Digital Imaging Basics
The production of digital images requires a process called Analog to Digital Conversion (ADC). Digital imaging is a radiographic technique that utilizes a wired or wireless hard sensor or phosphor plate sensors known as a receptor, instead of film. Digital images consist of pixels organized in a matrix of rows and columns. ADC consists of two steps: sampling and quantization. Sampling is a small range of voltage values that are grouped together as a single value. Once sampled, every sampled signal is assigned a value. For the dental provider to see the digital images, the computer must organize the pixels in their correct locations and display shades of gray that corresponds to the number that was assigned. This step is known as quantization.5
In digital imaging, the x-ray machine is still used, but the image is converted from analog to digital. When the photons from the x-ray tubehead strike the sensor, the analog image is converted to a digital image and then transferred to the digital imaging software (Figure 1). The digital images are composed of pixels or rows and columns of images aligned to represent the intensity (gray level) of the image. There is a value assigned to each pixel that represents the intensity or gray level of each location in the image.9 The computer software organizes the pixels and displays the dentistry of the object via multiple shades of gray. Due to pixel technology in digital sensors, anatomy such as bone trabeculation, lamina dura, and DEJ are easier to diagnose due to high contrast in digital imaging.
Figure 1. Digital Full-mouth Series Displayed on a Laptop Computer.
Image Source: Suni Medical Imaging, Inc., San Jose, CA.
Digital Imaging Radiation Exposure
Even though digital imaging requires less radiation than radiographic film, radiation is still produced at the source, e.g., dental x-ray machine. Digital imaging reduces the amount of radiation to the patient due to the sensitivity of the digital imaging sensors. Depending on the radiographic film used in the dental practice, e.g., D- or F-speed, radiation exposure time can be reduced as much as 90% when changing from radiographic film to digital sensors.1,5,6,7 For example, an exposure time required to produce a digital image is 0.05 seconds, where a radiographic film would require an exposure time of 0.2 seconds. Standard radiation safety procedures still requires the dental provider be at least 6 feet from the x-ray tubehead and the patient be covered in a lead apron with a thyroid collar.
Digital Imaging Equipment
Digital imaging requires an x-ray unit, sensors to capture the images, computer hardware and software to view, store, and transfer images, and if an indirect digital system, a scanning device.
A standard intraoral dental x-ray machine (Figure 2) may be used with radiographic film and digital imaging. However, the control panel must use exposure time in 1/100 of a second and not impulses.5 If the control panel cannot be converted to exposure time, the x-ray machine cannot be used with digital imaging. Contact your dental representative to see if your current x-ray machine can be used with a digital imaging system.
Figure 2. Intraoral X-ray Machine.
Image Source: Gendex Dental Systems, Hatfield, PA.