Bandpass Sampling for High-Frequency Tissue Displacement Measurement
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Solution Overview
Problem
Conventional medical imaging devices, such as ultrasound and MRI, face limitations in capturing high-frequency tissue motion due to low frame rates, which restrict the measurement of absolute tissue mechanical properties, particularly at frequencies above 25 Hz, and require complex hardware and data processing techniques.
Innovation Solution
The method employs bandpass sampling to measure tissue displacements using a low frame-rate imaging device, allowing for the characterization of soft tissue at frequencies higher than the device's frame rate without the need for accurate synchronization with the excitation pulse, enabling the measurement of high-frequency tissue motion and absolute viscoelastic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional medical imaging devices are used to capture tissue motion, then image quality is maintained, but the frame rate is too low to measure high-frequency tissue motion above 25 Hz
Solution Approach 1:
The patent changes the sampling parameters by using bandpass sampling at a lower frame rate (e.g., 50 Hz) to capture high-frequency tissue motion (e.g., 120 Hz). This involves selecting specific sampling frequencies that fall within the bandpass sampling criteria, allowing accurate reconstruction of high-frequency signals without requiring high frame rates. The key parameter change is transitioning from conventional Nyquist sampling (requiring fs > 2*fmax) to bandpass sampling (allowing fs to be lower when the signal is band-limited).
Solution Approach 2:
The patent dynamically adjusts the sampling strategy based on the known frequency characteristics of the excitation signal. By synchronizing the sampling process with the known frequency band of tissue motion, the system can adaptively capture the necessary information at lower frame rates while maintaining measurement accuracy for high-frequency components.
2Measurement precision
If the sampling frequency is increased to capture high-frequency tissue motion, then measurement accuracy improves, but the device complexity and data processing requirements increase
Solution Approach 1:
The patent reduces device complexity by changing the sampling frequency parameter to a lower value that still satisfies the bandpass sampling criteria. Instead of increasing the sampling frequency to meet the Nyquist criterion (fs > 2*fmax), the system uses a lower fs that is optimized for the specific frequency band of interest, thereby reducing hardware requirements and data processing loads while maintaining measurement precision.
Solution Approach 2:
The patent extracts only the necessary frequency components of tissue motion by using bandpass sampling. Instead of capturing the entire frequency spectrum at high rates, the system selectively samples within the specific frequency band where tissue motion occurs, removing unnecessary high-frequency and low-frequency components that would increase complexity without adding value.
3Device complexity
If conventional sampling methods are used, then simple hardware is required, but accurate measurement of absolute tissue mechanical properties at high frequencies is not achieved
Solution Approach 1:
The patent achieves accurate measurement of absolute tissue mechanical properties by changing the sampling parameter selection from conventional Nyquist-based sampling to bandpass sampling. This parameter change allows the use of simpler hardware (lower frame rate devices) while still capturing sufficient information to compute absolute viscoelastic parameters, because the sampling is optimized for the specific frequency characteristics of the excitation and tissue response.
Solution Approach 2:
The patent utilizes the periodic nature of the excitation signal and tissue response by applying bandpass sampling at frequencies related to the excitation frequency. The sampling is performed at specific intervals that are periodic and synchronized with the known frequency characteristics, enabling accurate reconstruction of the tissue response and computation of mechanical properties without requiring continuous high-rate sampling.
Data Source
AI summary
The characterization of tissue viscoelastic properties requires the measurement of tissue displacements over a region of interest at frequencies that exceed significantly the frame rates of conventional medical imaging devices. The present invention involves using bandpass sampling to track high-frequency tissue displacements. With this approach, high frequency signals limited to a frequency bandwidth can be sampled and reconstructed without aliasing at a sampling frequency that is lower than the Nyquist rate. With bandpass sampling, it is feasible to use conventional beam-forming on diagnostic ultrasound machines to perform high frequency dynamic elastography. The method is simple to implement as it does not require beam interleaving, additional hardware or synchronization and can be applied to magnetic resonance elastography.