Radiology Course page 17 – Digital

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Digital-imagingThe latest trend in technology for many dental offices is to go “paperless” or to have records stored digitally. In the dental field digital storage can be achieved by way of designing a new office or by converting an established office to digital use and storage.  There are many benefits to having a paperless office.  One example is that the files can be accessed and saved even after unforeseen situation, such as a fire, occurs.

The digital trend is also making clinician’s aware of obvious drawbacks to traditional film usage.  One such drawback is the time it takes to handle and/or retrieve a patient’s film, and then to duplicate it for submission to insurance or to give to the patient.  Additionally, the darkroom has upkeep costs and takes time to maintain.  Additionally, film requires an interconnected processing system that allows for clinician error in exposing and/or developing, which can affect the quality of the image. This can also mean an increased exposure to radiation to the patient, due to retakes in an effort to achieve a quality image for diagnostic use by the dentist.  Finally , with the increased use of digital radiography in dentistry, it is easy to see that traditional film usage is not as eco-friendly (although I suspect that some day the earth will run out of pixels).

In the mid 1980s a dental student named Francis Mouyen at the University of Toulouse in France was credited as the founder of digital x-rays.  At first images could not be stored, only printed.  This problem initiated the launching of many software and hardware development companies to remedy the problem.  Digital x-rays became recognized and first used in the United States after FDA (Food and Drug Administration) approval in 1990.  Since then digital radiography is widely used and quickly becoming the preferred method for many dental professionals.

Digital radiography is a huge motivator in advancing a dental office.  Digital images can be transmitted via modem in mere seconds. Images can be inserted into a word processing document (such as treatment plans) and printed on an high quality ink jet printer with excellent results. The patient radiographs can easily be transmitted from one dentist to another without losing quality. Additionally, the image can be manipulated to optimize brightness and contrast enabling the dentist to enhance an area of concern without losing quality.

Some say digital images are more graphic and detailed and therefore more ideal to use for patient education. Digital radiographs can be displayed in a magnified form for the patient education.  Patients can be shown more vividly caries existing in different degrees, periodontal bone loss can actually be measured on an image if the sensor, beam and the tooth were all parallel.  This is especially useful in endodontic procedures.   Furthermore, the intensity, contrast and brightness can be enhanced to make diagnosis more accurate. This also means saving a great deal of time and not waiting for records to be received through the mail, whether it be to intercommunicate with another dental professional or to make insurance claims more efficient and to bill on a claim or to get preauthorization more rapidly on a diagnosed treatment for a patient.

The costs to implement digital radiography will be discussed shortly but as another benefit it is more cost effective in the long term to use the digital method.  It is a valuable benefit that each image will always be tied to a specific patient, as it was created.  This seems to limit clinical-error as once the individual patient’s file is opened on a computer there is no way to mislabel the patient’s name compared to the possibility of traditional films being mounted incorrectly or, unfortunately, sometimes with the wrong patient information listed on the mount.

However, the most beneficial aspect, by far, to using digital radiography over the traditional film method is LESS radiation exposure to the patient!.  This referred to as the “ALARA” principle: the patient receives more benefit than harm.  It is an acronym for “as low as reasonably achievable.”  It should be pointed out, however, that offices using digital radiography should still be following FDA/ADA guidelines-including but not limited to placing lead-free aprons on patients during exposure time.

Critics of digital radiography present some fair concerns.  The general size of the digital sensor and holder is bulkier and more rigid than dental x-ray film, and a bit more less comfortable for the patient.  Additionally, when using the digital system, it is necessary that a cord hang out of the patient’s mouth causing further discomfort.  However, there are many digital sensor aids to help with patient comfort, as well as, act as a barrier for infection control. These aids also help protect slightly against damage to the sensor and can prevent slippage as sensor sits in the mouth for exposure. As technology advances, hopefully, too, will the comfort to the patient.

Infection control is a very important aspect when dealing with digital radiography and will be discussed in more detail later.  Specifically, it involves the use of more barriers between the patient and the machine as the actual hardware can be sensitive to common chemical sprays used for disinfection.  All members of an office should learn and practice the preferred cleaning method dictated by the company who installed the specific digital system used.  There are concerns regarding effective infection control being followed perhaps more so than with film usage, however unfounded.

Though digital radiography has many advantages there are also a number of concerns surrounding the exclusive use of digital imagery. There is a difference in size between digital and regular film. For example, the actual digital detector housed in the sensor is smaller than a #2 film and so does not always get the desired oral structures in one dental image.  Sometimes more than one image must be taken to get the same structures that could have been seen on one #2 film.

As previously mentioned although it is true that the dental office will save money over time if the office uses digital imaging, the initial costs are quite substantial.  In our office, in 2009, it cost us about $50,000 to set up a system for 4 operatories.  This included two sensors, 4 new computers (workstations) with two displays in each operatory (0ne for the patient and one for us), software, and technical support to install it and teach us how to use the software.  Solid state sensors are very expensive, ranging between $8,000 and $10,000 apiece.  Furthermore, there is a yearly fee for “insurance” so that if one is damaged for any reason, it will be replaced immediately at no charge.  So far, ours have not broken down over the year we have been using them.  The PSP plates (not the sensors described above) used in the Phosphor Plate System method cost only $30 each, but they are fragile and tend to accumulate scratches with misuse.  Although the latter system seems cheaper there exist other drawbacks with it that will be discussed later.

There has been concern surrounding the security of a patient’s records being stored accurately on a computer system, as well as, any ability to tamper with stored records (especially digital images) to ensure coverage from an insurance company.  Both of these concerns, although legitimate, when investigated show it would take complex, not to mention, highly illegal processes to breach the security in any way.  When an image is saved and stored, the original image contains a perpetual creation date attached to it. Each digital image is always connected to that patient’s file, as well as when it was initially taken and stored.  There is no way to alter the name.  It is therefore vital to ensure that the correct patient file is open on the computer BEFORE digital images are taken.  This will guarantee the images directly attached to a patient’s file cannot be misfiled, etc.

Computers also track and store when the image was last accessed, if and when it was altered in any way, and how. No matter what contrast and brightness changes are made on the image it cannot change the time stamp of when the image was taken.  Only limited changes can be made to the image.  Digital software companies are now using watermarks that are created on the altered image (permanently) so that both insurance companies and all those connected to the patient will know if the image has been altered.  Another way in which digital storage can be considered safer is that the image cannot be accidentally confused with another patients x-rays coming out of a processor and, subsequently submitting the wrong one to an insurance carrier or to the patient!  Also, it is important to note that when fraud is committed it is usually not as concerning to have an “altered” image as it is to investigate and find questionable alterations in patient histories and/or treatment records….  Such changes made on digital storage software are recorded and easily traceable on computers versus making changes in a “paper chart.”

Digital radiology branches off into 3 main systems: Direct, Semi-Indirect, and Indirect

Indirect systems have the benefit of the ability to utilize pre-existing equipment.  This also translates into a substantially lower cost than other systems.  It involves primarily taking a traditional exposed film and using either a flatbed scanner or a slide scanner to copy the image into a JPG of TIFF file that can be stored in the computer.  The clinician can take a picture of the traditional film with a digital camera to transfer image into a digital format.  Software from Televere Systems called TigerView takes images from a scanner and automatically arranges them in proper orientation and order. These images can be manipulated, rotated, and enhanced. Zoom, contrast, brightness, and orientation are also variables.  It is the most reasonable in cost of the three but not as popular or “high tech” as the Direct System.

The Semi-Direct System uses methods from both the Direct and the Indirect Systems.  It is similar to the Indirect System in that the stored image is scanned into the computer.  The Semi-Direct method uses a photo-stimulable phosphor (PSP) – also known as a “storage phosphor plate.” In a more detailed look at how the process of the Semi-Direct System works the storage phosphor plates are used to temporarily store the image until it can be transferred into a computer.  Special packets are used to hold the phosphor plate.  These look similar to traditional films.    This system is considered much more comfortable to patient, than the digital sensors used in the direct technique because they are thinner.  The phosphor is placed in the patient’s mouth in the same way as a standard dental x-ray film would be.  The plates are covered with phosphor crystals.  These crystals temporarily store the energy of the x-ray protons forming a latent image, similar to the one formed on an x-ray film. The plates are then put into a scanner that “reads” the stored image by way of a laser beam.  The scanner, which is connected to the computer, then transfers the image into the patient’s computerized chart.   The transfer of the phosphor plates to the scanner must be carried out in darkness or the plates will be erased by the ambient room light.  Finally, to reuse the plates, they are laid out in bright light, which erases the stored image.  The direct system is much faster overall than either the semi-direct, or the indirect system, and the images may be marginally better.

The direct system is done with a solid state sensor.  The word “direct” refers to the fact that the digital image is produced directly, without the extra steps involved in having to manually “develop” a phosphor plate, or scan an x-ray film into a digital file. There exist two separate types of sensors used in a solid-state or Direct System.  The most widely used,  is the charge-coupled device (CCD).  CCD’s are used in digital cameras, as well as, digital radiography.  A second system, recently developed is called the CMOS sensor, which works differently than the CCD, but delivers the same result.  There is a bit of a battle going on between developers to see which system wins out in the long run.

A CCD is a semiconductor chip with a rectangular grid of millions of light-sensitive elements, used for converting light images into electrical signals.  When an image is taken in this technique the radiation/energy stimulates the sensor and creates the image.  There is a scintillation layer atop the electronic chip that turns the x-ray photons into light photons.  Each of the millions of light sensitive elements in the CCD underlying the scintillation layer then converts the light photons into an analog electrical impulse.  These impulses are then converted into digital numbers between 0 and 65536 (for the newest generation of sensors).   The numbers transmitted correspond to the intensity of the light transmitted to each tiny element in the rectangular array by the scintillating layer.  In this way, the image is converted to millions of tiny digital picture elements (pixels), which are reassembled by the computer into a coherent image.  CCD’s used in dental imaging are essentially the same as the CCD’s used in newly popular digital cameras.  In your home camera, the CCD contains color filter arrays for each pixel so the image can be reassembled in color.  Since dental radiographs are monochrome, the dental CCD does not contain these filters.

A digital radiograph is composed of shades of gray spanning from black to white, and is known as a “continuous tone” image. This means that the shades of gray blend together with no noticeable interruptions. To convert data from the sensor into digital form, each element of the image is converted into an individual piece of information by an analog to digital or “A to D” converter. This information describes the light intensity (brightness) and its location in relation to the picture as a whole. Each small piece of information is called a pixel (short for “picture element”). The computer reassembles the pixels in the correct order and brightness to build a digital image. Manufacturers of current image processor equipment use a standard 12-bit or 4096 levels of gray for the images. The latest image processors use a sixteen bit or 65536 levels of gray.  Increasing the number of bits representing the brightness expands the gray scale so that the digital image more closely resembles the original image. The higher the number of pixels used to define the image, and the more closely they are packed, the closer we approach the spatial appearance of the original image. This means that a properly displayed digital image will appear to be identical to the same image presented on an x-ray film. The more pixels and bits of information involved in the picture, the more memory the computer requires for processing and storing the image.

A typical imaging system is composed of a image receptor like a camera or a CCD, a framegrabber with A/D and D/A converter, a host computer with hard disk storage, and image processor software or hardware and a video monitor. Once the image is in the computer, it can be manipulated, enhanced, enlarged, filtered, and compared to other images. The technique used to capture the image must have the ability to be reproduced so two images of the same area taken at different times can be accurately compared. [i]

The other type of sensor not as widely used, is the complementary metal oxide semiconductor (or CMOS)-based chip. The primary difference in the latter CMOS sensor is that the electronic components are integrated inside the electronic chip instead of having a scintillation layer like the CCD sensor.  Although it saves time and money to produce the CMOS sensors with an internal mechanism, the charge-coupled device is used more often, probably because the CCD was on the market first.  There seems to be no difference in the quality of the images by either method.

The technique used for digital radiography still uses sensor holding devices similar to those used in the traditional film technique.  When a digital system is installed in an office, the sensor generally comes with Rinn-type sensor positioning devices.  Additionally, guidelines to software and computer maintenance are given and should be followed to achieve optimal results.  Each computer screen should be placed so that it is ergonomically appropriate to clinician and so that it can be used in patient education, if desired.  Lead-free aprons are still needed and each office should follow the FDA/ADA guidelines similar to those used in the traditional film method.

One final consideration by Sellen and Harper, authors of “Writing about the paperless office”: While assessing the NEED to transfer a dental office over to an entire digital format, “Change for the sake of change is hugely problematic.  Going paperless for the sake of ‘out with the old, in with the new’ is destined to end in failure.”  (I use digital x-rays, but I still write my records longhand because it’s actually faster for me, and my receptionist is infinitely better at clerical/insurance code matters than I am.  Call me a troglodite!)

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[i] S. Brent Dove Dental Diagnostic Science  Copyright UTHSCSA 1995 All right reserved

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