Image-Based Retrospective Gating for MR Thermometry
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Solution Overview
Problem
Proton Resonance Frequency (PRF) thermometry in MRI faces challenges with motion between image frames, particularly in organs like the liver and heart, leading to misalignment and reduced accuracy in temperature difference estimates due to existing methods' limitations in navigator-gated and physiological signal-gated acquisitions.
Innovation Solution
A computer-implemented method for selecting thermal images based on image similarity measures, where baseline images are analyzed to identify the most stable motion state, generating a template image, and setting an acceptance threshold for thermal images to ensure accurate temperature difference mapping without requiring navigators or physiological monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If navigator-gated acquisition is used to minimize misalignment between snapshot MR phase images, then alignment accuracy is improved, but device complexity and acquisition time increase due to required pulse sequence adaptation and navigator signal acquisition
Solution Approach 1:
The patent extracts and removes the navigator gating component from the acquisition system, replacing it with a retrospective gating method that operates independently of the pulse sequence. This eliminates the need for navigator signal acquisition and pulse sequence adaptation while maintaining alignment accuracy through post-processing image registration and frame selection based on motion state analysis
Solution Approach 2:
The patent performs preliminary motion state analysis on a set of baseline images acquired without gating to establish an acceptance criterion before actual thermometry acquisition. This preliminary characterization of organ motion patterns enables subsequent retrospective gating without requiring real-time navigator signals or physiological monitoring during the therapeutic acquisition
2Measurement precision
If physiological signal-gated acquisition is used to determine motion state, then alignment accuracy is improved, but reliability decreases due to irregular patterns in physiological signal detection and lack of 1-1 correspondence to organ displacement
Solution Approach 1:
The patent employs self-service by using the actual MR images themselves as the basis for motion state determination, rather than relying on external physiological signals. The image intensity and phase information directly reflect the organ's motion state, providing a reliable and accurate measure that is inherently correlated with actual displacement without requiring separate physiological monitoring systems
Solution Approach 2:
The patent replaces the mechanical/physiological signal-based gating system with an image-based retrospective gating system. Instead of using ECG or respiratory bellows signals to trigger acquisition, the method uses post-acquisition analysis of image data to identify frames in stable motion states, substituting direct physiological measurement with image-derived motion assessment
3Adaptability or versatility
If intensity-based image registration is used to correct misalignment, then versatility is improved, but through-plane motion correction fails in case of poor initial alignment
Solution Approach 1:
The patent performs preliminary selection of image frames that are in stable motion states before registration is attempted. By pre-filtering the image set to include only frames with similar motion characteristics (as determined by analysis of baseline images), the method ensures that initial alignment is sufficient for successful registration, avoiding the failure mode of poor initial alignment while maintaining versatility across different imaging scenarios
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 improves the accuracy of temperature difference mapping by reducing temporal standard deviation and aligning thermal images, enhancing the reliability of PRF thermometry for moving organs by using image-based retrospective gating.
Implementation Method 1
determining an acceptance threshold based on an image similarity measure (ISM) between each of the set of baseline images and the template image
Implementation Method 2
The proton resonance frequency shift (PRFS) based Magnetic Resonance (MR) thermometry method captures this temperature change by subtracting a phase image acquired prior to the thermal therapy
Data Source
AI summary
Embodiments provide a computer-implemented method for selecting thermal images for generating a temperature difference map through proton resonance frequency (PRF) thermometry, including: acquiring a set of baseline images prior to a thermal treatment of an organ of interest; identifying a subset of baseline images in a most stable motion state from the set of baseline images; averaging the subset of baseline images to generate a template image; determining an acceptance threshold based on an image similarity measure (ISM) between each of the set of baseline images and the template image; acquiring a set of thermal images during the thermal treatment; and selecting a subset of thermal images from the set of thermal images, wherein each of the subset of thermal images has the image similarity measure above the acceptance threshold.