scholarly journals Fast Correction of “Finite Aperture Effect” in Photoacoustic Tomography Based on Spatial Impulse Response

Photonics ◽  
2021 ◽  
Vol 8 (9) ◽  
pp. 356
Author(s):  
Xiaofei Luo ◽  
Jiaying Xiao ◽  
Congcong Wang ◽  
Bo Wang
Keyword(s):  
Impulse Response ◽  
Finite Size ◽  
Biological Tissues ◽  
New Method ◽  
Lateral Resolution ◽  
Diffusion Limit ◽  
Reconstruction Method ◽  
Rotation Center ◽  
Finite Aperture ◽  
Aperture Effect

Photoacoustic computed tomography (PACT) is a fast-developing imaging technique, which can provide structural and functional information in biological tissues with high-resolution beyond the depth of the optical diffusion limit. However, the most current PACT reconstruction method generally employs a point detector assumption, whereas in most PAT systems with circular or spherical scanning modes, the transducer is mostly flat and with a finite size. This model mismatch leads to a notable deterioration in the lateral direction in regions far from the rotation center, which is known as the “finite aperture effect”. In this work, we propose to compensate a novel Back-projection (BP) method based on the transducer’s spatial impulse response (SIR) for fast correction of the “finite aperture effect”. The SIR accounts for the waveform change of the transducer for an arbitrary point source due to the geometry of the detection surface. Simulation results showed that the proposed SIR-BP method can effectively improve the lateral resolution and signal to noise ratio (SNR) in the off-center regions. For a target 4.5 mm far from the rotation center, this new method improved the lateral resolution about five times along with a 7 dB increase in the SNR. Experimental results also showed that this SIR-BP method can well restore the image angular blur to recover small structures, as demonstrated by the imaging of leaf veins. This new method offers a valuable alternative to the conventional BP method, and can guide the design of PAT systems based on circular/spherical scan.

scholarly journals Reconstructing the NH Mean Temperature: Can Underestimation of Trends and Variability Be Avoided?

2011 ◽  
Vol 24 (3) ◽  
pp. 674-692 ◽  
Author(s):  
Bo Christiansen
Keyword(s):  
Low Frequency ◽  
New Method ◽  
Temperature Fields ◽  
Reconstruction Method ◽  
Climate Reconstructions ◽  
Reconstruction Methods ◽  
Low Frequency Variability ◽  
Climate Simulations ◽  
Mean Climate ◽  
Geographical Locations

Abstract There are indications that hemispheric-mean climate reconstructions seriously underestimate the amplitude of low-frequency variability and trends. Some of the theory of linear regression and error-in-variables models is reviewed to identify the sources of this problem. On the basis of the insight gained, a reconstruction method that is supposed to minimize the underestimation is formulated. The method consists of reconstructing the local temperatures at the geographical locations of the proxies, followed by calculating the hemispheric average. The method is tested by applying it to an ensemble of surrogate temperature fields based on two climate simulations covering the last 500 and 1000 yr. Compared to the regularized expectation maximization (RegEM) truncated total least squares (TTLS) method and a composite-plus-scale method—two methods recently used in the literature—the new method strongly improves the behavior regarding low-frequency variability and trends. The potential importance in real-world situations is demonstrated by applying the methods to a set of 14 decadally smoothed proxies. Here the new method shows much larger low-frequency variability and a much colder preindustrial temperature level than the other reconstruction methods. However, this should mainly be seen as a demonstration of the potential losses and gains of variability, as the reconstructions based on the 14 decadally smoothed proxies are not very robust.

Intermittent-contact capacitance spectroscopy – A new method for determining C(V) curves with sub-micron lateral resolution

2010 ◽  
Vol 50 (9-11) ◽  
pp. 1511-1513 ◽  
Author(s):  
Roland Biberger ◽  
Guenther Benstetter ◽  
Holger Goebel ◽  
Alexander Hofer
Keyword(s):  
New Method ◽  
Lateral Resolution ◽  
Intermittent Contact ◽  
Capacitance Spectroscopy

Analysis of Recrystallization Behavior of Hot-Deformed Austenite Reconstructed from EBSD Orientation Maps of Lath Martensite

2016 ◽  
Vol 879 ◽  
pp. 2389-2394
Author(s):  
Manabu Kubota ◽  
Kohsaku Ushioda ◽  
Goro Miyamoto ◽  
Tadashi Furuhara
Keyword(s):  
Hot Deformation ◽  
Lath Martensite ◽  
New Method ◽  
Reconstruction Method ◽  
Low Alloy Steels ◽  
Recrystallization Behavior ◽  
Compression Direction ◽  
Orientation Map ◽  
Alloy Steels ◽  
Parent Austenite

The recrystallization behavior of hot-deformed austenite of 0.55% C low alloy steels at 900, 850 and 800°C was investigated by a conventional double-hit compression test and a new method which reconstructs the parent austenite orientation map from an EBSD (electron backscattering diffraction) orientation map of daughter lath martensite. The new method can clearly reconstruct the parent austenite structure at high temperature from the daughter lath martensite structure and we can obtain the information on crystal orientation of the work-hardened austenite. It was revealed that recrystallization of austenite at 800 °C is significantly retarded by the addition of 0.1% V. The strong texture of <110> parallel to the compression direction develops just after the hot-deformation, but this texture becomes weaker as the recrystallization progresses. By applying the reconstruction method, it becomes possible to evaluate various phenomena related to the hot-deformation of austenite

scholarly journals Three-Dimensional High-Energy Electron Radiography Method for Static Mesoscale Samples Diagnostics

2019 ◽  
Vol 9 (18) ◽  
pp. 3764
Author(s):  
Quantang Zhao ◽  
Yuanyuan Ma ◽  
Jiahao Xiao ◽  
Shuchun Cao ◽  
Xiaokang Shen ◽  
...  
Keyword(s):  
Three Dimensional ◽  
High Energy ◽  
Energy Electron ◽  
New Method ◽  
Reconstruction Method ◽  
High Energy Electron ◽  
Spherical Sample ◽  
Internal Structures ◽  
Dimensional Reconstruction ◽  
Application Potential

In this paper, we propose a new method for static mesoscale sample diagnosis using three-dimensional radiography with high-energy electron radiography (HEER). The principle of three-dimensional high-energy electron radiography (TDHEER) is elucidated, and the feasibility of this method is confirmed by start-to-end simulation results. TDHEER is realized by combining HEER with the three-dimensional reconstruction method, by which more information about the samples can be attained, especially regarding the samples’ internal structures. With our study, the internal structures and the three-dimensional positions of the spherical sample are determined with a ~3 μm resolution. We believe that this new method enhances the HEER diagnostic capability and extends its application potential in mesoscale sciences.

Diffractive Lenses for High Resolution Laser Based Failure Analysis

2005 ◽  
Author(s):  
Frank Zachariasse ◽  
Martijn J. Goossens
Keyword(s):  
High Resolution ◽  
Failure Analysis ◽  
Laser Scanning ◽  
New Method ◽  
Lateral Resolution ◽  
Back Side ◽  
Diffractive Lens ◽  
Standard Equipment ◽  
Diffractive Lenses ◽  
Better Than

Abstract In this paper we present a new method to increase the lateral resolution available in laser scanning failure analysis tools. By fabricating a diffractive lens on the back side of the die, the area of the circuit of interest, directly underneath the lens, may be studied with a lateral resolution up to 3.5 times better than without the lens. This method is easily implemented with standard equipment already present in most failure analysis laboratories, and overcomes some significant problems encountered with alternative resolution enhancing schemes.

The PSTD Method with the 4th-Order Time Integration for 3D TAT Reconstruction of a Breast Model

2014 ◽  
Vol 22 (04) ◽  
pp. 1450011 ◽  
Author(s):  
Gang Ye ◽  
Chunhua Deng ◽  
Qing Huo Liu
Keyword(s):  
Acoustic Waves ◽  
Breast Tissue ◽  
Biological Tissues ◽  
Phase Distortion ◽  
Acoustic Properties ◽  
Reconstruction Method ◽  
Time Resolved ◽  
Reconstruction Process ◽  
Breast Phantom ◽  
Ultrasound Signals

The thermoacoustic tomography (TAT) is a novel noninvasive and nonionizing medical imaging modality for breast cancer detection. In the TAT, a short pulse of microwave is irradiated to the breast tissue. The tissue absorbs the microwave energy and is heated up momentarily, thus it generates acoustic waves due to the thermoelastic expansion. If the pulse width of the microwave radiation is around one microsecond, the generated acoustic waves are ultrasonic and are in the MHz range. Wide-band ultrasonic transducers are employed to acquire the time-resolved ultrasound signals, which carry information about the microwave absorption properties (mainly related to conductivities) of different tissues. An image showing such properties can then be reconstructed from the time-resolved ultrasound signals. Most existing TAT reconstruction methods are based on the assumption that the tissue under study is acoustically homogeneous. In practice, however, most biological tissues are inhomogeneous. For example, the speed of sound has about 10% variation in breast tissue. The acoustic heterogeneity will cause phase distortion of the pressure field, which will in turn cause blurring in the reconstructed image, thus limiting the ability to resolve small objects. In this work, a 3D inhomogeneous reconstruction method based on pseudo-spectral time-domain (PSTD) is presented to overcome this problem. The method includes two steps. The first step is a homogeneous reconstruction process, from which an initial image is obtained. Since the inhomogeneity itself is usually an acoustic source, the shape and location of the inhomogeneity can be estimated. Then, the acoustic properties of the inhomogeneities (available from the literatures for known tissue types) are assigned to the classified regions, and the other reconstruction based on the updated acoustic property map is conducted. With this process, the phase distortion can be effectively corrected. So it can improve the ability to image small objects. A 3D breast phantom is used to study the proposed method. The breast phantom was generated based on the data set of the Visible Human Project. Regions of different tissue types have been classified and acoustic and electric properties are assigned to such regions. Small phantom tumors placed in the breast phantom have been reconstructed successfully with the inhomogeneous reconstruction method. Improved resolution has been achieved compared to that obtained by homogeneous method.

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