Spatial weight matrix in dimensionality reduction reconstruction for microelectromechanical system-based photoacoustic microscopy

A micro-electromechanical system(MEMS)scanning mirror accelerates the raster scanning of optical-resolution photoacoustic microscopy(OR-PAM).However,the nonlinear tilt angular-voltage characteristic of a MEMS mirror introduces distortion into the maximum back-projection image.Moreover,the size of the airy disk,ultrasonic sensor properties,and thermal effects decrease the resolution.Thus,in this study,we proposed a spatial weight matrix(SWM)with a dimensionality reduction for image reconstruction.The three-layer SWM contains the invariable information of the system,which includes a spatial dependent distortion correction and 3D deconvolution.We employed an ordinal-valued Markov random field and the Harris Stephen algorithm,as well as a modified delay-and-sum method during a time reversal.The results from the experiments and a quantitative analysis demonstrate that images can be effectively reconstructed using an SWM;this is also true for severely distorted images.The index of the mutual information between the reference images and registered images was 70.33 times higher than the initial index,on average.Moreover,the peak signal-to-noise ratio was increased by 17.08%after 3D deconvolution.This accomplishment offers a practical approach to image reconstruction and a promising method to achieve a real-time distortion correction for MEMS-based OR-PAM.

Correction to: Spatial weight matrix in dimensionality reduction reconstruction for micro-electromechanical system-based photoacoustic microscopy

Following publication of the original article[1],the keywords are missing in the article.Keywords:Photoacoustic microscopy,Spatial weight matrix,Dimensionality reduction,Distortion correction,Mutual information The original article has been updated.

Towards in vivo photoacoustic human imaging:Shining a new light on clinical diagnostics

Multiscale visualization of human anatomical structures is revolutionizing clinical diagnosis and treatment.As one of the most promising clinical diagnostic techniques,photoacoustic imaging(PAI),or optoacoustic imaging,bridges the spatial-resolution gap between pure optical and ultrasonic imaging techniques,by the modes of optical illumination and acoustic detection.PAI can non-invasively capture multiple optical contrasts from the endogenous agents such as oxygenated/deoxygenated hemoglobin,lipid and melanin or a variety of exogenous specific biomarkers to reveal anatomy,function,and molecular for biological tissues in vivo,showing significant potential in clinical diagnostics.In 2001,the worldwide first clinical prototype of the photoacoustic system was used to screen breast cancer in vivo,which opened the prelude to photoacoustic clinical diagnostics.Over the past two decades,PAI has achieved monumental discoveries and applications in human imaging.Progress towards preclinical/clinical applications includes breast,skin,lymphatics,bowel,thyroid,ovarian,prostate,and brain imaging,etc.,and there is no doubt that PAI is opening new avenues to realize early diagnosis and precise treatment of human diseases.In this review,the breakthrough researches and key applications of photoacoustic human imaging in vivo are emphatically summarized,which demonstrates the technical superiorities and emerging applications of photoacoustic human imaging in clinical diagnostics,providing clinical translational orientations for the photoacoustic community and clinicians.The perspectives on potential improvements of photoacoustic human imaging are finally highlighted.

Photoacoustic-enabled automatic vascular navigation:accurate and naked-eye real-time visualization of deep-seated vessels

Accurate localization of blood vessels with image navigation is a key element in vascular-related medical research and vascular surgery.However,current vascular navigation techniques cannot provide naked-eye visualization of deep vascular information noninvasively and with high resolution,resulting in inaccurate vascular anatomy and diminished surgical success rates.Here,we introduce a photoacousticenabled automatic vascular navigation method combining photoacoustic computed tomography with augmented and mixed reality,for the first time,to our knowledge,enabling accurate and noninvasive visualization of the deep microvascular network within the tissues in real time on a real surgical surface.This approach achieves precise vascular localization accuracy(<0.89 mm)and tiny vascular relocation latency(<1 s)through a zero-mean normalization idea-based visual tracking algorithm and a curved surfacefitting algorithm.Further,the subcutaneous vessels of minimum diameter(∼0.15 mm)in rabbit thigh and the maximum depth(∼7 mm)in human arm can be vividly projected on the skin surface with a computer visionbased projection tracking system to simulate preoperative and intraoperative vascular localization.Thereby,this strategy provides a way to visualize deep vessels without damage on the surgical surface and with precise image navigation,opening an avenue for the application of photoacoustic imaging in surgical operations.

Tomography-assisted Doppler photoacoustic microscopy:proof of concept

The previous methods to measure flow speed by photoacoustic microscopy solely focused on either the transverse or the axial flow component, which did not reflect absolute flow speed. Here, we present absolute flow speed maps by combining Doppler bandwidth broadening with volumetric photoacoustic microscopy. Photoacoustic Doppler bandwidth broadening and photoacoustic tomographic images were applied to measure the transverse flow component and the Doppler angle, respectively. Phantom experiments quantitatively demonstrated that ranges of 55° to 90° Doppler angle and 0.5 to 10 mm/s flow speed can be measured. This tomography-assisted method provides the foundation for further measurement in vivo.

High-fluence relay-based disposable photoacoustic-ultrasonic endoscopy for in vivo anatomical imaging of gastrointestinal tract

Photoacoustic endomicroscopy combined with ultrasound(PAEM-US)has been a long-standing expectation for gastrointestinal tumor examination.Here,we introduce a prototype disposable PAEM-US catheter and corresponding power interface unit,featuring catheter switchability,self-internal three-dimensional scanning,and system repeatability for gastrointestinal endoscopy.By utilizing high-fluence relays,cascade insertion loss of the optical waveguide is minimized to 0.6 dB with a high performance of power resistance,and a focus-customizable acousto-optic coaxial probe is designed for high-sensitivity optical-resolution photoacoustic imaging.Imaging capability was demonstrated with in vivo anatomical imaging at 30 frames per second.Imaging results showed co-registered microscopic visualization of the microvascular and stratification of the rat colorectum with lateral resolution of 18μm and axial resolution of 63μm,holding great potential in the clinical detection of gastrointestinal diseases.