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Dale
A. Miles DDS, MS, FRCD
Introduction
"Don't shoot the messenger!" At least
not right away. In solid-state detector
imaging (CCD or CMOS), if we think
of the sensor as a messenger for the
image you use to interpret, it may
not be the sensor's fault that the
image quality you see is less than
ideal. The senor or receptor is not
the only component that affects image
quality. The digital image (and even
the conventional film image) is the
result of the sum total of all the
parts it took to get it to your monitor
effectively. In dentistry to keep
things simple we'll consider these
parts to include the:
- x-ray generator
- sensor
- frame grabber/video
board
-
monitor
ASIDE:
Actually in digital medical imaging
this "imaging chain" includes the
generator, x-ray tube, image intensifier,
camera optics, pickup- tube or CCD
(Charge-Coupled Device) camera, analog-to-digital
(A/D) converters, image processors,
digital-to-analog converters, and
TV/computer monitors.
If any
of these components is faulty or inappropriate,
the resulting image will usually be
disappointing. Let's examine these
components.
The
X-ray Generator
You probably didn't realize that
your old x-ray generator could be
the prime "culprit" in the production
of an un-diagnostic radiographic
image. After all, when the sales
person showed you the system, the
images looked great! They used a
good x-ray generator, displayed
on a high quality monitor and the
images looked so much better than
most of your film images, right?
You get the system installed, take
your first image and it too looks
great. Then, once the salesperson
leaves image quality starts to vary
and you get images periodically
that look awful. First thing to
blame is your new sensor, right?
WRONG! In a perfect world it would
be that simple. This is not a perfect
world.
The
first thing to look at in our "imaging
chain" is your x-ray. Is it old?
Have you had it since you opened
your office? When was it last inspected?
Very few of the x-ray generators
currently used in dental offices
have characteristics that are ideally
suited for a solid-state detector
device.
Ideally, an x-ray generator to be
used with a solid-state detector
should have the following characteristics:
- low kV (70 kV
or less)
- low mA (5 mA
or even less may be ideal)
- an extremely
accurate timer
- a timer capable
of producing very short exposure
times accurately
- the smallest
focal spot feasible
- a DC (direct
current) circuit
If your
generator is old (and yes, I know
it worked well with film for the last
15 years), you may have to consider
buying a new generator or even several.
Most x-ray machines have inaccurate
timers, a higher than needed kV setting,
and are AC (alternating current) type
generators that produce a more heterogeneous
x-ray beam which works less well with
the contemporary sensor. We are always
loathe to change anything that works
in our office but, in the case of
your x-ray generator, it may be time
to "upgrade" if you "Go Digital".
The
Sensor (detector, solid-state detector,
CCD, CMOS, CMOS APS, chip, etc…)
In
digital imaging when the word sensor
is used it means an electronic device
or solid-state detector; a silicon
chip with an embedded circuit to
act as the image receptor. We are
NOT talking about a phosphor (reusable
phosphor, storage phosphor, photostimulable
phosphor) in this imaging chain.
That's a "whole other story".
As
the brothers Hans and Frans said
on Saturday Night Live "Hear me
know and believe me later"…ANY OF
THE CURRENT DIGITAL SENSOR SYSTEMS
CAN DO AN EXCELLENT JOB WITH ANY
IMAGE TASK IN DENTISTRY…you just
have to find the one that's right
for you, your staff and your office.
A current list of solid-state detector
vendors appears below. They are
broken down into "sellers" and "manufacturer".
The manufacturer/supplier supplies
the sensor to a seller.
Vendors
and manufacturers of solid-state
digital sensors
Product Name
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Seller
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Manufacturer
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CDMx Digital X-ray
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CamSight
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Suni Imaging
|
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CygnusRay
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Progeny/Cygnus Imaging
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Fimet
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DEXIS
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DEXIS
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Lockheed Martin/L’Orale
|
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DIXI2
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Planmeca USA
|
|
|
Dr. Suni
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Suni Imaging
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Suni Imaging
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|
Eva
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Dent-X AFP
|
?
|
|
ImageRay
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Dentrix/HenrySchein
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Suni Imaging
|
|
GX-S
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Gendex/Dentsply
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Marconi
|
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LightYear
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LightYear Technology
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Suni Imaging
|
|
Mediadent SDX
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Multimedia Dental Systems
|
?
|
|
CDR
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Schick Technologies, Inc.
|
Schick Technologies
|
|
CDR Wireless
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Schick Technologies, Inc.
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Schick Technologies
|
|
SidexisIO2
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Sirona, The Dental Company
|
|
|
Sigma-IO
|
Instrumentarium Imaging, Inc.
|
|
|
RVGui
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Trophy Imaging (PracticeWorks/Kodak)
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Trophy/E2V?
|
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QuickRay
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Video Dental Concepts
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Suni Imaging
|
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ViperRay
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Integra Medical/Henry Schein
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Suni Imaging
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As
a consumer, you need to ask what
type of sensor the company sells
and who supplies provides the sensor
to them. For example, Suni Imaging
makes several different image receptors
and provides these to several companies
(see table). Other companies that
supplies sensors to various dental
companies are E2V Technologies (England
and Germany), Photobit (California),
and Atmel (California).
The
Frame-grabber (video board)
The
frame grabber (also called a video
board) is probably the most important
and least understood element in
a digital image processing system.
A frame grabber converts the captured
analog, electronic signal from the
sensor and converts it to a digital
format for transfer as a digital
image to the computer. Some frame
grabbers also have technology (image
processing capability) to improve
the signal before displaying the
image on the monitor. I believe
this is termed “input signal conditioning”
- some systems may have it, some
may not. In addition, frame grabbers
may also employ LUTs (Look Up Tables)
to improve image quality prior to
display. LUTs are extremely effective
tools for equalizing or normalizing
images captured under poor exposure
conditions. I’m assuming that most
digital x-ray system vendors would
employ a high quality video board
in their system; however, if you
already have a computer with a “board”
they may tell you that you can use
your own. If you have a poor quality
frame grabber/video board, you may
not get the best image quality the
system is capable of !
The
Monitor
In
December 2002 I posted an article
on this site about “Flat Panels
Vs. CRTs”. Most of us would prefer
a flat panel monitor to a boxy CRT
(cathode ray tube). Please re-read
my article to determine which display
best suits your needs. However,
if you prefer a flat panel, like
I do, because their both ergonomic
and “sexy”, there are a couple of
“specs” you need to remember. These
are:
- Contrast
ratio (at least 400:1)
- Dpi
(less than 0.27mm)
Most
monitors meet the first criterion
well. Contrast ratios in LCD (flat
panel) monitors are quite high. Fewer
LCD monitors meet the second criterion.
Inexpensive monitors are usually 0.29
or even higher dpi and are not suitable
for viewing, processing gray scale,
radiographic images. Buy a GOOD flat
panel monitor if you’re going to view
x-ray images in the operatory and
make decisions off of them! I listed
several that have these characteristics
back in December 2002. I’m sure there
are even more choices now and that
the prices are even better than posted.
Some good brands to research are:
- Viewsonic
- Samsung
- NEC
-
Sony
Flat
panel Vs. CRT “Pros and Cons”
(adapted from
http://www.viewz.com/shoppingguide/monitor.shtml)
Flat Panel Monitors
Pros:
• Desktop space-saver
• Good picture
quality
• Prices are
falling
• Environmentally
friendly
• 15"
flat panel gives you the same viewable
screen as a 17" CRT monitor
Cons:
• Viewing angle
is much less than that of CRT monitors
• One single
resolution.
CRT:
Pros:
• Great quality
for the price
• More detailed
graphics
• 100 years
of technology
• Works at
multiple resolutions
• Can view
screen from different angles
Cons:
• Bigger and
bulkier than a flat panel.
Happy
hunting as you "Go Digital"…."hope
this helps"….Dale
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