Digital Radiography in Dentistry or Digital imaging is available for almost more than a decade. It has successfully replaced conventional Radiographic films. This post will discuss about what is Digital Radiography in Dentistry, its principles, how it works, types, applications, advantages and disadvantages.
What is Digital Radiography in Dentistry
Digital Radiography is the result of the interaction of X-rays with electrons that are present in electronic sensor pixels (picture elements). It also involves the conversion of analog data to digital data through computer processing and displays the visible image on a computer screen. The discovery of X-rays happened in the year 1895. Since then the radiographic film has been the to-go medium for capturing, storing and displaying radiographic images. The practitioners are familiar and comfortable with the technique and interpretation.
Fig. 1 – Introduction to Digital Radiography in Dentistry
Digital Radiography is being adopted by dental professionals too. Digital imaging advocates the use of computer technology to capture, display, enhance and store Radiographic images. Digital Imaging or Digital Radiography offers advantages over film, but also like any other technology, it has challenges to overcome.
Types of Digital Radiography Images
There are two types of technologies that create digital images without using analog precursor. They are:
- Direct Digital Images
- Indirect or Scanned Digital Images (Semi Direct Digital Images)
Fig. 2 – (a) Digital Dental Radiography Machine (b) Dental Radiography Portable Machine
Direct Digital Images
Direct Digital Image production requires a number of components. The components include an X-ray source, sensor, digital interface card, computer with an analog-digital converter (ADC), screen, software and printer. The system requirements are processor, 640 KB internal memory with SVGA graphics card and also a high-resolution monitor with 1024 x 768 pixels.
Indirect or Scanned Digital Images
In Indirect Digital Imaging, the original image is captured in a digital format. The image is formed by discrete packets of information and this is called as pixels (picture elements). Indirect Digital Imaging implies that the image is captured in an analog format. It is later converted into digital format. As with any data conversion, the analog to digital conversion (ADC) also results in the loss and/or alteration of information.
The Indirect Digital Imaging technique first began as a device that optically scans a conventional film image (analog) and later is converted into digital image. This technique required an optical scanner that has the ability to process transparent images as well as software to produce the digital image. As imaging systems became more advanced, other techniques for capturing the digital image from an analog original were developed.
How does Digital Radiography Work
Let us understand the working principle of Digital Radiography in two ways.
- Working Principle of Direct Digital Images using Solid-State Sensor
- Working Principle of Indirect or Scanned Digital Images using Phosphor Plates
Working Principle of Direct Digital Images using Solid-State Sensor
Direct Digital Images are acquired using a Solid-State Sensor. Direct Digital Sensors can be a charge-coupled device (CCD) or a complementary metal-oxide-pixel sensor (CMOS-APS). The CCD is a solid-state detector. It has an array of X-ray or light-sensitive pixels that are placed on a pure silicon chip. A pixel consists of a small electron well. Into this well, the X-Ray or light energy will be deposited after exposure. The CCD pixel size is approximately 40µ. The rows of pixels are arranged in a matrix which has 512 x 512 pixels.
The CMOS-APS is one of the recent developments in direct digital sensor technology. Externally, CMOS sensors appear identical to CCD detectors. But they use pixel technology and are less expensive. It eliminates the need for charge transfer and improves the reliability and lifespan of the sensor. CMOS sensors have several advantages like design integration, low power requirements, and low cost but, have more fixed pattern noise and a small active area for image acquisition. The sensors are rigid and thicker than radiographic film and also have a smaller sensitive area for image capture.
Fig. 3 – Sensors of Different Size
There are two types of digital sensor designs namely:
- Area Arrays
- Linear Arrays
They are used for intra-oral imaging. Area Array CCDs can be divided into two main formats: Fiber optically coupled sensors and Direct Sensors.
Linear Arrays are used in extra-oral imaging.
Working Principle of Indirect or Scanned Digital Images using Phosphor Plates (Indirect Photostimulable Phosphor Plates)
Imaging technique that employs Photostimulable Phosphor Plates (PSP) can be described as Indirect Digital Imaging. The image is captured on a Phosphor Plate as analog information. Later it is converted into a Digital format when the Plate is processed. Photostimulable Phosphor Radiographic System was introduced in 1981. The PSP consists of a Polyester base. The base is coated with a Crystalline Halide Emulsion that converts X-Rays into stored energy.
The Crystalline emulsion contains a Europium-activated Barium Fluorohalide compound. When the PSP is scanned using a Helium-Neon laser beam, the energy stored is released as blue fluorescent light. The emitted light is caught and intensified. This is done by a Photo-multiplier tube. Later these are converted into digital data (digital radiography). The imaging plates must be treated to remove residual energy. The cordless nature of PSP plates helps in ease of receptor placement. The receptor is almost the same size as conventional film and is little flexible. Before reuse, the receptors must be erased by exposure to white light.
Fig. 4 – Phosphor Plates for Digital Radiography
Image Processing and Sharing in Digital Radiography
Method that aids to improve, restore, analyze or in any way alter a digital image is Image processing. Viewing the image on a computer aids the clinician to access and assess the information captured in the image. But it does not allow the image to be shared with other clinicians. A digital image can be sent to other sites if it is equipped with the appropriate software. The software should be capable of converting digital information into a visible image. When both sites have the same software or can produce an image that can be read by many different image processing software, this can be made possible. This type of Digital Radiography is called Tele-Radiography.
The size of the image and the speed of the image transfer are important factors to consider while sending radiographic images to distant sites. There is also concern with respect to the license when an image is transmitted to a different state for consultation. These issues are currently being addressed. This led to the development of the DICOM Standard or Digital Imaging and Communications in Medicine. The current version is 3.0. Dentistry recognizes the DI-COM 3.0 standard, but there is yet to be a uniform implementation of the standard. By being DICOM compliant, the system utilizes common file formats, and these are recognized universally. This is of importance while image submission to insurance companies is considered.
Another alternative for sharing images is by using a printed copy of the image. Many printers are available and the factors for choosing a printer are cost, output resolution, gray scale and paper requirements. Dots per inch or dpi is the measurement for output resolution. A 600 dpi printer Will be able to display an image with a resolution of 12 lp/mm. Some printers need special paper for the output of radiographic images. The cost of the paper is a consideration when determining the cost/benefit ratio of the use of a radiographic digital imaging system. The printer must also be able to generate an image with 28 or 256 shades of grey.
Applications of Digital Radiography in Dentistry
Applications of Digital Radiography in Dentistry are:
- To procure the information required for Dental procedures.
- To confirm the disease related to teeth.
- To detect the issue and condition of the teeth and surrounding parts.
Advantages of Digital Radiography in Dentistry
Advantages of Digital Radiography in Dentistry include:
- Digital Radiography in Dentistry reduces radiation exposure by 75%.
- It can control the exposure of each image in real-time. It can enlarge images, make enhancements to color and superimpose textures.
- Digital X-ray provides image quality that surpasses traditional film. Ability to visualize tiny fractures and imperfections that might have been missed on film.
- The need to file and store hard-copy radiographic images is eliminated.
- Eliminates the need for film processors and space they require.
- Images are stored and viewed readily.
Disadvantages of Digital Radiography in Dentistry
Disadvantages of Digital Radiography in Dentistry include:
- Sensor size is thicker and bulkier than dental films, causing discomfort to patients.
- Fragility: PSP plates are prone to damage from bending, frequent replacements.
- Digital sensors and PSP plates can’t be sterilized. Hence it requires protective plastic barriers. This protective barrier must be changed between patients to prevent cross-contamination and infection.