The Basics

Just a quick review of Optoacoustics because our IBMI meeting today was basically a seminar summarising the main points of the technology towards 5D Optoacoustics Imaging. It is a new and it’s emerging rapidly. Today, Lewis talked about the spacial resolution of pure optics as 1/10 of depth penetration. Perhaps the major limiting factor with this system is that it’s not possible to image a whole human in optics because of light limitations and boundaries- not yet anyways. It does however take a 3D imaging with good resolution, it is dynamic with functional and molecular specificity.

Multi-spectral optoacoustic tomography for example is a combine method of optical and acoustic modalities. This is a great technology because of its higher resolution at higher tissue penetration. It enables visualisation in optical microscopy which enables macroscopic transition and vice versa. Ultrasound govern this resolution. It also has inherently fast image process because images can be formed after a single pulse. 

How does it work?  

Unlike MRI, PET and other similar imaging technologies, the basics of Optoacoustics relies on generation of acoustic waves. This is generated from absorption changes in tissue from pulses of laser light. The degree is so minuscule but enough to cause rise in temperature which then generates thermoelastic expansion and in turn bring about acoustic waves. Ultimately, it is a measure of pressure as a function of time. The information is 1D and of course 3D image are much more informative. To do this, signals are collected at different locations and information are reconstructed. There are a number of ways to do this. Dynamic Imaging is achievable with time resolution being determined by time of flight of ultrasonic waves. This time resolution is established by pulse repetition rate laser. There are a number of agents used to aid this. To name a few, imaging proteins, ICG, IR800 CW and so on.

The phenomenon now known as photoacoustic effect was first discovered by Alexander Graham Bell in 1880. Sadly, the invention was deemed impractical at the time and there was a rise in optical fibre research in which he concentrated on. A century later, photoacoustic effect is making a comeback. This time in the field of imaging technologies.

If you think about conventional Imaging compared vs Molecular Imaging, we can say that MSOT has great promise covering a wide range of advantages covering excellent in-vivo optical contrast, multiscale in which a whole body small animal coverage in real time 2D and 3D imaging. This tool is a promising system in which facilitates brain mapping, brain tumour targets and their treatment at higher resolution than ever before.

 How is it quantified?  

This depends. There are several factors that have to be taken into account but the main one is the attenuation of light propagation in tissues as a function of depth. In any case, appropriate ultrasound transducer detectors are used with either microphones or piezoelectric sensors.

What are latest projects? 

“The Cup” is one of the latest transducers that have been built. Reconstruction of images is done either with back-projection or model-based. By Imaging with “single-shot” illumination, it is possible to see the whole head of a mouse in 3D with the system. It also has the ability to real-time tracking of vasculature. Here, a video was shared  and you can indeed see where the blood flow is going in a person’s wrist and finger. Bear in mind that real-time reconstruciton takes time and efficient implementation of 3D back-projection reconstruction in GPU allows real-time visualisation.

So what about MSOT? What is the oxygenation noise with respect to intrinsic contrast signal? At the moment, the lasers can go up to 50 Hz purse per second, translating to 20-30 mJ per pulse between 700-900 nm. This means fast dynamics with respect to imaging of the heart beat of an adult mouse in vivo using ICG injection for example.

Finally, what about the 5D Optoacoustics? 

The transducer allows imaging of different parts of the human body with real-time visualisation of so far, two frames per second. The future of this work seems to include better coupling design for hand-held use, improve quantitativeness (oxygenated estimation) and acquisitions. Penetration depth would be ideally two cm by so far only up to one cm was achieved. I have no doubt that in the very near future, I will be sitting once again, to the same talk with results far beyond its measures.

Pictures are pending or just directly check out our website for more infos.

Over and Out,

Sheryl