Download Slides to IAEA Radiation Oncology Physics Handbook

Chapter 10: Special Topics
Slide set of 71 slides based on the chapter authored by
D. McLean and J. Shepherd
of the IAEA publication (ISBN 978-92-0-131010-1):
Diagnostic Radiology Physics:
A Handbook for Teachers and Students
Objective:
To familiarize the student with Dental radiography, Mobile
Radiography and fluoroscopy, Dual-Energy X-Ray absorptiometry,
Conventional tomography and tomosynthesis
Slide set prepared
by S. Edyvean
IAEA
International Atomic Energy Agency
CHAPTER 10.
SPECIAL TOPICS IN RADIOGRAPHY
10.1. Introduction
10.2. Dental radiography
10.3. Mobile Radiography and fluoroscopy
10.4. Dual-Energy X-Ray absorptiometry
10.5. Conventional tomography and tomosynthesis
Bibliography
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Review of Radiology Physics: A Handbook for Teachers and Students - 1.
10.1. INTRODUCTION
 Previous chapters covered 2- dimensional imaging
 Later chapters cover cross-sectional imaging (CT,MR,
ultrasound)
 This chapter presents a number of special X ray imaging
modalities and their associated techniques - forming a
transition between projection and cross sectional imaging
 Special X-ray imaging techniques
•
•
•
•
Dental radiography
Mobile Radiography and fluoroscopy
Dual-Energy X-Ray absorptiometry
Conventional tomography and tomosynthesis
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10.2. DENTAL RADIOGRAPHY
10.2.1. Introduction
 The tooth can be imaged in three ways
• Intra oral examination with the x-ray tube external and a bitewing
film placed inside the mouth
• Extra oral examination where both the X-ray tube and detector is
external to the patient to form an OPG
• A conebeam CT image
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10.2. DENTAL RADIOGRAPHY
10.2.1. Introduction
 An intra oral examination with bite-wing
• Is the most common examination, and is a low cost technique
• Places very small demands on X ray generation since the tooth is
a low attenuation static object
• The image receptor is placed inside the mouth, and irradiated
externally.
bite-wing film
teeth
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X-ray tube
Review of Radiology Physics: A Handbook for Teachers and Students - 1.1.1 Slide 1
10.2. DENTAL RADIOGRAPHY
10.2.1. Introduction
 Orthopantomograph (OPG),
• Two dimensional images when radiographs of the entire set of
teeth are required
• The image receptor and the X ray source are external to the
patient
• The X ray beam is transmitted through the head - demanding
significant X ray generation power and complex motion control for
the X ray tube and image receptor
• Image receptors are film or digital detectors
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10.2. DENTAL RADIOGRAPHY
10.2.1. Introduction
 Cone-beam dental CT
• For three dimensional information
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10.2. DENTAL RADIOGRAPHY
10.2.2. Technology
 Intra oral radiography
 The intra oral X ray tube is a small robust device with a
stationary target operating with a tube current of only a few
mA
Dental X ray tube with a stationary anode.
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10.2. DENTAL RADIOGRAPHY
10.2.2. Technology
 Intra oral radiography (continued)
 The generator is typically very simple often with fixed tube
voltage and tube current allowing output changes only by
variations in exposure time.
 Major concerns with this device are for the stability of the
tube head and the collimation of the beam.
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10.2. DENTAL RADIOGRAPHY
10.2.2. Technology
 Intra oral radiography (continued)
 International standards require that the focus to the patient
surface distance (FSD) be 200 mm.
 This is assured with the use of a collimating attachment
that also restricts the beam to the region of the mouth
being radiographed.
bite-wing film
teeth
200
mm
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X-ray
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Review of Radiology Physics: A Handbook for Teachers and Students - 1.1.1 Slide 1
10.2. DENTAL RADIOGRAPHY
10.2.2. Technology
 Intra oral radiography (continued)
 The X ray equipment requires periodic QC checking
 The process of film processing requires more diligent
attention.
 The unscreened film is removed from the light tight
moisture protective wrapping and is processed either
manually or with varying degrees of automation.
 Hand processing is probably most common and ideally
requires control of temperature and processing time.
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10.2. DENTAL RADIOGRAPHY
10.2.2. Technology
 Intra oral radiography (continued)
 For higher volume clinics this can be automated with film
mounted on hangers that progress through the
development, stop bath, fixation and rinse processes.
 Typically these devices have timing and temperature
control but do not control chemical activity through
replenishment.
 This is achieved in fully automatic processors, however
these are typically restricted to major dental hospitals.
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10.2. DENTAL RADIOGRAPHY
10.2.2. Technology
 Intra oral radiography (continued)
 The uncertainties in film processing are best controlled
through sensitometry.
 Light sensitometers are rare in dentistry due to the small
film format,
• However adequate results can be achieved by using a simple
radiograph of a 3 step ‘wedge’
• This can be easily manufactured by folding the lead foil found in
the film wrap or purchased commercially
 Increasingly digital detectors are replacing film.
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10.2. DENTAL RADIOGRAPHY
10.2.2. Technology
 Intra oral radiography (continued)
 Digital image capture can be achieved from an intensifying
screen that is linked to a CCD camera through a tapered
fibre optic coupling.
 The electronic signal can be transferred to an acquisition
computer either through a direct cable or through ‘blue
tooth’ radio frequency transmission.
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10.2. DENTAL RADIOGRAPHY
10.2.2. Technology
 OPG (Orthopantomograph)
 An OPG image is created by complex equipment where
the X ray tube and image receptor assembly move in a
horizontal plane around the head of the patient.
OPG image of the teeth
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10.2. DENTAL RADIOGRAPHY
10.2.2. Technology
 OPG (Orthopantomograph) (continued)
• A narrow beam of radiation is formed by the tube collimation
• the image receptor moves within the assembly behind a lead
aperture
Collimators
The basic movements
of the OPG unit
around the mandible
are illustrated
Rotation centres
Image receptor
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aperture
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10.2. DENTAL RADIOGRAPHY
10.2.2. Technology
 OPG (Orthopantomograph) (continued)
 The device uses the principle of tomography and more
importantly the principle of panoramic photography.
 This process can be illustrated through consideration of
the panoramic camera used in photography.
 Here an acquisition aperture is used to expose an image
plate that is moved behind the aperture slit to capture the
image of a ‘panorama’ while the camera simultaneously
slowly rotates to scan a scene.
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10.2. DENTAL RADIOGRAPHY
10.2.2. Technology
 Cone-beam CT
 CT imaging has been used for some time in dentistry,
including the use of custom designed units for dental
applications.
 Their use has become more widespread recently with the
advent of cone beam technology
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10.2. DENTAL RADIOGRAPHY
10.2.2. Technology
 Cone-beam CT (continued)
 There are many cone beam CT (CBCT) models available
using a variety of acquisition schemes
 They have in common a flat panel detector for acquisition,
typically using either DR technology or an intensifying
screen with a CCD camera (see chapter 7).
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10.2. DENTAL RADIOGRAPHY
10.2.2. Technology
 Cone-beam CT (continued)
 Typically a CBCT can acquire a full field of view (FOV) that
covers the whole head
• although acquisitions that are restricted to the mandible with as
little as 10% of full FOV are possible.
 The use of these lower cost CT units opens up new
potentials in some areas of dental diagnosis
 However they have significantly higher dose compared to
OPG procedures
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10.2. DENTAL RADIOGRAPHY
10.2.3. Dental Dosimetry
 Since dental examinations are amongst the most
numerous, the dosimetry of these procedures is of high
interest.
 Relevant principles and measurement techniques of
dosimetry can be found in
• Chapter 21 of this handbook
• and in the IAEA Technical Report Series No.457
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10.2. DENTAL RADIOGRAPHY
10.2.3. Dental Dosimetry
 There are large variations in recorded doses between Xray facilities.
 A recent study in Europe showed that for an intra oral
bitewing projection
• the average incident air kerma varied from 1 to 2 mGy
• with a corresponding KAP measurement of 20 to 40 mGy cm2.
• The dose in centres that use slower film would be expected to be
significantly higher.
 Data for OPG examinations from Europe showed
• KAP values ranging from 40 to 150 mGy cm2
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10.2. DENTAL RADIOGRAPHY
10.2.3. Dental Dosimetry
 The estimation of a population effective dose is difficult
owing to the complex distribution of critical organs
 There are few radiosensitive organs around the mandible
with some exceptions
• The thyroid, red bone marrow, brain, and salivary glands
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10.2. DENTAL RADIOGRAPHY
10.2.3. Dental Dosimetry
 The thyroid is the main radiosensitive organ around the
mandible
• Well collimated X ray units should not directly irradiate this organ
• but it will probably receive appreciable scattered radiation
 Other radiosensitive organs include
• the red bone marrow of the mandible
• the brain
 The salivary glands also need to be considered as they
are extensively irradiated
• They are now included as a remainder organ in the calculation of
effective dose in accordance with ICRP 103.
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10.2. DENTAL RADIOGRAPHY
10.2.3. Dental Dosimetry
 OPG examinations estimates of effective dose give
• average values of ~ 7 mSv using weighting factors from ICRP 60
• The use of ICRP 103 weighting factors has been variously
estimated to increase effective dose in dentistry by 50% to 400%.
 Since CBCT units operate with a large FOV, their effective
doses are considerably higher than for OPG
• with estimates of dose varying from 60 mSv to 550mSv, for full
FOV
• still considerably lower than conventional head CT with effective
doses of about 2 mSv.
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10.3. MOBILE RADIOGRAPHY AND FLUOROSCOPY
10.3.1.
Introduction
 Mobile X ray equipment ranges from small dental units to
CT and MRI units carried in a large vehicle.
 However this chapter is restricted to simple radiographic
and fluoroscopy equipment.
 Mobile equipment is needed when the patient cannot be
brought to a fixed installation for a radiographic
examination.
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10.3. MOBILE RADIOGRAPHY AND FLUOROSCOPY
10.3.1.
Introduction
 Limitations of mobile equipment relate to
• the availability of a suitable electrical power supply,
• the size and weight of the equipment and the consequent effort
required to move it.
 The equipment design of mobile X ray equipment is varied
and innovative in order to maximise the benefit given the
above constraints.
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10.3. MOBILE RADIOGRAPHY AND FLUOROSCOPY
10.3.2.
Technology
 Fixed angiographic X ray machines require a capacity to
draw up to 100 kW with a high current multiphase supply.
 Assuming no loss in the high voltage transformer
• the X ray output power in the secondary circuit will equal that of the
primary power drawn from the electrical supply (cf Chapter 6)
 Therefore a domestic single phase electric supply may
typically be limited to 2.4 kW
 While low power is usually not a limitation for fluoroscopic
application – this is a challenge for some radiography.
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10.3. MOBILE RADIOGRAPHY AND FLUOROSCOPY
10.3.2.
Technology
 One solution is to charge a capacitor which is discharged
across the X ray tube – the ‘capacitor discharge’ mobile.
 However the tube voltage will fall rapidly during the
discharge of the capacitor
• leading to excessive surface kerma for large patient thicknesses.
 It is more advantageous to have an integral battery power
supply which is converted to a medium to high frequency
AC signal (cf chapter 5)
• This leads to substantial reductions in the thickness of the coils
needed in the transformer design.
• There is also the added advantage that it can be used when there
is no electrical power supply available at the examination site.
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10.3. MOBILE RADIOGRAPHY AND FLUOROSCOPY
10.3.2.
Technology
 The variety of possible generator designs leads to the
possibility of many types of radiographic waveforms being
used in the high voltage circuit for X ray generation.
 This leads to varying tube outputs and beam qualities for
the same radiographic settings of tube voltage and tube
current (cf chapter 5)
 Care is therefore needed when determining dosimetric
factors for mobile units.
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10.3. MOBILE RADIOGRAPHY AND FLUOROSCOPY
10.3.3.
Image quality
 Image quality and general quality control for mobile X ray
units generally follows that used for fixed units.
 The use of high fluoroscopic image quality can lead to
reduced procedural time, and hence reduced radiation
exposure time.
 An important part of image quality is the setup of viewing
monitors and the ambient conditions used for operation.
 Every effort should be made to view monitors in low
ambient lighting conditions.
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10.3. MOBILE RADIOGRAPHY AND FLUOROSCOPY
10.3.4.
Radiation protection
 Mobile X ray equipment raises concerns about
occupational and the public radiation exposure, as it is not
operated in a purpose-built shielded environment.
 Assuming all X ray equipment has been checked for tube
leakage, the source of radiation of occupational concern
during the procedure is scatter from the input surface of
the patient.
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10.3. MOBILE RADIOGRAPHY AND FLUOROSCOPY
10.3.4.
Radiation protection
 It is advised that the medical physicist take field
measurements of air kerma levels due to the patient
scattered radiation using a patient phantom for typical
radiographic and fluoroscopic procedures.
 As mobile radiography may take place in environments
where other patients or members of the public may be in
close proximity it is essential that good communication
exists between the medical physicist and the staff at the
location for the radiographic procedure.
 These staff should attend appropriate radiation safety
courses that include information about radiation risk from
mobile radiography.
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10.3. MOBILE RADIOGRAPHY AND FLUOROSCOPY
10.3.4.
Radiation protection
 In many cases, such as for mobile chest radiography, the
use of good radiographic practice with basic radiation
protection allows safe usage in most hospital
environments.
 Simple measurements should be made to demonstrate the
safety (or otherwise) of mobile X ray equipment use.
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10.4. DUAL-ENERGY X-RAY ABSORPTIOMETRY
 The principle of operation involves two images
• from the attenuation of a low and a high X-ray energy beam
 Using special imaging equipment
• comprising of special beam filtering and near-perfect spatial
registration of the two attenuation maps
Detector(s) within
gantry head
x-ray source
within couch
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10.4. DUAL-ENERGY X-RAY ABSORPTIOMETRY
 Schematic showing the
components of a DXA system.
 The gantry configuration
shows a pencil beam system
• pinhole source collimator
• and a single detector
Movement of source
and detector to
acquire attenuation
data
 These scan the patient to
acquire the attneuation data
. (courtesy of J. Shepherd, UCSF).
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10.4. DUAL-ENERGY X-RAY ABSORPTIOMETRY
 Other systems with slit may
source collimators and
segmented line detectors
are called fan-beam
systems, and have the
advantage of higher spatial
resolution and shorter scan
times
Get permission
or re-draw
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10.4. DUAL-ENERGY X-RAY ABSORPTIOMETRY
 The process for determining material composition can be
outlined from consideration of the total attenuation of an
X-ray flux passing through a subject as represented by
the following formula
i1
μt

i1 i i
I  IO e
 IO e

N

N
μi t i (
ρi
)
ρi
 IO e

μ
  tρ
i1 ρ  i i
 i

N
 IO e

μ
 ξ
i1 ρ  i
 i

N
• where Io is the unattenuated X-ray intensity before it passes
through a N materials with a thicknesses, ti ,
• μi is the total linear attenuation, (µ/ρ)i is the mass attenuation
coefficient of the ith material, and ξi is the ith areal density = ρiti.
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10.4. DUAL-ENERGY X-RAY ABSORPTIOMETRY
 DXA can only solve for two materials simultaneously.
 However, three materials may be quantified: bone, lean,
and fat mass, by using three fundamental assumptions,
1. X-ray transmission through the body for the two energy windows
can be accurately described by exponential attenuation
processes
2. Pixels of the human body image can describe two-components
• i.e. either soft tissue and bone mineral, or, when bone is not present, fat and
lean mass. Thus, although DXA can only solve for two compartments within
individual pixels, it can describe a 3-component model for body composition.
3. The soft tissue overlaying the bone in the image has a
composition and X-ray properties
• that can be predicted by the composition and X-ray properties of the tissue
near, but not overlaying, the bone.
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10.4. DUAL-ENERGY X-RAY ABSORPTIOMETRY
 For example - simplified DXA equations will be derived
for two monochromatic X-ray exposures with different
energies (a high and low energy).
 The full solution would require integration of the
attenuation across the x-ray spectrum for each energy.
 The attenuation equation for each exposure results in the
following two equations:
I L  IOe
L
   L


     s     b 
    s
   b 
I H  IOe
H
   H


     s     b 
    s

  b
where the H and L superscripts represent the high and low
energy X-ray beams respectively, and the “s” and “b” subscripts
represent soft tissue and bone.
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10.4. DUAL-ENERGY X-RAY ABSORPTIOMETRY
 The solution of these equations for the areal density of
bone is given by
IH 
IL
RS ln H   ln L
 IO 
 IO
b 
L
H


     RS
  b   b


  areal Bone Mineral Density (aBMD)
• Where RS is commonly referred to as the “ratio value” for soft
tissue measured for tissue surrounding but not containing the
bone.
L

 

RS   HS

 
  S
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10.4. DUAL-ENERGY X-RAY ABSORPTIOMETRY
 Principle of DXA is shown
with 4 intensity profiles
 The high energy absorption
profile is multiplied by the soft
tissue R-value, Rs, which
accounts for differences in
high and low energy
absorption of soft tissue.
 Rs is calculated for pixels that
do not contain bone
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(drawing courtesy of J. Shepherd, UCSF).
Review of Radiology Physics: A Handbook for Teachers and Students - 1.1.1 Slide 1
10.4. DUAL-ENERGY X-RAY ABSORPTIOMETRY
 In order to use a DXA unit to determine bone mineral
density the DXA unit must be calibrated with a phantom
suitable for a particular examination, for example spine,
and for a particular DXA system type.
 Universal phantoms that can be used between different
types of systems have been developed, however the
calibration of DXA units is an important practical subject
essential for the viability of DXA usage.
Examples of standard phantoms available
European spine
Phantom - QRM
Bio-Imaging Technologies, Inc
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Hologic
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10.4. DUAL-ENERGY X-RAY ABSORPTIOMETRY
 The T-score and the Z-score are parameters used.
 The T-score is the primary diagnostic value used for
osteoporosis.
 The T-score is inversely related to fracture risk.
 By international convention, the T-score is the difference
between the patient’s aBMD and a young reference
aBMD in units of the population standard deviation:
T  score 
aBMDpatient  aBMD Young Adult Mean
SD Young Adult Mean
• where SD is the standard deviation of the population of young
adults.
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10.4. DUAL-ENERGY X-RAY ABSORPTIOMETRY
 The Z-score is used to diagnose low bone mass in young
adults and children.
 It is the difference between the patient’s aBMD and an
age- and typically ethnicity-matched reference aBMD
and standard deviations:
Z  score 
aBMDpatient  aBMD Age ,Ethnicity matched Adult Mean
SD Age ,Ethnicity matched Adult Mean
 The reference values used to calculate T and Z-scores
are derived from normative databases of local
populations.
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10.4. DUAL-ENERGY X-RAY ABSORPTIOMETRY
 More information on the standards used to calculate T
and Z-scores can be found in the Postitions of the
International Society for Clinical Densitometry
(www.iscd.org).
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10.5.CONVENTIONAL TOMOGRAPHY AND TOMOSYNTHESIS
 The usefulness of sectional images, that remove the
image of unwanted overlying tissues, has been well
understood since the early days of X ray imaging.
 The formation of such images is through an analogue
process known as conventional tomography.
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10.5.CONVENTIONAL TOMOGRAPHY AND TOMOSYNTHESIS
10.5.1. Principles
 Conventional tomography uses the principle of image
blurring to remove overlying structures from a radiological
image while allowing one section of body to remain in
focus.
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10.5.CONVENTIONAL TOMOGRAPHY AND TOMOSYNTHESIS
10.5.1. Principles
 During image acquisition the X
ray tube is in motion
 The image receptor moves
simultaneously in the opposite
direction
 The projected image in the
focal plane moves in same
direction as the image receptor
movement of
X-ray tube
focal plane
objects in
focal plane
movement
of images
movement of image receptor
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10.5.CONVENTIONAL TOMOGRAPHY AND TOMOSYNTHESIS
10.5.1. Principles
 The section in focus is the focal
plane
 Regions of the body above and
below the focal plane are
increasingly blurred as their
distance from this plane
increases.
movement of
X-ray tube
focal
plane
fulcrum or
pivot point
Only the red triangle remains in the
same position on the image receptor
Illustration of final image
movement of image receptor
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10.5.CONVENTIONAL TOMOGRAPHY AND TOMOSYNTHESIS
10.5.1. Principles
 Conventional tomography with curved focal plane
 Conventional tomography is easily be extended for use
in dental radiography by acquiring a curved focal lane
 The principle is to use a variable speed for the image
receptor
• The focal plane is known as the focal trough
• The variable speed gives rise to a curved curved focal trough
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Review of Radiology Physics: A Handbook for Teachers and Students - 1.1.1 Slide 1
10.5.CONVENTIONAL TOMOGRAPHY AND TOMOSYNTHESIS
10.5.1. Principles
 Conventional tomography with curved focal plane
• The principle is that if the image receptor speed is increased the
focal plane moves upwards in this example (and vice versa)
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Review of Radiology Physics: A Handbook for Teachers and Students - 1.1.1 Slide 1
10.5.CONVENTIONAL TOMOGRAPHY AND TOMOSYNTHESIS
10.5.1. Principles
 For the curved focal trough the image
receptor speed changes during motion
 In this example
X-ray tube
moving at
constant
speed
• The X ray tube moves at constant speed to
the right
• The image receptor accelerates to the left
during motion
• Consequently the focal plane moves away
from the image receptor.
• Note the thickness of the focal trough
changes in accordance to distance from the
image receptor
focal
plane
focal
trough
Accelerating movement
of image receptor
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Review of Radiology Physics: A Handbook for Teachers and Students - 1.1.1 Slide 1
10.5.CONVENTIONAL TOMOGRAPHY AND TOMOSYNTHESIS
10.5.1. Principles
 Tomosynthesis - a development of conventional
tomography with the use of digital technology to ‘digitally’
change the speed of the image receptor
 In this case one acquisition run might consist of 10
individual X ray images each read and erased in
sequence throughout the one tube movement.
 The images are digitally added to reconstruct different
focal planes in the body. It can be seen that the focal
plane can be altered by advancing or retarding each
image in the series by an increasing amount.
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Review of Radiology Physics: A Handbook for Teachers and Students - 1.1.1 Slide 1
10.5.CONVENTIONAL TOMOGRAPHY AND TOMOSYNTHESIS
10.5.1. Principles
 Illustration of Tomosynthesis
A
B
C
D
• The X ray tube moves at a
constant speed to the right
• The image receptor moves at a
constant speed to the left.
• In this figure 4 samplings of the
image are shown at tube positions
A, B, C and D.
• Tomographic images focused on
planes I, II and III are created by
combining the 4 sampled images
with appropriate offsets
Plane I
Plane II
Plane III
D
B
A
A
B
C
D
Plane I
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C
Plane II
Plane III
Review of Radiology Physics: A Handbook for Teachers and Students - 1.1.1 Slide 1
10.5.CONVENTIONAL TOMOGRAPHY AND TOMOSYNTHESIS
10.5.1. Principles
 Tomosynthesis is a method for performing highresolution limited-angle tomography
 It can be treated as a special case of computed
tomography in which data is acquired over a limited
angular range.
 The computed image can then be obtained using the
various CT reconstruction methods.
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Review of Radiology Physics: A Handbook for Teachers and Students - 1.1.1 Slide 1
10.5.CONVENTIONAL TOMOGRAPHY AND TOMOSYNTHESIS
10.5.2. Tomographic applications
 Conventional tomography has been almost completely
replaced by computed tomography in the modern
radiology department.
 Areas where it is still used are
• intravenous pyelograms (IVPs) where contrast in the kidney can be
conveniently placed within the focal plane to allow clear
visualisation of the contrast agent. This examination is largely
replaced by CT.
• pantomographic dental radiography
(Orthopantomogram - OPG)
IVP
OPG
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Review of Radiology Physics: A Handbook for Teachers and Students - 1.1.1 Slide 1
10.5.CONVENTIONAL TOMOGRAPHY AND TOMOSYNTHESIS
10.5.2. Tomographic applications
 Conventional tomography requires one tube acquisition for
each focal plane image or slice.
• Therefore examinations requiring many slices are inherently high
dose procedures.
 The use of tomosynthesis, on the other hand, requires only
one tube motion to capture enough data to reconstruct
multiple slices within the body.
• Today it is an emerging technology, with its most notable application
so far being in mammography
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Review of Radiology Physics: A Handbook for Teachers and Students - 1.1.1 Slide 1
BIBLIOGRAPHY
 CENTRE FOR EVIDENCE-BASED PURCHASING, Digital
cone beam tomography (DCBT) systems. CEP 10048;
NHS PASA March 2010 [online] (2010).
http://www.pasa.nhs.uk/PASAWeb/NHSprocurement/CEP/
CEPproducts.htm.
 HELMROT, E., ALM CARLSSON, G., Measurement of
radiation dose in dental radiology, Radiation Protection
Dosimetry 114 (2005) 168-171.
 INTERNATIONAL ATOMIC ENERGY AGENCY,
Guidelines for the use of DXA in measuring bone density
and soft tissue body composition, Rep. TBA, IAEA, Vienna
(2010).
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Review of Radiology Physics: A Handbook for Teachers and Students - 1.1.1 Slide 1
BIBLIOGRAPHY
 LANGLAND, O.E., LANGLAIS, R.P., Principles of Dental
Imaging, Williams & Wilkins, Baltimore, MA (1997).
 LUDLOW, J.B., DAVIES-LUDLOW, L.E., BROOKS, S.L.,
HOWERTON, W.B., Dosimetry of 3 CBCT devices for oral
and maxillofacial radiology: CB Mercuray, NewTom 3G
and i-CAT, Dentomaxillofacial Radiology 35 (2006) 219–
226.
 WILLIAMS, J.R., MONTGOMERY, A., Measurement of
dose in panoramic dental radiology, British Journal of
Radiology 73 (2000) 1002-1006.
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