Sensors

Editorial

Jump to: Research, Review

3 pages, 152 KiB

Open AccessEditorial

Recent Advances in Imaging Sensors and Applications

by Changhan Yoon and Changho Lee

Sensors 2021, 21(12), 3970; https://doi.org/10.3390/s21123970 - 09 Jun 2021

Cited by 1 | Viewed by 1693

Abstract

Recent advances in sensor technology have allowed us to develop many interesting applications and enhance the quality of human life [...] Full article

(This article belongs to the Special Issue Imaging Sensors and Applications)

Research

Jump to: Editorial, Review

18 pages, 5828 KiB

Open AccessArticle

Novel Bandwidth Expander Supported Power Amplifier for Wideband Ultrasound Transducer Devices

by Kyeongjin Kim and Hojong Choi

Sensors 2021, 21(7), 2356; https://doi.org/10.3390/s21072356 - 28 Mar 2021

Cited by 7 | Viewed by 2359

Abstract

Ultrasound transducer devices have their own frequency ranges, depending on the applications and specifications, due to penetration depth, sensitivity, and image resolution. For imaging applications, in particular, the transducer devices are preferable to have a wide bandwidth due to the specific information generated [...] Read more.

Ultrasound transducer devices have their own frequency ranges, depending on the applications and specifications, due to penetration depth, sensitivity, and image resolution. For imaging applications, in particular, the transducer devices are preferable to have a wide bandwidth due to the specific information generated by the tissue or blood vessel structures. To support these ultrasound transducer devices, ultrasound power amplifier hardware with a wide bandwidth can improve the transducer performance. Therefore, we developed a new bandwidth expander circuit using specially designed switching architectures to increase the power amplifier bandwidth. The measured bandwidth of the power amplifier with the help of the bandwidth expander circuit increased by 56.9%. In addition, the measured echo bandwidths of the 15-, 20-, and 25-MHz transducer devices were increased by 8.1%, 6.0%, and 9.8%, respectively, with the help of the designed bandwidth expander circuit. Therefore, the designed architecture could help an ultrasound system hardware with a wider bandwidth, thus supporting the use of different frequency ultrasound transducer devices with a single developed ultrasound system. Full article

(This article belongs to the Special Issue Imaging Sensors and Applications)

► Show Figures

Figure 1

9 pages, 2016 KiB

Open AccessCommunication

Synthetic Aperture Imaging Using High-Frequency Convex Array for Ophthalmic Ultrasound Applications

by Hae Gyun Lim, Hyung Ham Kim and Changhan Yoon

Sensors 2021, 21(7), 2275; https://doi.org/10.3390/s21072275 - 24 Mar 2021

Cited by 7 | Viewed by 2906

Abstract

High-frequency ultrasound (HFUS) imaging has emerged as an essential tool for pre-clinical studies and clinical applications such as ophthalmic and dermatologic imaging. HFUS imaging systems based on array transducers capable of dynamic receive focusing have considerably improved the image quality in terms of [...] Read more.

High-frequency ultrasound (HFUS) imaging has emerged as an essential tool for pre-clinical studies and clinical applications such as ophthalmic and dermatologic imaging. HFUS imaging systems based on array transducers capable of dynamic receive focusing have considerably improved the image quality in terms of spatial resolution and signal-to-noise ratio (SNR) compared to those by the single-element transducer-based one. However, the array system still suffers from low spatial resolution and SNR in out-of-focus regions, resulting in a blurred image and a limited penetration depth. In this paper, we present synthetic aperture imaging with a virtual source (SA-VS) for an ophthalmic application using a high-frequency convex array transducer. The performances of the SA-VS were evaluated with phantom and ex vivo experiments in comparison with the conventional dynamic receive focusing method. Pre-beamformed radio-frequency (RF) data from phantoms and excised bovine eye were acquired using a custom-built 64-channel imaging system. In the phantom experiments, the SA-VS method showed improved lateral resolution (>10%) and sidelobe level (>4.4 dB) compared to those by the conventional method. The SNR was also improved, resulting in an increased penetration depth: 16 mm and 23 mm for the conventional and SA-VS methods, respectively. Ex vivo images with the SA-VS showed improved image quality at the entire depth and visualized structures that were obscured by noise in conventional imaging. Full article

(This article belongs to the Special Issue Imaging Sensors and Applications)

► Show Figures

Figure 1

20 pages, 10269 KiB

Open AccessArticle

A Novel AVM Calibration Method Using Unaligned Square Calibration Boards

by Jung Hyun Lee and Dong-Wook Lee

Sensors 2021, 21(7), 2265; https://doi.org/10.3390/s21072265 - 24 Mar 2021

Cited by 3 | Viewed by 3255

Abstract

An around view monitoring (AVM) system acquires the front, rear, left, and right-side information of a vehicle using four cameras and transforms the four images into one image coordinate system to monitor around the vehicle with one image. Conventional AVM calibration utilizes the [...] Read more.

An around view monitoring (AVM) system acquires the front, rear, left, and right-side information of a vehicle using four cameras and transforms the four images into one image coordinate system to monitor around the vehicle with one image. Conventional AVM calibration utilizes the maximum likelihood estimation (MLE) to determine the parameters that can transform the captured four images into one AVM image. The MLE requires reference data of the image coordinate system and the world coordinate system to estimate these parameters. In conventional AVM calibration, many aligned calibration boards are placed around the vehicle and are measured to extract the reference sample data. However, accurately placing and measuring the calibration boards around a vehicle is an exhaustive procedure. To remediate this problem, we propose a novel AVM calibration method that requires only four randomly placed calibration boards by estimating the location of each calibration board. First, we define the AVM errors and determine the parameters that minimize the error in estimating the location. We then evaluate the accuracy of the proposed method through experiments using a real-sized vehicle and an electric vehicle for children to show that the proposed method can generate an AVM image similar to the conventional AVM calibration method regardless of a vehicle’s size. Full article

(This article belongs to the Special Issue Imaging Sensors and Applications)

► Show Figures

Figure 1

21 pages, 954 KiB

Open AccessArticle

MRI-Based Brain Tumor Classification Using Ensemble of Deep Features and Machine Learning Classifiers

by Jaeyong Kang, Zahid Ullah and Jeonghwan Gwak

Sensors 2021, 21(6), 2222; https://doi.org/10.3390/s21062222 - 22 Mar 2021

Cited by 256 | Viewed by 16051

Abstract

Brain tumor classification plays an important role in clinical diagnosis and effective treatment. In this work, we propose a method for brain tumor classification using an ensemble of deep features and machine learning classifiers. In our proposed framework, we adopt the concept of [...] Read more.

Brain tumor classification plays an important role in clinical diagnosis and effective treatment. In this work, we propose a method for brain tumor classification using an ensemble of deep features and machine learning classifiers. In our proposed framework, we adopt the concept of transfer learning and uses several pre-trained deep convolutional neural networks to extract deep features from brain magnetic resonance (MR) images. The extracted deep features are then evaluated by several machine learning classifiers. The top three deep features which perform well on several machine learning classifiers are selected and concatenated as an ensemble of deep features which is then fed into several machine learning classifiers to predict the final output. To evaluate the different kinds of pre-trained models as a deep feature extractor, machine learning classifiers, and the effectiveness of an ensemble of deep feature for brain tumor classification, we use three different brain magnetic resonance imaging (MRI) datasets that are openly accessible from the web. Experimental results demonstrate that an ensemble of deep features can help improving performance significantly, and in most cases, support vector machine (SVM) with radial basis function (RBF) kernel outperforms other machine learning classifiers, especially for large datasets. Full article

(This article belongs to the Special Issue Imaging Sensors and Applications)

► Show Figures

Figure 1

17 pages, 6964 KiB

Open AccessArticle

IoT-Based Research Equipment Sharing System for Remotely Controlled Two-Photon Laser Scanning Microscopy

by Eunwoo Park, Jaehyun Lim, Byung Cheol Park and Daekeun Kim

Sensors 2021, 21(4), 1533; https://doi.org/10.3390/s21041533 - 23 Feb 2021

Cited by 3 | Viewed by 2443

Abstract

In this study, two-photon laser scanning microscopy (TPLSM) based on the internet of things (IoT) is proposed as a remote research equipment sharing system, which enables the remote sharing economy. IoT modules, where data are transmitted to and received from the remote users [...] Read more.

In this study, two-photon laser scanning microscopy (TPLSM) based on the internet of things (IoT) is proposed as a remote research equipment sharing system, which enables the remote sharing economy. IoT modules, where data are transmitted to and received from the remote users in the web service via IoT, instead of a data acquisition (DAQ) system embedded in the conventional TPLSM, are installed in the IoT-based TPLSM (IoT-TPLSM). The performance for each IoT module is evaluated independently, and it is confirmed that it works well even in a personal computer-free environment. In addition, a message queuing telemetry transport (MQTT) protocol is applied to the DAQ interface in the web service, and a graphic user interface for enabling the remote users to operate IoT-TPLSM remotely is also designed and implemented. For the image acquisition demonstration, the stained cellular images and the autofluorescent tissue images are obtained in IoT-TPLSM. Lastly, it is confirmed that the comparable performance is provided with the conventional TPLSM by evaluating the imaging conditions and qualities of the three-dimensional image stacks processed in IoT-TPLSM. Full article

(This article belongs to the Special Issue Imaging Sensors and Applications)

► Show Figures

Figure 1

12 pages, 2455 KiB

Open AccessCommunication

Integrated Quad-Scanner Strategy-Based Optical Coherence Tomography for the Whole-Directional Volumetric Imaging of a Sample

by Sm Abu Saleah, Daewoon Seong, Sangyeob Han, Ruchire Eranga Wijesinghe, Naresh Kumar Ravichandran, Mansik Jeon and Jeehyun Kim

Sensors 2021, 21(4), 1305; https://doi.org/10.3390/s21041305 - 11 Feb 2021

Cited by 8 | Viewed by 2645

Abstract

Whole-directional scanning methodology is required to observe distinctive features of an entire physical structure with a three dimensional (3D) visualization. However, the implementation of whole-directional scanning is challenging for conventional optical coherence tomography (OCT), which scans a limited portion of the sample by [...] Read more.

Whole-directional scanning methodology is required to observe distinctive features of an entire physical structure with a three dimensional (3D) visualization. However, the implementation of whole-directional scanning is challenging for conventional optical coherence tomography (OCT), which scans a limited portion of the sample by utilizing unidirectional and bidirectional scanning methods. Therefore, in this paper an integrated quad-scanner (QS) strategy-based OCT method was implemented to obtain the whole-directional volumetry of a sample by employing four scanning arms installed around the sample. The simultaneous and sequential image acquisition capabilities are the conceptual key points of the proposed QS-OCT method, and were implemented using four precisely aligned scanning arms and applied in a complementary way according to the experimental criteria. To assess the feasibility of obtaining whole-directional morphological structures, a roll of Scotch tape, an ex vivo mouse heart, and kidney specimens were imaged and independently obtained tissue images at different directions were delicately merged to compose the 3D volume data set. The results revealed the potential merits of QS-OCT-based whole-directional imaging, which can be a favorable inspection method for various discoveries that require the dynamic coordinates of the whole physical structure. Full article

(This article belongs to the Special Issue Imaging Sensors and Applications)

► Show Figures

Figure 1

18 pages, 7227 KiB

Open AccessArticle

Transrectal Ultrasound and Photoacoustic Imaging Probe for Diagnosis of Prostate Cancer

by Jihun Jang, Jinwoo Kim, Hak Jong Lee and Jin Ho Chang

Sensors 2021, 21(4), 1217; https://doi.org/10.3390/s21041217 - 09 Feb 2021

Cited by 9 | Viewed by 5321

Abstract

A combined transrectal ultrasound and photoacoustic (TRUS–PA) imaging probe was developed for the clear visualization of morphological changes and microvasculature distribution in the prostate, as this is required for accurate diagnosis and biopsy. The probe consisted of a miniaturized 128-element 7 MHz convex [...] Read more.

A combined transrectal ultrasound and photoacoustic (TRUS–PA) imaging probe was developed for the clear visualization of morphological changes and microvasculature distribution in the prostate, as this is required for accurate diagnosis and biopsy. The probe consisted of a miniaturized 128-element 7 MHz convex array transducer with 134.5° field-of-view (FOV), a bifurcated optical fiber bundle, and two optical lenses. The design goal was to make the size of the TRUS–PA probe similar to that of general TRUS probes (i.e., about 20 mm), for the convenience of the patients. New flexible printed circuit board (FPCB), acoustic structure, and optical lens were developed to meet the requirement of the probe size, as well as to realize a high-performance TRUS–PA probe. In visual assessment, the PA signals obtained with the optical lens were 2.98 times higher than those without the lens. Moreover, the in vivo experiment with the xenograft BALB/c (Albino, Immunodeficient Inbred Strain) mouse model showed that TRUS–PA probe was able to acquire the entire PA image of the mouse tight behind the porcine intestine about 25 mm depth. From the ex vivo and in vivo experimental results, it can be concluded that the developed TRUS–PA probe is capable of improving PA image quality, even though the TRUS–PA probe has a cross-section size and an FOV comparable to those of general TRUS probes. Full article

(This article belongs to the Special Issue Imaging Sensors and Applications)

► Show Figures

Figure 1

15 pages, 14654 KiB

Open AccessArticle

Pilot Study: Quantitative Photoacoustic Evaluation of Peripheral Vascular Dynamics Induced by Carfilzomib In Vivo

by Thi Thao Mai, Manh-Cuong Vo, Tan-Huy Chu, Jin Young Kim, Chulhong Kim, Je-Jung Lee, Sung-Hoon Jung and Changho Lee

Sensors 2021, 21(3), 836; https://doi.org/10.3390/s21030836 - 27 Jan 2021

Cited by 8 | Viewed by 2993

Abstract

Carfilzomib is mainly used to treat multiple myeloma. Several side effects have been reported in patients treated with carfilzomib, especially those associated with cardiovascular events, such as hypertension, congestive heart failure, and coronary artery disease. However, the side effects, especially the manifestation of [...] Read more.

Carfilzomib is mainly used to treat multiple myeloma. Several side effects have been reported in patients treated with carfilzomib, especially those associated with cardiovascular events, such as hypertension, congestive heart failure, and coronary artery disease. However, the side effects, especially the manifestation of cardiovascular events through capillaries, have not been fully investigated. Here, we performed a pilot experiment to monitor peripheral vascular dynamics in a mouse ear under the effects of carfilzomib using a quantitative photoacoustic vascular evaluation method. Before and after injecting the carfilzomib, bortezomib, and PBS solutions, we acquired high-resolution three-dimensional PAM data of the peripheral vasculature of the mouse ear during each experiment for 10 h. Then, the PAM maximum amplitude projection (MAP) images and five quantitative vascular parameters, i.e., photoacoustic (PA) signal, diameter, density, length fraction, and fractal dimension, were estimated. Quantitative results showed that carfilzomib induces a strong effect on the peripheral vascular system through a significant increase in all vascular parameters up to 50%, especially during the first 30 min after injection. Meanwhile, bortezomib and PBS do not have much impact on the peripheral vascular system. This pilot study verified PAM as a comprehensive method to investigate peripheral vasculature, along with the effects of carfilzomib. Therefore, we expect that PAM may be useful to predict cardiovascular events caused by carfilzomib. Full article

(This article belongs to the Special Issue Imaging Sensors and Applications)

► Show Figures

Figure 1

15 pages, 3193 KiB

Open AccessArticle

Mapping of Back Muscle Stiffness along Spine during Standing and Lying in Young Adults: A Pilot Study on Spinal Stiffness Quantification with Ultrasound Imaging

by Christina Zong-Hao Ma, Long-Jun Ren, Connie Lok-Kan Cheng and Yong-Ping Zheng

Sensors 2020, 20(24), 7317; https://doi.org/10.3390/s20247317 - 19 Dec 2020

Cited by 10 | Viewed by 2612

Abstract

Muscle stiffness in the spinal region is essential for maintaining spinal function, and might be related to multiple spinal musculoskeletal disorders. However, information on the distribution of muscle stiffness along the spine in different postures in large subject samples has been lacking, which [...] Read more.

Muscle stiffness in the spinal region is essential for maintaining spinal function, and might be related to multiple spinal musculoskeletal disorders. However, information on the distribution of muscle stiffness along the spine in different postures in large subject samples has been lacking, which merits further investigation. This study introduced a new protocol of measuring bilateral back muscle stiffness along the thoracic and lumbar spine (at T3, T7, T11, L1 & L4 levels) with both ultrasound shear-wave elastography (SWE) and tissue ultrasound palpation system (TUPS) in the lying and standing postures of 64 healthy adults. Good inter-/intra-reliability existed in the SWE and TUPS back muscle stiffness measurements (ICC ≥ 0.731, p < 0.05). Back muscle stiffness at the L4 level was found to be the largest in the thoracic and lumbar regions (p < 0.05). The back muscle stiffness of males was significantly larger than that of females in both lying and standing postures (p < 0.03). SWE stiffness was found to be significantly larger in standing posture than lying among subjects (p < 0.001). It is reliable to apply SWE and TUPS to measure back muscle stiffness. The reported data on healthy young adults in this study may also serve as normative reference data for future studies on patients with scoliosis, low back pain, etc. Full article

(This article belongs to the Special Issue Imaging Sensors and Applications)

► Show Figures

Figure 1

14 pages, 3895 KiB

Open AccessArticle

In Vivo Evaluation of Plane Wave Imaging for Abdominal Ultrasonography

by Sua Bae, Jintae Jang, Moon Hyung Choi and Tai-Kyong Song

Sensors 2020, 20(19), 5675; https://doi.org/10.3390/s20195675 - 05 Oct 2020

Cited by 3 | Viewed by 2988

Abstract

Although plane wave imaging (PWI) has been extensively employed for ultrafast ultrasound imaging, its potential for sectorial B-mode imaging with a convex array transducer has not yet been widely recognized. Recently, we reported an optimized PWI approach for sector scanning that exploits the [...] Read more.

Although plane wave imaging (PWI) has been extensively employed for ultrafast ultrasound imaging, its potential for sectorial B-mode imaging with a convex array transducer has not yet been widely recognized. Recently, we reported an optimized PWI approach for sector scanning that exploits the dynamic transmit focusing capability. In this paper, we first report the clinical applicability of the optimized PWI for abdominal ultrasonography by in vivo image and video evaluations and compare it with conventional focusing (CF) and diverging wave imaging (DWI), which is another dynamic transmit focusing technique generally used for sectorial imaging. In vivo images and videos of the liver, kidney, and gallbladder were obtained from 30 healthy volunteers using PWI, DWI, and CF. Three radiologists assessed the phantom images, 156 in vivo images, and 66 in vivo videos. PWI showed significantly enhanced (p < 0.05) spatial resolution, contrast, and noise and artifact reduction, and a 4-fold higher acquisition rate compared to CF and provided similar performances compared to DWI. Because the computations required for PWI are considerably lower than that for DWI, PWI may represent a promising technique for sectorial imaging in abdominal ultrasonography that provides better image quality and eliminates the need for focal depth adjustment. Full article

(This article belongs to the Special Issue Imaging Sensors and Applications)

► Show Figures

Figure 1

14 pages, 2747 KiB

Open AccessArticle

Feasibility Study of Precise Balloon Catheter Tracking and Visualization with Fast Photoacoustic Microscopy

by Jahae Kim, Thi Thao Mai, Jin Young Kim, Jung-Joon Min, Chulhong Kim and Changho Lee

Sensors 2020, 20(19), 5585; https://doi.org/10.3390/s20195585 - 29 Sep 2020

Cited by 10 | Viewed by 3918

Abstract

Correct guiding of the catheter is a critical issue in almost all balloon catheter applications, including arterial stenosis expansion, coronary arterial diseases, and gastrointestinal tracking. To achieve safe and precise guiding of the balloon catheter, a novel imaging method with high-resolution, sufficient depth [...] Read more.

Correct guiding of the catheter is a critical issue in almost all balloon catheter applications, including arterial stenosis expansion, coronary arterial diseases, and gastrointestinal tracking. To achieve safe and precise guiding of the balloon catheter, a novel imaging method with high-resolution, sufficient depth of penetration, and real-time display is required. Here, we present a new balloon catheter guiding method using fast photoacoustic microscopy (PAM) technique for precise balloon catheter tracking and visualization as a feasibility study. We implemented ex vivo and in vivo experiments with three different medium conditions of balloon catheter: no air, air, and water. Acquired cross-sectional, maximum amplitude projection (MAP), and volumetric 3D PAM images demonstrated its capability as a new imaging guiding tool for balloon catheter tracking and visualization. Full article

(This article belongs to the Special Issue Imaging Sensors and Applications)

► Show Figures

Figure 1

18 pages, 7251 KiB

Open AccessArticle

Investigation of the Effect of the Skull in Transcranial Photoacoustic Imaging: A Preliminary Ex Vivo Study

by Rayyan Manwar, Karl Kratkiewicz and Kamran Avanaki

Sensors 2020, 20(15), 4189; https://doi.org/10.3390/s20154189 - 28 Jul 2020

Cited by 33 | Viewed by 6662

Abstract

Although transcranial photoacoustic imaging (TCPAI) has been used in small animal brain imaging, in animals with thicker skull bones or in humans both light illumination and ultrasound propagation paths are affected. Hence, the PA image is largely degraded and in some cases completely [...] Read more.

Although transcranial photoacoustic imaging (TCPAI) has been used in small animal brain imaging, in animals with thicker skull bones or in humans both light illumination and ultrasound propagation paths are affected. Hence, the PA image is largely degraded and in some cases completely distorted. This study aims to investigate and determine the maximum thickness of the skull through which photoacoustic imaging is feasible in terms of retaining the imaging target structure without incorporating any post processing. We identify the effect of the skull on both the illumination path and acoustic propagation path separately and combined. In the experimental phase, the distorting effect of ex vivo sheep skull bones with thicknesses in the range of 0.7~1.3 mm are explored. We believe that the findings in this study facilitate the clinical translation of TCPAI. Full article

(This article belongs to the Special Issue Imaging Sensors and Applications)

► Show Figures

Figure 1

17 pages, 8577 KiB

Open AccessArticle

The Contribution of Elastic Wave NDT to the Characterization of Modern Cementitious Media

by Gerlinde Lefever, Didier Snoeck, Nele De Belie, Sandra Van Vlierberghe, Danny Van Hemelrijck and Dimitrios G. Aggelis

Sensors 2020, 20(10), 2959; https://doi.org/10.3390/s20102959 - 23 May 2020

Cited by 27 | Viewed by 2679

Abstract

To mitigate autogenous shrinkage in cementitious materials and simultaneously preserve the material’s mechanical performance, superabsorbent polymers and nanosilica are included in the mixture design. The use of the specific additives influences both the hydration process and the hardened microstructure, while autogenous healing of [...] Read more.

To mitigate autogenous shrinkage in cementitious materials and simultaneously preserve the material’s mechanical performance, superabsorbent polymers and nanosilica are included in the mixture design. The use of the specific additives influences both the hydration process and the hardened microstructure, while autogenous healing of cracks can be stimulated. These three stages are monitored by means of non-destructive testing, showing the sensitivity of elastic waves to the occurring phenomena. Whereas the action of the superabsorbent polymers was evidenced by acoustic emission, the use of ultrasound revealed the differences in the developed microstructure and the self-healing of cracks by a comparison with more commonly performed mechanical tests. The ability of NDT to determine these various features renders it a promising measuring method for future characterization of innovative cementitious materials. Full article

(This article belongs to the Special Issue Imaging Sensors and Applications)

► Show Figures

Figure 1

14 pages, 4402 KiB

Open AccessArticle

Analysis of Wave Patterns Under the Region of Macro-Fiber Composite Transducer to Improve the Analytical Modelling for Directivity Calculation in Isotropic Medium

by Kumar Anubhav Tiwari, Renaldas Raisutis and Liudas Mazeika

Sensors 2020, 20(8), 2280; https://doi.org/10.3390/s20082280 - 17 Apr 2020

Cited by 2 | Viewed by 2229

Abstract

Analytical modelling is an efficient approach to estimate the directivity of a transducer generating guided waves in the research field of ultrasonic non-destructive testing of the large and complex structures due to its short processing time as compared to the numerical modelling and [...] Read more.

Analytical modelling is an efficient approach to estimate the directivity of a transducer generating guided waves in the research field of ultrasonic non-destructive testing of the large and complex structures due to its short processing time as compared to the numerical modelling and experimental techniques. The wave patterns or the amplitude variations along the region of ultrasonic transducer itself depend on its behavior, excitation frequency, and the type of propagating wave mode. Depending on the wave-pattern of a propagating wave mode, the appropriate value of the amplitude correction factor must be multiplied to the amplitudes of the excitation signal for the accurate evaluation of directivity pattern of the ultrasonic transducers generating guided waves in analytical modelling. The objective of this work is to analyse the wave patterns under the region of macro-fiber composite (MFC) transducer to improve the accuracy of a previously developed analytical model for the prediction of directivity patterns. Firstly, the amplitude correction factor based on the wave patterns under the region of P1-type MFC (MFC-2814) transducer at two different frequencies (80 kHz, 3 periods and 220 kHz, 3 period) glued on 2 mm Al alloy plate has been estimated analytically in the case of an asymmetric (A0) guided Lamb wave. The validation of analytically estimated amplitude correction factor is performed by a proposed experimental method that allows analyzing the behaviour of MFC transducer under its region by gluing MFC on bottom surface and scanning the receiver on the top surface of the sample. Later on, the estimated amplitude correction factor is included in the previously developed 2D analytical model for the improvement in the directivity patterns of the A0 mode. The modified analytical model shows a significant improvement in the directivity pattern of the A0 wave mode in comparison to the results obtained by the previous model without considering the proper wave patterns. The results reveal that errors between the directivity estimated by the present modified 2D analytical model and experimental investigation are reduced by more than 58% in comparison to the previously developed analytical model. Full article

(This article belongs to the Special Issue Imaging Sensors and Applications)

► Show Figures

Figure 1

18 pages, 7678 KiB

Open AccessArticle

Improved Depth-of-Field Photoacoustic Microscopy with a Multifocal Point Transducer for Biomedical Imaging

by Thanh Phuoc Nguyen, Van Tu Nguyen, Sudip Mondal, Van Hiep Pham, Dinh Dat Vu, Byung-Gak Kim and Junghwan Oh

Sensors 2020, 20(7), 2020; https://doi.org/10.3390/s20072020 - 03 Apr 2020

Cited by 14 | Viewed by 3681

Abstract

In this study, a photoacoustic microscopy (PAM) system based on a multifocal point (MFP) transducer was fabricated to produce a large depth-of-field tissue image. The customized MFP transducer has seven focal points, distributed along with the transducer’s axis, fabricated by separate spherically-focused surfaces. [...] Read more.

In this study, a photoacoustic microscopy (PAM) system based on a multifocal point (MFP) transducer was fabricated to produce a large depth-of-field tissue image. The customized MFP transducer has seven focal points, distributed along with the transducer’s axis, fabricated by separate spherically-focused surfaces. These surfaces generate distinct focal zones that are overlapped to extend the depth-of-field. This design allows extending the focal zone of 10 mm for the 11 MHz MFP transducer, which is a great improvement over the 0.48 mm focal zone of the 11 MHz single focal point (SFP) transducer. The PAM image penetration depths of a chicken-hemoglobin phantom using SFP and MFP transducers were measured as 5 mm and 8 mm, respectively. The significant increase in the PAM image-based penetration depth of the chicken-hemoglobin phantom was a result of using the customized MFP transducer. Full article

(This article belongs to the Special Issue Imaging Sensors and Applications)

► Show Figures

Graphical abstract

16 pages, 4149 KiB

Open AccessArticle

3D Measurement of Human Chest and Abdomen Surface Based on 3D Fourier Transform and Time Phase Unwrapping

by Haibin Wu, Shuang Yu and Xiaoyang Yu

Sensors 2020, 20(4), 1091; https://doi.org/10.3390/s20041091 - 17 Feb 2020

Cited by 7 | Viewed by 2630

Abstract

Monitoring respiratory movements is an effective way to improve radiotherapy treatments of thoracic and abdominal tumors, but the current approach is limited to measuring specific points in the chest and abdomen. In this paper, a dynamic three-dimensional (3D) measurement approach of the human [...] Read more.

Monitoring respiratory movements is an effective way to improve radiotherapy treatments of thoracic and abdominal tumors, but the current approach is limited to measuring specific points in the chest and abdomen. In this paper, a dynamic three-dimensional (3D) measurement approach of the human chest and abdomen surface is proposed, which can infer tumor movement more accurately, so the radiotherapy damage to the human body can be reduced. Firstly, color stripe patterns in the RGB color model are projected, then after color correction, the collected stripe image sequences are separated into the three RGB primary color stripe image sequences. Secondly, a fringe projection approach is used to extract the folded phase combined 3D Fourier transform with 3D Gaussian filtering. By the relationship between adjacent fringe images in the time sequence, Gaussian filter parameters with individual characteristics are designed and optimized to improve the accuracy of wrapped phase extraction. In addition, based on the difference between the fractional parts of the folded phase error, one remainder equation can be determined, which is used for time-phase unwrapping. The simulation model and human experiments show that the proposed approach can obtain the 3D image sequences of the chest and abdomen surface in respiratory motion effectively and accurately with strong anti-interference ability. Full article

(This article belongs to the Special Issue Imaging Sensors and Applications)

► Show Figures

Figure 1

18 pages, 6333 KiB

Open AccessArticle

Active 3D Imaging of Vegetation Based on Multi-Wavelength Fluorescence LiDAR

by Xingmin Zhao, Shuo Shi, Jian Yang, Wei Gong, Jia Sun, Biwu Chen, Kuanghui Guo and Bowen Chen

Sensors 2020, 20(3), 935; https://doi.org/10.3390/s20030935 - 10 Feb 2020

Cited by 13 | Viewed by 3450

Abstract

Comprehensive and accurate vegetation monitoring is required in forestry and agricultural applications. The optical remote sensing method could be a solution. However, the traditional light detection and ranging (LiDAR) scans a surface to create point clouds and provide only 3D-state information. Active laser-induced [...] Read more.

Comprehensive and accurate vegetation monitoring is required in forestry and agricultural applications. The optical remote sensing method could be a solution. However, the traditional light detection and ranging (LiDAR) scans a surface to create point clouds and provide only 3D-state information. Active laser-induced fluorescence (LIF) only measures the photosynthesis and biochemical status of vegetation and lacks information about spatial structures. In this work, we present a new Multi-Wavelength Fluorescence LiDAR (MWFL) system. The system extended the multi-channel fluorescence detection of LIF on the basis of the LiDAR scanning and ranging mechanism. Based on the principle prototype of the MWFL system, we carried out vegetation-monitoring experiments in the laboratory. The results showed that MWFL simultaneously acquires the 3D spatial structure and physiological states for precision vegetation monitoring. Laboratory experiments on interior scenes verified the system’s performance. Fluorescence point cloud classification results were evaluated at four wavelengths and by comparing them with normal vectors, to assess the MWFL system capabilities. The overall classification accuracy and Kappa coefficient increased from 70.7% and 0.17 at the single wavelength to 88.9% and 0.75 at four wavelengths. The overall classification accuracy and Kappa coefficient improved from 76.2% and 0.29 at the normal vectors to 92.5% and 0.84 at the normal vectors with four wavelengths. The study demonstrated that active 3D fluorescence imaging of vegetation based on the MWFL system has a great application potential in the field of remote sensing detection and vegetation monitoring. Full article

(This article belongs to the Special Issue Imaging Sensors and Applications)

► Show Figures

Figure 1

Review

Jump to: Editorial, Research

19 pages, 3095 KiB

Open AccessFeature PaperReview

Current Development and Applications of Super-Resolution Ultrasound Imaging

by Qiyang Chen, Hyeju Song, Jaesok Yu and Kang Kim

Sensors 2021, 21(7), 2417; https://doi.org/10.3390/s21072417 - 01 Apr 2021

Cited by 24 | Viewed by 6428

Abstract

Abnormal changes of the microvasculature are reported to be key evidence of the development of several critical diseases, including cancer, progressive kidney disease, and atherosclerotic plaque. Super-resolution ultrasound imaging is an emerging technology that can identify the microvasculature noninvasively, with unprecedented spatial resolution [...] Read more.

Abnormal changes of the microvasculature are reported to be key evidence of the development of several critical diseases, including cancer, progressive kidney disease, and atherosclerotic plaque. Super-resolution ultrasound imaging is an emerging technology that can identify the microvasculature noninvasively, with unprecedented spatial resolution beyond the acoustic diffraction limit. Therefore, it is a promising approach for diagnosing and monitoring the development of diseases. In this review, we introduce current super-resolution ultrasound imaging approaches and their preclinical applications on different animals and disease models. Future directions and challenges to overcome for clinical translations are also discussed. Full article

(This article belongs to the Special Issue Imaging Sensors and Applications)

► Show Figures

Figure 1

35 pages, 15833 KiB

Open AccessReview

Why Are Viscosity and Nonlinearity Bound to Make an Impact in Clinical Elastographic Diagnosis?

by Guillermo Rus, Inas H. Faris, Jorge Torres, Antonio Callejas and Juan Melchor

Sensors 2020, 20(8), 2379; https://doi.org/10.3390/s20082379 - 22 Apr 2020

Cited by 47 | Viewed by 4385

Abstract

The adoption of multiscale approaches by the biomechanical community has caused a major improvement in quality in the mechanical characterization of soft tissues. The recent developments in elastography techniques are enabling in vivo and non-invasive quantification of tissues’ mechanical properties. Elastic changes in [...] Read more.

The adoption of multiscale approaches by the biomechanical community has caused a major improvement in quality in the mechanical characterization of soft tissues. The recent developments in elastography techniques are enabling in vivo and non-invasive quantification of tissues’ mechanical properties. Elastic changes in a tissue are associated with a broad spectrum of pathologies, which stems from the tissue microstructure, histology and biochemistry. This knowledge is combined with research evidence to provide a powerful diagnostic range of highly prevalent pathologies, from birth and labor disorders (prematurity, induction failures, etc.), to solid tumors (e.g., prostate, cervix, breast, melanoma) and liver fibrosis, just to name a few. This review aims to elucidate the potential of viscous and nonlinear elastic parameters as conceivable diagnostic mechanical biomarkers. First, by providing an insight into the classic role of soft tissue microstructure in linear elasticity; secondly, by understanding how viscosity and nonlinearity could enhance the current diagnosis in elastography; and finally, by compounding preliminary investigations of those elastography parameters within different technologies. In conclusion, evidence of the diagnostic capability of elastic parameters beyond linear stiffness is gaining momentum as a result of the technological and imaging developments in the field of biomechanics. Full article

(This article belongs to the Special Issue Imaging Sensors and Applications)

► Show Figures

Graphical abstract

Journal Menu

Journal Browser

Imaging Sensors and Applications

Share This Special Issue

Special Issue Editors

Special Issue Information

Keywords

Published Papers (20 papers)

Editorial

Research

Review

Further Information

Guidelines

MDPI Initiatives

Follow MDPI