MRI Electron Density Mapping via Co-Registered CT Atlas

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Solution Overview

Problem

Magnetic Resonance Imaging (MRI) lacks an absolute scale, making it difficult to use MRI images for radiation therapy planning and PET attenuation correction, as they do not provide the necessary Hounsfield units required for dose calculation and electron density information.

Innovation Solution

A system and method that utilize a co-registered atlas of CT and MRI reference images to associate electron density information from CT images with corresponding MRI images, allowing for the transfer of CT-specific information to MRI images, enabling accurate dose calculations and attenuation correction.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If MRI images are used for radiation therapy planning, then soft tissue discrimination is improved, but electron density information is lost

Engineering Contradiction:

Improvesoft tissue discriminationVSAvoidelectron density information

Core Design Contradiction:

Measurement precisionVSLoss of information

Solution Approach 1:

The patent uses a co-registered atlas as an intermediary that bridges MRI and CT image spaces. The atlas contains both MRI images with superior soft tissue discrimination and CT images with accurate electron density information. By registering the patient's MRI to the atlas, the system transfers electron density information from the CT component of the atlas to the patient's MRI, thus resolving the contradiction between soft tissue discrimination and electron density information availability.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent creates a virtual copy of CT electron density information by mapping it onto the MRI image through the co-registered atlas. Instead of requiring actual CT scans for electron density measurement, the system copies and transfers the electron density values from the atlas to the patient's MRI image, enabling dose calculation and attenuation correction without direct CT measurement.

Inventive Principle:

Principle #26Copying

2Loss of information

If CT images are used for electron density measurement, then Hounsfield units are available, but soft tissue discrimination is reduced

Engineering Contradiction:

ImproveHounsfield unitsVSAvoidsoft tissue discrimination

Core Design Contradiction:

Loss of informationVSMeasurement precision

Solution Approach 1:

The patent merges the advantages of both CT and MRI modalities into a single co-registered atlas. The atlas integrates CT images providing Hounsfield units and electron density information with MRI images providing superior soft tissue discrimination. This merged atlas serves as a reference that contains both types of information simultaneously, allowing the system to leverage the strengths of both imaging modalities.

Inventive Principle:

Principle #5Merging (Combining)

3Adaptability or versatility

If MRI-based RTP is implemented, then radiation therapy planning is enabled, but accurate dose calculation becomes difficult

Engineering Contradiction:

ImproveMRI-based radiation therapy planningVSAvoiddose calculation accuracy

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The co-registered atlas acts as an intermediary that enables accurate dose calculation in MRI-based radiation therapy planning. The atlas provides the necessary electron density information mapped onto the MRI image, which is essential for dose calculation. Without this intermediary, MRI-based planning would lack the quantitative accuracy needed for reliable dose computation.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Measurement precision

If PET attenuation correction is performed, then imaging accuracy is improved, but CT images are required which are not available in MRI systems

Engineering Contradiction:

ImprovePET attenuation correction accuracyVSAvoidCT image availability

Core Design Contradiction:

Measurement precisionVSLoss of information

Solution Approach 1:

The patent copies CT electron density information onto MRI images using the co-registered atlas. This virtual copying of CT data enables PET attenuation correction to be performed on MRI-based systems without requiring actual CT scans. The electron density values from the atlas are mapped to the patient's MRI, providing the necessary information for accurate PET correction.

Inventive Principle:

Principle #26Copying

Data Source

PatentUS8787648B2CT surrogate by auto-segmentation of magnetic resonance images

Publication Date: 2014.07.22 KONINKLIJKE PHILIPS NV

AI summary

When modeling anatomical structures in a patient for diagnosis or therapeutic planning, an atlas (26) of segmented co-registered CT and MRI anatomical structure reference images can be accessed, and an image of one or more such structures can be selected and overlaid with an MRI image of corresponding structure(s) in a clinical image of a patient. A user can click and drag landmarks or segment edges on the reference MRI image to deform the reference MRI image to align with the patient MRI image. Registration of a landmark in the patient MRI image to the reference MRI image also registers the patient MRI image landmark with a corresponding landmark in the co-registered reference CT image, and electron density information from the reference CT image landmark is automatically attributed to the corresponding registered patient MRI landmark.