Real-time Ultrasound System Research Articles

Optimization of classifying accurate and misarticulated speech sounds for use in a gamified real-time ultrasound biofeedback system

Integrating ultrasound biofeedback therapy (UBT) into a real-time, gamified interface to provide articulatory feedback for speech remediation promotes an external focus of attention, thereby reducing the complex cognitive demands required for standard UBT. Previous studies have shown that accuracy of American English rhotic /r/ can be predicted by a single parameter, the difference between tongue dorsum and blade displacements measured by ultrasound imaging during speech production. This parameter has classified speech productions of rhotic syllables as correct versus misarticulated with a classification accuracy up to 85%. However, implementation of this classification approach into real-time gamified UBT, including both measurement timing and establishment of difficulty levels for progressive therapy, would benefit from optimization using a larger dataset. 2,450 productions of 10 distinct rhotic syllables (including prevocalic and postvocalic contexts) from 50 children, with and without misarticulations, were analyzed. For each production, ultrasound image sequences were processed by TonguePART software to acquire tongue displacement trajectories, and accuracy was judged by trained listeners using a visual analog scale. Analyses were conducted to optimize selection of the image frame for classification, determine parameter thresholds appropriate for real-time prediction of /r/ production accuracy, and integrate these thresholds into a difficulty level design for gamified UBT.

Requirements and Hardware Limitations of High-Frame-Rate 3-D Ultrasound Imaging Systems

The spread of high frame rate and 3-D imaging techniques has raised pressing requirements for ultrasound systems. In particular, the processing power and data transfer rate requirements may be so demanding to hinder the real-time (RT) implementation of such techniques. This paper first analyzes the general requirements involved in RT ultrasound systems. Then, it identifies the main bottlenecks in the receiving section of a specific RT scanner, the ULA-OP 256, which is one of the most powerful available open scanners and may therefore be assumed as a reference. This case study has evidenced that the “star” topology, used to digitally interconnect the system’s boards, may easily saturate the data transfer bandwidth, thus impacting the achievable frame/volume rates in RT. The architecture of the digital scanner was exploited to tackle the bottlenecks by enabling a new “ring“ communication topology. Experimental 2-D and 3-D high-frame-rate imaging tests were conducted to evaluate the frame rates achievable with both interconnection modalities. It is shown that the ring topology enables up to 4400 frames/s and 510 volumes/s, with mean increments of +230% (up to +620%) compared to the star topology.

Hardware Fusion with PET/CT in a Real-Time Ultrasound Navigation System Increases the Yield of Ultrasound-Guided Fine-Needle Cytology in Head and Neck Cancer

Hardware Fusion with PET/CT in a Real-Time Ultrasound Navigation System Increases the Yield of Ultrasound-Guided Fine-Needle Cytology in Head and Neck Cancer

Ovarian follicular dynamics in Boran and Crossbred heifers in Ethiopia: Implications for assisted reproductive techniques

The study was conducted to characterize the follicular dynamics of purebred Boran (Bos indicus) and Boran * Holstein Friesian crossbred heifers during estrous cycles; for use in ovum pick up and in-vitro embryo production. Insight of reproductive physiology of cattle would help to understand and exploit the reproductive potential of elite animals for breed improvement. Follicular development, growth and atresia during estrous cycles were evaluated using a trans-rectal real-time B-mode ultrasound system for three consecutive estrus cycles. Luteal activity was evaluated by serum progesterone level. Follicular aspirations were done to investigate the potential of Boran cattle and their crosses for transvaginal oocyte production; using a vacuum pressure pump and Aloka SSD Prosound-2 ultrasound device. Boran heifers (n=15) manifested two (n = 6, 40%), three (n = 5, 33%), four (n= 3, 20%) and five (n=1, 6.7%) follicular waves. Crossbred heifers (n=14) showed one (n= 2, 14%), two (n= 6, 43%) and three (n= 6, 43%) follicular waves. Interovulatory interval was 21.1 ± 3.4 and 21.4 ± 2.7 days for Boran (n=45) and crossbred (n=42) heifers, respectively. The progesterone level in Boran and Crossbred heifers during diestrus was 9.5 ± 11.0 and 4.6 ± 8.8 ng/ml, respectively. The maximum diameter of the ovulatory follicle for crossbred heifers was higher (15.4 ± 1.6 mm) than the diameter of the Boran (14.0 ± 1.9 mm) heifers (p<0.005). Differences (p<0.005) were observed in the size of both right (26.6 ± 5.14 and 28.6 ± 5.1 mm) and left (21.7 ± 4.85 and 24.1 ± 5.07 mm) ovaries of Boran and Crossbred heifers, respectively. Difference (p<0.005) was also observed in follicular count of the right ovaries of Boran (4.84 ± 1.96) and Crossbred (5.13 ± 2.05) heifers. Oocyte recovery rate in once weekly collection scheme for Boran and their crossbred heifers was (n=19, 42.08%) and (n=17, 42.55%), respectively. The recovery rate for twice weekly collection scheme was (n=24, 34.53%) and (n=23, 40.44%) for Boran and crossbred heifers, respectively. Follicular dynamics in Boran heifers is characterized by a higher incidence of cycles with two, three and four waves, associated with a low persistence of the dominant follicles; and smaller size of ovulatory follicles and less intense heat signs from their crossbred counterpart. Boran heifers proved to have potential for comparable number of follicular population and ease of aspiration procedures that can be tapped for advancedreproductive techniques.
 Keywords: Estrus cycle; follicular wave; ovarian follicle; ovum pickup; ultrasound.

Automated Needle Digitization in Ultrasound-based Prostate High Dose-rate Brachytherapy Using a Deep Learning Algorithm

Prostate high dose-rate brachytherapy (HDR) delivers the radiation using a radioactive Ir-192 seed through interstitial needles and the needle implants are guided by a real-time ultrasound (US) imaging system. The success of this therapy relies highly on accurate digitization of the needles in the treatment planning US images. In current clinical procedures, the needles' trajectories are manually labeled by physicists, which is time-consuming and prone to errors. In recent years, deep learning techniques have brought many breakthroughs, especially in medical imaging processing. We thus propose a deep learning-based method to segment the needles accurately in the US images. The training data including the US images, needle positions and treatment plans were collected from the clinical database with IRB approval. Before training, images in the Cartesian coordinate were transferred into the polar plane and then split into smaller batches so that each contains one needle. Data augmentation techniques were used to avoid overfitting. The needle segmented neural network was based on U-Net with an encoder-decoder structure and shortcuts connecting directly the encoder layers and the corresponding decoder ones. The network structure and parameters were optimized for the needle segmentation problem. To estimate the positions of the needle tips, a separate convolutional neural network with the architecture of Vgg16 was developed and the 3D position accuracy was obtained. Data from 441 patients and 13200 needles was utilized. The needle trajectories were successfully segmented with mean errors of 0.67 mm and 0.32 mm in left-right (X) and anterior-posterior (Y) directions of the original US images and the estimation errors within 2 mm in X and Y directions are 95.4% and 99.2%, respectively. As for the needle tip localization, the positioning accuracies in X, Y, and Z (superior-inferior) are 0.72 mm, 0.37 mm and 1.88 mm, with 94.2%, 98.3% and 67.5% of the data have error of less than 2 mm, respectively. A novel method based on deep learning and neural networks was successfully developed to digitize HDR brachytherapy needles automatically. This method can be served as a valuable tool during brachytherapy procedures and has the potential to improve the efficiency and quality of treatment delivery, contributing overall to the patient care.

Towards clinical photoacoustic and ultrasound imaging: Probe improvement and real-time graphical user interface.

Photoacoustic imaging is a non-invasive and non-ionizing biomedical technique that has been investigated widely for various clinical applications. By taking the advantages of conventional ultrasound imaging, hand-held operation with a linear array transducer should be favorable for successful clinical translation of photoacoustic imaging. In this paper, we present new key updates contributed to the previously developed real-time clinical photoacoustic and ultrasound imaging system for improving the clinical usability of the system. We developed a seamless image optimization platform, designed a real-time parameter control software with a user-friendly graphical user interface, performed Monte Carlo simulation of the optical fluence in the imaging plane, and optimized the geometry of the imaging probe. The updated system allows optimizing of all imaging parameters while continuously acquiring the photoacoustic and ultrasound images in real-time. The updated system has great potential to be used in a variety of clinical applications such as assessing the malignancy of thyroid cancer, breast cancer, and melanoma. Impact statement Photoacoustic imaging is a promising biomedical imaging modality that can visualize both structural and functional information of biological tissue. Because of its easiness to be integrated with conventional ultrasound imaging systems, numerous studies have been conducted to develop and apply clinical photoacoustic imaging systems. However, most of the systems were not suitable for general-purpose clinical applications due to one of the following reasons: target specific design, immobility, inaccessible operation sequence, and lack of hand-held operation. This study demonstrates a real-time clinical photoacoustic and ultrasound imaging system, which can overcome the limitations of the previous systems for successful clinical translation.

Co-registered photoacoustic and ultrasound imaging of human colorectal cancer.

.Colorectal cancer is the second most common malignancy diagnosed globally. Critical gaps exist in diagnostic and surveillance imaging modalities for colorectal neoplasia. Although prior studies have demonstrated the capability of photoacoustic imaging techniques to differentiate normal from neoplastic tissue in the gastrointestinal tract, evaluation of deep tissue with a fast speed and a large field of view remains limited. To investigate the ability of photoacoustic technology to image deeper tissue, we conducted a pilot study using a real-time co-registered photoacoustic tomography (PAT) and ultrasound (US) system. A total of 23 ex vivo human colorectal tissue samples were imaged immediately after surgical resection. Co-registered photoacoustic images of malignancies showed significantly increased PAT signal compared to normal regions of the same sample. The quantitative relative total hemoglobin (rHbT) concentration computed from four optical wavelengths, the spectral features, such as the mean spectral slope, and 0.5-MHz intercept extracted from PAT and US spectral data, and image features, such as the first- and second-order statistics along with the standard deviation of the mean radon transform of PAT images, have shown statistical significance between untreated colorectal tumors and the normal tissue. Using either a logistic regression model or a support vector machine, the best set of parameters of rHbT and PAT intercept has achieved area-under-the-curve (AUC) values of 0.97 and 0.95 for both training and testing data sets, respectively, for prediction of histologically confirmed invasive carcinoma.

Development of Super-Resolution Sharpness-Based Axial Localization for Ultrasound Imaging

Super-resolution ultrasound mostly uses image-based methods for the localization of single scatterers. These methods are largely based on the center of mass (COM) calculation. Sharpness-based localization is an alternative to COM for scatterer localization in the axial direction. Simulated ultrasound point scatterer data (center frequency $f_{0} = 7$ MHz and wavelength $\lambda = 220\,\,\mu \text{m}$ ) showed that the normalized sharpness method can provide scatterer axial localization with an accuracy down to $2~\mu \text{m}$ ( $ ), which is a two-order of magnitude improvement compared to that achievable by the conventional imaging ( $\approx \lambda $ ), and a five-fold improvement compared to the COM estimate ( $\approx 10~\mu \text{m}$ or $0.05\lambda $ ). Similar results were obtained experimentally using wire-target data acquired by the Synthetic Aperture Real-time Ultrasound System. The performance of the proposed method was also found to be consistent across different types of ultrasound transmission. The localization precision deteriorates in the presence of noise, but even in very low signal-to-noise ratio (SNR = 0 dB), the uncertainty was not higher than $6~\mu \text{m}$ , which outperforms the COM estimate. The method can be implemented in image data as well as by using the raw signals. It is proposed that the signal-derived localization should replace the image-based equivalent, as it provides at least 10 times improved accuracy.

Resolving Ultrasound Contrast Microbubbles Using Minimum Variance Beamforming.

Minimum Variance (MV) beamforming is known to improve the lateral resolution of ultrasound images and enhance the separation of isolated point scatterers. This paper aims to evaluate the adaptive beamformer's performance with flowing microbubbles (MBs) which are relevant to super-resolution ultrasound imaging. Simulations using point scatterer data from single emissions were complemented by an experimental investigation performed using a capillary tube phantom and the Synthetic Aperture Real-time Ultrasound System (SARUS). The MV performance was assessed by the minimum distance that allows the display of two scatterers positioned side-by-side, the lateral Full-Width-at-Half-Maximum (FWHM), and the Peak-Sidelobe-Level (PSL). In the tube, scatterer responses separated by down to [Formula: see text] (or 1.05λ ) were distinguished by the MV method, while the standard Delay-And-Sum (DAS) beamformers were unable to achieve such separation. Up to ninefold FWHM decrease was also measured in favor of the MV beamformer for individual echoes from MBs. The lateral distance between two scatterers impacted on their FWHM value, and additional differences in the scatterers' axial or out-of-plane position also impacted on their size and appearance. The simulation and experimental results were in agreement in terms of lateral resolution. The point scatterer study showed that the proposed MV imaging scheme provided clear resolution benefits compared to DAS. Current super-resolution methods mainly depend on DAS beamformers. Instead, the use of the MV method may provide a larger number of detected, and potentially better localized, MB scatterers.

Handheld Real-Time LED-Based Photoacoustic and Ultrasound Imaging System for Accurate Visualization of Clinical Metal Needles and Superficial Vasculature to Guide Minimally Invasive Procedures.

Ultrasound imaging is widely used to guide minimally invasive procedures, but the visualization of the invasive medical device and the procedure’s target is often challenging. Photoacoustic imaging has shown great promise for guiding minimally invasive procedures, but clinical translation of this technology has often been limited by bulky and expensive excitation sources. In this work, we demonstrate the feasibility of guiding minimally invasive procedures using a dual-mode photoacoustic and ultrasound imaging system with excitation from compact arrays of light-emitting diodes (LEDs) at 850 nm. Three validation experiments were performed. First, clinical metal needles inserted into biological tissue were imaged. Second, the imaging depth of the system was characterized using a blood-vessel-mimicking phantom. Third, the superficial vasculature in human volunteers was imaged. It was found that photoacoustic imaging enabled needle visualization with signal-to-noise ratios that were 1.2 to 2.2 times higher than those obtained with ultrasound imaging, over insertion angles of 26 to 51 degrees. With the blood vessel mimicking phantom, the maximum imaging depth was 38 mm. The superficial vasculature of a human middle finger and a human wrist were clearly visualized in real-time. We conclude that the LED-based system is promising for guiding minimally invasive procedures with peripheral tissue targets.

Directional Transverse Oscillation Vector Flow Estimation.

A method for estimating vector velocities using transverse oscillation (TO) combined with directional beamforming is presented. In directional TO (DTO), a normal focused field is emitted and the received signals are beamformed in the lateral direction transverse to the ultrasound beam to increase the amount of data for vector velocity estimation. The approach is self-calibrating as the lateral oscillation period is estimated from the directional signal through a Fourier transform to yield quantitative velocity results over a large range of depths. The approach was extensively simulated using Field IIpro and implemented on the experimental Synthetic Aperture Real-time Ultrasound System (SARUS) scanner in connection with a BK Medical 8820e convex array transducer. Velocity estimates for DTO are found for beam-to-flow angles of 60°, 75°, and 90°, and vessel depths from 24 to 156 mm. Using 16 emissions, the standard deviation (SD) for angle estimation at depths ranging from 24 to 104 mm is between 6.01° and 0.93° with a mean SD of 2.8°. The mean relative SD for the lateral velocity component is 9.2% and the mean relative bias -3.4% or four times lower than for traditional TO. The approach also works for deeper lying vessels with a slight increase in SD to 15.7%, but a maintained bias of -3.5% from 126 to 156 mm. Data for a pulsating flow have also been acquired for 15 cardiac cycles using a CompuFlow 1000 pump. The relative SD was here 7.4% for a femoral artery waveform.

A Review on Real-Time 3D Ultrasound Imaging Technology.

Real-time three-dimensional (3D) ultrasound (US) has attracted much more attention in medical researches because it provides interactive feedback to help clinicians acquire high-quality images as well as timely spatial information of the scanned area and hence is necessary in intraoperative ultrasound examinations. Plenty of publications have been declared to complete the real-time or near real-time visualization of 3D ultrasound using volumetric probes or the routinely used two-dimensional (2D) probes. So far, a review on how to design an interactive system with appropriate processing algorithms remains missing, resulting in the lack of systematic understanding of the relevant technology. In this article, previous and the latest work on designing a real-time or near real-time 3D ultrasound imaging system are reviewed. Specifically, the data acquisition techniques, reconstruction algorithms, volume rendering methods, and clinical applications are presented. Moreover, the advantages and disadvantages of state-of-the-art approaches are discussed in detail.

Synthetic Aperture Ultrasound Fourier Beamformation Using Virtual Sources.

An efficient Fourier beamformation algorithm is presented for multistatic synthetic aperture ultrasound imaging using virtual sources. The concept is based on the frequency domain wavenumber algorithm from radar and sonar and is extended to a multielement transmit/receive configuration using virtual sources. Window functions are used to extract the azimuth processing bandwidths and weight the data to reduce side lobes in the final image. Field II simulated data and SARUS (Synthetic Aperture Real-time Ultrasound System) measured data are used to evaluate the results in terms of point spread function, resolution, contrast, signal-to-noise ratio, and processing time. Lateral resolutions of 0.53 and 0.66 mm are obtained for Fourier Beamformation Using Virtual Sources (FBV) and delay and sum (DAS) on point target simulated data. Corresponding axial resolutions are 0.21 mm for FBV and 0.20 mm for DAS. The results are also consistent over different depths evaluated using a simulated phantom containing several point targets at different depths. FBV shows a better lateral resolution at all depths, and the axial and cystic resolutions of -6, -12, and -20 dB are almost the same for FBV and DAS. To evaluate the cyst phantom metrics, three different criteria of power ratio, contrast ratio, and contrast-to-noise ratio have been used. Results show that the algorithms have a different performance in the cyst center and near the boundary. FBV has a better performance near the boundary; however, DAS is better in the more central area of the cyst. Measured data from phantoms are also used for evaluation. The results confirm applicability of FBV in ultrasound, and 20 times less processing time is attained in comparison with DAS. Evaluating the results over a wide variety of parameters and having almost the same results for simulated and measured data demonstrates the ability of FBV in preserving the quality of image as DAS, while providing a more efficient algorithm with 20 times less computations.

Development of a real-time lumbar ultrasound image processing system for epidural needle entry site localization.

A fully-automatic ultrasound image processing system that can determine the needle entry site for epidural anesthesia (EA) in real time is presented in this paper. Neither the knowledge of anesthetists nor additional hardware is required to operate the system, which firstly directs the anesthetists to reach the desired insertion region in the longitudinal view, i.e., lumbar level L3-L4, and then locates the ideal puncture site by instructing the anesthetists to rotate and slightly adjust the position of ultrasound probe. In order to implement these functions, modules including image processing, panorama stitching, feature extraction/selection, template matching and support vector machine (SVM) classification are incorporated in this system. Additionally, a user-friendly graphical user interface (GUI), which displays the processing results and guides anesthetists intuitively, is further designed to conceal the intricacy of algorithms. Feasibility and effectiveness of the proposed system has been evaluated through a set of realtime tests on 53 volunteers from a local hospital.

Development of a Wireless and Near Real-Time 3D Ultrasound Strain Imaging System.

Ultrasound elastography is an important medical imaging tool for characterization of lesions. In this paper, we present a wireless and near real-time 3D ultrasound strain imaging system. It uses a 3D translating device to control a commercial linear ultrasound transducer to collect pre-compression and post-compression radio-frequency (RF) echo signal frames. The RF frames are wirelessly transferred to a high-performance server via a local area network (LAN). A dynamic programming strain estimation algorithm is implemented with the compute unified device architecture (CUDA) on the graphic processing unit (GPU) in the server to calculate the strain image after receiving a pre-compression RF frame and a post-compression RF frame at the same position. Each strain image is inserted into a strain volume which can be rendered in near real-time. We take full advantage of the translating device to precisely control the probe movement and compression. The GPU-based parallel computing techniques are designed to reduce the computation time. Phantom and in vivo experimental results demonstrate that our system can generate strain volumes with good quality and display an incrementally reconstructed volume image in near real-time.

Safety Assessment of Advanced Imaging Sequences I: Measurements.

A method for rapid measurement of intensities (I(spta)), mechanical index (MI), and probe surface temperature for any ultrasound scanning sequence is presented. It uses the scanner's sampling capability to give an accurate measurement of the whole imaging sequence for all emissions to yield the true distributions. The method is several orders of magnitude faster than approaches using an oscilloscope, and it also facilitates validating the emitted pressure field and the scanner's emission sequence software. It has been implemented using the experimental synthetic aperture real-time ultrasound system (SARUS) scanner and the Onda AIMS III intensity measurement system (Onda Corporation, Sunnyvale, CA, USA). Four different sequences have been measured: a fixed focus emission, a duplex sequence containing B-mode and flow emissions, a vector flow sequence with B-mode and flow emissions in 17 directions, and finally a SA duplex flow sequence. A BK8820e (BK Medical, Herlev, Denmark) convex array probe is used for the first three sequences and a BK8670 linear array probe for the SA sequence. The method is shown to give the same intensity values within 0.24% of the AIMS III Soniq 5.0 (Onda Corporation, Sunnyvale, CA, USA) commercial intensity measurement program. The approach can measure and store data for a full imaging sequence in 3.8-8.2 s per spatial position. Based on I(spta), MI, and probe surface temperature, the method gives the ability to determine whether a sequence is within U.S. FDA limits, or alternatively indicate how to scale it to be within limits.

Preliminary work of real-time ultrasound imaging system for 2-D array transducer.

Ultrasound (US) has emerged as a non-invasive imaging modality that can provide anatomical structure information in real time. To enable the experimental analysis of new 2-D array ultrasound beamforming methods, a pre-beamformed parallel raw data acquisition system was developed for 3-D data capture of 2D array transducer. The transducer interconnection adopted the row-column addressing (RCA) scheme, where the columns and rows were active in sequential for transmit and receive events, respectively. The DAQ system captured the raw data in parallel and the digitized data were fed through the field programmable gate array (FPGA) to implement the pre-beamforming. Finally, 3-D images were reconstructed through the devised platform in real-time.

Acoustic reciprocity of spatial coherence in ultrasound imaging.

A conventional ultrasound image is formed by transmitting a focused wave into tissue, time-shifting the backscattered echoes received on an array transducer, and summing the resulting signals. The van Cittert-Zernike theorem predicts a particular similarity, or coherence, of these focused signals across the receiving array. Many groups have used an estimate of the coherence to augment or replace the B-mode image in an effort to suppress noise and stationary clutter echo signals, but this measurement requires access to individual receive channel data. Most clinical systems have efficient pipelines for producing focused and summed RF data without any direct way to individually address the receive channels. We describe a method for performing coherence measurements that is more accessible for a wide range of coherence-based imaging. The reciprocity of the transmit and receive apertures in the context of coherence is derived and equivalence of the coherence function is validated experimentally using a research scanner. The proposed method is implemented on a commercial ultrasound system and in vivo short-lag spatial coherence imaging is demonstrated using only summed RF data. The components beyond the acquisition hardware and beamformer necessary to produce a real-time ultrasound coherence imaging system are discussed.

A fast minimum variance beamforming method using principal component analysis.

Minimum variance (MV) beamforming has been studied for improving the performance of a diagnostic ultrasound imaging system. However, it is not easy for the MV beamforming to be implemented in a real-time ultrasound imaging system because of the enormous amount of computation time associated with the covariance matrix inversion. In this paper, to address this problem, we propose a new fast MV beamforming method that almost optimally approximates the MV beamforming while reducing the computational complexity greatly through dimensionality reduction using principal component analysis (PCA). The principal components are estimated offline from pre-calculated conventional MV weights. Thus, the proposed method does not directly calculate the MV weights but approximates them by a linear combination of a few selected dominant principal components. The combinational weights are calculated in almost the same way as in MV beamforming, but in the transformed domain of beamformer input signal by the PCA, where the dimension of the transformed covariance matrix is identical to the number of some selected principal component vectors. Both computer simulation and experiment were carried out to verify the effectiveness of the proposed method with echo signals from simulation as well as phantom and in vivo experiments. It is confirmed that our method can reduce the dimension of the covariance matrix down to as low as 2 × 2 while maintaining the good image quality of MV beamforming.

Array-Based Real-Time Ultrasound and Photoacoustic Ocular Imaging

Although various ophthalmic imaging methods, including fundus photography and optical coherence tomography, have been applied for effective diagnosis of ocular diseases with high spatial resolution, most of them are limited by shallow imaging penetration depth and a narrow field of view. Also, many of those imaging modalities are optimized to provide microscopic anatomical information, while functional or cellular information is lacking. Compared to other ocular imaging modalities, photoacoustic imaging can achieve relatively deep penetration depth and provide more detailed functional and cellular data based on photoacoustic signal generation from endogenous contrast agents such as hemoglobin and melanin. In this paper, array-based ultrasound and photoacoustic imaging was demonstrated to visualize pigmentation in the eye as well as overall ocular structure. Fresh porcine eyes were visualized using a real-time ultrasound micro-imaging system and an imaging probe supporting laser pulse delivery. In addition, limited photoacoustic imaging field of view was improved by an imaging probe tilting method, enabling visualization of most regions of the retina covered in the ultrasound imaging.