Papers by Eduardo Gonzalez
Effect of Light Source Motion on Photoacoustic Image Quality and Safety
Frontiers in Optics + Laser Science 2022 (FIO, LS)
Subtle displacement of a light source during photoacoustic imaging reduces possible tissue damage... more Subtle displacement of a light source during photoacoustic imaging reduces possible tissue damage relative to a stationary source, without degrading image quality, which is promising for laser-safe photoacoustic-guided surgery.
Journal of Biomedical Optics
Significance: Methylene blue (MB) is an exogenous contrast agent that has the potential to assist... more Significance: Methylene blue (MB) is an exogenous contrast agent that has the potential to assist with visualization and penetration challenges in photoacoustic imaging. However, monitoring the local concentration between MB and endogenous chromophores is critical for avoiding unnecessary MB accumulations that could lead to adverse effects such as hemolysis when exposed to increased dose and photodamage when exposed to high laser energies. Aim: We developed a modified version of a previously proposed acoustic-based atlas method to estimate concentration levels from a mixture of two photoacoustic-sensitive materials after two laser wavelength emissions. Approach: Photoacoustic data were acquired from mixtures of 100-μM MB and either human or porcine blood (Hb) injected in a plastisol phantom, using laser wavelengths of 710 and 870 nm. An algorithm to perform linear regression of the acoustic frequency response from an atlas composed of pure concentrations was designed to assess the concentration levels from photoacoustic samples obtained from 11 known MB/Hb volume mixtures. The mean absolute error (MAE), coefficient of determination (i.e., R 2), and Spearman's correlation coefficient (i.e., ρ) between the estimated results and ground-truth labels were calculated to assess the algorithm performance, linearity, and monotonicity, respectively. Results: The overall MAE, R 2 , and ρ were 12.68%, 0.80, and 0.89, respectively, for the human Hb dataset and 9.92%, 0.86, and 0.93, respectively, for the porcine Hb dataset. In addition, a similarly linear relationship was observed between the acoustic frequency response at 2.3 MHz and 870-nm laser wavelength and the ground-truth concentrations, with R 2 and jρj values of 0.76 and 0.88, respectively. Conclusions: Contrast agent concentration monitoring is feasible with the proposed approach. The potential for minimal data acquisition times with only two wavelength emissions is advantageous toward real-time implementation in the operating room.
2021 43rd Annual International Conference of the IEEE Engineering in Medicine & Biology Society (EMBC), 2021
Crawling Waves Sonoelastography (CWS) is an ultrasound elastography approach for the Shear Waves ... more Crawling Waves Sonoelastography (CWS) is an ultrasound elastography approach for the Shear Waves Speed (SWS) estimation. Several studies show promising results for tissue characterization. The algorithms used to calculate the SWS have been commonly implemented considering an opposing vibration sources to the side of the tissue of interest. However, implementing this mechanical setup has important limitations considering the geometry of the body. For that reason, a propagation from the top to the surface can be useful. Previous estimators such as Phase Derivative have been modified and tested in phantom studies, however, the presences of artifacts limited the performed of the SWS map. In this study, the Regularized Wavelength Average Velocity Estimator (R-WAVE) technique is modified and evaluated (RWm) to be used for normal propagation. The results of heterogeneous simulations and phantoms experiments showed consistent results with the literature (ie:
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
The successful integration of computer vision, robotic actuation, and photoacoustic imaging to fi... more The successful integration of computer vision, robotic actuation, and photoacoustic imaging to find and follow targets of interest during surgical and interventional procedures requires accurate photoacoustic target detectability. This detectability has traditionally been assessed with image quality metrics, such as contrast, contrast-to-noise ratio, and signal-to-noise ratio (SNR). However, predicting target tracking performance expectations when using these traditional metrics is difficult due to unbounded values and sensitivity to image manipulation techniques like thresholding. The generalized contrast-to-noise ratio (gCNR) is a recently introduced alternative target detectability metric, with previous work dedicated to empirical demonstrations of applicability to photoacoustic images. In this article, we present theoretical approaches to model and predict the gCNR of photoacoustic images with an associated theoretical framework to analyze relationships between imaging system parameters and computer vision task performance. Our theoretical gCNR predictions are validated with histogram-based gCNR measurements from simulated, experimental phantom, ex vivo, and in vivo datasets. The mean absolute errors between predicted and measured gCNR values ranged from 3.2 × 10 −3 to 2.3 × 10 −2 for each dataset, with channel SNRs ranging −40 to 40 dB and laser energies ranging 0.07 µJ to 68 mJ. Relationships among gCNR, laser energy, target and background image parameters, target segmentation, and threshold levels were also investigated. Results provide a promising foundation to enable predictions of photoacoustic gCNR and visual servoing segmentation accuracy. The efficiency of precursory surgical and interventional tasks (e.g., energy Manuscript
Photons Plus Ultrasound: Imaging and Sensing 2021, 2021
In spinal fusion surgeries, it is critical to maintain correct trajectories during the process of... more In spinal fusion surgeries, it is critical to maintain correct trajectories during the process of creating pedicle holes for screw insertion, in order to avoid accidental bone breaches and screw misplacement, which are characterized by screws placed within surrounding cortical bone rather than the cancellous core of the pedicle. One key difference between these two bone types is the greater porosity of the cancellous bone when compared to the more dense, more compact cortical bone. This work investigates the feasibility of using photoacoustic imaging to differentiate cortical from cancellous bone in the lumbar vertebrae of an intact human cadaver, with the ultimate goal of developing a novel photoacoustic surgical system to prevent breaches. Eleven pedicle cannulations were performed in the lumbar vertebrae of a human cadaver, including six holes in the cancellous core and five partial or complete breaches of surrounding cortical bone. Amplitude-based delay-and-sum (DAS), coherencebased short-lag spatial coherence (SLSC), and locally weighted SLSC (LW-SLSC) beamforming were used to characterize differences in the morphology of photoacoustic signals originating from cancellous and cortical bone. Statistically significant differences between the median of measured areas from cortical and cancellous bone measured 6.61 mm 2 for -6 dB contours obtained with DAS beamforming and ranged from 2.89 mm 2 to 42.13 mm 2 for -10 dB and -15 dB contours obtained with DAS, SLSC, and LW-SLSC beamforming (p<0.001). In addition, coherence-based photoacoustic imaging enabled localization of the tip of the optical fiber that was inserted into each prepared pedicle hole. Therefore, both DAS and SLSC beamforming has the potential to synergystically detect the tip of surgical tools and differentiate between signals originating from cortical and cancellous bone. These results are promising for surgical guidance within the desired cancellous core of the pedicle and away from the surrounding cortical bone, in order to avoid costly and painful bone breaches during surgery.
Frontiers in Photonics, 2021
Spectral unmixing techniques for photoacoustic images are often used to isolate signal origins (e... more Spectral unmixing techniques for photoacoustic images are often used to isolate signal origins (e.g., blood, contrast agents, lipids). However, these techniques often require many (e.g., 12–59) wavelength transmissions for optimal performance to exploit the optical properties of different biological chromophores. Analysis of the acoustic frequency response of photoacoustic signals has the potential to provide additional discrimination of photoacoustic signals from different materials, with the added benefit of potentially requiring only a few optical wavelength emissions. This study presents our initial results testing this hypothesis in a phantom experiment, given the task of differentiating photoacoustic signals from deoxygenated hemoglobin (Hb) and methylene blue (MB). Coherence-based beamforming, principal component analysis, and nearest neighbor classification were employed to determine ground-truth labels, perform feature extraction, and classify image contents, respectively. ...
Optimization of a dual wavelength atlas technique to differentiate methylene blue from hemoglobin in photoacoustic signals
Photons Plus Ultrasound: Imaging and Sensing 2022, 2022
2020 IEEE International Ultrasonics Symposium (IUS), 2020
Spectral unmixing techniques for photoacoustic images are often used to isolate signal origins (e... more Spectral unmixing techniques for photoacoustic images are often used to isolate signal origins (e.g., blood, contrast agents, lipids). However, these techniques tend to exploit the optical properties of different biological chromophores and do not typically consider acoustic properties. Analysis of the acoustic frequency response of photoacoustic signals has the potential to provide additional discrimination of photoacoustic responses from different materials, with the added benefit of potentially requiring few optical wavelength emissions. This study presents our initial results testing this hypothesis in a phantom experiment, given the task of differentiating between photoacoustic signals from deoxygenated hemoglobin (Hb) and methylene blue (MB). Coherence-based beamforming, principal component analysis, and nearest neighbor classification were employed to determine ground-truth labels, perform feature extraction, and classify image contents, respectively. The mean ± one standard deviation of classification accuracy was increased from 0.67 ± 0.05 to 0.81 ± 0.11 when increasing the number of wavelength emissions from one to two, respectively. When using an optimal laser wavelength pair of 690 and 870 nm, the sensitivity and specificity of detecting MB over Hb were 1.00 and 1.00, respectively. Results are highly promising for the differentiation of photoacoustic-sensitive materials with comparable performance to that achieved with a more conventional multispectral laser wavelength approach.
IEEE Transactions on Biomedical Engineering, 2021
2021 43rd Annual International Conference of the IEEE Engineering in Medicine & Biology Society (EMBC), 2021
Crawling Wave Sonoelastography (CWS) is an elastography ultrasound-based imaging approach that pr... more Crawling Wave Sonoelastography (CWS) is an elastography ultrasound-based imaging approach that provides tissue stiffness information through the calculation of Shear Wave Speed (SWS). Many SWS estimators have been developed; however, they report important limitations such as the presence of artifacts, border effects or high computational cost. In addition, these techniques require a moving interference pattern which could be challenging for in vivo applications. In this study, a new estimator based on the Continuous Wavelet Transform (CWT) is proposed. This allows the generation of a SWS image for every sonoelasticity video frame. Testing was made with data acquired from experiments conducted on a gelatin phantom with a circular inclusion. It was excited with two vibration sources placed at both sides with frequencies ranging from 200 Hz to 360 Hz in steps of 20 Hz. Results show small variation of the SWS image across time. Additionally, images were compared with the Phase Derivative method (PD) and the Regularized Wavelength Average Velocity Estimator (R-WAVE). Similar SWS values were obtained for the three estimators within a certain region of interest in the inclusion (At 360 Hz, CWT: 5.01±0.2m/s, PD: 5.11±0.28m/s, R-WAVE: 4.51±0.62m/s) and in the background (At 360 Hz, CWT: 3.67±0.15m/s, PD: 3.69±0.23m/s, R-WAVE: 3.58±0.24m/s). CWT also presented the lowest coefficient of variation and the highest contrast-to-noise ratio for most frequencies, which allows better discrimination between regions. Clinical relevance-This study presents a new Shear Wave Speed estimator for Crawling Wave Sonoelastography, which can be useful to characterize soft tissue and detect lesions.
Registration of multimodal images is a powerful tool for transferring preoperative plans into an ... more Registration of multimodal images is a powerful tool for transferring preoperative plans into an intraoperative environment, thereby enhancing the surgeons accuracy to localize instruments in the operating room. Intraoperative ultrasound (US) to preoperative Computer Tomography (CT) registration is often a challenging task due to multiple factors, including the low signal-to-noise ratio of the US images and the presence of artifacts. This work explores Short Lag Spatial Coherence (SLSC) beamforming as an alternative to traditional Delay-And-Sum (DAS) ultrasound images to increase contrast and resolution for US-to-CT registration tasks. . The objective of this work is to explore Short-Lag Spatial Coherence (SLSC) beamforming as an alternative to delay-and-sum (DAS) beamforming to reduce speckle noise and enhance bone boundaries. In addition, we propose Locally Weighted SLSC (LW-SLSC) beamforming to further improve bone segmentation.
A beamformer-independent method to predict photoacoustic visual servoing system failure from a single image frame
2021 IEEE International Ultrasonics Symposium (IUS), 2021
A novel portable device for crawling waves sonoelastography: experimental study
15th International Symposium on Medical Information Processing and Analysis, 2020
Crawling Waves Sonoelastography (CWS) is an elastography technique based on an interference patte... more Crawling Waves Sonoelastography (CWS) is an elastography technique based on an interference pattern produced by the application of two external vibration sources. In this study, a 3D printed holder was designed to overcome the compatibility limitations of normal excitation modules for different ultrasound systems, previously developed in the literature. This holder was assembled with a transducer and two voice coil actuators, and its performance was tested in homogeneous and inclusion tissue-mimicking phantom. A phase derivative estimator was used to reconstruct the shear wave speed (SWS) map. The coefficient of variation (CV), bias and contrast- to-noise ratio (CNR) were used as quantitative metrics for comparison. These metrics have shown a comparable SWS estimation in the background (SWSb) of the homogeneous phantom with previous studies (e.g. SWSb = 3.58± 0.42 m/s). In the same way, the SWS of the inclusion (SWSi) was distinguished from the background with an accurate SWS value (e.g. SWSi = 5.64 ±0.42 m/s and SWSb = 3.70 ±0.16 m/s). The results suggest that the portable device is capable of achieving a good performance according to their values of bias, CV and CNR. The extension of this work is oriented to ex vivo and in vivo experiments.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control, Jan 23, 2018
Imaging of musculoskeletal tissue dynamics is currently an exploratory field with the goal of aid... more Imaging of musculoskeletal tissue dynamics is currently an exploratory field with the goal of aiding rehabilitation and performance evaluation of pathological or asymptomatic patients. In this pilot study, initial elasticity assessments of the biceps bracchi was conducted in a novel Crawling Wave Sonoelastography (CWS) system implemented on a research ultrasound instrument with GPU capabilities, displaying quantitative elasticity values at 4 FPS. The CWS system computes the tissue stiffness with the generation of a interference pattern from external vibrators, which can overcome depth limitations of imaging systems with internal excitation sources. Validation on gelatin-based phantoms reported low bias of elasticity values (4.7%) at low excitation frequencies. Preliminary results on in vivo muscle characterization are in accordance with average elasticity values for relaxed and contracted tissues found in the literature, as well for a range of weight loads.
A comparative study between parallel and normal excitation for crawling wave sonoelastography
12th International Symposium on Medical Information Processing and Analysis, 2017
Crawling wave sonoelastography (CWS) provides quantitative stiffness information from an examined... more Crawling wave sonoelastography (CWS) provides quantitative stiffness information from an examined tissue by the application of two mechanical vibrations that generates an interference pattern which is analyzed to reconstruct a shear wave speed (SWS) image. While CWS performance using parallel excitation setup (PES) has been widely studied in the literature, its implementation is complicated to apply in tissue (i.e. breast, liver) of the technique in human tissue often requires a normal excitation setup. The aim of this study is to validate the SWS estimation using a normal excitation setup with two different types of coupling attachments for the surface -i.e. surface plate (SP), rounded head (RH)- and perform a quantitative comparison among the three techniques (PES,SP,RH) in homogeneous and heterogeneous gelatin phantoms. The comparison of the three excitation methods was performed using signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), coefficient of variation(CV) and bias over a range of excitation frequencies. (PES:3.74 ±0.14 m/s, SP: 3.43 ±0.14 m/s and RH: 3.32 ± 0.07 m/s) and in the inclusion (PES:4.96 ± 0.18 m/s, SP: 4.88 ± 0.32 m/s and RH: 4.64 ± 0.29 m/s) show that both normal excitation setups are comparable to the PES to estimate the SWS. This suggests that this type of setup could be used for ex vivo and in vivo analysis.
2016 IEEE 13th International Symposium on Biomedical Imaging (ISBI), 2016
A number of shear wave speed estimators have been developed for crawling wave sonoelastography. I... more A number of shear wave speed estimators have been developed for crawling wave sonoelastography. In this study, a new low-cost estimator based on spatial wavelength averaging along the slow-time domain is presented while assessing its performance through gelatin-based inclusion and homogeneous phantoms. Results showed favorable estimation mean accuracy (93.8%) on the homogeneous phantoms at different concentrations. However, underestimation is present in stiffer inclusions with size smaller than the true wavelength of the interference pattern (83.4% mean accuracy). Still, the new approach's differentiation of stiffness allows rapid visualization of a tissue as a qualitative imaging technique. Moreover, the estimator results are suitable for further processing as a reference mask implemented in several shear wave speed estimators.
Journal of Biomedical Optics, 2020
Significance: Photoacoustic-based visual servoing is a promising technique for surgical tool tip ... more Significance: Photoacoustic-based visual servoing is a promising technique for surgical tool tip tracking and automated visualization of photoacoustic targets during interventional procedures. However, one outstanding challenge has been the reliability of obtaining segmentations using low-energy light sources that operate within existing laser safety limits. Aim: We developed the first known graphical processing unit (GPU)-based real-time implementation of short-lag spatial coherence (SLSC) beamforming for photoacoustic imaging and applied this real-time algorithm to improve signal segmentation during photoacoustic-based visual servoing with low-energy lasers. Approach: A 1-mm-core-diameter optical fiber was inserted into ex vivo bovine tissue. Photoacoustic-based visual servoing was implemented as the fiber was manually displaced by a translation stage, which provided ground truth measurements of the fiber displacement. GPU-SLSC results were compared with a central processing unit (CPU)-SLSC approach and an amplitude-based delay-and-sum (DAS) beamforming approach. Performance was additionally evaluated with in vivo cardiac data. Results: The GPU-SLSC implementation achieved frame rates up to 41.2 Hz, representing a factor of 348 speedup when compared with offline CPU-SLSC. In addition, GPU-SLSC successfully recovered low-energy signals (i.e., ≤268 μJ) with mean ± standard deviation of signal-to-noise ratios of 11.2 AE 2.4 (compared with 3.5 AE 0.8 with conventional DAS beamforming). When energies were lower than the safety limit for skin (i.e., 394.6 μJ for 900-nm wavelength laser light), the median and interquartile range (IQR) of visual servoing tracking errors obtained with GPU-SLSC were 0.64 and 0.52 mm, respectively (which were lower than the median and IQR obtained with DAS by 1.39 and 8.45 mm, respectively). GPU-SLSC additionally reduced the percentage of failed segmentations when applied to in vivo cardiac data. Conclusions: Results are promising for the use of low-energy, miniaturized lasers to perform GPU-SLSC photoacoustic-based visual servoing in the operating room with laser pulse repetition frequencies as high as 41.2 Hz.
Uploads
Papers by Eduardo Gonzalez