MR Image Creation Using Whole-Body and Local Transmission Coils
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Solution Overview
Problem
Current MR imaging techniques face challenges in achieving high signal quality and contrast while minimizing specific absorption rate (SAR) for examination subjects, especially for body parts that cannot be fully enclosed by local volume coils, leading to inhomogeneous excitation fields and increased heating.
Innovation Solution
A method utilizing a combination of a whole-body coil and a local transmission coil to radiate magnetic RF pulses, where the whole-body coil provides homogeneous excitation and the local transmission coil refocuses spins to minimize SAR and maximize imaging quality, using a turbo spin echo sequence with controlled flip angles and refocusing pulses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-intensity RF magnetic fields are used to maximize signal quality and contrast, then image quality is improved, but specific absorption rate (SAR) increases leading to excessive heating
Solution Approach 1:
The patent divides the RF transmission function into two separate coils: a whole-body coil for homogeneous excitation and a local transmitting coil for refocusing pulses. This segmentation allows each coil to operate at optimized power levels, with the local coil delivering high-intensity pulses only to the region of interest, thereby maintaining signal quality while reducing overall SAR
Solution Approach 2:
The local transmitting coil is positioned to provide concentrated RF energy only to the specific body part being examined, creating a localized high-field region. This ensures high signal quality in the target area while minimizing RF exposure and heating in surrounding tissues, thus resolving the contradiction between signal quality and SAR
2Object-affected harmful factors
If local volume coils are used to reduce SAR and examination time, then SAR and coding time are reduced, but field strength drops at the edges of the field of view
Solution Approach 1:
The patent combines the advantages of both whole-body and local coils by using the whole-body coil for the initial 90° excitation pulse (which benefits from homogeneous coverage) and the local transmitting coil for subsequent refocusing pulses (which benefit from high local field strength). This merging approach eliminates the field strength dropout at edges while maintaining low SAR
3Object-affected harmful factors
If transmitting TX surface coils are used to achieve low SAR, then SAR is reduced, but excitation field homogeneity deteriorates
Solution Approach 1:
The patent segments the RF pulse sequence into two functional parts: homogeneous excitation by the whole-body coil and localized refocusing by the transmitting coil. This segmentation allows the system to achieve both low SAR (through the efficient local coil) and homogeneous excitation (through the whole-body coil), resolving the contradiction between these two requirements
4Object-affected harmful factors
If local volume coils are used for body parts that cannot be enclosed, then SAR is reduced, but image quality is limited due to lower refocusing pulse intensities
Solution Approach 1:
The local transmitting coil is strategically positioned to concentrate RF energy precisely on the body part of interest, creating a localized high-field region. This allows high refocusing pulse intensities to be applied only where needed, maintaining high image quality while keeping overall SAR low. The coil's spatial selectivity enables it to overcome the intensity limitation of whole-body coils for difficult-to-access body parts
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
This approach allows for high-quality MR imaging with minimized SAR, enabling examination of difficult-to-access body parts while adhering to SAR limits, by ensuring homogeneous excitation and reducing energy absorption.
Implementation Method 1
at least one magnetic RF pulse is radiated over the entire object of investigation through a whole-body coil
Implementation Method 2
allows an object under investigation to be excited in an MR system by a special MR imaging sequence
Implementation Method 3
at least one RF pulse is emitted through the local transmitting coil... all RF refocusing pulses of the readout module are injected with the local transmitting coil
Implementation Method 4
partial absorption of the irradiated energy by the object occurs, resulting in heating. A measure of this absorption or heating is the specific absorption rate (SAR)
Data Source
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AI summary
The invention relates to a method for generating an MR image of an examination subject using an MR imaging sequence in an MR system, comprising the following steps: - Irradiating at least one RF pulse (3, 4) through a whole-body coil (21) of the MR system during the imaging sequence, - Irradiating at least one RF pulse (5) through a local transmitting coil (22) of the MR system during the imaging sequence, - Readout of MR signals generated by the irradiated RF pulses (3, 4, 5), - Generating the MR image from the readout MR signals.