learn digital

  Home
  Dr Dale Miles
  What's New
  Articles
  Links
  Training
  Have a Question?
  Cone Beam Manufacturing
  Cone Beam Information
  CBCT Software Solutions


Dr Dale Miles - learndigital.net
Dr. Dale Miles


 
 

The "Electronic Imaging Chain" Its Effect on Your Digital radiographic Images

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

Seller

Manufacturer

CDMx Digital X-ray

CamSight

Suni Imaging

CygnusRay

Progeny/Cygnus Imaging

Fimet

DEXIS

DEXIS

Lockheed Martin/L’Orale

DIXI2

Planmeca USA

 

Dr. Suni

Suni Imaging

Suni Imaging

Eva

Dent-X AFP

?

ImageRay

Dentrix/HenrySchein

Suni Imaging

GX-S

Gendex/Dentsply

Marconi

LightYear

LightYear Technology

Suni Imaging

Mediadent SDX

Multimedia Dental Systems

?

CDR

Schick Technologies, Inc.

Schick Technologies

CDR Wireless

Schick Technologies, Inc.

Schick Technologies

SidexisIO2

Sirona, The Dental Company

 

Sigma-IO

Instrumentarium Imaging, Inc.

 

RVGui

Trophy Imaging (PracticeWorks/Kodak)

Trophy/E2V?

QuickRay

Video Dental Concepts

Suni Imaging

ViperRay

Integra Medical/Henry Schein

Suni Imaging

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

 

 
© Dr Dale Miles DDS, MS, FRCD
All rights reserved.