Functional optoacoustic imaging of moving objects using microsecond-delay acquisition of multispectral three-dimensional tomographic data

Xosé Luís Deán-Ben, Erwin Bay, Daniel Razansky
2014 Scientific Reports  
The breakthrough capacity of optoacoustics for three-dimensional visualization of dynamic events in real time has been recently showcased. Yet, efficient spectral unmixing for functional imaging of entire volumetric regions is significantly challenged by motion artifacts in concurrent acquisitions at multiple wavelengths. Here, we introduce a method for simultaneous acquisition of multispectral volumetric datasets by introducing a microsecond-level delay between excitation laser pulses at
more » ... ent wavelengths. Robust performance is demonstrated by real-time volumetric visualization of functional blood parametrers in human vasculature with a handheld matrix array optoacoustic probe. This approach can avert image artifacts imposed by velocities greater than 2 m/s, thus, does not only facilitate imaging influenced by respiratory, cardiac or other intrinsic fast movements in living tissues, but can achieve artifact-free imaging in the presence of more significant motion, e.g. abrupt displacements during handheld-mode operation in a clinical environment. F irst optoacoustic images from living biological tissues were demonstrated over a decade ago 1,2 . The unique advantages of this hybrid imaging technology drive continuous technical advancements as well as its use in a number of novel biomedical applications. In optoacoustics, sound waves are induced by absorption of timevariant light radiation 3 , which allows for high-resolution imaging of rich optical contrast beyond the depthpenetration limits imposed by light scattering. Thus, otherwise unresolvable or undetectable anatomy and function can now be visualized at millimeter to centimeter scale depths in living organisms 4,5 . Translation into clinical practice occurs to be the natural next step so that the unique strengths offered by the optoacoustic technology can be fully exploited. Several dedicated systems using endoscopic, hand-held, or stationary design approaches have been recently proposed for clinical use, with multiple applications envisioned in diagnosis of breast cancer 6,7 and cardiovascular disease 8 , ocular imaging 9 , visualization of arthritis 10 , lymphatic system 11 , skin abnormalities 12 , prostate 13 and thyroid glands 14 . Of particular convenience is the use of hand-held probes, which permits real-time visualization of dynamic events, and has the potential to speed up clinical examinations on a broad range of applications. In fact, these are also the main assets that propelled ultrasonography into the most-widely-employed imaging modality in today's clinical practice. On the other hand, the optoacoustic tomographic reconstruction problem and physics behind the signal excitation substantially differ from ultrasonography. While linear arrays are typically used in ultrasound imaging, curved array geometries proved to be a significantly better strategy for collection of optoacoustic responses and further resulted in more accurate reconstructions 15,16 . Moreover, optoacoustic excitation via laser light offers additional exclusive capacities, such as intrinsic ability to acquire full tomographic datasets within a single interrogation laser pulse, thus achieving real-time three-dimensional imaging capacity [17] [18] [19] . Most importantly, by acquisition of images at multiple optical wavelengths, multispectral optoacoustic tomography (MSOT) can map functional contrast as well as the bio-distribution of molecular agents in tissues 20,21 . Real-time acquisition of multispectral datasets imposes significant technological challenges when considering motion in living subjects, e.g. due to breathing or heartbeat. Even more significant artifacts may be introduced by operating optoacoustic imaging devices in a hand-held mode. Several prior attempts to avoid motion-related artifacts in multispectral optoacoustic imaging were done using high repetition lasers in optoacoustic endoscopy 22 OPEN SUBJECT AREAS: IMAGING AND SENSING THREE-DIMENSIONAL IMAGING
doi:10.1038/srep05878 pmid:25073504 pmcid:PMC4115207 fatcat:7dwhhtslqja35gb4azairqqs2q