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Title:Effect of null subtraction imaging technique on grating lobes
Author(s):Min, Byung Hoon
Contributor(s):Oelze, Michael L.
Subject(s):null subtraction imaging
Abstract:In ultrasonic imaging, the presence of grating lobes results in imaging artifacts, causing image degradation and distortion. The grating lobes occur when the center-to-center spacing between elements of the arrays, i.e., the pitch, of the transducer is greater than or equal to the wavelength. When the pitch size of the array is smaller, the presence of grating lobes is determined by the steering angle. Generally, apodization is used to reduce the amplitude of the side lobes at the expense of widening the main lobe, which decreases the lateral resolution. Null subtraction imaging (NSI) is a non-linear imaging processing technique that uses three different apodization functions to decrease the amplitude of the side lobes while dramatically improving the lateral resolution. Due to the subtraction involved in the nonlinear processing scheme, we hypothesized that the NSI would also reduce the grating lobe levels. To appraise the performance of the NSI technique on grating lobes, theoretical simulations were performed using Field-II and experimental measurements were performed using an L9-4/38 array connected to an Ultrasonix Tablet system with a SonixDAQ to scan a single wire target. The image was reconstructed using delays to acquire grating lobes when steered, and then beamformed with NSI and rectangular apodization to compare the amplitudes and spot sizes of grating lobe levels. The simulation results revealed up to six times decrease in the grating lobe to main lobe ratio for NSI compared to rectangular apodization, while experimentally the grating lobe to main lobe ratio hardly showed changes. The experimental results showed that the grating lobe appeared very thin and confined with the spot size of 0.09 mm^2 for the NSI compared to 2.03 mm^2 for the rectangular apodization.
Issue Date:2017-05
Date Available in IDEALS:2017-08-22

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