After bone and dental, we have lung imaging, which can be done both in vivo and ex vivo. Typically, the resolution for ex vivo will be a lot higher compared to in vivo studies. The resolution range we are working in is in the micrometer scale, that's where the name microCT name comes from.
Some other applications will require a contrast agent to be injected, for example in cardiac imaging and vascularization.
Please outline the methodology behind microCT.
There are several steps involved with microCT. The first step is to scan the sample, and to do this you put an extracted bone, tissue or a live animal in a microCT system. Here, we discriminate between two types of microCT systems. You have the in vivo scanners for whole animals., which include a temperature sensor, ECG sensors and breathing detectors. You put the mouse on a bed and then enter with a camera and an x-ray source rotating around the sample.
A very similar technology, but different from an architectural point of view, is the ex vivo scanners. The camera doesn't rotate around the sample - rather, it's the sample which will rotate on the sample stage in between the source and the camera.
To acquire images, it uses the same technology. During your scan, you will shoot these radiographs as you would in the clinic, at several angles around the object. This will give you a stack of radiographs, projection images, which are then step reconstructed. That's a back-projection algorithm, which will combine all this information and give you a stack of cross sectional images.
You can then create visualizations using the images, by loading them in a 3D rendering software package, also provided by Bruker to support the images created using Brukers microCT instrumentation.
Important to note here is that all the software we use is developed in house in Bruker MicroCT, compared to some other companies who rely on third party software. Either the 3D rendering or the analysis can be done.
After the scan and reconstruction comes the third and final part of microCT - what do we want to do with this 3D information?
For the analysis, we will split up between either morphometric analysis where you will extract information about shapes, volumes, thicknesses, separation, voracities, or a density analysis where you will get information about how radio dense certain areas are.
Are there different types of microCT? If so, how do they differ in the measurements they make?
First of all we have in vivo versus ex vivo, whether you set up the system to scan live animals or something not living. Then we'll specify a system and the resolution, and you can insert different sources and cameras.
The source will determine the penetrating power from the x-ray, so the more energy you have, the bigger and denser the objects you can scan. Very low voltages would be sufficient to scan soft tissues, for example, whereas with higher voltages you can scan bones. The whole idea behind it is that the x-rays must make it through the object to reach the camera. If all the x-rays are stopped in the object, there will not be any image on the camera. That's one side of the scanner, the x-ray source and the voltage.
You can either use CCD cameras or flat panel cameras; CCD refers to more high-resolution cameras, whereas the flat panel cameras might have bigger pixels and slightly lower resolution.
For the ex vivo specimen samples, we have scanners which use those two types of cameras. The CCD allows a smaller area to be scanned at very high resolutions, going down to the micron level. The flat panel doesn't have such high resolution but allows a larger area to be imaged more quickly and it's also able to go to higher energies and penetrate through denser objects. These two broad types have different ranges and both in the ex vivo and the in vivo scanners, we either have the CCD focusing on high resolution or the flat panels for high energy, larger samples and high speed.
However where all of our Bruker microCT systems are alike, is the focus on user friendliness, which is appreciated in many parts of the life sciences field.