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Published on: June 12, 2021
Isolation of microbubbles beyond Sparrow's resolution limit in super-resolution ultrasonography using phase patterned
Junseok An1, Naohiro Sugita2, Tadahiko Shinshi2
1Department of Mechanical Engineering, Institute of Science Tokyo, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8501, Japan.
Abstract:
Objective. Super-resolution ultrasonography (SR-US) provides detailed microvasculature images, improving diagnostic precision. However, it typically depends on tacking microbubbles (MBs) used as contrast agents at low concentration. This process requires acquiring a large amount of acoustic data, leading to longer acquisition times. In this paper, we describe a method that allows for the use of higher concentrations of MBs, which reduces the acquisition time and enables high-speed SR-US. Our approach involves isolating and detecting individual MBs even when they are located close to each other, making it possible to use higher bubble concentrations efficiently.Approach. In this study, as introduced in previous research, we use phase patterned waves (PPWs) to isolate MBs by adjusting the intensities of each bubble's point spread function (PSF). The PPWs create high and low sound pressure across the lateral plane, optimizing the variation in PSF intensities for MBs positioned side by side. Unlike conventional irradiation method of ultrasound plane waves, PPWs cause significant sound pressure attenuation with increasing axial distance due to destructive interference. This effect allows us to alternate the PSF intensities for MBs aligned along the axial direction. By estimating the positions of MBs in both the lateral and axial directions and combining them into two-dimensional coordinates, we can accurately determine the final positions of the MBs.Main results. We applied PPWs and conventional ultrasound irradiation methods to estimate the positions of two MBs, achieving accuracy within 25% of the wavelength from their actual locations, even when the bubbles were closer than Sparrow's resolution limit. Furthermore, using an overlapped PSF model, we improved the accuracy of the estimated positions to within an average of 15% of the wavelength from their true locations, regardless of the number of overlapping MBs or their relative positions.Significance. Isolating MBs using PPWs is expected to enable high concentrations of MBs in SR-US, paving the way for high-speed SR-US.
Insights
This study introduces phase patterned waves (PPWs) to isolate microbubbles (MBs) in super-resolution ultrasonography (SR-US). This method enables higher MB concentrations, reducing acquisition time for high-speed SR-US imaging.
Area of Science:
- Medical Imaging
- Acoustic Physics
- Biomedical Engineering
Background:
- Super-resolution ultrasonography (SR-US) offers detailed microvasculature imaging for enhanced diagnostics.
- Current SR-US methods require low concentrations of microbubbles (MBs), leading to lengthy data acquisition times.
- Efficiently imaging at higher MB concentrations is crucial for advancing SR-US speed and diagnostic capabilities.
Purpose of the Study:
- To develop and validate a novel method for isolating and detecting individual microbubbles (MBs) at high concentrations.
- To enable high-speed super-resolution ultrasonography (SR-US) by reducing acoustic data acquisition times.
- To improve the efficiency and accuracy of MB detection in SR-US imaging.
Main Methods:
- Utilized phase patterned waves (PPWs) to precisely control the sound pressure and isolate individual MBs by adjusting their point spread function (PSF) intensities.
- Exploited destructive interference in PPWs to achieve axial distance discrimination of MBs, complementing lateral discrimination.
- Combined lateral and axial position estimations to determine precise 2D coordinates of MBs, even when closely spaced.
Main Results:
- Achieved accurate MB position estimation within 25% of the wavelength, surpassing Sparrow's resolution limit for closely located MBs.
- Improved positional accuracy to an average of 15% of the wavelength using an overlapped PSF model, irrespective of MB proximity or number.
- Demonstrated the capability to isolate and detect individual MBs effectively even at high concentrations.
Conclusions:
- The developed PPW-based method successfully isolates individual MBs at high concentrations, overcoming limitations of conventional ultrasound plane waves.
- This technique significantly reduces acoustic data acquisition time, paving the way for high-speed SR-US.
- The enhanced MB detection accuracy holds promise for improved diagnostic precision and clinical applications of SR-US.
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