Single-side access, isotropic resolution and multispectral 3D photoacoustic imaging with rotate-translate scanning of ultrasonic detector array

Photoacoustic imaging can achieve high-resolution three-dimensional visualization of optical absorbers at penetration depths ~ 1 cm in biological tissues by detecting optically-induced high ultrasound frequencies. Tomographic acquisition with ultrasound linear arrays offers an easy implementation of single-side access, parallelized and high-frequency detection, but usually comes with an image quality impaired by the directionality of the detectors. Indeed, a simple translation of the array perpendicularly to its median imaging plane is often used, but results both in a poor resolution in the translation direction and in strong limited view artifacts. To improve the spatial resolution and the visibility of complex structures while keeping a planar detection geometry, we introduce, in this paper, a novel rotate-translate scanning scheme, and investigate the performance of a scanner implemented at 15 MHz center frequency. The developed system achieved a quasi-isotropic uniform 3D resolution of ~170 um over a cubic volume of side length 8.5 mm, i.e. an improvement in the resolution in the translation direction by almost one order of magnitude. Dual wavelength imaging was also demonstrated with ultrafast wavelength shifting. The validity of our approach was shown in vitro. We discuss the ability to enable in vivo imaging for preclinical and clinical studies.Comment: 43 pages, 5 figure

Photoacoustic Neuroimaging - Perspectives on a Maturing Imaging Technique and its Applications in Neuroscience

A prominent goal of neuroscience is to improve our understanding of how brain structure and activity interact to produce perception, emotion, behavior, and cognition. The brain’s network activity is inherently organized in distinct spatiotemporal patterns that span scales from nanometer-sized synapses to meter-long nerve fibers and millisecond intervals between electrical signals to decades of memory storage. There is currently no single imaging method that alone can provide all the relevant information, but intelligent combinations of complementary techniques can be effective. Here, we thus present the latest advances in biomedical and biological engineering on photoacoustic neuroimaging in the context of complementary imaging techniques. A particular focus is placed on recent advances in whole-brain photoacoustic imaging in rodent models and its influential role in bridging the gap between fluorescence microscopy and more non-invasive techniques such as magnetic resonance imaging (MRI). We consider current strategies to address persistent challenges, particularly in developing molecular contrast agents, and conclude with an overview of potential future directions for photoacoustic neuroimaging to provide deeper insights into healthy and pathological brain processes

Real-time blood oxygenation tomography with multispectral photoacoustics

Multispectral photoacoustics is an emerging biomedical imaging modality which combines the penetration depth and resolution of high frequency medical ultrasonography with an optical absorption contrast. This enables tomographic imaging of blood oxygen saturation, a functional biomarker with wide applications. Already, photoacoustic imaging (PAI) is widely applied for small animal imaging in preclinical research. While PAI is a multiscale modality, its translation to clinical research and interventional use remains challenging. The objective of this thesis was to investigate the usefulness of multispectral PAI as a technique for interventional tomographic imaging of blood oxygenation. This thesis presents open challenges alongside research contributions to address them. These contributions are, (1) The design and implementation of an interventional PAI system, (2) Methods for real-time photoacoustic (PA) image processing and quantification of tissue absorption and blood oxygenation, and finally (3) the application of multispectral PAI to translational neurosurgical research – performing the first high spatiotemporal resolution tomography of spreading depolarization, and at the same time the first interventional PAI on any gyrencephalic (folded) brain. Such interventional imaging in neurology is one of many promising fields of application for PAI

Reliability and comparison of 3-dimensional surface imaging of the face using a hand-held and whole body surface scanner

Objective: 3-Dimensional surface (3DSI) imaging has been shown to be a useful tool for plastic surgeons in the preoperative, intraoperative and postoperative setting. And to the knowledge of the authors no data about the reproducibility and accuracy of 3-Dimensional surface imaging of the face using a whole-body scanner is available. Thus, the objective of this investigation was to assess the reproducibility of facial scans acquired using a whole-body imaging device and to compare the precision of distance measurements in the face using a hand-held surface imaging device and a whole-body surface imaging device. Furthermore, the reproducibility of the whole body scanner was investigated. Material and Methods: This investigation enrolled a total of 22 healthy volunteers with a mean age of 29.36 years. Two consecutive 3-D images of the volunteers were obtained utilizing a whole-body imaging device(WB360) and a hand-hold imaging device(Vectra H2). For the whole-body imaging predefined distances in the face were performed in each scan and compared. Furthermore, surface deviation between two consecutively captured scans was assessed. Results: For the reliability of whole-body scan, the distance with the smallest statistical significance was found to be at the nose with p = 0.998, while the biggest statistical significance was found in the midface with p = 0.658. The area with the biggest surface deviation between the superimposed scans was the neck with a RMS of 1.62 ± 1.71 mm and the area with the smallest surface deviation was the forehead with a RMS of 0.17 ± 0.05 mm. For the comparison of the both scanners our results revealed that the measured difference between the length and the standard reference did not differ statistically significant between the two investigated devices in all investigated areas of the face (p > 0.266), however the measured difference of the width and the width of the standard reference differed statistically significant in all areas of the face across the investigated devices (p < 0.032). Conclusion: The whole – body-imaging device investigated in this study can be utilized to capture the face and provides enough accuracy to compare scans. Even though not directly investigated, it can be hypothesized that the error caused by repositioning the patient between a baseline and a follow – up scan will not be too big to consider measurements performed with the whole – body-imaging device as impractical. Both, measurements obtained from scans acquired using the hand held imaging device and the whole – body-imaging device differed significantly from the standard reference. Users should be aware of deviations when obtaining 3DSI using the presented imaging devices but should not refrain from using them, as the absolute differences might be too small to play a role in both, clinical and research, setting

Skin surface detection in 3D optoacoustic mesoscopy based on dynamic programming,

Optoacoustic (photoacoustic) mesoscopy offers unique capabilities in skin imaging and resolves skin features associated with detection, diagnosis, and management of disease. A critical first step in the quantitative analysis of clinical optoacoustic images is to identify the skin surface in a rapid, reliable, and automated manner. Nevertheless, most common edge- and surface-detection algorithms cannot reliably detect the skin surface on 3D raster-scan optoacoustic mesoscopy (RSOM) images, due to discontinuities and diffuse interfaces in the image. We present herein a novel dynamic programming approach that extracts the skin boundary as a 2D surface in one single step, as opposed to consecutive extraction of several independent 1D contours. A domain-specific energy function is introduced, taking into account the properties of volumetric optoacoustic mesoscopy images. The accuracy of the proposed method is validated on scans of the volar forearm of 19 volunteers with different skin complexions, for which the skin surface has been traced manually to provide a reference. In addition, the robustness and the limitations of the method are demonstrated on data where the skin boundaries are low-contrast or ill-defined. The automatic skin surface detection method can improve the speed and accuracy in the analysis of quantitative features seen on the RSOM images and accelerate the clinical translation of the technique. Our method can likely be extended to identify other types of surfaces in the RSOM and other imaging modalities