Digital radiography: Basics

This will be the first of a new series on digital radiography. I won’t be going into deep detail about the mechanisms of how the different digital radiography systems work but more covering things that a salesperson may tell you or that you’ll see in ads and how to discern if what they are saying is important or not.  This first shorter post will be on the two different types of digital radiography: computed radiography and digital radiography.

Computed radiography

Computed radiography (CR) uses photostimulable phosphors, more commonly known as phosphor plates.  This system is very similar to film. First you expose the phosphor plate and then it must be ‘processed’ (scanned) by a scanner for the image to be visible.  This scanning process is much faster than film with images visible in 15 – 20 seconds after being placed in a scanner.  Typical automatic film processors take approximately 4 1/2 – 5 minutes for the final radiograph.  Now for some quick pros and cons of computed radiography systems.

Pros include:

  • fast learning curve due to similar size of film
  • ease of positioning in patients mouth due to small size and flexibility of phosphor plate
  • same sizes as film available (0, 1, 2, 3, 4)

Cons include:

  • slower processing compared to digital radiography
  • phosphor plates can become damaged (scratches) over time due to handling causing them to need to be replaced
  • images need to be ‘erased’ off phosphor plate (this isn’t an issue if your scanner has a built-in auto erase that is turned on)

Digital radiography

Digital radiography (DR) uses sensors or flat panel sensors.  There are two types of sensors currently on the market; charge-coupled device (CCD) and complementary metal oxide semiconductors (CMOS).  There is no current research showing either system produces higher quality diagnostic images.  The flat panel sensors are found on digital extraoral units (pantomographs, lateral cephalometric skull, etc.)  This system is different from film in that it is directly attached to a computer or capturing box via a wire.  When a sensor is exposed the image is ‘immediately’ (within 2-3 seconds) viewable on the computer it is attached to.  Now for some quick pros and cons of digital radiography systems.

Pros include:

  • immediate image (very helpful in endodontics and/or emergency care)
  • decreased exposure time compared to computed radiography

Cons include:

  • bulky size and wire can be difficult to position in a patients mouth
  • only sizes available are 0, 1, 2 (however, these sizes are not regulated and a size 1 with one company may be what another company calls a size 2)

While, this is only a short introduction, the next few weeks I will cover contrast resolution (bits), spatial resolution (line pair per millimeter), detector latitude and sensitivity to x rays.