary is 10%.
• Radiographic grids increase patient dose in radiography. Their use for the examination of thicker body
parts is a fair compromise because they remove scattered radiation emanating from the patient that
would otherwise degrade the completed image.
• Because of increased sensitivity of photostimulable
phosphor to scatter radiation before and after exposure
to a radiographic beam, a grid may be used more frequently during computed radiography (CR) imaging.
The use of a grid does increase patient dose but significantly improves radiographic contrast and visibility
of detail.
• To limit the effects of inverse fall-off of radiation
intensity with distance during a mobile radiographic
examination, an x-ray source-skin distance (SSD) of
at least 30 cm (12 inches) must be used.
• With digital radiography, the image receptor is divided
into small detector elements that make up the twodimensional picture elements, or pixels, of the image.
• Radiographers must always strive to select correct
technical exposure factors from the beginning to
avoid overexposing patients when digital images are
obtained.
• The digital image ultimately acquired in both CR
and digital radiography (DR) can be displayed on a
monitor for viewing and evaluation and can also be
printed if a hard copy is desired.
• Fluoroscopic procedures produce the largest patient
radiation rates levels in diagnostic radiology. Therefore, multiple safety guidelines should always be adhered to.
• During C-arm fluoroscopic procedures, the patient-image intensifier distance should be as short
as possible.
• During digital fluoroscopy, the use of pulsed progressive systems with last image hold and roadmapping will significantly lower patient dose.
• High-level control fluoroscopy (HLCF) is often engaged in interventional procedures and produces
entrance radiation rate levels that are substantially
higher than those allowed for routine fluoroscopic
procedures.
• If skin dose is received in the range of 1 to 2 Gyt, the
Food and Drug Administration (FDA) requires that
a notation be placed in the patient’s record.
G E N E R A L D I S C U S S I O N Q U E S T I O N S
1. What are the x-ray tube housing construction require-
ments when a tube is operated at its highest voltage at
the highest current that allows continuous operation?
2. What must the control panel, or console, indicate?
3. How do light-localizing variable-aperture rectan-
gular collimators reduce the amount of scattered
radiation being produced during a radiographic
examination?
4. How does filtration of the radiographic beam re-
duce exposure to the patient’s skin and superficial
tissues?
5. When should a radiological physicist measure the
6. What are acceptable HVL values for radiographic
7. What is exposure linearity?
8. What is the effective metric equivalent unit for the
9. Why is the use of a radiographic grid acceptable if
10. What can a radiographer do to avoid overexposing
half-life of a diagnostic x-ray beam?
and fluoroscopic systems?
English unit 40 inches?
its use increases patient dose?
the patient when a CR system is used?
CHAPTER 11 Equipment Design for Radiation Protection
225
11. What effect does the use of pulsed, or intermittent,
fluoroscopy have on patient dose?
12. Why is there concern over the use of mobile C-arm
fluoroscopes during surgical, vascular, interventional, and other potentially lengthy procedures?
13. To what does the scientific term luminance refer?
14. What strategies can physicians employ during inter-
ventional fluoroscopic procedures to control patient
radiation dose and minimize exposure of occupationally exposed personnel and any other assisting
personnel?
15. During digital fluoroscopy, how does the use of a
pulsed progressive system lower patient dose?
16. How is the appearance of vascular structures im-
proved by digital subtraction angiography?
R E V I E W Q U E S T I O N S
1. The radiographic beam should be collimated so that
it is which of the following?
A. Slightly larger than the image receptor
B. No larger than the image receptor
C. Twice as large as the image receptor
D. Four times as large as the image receptor
2. Both alignment and length and width dimensions of
the radiographic and light beams must correspond
to within:
A. 1% of the SID
B. 2% of the SID
C. 5% of the SID
D. 10% of the SID
3. What is the function of a filter in diagnostic radiology?
A. To permit only alpha rays to reach the patient’s skin
B. To permit only beta particles to interact with the
atoms of the patient’s body
C. To decrease the x-radiation dose to the patient’s
skin and superficial tissue
D. To remove gamma radiation from the useful beam
4. HVL may be defined as the thickness of a designated
absorber required to do which of the following?
A. Increase the intensity of the primary beam by
50% of its initial value
B. Increase the intensity of the primary beam by
25% of its initial value
C. Decrease the intensity of the primary beam by
50% of its initial value
D. Decrease the intensity of the primary beam by
25% of its initial value
17. How is the progression of a catheter through com-
plicated vasculature improved by roadmapping?
18. If a radiographer is operating a C-arm fluoroscope
during an interventional procedure, what is the
consequence if the operator stands too close to the
patient while the x-ray beam is energized?
19. If during a lengthy fluoroscopic procedure, a non-
radiologist physician loses track of how long the
procedure is taking and how much radiation is being delivered to a localized area of the patient’s
body, what is the radiographer’s ethical responsibility?
20. What is an arteriovenous malformation and what
imaging procedure would be used to visualize the
anatomical structures of interest?
5. The photostimulable phosphor in the computed ra-
diography imaging plate is more sensitive to scatter
radiation before and after it is sensitized through
exposure to a radiographic beam. Because of this
increased sensitivity, which of the following is true?
1. Five millimeters of added aluminum equivalent filtration must always be used during
routine CR imaging.
2. A radiographic grid may be used more frequently during CR imaging.
3. Any source-to-image receptor distance can be
used during CR imaging without adjustment
in technical exposure factors.
A. 1 only
B. 2 only
C. 3 only
D. 1, 2, and 3
6. To minimize skin exposure to electrons produced by
photon interaction with the collimator, how far below
the collimator should the patient’s skin surface be?
A. At least 1 cm below
B. At least 5 cm below
C. At least 10 cm below
D. At least 15 cm below
7. Which of the following aluminum equivalents for
total permanent filtration meets the minimum requirement for mobile diagnostic and fluoroscopic
equipment?
A. 0.5 mm aluminum equivalent
B. 1.0 mm aluminum equivalent
226
CHAPTER 11 Equipment Design for Radiation Protection
C. 2.0 mm aluminum equivalent
D. 2.5 mm aluminum equivalent
8. The trough, or bilateral wedge, filter, which is used in
some dedicated chest radiographic units, is an example of which of the following?
A. Compensating filter
B. Filter used in all digital imaging systems
C. Filter used in all dedicated mammographic units
D. Filter used in all computed tomography systems
9. To decrease patient exposure during fluoroscopic
procedures, the fluoroscopist can:
1. Limit the size of the fluoroscopic field to include
only the area of anatomy that is of clinical interest
2. Employ the practice of pulsed fluoroscopy to
reduce the overall length of exposure
3. Choose to use a conventional fluoroscope instead of an image intensification fluoroscope
A. 1 and 2 only
B. 1 and 3 only
C. 2 and 3 only
D. 1, 2, and 3
10. A diagnostic-type protective tube housing must be
constructed so that leakage radiation measured at a
distance of 1 m from the x-ray source does not exceed ______ when the tube is operated at its highest
voltage at the highest current that allows continuous operation.
A. 5 Gya/hr
B. 3 Gya/hr
C. 1 Gya/hr
D. 0.1 Gya/hr
11. Which of the following changes might improve the
visibility of vessels in an interventional angiography
study but may cause harm to the patient?
A. Digital subtraction angiography
B. Increase the amount of contrast material
C. Use roadmapping
D. Use pulsed fluoroscopy
12. Pulsed, or intermittent, fluoroscopy involves man-
ual or automatic periodic activation of the fluoroscopic x-ray tube by the fluoroscopist, rather than
continuous activation. Which of the following are
benefits of this practice?
1. Automatically magnifies the fluoroscopic image
2. Helps to extend the life of the x-ray tube
3. Significantly decreases patient dose, especially
in long procedures
A. 1 and 2 only
B. 1 and 3 only
C. 2 and 3 only
D. 1, 2, and 3
13. A resettable device on a fluoroscopic unit that mea-
sures the collective x-ray beam-on time and sounds
an audible alarm or in some cases interrupts the
exposure after the fluoroscope has been activated
for 5 minutes is termed a:
A. Cumulative timer
B. Interruption timer
C. Interventional timer
D. Subtraction timer
14. Non-digital fluoroscopy involves the use of a signal
amplification device called an:
A. Flat panel detector
B. Image intensifier tube
C. Photostimulable phosphor
D. Progressive subtraction device
15. When changing one mA station to a neighboring
mA station, the most linearity can vary is:
A. 5%
B. 10%
C. 20%
D. 50%