Light can be a powerful tool for extracting information from biological tissue. While a laser can lead to high quality microscopy, it can also produce speckle that distorts the images. At Yale University researchers realized that the resulting speckle holds a lot of dynamic information about the object being imaged, and so combining it with traditional microscopy can lead to new possibilities. The researchers created a laser system that is able to very rapidly switch between different imaging modes, harnessing both video microscopy and speckle analysis in a way that the two don’t interfere with each other.
The technique uses a “vertical external-cavity surface-emitting laser (VECSEL)” to run both types of imaging from a single device. As well known, laser speckle contrast imaging has been used for decades but lacked the details from simultaneous microscopy to be able to understand the complex dynamics of flow through tiny objects like small animal hearts.
The researchers were able to analyze tadpole hearts using the new imaging system in a way that was previously impossible. They produced low-coherence images that outlined the structure of the heart and then would switch to high coherence that provided information about the blood flow through the same heart.
The researchers envision the technology one day finding its way into the clinical world where it would be used for measuring blood flow through tissues for diagnostic purposes and to aid in surgery.
Some details from the Optical Society:
The new light source features a very simple design of only five optical elements plus a VECSEL. The VECSEL emits light from multiple sites, with the light from each site slightly out of step with all the others. The researchers used all 1,000 independent modes of light coming from the VECSEL to generate low-coherence light. By adding a pinhole to the laser cavity, they were able to concentrate all the laser power into just a couple of modes to create high-coherence light for laser speckle contrast imaging.
As a next step, the researchers plan to refine the system by using a type of digital mirror array called a spatial light modulator to switch between low and high coherence many times during one heart beat. This would allow almost simultaneous imaging of blood flow and structure.