Optical coherence tomography (OCT) is a non-invasive imaging method that provide high-resolution tomographic images. Attempts to incorporate OCT in dental practice have been ongoing, but the relatively bulky systems have limited their clinical utility. In this study, we utilized a microelectromechanical system (MEMS) to optimize the size of these OCT scanners to be similar to commercial intra-oral scanner (IOS) products. The optical axis of the internal scanner is designed in a Z shape to maximize the beam size reflected by the MEMS mirrors. To prove its usefulness in practical dentistry, we imaged the teeth in the oral cavity by position. Imaged teeth by position in the oral cavity demonstrated that the developed system can image deep into the oral cavity without difficulty. As a next step, we imaged teeth with cervical abrasion in three dimensions (3D) and high resolution. We classified the teeth into two types based on how the cervix was worn, and the degree of wear was quantitatively analyzed by performing A-scan profiling. This study demonstrates that the developed dental OCT system is effective in actual dental clinical practice and can be utilized for a variety of dental conditions.
KEYWORDS: Cornea, Transplantation, Deep learning, Optical coherence tomography, 3D modeling, Ultrasonography, Time metrology, Medical devices, Image segmentation, Eye
For several decades after corneal transplantation was performed for the first time, studies to predict the success of corneal transplantation have been conducted. To obtain a successful corneal transplantation, various factors other than biocompatibility between the donor cornea and the transplant recipient's eye must be satisfied. Therefore, various studies are being conducted to develop an artificial cornea that does not require a donor. One of the important indicators contributing to the success of corneal transplantation is measurement of corneal thickness (CT) after corneal transplantation. In previous studies, to measure the CT and transplanted cornea, partial CT measurement using an algorithm was mainly performed in optical coherence tomography (OCT) images. However, a single algorithm eventually has limitations in determining the suitability of the entire transplanted cornea. In this study, we automatically segmented the region of the artificial cornea implanted in the rabbit cornea through U-Net based models, and based on this, we measured and analyzed the three-dimensional total thickness of the conventional cornea and the artificial cornea. Our results suggest that the thickness of the transplanted and existing corneas can be automatically measured over time to provide information as an indicator for determining the success of corneal transplants.
Dental cervical abrasion is wear on the neck of the tooth where it meets the gums. To treat cervical abrasion, a therapeutic resin is used to fill the worn area. It is difficult to check whether the resin has structural defects such as internal voids. If the resin is not properly cured or has internal voids and bubbles, it can easily fall off when subjected to an external impact. OCT can be used to non-destructively inspect the internal structure after treatment. By acquiring cross-sectional images of the treated area, OCT can be used to check if bubbles have formed inside the resin. In addition, to check the volume of resin used in the treatment, an algorithm is used to extract the resin portion from each tomographic image.
Blood vessel imaging is essential for diagnosing and treating ear-related diseases like tinnitus caused by altered blood flow. However, existing methods using cadaver samples have limitations due to vessel collapse or loss. This study utilizes optical coherence tomography angiography (OCTA), a non-invasive, label-free imaging of ear blood vessels. Customized imaging tips and a complex differential variance algorithm enhance OCTA image quality. Vascular distribution in 10 volunteers (5 male, 5 female) is successfully imaged. Internal factors, such as skin condition and body fat percentage, affect image quality by influencing light penetration, signal-to-noise ratio, and system robustness. Quantitative values for 20 parameters are obtained, enabling comparative analysis of blood vessel images. The findings demonstrate OCTA's potential in diagnosing and treating ear-related diseases and provide insights into blood vessel dynamics.
One common limitation of spectral-domain optical coherence tomography (SD-OCT) is the mismatch between line-scan camera pixels and the wavelength of the source spectrum, causing image thickening in deeper regions and compromising imaging quality. Various studies have addressed this issue by attempting to improve the alignment between camera pixels and wavelength, with a focus on mitigating the nonlinearity of wavenumbers in SD-OCT systems. To enhance signal quality in deeper imaging regions, several wavenumber linearization (k-linearization) methods have been explored. In our research, we have introduced a novel k-linearization approach based on the diffraction grating equation. The specifications of the light source in our SD-OCT system were utilized for algorithm simulation. Our method concentrated on the difference in diffraction angles at the diffraction grating within the spectrometer to determine the incident wavenumber per pixel. By applying the acquired k-index to our system, we observed an improvement in intensity roll-off and a reduction in the thickening of images in the high-frequency region of the sample. One notable advantage of our proposed method is its effectiveness in obtaining a suitable k-index for systems with simple specifications. Additionally, it can be easily tailored to meet the specific requirements of different systems. This ensures that our approach is not only innovative but also adaptable to diverse SD-OCT setups.
The ischemic stroke animal model has gained increasing popularity to elucidate the pathophysiology and evaluate the efficacy of reperfusion and neuroprotective strategies for ischemic injuries. Various conventional methods to induce the ischemic models have been reported, however, it is difficult to control specific neurological deficits, mortality rates, and the extent of the infarction since the size of the affected region is precisely controlled, which limits the closeness of animal model to human stroke. In this study, we report a novel creation method of the target ischemic stroke model by simultaneous vessel monitoring and photothrombosis induction using localization photoacoustic microscopy (L-PAM), which minimizes infarct size at a precise location with high reproducibility. By utilizing the proposed L-PAM system, we resolve the occurred position error of the scanner for high-speed imaging caused by external resistance, which enables the precise localization up to a single micro-vasculature. The reproducibility and validity of the suggested target ischemic stroke model-inducing method have been successfully proven through repeated experiments and histological analyses. These results demonstrate that the proposed method is able to induce the closest ischemic stroke model to the clinical pathology for brain ischemia research from inducement dynamics, occurrence mechanisms to the recovery process.
KEYWORDS: 3D image reconstruction, Image restoration, Deep learning, 3D image processing, Data modeling, Photoacoustic microscopy, Biological imaging, 3D modeling, Spatial resolution, Polygon scanners
Photoacoustic microscopy (PAM) is a non-invasive, label-free functional imaging technique that provides high absorption contrast with high spatial resolution. Spatial sampling density and data size are key determinants of PAM imaging speed. Therefore, under sampling methods that reduce the number of scan points are usually employed to improve the imaging speed of PAM by increasing the scan step size. Because under sampling techniques sacrifice spatial sampling density, deep learning-based reconstruction techniques have been explored as alternatives. However, these methods have been applied to reconstruct two-dimensional PAM images related to spatial sampling density. Therefore, by considering the number of data points, the data size, and the characteristics of PAM to provide three-dimensional (3D) volume data, this study proposes a deep-learning-based complete reconstruction of under sampled 3D PAM data. newly reported to Obtained from real experiments (i.e. not manually generated). Quantitative analysis results show that the proposed method exhibits robustness and outperforms interpolation-based reconstruction methods at various under sampling ratios, resulting in 80x faster imaging speed and 800x smaller data. Improves PAM system performance with size. Furthermore, the applicability of this method is experimentally verified by enlarging a sparsely sampled test dataset. His proposed deep learning-based PAM data reconstruction has been demonstrated to be the closest model available under experimental conditions, significantly reducing the data size for processing and effectively reducing the imaging time.
Doppler optical coherence tomography (DOCT) is a non-destructive imaging technique designed to measure the movement of a sample by applying the Doppler effect to optical coherence tomography (OCT) signal data. It was designed to acquire a tomography image of the tympanic membrane (TM) and a calculated Doppler signal in real time with OCT using the CUDA parallel processing algorithm while inducing vibration of the TM with an audio signal. Afterwards, the thickness of the TM inside the ROI was measured using software, and the degree of response was analyzed according to the thickness. To measure the tomographic thickness of the TM responding to sound waves, image processing was used to acquire the upper and lower boundaries of the TM. To reduce the error in thickness measurement according to the angle of the TM, the shortest distance between the upper and lower boundaries at each pixel was used to reduce the error in the thickness measurement. In addition, by mapping the thickness information to a two-dimensional array, the movement of the TM in response to sound waves was finally analyzed through a histogram according to the thickness of the TM. Finally, we were able to obtain the tendency of the response according to the thickness of the TM, and quantitatively analyze the change in the reactivity according to the area of the TM.
Residual adhesive on tooth surface after bracket removal has to be identified at an advanced stage to avoid further effects on orthodontic and dental procedures, which has to be identified at an advanced stage. Since conventional visual inspection has a major limitation in identifying residuals, non-invasive identification with multi-dimensional assessments using swept-source optical coherence tomography (SS-OCT) is proposed for the precise identification of residual adhesive on the tooth surface during dental bracket replacements. The feasibility was examined using ex-vivo bovine teeth specimens after the removal of orthodontic implant from the tooth surface. Multi-dimensional assessments, such as residual adhesive boundary, color-scaled enface, adhesive area and thickness information were obtained using OCT to confirm the feasibility of the method. The detection algorithm finds the boundary which is between the dental surface and residual adhesive. The residual adhesive is separated based on the boundary. The area of residual adhesive is measured by an optical microscope and the detection algorithm. The difference between the optical microscope and detection algorithm measured area is lower than 10%. The results revealed that the performed OCT assessments can be beneficial for real-time application during orthodontic procedures as a primary inspection tool. Multi-dimensional assessment method used OCT and confirmed feasibility study shows that OCT can be used the detailed novel diagnosis system and effective tools for dental.
Photoacoustic microscopy (PAM) is a non-invasive, label-free functional imaging technique that provides high absorption contrast with high spatial resolution. Spatial sampling density and data size are important determinants of the imaging speed of PAM. Therefore, undersampling methods that reduce the number of scanning points are typically adopted to enhance the imaging speed of PAM by increasing the scanning step size. For the reason that undersampling methods sacrifice spatial sampling density, deep learning-based reconstruction methods have been considered as an alternative; however, these methods have been applied to reconstruct the two-dimensional PAM images, which is related to the spatial sampling density. Therefore, by considering the number of data points, data size, and the characteristics of PAM that provides three-dimensional (3D) volume data, in this study, we newly reported deep learning-based fully reconstructing the undersampled 3D PAM data, which is obtained at the actual experiment (i.e., not manually generated). The results of quantitative analyses demonstrate that the proposed method exhibits robustness and outperforms interpolation-based reconstruction methods at various undersampling ratios, enhancing the PAM system performance with 80-times faster-imaging speed and 800-times lower data size. Moreover, the applicability of this method is experimentally verified by upscaling the sparsely sampled test dataset. The proposed deep learning-based PAM data reconstructing is demonstrated to be the closest model that can be used under experimental conditions, effectively shortening the imaging time with significantly reduced data size for processing.
Research for miniaturization and portability of optical coherence tomography, which has received considerable attention as one of the pre-diagnosis methods, has been conducted for several years to further expand the utility of optical coherence tomography. In this study, we introduce a method that can dramatically reduce the size of a system and resources using a Raspberry Pi miniature computer and the proposed small spectrometer. The optical systems of the sample stage and the reference stage were configured as half-inch optical components to reduce the size of the system. The size of the sample stage was minimized by using a MEMS scanning mirror. We designed a board that converts the unipolar drive signal into a bipolar signal to drive the MEMS scanning mirror with Raspberry Pi. The MEMS mirror was controlled by a commercial AD/DA conversion board and a developed board that can be controlled via the general-purpose input-output (GPIO) pin of Raspberry Pi. Furthermore, we also designed the spectrometer to fit the 1-inch optical system. The camera was selected as a product that can supply power and transmit data through the USB terminal to operate all other components, including the camera, through a portable charger. Due to camera performance limitations, A-scan 5 kHz was the maximum speed, but the resolution was axial 8.5 μm (Air) and lateral 17.54 μm, showing similar performance to a commercial system. Although the operating speed is slow, it is expected to be used in various fields due to its portability advantage.
Surgery of chronic otitis media (COM) is a sensitive procedure, where the success rate crucially depends on the surgeon and the significant depth visibility of the surgical microscope. Additionally, videotapes have been frequently adapted for surgical guidance at operation theaters. While these approaches provide great views and assistance during the surgery, it has proven more challenging to derive morphological and volumetric information on subsurface layers of COM. To address this issue, an intra-surgical spectral-domain optical coherence tomography (OCT) microscope system with an extended working distance of 280 mm was developed, which has augmented reality on the ocular eyepiece of a surgical microscope for more effective visualization of morphological structures during mastoidectomy or tympanoplasty. The cross-sectional OCT images guide surgeons to more easily identify targeted regions by displaying depth direction information in real-time during surgery. Three patients with COM participated in this study, and the lesion conditions of the temporal bone were observed with pre-operative computed tomography (CT) before the surgery. Moreover, pure tone audiogram examinations were performed to evaluate pre- and post-surgical conditions. The pure tone audiogram reveals that the operation was well performed based on the air-bone gap (ABG) reduction, and it can be confirmed that the hearing level was also improved. The success of the surgical procedure was confirmed through the intraoperative OCT images, and the post-examined audiogram results further confirmed the improvement of hearing. Hence, the integration of intra-surgical OCT and audiogram inspection methods revealed the potential merits of the proposed methodology.
SignificanceX-ray imaging is frequently used for gastrointestinal imaging. Photoacoustic imaging (PAI) of the gastrointestinal tract is an emerging approach that has been demonstrated for preclinical imaging of small animals. A contrast agent active in both modalities could be useful for imaging applications.AimWe aimed to develop a dual-modality contrast agent comprising an admixture of barium sulfate with pigments that absorb light in the second near-infrared region (NIR-II), for preclinical imaging with both x-ray and PAI modalities.ApproachEleven different NIR-II dyes were evaluated after admixture with a 40% w/v barium sulfate mixture. The resulting NIR-II absorption in the soluble fraction and in the total mixture was characterized. Proof-of-principle imaging studies in mice were carried out.ResultsPigments that produced more uniform suspensions were assessed further for photoacoustic contrast signal at a wavelength of 1064 nm that corresponds to the output of the Nd:YAG laser used. Phantom imaging studies demonstrated that the pigment-barium sulfate mixture generated imaging contrast in both x-ray and PAI modalities. The optimal pigment selected for further study was a cyanine tetrafluoroborate salt. Ex-vivo and whole-body mouse imaging demonstrated that photoacoustic and x-ray contrast signals co-localized in the intestines for both imaging modalities.ConclusionThese data demonstrate that commercially-available NIR-II pigments can simply be admixed with barium sulfate to generate a dual-modality contrast agent appropriate for small animal gastrointestinal imaging.
Optical coherence tomography (OCT) is a high-resolution and non-invasive internal structural imaging technique. Since the first introduction of OCT, it has been widely studied to enhance the scanning speed of the system to enhance the applicability. Spectral-domain OCT (SD-OCT) is one of the representative types of Fourier-domain OCT, which consisted with lower prices than swept-source OCT and offers higher axial resolution, but there are limited hardware performance to improve the scanning speed. In this paper, we introduced the space-time division multiplexing (STDM) method-based superfast SD-OCT with 1 MHz A-scan rate. In terms of the time-division method, dual-cameras were implemented in a single spectrometer to reduce the alignment error between each camera and fully utilize the operating time of camera by remove the dead time. In addition, the path length difference of the two-sample arm is accurately controlled to utilize the space-division method. By concurrently integrating the time- and space-division methods in STDM with GPU parallel computing, 32 volume/sec was acquired. The quantitative evaluation of the performance of STDM-OCT was analyzed with sensitivity roll-off and image quality comparison measured at different depth. The proposed STDM-OCT is able to enlarge the application of OCT including biomedical research areas, which require a high-speed scanning system.
The aim of this research was to visualize and measure the human gingival sulcus in vivo using the swept-source optical coherence tomography system based on 1310 nm wavelength source with the developed classification algorithm of gingival sulcus. Apart from the algorithm based examination procedure, the OCT cross-sectional images were involved in A-scan depth profile analysis to illustrate the intensity fluctuation of teeth and the periodontal tissue structures to clarify the end point of gingival sulcus. The quantitative measurement was assessed with 1.10 ± 0.26 mm. Thus, the swept-source optical coherence tomography system could be used to perform the gingival sulcus imaging.
Significant technical and optical advancements are required for intraoperative optical coherence tomography (OCT) to perform boundless surgical applications in otology, since the translation of OCT for surgical-microscope facilitates the simultaneous OCT and microscopic visualization of soft tissue structures of the surgical region with a high-resolution in real-time. Herein, we developed an augmented-reality intrasurgical OCT microscope system with an extended 280 mm working distance, which simply provides a sufficient space for the manipulation during surgeries compared to conventional techniques. Ex vivo experiments were initially performed to evaluate the enhanced system performances and secondly, the developed system was well-utilized to clinically assess the preliminary findings of tympanomastoidectomy in six patients with chronic otitis media. The OCT system evaluated the residual inflammation of region of interest in the mastoid bone and most importantly OCT was sufficiently useful for visualizing the connection between the graft and remnant tympanic membrane intraoperatively. Use of this extended-working distance OCT integrated surgical-microscope enables the surgeons to precisely define the aforementioned surgical requirements, while performing intraoperative imaging over the complete range.
The conventional Fourier domain optical coherence tomography system requires single scanner for two dimensional cross-sectional image and two scanners for volumetric image. Parallel spectral domain optical coherence tomography has advantage of single scanner for volumetric image, while two dimensional cross-sectional images are obtained by parallel acquisition of illuminated line on sample using area camera. In this study, the industrial inspection of optical thin film on touch screen panels was demonstrated using parallel spectral domain optical coherence tomography. The cross-sectional and volumetric images were acquired to detect the internal sub layer defects in optical thin film which are difficult to observe using visual or machine vision based inspection methods. The results indicate the possible application of the proposed system in touch screen panels inspection for quality assurance of product at consumer end.
KEYWORDS: Optical coherence tomography, In vivo imaging, Sodium, Microscopes, Scanning electron microscopy, Magnetic resonance imaging, Real time imaging, Image resolution, Agriculture, Imaging systems
In this study, Optical coherence tomography (OCT) is demonstrated as a plausible optical tool for in vivo detection of plant seeds and its morphological changes during growth. The experiment was carried out on Capsicum annuum seeds that were treated with different molar concentrations of NaCl to investigate the most optimal concentration for the seed growth. The monitoring process was carried out for 9 consecutive days. The in vivo 2D OCT images of the treated seeds were obtained and compared with seeds that were grown with sterile distilled water. The obtained results confirm the feasibility of using OCT for the proposed application. Normalized A-scan analysis method is utilized for supporting the concluded results.
In this study, we monitored the optical clearing effects by immersing ex vivo guinea pig cochlea samples in ethylenediaminetetraacetic acid (EDTA) to study the internal microstructures in the morphology of guinea pig cochlea. The imaging limitations due to the guinea pig cochlea structures were overcome by optical clearing technique. Subsequently, the study was carried out to confirm the required approximate immersing duration of cochlea in EDTA-based optical clearing to obtain the best optimal depth visibility for guinea pig cochlea samples. Thus, we implemented a decalcification-based optical clearing effect to guinea pig cochlea samples to enhance the depth visualization of internal microstructures using swept source optical coherence tomography (OCT). The obtained nondestructive two-dimensional OCT images successfully illustrated the feasibility of the proposed method by providing clearly visible microstructures in the depth direction as a result of decalcification. The most optimal clearing outcomes for the guinea pig cochlea were obtained after 14 consecutive days. The quantitative assessment results verified the increase of the intensity as well as the thickness measurements of the internal microstructures. Following this method, difficulties in imaging of internal cochlea microstructures of guinea pigs could be avoided. The obtained results verified that the depth visibility of the decalcified ex vivo guinea pig cochlea samples was enhanced. Therefore, the proposed EDTA-based optical clearing method for guinea pig can be considered as a potential application for depth-enhanced OCT visualization.
A dual illumination system is proposed for cornea and retina imaging using spectral domain optical coherence tomography (SD-OCT). The system is designed to acquire cornea and retina imaging with dual illumination with limited optics and using a single spectrometer. The beam propagation for cornea and retina imaging in dual illumination enables to acquire the images of different segments. This approach will reduce the imaging time for separate corneal and retinal imaging. The in vivo imaging of both the cornea and retina of a health volunteer shows the feasibility of the system for clinical applications
Here we describe the possible application of optical coherence tomography (OCT) to inspect Marssonina coronaria infected apple blotch disease of in situ apple leaves. To fulfill the in situ field inspection requirement, we developed a compact wearable OCT system. For the confirmation of OCT results, simultaneous experiment was performed in realtime using loop-mediated isothermal amplification (LAMP), which is frequently used in agriculture. LAMP method was developed as an alternative approach for the inspection of disease. We performed field inspection for 30 consecutive days, and all the acquired results from both OCT and lamp were compared to confirm the correlation. A clear identification between healthy specimens, apparently healthy but infected specimens, and infected specimens could be obtained through the real-time OCT images, and the correlation between OCT and lamp results was confirmed through the obtained realtime lamp results. Based on this feasibility study, we conclude that the combination of both these diagnosing modalities can be effective for various novel agricultural discoveries.
Seed germination rate differs based on chemical treatments, and nondestructive measurements of germination rate have become an essential requirement in the field of agriculture. Seed scientists and other biologists are interested in optical sensing technologies-based biological discoveries due to nondestructive detection capability. Optical coherence tomography (OCT) has recently emerged as a powerful method for biological and plant material discoveries. We report an extended application of OCT by monitoring the germination rate acceleration of chemically primed seeds. To validate the versatility of the method, Capsicum annum seeds were primed using three chemical compounds: sterile distilled water (SDW), butandiol, and 1-hexadecene. Monitoring was performed using a 1310-nm swept source OCT system. The results confirmed more rapid morphological variations in the seeds treated with 1-hexadecene medium than the seeds treated with SDW and butandiol within 8 consecutive days. In addition, fresh weight measurements (gold standard) of seeds were monitored for 15 days, and the obtained results were correlated with the OCT results. Thus, such a method can be used in various agricultural fields, and OCT shows potential as a rigorous sensing method for selecting the optimal plant growth-promoting chemical compounds rapidly, when compared with the gold standard methods.
A method for depth enhancement is presented using a bidirectional imaging modality for spectral domain optical coherence tomography (SD-OCT). Two precisely aligned sample arms along with two reference arms were utilized in the optical configuration to scan the samples. Using exemplary images of the optical resolution target, Scotch tape, a silicon sheet with two needles, and a leaf, we demonstrated how the developed bidirectional SD-OCT imaging method increases the ability to characterize depth-enhanced images. The results of the developed system were validated by comparing the images with the standard OCT configuration (single-sample arm setup). Given the advantages of higher resolution and the ability to visualize deep morphological structures, this method can be utilized to increase the depth dependent fall-off in samples with limited thickness. Thus, the proposed bidirectional imaging modality is apt for cross-sectional imaging of entire samples, which has the potential capability to improve the diagnostic ability.
We conducted an initial feasibility study using real-time magneto-motive optical Doppler tomography (MM-ODT) with enhanced contrast to investigate the detection of superparamagnetic iron oxide (SPIO) magnetic nanoparticles implanted into in vivo melanoma tissue. The MM-ODT signals were detected owing to the phase shift of the implanted magnetic nanoparticles, which occurred due to the action of an applied magnetic field. An amplifier circuit-based solenoid was utilized for generating high-intensity oscillating magnetic fields. The MM-ODT system was confirmed as an effective in vivo imaging method for detecting melanoma tissue, with the performance comparable to those of conventional optical coherence tomography and optical Doppler tomography methods. Moreover, the optimal values of the SPIO nanoparticles concentration and solenoid voltage for obtaining the uppermost Doppler velocity were derived as well. To improve the signal processing speed for real-time imaging, we adopted multithread programming techniques and optimized the signal path. The results suggest that this imaging modality can be used as a powerful tool to identify the intracellular and extracellular SPIO nanoparticles in melanoma tissues in vivo.
Photoacoustic imaging (PAI) is an emerging hybrid imaging modality that can provide a strong optical absorption contrast using the photoacoustic (PA) effect, and breaks through the fundamental imaging depth limit of existing optical microscopy such as optical coherence tomography (OCT), confocal or two-photon microscopy. In PAI, a short-pulsed laser is illuminated to the tissue, and the PA waves are generated by thermoelastic expansion. Despite the high lateral resolution of optical-resolution photoacoustic microscopy (OR-PAM) thanks to the tight optical focus, the lateral resolution of OR-PAM is limited to the optical diffraction limit, which is approximately a half of the excitation wavelength. Here, we demonstrate a new super-resolution photoacoustic microscopy (SR-PAM) system by breaking the optical diffraction limit. The conventional microscopes with nanoscale resolutions such as a scanning electron microscope (SEM) and transmission electron microscope (TEM) are typically used to image the structures of nanomaterials, but these systems should work in a high vacuum environment and cannot provide the optical properties of the materials. Our newly developed SR-PAM system provides the optical properties with a nanoscale resolution in a normal atmosphere. We have photoacoustically imaged single gold nanoparticles with an average size of 80 nm in diameter and shown their PA expansion properties individually. The lateral resolution of this system was approximately 20 nm. Therefore, this tool will provide an unprecedented optical absorption property with an accurate nanoscale resolution and greatly impact on materials science and nanotechnology field.
The aim of this study was to analyze the effectiveness of decalcification using ethylenediaminetetraacetic acid (EDTA) as an optical clearing method to enhance the depth visibility of internal soft tissues of cochlea. Ex vivo mouse and guinea pig cochlea samples were soaked in EDTA solutions for decalcification, and swept source optical coherence tomography (OCT) was used as imaging modality to monitor the decalcified samples consecutively. The monitored noninvasive cross-sectional images showed that the mouse and guinea pig cochlea samples had to be decalcified for subsequent 7 and 14 days, respectively, to obtain the optimal optical clearing results. Using this method, difficulties in imaging of internal cochlea microstructures of mice could be evaded. The obtained results verified that the depth visibility of the decalcified ex vivo samples was enhanced.
The development of the first miniaturized parallel acoustic delay line (PADL) probe for handheld photoacoustic tomography (PAT) is reported. Using fused-silica optical fibers with low acoustic attenuation, we constructed two arrays of eight PADLs. Precision laser micromachining was conducted to produce robust and accurate mechanical support and alignment structures for the PADLs, with minimal acoustic distortion and interchannel coupling. The 16 optical-fiber PADLs, each with a different time delay, were arranged to form one input port and two output ports. A handheld PADL probe was constructed using two single-element transducers and two data acquisition channels (equal to a channel reduction ratio of 8∶1). Photoacoustic (PA) images of a black-ink target embedded in an optically scattering phantom were successfully acquired. After traveling through the PADLs, the eight channels of differently time-delayed PA signals reached each single-element ultrasonic transducer in a designated nonoverlapping time series, allowing clear signal separation for PA image reconstruction. Our results show that the PADL technique and the handheld probe can potentially enable real-time PAT, while significantly reducing the complexity and cost of the ultrasound receiver system.
We have demonstrated a novel microbubbles methylene blue solution, called to “MB2” solution for a dual modality contrast. We have photoacoustically and ultrasonically imaged and quantified aqueous solutions of MB2 by varying the concentration of either microbubbles or methylene blue to investigate the dual modal imaging capability. Interestingly, as the microbubbles concentration increased with the constant methylene blue concentration, photoacoustic (PA) signal was greatly attenuated in the MB2 solution. Conversely, when methylene blue concentration increased with the fixed microbubbles concentration, no interference was observed in ultrasound (US) signals. To further confirm our findings, we switched the PA and ultrasound (US) signals using conventional ultrasound. We compared the PA and US signals of the MB2 solution before and after sonication. The PA amplitude increased 2.5 times. Conversely, the US signals were initially strong, but decreased 2.5 times following sonication. Moreover, we used a clinically modified PA/US imaging system to disrupt the microbubbles in MB2 and recover the PA signals.
We have developed an intraoperative surgical photoacoustic microscopy (IS-PAM) system by integrating an optical resolution photoacoustic microscopy (OR-PAM) and conventional surgical microscope. Based on the common optical path in the OR-PAM and microscope system, we can acquire the PAM and microscope images at the same time. Furthermore, by utilizing a mini-sized beam projector, 2D PAM images are back-projected onto the microscope view plane as augmented reality. Thus, both the conventional microscopic and 2D cross-sectional PAM images are displayed on the plane through an eyepiece lens of the microscope. In our method, additional image display tool is not required to show the PAM image. Therefore, it potentially offers significant convenience to surgeons without movement of their sights during surgeries. In order to demonstrate the performance of our IS-PAM system, first, we successfully monitored needle intervention in phantoms. Moreover, we successfully guided needle insertion into mice skins in vivo by visualizing surrounding blood vessels from the PAM images and the magnified skin surfaces from the conventional microscopic images simultaneously.
KEYWORDS: Optical fibers, Acoustics, Ultrasonography, Transducers, Data acquisition, Signal detection, Acquisition tracking and pointing, Photoacoustic tomography, Signal attenuation, Distortion
In current photoacoustic tomography (PAT), l-D or 2-D ultrasound arrays and multi-channel data acquisition (DAQ) electronics are used to detect the photoacoustic signals simultaneously for “real-time” image construction. However, as the number of transducer elements and DAQ channels increase, the construction and operation of the ultrasound receiving system will become complex and costly. This situation can be addressed by using parallel acoustic delay lines (PADLs) to create true time delays in multiple PA signal channels. The time-delayed PA signals will reach the ultrasound transducer at different times and therefore can be received by one single-element transducer without mixing with each other. In this paper, we report the development of the first miniaturized PADL probe suitable for handheld operations. Fusedsilica optical fibers with low acoustic attenuation were used to construct the 16 PADLs with specific time delays. The handheld probe structure was fabricated using precision laser-micromachining process to provide robust mechanical support and accurate alignment of the PADLs with minimal acoustic distortion and inter-channel coupling. The 16 optical-fiber PADLs were arranged to form one input port and two output ports. Photoacoustic imaging of a black-ink target embedded in an optically-scattering phantom was successfully conducted using the handheld PADL probe with two single-element transducers and two DAQ channels (equal to a channel reduction ratio of 8:1). Our results show that the PADL technique and the handheld probe could provide a promising solution for real-time PAT with significantly reduced complexity and cost of the ultrasound receiver system.
Ultrasound and photoacoustic imaging are highly complementary modalities since both use ultrasonic detection for operation. Increasingly, photoacoustic and ultrasound have been integrated in terms of hardware instrumentation. To generate a broadly accessible dual-modality contrast agent, we generated microbubbles (a standard ultrasound contrast agent) in a solution of methylene blue (a standard photoacoustic dye). This MB 2 solution was formed effectively and was optimized as a dual-modality contrast solution. As microbubble concentration increased (with methylene blue concentration constant), photoacoustic signal was attenuated in the MB 2 solution. When methylene blue concentration increased (with microbubble concentration held constant), no ultrasonic interference was observed. Using an MB 2 solution that strongly attenuated all photoacoustic signal, high powered ultrasound could be used to burst the microbubbles and dramatically enhance photoacoustic contrast (>800 -fold increase), providing a new method for spatiotemporal control of photoacoustic signal generation.
We report the development of a combined dual-modal photoacoustic and optical coherence tomography (PA-OCT) system using a single near-infrared (NIR) supercontinuum laser source which can provide both optical absorption and scattering contrasts simultaneously. By using a small sized pulsed Nd:YAG microchip laser and a photonic crystal fiber, we fabricated a pulsed broadband supercontinuum source from 600 to 1700 nm. Under the same optical hardware system, intrinsically registered PA and OCT images are acquired in a single scanning. In order to demonstrate feasibility of our system, we successfully acquired the PA and OCT images of black and white hairs images at the same time. The black hair was detected in both PA and OCT images, while the white hair appeared only in the OCT image. This result suggests the potential of compact, cost-effective, and simple dual-modal PA-OCT system. Moreover, we believe that this approach will be a key point for commercialization and clinical translation.
Optical-resolution photoacoustic microscopy (OR-PAM) becomes a premier microscopic imaging tool in biomedicine
because it provides agent-free optical absorption information in tissues. By tightly focusing light to a spot, the fine
lateral resolution can be achieved in OR-PAM. The focal spot size is typically determined by the numerical aperture of
the used objective lens. Here, we demonstrate focus-free OR-PAM using a Bessel beam generator. In this approach, no
objective lens is required. We have photoacoustically imaged a carbon fiber with a diameter of ~6 μm, and the
measured lateral resolution was ~6-7 μm. Beneficially, the complexities of the existing OR-PAM systems can be greatly
relieved.
Achieving real-time photoacoustic (PA) tomography typically requires massive ultrasound transducer arrays and data
acquisition (DAQ) electronics to receive PA waves simultaneously. In this paper, we report the first demonstration of a
photoacoustic tomography (PAT) system using optical fiber-based parallel acoustic delay lines (PADLs). By employing
PADLs to introduce specific time delays, the PA signals (on the order of a few micro seconds) can be forced to arrive at
the ultrasonic transducers at different times. As a result, time-delayed PA signals in multiple channels can be ultimately
received and processed in a serial manner with a single-element transducer, followed by single‐channel DAQ electronics. Our results show that an optically absorbing target in an optically scattering medium can be photoacoustically imaged using the newly developed PADL-based PAT system. Potentially, this approach could be adopted to significantly reduce the complexity and cost of ultrasonic array receiver systems.
Optical-resolution photoacoustic microscopy (OR-PAM) becomes a premier microscopic imaging tool in biomedicine because it provides agent-free optical absorption information in tissues. By tightly focusing light to a spot, a significantly improved lateral resolution can be achieved in OR-PAM. The focal spot size is typically determined by the numerical aperture of the used objective lens. Here, we demonstrate objective-free OR-PAM using a fiber optic Bessel beam generator. In this approach, no objective lens is required and, beneficially, the complexities of conventional OR-PAM systems can be greatly relieved. We have obtained photoacoustic images of a carbon fiber with a diameter of ∼6 μm, whose lateral resolution was measured to be better than 6 to 7 μm.
Achieving real-time photoacoustic (PA) tomography typically requires multi-element ultrasound transducer arrays and their associated multiple data acquisition (DAQ) electronics to receive PA waves simultaneously. We report the first demonstration of a photoacoustic tomography (PAT) system using optical fiber-based parallel acoustic delay lines (PADLs). By employing PADLs to introduce specific time delays, the PA signals (on the order of a few micro seconds) can be forced to arrive at the ultrasonic transducers at different times. As a result, time-delayed PA signals in multiple channels can be ultimately received and processed in a serial manner with a single-element transducer, followed by single-channel DAQ electronics. Our results show that an optically absorbing target in an optically scattering medium can be photoacoustically imaged using the newly developed PADL-based PAT system. Potentially, this approach could be adopted to significantly reduce the complexity and cost of ultrasonic array receiver systems.
Normally, urine flows down from kidneys to bladders. Vesicoureteral reflux (VUR) is the abnormal flow of urine from
bladders back to kidneys. VUR commonly follows urinary tract infection and leads to renal infection. Fluoroscopic
voiding cystourethrography and direct radionuclide voiding cystography have been clinical gold standards for VUR
imaging, but these methods are ionizing. Here, we demonstrate the feasibility of a novel and nonionizing process for
VUR mapping in vivo, called photoacoustic cystography (PAC). Using a photoacoustic (PA) imaging system, we have
successfully imaged a rat bladder filled with clinically being used methylene blue dye. An image contrast of ~8 was
achieved. Further, spectroscopic PAC confirmed the accumulation of methylene blue in the bladder. Using a laser pulse
energy of less than 1 mJ/cm2, bladder was clearly visible in the PA image. Our results suggest that this technology
would be a useful clinical tool, allowing clinicians to identify bladder noninvasively in vivo.
A reflection-type side-polished optical fiber submersion sensor with an optical fiber mirror in a manhole is proposed.
When this sensor is submerged into distilled water in a manhole and the measurement is made at about 1km from the
sensor, the throughput power gain is changed by about 2.04dB at 1540nm and the resonance wavelength shifts from
1540nm to 1541.6nm.
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