Spotlight on Sensors: The Anatomy of a Quality Digital Sensor

If you’re into technology—like I am—it’s always interesting to deconstruct a technology to better understand how it works. For this reason, I wanted to discuss the different components of an intraoral digital X-ray sensor and how they help you capture the digital images you need. Not all sensors contain the same parts, which is something to consider before making a sensor purchase. By buying a higher quality sensor for your practice, you can:

  • optimize the signal-to-noise ratio leading to better contrast resolution and spatial resolution;
  • properly disinfect the sensor, protecting against cross contamination; and
  • ensure your sensor lasts longer, resulting in lower practice expenses.

 

Diagram of an intraoral sensor

Diagram of an intraoral sensor

The invisible X-ray beam from the generator will first come into contact with a high sensitivity scintillator. Composed of Cesium Iodide or molecules with like qualities, this layer converts X-ray photons into light photons—after being colliding with an X-ray photon. The resulting light photon can be easily detected by the CCD or CMOS sensor component.

The next layer of the sensor is the optical fiber. Composed of millions of “pipes”, the optical fiber channels the light photons generated by the scintillator from its input to its output. By turning the output into a pure signal made of light, this layer serves as a filter to protect the CCD or CMOS sensor from directly interacting with X-ray photons.

At this point, it’s important to point out that not all sensors contain an optical fiber component; therefore, it’s important to do your research when you select a digital radiography system. Optical fibers can help with quality because they “catch” any X-ray photons that are not converted to light by the scintillator. This reduces the noise that would occur if a high-energy X-ray beam collided with the CCD or CMOS sensor. The optical fiber not only improves the image quality, but also protects the CCD or CMOS from damage over time.

The next layer in the sensor is either the charge-coupled device (CCD) or the complementary metal oxide semiconductor (CMOS). With a CCD, each cell is an analog device. When light is filtered through the scintillator or optical fiber strikes the chip, it’s stored as a small electrical charge that is then converted—one pixel at a time—to a voltage value as they’re read. This is then passed on to circuitry that translates the voltage into digital information.

On the other hand, CMOS is an active pixel sensor that uses extra circuitry next to the photo sensors to convert energy from the light into a voltage value. This information is then converted by additional circuitry into digital information.

While CCD sensors have been around longer, more manufacturers are beginning to switch to CMOS for direct digital.

The way the sensor is sealed is also very important. Hermitical sealing ensures that the sensor is “air tight”. This protects the sensor from the ingress of intra oral fluids and also allows the sensor to be immersed in contact disinfectant to ensure that the sensor can be properly cleansed to prevent cross contamination.

How do the components of a sensor influence your purchasing decision?

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