Metal Needle Localization in Distorted MRI Using Susceptibility Maps
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Solution Overview
Problem
Existing MRI methods struggle to accurately determine the position of metal objects like needles due to magnetic susceptibility-induced distortions, which cause spatial misregistration and signal loss, limiting precision and requiring long scan times or additional instrumentation.
Innovation Solution
A system and method that uses a processor to access distorted MR images, determine magnetic susceptibility maps, and generate simulated MR images by modifying reference images to accurately estimate the position of interventional devices, leveraging differentiable functions and optimization techniques to align simulated and acquired images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional MRI imaging is used, then the scan time is short, but the position determination precision is poor due to magnetic susceptibility-induced distortions and signal loss around metal objects
Solution Approach 1:
The patent applies preliminary action by acquiring a reference image without the metal object before the actual scan. This reference image serves as a baseline to later compute distortion fields and correct metal object position, avoiding the need for lengthy retrospective correction scans while enabling precise position determination through pre-computed distortion models.
Solution Approach 2:
The patent introduces an intermediary approach by using a computed distortion field as a mediator between the distorted MRI image and the true anatomical structure. This distortion field, derived from the reference image and metal object position, acts as a correction map that transforms distorted measurements into accurate spatial coordinates without requiring extended scanning time.
2Measurement precision
If view angle tilting is applied to compensate slice-dimension distortions, then distortion is reduced, but in-plane blurring is induced
Solution Approach 1:
The patent applies parameter changes by computing a distortion field that captures the specific geometric warping caused by the metal object's magnetic susceptibility. Instead of using fixed view angle tilting that causes blurring, the method adapts the correction parameters to the actual distortion pattern, allowing independent correction of slice-dimension distortions while preserving in-plane resolution through parameter-specific distortion modeling.
3Measurement precision
If multi-spectral imaging with phase encoding is applied, then slice distortions are resolved, but scan time increases to several minutes
Solution Approach 1:
The patent uses preliminary action by acquiring a single reference image without the metal object and pre-computing the distortion field from this reference. This eliminates the need for time-consuming multi-spectral imaging sequences, as the distortion correction model is prepared in advance and can be applied instantly to the actual scan, reducing scan time from several minutes to a fraction of a second.
4Measurement precision
If white marker imaging is used to identify needle location, then needle position can be determined, but additional gradient tuning is required depending on needle properties and orientation
Solution Approach 1:
The patent applies self-service by using the metal object's own magnetic susceptibility properties to generate the distortion field for position determination. The metal object itself creates the distortion that is measured and used for correction, eliminating the need for external white marker implants or complex gradient tuning. The system leverages the object's inherent properties to achieve self-identification and self-correction.
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
Precisely and accurately determines the position and orientation of metal objects in MRI scans, overcoming distortion challenges and enabling real-time, precise needle localization without lengthy scan times.
Implementation Method 1
determining a magnetic susceptibility map based on susceptibility properties of the interventional device and the estimated position of the interventional device
Data Source
AI summary
A method for generating a magnetic resonance (MR) image in the presence of an interventional device that induces distortions is provided. The method includes using a processor to perform steps that include accessing a distorted MR image of a subject with the interventional device arranged in the subject. The steps also include using the distorted MR image to determine parameters of a set of spatially differentiable functions that describe an estimated position of the interventional device in the subject. The steps further include determining a magnetic susceptibility map based on susceptibility properties of the interventional device and the estimated position of the interventional device. The steps also include generating a simulated MR image by modifying a reference image of the subject based on the magnetic susceptibility map and updating the estimated position using the simulated MR image to generate an updated position of the interventional device in the subject.