Two-Dimensional Photoacoustic/Ultrasonic Endoscopic Imaging Based on a Line-Focused Transducer

Existing acoustic-resolution photoacoustic/ultrasonic endoscopy (PA/USE) generally employs a point-focused transducer for ultrasound detection, which is only sensitive in its focal region, thus the lateral resolution and sensitivity drop dramatically when the targets move far from its focus. Even if a dynamic focusing algorithm is applied, the sensitivity out of the transducer focus is still much lower than that in the focus in ultrasonic imaging mode. In this work, we propose an acoustic-resolution PA/USE with a line-focused transducer to realize automatic focusing for the first time. In comparison to a point-focused transducer, the line-focused transducer emits a more uniform sound field, causing the original signal intensity and signal-to-noise ratio (SNR) of the front and rear targets to be closer in the radial direction, which is beneficial for improving target signal uniformity in ultrasonic imaging. Simultaneously, we improved the resolution of the defocus area by modifying a prior work of back-projection (BP) reconstruction algorithm typically used in point-focused transducer based PAE and applying it to line-focused PA/USE. This combined approach may significantly enhance the depth of field of ultrasonic imaging and the resolution of the defocus zone in PA/US imaging, compared to the conventional method. Sufficient numerical simulations and phantom experiments were performed to verify this method. The results show that our method can effectively improve the lateral resolution in the image’s defocused region to achieve automatic focusing and perfectly solve the defect of the target signal difference in the far-focus region in ultrasonic imaging, while also enhancing the image SNR and contrast. The proposed method in this paper lays foundations for the realization of photoacoustic/ultrasonic combined endoscopy with enhanced lateral resolution and depth of field, which can potentially benefit a many of biomedical applications.

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Synthetic aperture imaging in acoustic microscopy

10.32920/ryerson.14663121 ◽

2021 ◽

Author(s):

Golafsoun Ameri

Keyword(s):

Image Resolution ◽

Acoustic Microscopy ◽

Synthetic Aperture ◽

Lateral Resolution ◽

Depth Of Field ◽

Single Element ◽

Focal Region ◽

Array Transducer ◽

Small Depth ◽

Better Than

Acoustic microscopy (AM) provides micro-meter resolution using a highly focused single-element transducer. A drawback in AM is a relatively small depth of field, resulting in poor resolution outside the focus. Synthetic aperature focusing technique (SAFT) can be used to improve the image resolution throughout the field of view. SAFT mathematically synthesizes the effect of an array transducer and produces dynamic focusing and depth-independent resolution. SAFT in time domain with and without apodization, TD-SAFT and ATD-SAFT, respectively, and in frequency domain (FD-SAFT) were implemented and tested using simulated and experimental radio-frequency data from an acoustic microscope at 400 MHz. Lateral resolution of all the SAFT reconstructed images were better than those of the conventional B-mode images. While TD-SAFT and FD-SAFT permformed better than ATD-SAFT in improving the lateral resolution, ATD-SAFT provided lower side lobes. In conclusion, SAFT improves resolution in AM outside the focal region.

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Fundamental Study on Development of Air-Coupled Ultrasonic Imaging Measurement for Fuel Debris Inspection

Volume 9: Student Paper Competition ◽

10.1115/icone26-82150 ◽

2018 ◽

Author(s):

Hironobu Kiuchi ◽

Shun Kimura ◽

Ari Hamdani ◽

Hideharu Takahashi ◽

Hiroshige Kikura ◽

...

Keyword(s):

Nuclear Power ◽

Focused Ultrasound ◽

Imaging System ◽

Signal To Noise Ratio ◽

Ultrasonic Imaging ◽

Sound Field ◽

Beam Width ◽

Imaging Method ◽

Fundamental Study ◽

Control Rod

Retrieval of fuel debris is one of the most urgent issues regarding the decommissioning of Fukushima Daiichi Nuclear Power Plant (NPP). A retrieval of fuel debris requires a measurement system which can be applied in the severe environment to investigate inside the Reactor Pressure Vessel (RPV) and the Control Rod Drive (CRD) housing. In this study, an air-coupled ultrasonic measurement is proposed because of the feasibility of its application in the severe environment such as the high-radiation atmosphere. However, compared with using it in water or solids, there are some difficulties with applying the air-coupled ultrasonic technique. Therefore, we employed a point-focused transducer which can converge ultrasonic energy in a small area. As a fundamental study, this paper focuses on the experimental assessment of the potential feasibility and property of the developed air-coupled ultrasonic imaging. Firstly, to obtain the property and characteristics of the point-focused transducer, the sound field of the transducer was measured. The sound field showed the convergence rate, acoustic intensity and the beam width of the transducer. Secondly, in order to improve Signal to Noise ratio (SN ratio), the ultrasonic imaging method using a frequency correlation was designed taking the feeble ultrasonic echoes from complex shape object into consideration. Finally, the shape of a test specimen, which imitates a fuel debris, was measured with the developed imaging system. The ultrasonic image of the specimen showed a good agreement with a photo. In conclusion, the imaging using air-coupled point-focused ultrasound was developed to successfully visualize a mock fuel debris from a relatively short distance of 40 mm – 100 mm.

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Synthetic aperture imaging in acoustic microscopy

10.32920/ryerson.14663121.v1 ◽

2021 ◽

Author(s):

Golafsoun Ameri

Keyword(s):

Image Resolution ◽

Acoustic Microscopy ◽

Synthetic Aperture ◽

Lateral Resolution ◽

Depth Of Field ◽

Single Element ◽

Focal Region ◽

Array Transducer ◽

Small Depth ◽

Better Than

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Cryomicroscopy of crotoxin complex crystals at 400 KV

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100156109 ◽

1989 ◽

Vol 47 ◽

pp. 826-827

Author(s):

Jaap Brink ◽

Wah Chiu

Keyword(s):

Signal To Noise Ratio ◽

3D Structure ◽

Three Dimensional ◽

Carbon Films ◽

Depth Of Field ◽

Basic Subunit ◽

Ewald Sphere ◽

Diffraction Patterns ◽

Complex Crystals ◽

Acidic Subunit

The crotoxin complex is a potent neurotoxin composed of a basic subunit (Mr = 12,000) and an acidic subunit (M = 10,000). The basic subunit possesses phospholipase activity whereas the acidic subunit shows no enzymatic activity at all. The complex's toxocity is expressed both pre- and post-synaptically. The crotoxin complex forms thin crystals suitable for electron crystallography. The crystals diffract up to 0.16 nm in the microscope, whereas images show reflections out to 0.39 nm2. Ultimate goal in this study is to obtain a three-dimensional (3D-) structure map of the protein around 0.3 nm resolution. Use of 100 keV electrons in this is limited; the unit cell's height c of 25.6 nm causes problems associated with multiple scattering, radiation damage, limited depth of field and a more pronounced Ewald sphere curvature. In general, they lead to projections of the unit cell, which at the desired resolution, cannot be interpreted following the weak-phase approximation. Circumventing this problem is possible through the use of 400 keV electrons. Although the overall contrast is lowered due to a smaller scattering cross-section, the signal-to-noise ratio of especially higher order reflections will improve due to a smaller contribution of inelastic scattering. We report here our preliminary results demonstrating the feasability of the data collection procedure at 400 kV.Crystals of crotoxin complex were prepared on carbon-covered holey-carbon films, quench frozen in liquid ethane, inserted into a Gatan 626 holder, transferred into a JEOL 4000EX electron microscope equipped with a pair of anticontaminators operating at −184°C and examined under low-dose conditions. Selected area electron diffraction patterns (EDP's) and images of the crystals were recorded at 400 kV and −167°C with dose levels of 5 and 9.5 electrons/Å, respectively.

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Nondestructive Inspection of Thin, Low-Z Samples using Multiplexed Compton Scatter Tomography

MRS Proceedings ◽

10.1557/proc-503-297 ◽

1997 ◽

Vol 503 ◽

Cited By ~ 1

Author(s):

B. L. Evans ◽

J. B. Martin ◽

L. W. Burggraf

Keyword(s):

Signal To Noise Ratio ◽

Reconstruction Algorithm ◽

Filtered Backprojection ◽

Line Broadening ◽

Compton Scatter ◽

X Ray ◽

Tomography System ◽

Transmission Computed Tomography ◽

High Purity Germanium ◽

Scattered Energy

ABSTRACTThe viability of a Compton scattering tomography system for nondestructively inspecting thin, low Z samples for corrosion is examined. This technique differs from conventional x-ray backscatter NDI because it does not rely on narrow collimation of source and detectors to examine small volumes in the sample. Instead, photons of a single energy are backscattered from the sample and their scattered energy spectra are measured at multiple detector locations, and these spectra are then used to reconstruct an image of the object. This multiplexed Compton scatter tomography technique interrogates multiple volume elements simultaneously. Thin samples less than 1 cm thick and made of low Z materials are best imaged with gamma rays at or below 100 keV energy. At this energy, Compton line broadening becomes an important resolution limitation. An analytical model has been developed to simulate the signals collected in a demonstration system consisting of an array of planar high-purity germanium detectors. A technique for deconvolving the effects of Compton broadening and detector energy resolution from signals with additive noise is also presented. A filtered backprojection image reconstruction algorithm with similarities to that used in conventional transmission computed tomography is developed. A simulation of a 360–degree inspection gives distortion-free results. In a simulation of a single-sided inspection, a 5 mm × 5 mm corrosion flaw with 50% density is readily identified in 1-cm thick aluminum phantom when the signal to noise ratio in the data exceeds 28.

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Ultrasonic Block Compressed Sensing Imaging Reconstruction Algorithm Based on Wavelet Sparse Representation

Current Medical Imaging Formerly Current Medical Imaging Reviews ◽

10.2174/1573405615666191209151746 ◽

2020 ◽

Vol 16 (3) ◽

pp. 262-272

Author(s):

Guangzhi Dai ◽

Zhiyong He ◽

Hongwei Sun

Keyword(s):

Compressed Sensing ◽

Sparse Representation ◽

Linear Array ◽

Imaging System ◽

Ultrasonic Imaging ◽

Large Data ◽

Reconstruction Algorithm ◽

Array Transducer ◽

Total Data ◽

Block Compressed Sensing

Background: This study is carried out targeting the problem of slow response time and performance degradation of imaging system caused by large data of medical ultrasonic imaging. In view of the advantages of CS, it is applied to medical ultrasonic imaging to solve the above problems. Objective: Under the condition of satisfying the speed of ultrasound imaging, the quality of imaging can be further improved to provide the basis for accurate medical diagnosis. Methods: According to CS theory and the characteristics of the array ultrasonic imaging system, block compressed sensing ultrasonic imaging algorithm is proposed based on wavelet sparse representation. Results: Three kinds of observation matrices have been designed on the basis of the proposed algorithm, which can be selected to reduce the number of the linear array channels and the complexity of the ultrasonic imaging system to some extent. Conclusion: The corresponding simulation program is designed, and the result shows that this algorithm can greatly reduce the total data amount required by imaging and the number of data channels required for linear array transducer to receive data. The imaging effect has been greatly improved compared with that of the spatial frequency domain sparse algorithm.

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Model-based reconstruction algorithm in the detection of acute trauma-related lesions in brain CT examinations

The Neuroradiology Journal ◽

10.1177/19714009211008751 ◽

2021 ◽

pp. 197140092110087

Author(s):

Andrea De Vito ◽

Cesare Maino ◽

Sophie Lombardi ◽

Maria Ragusi ◽

Cammillo Talei Franzesi ◽

...

Keyword(s):

Image Quality ◽

Iterative Reconstruction ◽

Signal To Noise Ratio ◽

Reconstruction Algorithm ◽

Signal To Noise ◽

Subjective Image Quality ◽

Model Based ◽

Hybrid Iterative Reconstruction ◽

Noise Ratio ◽

Enhanced Computed Tomography

Background and purpose To evaluate the added value of a model-based reconstruction algorithm in the assessment of acute traumatic brain lesions in emergency non-enhanced computed tomography, in comparison with a standard hybrid iterative reconstruction approach. Materials and methods We retrospectively evaluated a total of 350 patients who underwent a 256-row non-enhanced computed tomography scan at the emergency department for brain trauma. Images were reconstructed both with hybrid and model-based iterative algorithm. Two radiologists, blinded to clinical data, recorded the presence, nature, number, and location of acute findings. Subjective image quality was performed using a 4-point scale. Objective image quality was determined by computing the signal-to-noise ratio and contrast-to-noise ratio. The agreement between the two readers was evaluated using k-statistics. Results A subjective image quality analysis using model-based iterative reconstruction gave a higher detection rate of acute trauma-related lesions in comparison to hybrid iterative reconstruction (extradural haematomas 116 vs. 68, subdural haemorrhages 162 vs. 98, subarachnoid haemorrhages 118 vs. 78, parenchymal haemorrhages 94 vs. 64, contusive lesions 36 vs. 28, diffuse axonal injuries 75 vs. 31; all P<0.001). Inter-observer agreement was moderate to excellent in evaluating all injuries (extradural haematomas k=0.79, subdural haemorrhages k=0.82, subarachnoid haemorrhages k=0.91, parenchymal haemorrhages k=0.98, contusive lesions k=0.88, diffuse axonal injuries k=0.70). Quantitatively, the mean standard deviation of the thalamus on model-based iterative reconstruction images was lower in comparison to hybrid iterative one (2.12 ± 0.92 vsa 3.52 ± 1.10; P=0.030) while the contrast-to-noise ratio and signal-to-noise ratio were significantly higher (contrast-to-noise ratio 3.06 ± 0.55 vs. 1.55 ± 0.68, signal-to-noise ratio 14.51 ± 1.78 vs. 8.62 ± 1.88; P<0.0001). Median subjective image quality values for model-based iterative reconstruction were significantly higher ( P=0.003). Conclusion Model-based iterative reconstruction, offering a higher image quality at a thinner slice, allowed the identification of a higher number of acute traumatic lesions than hybrid iterative reconstruction, with a significant reduction of noise.

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Optimization of SPECT/CT imaging protocols for quantitative and qualitative 99mTc SPECT

EJNMMI Physics ◽

10.1186/s40658-021-00405-3 ◽

2021 ◽

Vol 8 (1) ◽

Author(s):

Dennis Kupitz ◽

Heiko Wissel ◽

Jan Wuestemann ◽

Stephanie Bluemel ◽

Maciej Pech ◽

...

Keyword(s):

Signal To Noise Ratio ◽

Quantitative Imaging ◽

Scatter Correction ◽

Reconstruction Algorithm ◽

Weighting Factor ◽

Quantitative Spect ◽

Pet Ct ◽

Spect Acquisition ◽

The Mean ◽

A Minor

Abstract Background The introduction of hybrid SPECT/CT devices enables quantitative imaging in SPECT, providing a methodological setup for quantitation using SPECT tracers comparable to PET/CT. We evaluated a specific quantitative reconstruction algorithm for SPECT data using a 99mTc-filled NEMA phantom. Quantitative and qualitative image parameters were evaluated for different parametrizations of the acquisition and reconstruction protocol to identify an optimized quantitative protocol. Results The reconstructed activity concentration (ACrec) and the signal-to-noise ratio (SNR) of all examined protocols (n = 16) were significantly affected by the parametrization of the weighting factor k used in scatter correction, the total number of iterations and the sphere volume (all, p < 0.0001). The two examined SPECT acquisition protocols (with 60 or 120 projections) had a minor impact on the ACrec and no significant impact on the SNR. In comparison to the known AC, the use of default scatter correction (k = 0.47) or object-specific scatter correction (k = 0.18) resulted in an underestimation of ACrec in the largest sphere volume (26.5 ml) by − 13.9 kBq/ml (− 16.3%) and − 7.1 kBq/ml (− 8.4%), respectively. An increase in total iterations leads to an increase in estimated AC and a decrease in SNR. The mean difference between ACrec and known AC decreased with an increasing number of total iterations (e.g., for 20 iterations (2 iterations/10 subsets) = − 14.6 kBq/ml (− 17.1%), 240 iterations (24i/10s) = − 8.0 kBq/ml (− 9.4%), p < 0.0001). In parallel, the mean SNR decreased significantly from 2i/10s to 24i/10s by 76% (p < 0.0001). Conclusion Quantitative SPECT imaging is feasible with the used reconstruction algorithm and hybrid SPECT/CT, and its consistent implementation in diagnostics may provide perspectives for quantification in routine clinical practice (e.g., assessment of bone metabolism). When combining quantitative analysis and diagnostic imaging, we recommend using two different reconstruction protocols with task-specific optimized setups (quantitative vs. qualitative reconstruction). Furthermore, individual scatter correction significantly improves both quantitative and qualitative results.

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Ultrasonic Imaging of Thick Carbon Fiber Reinforced Polymers through Pulse-Compression-Based Phased Array

Applied Sciences ◽

10.3390/app11041508 ◽

2021 ◽

Vol 11 (4) ◽

pp. 1508

Author(s):

Muhammad Khalid Rizwan ◽

Stefano Laureti ◽

Hubert Mooshofer ◽

Matthias Goldammer ◽

Marco Ricci

Keyword(s):

Carbon Fiber ◽

Pulse Compression ◽

Phased Array ◽

Signal To Noise Ratio ◽

Near Field ◽

Ultrasonic Imaging ◽

Fiber Reinforced Polymers ◽

Fiber Reinforced ◽

Custom Made ◽

Carbon Fiber Reinforced

The use of pulse-compression in ultrasonic non-destructive testing has assured, in various applications, a significant improvement in the signal-to-noise ratio. In this work, the technique is combined with linear phased array to improve the sensitivity and resolution in the ultrasonic imaging of highly attenuating and scattering materials. A series of tests were conducted on a 60 mm thick carbon fiber reinforced polymer benchmark sample with known defects using a custom-made pulse-compression-based phased array system. Sector scan and total focusing method images of the sample were obtained with the developed system and were compared with those reconstructed by using a commercial pulse-echo phased array system. While an almost identical sensitivity was found in the near field, the pulse-compression-based system surpassed the standard one in the far-field producing a more accurate imaging of the deepest defects and of the backwall of the sample.

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Study on Sound Field of High Intensity Focused Ultrasound with Short Focal Length

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.195-196.364 ◽

2012 ◽

Vol 195-196 ◽

pp. 364-369 ◽

Cited By ~ 1

Author(s):

Jin Hua Zhao ◽

Li Li Yu ◽

Chun Hui ◽

Bin Feng Huang ◽

Chao Li ◽

...

Keyword(s):

Nonlinear Effect ◽

Sound Pressure ◽

Focal Length ◽

Sound Field ◽

High Intensity Focused Ultrasound ◽

Beam Equation ◽

Focal Region ◽

Interface Position ◽

Short Focal Length ◽

Planar Wave

In this paper, numerical simulation of sound field with short focal length is performed, which is based on spheroidal beam equation (SBE) in frequency-domain for transducer with a wide aperture angle. And we made some experiments on vitro bovine liver to explore the characteristic of sound pressure and-3dB sound focal region at different positions of incident interface. It is found that with a fixed curvature radius if the focal length is shorter under the skin, the amplitude of sound pressure will be higher on the focus and the shape of-3dB sound focal region will be smaller. When the incident interface is in the range of planar wave, nonlinear effect is strong and the focus will change with the interface position. Especially when the position is near to transition location between planar wave and spheroidal wave, the nonlinear effect is lowered. While the focus is closer to the sound source so as to burn the scarfskin easily. When the interface is in the range of spheroidal wave, the focus position changes little but the side lobe effect due to refraction is obvious. And the focusing performance of transducer will be affected. The experimental results validate the accuracy of theoretical results. It is concluded that the position of incident interface should be selected reasonably with short focal length in the treatment of superficial tissue.

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