Noninvasive Assessment of Early Dental Lesion Using a Dual-Contrast Photoacoustic Tomography

Adaptively multi-scale microstructure characterization of cancellous bone via Photoacoustic signal decomposition

Osteoporosis is a systemic disease with a high incidence in the elderly and seriously affects the quality of life of patients. Photoacoustic (PA) technology, which combines the advantages of light and ultrasound, can provide information about the physiological structure and chemical information of biological tissues in a non-invasive and non-radiative way. Due to the complex structural characteristics of bone tissue, PA signals generated by bone tissue are non-stationary and nonlinear. However, conventional PA signal processing methods are not effective for non-stationary signal processing. In this study, an empirical mode decomposition (EMD)-based Hilbert-Huang transform (HHT) PA signal analysis method, called HHT PA signal analysis (HPSA), was developed to assess the microstructure information of bone tissue, which is closely related to bone health. The feasibility of the HPSA method in bone health assessment was proven by numerical simulation and experimental studies on animal samples with different bone volume/total volume (BV/TV) and bone mineral densities. First, based on adaptive EMD, the different modes correlated with multi-scale information were mined from the PA signal, the correlations between different intrinsic mode function (IMF) modes and BV/TVs were analyzed, and the optimal mode for more efficient PA time-frequency analysis was selected. Second, multi-wavelength HPSA was used to assess the changes in the chemical components of the bone tissue. The results demonstrate that the HPSA method can distinguish bones with different BV/TVs and microstructure conditions adaptively with high efficiency. They further emphasize the potential of PA techniques in characterizing biological tissues in bones for early and rapid detection of bone diseases.

Ex vivo human teeth imaging with various photoacoustic imaging systems

Dental caries cause pain and if not diagnosed, it may lead to the loss of teeth in extreme cases. Dental X-ray imaging is the gold standard for caries detection; however, it cannot detect hidden caries. In addition, the ionizing nature of X-ray radiation is another concern. Hence, other alternate imaging modalities like photoacoustic (PA) imaging are being explored for dental imaging. Here, we demonstrate the feasibility of acoustic resolution photoacoustic microscopy (ARPAM) to image a tooth with metal filling, circular photoacoustic computed tomography (cPACT) to acquire images of teeth with caries and pigmentation, and linear array-based photoacoustic imaging (lPACT) of teeth with caries and pigmentation. The cavity measured with lPACT imaging is compared with the X-ray computed tomography image. The metal filling and its boundaries are clearly seen in the ARPAM image. cPACT images at 1064 nm were a better representative of the tooth surface compared to the images acquired at 532 nm. It was possible to detect the cavities present in the dentine when lPACT imaging was used. The PA signal from the pigmented caries on the lateral surface (occlusion view) of the tooth was high when imaged using the lPACT system.

Oral processing behavior and dental caries; an insight into a new relationship

INTRODUCTION

Previous evidence suggests an individual variation in the preferred oral processing behavior. Individuals can be classified as firm processing(FPL) or soft processing likers(SPL). FPL(crunchers and chewers) prefer using their teeth while SPL(smooshers and suckers) prefer using the tongue and the palate when processing different food items. Variation in the preferred oral processing behavior has been associated with differences in food texture preference and eating time. Time is one of the factors directly related to the development of dental caries(tooth decay). Oral retention and eating times are associated with greater caries experience. This study aims to explore if a relationship exists between the preferred oral processing behavior and the individual's caries experience.

MATERIALS AND METHODS

This was a cross-sectional, dental center-based study conducted at Jordan University of Science and Technology. Five hundred participants consented to fill out the preferred oral processing behavior(POPB) questionnaire. Anthropometric measurements (including weight, height, and waist circumference) were recorded. A single trained and calibrated dentist registered each participant's caries experience and plaque levels using the DMFS index and plaque index of Silness and Loe.

RESULTS

A total of 351(70.2%) and 149(29.8%) participants were typed as FPL and SPL, respectively. SPL demonstrated higher levels of dental caries experience compared to FPL. The mean DMFS score for SPL was 28.8(±25.43) while for FPL was 18.71(± 18.34). This difference remained significant after adjustment for confounders(P<0.001). SPL exhibited a significantly higher mean score for the "M" component(P <0.001) while no significant difference in the mean score of the "D"(P = 0.076) and "F"(P = 0.272) components was observed when compared to FPL.

CONCLUSION

The current findings provide new insight into a possible relationship between the preferred oral processing behavior and an individual's caries experience. A relationship in which the preferred oral processing behavior can potentially affect and/or be affected by the dental caries experience.

Broadband transparent ultrasound transducer with polymethyl methacrylate as matching layer for in vivo photoacoustic microscopy

Photoacoustic imaging (PAI) uniquely combines optics and ultrasound, presenting a promising role in biomedical imaging as a non-invasive and label-free imaging technology. As the traditional opaque ultrasound (US) transducers could hinder the transportation of the excitation light and limit the performance of PAI system, piezoelectric transparent ultrasonic transducers (TUTs) with indium tin oxide (ITO) electrodes have been developed to allow light transmission through the transducer and illuminate the sample directly. Nevertheless, without having transparent matching materials with appropriate properties, the bandwidth of those TUTs was generally narrow. In this work, we propose to employ polymethyl methacrylate (PMMA) as the matching layer material to improve the bandwidth of lithium niobate (LN)-based TUTs. The effects of PMMA matching layer on the performance of TUTs have been systematically studied. With the optimized PMMA matching layer, the very wide bandwidth of > 50 % could be achieved for the TUTs even with different transducer frequencies, leading to the great enhancement of axial resolution when compared to the similar reported work. In addition, the imaging performance of the developed TUT prototype has been evaluated in a PAI system and demonstrated by both phantom and in vivo small animal imaging.

Recent development of photoacoustic imaging in dentistry: A review on studies over the last decade

Background

This work performs a literature review of photoacoustic imaging (PAI) in dentistry and discusses the development of PAI in relation to oral health.

Methods

A search method was used to locate papers published between 2011 and 2023 in Google Scholar and PubMed databases, and 25 studies were selected. Reports on PAI in dentistry were included. Articles not written in English or whose full text could not be accessed were excluded. The remaining publications were checked and evaluated to determine whether they contain supportive materials for PAI in dentistry.

Results

The majority of articles about PAI in dentistry are associated with caries studies. Photoacoustic microscopy is the most commonly utilized PAI system. PAI studies generally focus on ex-vivo investigations using extracted human teeth. The acoustic signal obtained from carious teeth is greater than that obtained from normal teeth. In addition to imaging oral soft tissues from animal models and the periodontal pocket depth in human volunteers, PAI is applied to evaluate dental implants and oral biofilms.

Conclusion

There have been numerous investigation on PAI in dentistry, but it is not yet applicable in dental practice. In the future, PAI studies are expected to contribute to the invention of an alternative non-ionizing imaging technology that is comfortable for patients, user friendly, and capable of providing reliable information at a reasonable cost.

Photoacoustic imaging of hidden dental caries using visible-light diode laser

BACKGROUND

Hidden caries is a type of tooth decay that is difficult to identify through visual diagnosis because teeth with hidden caries appear normal on the tooth surface but are damaged underneath.

METHODS

A photoacoustic imaging system based on visible light using a diode laser with a wavelength of 532 nm was developed to detect hidden caries in teeth.

RESULTS

The results indicate that the average of acoustic intensity level for healthy teeth is -74.2 ± 0.1 dB, and the average of acoustic intensity range for teeth with hidden caries is -81.2 ± 0.5 dB. The intensity level for the caries area varies depending on the severity of caries.

CONCLUSION

Based on the acoustic intensity level measured by the interaction of teeth with laser light, the photoacoustic imaging system in the study can accurately detect the presence of hidden caries and recognize the difference between caries teeth and healthy teeth. This research can be developed into a prototype of a simple device that makes it easy to operate in dental practice.

Photoacoustic tomography versus cone-beam computed tomography versus micro-computed tomography: Accuracy of 3D reconstructions of human teeth

OBJECTIVES

In this in-vitro study, teeth were imaged using photoacoustic tomography (PAT), cone-beam computed tomography (CBCT), and micro-computed tomography (μ-CT). The study had aim: to identify the best wavelength for PAT images to determine the accuracy of the three imaging methods, and to determine whether PAT images of teeth can achieve acceptable reconstruction quality.

METHODS

Nineteen human mandibular single-rooted incisors were extracted from patients with trauma or periodontitis. To determine the best wavelength for acquiring photoacoustic images, all 19 teeth were scanned in vitro with PAT, using different laser wavelengths between 680 and 960 nm. The images were analyzed using image analysis software. To assess the accuracy of PAT and compare it with the accuracy of CBCT, each tooth was also scanned in vitro using CBCT and the reference standard technique of μ-CT. Subsequently, three different three-dimensional models, one for each imaging technique, were created for each tooth. Finally, the three different three-dimensional models acquired for the same tooth were matched and analyzed regarding volume and surface.

RESULTS

The highest quality tooth images were achieved using the 680 nm wavelength, which showed the best contrast ratio. The full geometry of the dental root (μ-CT compared with PAT) could be visualized with relative standard deviations of 0.12 mm for the surface and -7.33 mm3 for the volume (n = 19). The full geometry of the dental root (μ-CT compared with CBCT) could be visualized with relative standard deviations of 0.06 mm for the surface and -14.56 mm3 for the volume (n = 19). The difference between the PAT-μ-CT group and CBCT-μ-CT group regarding the total average of the root surface area was not significant (p>0.06).

CONCLUSION

Images, which were acquired using PAT at 680nm showed the best contrast ration, enabling the identification of dentin, cementum and the dental pulp. No significant differences were found between the PAT-μ-CT group and CBCT-μ-CT group regarding the total average of the RSA and the total volume. Thus, three-dimensional reconstructions based on in-vitro PAT are already of acceptable reconstruction quality.

Diagnosis of cracked tooth: Clinical status and research progress

Cracked tooth is a common dental hard tissue disease.The involvement of cracks directly affects the selection of treatment and restoration of the affected teeth.It is helpful to choose more appropriate treatment options and evaluate the prognosis of the affected tooth accurately to determine the actual involvement of the crack.However, it is often difficult to accurately and quantitatively assess the scope of cracks at present.So it is necessary to find a real method of early quantitative and non-destructive crack detection.This article reviews the current clinical detection methods and research progress of cracked tooth in order to provide a reference for finding a clinical detection method for cracked tooth.

Enhancing Finite Element-Based Photoacoustic Tomography by Localized Reconstruction Method

Iterative reconstruction algorithm based on finite element (FE) modeling is a powerful approach in photoacoustic tomography (PAT). However, an iterative inverse algorithm using conventional FE meshing of the entire imaging zone is computationally demanding, which hinders this powerful tool in applications where quick image acquisition and/or a large image matrix is needed. To address this challenge, parallel computing techniques are proposed and implemented in the field. Here, we present an alternative approach for 2D PAT, which locoregionally reconstructs the region of interest (ROI) instead of the full imaging zone. Our simulated and phantom experimental results demonstrate that this ROI reconstruction algorithm can produce almost the same image quality as the conventional full zone-based reconstruction algorithm; however, the computation time can be significantly reduced without any additional hardware cost by more than two orders of magnitude (100-fold). This algorithm is further applied and validated in an in vivo study. The major vessel structures in a rat’s brain can be imaged clearly using our ROI-based approach, coupled with a mesh of 11,801 nodes. This novel algorithm can also be parallelized using MPI or GPU acceleration techniques to further enhance the reconstruction performance of FE-based PAT.

Exploiting Nanomaterials for Optical Coherence Tomography and Photoacoustic Imaging in Nanodentistry

There is already a societal awareness of the growing impact of nanoscience and nanotechnology, with nanomaterials (with at least one dimension less than 100 nm) now incorporated in items as diverse as mobile phones, clothes or dentifrices. In the healthcare area, nanoparticles of biocompatible materials have already been used for cancer treatment or bioimaging enhancement. Nanotechnology in dentistry, or nanodentistry, has already found some developments in dental nanomaterials for caries management, restorative dentistry and orthodontic adhesives. In this review, we present state-of-the-art scientific development in nanodentistry with an emphasis on two imaging techniques exploiting nanomaterials: optical coherence tomography (OCT) and photoacoustic imaging (PAI). Examples will be given using OCT with nanomaterials to enhance the acquired imaging, acting as optical clearing agents for OCT. A novel application of gold nanoparticles and nanorods for imaging enhancement of incipient occlusal caries using OCT will be described. Additionally, we will highlight how the OCT technique can be properly managed to provide imaging with spatial resolution down to 10's-100's nm resolution. For PAI, we will describe how new nanoparticles, namely TiN, prepared by femtosecond laser ablation, can be used in nanodentistry and will show photoacoustic microscopy and tomography images for such exogenous agents.

A Comprehensive Review on the Optical Micro-Electromechanical Sensors for the Biomedical Application

This study presented an overview of current developments in optical micro-electromechanical systems in biomedical applications. Optical micro-electromechanical system (MEMS) is a particular class of MEMS technology. It combines micro-optics, mechanical elements, and electronics, called the micro-opto electromechanical system (MOEMS). Optical MEMS comprises sensing and influencing optical signals on micron-level by incorporating mechanical, electrical, and optical systems. Optical MEMS devices are widely used in inertial navigation, accelerometers, gyroscope application, and many industrial and biomedical applications. Due to its miniaturised size, insensitivity to electromagnetic interference, affordability, and lightweight characteristic, it can be easily integrated into the human body with a suitable design. This study presented a comprehensive review of 140 research articles published on photonic MEMS in biomedical applications that used the qualitative method to find the recent advancement, challenges, and issues. The paper also identified the critical success factors applied to design the optimum photonic MEMS devices in biomedical applications. With the systematic literature review approach, the results showed that the key design factors could significantly impact design, application, and future scope of work. The literature of this paper suggested that due to the flexibility, accuracy, design factors efficiency of the Fibre Bragg Grating (FBG) sensors, the demand has been increasing for various photonic devices. Except for FBG sensing devices, other sensing systems such as optical ring resonator, Mach-Zehnder interferometer (MZI), and photonic crystals are used, which still show experimental stages in the application of biosensing. Due to the requirement of sophisticated fabrication facilities and integrated systems, it is a tough choice to consider the other photonic system. Miniaturisation of complete FBG device for biomedical applications is the future scope of work. Even though there is a lot of experimental work considered with an FBG sensing system, commercialisation of the final FBG device for a specific application has not been seen noticeable progress in the past.

Photoacoustic imaging of occlusal incipient caries in the visible and near-infrared range

Purpose

This study aimed to demonstrate the presence of dental caries through a photoacoustic imaging system with visible and near-infrared wavelengths, highlighting the differences between the 2 spectral regions. The depth at which carious tissue could be detected was also verified.

Materials and Methods

Fifteen permanent molars were selected and classified as being sound or having incipient or advanced caries by visual inspection, radiography, and optical coherence tomography analysis prior to photoacoustic scanning. A photoacoustic imaging system operating with a nanosecond pulsed laser as the light excitation source at either 532 nm or 1064 nm and an acoustic transducer at 5 MHz was developed, characterized, and used. En-face and lateral (depth) photoacoustic signals were detected.

Results

The results confirmed the potential of the photoacoustic method to detect caries. At both wavelengths, photoacoustic imaging effectively detected incipient and advanced caries. The reconstructed photoacoustic images confirmed that a higher intensity of the photoacoustic signal could be observed in regions with lesions, while sound surfaces showed much less photoacoustic signal. Photoacoustic signals at depths up to 4 mm at both 532 nm and 1064 nm were measured.

Conclusion

The results presented here are promising and corroborate that photoacoustic imaging can be applied as a diagnostic tool in caries research. New studies should focus on developing a clinical model of photoacoustic imaging applications in dentistry, including soft tissues. The use of inexpensive light-emitting diodes together with a miniaturized detector will make photoacoustic imaging systems more flexible, user-friendly, and technologically viable.

Multiple information extracted from photoacoustic radio-frequency signal and the application on tissue classification

Photoacoustic imaging is a hybrid biomedical imaging technique, combining rich optical contrasts and good acoustic resolution in deep tissues. As a noninvasive and nonionized imaging method, photoacoustic imaging has shown great potentials in biomedicine in the past decade. In this review, we give a brief introduction of the physical principle and three major implementations of photoacoustic imaging. Then, we present pictures of some recent progress about the extraction of new imaging parameters from photoacoustic radio-frequency signals. These parameters are highly associated with the tissue microstructure characteristics, including characteristic size, number density, and elasticity. This information could give us insight into various properties of tissue in-depth and be applied to tissue classification for basic research and clinical settings.

Using Meglumine Diatrizoate to improve the accuracy of diagnosis of cracked teeth on Cone-beam CT images

AIM

To explore in a laboratory setting the feasibility of using Meglumine Diatrizoate (MD) to improve the accuracy of diagnosis of cracked teeth on cone-beam CT (CBCT) images.

METHODOLOGY

Twenty-four teeth were cracked artificially by soaking them cyclically in liquid nitrogen and hot water. The number and position of crack lines were evaluated with a dental operating microscope and used as the gold standard. The artificially cracked teeth were then examined using routine scanning (RS) and enhanced scanning (ES) modes, respectively. For the ES mode, MD was painted on the surface of the crack lines, and then, CBCT scanning with the same parameters was performed after 10 min. A radiological graduate student and an experienced radiologist evaluated the presence or absence of crack lines, respectively. The differences between the RS and ES modes were determined and assessed using McNemar's test. Inter-examiner agreement and intra-examiner agreement were assessed using kappa analysis.

RESULTS

Fifty-seven crack lines were found in the 24 cracked teeth. In the RS mode, the accuracy of detection of crack lines was 23% (radiological graduate student) and 32% (experienced radiologist), whereas in the ES mode, the accuracy was 61% (radiological graduate student) and 65% (experienced radiologist). The inter-examiner agreement was 0.693 in RS mode and 0.849 in ES mode. The intra-examiner agreement was 0.872 and 0.949 for the radiological graduate student in RS and ES mode respectively; and one for the experienced radiologist both in RS and ES mode.

CONCLUSIONS

Compared with routine scanning mode, more crack lines could be detected in enhanced scanning mode using Meglumine Diatrizoate as a contrast medium. MD could be a potential contrast medium to improve the accuracy of detection of crack lines on CBCT images.

Quantification of number density of random microstructure from a photoacoustic signal by using Nakagami statistics

Tissue microstructure characterization is a valuable tool in diagnosis and staging of many diseases. In this study, we propose a photoacoustic Nakagami statistics method to noninvasively evaluate the number density of random microstructure. The Nakagami parameters are acquired by fitting the photoacoustic signal envelope histogram with Nakagami distribution function. Theoretical calculations and phantom experiments demonstrate that the Nakagami shape parameter is only related to the number density of random microstructure and monotonically increases with the number density. Based on this finding, we propose a photoacoustic tomography modality with the imaging contrast of the Nakagami shape parameter. Experiments show that the proposed method can provide more comprehensive and accurate description of tissue microstructure.

High-speed Intraoperative Assessment of Breast Tumor Margins by Multimodal Ultrasound and Photoacoustic Tomography

Conventional methods for breast tumor margins assessment need a long turnaround time, which may lead to re-operation for patients undergoing lumpectomy surgeries. Photoacoustic tomography (PAT) has been shown to visualize adipose tissue in small animals and human breast. Here, we demonstrate a customized multimodal ultrasound and PAT system for intraoperative breast tumor margins assessment using fresh lumpectomy specimens from 66 patients. The system provides the margin status of the entire excised tissue within 10 minutes. By subjective reading of three researchers, the results show 85.7% [95% confidence interval (CI), 42.0% - 99.2%] sensitivity and 84.6% (95% CI, 53.7% - 97.3%) specificity, 71.4% (95% CI, 30.3% - 94.9%) sensitivity and 92.3% (95% CI, 62.1% - 99.6%) specificity, and 100% (95% CI, 56.1% - 100%) sensitivity and 53.9% (95% CI, 26.1% - 79.6%) specificity respectively when cross-correlated with post-operational histology. Furthermore, a machine learning-based algorithm is deployed for margin assessment in the challenging ductal carcinoma in situ tissues, and achieved 85.5% (95% CI, 75.2% - 92.2%) sensitivity and 90% (95% CI, 79.9% - 95.5%) specificity. Such results present the potential of using mutlimodal ultrasound and PAT as a high-speed and accurate method for intraoperative breast tumor margins evaluation.

Noninvasive low-cycle fatigue characterization at high depth with photoacoustic eigen-spectrum analysis

In this work, photoacoustic eigen-spectrum analysis was proposed for noninvasively characterizing the mechanical properties of materials. We theoretically predicted the relationship between the photoacoustic eigen-spectra of cylindrical optical absorbers and their mechanical properties. Experimental measurements of eigen-spectra extracted from photoacoustic coda waves agreed well with the theoretical predictions. We then applied the photoacoustic eigen-spectrum analysis for contactless monitoring of low-cycle fatigue damage. Experiments showed that the photoacoustic eigen-spectra were closely related to the degree of low-cycle fatigue. This study might enhance the contrast of photoacoustic imaging ford mechanical characterization.

In Vivo Imaging of Microvasculature during Anesthesia with High-Resolution Photoacoustic Microscopy

Anesthesia monitoring is extremely important in improving the quality of anesthesia and ensuring the safety of patients in operation. Photoacoustic microscopy (PAM) is proposed to in vivo image the skin microvasculature of 10 nude mice undergoing general anesthesia by using the isoflurane gas with a concentration of 3%. Benefiting from strong optical absorption of hemoglobin, PAM has good contrast and high resolution in mapping of microvasculature. A series of high quality images can clearly reveal the subtle changes of capillaries in morphology over time. Two indices, vessel intensity and vessel density, are extracted from these images to measure the microvasculature quantitatively. The imaging results show that the vessel intensity and density are increased over time. After 65 min, the vessel intensity increased 42.7 ± 8.6% and the density increased 28.6 ± 12.2%. These indices extracted from photoacoustic images accurately reflect the greater blood perfusion undergoing general anesthesia. Additionally, abnormal reductions of vessel intensity and density are also observed as overtime anesthesia. This preclinical study suggests that PAM holds potential to monitor anesthesia by imaging the skin microvasculature.

Photoacoustic Imaging for Noninvasive Periodontal Probing Depth Measurements

The periodontal probe is the gold standard tool for periodontal examinations, including probing depth measurements, but is limited by systematic and random errors. Here, we used photoacoustic ultrasound for high-spatial resolution imaging of probing depths. Specific contrast from dental pockets was achieved with food-grade cuttlefish ink as a contrast medium. Here, 39 porcine teeth (12 teeth with artificially deeper pockets) were treated with the contrast agent, and the probing depths were measured with novel photoacoustic imaging and a Williams periodontal probe. There were statistically significant differences between the 2 measurement approaches for distal, lingual, and buccal sites but not mesial. Bland-Altman analysis revealed that all bias values were < ±0.25 mm, and the coefficients of variation for 5 replicates were <11%. The photoacoustic imaging approach also offered 0.01-mm precision and could cover the entire pocket, as opposed to the probe-based approach, which is limited to only a few sites. This report is the first to use photoacoustic imaging for probing depth measurements with potential implications to the dental field, including tools for automated dental examinations or noninvasive examinations.

GPU-based acceleration and mesh optimization of finite-element-method-based quantitative photoacoustic tomography: a step towards clinical applications

Finite element method (FEM)-based time-domain quantitative photoacoustic tomography (TD-qPAT) is a powerful approach, as it provides highly accurate quantitative imaging capability by recovering absolute tissue absorption coefficients for functional imaging. However, this approach is extremely computationally demanding, and requires days for the reconstruction of one set of images, making it impractical to be used in clinical applications, where a large amount of data needs to be processed in a limited time scale. To address this challenge, here we present a graphic processing unit (GPU)-based parallelization method to accelerate the image reconstruction using FEM-based TD-qPAT. In addition, to further optimize FEM-based TD-qPAT reconstruction, an adaptive meshing technique, along with mesh density optimization, is adopted. Phantom experimental data are used in our study to evaluate the GPU-based TD-qPAT algorithm, as well as the adaptive meshing technique. The results show that our new approach can considerably reduce the computation time by at least 136-fold over the current central processing unit (CPU)-based algorithm. The quality of image reconstruction is also improved significantly when adaptive meshing and mesh density optimization are applied.

Photoacoustics and speed-of-sound dual mode imaging with a long depth-of-field by using annular ultrasound array

Speed-of-sound and optical absorption reflect the structure and function of tissues from different aspects. A dual-mode microscopy system based on a concentric annular ultrasound array is proposed to simultaneously acquire the long depth-of-field images of speed-of-sound and optical absorption of inhomogeneous samples. First, speed-of-sound is decoded from the signal delay between each element of the annular array. The measured speed-of-sound could not only be used as an image contrast, but also improve the resolution and accuracy of spatial location of photoacoustic image in inhomogeneous acoustic media. Secondly, benefitting from dynamic focusing of annular array and the measured speed-of-sound, it is achieved an advanced acoustic-resolution photoacoustic microscopy with a precise position and a long depth-of-field. The performance of the dual-mode imaging system has been experimentally examined by using a custom-made annular array. The proposed dual-mode microscopy might have the significances in monitoring the biological physiological and pathological processes.

Original Research. Photoacoustic Microscopy in Dental Medicine

Introduction: Photoacoustic microscopy, also known as optoacoustic imaging, is a comparatively new method of investigation in dental medicine, which uses a laser-generated ultrasound (short laser pulses) to achieve images for interpretation. Photoacoustic microscopy can be used in a broad spectrum, from detecting tooth decay at its earliest stages to dental anatomy analysis. Material and methods: The energy emitted by the photoacoustic pulse is moderately absorbed by the target and exchanged into heat, leading to a local transitory temperature upsurge. The tension propagates and grows as ultrasonic waves, distinguished by the ultrasonic transducers which are planted apart from the tissue. The photoacoustic microscope has a tunable dye laser which passes through a condensing lens, an objective and ultimately an ultrasonic transducer attached to an acoustic lens to capture and receive information about the scanned probe from a sample moved on the X, Y dimensions. Results: The precise anatomy of layered concentric structures can be clearly observed in photoacoustic microscopy. The image value of the inner layer can be higher, indicating strong optical absorption, while the image value of the outer layer is lower, indicating weaker optical absorption. Meanwhile, the inner layer has the exact same size as the dentin structure and the outer layer has the exact same size as the enamel structure in this cross-section. Conclusions: The photoacoustic microscope (all-optical) comes out to be a future and promising tool for detecting early-stage caries and lesions on the surface of the teeth, where micro-leakage occurs at the interface of tooth restoration, and also the anatomy of dental tissues.