Digital Radiography - National Network for Oral Health Access

Digital Radiography
2006 National Primary Oral Health
Care Conference
Robert A. Cederberg, MA, DDS
December 10 – 14, 2006
Scottsdale, Arizona

Development of Dental
Digital Radiography
Background, history and development of
dental digital radiography
Evolution of the technology & systems
Conversion from film to digital and options
for the office or clinic
Advantages and disadvantages
Applications and functions
Adjunctive techniques

Background
The development of computed axial
tomography (CAT) in 1972 and
subsequent advances in digital sensors
allowed for dental applications.

History of Digital in Dentistry
Trophy Radiologie introduced the RVG in 1982
Sensor - CCD (charged-coupled device) with
phosphor screen, active area 17mm x 26mm

Design and Development
First sensors where designed with CCD
chip layered with a phosphor screen, latter
sensors were developed which were direct
exposure.

Digital System Components
Digital imaging requires a sensor (detector),
analog to digital converter (A/D converter),
computer or CPU, monitor, printer. Additionally,
modem or other (cable, T1, DSL) connection for
Teleradiograhpy is important.

Steps in Digital Acquisition
Electromagnetic energy in the form of x-ray
photons strike the detector (CCD electrical
charge stored in pixels), (PSP latent image
formation)
A/D converter converts the electrical charge into
a digital format (PSP visible light intensities
converted to digital format)
A number is assigned to each voltage output
ranging from 0 to 256 (2 8 ) or 256 shades of gray in
the image
Once image is acquired and stored – post
processing, i.e. image manipulation

Enhancements
1987 - Direct exposure CCDs
Early 90’s – Photostimuable Phosphor
(PSP) technology
Early 90’s – Complementary Metal Oxide
Semiconductor (CMOS)
Flat Panel Detectors – CBCT (Cone Beam
Computed Tomography)
Late 90’s – software improvements,
monitor fidelity improvements.

Evolution of Dental X-ray
Image Receptors
Discovery of x rays in 1895, first image
receptors were glass plates.
1900 – celluloid film
1919 – single emulsion dental film packets
1924 – double emulsion dental film
1940 – Ultraspeed film – D speed
1980 – Ektaspeed film – E speed
1982 – first intraoral digital sensor

Direct Digital Radiography

Basic Digital System
X-ray source
Components
Sensor or detector (CCD, CMOS and
storage phosphor)
Computer or CPU
Modem
Printer

Sensors
CCD (Charged Couple Device): silicon
chip with an embedded electronic circuit.
PSP (Photostimuable Storage Phosphor):
plastic plate coated with a photostimuable
phosphor layer.
CMOS-APS (Complementary Metal Oxide
Semiconductor - Active Pixel Sensor):
silicon chip with an ADC for each column
of pixels.

Optime PSP plates
Sizes 0, 1and 2
Digital Sensors
Trophy Sensor
Size 2
Schick Sensors
Sizes 0, 1 and 2

The Physics of CCD Sensors

Available Sensors

CMOS Sensor

The Physics of PSP Sensors

Conversion from Film to
Digital
Probably easiest to slowly transition into
digital.
Probably best to consider utilizing more
than one digital system since no one
system will satisfy all of the imaging
needs within one office or clinic, i.e. for
intraoral imaging, both a PSP and CCD
combination.

Conversion from Film to
Work flow study
Digital

Conversion from Film to
Digital
Main advantage – no darkroom needed
Elimination of the mess of darkroom
chemistry, cost and maintenance of film
processors
Many cities and local municipalities now
regulate waste water discharge and
require silver collectors to be installed on
processors which adds additional mess as
well as expense

Techniques and
Systems
Techniques vary only by the type of detector
used: either CCD or Storage Phosphor
All systems offer the ability to manipulate the
image: i.e. image enhancement, colorization, etc.

Intraoral CCD Based
Systems
Product Name Company
CDR Schick
CygnusRay MPS Cygnus Technologies
Dexis ProVision Dental Systems
Dixi®2 Planmeca Group
Dixsy Villa Sistemi Medicali
FI iOX megapixel Fimet
MPDx Remedent N.V.

Intraoral CCD Based
Systems
Product Name Company
SIDEXIS Sirona
SIGMA PaloDex Group
SuniRay TM Suni Medical Imaging
RVG Trophy
VistaRay DÜrr Dental
VisualiX USB Gendex

Intraoral PSP Systems
Product Name Company
Panorama Xi Orex
Combi-Xi Orex
DenOptix Gendex - Dentsply
Digora Optime PaloDex Group
VistaScan DÜrr Dental
VistaScan Intra DÜrr Dental

Panoramic CCD Based
Systems
Product Name Company
CDRPan Schick
Digipan Trophy
Dimax2, Proline, Promax Planmeca Group
DXIS® Signet
Orthopantomograph OP100D PaloDex Group
Orthoceph OC100D PaloDex Group
ORTHOPHOS DS Sirona

Panoramic CCD Based
Systems
Product Name Company
Cranex Base X D PaloDex Group
Cranex Excel D PaloDex Group
Scanora D PaloDex Group
Orthoralix 9200 (DDE, DPI) Gendex - Dentsply
Versaview (5D, SDCP) Morita

Panoramic PSP Based
Systems
Product Name Company
Combi-Xi Orex
DenOptix Gendex - Dentsply
DenOptix Ceph Gendex - Dentsply
DEXpan Pro Vision Dental
Digora PCT PaloDex Group
Paxorama Xi Orex
VistaScan DÜrr Dental

Digital
Image
Digital X-ray Image?
182
177
180
207
152
175
141
179
51 173
169 52
165 111
130 69
Physical
Definition
Mathematical
Definition

PIXEL
The matrix element of a digital array which identifies a gray
level at that point. It can be processed and manipulated,
usually expressed in 0-255 values.
Gray Scale
O = Black
255 = White
O 255

Digital Imaging: Advantages
Image enhancement and analysis - may increase
diagnostic validity of x-rays of non-optimal
density.
No-processing problems - darkroom, processor
and processing chemistry not required
(environmentally friendly).
Less exposure errors - density and contrast
enhancement.
Allows for quantitative evaluation.
Lower absorbed doses - 20 to 90% compared to
D-speed film.
Better patient communication and time saver.

Digital Imaging: Disadvantages
High cost (Processor/sensor, CPU, monitor,
printer) - CCD and CMOS sensors – 5 to $7,000
Inflexible cassette for CCD and CMOS sensor -
may not allow proper placement in all intraoral
locations.
Spatial Resolution not as good as film - film 16 to
20 lp/mm, digital 7 - 13 lp/mm.
Printed copy not as good as screen - resolution is
lost when image is printed.
Not standardized - proprietary hardware and
software.
Learning curve for staff.

PaloDex Group Soredex:
Optime

Taking The Radiograph
Place onto
positioning device
Use your current xray
equipment
Take x-ray with
reduced exposure

Digora Optime Hardware
Imaging Plate Processing

Digital Imaging
Software Features
Zoom
Contrast/Brightness
Pseudocolor
Rotation
Annotation
Filters
3D
Analysis (Line, Angle)
Manipulating implant
Video Inversion

Negative Conversion

Pseudo-Colorization

3D Function

Measuring Distance and
Angle

Applications
Patient Education
Quantifying the image
Implant planning
Teleradiography
Other

Patient Education

Quantifying the Image
All systems provide the ability to measure
lengths and angles and to analyze the
density gradients throughout the image.

Implant Planning
Some systems provide for implant
overlays which are helpful in assessing
potential implant sites.

Teleradiography
Transmission of digital images to remote
sites is a major driving force in the
evolution of digital radiography.
Remote consultation, Insurance approval.

DenOptix QST

Digital X-ray Imaging
100% re-usable
Same size as film
Flexible
Thin
No wires like CCD
sensor
Use with existing
x-ray equipment
Plates

Preparing the plates
To prevent cross
contamination, the
plates are placed in a
disposable plastic
barrier

Preparing the plates
Panometric and
Cephalometric
are placed in the
cassette with
screens

Taking an x-ray
Tear the barriers
and drop the
imaging plate into
the dark box
Be careful of light
exposure and
contamination

The DenOptix Scanner
Scans all image plate
sizes
Integrates with
practice management
software
Simple to learn
No patient discomfort

Scanning
In a semi-darkened
area
� Load the plate on the
carousel (can hold up
to 29 plates)
� Attach the pan/ceph
plates

Scanning
Place the loaded carousel
into the scanner
Close the lid
Begin scanning
� 1 min 12 secs for up to 8
I/O
� 2 min 30 secs for a Pan
� 3 min 30 secs for a
Ceph

Sensor - CCD or CMOS
GX-S
RFG
CDR (Schick)
Sidexis
Dixi (Planmeca)

DC Intraoral Unit

Panoramic
Unit

The source of x-rays,
the tube…
Must have
� Smallest focal
point
� AC - DC
� Range of Kv,
mA adapted
to dental xrays
(digital or
not)

The detector
Film, sensor, imaging plates
Image quality parameters are:
� Quantum Mottle Noise (signal/noise
ratio)
� Resolution
� Sensitivity or dynamic range
All three are important!!

Signal/Noise Ratio
Depends on the amount of photons that
strike the image sensor
Noise level: PSP < film < CCD
Images with lots of noise are described
as “grainy”

Resolution
X-ray photon detection takes place in
layers vs on a surface
Resolution is limited by the thickness of
the layer, not pixel size
� Measured by line pairs resolved per mm
(lp/mm)
� Limited by what the eye can detect
� Film = 20 lp/mm
� PSP = 7 - 14 lp/mm (I/O)
� Sensor = 10 - 24 lp/mm (I/O)
Diagnostic resolution is the key.

Resolution
600 dpi 300 dpi

A good image means…
Good x-ray source
� Small focal spot, collimator, x-ray beam
quality
Good positioning
Good detector

RINN Sensor Holder

Dexis Sensor

Comparison of Image
Receptor Characteristics
Contrast resolution
Spatial resolution
Sensor/receptor latitude
Sensor/receptor sensitivity
MTF, SNR (NEQ and DQE)
Contrast and spatial resolution of the
human eye

Contrast Resolution
The ability to distinguish different densities
in the radiographic image.
Factors affecting contrast resolution:
1. Attenuation characteristics of the tissues
being imaged.
2. Sensor bit depth and noise level.
3. Monitor resolution, bit depth, dot pitch,
luminance and display size.
4. Ambient lighting.

Contrast Resolution
Digital imaging systems are capable of
capturing up to 256 different densities,
monitors/operating systems are only
capable of displaying 242 different
densities.
The human eye can only distinguish 32
different densities.

Spatial Resolution
The capacity of the image to display fine detail.
*The theoretical limit of resolution is a
function of the pixel size of the system.*
Image receptor pixel sizes: film – 8 microns,
high res. CCD – 20 microns, PSP – 40 microns.
Resolution: film = > 20 lp/mm, CCD = 25 lp/mm
(theoretical with software enhancements), PSP
= 12.5 lp/mm.

Sensor Latitude
The ability of the sensor to capture a range
of x-ray exposures.
A desirable quality of a sensor/receptor is
the ability to display a full range of
densities.
Dynamic range of film extends to 4 orders
of magnitude (with hot lighting),
CCD/CMOS sensors extend to 2 orders of
magnitude and PSP sensors extend to 5
orders of magnitude of x-ray exposure.

Sensor Sensitivity
Sensitivity of a sensor is its ability to
respond to small amounts of radiation.
Sensitivity of film is directly related to film
speed.
Sensitivity of digital sensors affected by
pixel size and system noise.
PSP systems allow dose reductions of
about 50% compared to F-speed film.
CCD/CMOS less dose reduction than PSP.

Modulation Transfer
Function (MTF)
MTF is a measure of the combined effects of
sharpness and resolution.
The MTF of E-speed film is superior to the
MTF of PSP at high spatial frequencies.
The 50% modulation level for PSP is
reached at 2.5 lp/mm whereas E-speed
film is not reached until 10 lp/mm.

Signal-to-Noise Ratio
(SNR) – NEQ and DQE
The ratio of the signal amplitude to the standard
deviation of the fluctuations in noise.
NEQ – noise equivalent quanta
DQE – detective quantum efficiency
At low spatial frequencies PSP systems have
superior NEQ to E-speed film across the
exposure range. Data suggested that a PSP
sensors are able to absorb more quanta
(photons) per unit area as compared to film.

Signal-to-Noise Ratio
(SNR) – NEQ and DQE
Higher quantum absorption of PSP leads
to a superior DQE as compared to E-speed
film.
Theoretically higher quantum absorption
and higher DQE of PSP sensors could
provide a more efficient absorption of
photons and thereby an image with
improved definition.

Contrast & Spatial Resolution
of the Human Eye
In terms of contrast, the displayed image
provides up to 8 times the amount of information
that the eye can actually see.
The minimum contrast threshold (greatest
perceptual sensitivity) corresponds to a spatial
frequency of approximately 5 lp/cm or about a
1mm wide pixel size. Consequently, the sensor
can display approximately 2.5 times the amount
of information that the eye can actually perceive.

Lesion Recognition Research
Studies have looked at both natural
carious lesions and simulated lesions and
tested the resolving power of film vs
digital.
Conclusion – The ability to recognize
incipient caries lesions is NOT dependent
on image receptor (film or digital), the
system used or the manner in which it is
displayed.

References
Brettle DS, Workman A, et al. The imaging performance of a storage
phosphor system for dental radiography, Br. J. Radiol. 69, 256-61
(1996).
Cowen AR, Workman A, Price JS. Physical aspects of photostimuable
phosphor computed radiography, Br. J. Radiol. 66, 332-45 (1993).
Wang J, Langer S. A brief review of human perception factors in digital
displays for picture archiving and communications systems, J. Digit.
Imaging. 10(4), 158-68 (1997).
Cederberg RA, Tidwell E, et al. Endodontic working length assessment
comparison of storage phosphor digital imaging and radiographic
film. OOOOE. 85, 325-8 (1998).
Cederberg RA, Frederiksen NL, et al. Influence of the digital image
display monitor on observer performance. Dentomaxillofac Radiol.
28, 203-7 (1999).

Image Examples
From Planmeca’s website

Planmeca Bite Wing Series – left side

OpTime Bite Wing Series – left side

Planmeca image
OpTime image

Conclusion
Storage phosphor technology provides
film-like sensors which are easier to place
for all intraoral imaging sites.
More comfortable for the patient and
placement especially for premolar
bitewings allows operator to image the
distal of the canines.
Elapsed time for completion of image is
actually less than for some hard-wired
systems.

Conclusion
Portable – no need to be tied to a
computer. Can be taken in any operatory
with a tube head and even with a hand
held unit.
Widest dynamic range of any sensor
allows for potential recovery of diagnostic
information in an otherwise underexposed
image.
Improved DQE theoretically provides
better image clarity & definition.

Conclusion
Some common fallacies concerning the
superiority of film and/or CCD/CMOS
receptors over PSP receptors:
One sensor type will be sufficient for all
intraoral imaging applications. Probably
only true for film and PSP. Depending on
the type of hard-wired sensor there may
difficulty obtaining certain images such as
molar periapicals and premolar bitewings.

Conclusion
Some common fallacies concerning the
superiority of film and/or CCD/CMOS
receptors over PSP receptors:
CCD/CMOS systems claims of superior
resolutions of 25 lp/mm or greater as
compared to PSP. The human eye has the
best acuity at pixel sizes approximating
1 mm, 2.5 times the resolving power of
most PSP systems. Is it enough to detect
decay? Yes! But, image clarity is more
important.

Digital Subtraction
Radiography

Cone Beam CT

Flat Panel Detector
Amorphous Silicon Flat Panel Detector

Effective Dose Comparison
i-CAT 20 sec scan 68 uSv
i-CAT 10 sec scan 34 uSv
Daily background 8 uSv
Panoramic – film 10-15 uSv
Panoramic – digital 4.7-14.9 uSv
Full Mouth Series – film 150 uSv
Hitachi MercuRay CBCT 485 uSv
Medical CT 1200-3300 uSv

Panoramic

X-Sectional Imaging

Localization

Orthodontics

Pathology

What Does the Future of Digital
Radiography Look Like?
Evolution and development of existing
systems – It’s here to stay!
Further integration of other technologies
into existing systems.
CBCT will become ‘standard of care’ for all
dental imaging needs. CBCT will become
more widely used, price will come down.
Perhaps, a CBCT scan and bitewings will
someday be the dental exam standard.