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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 2
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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 3
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
X-ray tube

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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 5
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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 6
10.2. DENTAL RADIOGRAPHY
10.2.1. Introduction

Cone-beam dental CT
• For three dimensional information

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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 7
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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 8
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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 9
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 X-ray
200 tube
mm

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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 10
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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 11
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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 12
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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 13
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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 14
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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 15
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

The basic movements

of the OPG unit
around the mandible
are illustrated

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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 16
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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 17
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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 18
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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 19
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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 20
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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 21
10.2. DENTAL RADIOGRAPHY
10.2.3. Dental Dosimetry

There are large variations in recorded doses between X-

ray 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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 22
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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 23
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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 24
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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 25
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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 26
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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 27
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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 29
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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 30
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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 31
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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 32
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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 34
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 Movement of source

shows a pencil beam system and detector to

acquire attenuation
data
• pinhole source collimator
• and a single detector
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

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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 37
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
µ µ
ρi
∑ ∑
N N
∑i=1
N
− −   tρ −  ξ
∑ µi t i ( )
N
− µt i=1 ρ  i i i=1 ρ  i
 i  i
I = IO e i=1 i i
= IO e ρi
= IO e = IO e

• 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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 39
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:
 µ  L µ
L   µ  H µ
H 
−    ξ s +   ξ b  −    ξ s +   ξ b 
  ρ  s  ρ  b    ρ  s  ρ b 
I L = IOe I H = IOe

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 
ξb =  IO   IO  = areal Bone Mineral Density (aBMD)
L H
µ µ
  −   RS
 ρ  b  ρ b
• Where RS is commonly referred to as the “ratio value” for soft
tissue measured for tissue surrounding but not containing the
bone.
L
µ
 
 ρ S
RS = H
µ
 
 ρ 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

(drawing courtesy of J. Shepherd, UCSF).

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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 42
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 Hologic

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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 43
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:

aBMDpatient − aBMD Young Adult Mean

T − score =
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:
aBMDpatient − aBMD Age −,Ethnicity −matched Adult Mean
Z − score =
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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 45
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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 46
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
movement of
simultaneously in the opposite X-ray tube
direction
The projected image in the focal plane objects in
focal plane
focal plane moves in same
direction as the image receptor
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 movement of
X-ray tube
below the focal plane are
increasingly blurred as their
focal fulcrum or
distance from this plane plane pivot point
increases.
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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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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10.5.CONVENTIONAL TOMOGRAPHY AND TOMOSYNTHESIS
10.5.1. Principles

For the curved focal trough the image

receptor speed changes during motion X-ray tube
moving at
In this example constant
speed
• The X ray tube moves at constant speed to
the right
• The image receptor accelerates to the left focal
plane
during motion
• Consequently the focal plane moves away
from the image receptor. focal
trough
• Note the thickness of the focal trough
changes in accordance to distance from the
image receptor
Accelerating movement
of image receptor

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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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10.5.CONVENTIONAL TOMOGRAPHY AND TOMOSYNTHESIS
10.5.1. Principles

Illustration of Tomosynthesis
• 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

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10.5.CONVENTIONAL TOMOGRAPHY AND TOMOSYNTHESIS
10.5.1. Principles

Tomosynthesis is a method for performing high-

resolution 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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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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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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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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Diagnostic Radiology Physics: a Handbook for Teachers and Students – chapter 10, 59
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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