Anthropomorphic Phantom Material Composition for MR-CT Tissue Mimicry
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Solution Overview
Problem
Current phantoms fail to effectively mimic both MR and CT tissue characteristics for different human organs, limiting the comprehensive testing of MR-based radiotherapy workflows and quality assurance, particularly due to challenges in reproducing T1 and T2 relaxation times and electron density, and are not suitable for MR-based radiotherapy QA.
Innovation Solution
A system of materials comprising carrageenan-based gelatinizer with additives like gadolinium, agarose, glass microspheres, and calcium carbonate to create a phantom that mimics bone and a wide range of tissues, for MR (e.g., 0.35T to 3T) and CT imaging. The system of materials is a system of additive-doped carrageenan-based tissue mimicking materials, and a system of materials capable of providing tissue-like contrast for both CT and MR imaging. The system of materials is configured to produce tissue-like contrast in MR and CT imaging modalities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If specialized phantoms are used for separate MR and CT imaging calibration, then each modality can be quality-assured independently, but the phantom cannot simultaneously mimic both MR relaxation characteristics (T1, T2) and CT electron density properties of human tissues
Solution Approach 1:
The patent creates a universal phantom that performs multiple functions: it simultaneously provides MR imaging contrast through T1/T2 relaxation properties and CT imaging contrast through electron density properties. The tissue-mimicking material is formulated with specific components (agarose, gadolinium, NaF, calcium carbonate) that collectively enable the single phantom to replace both MR-specific and CT-specific phantoms, allowing comprehensive quality assurance for both modalities and their integration in MR-guided radiotherapy.
Solution Approach 2:
The patent employs a composite tissue-mimicking material system combining multiple substances: agarose gel as base material, gadolinium for T1 shortening, NaF for CT number adjustment, and calcium carbonate for bone mimicry. This composite formulation allows the material to exhibit both MR-relevant relaxation characteristics and CT-relevant electron density properties simultaneously, resolving the contradiction between single-modality specialization and multi-modality versatility.
2Measurement precision
If tissue mimicking materials are developed to match electron density and magnetic field properties, then accurate tissue representation is achieved, but practical challenges arise in longevity, castability, stability, deformability and ease of production
Solution Approach 1:
The patent systematically adjusts material parameters to achieve tissue equivalence: varying agarose concentration (1-2% w/v) to control gel strength and castability, adjusting gadolinium concentration (0.1-1 mM) to match T1 relaxation times of different tissues, modifying NaF content (0.1-1 g/L) to achieve specific CT numbers, and incorporating calcium carbonate particles for bone mimicry. These parameter optimizations balance measurement precision with manufacturing ease, ensuring the material is both accurate and practical.
Solution Approach 2:
The patent creates different regions within the phantom with locally optimized material compositions: soft tissue regions use agarose-gadolinium formulations for T1/T2 matching, bone regions incorporate calcium carbonate for electron density equivalence, and adipose tissue regions adjust lipid content and water composition. This local quality approach allows each region to be optimized for its specific tissue type while maintaining overall phantom stability and ease of production through a unified base formulation.
3Adaptability or versatility
If current material systems are used to mimic soft tissue, muscle and adipose tissue, then some tissue types are represented, but the system cannot mimic the MR characteristics of different types of adipose tissue such as glandular breast tissue and is limited at higher magnetic fields
Solution Approach 1:
The patent implements local quality by formulating distinct material compositions for different tissue types within the same phantom system. Adipose tissue is mimicked using safflower oil in polyurethane mesh with specific T1/T2 characteristics, while glandular breast tissue uses a different agarose-gadolinium concentration ratio to achieve shorter T1 and different T2 values. This allows the phantom to accurately represent multiple tissue types with their unique MR signatures, expanding tissue type coverage while maintaining reliability for each specific tissue representation.
Solution Approach 2:
The patent creates a dynamic material system where the MR characteristics can be adjusted for different field strengths. The tissue-mimicking materials are formulated to maintain their relaxation properties across 0.94T to 3T magnetic fields through careful selection of paramagnetic agents (gadolinium) and gel structure (agarose). This dynamic adaptability allows the same material system to reliably mimic tissue characteristics across different clinical MR scanner field strengths.
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 system of materials allows for realistic anthropomorphic phantoms that produce artifact-free T1- and T2-weighted MR images and accurate CT images, enabling comprehensive MR-based radiotherapy QA, including end-to-end testing and synthetic CT image generation, with adjustable T1 and T2 relaxation times and electron density.
Implementation Method 1
The time the proton takes to realign with the external magnetic field can be characterized as the T1 and T2 relaxation time constants. T1 and T2 relaxation times determine the time the proton spin vector takes to realign with the external magnetic field in the longitudinal and transverse directions respectively.
Implementation Method 2
a fourth amount of gadolinium contrast
Implementation Method 3
T1 and T2 relaxation times depend on the molecular tumbling rate of individual tissues.
Implementation Method 4
Contrast in CT is produced by the ability of X-rays to traverse through different tissue types. The more radiopaque a tissue is, the less likely X-rays will be able to traverse through it without large angle scattering. Radiopacity is described using the Hounsfield Unit (HU) scale.
Data Source
Figure 1a~1b
Figure 2
Figure 3~4
AI summary
A multimodality phantom apparatus includes a housing and a system of materials disposed within the housing. The system of material includes a first amount of a base material, a second amount of glass microspheres, a third amount of CaCO3, a fourth amount of gadolinium contrast and a fifth amount of agarose. The housing may include a plurality of compartments and at least one slot. The system of materials may be disposed within at least one compartment. The slot may be used to receive a dosimeter.