MRI Thermometry Phase Mapping Reference Medium
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing magnetic resonance imaging (MRI) systems fail to accurately compute temperature difference maps due to the presence of both constant and time-dependent phase errors, which are not corrected for, leading to inaccuracies in thermal imaging, particularly in in-vivo applications where dynamic temperature changes need to be measured with high precision.
Innovation Solution
The system uses a computing unit to access and process phase images of both a target medium and a reference medium, such as fat, to eliminate time-dependent phase errors by tracking system instability and correcting for phase errors introduced by B0 drift and changes in bulk susceptibility, allowing for the computation of accurate temperature difference maps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If phase corrected images are subtracted to yield temperature difference maps using known apparatus, then constant phase errors are eliminated, but time dependent phase errors occur and are not corrected
Solution Approach 1:
The patent introduces a reference medium (such as fat or water) as an intermediary that does not undergo temperature changes during the procedure. This reference medium serves as a mediator to track and correct time-dependent phase errors (B0 drift and shimming changes) independently of temperature effects. By comparing phase changes in the target medium against this stable reference, the system can distinguish between phase changes due to temperature and those due to system instability, thereby resolving the contradiction between eliminating constant phase errors and correcting time-dependent phase errors.
2Measurement precision
If proton frequency shift technique is used for thermal imaging, then temperature sensitivity is improved, but phase errors from B0 drift and shimming changes cause gross errors
Solution Approach 1:
The patent implements a feedback mechanism where the phase of the reference medium is continuously monitored throughout the imaging procedure. This reference phase serves as a feedback signal that reflects system instability (B0 drift and shimming changes). By subtracting this reference phase from the target medium phase, the system dynamically compensates for time-dependent phase errors, thereby maintaining the high temperature sensitivity of the proton frequency shift technique while eliminating the harmful phase errors from system instability.
3Loss of information
If phase unwrapping is performed to obtain absolute temperature maps, then independent temperature maps are provided, but the process is complicated and time consuming
Solution Approach 1:
The patent extracts and separates the time-dependent phase error component by measuring it independently in a reference medium that does not experience temperature changes. By taking out this error component from the total phase measurement, the system can directly compute temperature difference maps without performing complex phase unwrapping operations on the entire dataset. This extraction approach maintains temperature map completeness while significantly reducing processing time and complexity.
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 enables the generation of robust temperature difference maps with improved accuracy, capable of achieving thermal imaging sensitivity of about 0.2 degrees, essential for medical interventions like SAR management and RF-ablation control, by removing spurious phase errors and system imperfections.
Implementation Method 1
magnetic resonance signals emitted from an object subjected to a magnetic resonance imaging
Implementation Method 2
compute a first phase map by subtracting the first phase image from the third phase image for the target medium
Implementation Method 3
proton frequency shift (PFS) technique
Data Source
AI summary
A computing unit is arranged to access phase images computed from the image data and representative of the target medium and the reference medium and carry out computing steps to yield temperature difference map. The operation of the computing is controlled by a computer program carrying computing steps programmed as instructions to a processor. The apparatus (1) includes a storage unit (8) arranged to store suitable image data which are accessed by the computer program during the computations. The storage unit (8) stores system parameters of the magnetic resonance apparatus, like the strength of the main field (B0), gyromagnetic ratio (γ), and suitable parameters of a target medium, like screen constant (α), in a file (3). The apparatus (1) further includes a working memory (6), typically based on RAM. An output (9) of the apparatus includes the computed temperature difference map, which can be used to control a suitable medical diagnostic or therapeutic device, or it may be visualized to a user or be stored for archiving purposes. For feed-back purposes, the apparatus includes a display (7) to visualize the computed temperature difference map. Preferably, the temperature difference map is visualized within a suitable interactive graphic user interface (7a).