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. In order to prevent most dental procedures an excellent dental care is vital, try out steel bite pro.
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.