MRI SAR Dosimeter with Equivalent Phantom Load
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Solution Overview
Problem
Current MRI systems lack a scanner-independent method for accurately measuring RF power deposition and specific absorption rate (SAR) during magnetic resonance imaging, leading to potential heating and burns, and existing methods are either inaccurate or require access to sensitive scanner parameters.
Innovation Solution
A dosimeter device with a transducer that presents an electrical impedance load equivalent to a specimen, allowing it to measure SAR independently of the MRI scanner, using induction loops oriented in orthogonal directions and tuned to resonate at specific MRI frequencies, enabling accurate SAR computation and display.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing SAR measurement methods are used, then SAR can be measured, but the measurements are either inaccurate or require access to sensitive scanner parameters
Solution Approach 1:
The patent uses a phantom that copies the electrical properties (conductivity and dielectric constant) of human tissue to create an equivalent load. This phantom can be placed in the MRI scanner to measure SAR without requiring access to sensitive scanner parameters or complex measurement systems, thereby improving measurement accuracy while reducing system complexity
Solution Approach 2:
The patent introduces an intermediary phantom object that mediates between the RF field and the measurement system. The phantom absorbs RF energy and converts it to measurable electrical signals through its known electrical properties, enabling accurate SAR measurement without direct access to scanner parameters
2Productivity
If RF power deposition is not monitored, then MRI scans can proceed, but heating and burns may occur
Solution Approach 1:
The patent implements a feedback mechanism by measuring the actual RF power deposition in the phantom and using this information to monitor SAR levels during MRI scans. This allows real-time detection of excessive heating conditions while maintaining scanning productivity
Solution Approach 2:
The phantom performs self-service by automatically absorbing RF energy and converting it to measurable electrical signals. This self-monitoring capability provides continuous SAR information without requiring external intervention or complex monitoring systems, thereby preventing heating and burns while maintaining scan efficiency
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 dosimeter provides accurate, scanner-independent measurements of SAR, ensuring safe RF exposure levels and reducing the risk of heating and burns, while being simple to use and cost-effective, without requiring highly skilled operators.
Implementation Method 1
The mechanism for heating is the induction of eddy currents in the body by the time-dependent RF magnetic field in accordance with Faraday's Law
Implementation Method 2
induction loops oriented in orthogonal directions and tuned to resonate at specific MRI frequencies
Implementation Method 3
provide an output representative of signals induced in the transducer
Implementation Method 4
The key results are: (a) local peak and average specific power absorption rates (SARs) in W/kg or W/cm3 can be determined from the known RF pulse width, duty cycle, flip-angle, and sample size
Data Source
AI summary
Featured is a dosimeter device that measures SAR deposited by RF power deposition during MRI of a specimen. Such a dosimeter device includes a transducer that is configured to present a load to the MRI scanner in which the transducer is located and to provide an output representative of signals induced in the transducer. The transducer also is configured so that the presented load is substantially equivalent to another load which would be presented by the specimen during MRI of the specimen. Such a transducer also is configured so as to generate an MRI signal that is sufficient to allow the MRI scanner to adjust the RF power to a value substantially equal to that of the specimen. Also featured are methods for measuring SAR deposited by RF power deposition and apparatuses or system embodying such a dosimeter device.