2D Multi-Spectral MRI for Stainless-Steel Biopsy Needle Tracking
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Solution Overview
Problem
Conventional MRI imaging techniques face challenges in accurately localizing and tracking metallic biopsy needles due to artifacts such as distortions and signal voids, especially when using stainless-steel needles, which can misguide the needle path and complicate the targeting of smaller lesions.
Innovation Solution
The use of 2D multi-spectral imaging (2DMSI) techniques that segment the imaging field into spatial-spectral bins based on off-resonance frequency, allowing for selective excitation and acquisition of images to highlight the metallic objects, thereby reducing artifacts and enabling precise needle localization and tracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional GRE sequences are used for MRI guidance, then the metallic needle can be visualized through signal voids, but the signal voids cause distortions and misguide the needle path
Solution Approach 1:
The imaging field-of-view is segmented into multiple spatial-spectral bins based on off-resonance frequency and slice location. Each bin is selectively excited and imaged separately, allowing the system to capture both on-resonance and off-resonance information without the distortions that plague conventional single-sequence imaging.
Solution Approach 2:
The patent adds a spectral dimension to the traditional spatial imaging by incorporating frequency binning. This transforms the problem from 2D spatial localization to 3D spatial-spectral localization, enabling the system to separate needle signal from artifact through frequency discrimination.
2Object-affected harmful factors
If MR-compatible lower susceptibility materials are used for biopsy needles, then artifacts are reduced, but cutting performance and sample quality deteriorate
Solution Approach 1:
The patent converts the harmful off-resonance effects of conventional stainless-steel needles into useful information. By selectively imaging off-resonance frequency bins, the system makes the needle material's susceptibility difference beneficial for highlighting and tracking the needle, rather than merely tolerating it with MR-compatible materials.
Solution Approach 2:
The patent changes the imaging parameters (frequency selection, gradient inversion timing) to match the needle's resonant characteristics. By adjusting the RF modulation frequency to correspond to the needle's off-resonance frequency, the system optimizes needle visibility while maintaining the use of conventional stainless-steel materials with superior cutting performance.
3Measurement precision
If 2DMSI with multiple spatial-spectral bins is implemented, then needle tracking accuracy is improved, but data acquisition time and processing complexity increase
Solution Approach 1:
The patent employs periodic gradient inversion between excitation and refocusing pulses to selectively excite different spatial-spectral bins. This periodic action enables efficient sampling of multiple frequency bins through repeated acquisitions with different radiofrequency modulations, reducing the total acquisition time compared to non-periodic approaches.
Solution Approach 2:
The patent merges multiple acquired images of adjacent frequency bins into a single 2DMSI image combination using root-mean-squares or other combination techniques. This merging process consolidates the information from multiple bins while highlighting areas of off-resonance, thereby reducing processing complexity and enabling continuous repeated acquisition for real-time tracking.
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
2DMSI effectively reduces needle artifacts, allowing for more accurate localization and tracking of both MR-compatible and conventional stainless-steel biopsy needles, improving the depiction of surrounding tissue and enabling the use of a wider range of needle materials with potentially better cutting performance.
Implementation Method 1
MR-guidance for biopsy procedures features high intrinsic soft-tissue contrast
Implementation Method 2
segmenting is based on off-resonance frequency induced by the metallic object
Implementation Method 3
the metallic needle can induce field inhomogeneities, resulting in artifacts such as distortions or signal voids due to dephasing in gradient-recalled echo (GRE) sequences
Implementation Method 4
signal voids due to dephasing in gradient-recalled echo (GRE) sequences
Data Source
AI summary
A method using 2D multi-spectral imaging (2DMSI) for MRI imaging of a metallic object (such as a biopsy needle) and region surrounding the metallic object within an imaging field of view of an MRI apparatus includes segmenting the imaging field-of-view into spatial-spectral bins, where the segmenting is based on off-resonance frequency induced by the metallic object and slice location; selectively exciting each frequency bin of the spatial-spectral bins by inverting a slice selection gradient between excitation and refocusing pulses; performing repeated acquisition with different radiofrequency modulations to produce acquired images of adjacent bins; composing a 2DMSI image by root-sum-of-squares combination of the acquired images of adjacent bins; and highlighting in the 2DMSI image an area of furthest off-resonance bins based on 2DMSI off-resonance information by thresholding image intensity in frequency bins, thereby indicating a contour of the metallic object.