In this chapter, you will learn the advantages and basic concepts of digital radiography, including scanning and digitizing dental images. You will learn the various types and uses of intraoral and extraoral images. Using conventional x-ray film, you will learn how to use manual and automatic processing techniques, and how to duplicate films. You will also learn how to recognize common errors in film processing, and how to prevent them from occurring.

Digital Radiography

Digital radiography has been used in dentistry since 1987, and it has improved tremendously during this time. Today, in many areas of the United States and Canada, dentists and dental schools are changing from conventional film-based radiography to digital radiography (Fig. 39-1).

FIG. 39-1 A rear-mounted computer monitor allows the dental team to refer to the images and the patient record. A flat screen computer monitor is mounted from the ceiling, so patients can watch videos of their choice during dental treatment. (Courtesy Dr. Jeffery Elliott, Santa Rosa, CA.)

When digital radiography is discussed, the term digital images is used instead of radiographs, x-rays, or films. The digital images are not radiographs but electronic signals that are captured by sensors and displayed on a computer monitor almost instantaneously (Fig. 39-2). These images can be emailed to insurance companies and other dentists for consultations. If desired, hard copies of these images can be printed on image-quality paper.

FIG. 39-2 Digital images of a patient chart and digital panoramic image on a computer. (Courtesy Dr. Jeffery Elliott, Santa Rosa, CA.)

Although digital imaging systems are high tech, a conventional x-ray machine is still needed to expose the image, and the position of the image receptor (sensor or phosphor storage plate [PSP]) in the mouth is identical to positioning with film. In addition, strict infection control measures must be used because the sensors and PSPs are reused time and again. U.S. Food and Drug Administration (FDA)–cleared disposable, fluid-impervious barriers must be used on digital image sensors and phosphor plates. Digital image receptors are not able to tolerate heat sterilization.

Step-by-step procedures for the use of digital radiography systems vary by manufacturer. It is critical to refer to the manufacturer’s instruction booklet for information concerning operation of the system, equipment preparation, patient preparation, and exposure factors. Only general guidelines on sensor preparation and placement are discussed here.

Types of Digital Imaging Systems

Two basic methods are used to acquire a digital x-ray image: direct imaging and indirect imaging.

Direct Digital Imaging

In direct imaging, a solid-state sensor is the image receptor. It contains an x-ray–sensitive silicon chip with an electronic circuit embedded in the silicon (Fig. 39-3).

FIG. 39-3 Dexis Platinum Sensor: 1, Sensor housing. 2, Integrated electronics to maximize the imaging area. 3, Scatter guard to prevent x-ray back-scatter. 4, The x-ray beam is converted into visible light. 5, Fiber optics transmit light to the sensor for clear images. 6, High-resolution sensor brings out the smallest details. (Courtesy DEXIS LLC, Des Plaines, IL.)

The charge-coupled device (CCD) (sensor), the most commonly used digital receptor, is used in a variety of other imaging devices, such as telescopes, fax machines, personal data assistants (PDAs), video cameras, and even some panoramic machines and other extraoral imaging systems such as cone beam volumetric imaging (see Chapter 42).

Like telephones, some CCDs are wireless, and other types have a cable connected directly from the sensor to the computer. The wireless type of sensor uses radio frequency transmission to instantly transmit the image to the computer via radio waves (Fig. 39-4).

FIG. 39-4 A, Cable-type sensor. B, Wireless sensor. (A, Courtesy DEXIS LLC, Des Plaines, IL. B, Courtesy Schick Technologies, Long Island City, NY.)

Indirect Digital Imaging

Phosphor Storage Imaging

In phosphor storage plate (PSP) imaging systems, the image receptor is a thin flexible plate, the size of a conventional x-ray film, that has been coated with phosphor crystals (Fig. 39-5). The phosphor layer is able to store the energy of the x-ray photons for some time. A scanner is required to “read” the information stored on the plate by using a laser beam to release the energy from the plate and convert it into a digital image. The latent image will remain in the phosphor plate before the scanning phase for minutes to hours, depending on the environment in which the plates are stored. They should not be exposed to bright light or warmth because this will release the energy before it is read by the scanner. After the plates are scanned, they are exposed to bright light that erases all remaining energy, and the plates are ready to be used again. For infection control, the imaging plate is inserted into a specially designed barrier envelope. The barrier envelope is sealed by removing the adhesive strip and pressing the envelope closed. The imaging plate is protected and then can be used intraorally (Fig. 39-6). The imaging plate is positioned in the patient’s mouth using the same positioning techniques as are used with conventional dental x-ray film. After exposure, the imaging plate is carefully removed from the barrier envelope and then is placed in a scanner that uses a laser to display the image on the computer.

FIG. 39-5 Barrier envelope for phosphor plate.

FIG. 39-6 Front and back sides of phosphor plate.

The imaging plates cannot be autoclaved, and extreme care must be taken when handling to avoid scratches or dust.

Digitizing Images

Film-based radiographs may be digitized for viewing on a computer in much the same way as any other document. Desktop scanners capture and digitize the light signal of whatever is placed inside them. This process is similar to placing a film on a duplicator lightbox (discussed later in this chapter). This type of indirect digital imaging is slightly less detailed than direct digital imaging because the resultant image is similar to a “copy” of the image versus the “original” (Fig. 39-7).

FIG. 39-7 The desktop scanner scans the radiographs and digitizes the images to be viewed on a computer. (Courtesy Carestream Health, Rochester, NY.)

Digital Imaging Software Programs

Most computer software programs that are used in digital imaging are capable of performing electronic image enhancement. This means that the operator can change the following image variables together or separately (Fig. 39-8 and Box 39-1):

• Contrast

• Brightness

• Image size (zoom)

• Sharpness

• Inversion (white to black and black to white)

• Pseudocolor alteration

1 In digital radiography, what replaces the intraoral film?

2 What are the two fundamental techniques for intraoral digital radiography?

3 Which of the digital techniques requires scanning of image receptors?

FIG. 39-8 Example of how images can be manipulated with the software program. A, Changed contrast. B, Pseudocolor alteration. C, Inversion of image.

BOX 39-1

Advantages and Disadvantages of Digital Radiography

Advantages

Immediate Viewing of Images

In conventional radiography, reading the image is delayed because the film must be processed. Being able to immediately view the image is a significant clinical advantage

Note: Only charge-coupled devices (CCDs) provide immediate viewing. Phosphorous plate digital technology requires that the irradiated sensor be placed in a processing device to scan it and put the information into a computer, so that the image can be viewed.

Less Radiation

Digital radiography requires much less x-radiation than conventional film-based radiography because the sensor is more sensitive to x-rays than is conventional film. Exposure times for digital radiography are 70 to 80 percent less than those required for radiography with conventional film. With less radiation, the absorbed dose to the patient is significantly lower.

No Chemicals

It is not necessary to maintain, change, and dispose of processing chemicals. The need for a darkroom is eliminated, and gone are the stains and odors from the developing and fixing solutions.

Ability to Enhance Images

Digital radiography allows the dentist to change the contrast (to lighter or darker), enlarge images, place color enhancements, and so forth. It also allows for immediate and effective patient education.

Communication With Other Dentists

Digital radiography provides the ability to send images to other practitioners in a matter of minutes. This can be useful when consulting with another practitioner, especially when the patient is still in the chair. Email is the method most commonly used to send images.

No More Lost Films

Occasionally, a film is lost from a patient’s chart and cannot be replaced. With adequate backup procedures, stored digital images will not be lost.

Remote Consultation Capability

Digital images can be sent electronically by email or other electronic means. This is very useful for consultation or for insurance purposes. This process has been termed teledentistry.

Disadvantages

Cost

At the present time, the cost of purchasing a digital radiography setup can be substantial depending on the configuration. When considering the cost, one should carefully consider the advantages and disadvantages of digital radiography.

Converting Previous Records to Digital

Previous patient radiographs must be digitized (scanned) into digital records. To do this at one time for all the patient records in the practice can be very costly. It is best to do this gradually as patients come in for recall appointments. Spreading the labor costs over many months is more manageable.

Learning the Computer Software

As with all computer programs, users need time to become comfortable with the software. Software programs vary, depending on the manufacturer.

Thickness and Rigidity of Sensors

CCD sensors vary in thickness depending on the manufacturer. Care must be taken during placement to avoid discomfort to the patient. Phosphor storage plates (PSPs) are the thinnest, but they do not offer the advantage of immediate viewing of the image.

A sensor is used in place of intraoral dental film. When the x-ray beam strikes the sensor, an electronic charge is produced on the surface of the sensor. This electronic signal is digitized, or converted into “digital” form. The digital sensor in turn transmits this information to the computer. Software in the computer is used to store the image electronically.

Infection Control

The sensor or phosphor plate must be carefully covered with a barrier because it cannot be heat sterilized. Care must be taken when removing the barrier to avoid contamination of the sensor under the barrier. Follow the manufacturer’s recommendations regarding surface disinfection of the sensor. At this time, sensors and PSPs cannot withstand heat sterilization.

X-Ray Film and Film Processing

Although many dental practices are transitioning to digital techniques, a significant number of private dental practices are using conventional film-based techniques. The dental assistant must thoroughly understand the procedures and techniques necessary to process films into high-quality diagnostic dental images. It is also important to use the correct terminology. Film is the correct term to use before it has been processed. The film is in the packet; the film is placed in the bite-block; the film is exposed and processed. After the film has been processed, it becomes an image or radiograph.

Positioning Instruments

Positioning instruments (dental film and sensor holders) are used to position and hold dental x-ray films or the digital sensor in the patient’s mouth. The use of a positioner keeps the patient’s fingers from being exposed to x-radiation. Positioners also assist the operator in properly placing the film or sensor and the position indicator device (PID). When a rectangular PID is used, a film holder is absolutely necessary to avoid cone cuts, or clear areas of the film that are not exposed to radiation (see Chapter 38).

Various types of intraoral positioning instruments are currently available. The sensor holders used in digital radiography are almost identical to the x-ray film holders used in conventional techniques. The primary difference is seen in the size and shape of the holder.

Double-ended instruments used for the bisecting technique hold the film or phosphor plate between two serrated plastic grips that can be locked into place (Fig. 39-9).

FIG. 39-9 A, Snap-a-Ray Xtra Film and phosphor plate holder for the bisecting technique. B, Eezee-Grip Digital Sensor Holder for the bisecting technique. (Courtesy Dentsply Rinn, Elgin, IL.)

A basic style of film holder is the disposable polystyrene (Styrofoam) bite-block with a backing plate and a slot for film retention (Fig. 39-10). Other devices include the EndoRay (Dentsply International, York, Pennsylvania) (Fig. 39-11), which is used for images with endodontic instruments in the canal.

FIG. 39-10 Plastic- and styrofoam-type disposable bite-block film holders. (Courtesy Dentsply Rinn, Elgin, IL.)

FIG. 39-11 The EndoRay is designed to be used for images of teeth with endodontic instruments in them. (Courtesy Dentsply Rinn, Elgin, IL.)

Beam Alignment Devices

Devices used to align the beam are available from several manufacturers for both film-based and digital techniques. The beam alignment device assists in positioning of the PID in relation to the tooth and film or sensor. Rinn XCP instruments (Dentsply Rinn, Elgin, Illinois) use color-coded plastic bite-blocks, plastic aiming rings, and metal indicator arms for film-based techniques, and Rinn XCP-DS are examples of instruments used for holding digital sensors. Note: Several manufacturers produce digital sensors, and the size and shape of sensors vary slightly. You must be sure that you use a digital sensor holder designed to fit the specific brand of sensor you are using (Fig. 39-12).

4 How does the use of film holders protect the patient from unnecessary radiation?

5 What is the primary difference between a film holder and a digital sensor holder?

6 What is the purpose of a beam alignment device?

FIG. 39-12 A, Rinn sensors suitable for Gendex, VisualiX, USB/GX, Cygnus, and Visiodent systems. B, Digital sensor holding device. (Courtesy Dentsply Rinn, Elgin, IL.)

Dental Film

Film used in dental radiography is photographic film that has been adapted for dental use. A photographic image is produced on dental x-ray film when it is exposed to x-rays that have passed through teeth and adjacent tissues. The concept is similar to an image that is recorded on photographic film after it has been exposed to light through the shutter and lens of a camera.

The dental assistant must understand the composition of x-ray film and latent image formation. The assistant also must be familiar with the types of film used in dental radiography, as well as methods of film storage and protection.

Film Composition

Intraoral film consists of a semi-flexible acetate film base that is coated on both sides with an emulsion of silver bromide, silver halide, and silver iodide that is sensitive to radiation. Beginning with the film base, the following layers make up a />

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Jan 8, 2015 | Posted by mrzezo in Dental Nursing and Assisting | Comments Off

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39. Digital Imaging, Dental Film, and Processing Radiographs

Digital Imaging, Dental Film, and Processing Radiographs

Learning Outcomes

Key Terms

Digital Radiography