The term “solid-state” has been used in medical imaging for years, but what does it really mean? As a leading producer of solid-state nuclear cameras, Digirad is here to explain what makes a camera solid-state.
Pixilated crystals and speed
With solid-state technology, the camera detectors are comprised of thousands of individual detector elements, not a solid sheet of crystal and large photomultiplier tubes (PMTs) found in Anger cameras. Each solid-state detector element (pixel) is isolated from one another. When a scintillation event occurs on a particular crystal, its exact location can be quickly and correctly identified, making the detector substantially faster and more accurate.
Pixilated detectors also eliminate the need for time-consuming summing algorithms used in Anger technology. Scatter correction can be performed more quickly because the system is not spending an excessive amount of computer and electronic time trying to determine the location of the event.
Solid-state pixilated detectors eliminate issues related to linearity and summing, allowing a much simpler methodology with increased reliability. Solid-state technology also allows for lower levels of radiation to be used in imaging. Also, with solid-state imaging, attenuation correction can be performed using the same detectors for both the transmission and emission in a single sitting.
Direct and indirect conversion
There are two primary conversion methods for solid-state nuclear imaging; direct and indirect. Each conversion method is different, but both create increased reading confidence and an improved patient experience.
Direct conversion uses cadmium zinc telluride (CZT). When a photon is absorbed by the crystal, it creates an electric charge directly, hence the term direct conversion. Direct conversion is effective; however the manufacturing cost of CZT can be expensive.
Indirect conversion uses a silicon-based photodiode, coupled with cesium iodide (CsI) crystal material. When a photon comes in contact with the crystal, it produces light, which is converted to an electronic signal. This process is faster, and manufacturing cost of CsI detectors is much less than CZT.
Solid-state nuclear cameras offer significant advantages over Anger-based cameras. This state-of-the-art technology continues to revolutionize nuclear imaging and provide patients with the highest level of diagnostic confidence.