The use of echolocation for navigating in dense, cluttered environments is a challenge due to the need for rapid sampling of objects in the face of delayed echoes from objects. In the wild, echolocating bats frequently encounter this situation when leaving the roost or while hunting. If long-delay echoes from a distant object are received after the next pulse is sent out, these "aliased" echoes appear as close-range phantom objects. Little is known about how bats cope with these situations. In this work, we demonstrate a novel strategy to manage aliasing in cases where a single target is actively being tracked at close range. This paper presents three reactive strategies for a high pulse-rate sonar system to combat aliased echoes: (1) changing the interpulse interval to move the aliased echoes away in time from the tracked target, (2) changing positions to create a geometry without aliasing, and (3) a phase-based, transmission beam-shaping strategy to illuminate the target and not the aliasing object.
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http://dx.doi.org/10.3389/fnins.2018.00177 | DOI Listing |
Magn Reson Med
July 2021
Bernard and Irene Schwartz Center for Biomedical Imaging, Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University School of Medicine, New York, New York, USA.
Purpose: To develop a simultaneous dual-slab three-dimensional gradient-echo spectroscopic imaging (GSI) technique with frequency drift compensation for rapid (<6 min) bilateral measurement of fatty acid composition (FAC) in mammary adipose tissue.
Methods: A bilateral GSI sequence was developed using a simultaneous dual-slab excitation followed by 128 monopolar echoes. A short train of navigator echoes without phase or partition encoding was included at the beginning of each pulse repetition time period to correct for frequency variation caused by respiration and heating of the cryostat.
Sensors (Basel)
October 2018
Institute of Electronic Engineering, Xidian University, Xi'an 710071, China.
In multiple-input multiple-output synthetic aperture radar (MIMO⁻SAR) signal processing, a reliable separation of multiple transmitted waveforms is one of the most important and challenging issues, for the unseparated signal will degrade the performance of most MIMO⁻SAR applications. As a solution to this problem, a novel APC⁻MIMO⁻SAR system is proposed based on the azimuth phase coding (APC) technique to transmit multiple waveforms simultaneously. Although the echo aliasing occurs in the time domain and Doppler domain, the echoes can be separated well without performance degradation by implementing the azimuth digital beamforming (DBF) technique, comparing to the performance of the orthogonal waveforms.
View Article and Find Full Text PDFUltraschall Med
June 2018
Glen McLaughlin Ph. D., San Carlos, CA 94070, United States.
As a continuation of parts 1 1 and 2 2, this article discusses artifacts as caused by insufficient temporal resolution, artifacts in color and spectral Doppler sonography, and information regarding artifacts in sonography with contrast agents. There are artifacts that occur in B-mode sonography as well as in Doppler imaging methods and sonography with contrast agents, such as slice thickness artifacts and bow artifacts, shadows, mirroring, and artifacts due to refraction that appear, for example, as double images, because they are based on the same formation mechanisms. In addition, there are artifacts specific to Doppler sonography, such as the twinkling artifact, and method-based motion artifacts, such as aliasing, the ureteric jet, and due to tissue vibration.
View Article and Find Full Text PDFBiomed Eng Online
April 2018
Department of Diagnostic Imaging, Medical University of Lodz, Łódź, ul. Kopcińskiego 22, 90-153, Lodz, Poland.
Background: With the development of versatile magnetic resonance acquisition techniques there arises a need for more advanced imaging simulation tools to enable adequate image appearance prediction, measurement sequence design and testing thereof. Recently, there is a growing interest in phase contrast angiography (PCA) sequence due to the capabilities of blood flow quantification that it offers. Moreover, as it is a non-contrast enhanced protocol, it has become an attractive option in areas, where usage of invasive contrast agents is not indifferent for the imaged tissue.
View Article and Find Full Text PDFFront Neurosci
March 2018
Electrical and Computer Engineering Department, University of Maryland, College Park, College Park, MD, United States.
The use of echolocation for navigating in dense, cluttered environments is a challenge due to the need for rapid sampling of objects in the face of delayed echoes from objects. In the wild, echolocating bats frequently encounter this situation when leaving the roost or while hunting. If long-delay echoes from a distant object are received after the next pulse is sent out, these "aliased" echoes appear as close-range phantom objects.
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