Composite Calibration Marker for MRI-Linac Coordinate Registration

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Solution Overview

Problem

The integration of MRI and radiotherapy systems for real-time feedback faces calibration challenges due to errors introduced by replacing ball bearings with MR imaging markers and translating phantoms between systems, leading to inaccuracies in coordinate registration.

Innovation Solution

A marker comprising a non-magnetic first component with high material density for radiographic visibility and low hydrogen proton density for minimal MRI visibility, and a second component with high hydrogen proton density for strong MRI visibility, allowing for accurate imaging and calibration across both modalities.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If ball bearings are replaced with MR imaging markers in the phantom, then the phantom can be imaged by the MRI system, but the replacement introduces potential error if the two markers are not exactly co-located

Engineering Contradiction:

Improveimaging compatibilityVSAvoidcoordinate registration accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent combines both ball bearing and MR imaging marker into a single integrated marker assembly. The ball bearing is positioned at the exact same location as the MR imaging marker within the phantom, ensuring that both imaging modalities reference the identical physical location. This merging eliminates the co-location error that would arise from using separate markers.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The marker assembly is designed to serve multiple functions simultaneously: it acts as both a ball bearing target for x-ray imaging and an MR imaging marker for magnetic resonance imaging. By making the marker universal to both imaging systems, the patent eliminates the need for separate markers and ensures consistent reference points across different modalities.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Adaptability or versatility

If the phantom is translated between the x-ray and MRI systems, then the phantom can be imaged by both systems, but the translation introduces a further source of error

Engineering Contradiction:

Improvemulti-system imaging capabilityVSAvoidcoordinate registration accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent merges the x-ray imaging target (ball bearing) and MR imaging marker into a single co-located assembly within the phantom. This ensures that when the phantom is translated between systems, both imaging modalities are referencing the exact same physical location, eliminating translation-induced registration errors.

Inventive Principle:

Principle #5Merging (Combining)

3Adaptability or versatility

If a single marker material is used for both MRI and radiographic imaging, then the marker can be imaged by both systems, but the visibility and contrast may be compromised in one or both modalities

Engineering Contradiction:

Improvemulti-modality imagingVSAvoidimage contrast and visibility

Core Design Contradiction:

Adaptability or versatilityVSIllumination intensity

Solution Approach 1:

The patent employs a composite marker structure containing both a ball bearing (providing radiographic contrast through high density) and an MR imaging marker (providing MRI visibility through appropriate magnetic properties). This composite approach allows the single marker assembly to optimize visibility in both imaging modalities simultaneously, rather than compromising contrast in either modality.

Inventive Principle:

Principle #40Composite materials

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

The proposed marker enables precise calibration of MRI-Linac systems by providing clear contrast in both MRI and radiographic images, reducing errors and ensuring accurate registration of coordinate systems for improved therapeutic targeting.

Implementation Method 1

a first component having a first hydrogen proton density and a first mass density... different than the first hydrogen proton density, and a second mass density different than the first mass density

Methodology Applied

Scientific EffectX-ray absorption: Absorption (EM radiation)

Implementation Method 2

a second component having a second hydrogen proton density different than the first hydrogen proton density... for strong MRI visibility

Methodology Applied

Scientific EffectNuclear magnetic resonance: Magnetic Field

Data Source

PatentUS10022104B2Markers, phantoms and associated methods for calibrating imaging systems

Publication Date: 2018.07.17 ELEKTA AB

AI summary

Embodiments of the present invention provide markers, phantoms, and associated methods of calibration which are suitable for use in both magnetic resonance imaging and radiographic imaging systems. A marker includes a first marker component having a first hydrogen proton density and a first mass density; and a second marker component having a second hydrogen proton density different than the first hydrogen proton density, and a second mass density different than the first mass density. The first marker component and the second marker component are non-magnetic.