MRI B1 Field Control via Voltage Sensor Feedback
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Solution Overview
Problem
Magnetic resonance tomographs face challenges in achieving optimal B1 field strength for better signal-to-noise ratio while adhering to regulatory limits, particularly at lower frequencies, due to variations in antenna tuning and patient size, weight, and position.
Innovation Solution
A magnetic resonance tomograph design featuring a transmitter generating excitation pulses at the Larmor frequency, with a voltage sensor and matching circuit on the feed line to accurately measure and control the B1 field, ensuring safe power delivery by interrupting transmission when threshold values are exceeded.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the B1 alternating field strength is increased to improve signal-to-noise ratio, then imaging quality is improved, but patient safety is compromised due to overheating and induced voltages exceeding regulatory limits
Solution Approach 1:
The patent implements a feedback mechanism by placing a voltage sensor on the feed line at a specific distance (n*lambda/2) from the feed point. This sensor continuously monitors the voltage and provides real-time feedback to the control unit, which then adjusts the transmitter power to maintain B1 field strength within safe limits while optimizing signal-to-noise ratio for imaging quality
Solution Approach 2:
The patent changes the operating parameters by dynamically adjusting the transmitter power based on the voltage sensor readings. The control unit modifies the excitation pulse parameters (amplitude, frequency, duration) to maintain optimal B1 field strength without exceeding safety thresholds, thereby resolving the contradiction between imaging quality and patient safety
2Power
If the antenna tuning is optimized to achieve stronger B1 field at lower frequencies, then signal strength is improved, but the system becomes sensitive to patient size, weight, and position variations
Solution Approach 1:
The patent introduces dynamic adaptability by implementing a control system that continuously monitors voltage via the sensor and automatically adjusts transmitter parameters in real-time. This dynamic adjustment compensates for variations in patient size, weight, and position, maintaining optimal B1 field strength across different scanning conditions without requiring manual retuning
Solution Approach 2:
The system performs self-adjustment through the feedback loop where the voltage sensor monitors the actual B1 field conditions and the control unit automatically optimizes the transmitter output. This self-service mechanism eliminates the need for external intervention to adapt to patient variations, maintaining signal strength while accommodating different patient characteristics
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 design enables reliable measurement and control of the B1 field, ensuring patient safety and improved imaging quality by preventing overheating and voltage-induced hazards.
Implementation Method 1
A lambda wavelength is assigned to the excitation pulse. The wavelength lambda is the wavelength which the electromagnetic signal generated by the transmitter as an excitation pulse has
Implementation Method 2
The voltage sensor is arranged on the feed line at an effective distance of a multiple of half the wavelength lambda equal to n*lambda/2 from the feed point
Implementation Method 3
an antenna for emitting the excitation pulses
Implementation Method 4
align nuclear spins of the examination object with a strong external magnetic field and excite them to precess around this alignment by means of an alternating magnetic field
Implementation Method 5
The magnetic resonance tomograph also has a matching circuit between the voltage sensor and the feed point for matching the impedance of the transmitting antenna to the feed line
Implementation Method 6
With the help of magnetic gradient fields, a spatial coding is impressed on the signals, which subsequently enables the received signal to be assigned to a volume element
Data Source
Figure 1~2
Figure 3
AI summary
The invention relates to a magnetic resonance imaging (MRI) scanner and a method for operating the MRI scanner. The MRI scanner comprises a transmitter for generating excitation pulses with a wavelength of lambda, an antenna for transmitting the excitation pulses, a feed line, and a voltage sensor. The voltage sensor is arranged on the feed line at an effective distance from a feed point on the antenna that corresponds to a multiple of half the wavelength lambda.