Dale A. Miles DDS, MS, FRCD
Diplomate, ABOMR

Introduction

One of the concerns I hear from dentist considering digital imaging is their perceived need for a "hard copy"; that is, an x-ray.

Film based images have been the gold standard in our profession for almost 100 years. Changing that standard will have a great impact on the profession. So what are the reasons to change? The advantages, the disadvantages? Are we giving up something good for something bad? If we need hard copy doesn't have to be film? If we adopt soft copy interpretation, what are the best display methods? How do we archive that digital image to insure a lifetime of diagnostic quality? Let's examine each of these questions.

Reasons to Change to Digital Images

Advantages

Where should I begin? I lecture all over North America and the world on the advantages of going digital. I'm already a convert. I started this Website to try to accelerate and facilitate the conversion of dentists and dental educators to digital information management. So, please forgive some repetition here.

And if you except that computers are hereto staying, if you have them at the front desk and at home, then the next step is to integrate them chairside. You will be on your way to entering the digital dental age. Digital data requires computers and software. Digital images, whether their clinical or radiographic, are just another motive digital data. And, you already know that moving information between colleagues, you and the payor, you and your patient, etc... is necessary, desirable and inevitable to keep up with the digital changes impacting on our dental practices.

What are the Advantages of Digital Images?

Digital images are

1. Faster to acquire
2. More economical
3. More reproducible
4. Easily transmittable
5. More archival than film
6. "Processable" after acquisition
7. Better for clinical treatment decisions.

Are there Any Disadvantages of Digital Images?

Digital images require:

1. Using computers
2. More time to process the information
3. Learning a new skill
4. More space for equipment

Personally, I don't see these images as disadvantages, but perceived obstacles or challenges. Almost every doctor I asked, who has adopted digital x-ray technology, tells me that they would have a revolt on their hands if they went back to film. All the auxiliaries in the audience nod vigorously in agreement. Other articles on this Website address these perceived obstacles more completely.

Are We Giving Up Something Good for Something Bad?

The short answer is no, and emphatic no! There is no doubt that film is good, especially with the advances made in film emulsion and technology by Kodak recently. Insight ^TM, an F-speed film, represents another quantum leap in technology. Most D-speed film users, who had been dissatisfied with the E-speed group films, say that they now prefer Insight ^TM to their old D-speed film. I have to agree with their assessment. Our dental school uses insight exclusively and it's great! But, if you want to go digital you'll need to scan you’re Insight ^TM using a desktop scanner with a transparency adapter. This is truly a time-consuming process. Those of you who have tried it, no it! You can make any image digital, but the personnel and personal costs are much greater than they are for acquiring an image instantly with a solid-state detector such as a CCD or CMOS device.

And how many of you have or will go digital with all of your clinical images? If you really want to integrate all of your images into digital databases you have to use the solid-state detector systems or photostimulable phosphors. For the discussion of phosphors and solid state detectors see the article titled "Digital x-rays are here, why then aren't you using them?" found elsewhere in the articles on this Website republished from the Journal of the California Dental Association in December, 1999.

We are not giving up something good like insight or D-speed film for something bad! For any task we do in dentistry, all of the digital systems have the spatial resolution or detail we need to make accurate clinical decisions. And most have higher contrast resolution and gray scale latitude from films when we subjected to electronic image processing. There is no downside. And, the digital images don't go yellow or brown in our film cabinets (figure 1), take up less space, and can be attached is digital data to referral letters, insurance claims, patient letters, and email if necessary. Try that with film!

Figure1.

X-ray film improperly fixed that has yellowed with time

Do I really Need a "Hard Copy" of My Image ?

When it comes to "hard copy" of radiographic or clinical images, there are really only 2 choices, paper or x-ray film. Both clinical and radiographic images can be printed onto paper, and there are some advantages to having these printed images. If you do not plan on using your computers chairside, then you will still need a viewbox for film and a printer somewhere in the office for printing clinical photographs. If you really need a "hard copy" of an x-ray, why not print it to paper like you do your clinical images?

To do this you still need a computer and a desktop, flatbed scanner with a transparency adapter. But you still do not need to have the computer in the operatory. You can transfer the camera images to the computer if you’re using a digital still camera, and you will connect the scanner to the computer to scan photos (in reflective mode) or x-rays (or 35 mm slides) in the transmissive mode (hence the need for a transparency adapter).

It seems to me that, if you’ve adopted a clinical camera (and/or video camera) in the operatory, you should have a computer there as well. It is more practical and useful. If you have a computer in the operatory for these devices, then why not also use a digital x-ray system there as well?

You can see where I’m going with this discussion. If you’re going digital with other peripheral devices, why are you clinging to x-ray film with the darkroom and wasted time for processing? If you’re printing clinical photos or still images captured from a video camera, why not print your x-rays to paper as well?

How archival is a paper image ?

The answer to this is "I honestly don’t know". But, I do know that archiving images of any kind to CD ROMs or DVDs (digital videodiscs) is VERY ARCHIVAL! Kodak, for instance, guarantees the image quality of digital images recorded on their "Gold" CDR discs for 100 years! That’s certainly longer than you or I will practice or longer than any state statute requires.

And, if your images, clinical and radiographic, are stored in your computer, on CD ROMs or DVDs, you can print your "hard copy" any time with the same image quality as the original (figure 2). Very often you can’t do that with x-ray film.

So by now I hope you’re thinking "Hey, I don’t need a hard copy except in a few instances".

If so, how do you interpret your x-ray images if you don’t have film and a viewbox?

If I Read an X-ray as a Soft Copy, What Do I Need in the Way Of a Monitor ?

This concept of reading "soft copy" images is not new. If you think of it, you really do this already, just not with x-rays! If you stare at a computer monitor when you browse the web, you are already looking at "soft copy" images. And, if you have actually viewed an x-ray image on a dental website, you are really on the way to "going digital". You just haven’t thought about it and you haven’t had to "process" the image electronically to extract the information. But, you could!

To view these web and x-ray images, you’re already using a monitor. Depending on the money you invested in your computer, home or office, you are viewing images with varying degrees of spatial and contrast resolution. Since we are color "animals", we see can see color images on our monitors clearly at low resolution quality and it doesn’t disturb us because the color images containing several million colors and shades of those colors. But with x-ray image it’s a totally different story. Humans can only separate about 16 shades of gray. Most images displayed in the digital x-ray systems contain 256 shades of gray (this is called an 8-bit image; 2⁸ = 265 shades). Manufacturers will tell you they acquire 10- and 12-bit images containing thousands of gray shades, but for our diagnostic purposes, IT DOESN’T MATTER. We can only see 16, and so 256 is good enough for any dental diagnosis we have to make. All the systems have sufficient contrast resolution. And we can even improve that contrast or optimize it using tools in the software provided by the vendors of these systems.

However, that doesn’t mean we shouldn’t have a great monitor, because we also have to worry about spatial resolution. We are trying to find very small disease changes in dentistry, so we need a capture system that captures fine detail. We need monitors that display that fine detail. And, we need excellent printers to print that fine detail if we want a "hard copy".

Monitors

Monitors come in varying image resolutions. With a computer monitor the resolution is called the "dot pitch", measured in mm (millimeters). It is the distance between each pixel in the monitor display.  

On most monitors the dot pitch is around .26mm or .27mm. The higher the dot pitch number, the further apart the pixels.  As the pixels spread apart from one another, the fuzzier the image becomes.  Conversely, the closer together the pixels, the sharper the display. So, you’d like to use a monitor with a smaller number dot pitch. A .24 or .25 monitor would be better. For this resolution you will pay slightly more.

In addition, it’s been shown that LCD flat panel displays, although having great contrast detail and resolution, lack the latitude (the ability to display a wide range of gray shades) that conventional CRTs have¹. So, before you switch to those "sexy" flat panels, think about the display capabilities you will be giving up (figure 2).

Figure 2

Simulation of what a dental x-ray might look like on a "flat panel" monitor (left) Vs. a typical CRT computer monitor (right). Note that the high contrast of the "flat panel" is not able to display the correct bone height seen on the CRT with wider latitude (more grays).

Printers

Like with a good stereo system, if you have lousy speakers, you’ll have lousy sound. If you want your hard copy to look like the monitor image, don’t scrimp on the printer. There are many printers to choose from. Here is a list of high quality, but affordable printers (all ink jet types for under $500):

1. Kodak DMI 1200 (sold as a package with a digital camera, image software and paper)
   
2. Hewlett Packard 950C
3. Epson 740
4. Canon BJC 6000

Figure 3

Kodak DMI 1200 dental printer and radiographic image Of course you will also need to use high quality print paper. A glossy finish is best for displaying your image.

Figure 4
Click the image to Enlarge

Image printed on a Kodak DMI 1200 printer and Kodak paper

References