MRI Local Coil Detuning Circuit Using AC/DC Conversion
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Solution Overview
Problem
Current MRI systems require high currents for detuning local coils, leading to inefficiencies and potential interference with magnetic fields, and the use of pin multiplexing circuits complicates the design and affects field integrity.
Innovation Solution
A local coil with a tuning/detuning circuit that utilizes a small detuning control current and an AC/DC conversion circuit to achieve the same detuning effect as a larger current, eliminating the need for pin multiplexing circuits and reducing system complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a 100 mA current is used for detuning each local coil, then the detuning effect is achieved, but the total current increases to 6400 mA and system complexity increases
Solution Approach 1:
The patent combines multiple detuning control lines into a single line by using a pin multiplexing circuit. The multiplexing circuit allows one control line to sequentially control multiple local coils, reducing the total number of control lines from 64 (8 interfaces × 8 coils) to just 8 lines. This merging approach maintains the detuning effect while dramatically reducing the total current requirement and system complexity.
Solution Approach 2:
The patent changes the control parameter from direct current (DC) to alternating current (AC) by introducing an AC/DC conversion circuit. The AC signal from the control line is converted to DC to control the PIN diode's switching state. This parameter change enables the use of lower current levels while maintaining effective detuning control, as the AC signal can be converted to the necessary DC bias current for the diode to switch between conducting and blocking states.
2Device complexity
If a pin multiplexing circuit is used to control multiple local coils, then the number of control lines is reduced, but the circuit complexity increases and field interference occurs
Solution Approach 1:
The patent introduces an AC/DC conversion circuit as an intermediary between the control line and the PIN diode. This intermediary circuit converts the AC control signal to DC, which is then used to control the diode's switching state. The AC/DC conversion circuit acts as a buffer that isolates the control line from the coil, preventing direct DC current flow through the control line and thereby reducing field interference with the B0 and B1 magnetic fields.
3Adaptability or versatility
If a PIN diode is used for tuning/detuning control, then the coil can be switched between tuned and detuned states, but the diode requires 100 mA current which affects B0 or B1 field
Solution Approach 1:
The patent makes the control signal dynamic by using AC instead of DC. The AC control signal is converted to DC by the AC/DC conversion circuit, which then dynamically switches the PIN diode between conducting and blocking states. This dynamic control allows the diode to respond to tuning/detuning requirements without requiring continuous high DC current, thereby reducing the impact on B0 and B1 fields while maintaining adaptability.
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 solution reduces the total current required for detuning, simplifies the system design, and minimizes interference with the B0 and B1 fields, making the system more energy-efficient and environmentally friendly, while supporting a large number of local coils.
Implementation Method 1
the AC/DC conversion circuit converts an alternating current generated by an electromagnetic wave to a direct current
Implementation Method 2
The tuning/detuning circuit uses a capacitor and an inductor in the antenna part of the local coil to form a parallel resonant circuit
Data Source
AI summary
A local coil for an MRI system includes a signal antenna to receive a magnetic resonance signal and a tuning/detuning circuit to subject the signal antenna part to switch control according to a control signal. The tuning/detuning circuit is connected to the signal antenna part. The tuning/detuning circuit includes a control signal interface, a resonant circuit and an AC/DC conversion circuit. The control signal interface receives the control signal. The resonant circuit includes a diode. The AC/DC conversion circuit converts an alternating current generated by an electromagnetic wave to a direct current. The AC/DC conversion circuit is connected in series with the diode. A small detuning control current may be used, and detuning control circuitry may be reduced.