During medical investigations of the head, the presence of skull bone constitutes a major challenge in generating accurate diagnostics. Photoacoustic imaging technology, with its functional imaging capabilities, has demonstrated the potential for brain imaging at low cost and with low maintenance requirements. While photoacoustic signal generation in deep tissue and through the skull has been demonstrated, an effective method of aberration correction for transcranial photoacoustic imaging has not yet been developed. In this study, we present a method based on enfolded deep learning algorithms that accurately compensates for acoustic aberrations caused by the head layers, allowing hemorrhage detection. Using a realistic simulated framework, a large quantity of aberrated images is acquired, reconstructed, and corrected.
This paper introduces an innovative approach to enhance the circular scanning-based photoacoustic tomography (CSPAT) system for photoacoustic imaging. The proposed method involves using a circular detection geometry with three carefully placed ultrasound transducers (USTs). By strategically selecting the angles of the USTs, the field of view (FOV) is expanded, and tangential resolution is improved without requiring additional imaging time. The new CS-PAT system demonstrates practicality and convenience, providing higher signal-to-noise ratio and better structural similarity compared to the conventional system. This approach overcomes the limitations of the limited size of USTs and widens the application potential of CS-PAT in a straightforward and efficient manner.
SignificanceThere are many neuroscience questions that can be answered by a high-resolution functional brain imaging system. Such a system would require the capability to visualize vasculature and measure neural activity by imaging the entire brain continually and in rapid succession in order to capture hemodynamic changes. Utilizing optical excitation and acoustic detection, photoacoustic technology enables label-free quantification of changes in endogenous chromophores, such as oxyhemoglobin, deoxyhemoglobin, and total hemoglobin.AimOur aim was to develop a sufficiently high-resolution, fast frame-rate, and wide field-of-view (FOV) photoacoustic microscopy (PAM) system for the purpose of imaging vasculature and hemodynamics in a rat brain.ApproachAlthough the most PA microscopy systems use raster scanning (or less commonly Lissajous scanning), we have developed a simple-to-implement laser scanning optical resolution PAM system with spiral scanning (which we have named “spiral laser scanning photoacoustic microscopy” or sLS-PAM) to acquire an 18 mm diameter image at fast frame rate (more than 1 fps). Such a system is designed to permit continuous rat brain imaging without the introduction of photobleaching artifacts.ConclusionWe demonstrated the functional imaging capability of the sLS-PAM system by imaging cerebral hemodynamics in response to whisker and electrical stimulation and used it for vascular imaging of a modeled brain injury. We believe that we have demonstrated the development of a simple-to-implement PAM system, which could become an affordable functional neuroimaging tool for researchers.
Three-dimensional (3D) photoacoustic tomography is a method of choice for imaging round organs such as brain and breast. Many research groups have used a fully populated hemispherical transducer array with 256, 512, 1028, or 2048 elements and used that for 3D imaging. These transducer arrays are expensive and require a sophisticated data acquisition unit. Other groups have used much smaller number of transducers with a rotating mechanism which eventually filled out the entire hemisphere. We have built a 3D hemispherical array with 28 transducers which are placed on a 3D printed dome-like unit. The location of transducers however may be off-placed by a few millimeters (due to human error and errors in 3D printing). This may be to defocus the reconstructed image if the acceptable positions of transducers are not selected. In this work, we developed a compensation algorithm for misplacement of these transducers using Cuckoo search (CS) algorithm. The CS algorithm finds the optimum location for the transducers using levy flight which relies on levy distribution. The optimum location of each of these transducers is found within -4 mm to 4 mm of their locations. Universal back projection algorithm was used for image reconstruction and the sharpness of 3D image was used as the cost function; additionally, two more objective functions, the Brenner gradient, and the Tenenbaum gradient was investigated.
Full-waveform inversion (FWI) is an imaging technique that exploits the full information content of waves, including all the phases and their relative amplitude, to get a much higher resolution than tomographic methods, which only exploit a small fraction of the data. Over the last decade, FWI has reached maturity and emerged as the leading seismic imaging technique, along with the continuous development of high-performance computing. This trend also contributes to extending FWI towards new fields such as medical imaging. In this paper, we have developed a 2D extended formulation of FWI based on the alternating direction method of multipliers (ADMM) to estimate the speed of sound (SOS) and acoustic attenuation inside a heterogeneous medium from a circular array of 128 ultrasonic transducers. Our Extended 2D FWI has shown promising results when it is compared with travel time tomography and the classical formulation of FWI.
This study introduces a novel and powerful algorithm for optoacoustic tomography (OAT) in heterogeneous optical scattering media surrounded by optical fibers and ultrasonic transducers in a ring arrangement. The proposed algorithm uses the extended formulation of full-waveform inversion (FWI) based on the alternating direction method of multipliers (ADMM) and fluence compensation (FC). The speed of sound (SOS) map is required in this algorithm as prior information to perform classification and find different regions in the SOS map with equal optical absorption coefficients. The SOS map can be extracted by another FWI procedure applied to the acoustic data generated and recorded by transducers. The fluence map was calculated by Zemax inside the medium at near-infrared (NIR) optical wavelength. Finally, the proposed algorithm iteratively updates the optical absorption coefficients until the data computed with the estimated coefficients match the recorded photoacoustic signals at ultrasonic transducers. This approach shows extremely better results than classical time-reversal algorithms.
We have developed a fast, wide field-of-view, simple-to-implement laser scanning photoacoustic microscopy (PAM) system that is capable of imaging of the whole rat brain in < 1s. The system utilizes galvo scanners and a novel scanning scheme, that can counter the trade off between imaging speed and scanning area. We performed in-vivo imaging of rat brain to demonstrate the imaging capability of the system.
Photoacoustic imaging modality is a new biomedical imaging which provides images with high resolution and contrast from different parts of body. In this paper, we have designed a new optical system by using a fiber bundle in order to imaging of a hemorrhage inside of the infant's head. We used Monte Carlo algorithm to simulate light propagation in the infant's head, an acoustic k-space method to simulate photoacoustic signal propagation in it, and time reversal image reconstruction algorithm to get 3D image of the hemorrhage. According to our simulation, this new optical system can provides homogeneous illumination on the infant's head Leads to more accurate images. Furthermore, we have designed and optimized an optical system in order to coupling light from laser source into a fiber bundle with more than 94% efficiency.
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