Passive Transmitting Antenna Tuning for MRI B1 Homogeneity
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Solution Overview
Problem
Magnetic resonance tomography systems face challenges in achieving homogeneous excitation of nuclear spins due to the absorption of excitation pulses, particularly with increasing frequency, which affects the uniformity of the B1 field, and passive transmitting antennas struggle to provide consistent results across different patient geometries.
Innovation Solution
A passive transmitting antenna with a tuning apparatus that adjusts its resonance frequency and damping based on the relative position to an active transmitting antenna, using a distance meter or sensor to optimize the B1 field homogeneity by attenuating or amplifying the B1 field as needed, ensuring a symmetrical current distribution and improved field homogeneity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single local coil is used on the patient surface, then the signal-to-noise ratio is improved, but the homogeneity of nuclear spin excitation deteriorates due to absorption of excitation pulses
Solution Approach 1:
The patent divides the transmitting function into multiple components: an active transmitting antenna and multiple passive transmitting antennas distributed around the patient. This segmentation allows the active antenna to provide the primary excitation while passive antennas locally enhance and homogenize the B1 field in different regions, resolving the contradiction between signal-to-noise ratio and excitation homogeneity.
Solution Approach 2:
Passive transmitting antennas are positioned at specific locations around the patient to provide localized field enhancement. Each passive antenna creates a local B1 field that compensates for absorption effects in its vicinity, ensuring homogeneous excitation across the entire patient volume while maintaining high signal-to-noise ratio through the distributed array.
2Stability of the object's composition
If multiple active transmitting antennas are arranged around the patient, then the excitation homogeneity is improved, but the complexity of the transmitting facility increases
Solution Approach 1:
Passive transmitting antennas serve as intermediaries between the active transmitting antenna and the patient's nuclear spins. The passive antennas are excited by the active antenna and then locally enhance the B1 field, providing homogeneous excitation without requiring multiple independent active transmitting antennas with their associated complex control systems.
Solution Approach 2:
The passive transmitting antennas replicate the excitation function of active antennas without requiring the same level of complexity. They are passively excited by the active antenna and copy its transmitting behavior locally, achieving homogeneous excitation while keeping the overall system simpler than using multiple active antennas.
3Device complexity
If passive transmitting antennas are used to achieve local field increase by resonance, then the transmitting facility complexity is reduced, but the uniformity of excitation results deteriorates due to different patient geometries
Solution Approach 1:
The passive transmitting antennas incorporate tuning mechanisms that allow their resonance frequencies to be dynamically adjusted based on the patient's geometry and position. This dynamic tuning ensures that the passive antennas maintain optimal resonance conditions and provide uniform excitation results across different patient anatomies, overcoming the limitation of fixed-geometry passive antennas.
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 solution enables a more uniform and homogeneous B1 field distribution, enhancing the imaging quality by adjusting the resonance frequency and impedance of the passive transmitting antenna in response to the distance and position relative to the active antenna, thus improving the excitation of nuclear spins.
Implementation Method 1
The passive transmitting antenna (50) is inductively coupled to an active transmitting antenna (70) of a magnetic resonance tomography system (1)
Implementation Method 2
The passive transmitting antenna (50) has a resonance close to a Larmor frequency of the magnetic resonance
Data Source
AI summary
System and methods are provided for a passive transmitting antenna for a magnetic resonance tomography system and to a system including a passive transmitting antenna and magnetic resonance tomography system and a method for operation. The passive transmitting antenna includes a tuning apparatus with a tuning element. The tuning apparatus is configured to perform a tuning of the passive transmitting antenna as a function of a relative position of the passive transmitting antenna in a patient tunnel of the magnetic resonance tomography system.