Swept Frequency ARFI Transmit Beam for Uniform Tissue Displacement
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Solution Overview
Problem
Acoustic radiation force impulse (ARFI) imaging faces limitations due to the non-uniform response of hour-glass shaped ARFI pulses, which result in a limited range of locations for measuring tissue characteristics and undesired transducer heating, especially when trying to scan over a range of depths.
Innovation Solution
Implementing a swept frequency and time varying focal position in the ARFI transmit beam, where different frequencies are focused at different depths, allowing for a more uniform distribution of acoustic energy and increasing the range of depths and lateral extent for tissue displacement measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a focused ARFI beam with fixed focus is used, then the intensity of the push pulse is concentrated at a specific depth, but the beam shape causes a non-uniform response resulting in less signal-to-noise ratio for displacements measured in some locations and a limited range of locations for measuring tissue characteristics
Solution Approach 1:
The patent applies dynamics by making the focal position variable rather than fixed. The system dynamically adjusts the focal position of the ARFI beam to different depths, allowing the measurement range to be extended while maintaining uniform response across locations. This resolves the contradiction by enabling the system to adapt to different measurement depths without being constrained by a single fixed focus point.
Solution Approach 2:
The patent changes the parameter of focal position from a constant value to a variable that can be adjusted to different depths. By sweeping the focus through a range of depths, the system maintains optimal signal-to-noise ratio across multiple locations, thereby expanding the measurable tissue characteristic range while preserving measurement precision.
2Adaptability or versatility
If ARFI pushing pulses are repeated to measure displacement at different laterally spaced locations, then more locations can be measured, but it causes undesired transducer heating and introduces delays in scanning
Solution Approach 1:
The system dynamically varies the focal position across a range of depths within a single ARFI pulse sequence, allowing multiple depth locations to be measured without requiring repeated pulses at different lateral positions. This reduces the total number of pulses needed, thereby minimizing transducer heating while maintaining the ability to measure at multiple locations.
Solution Approach 2:
The patent implements continuous useful action by sweeping the focus continuously through different depths during the ARFI measurement process. This allows the system to gather measurement data from multiple locations in a single continuous operation rather than through discrete repeated pulses, reducing heating and scanning delays.
3Length of stationary object
If the focus is swept over depth to extend the usable imaging depth span, then more depths can be measured, but due to attenuation the intensity of the ARFI push pulse decreases with depth making sweeping alone inadequate
Solution Approach 1:
The patent applies parameter changes by adjusting both the focal position and the intensity of the ARFI push pulse as functions of depth. By compensating for attenuation through intensity adjustment while sweeping the focus, the system maintains adequate signal strength across the extended depth range, overcoming the energy loss that would otherwise limit the usable imaging depth span.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the signal-to-noise ratio, increases the number of locations available for measuring tissue characteristics, reduces transducer heating, and provides more accurate and uniform tissue displacement measurements across a broader region.
Implementation Method 1
transmitting an ARFI pushing pulse, ultrasound may be used to displace tissue directly or through generation of a shear or longitudinal wave
Data Source
AI summary
Frequency is swept in acoustic radiation force impulse (ARFI) scanning. Different frequencies are used at different times during the ARFI. For example, different frequencies are focused to different depths in the ARFI transmit beam. Since the frequency sweep is used for the ARFI pushing pulse rather than a transmit pulse for which echoes are received, the rate of change of the frequency is not dictated by the speed of sound. The rate of change of the frequency may be adjustable or set based on other factors, such as the type of tissue. In combination with a time varying focal position, the frequency sweep may better compensate for loss as compared to a focus sweep alone. The frequency sweep may better compensate for loss as compared to a single point focus ARFI.