On-coil Switched Mode Amplifier for MRI Parallel Transmission

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Solution Overview

Problem

Conventional parallel transmission techniques in MRI face challenges with scaling, fidelity, synchronization, and power efficiency due to the use of multiple, individually powered, single-channel analog RF transmitters, leading to complex power distribution, poor isolation, and inadequate amplitude and phase control.

Innovation Solution

The implementation of on-coil switched mode amplifiers using current-mode class-D amplifiers with digital control, featuring field effect transistors (FETs) and digital controllers, which allow for high-power, efficient parallel transmission with improved synchronization and isolation between coils, enabling higher fidelity and reduced physical complexity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If multiple individually powered single-channel analog RF transmitters are used for parallel transmission, then transmission speed and volumetric excitation capability are improved, but device complexity and power distribution management become complicated

Engineering Contradiction:

Improvetransmission speedVSAvoidpower distribution management

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent combines multiple transmitter channels into a single multi-channel RF transmitter unit that shares common power distribution infrastructure, control logic, and housing. This merging approach maintains the parallel transmission capability and high productivity while eliminating the complexity of managing multiple separate power distribution systems, as each channel draws power from the same shared source through integrated switching mechanisms.

Inventive Principle:

Principle #5Merging (Combining)

2Productivity

If multiple individually powered single-channel analog RF transmitters are used for parallel transmission, then transmission speed is improved, but isolation between coils deteriorates

Engineering Contradiction:

Improvetransmission speedVSAvoidinterference between coils

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The patent introduces an intermediary switching mechanism controlled by control logic that manages power distribution to each coil channel. This intermediary switching system enables selective activation and isolation of individual coils, preventing interference between simultaneously active channels while maintaining high transmission speed. The switching act as a mediator that coordinates power delivery to achieve both productivity and isolation.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Device complexity

If conventional analog RF transmitters are used, then system simplicity is maintained, but amplitude and phase control precision deteriorates

Engineering Contradiction:

Improvesystem simplicityVSAvoidamplitude and phase control

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent replaces conventional analog RF transmitter circuits with a switched-mode architecture that uses digital control logic and electronic switching to regulate power delivery. This substitution of analog mechanisms with digitally-controlled switching mechanisms enables precise amplitude and phase control through programmable logic while maintaining relative system simplicity through integration. The digital control logic provides fine-grained control over transmission parameters that analog systems cannot achieve.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 achieves higher efficiency and fidelity in parallel transmission by using on-coil switched mode amplifiers, enabling pulsed power outputs of over 1000 W with 85% efficiency and improved isolation between coils, while simplifying the physical layout and reducing interference issues.

Implementation Method 1

on-coil switched mode amplifiers using current-mode class-D amplifiers with digital control

Methodology Applied

Scientific EffectSwitched mode amplification:

Implementation Method 2

transformation of the digital control signal into an analog RF signal

Methodology Applied

Scientific EffectElectromagnetic radiation:

Implementation Method 3

featuring field effect transistors (FETs) and digital controllers

Methodology Applied

Scientific EffectField effect transistor operation: Electric Field

Data Source

PatentUS7671595B2On-coil switched mode amplifier for parallel transmission in MRI

Publication Date: 2010.03.02 SIEMENS AG MEDICAL SOLUTIONS

AI summary

Example systems, apparatus, circuits, and so on described herein concern parallel transmission in MRI. One example apparatus includes at least two field effect transistors (FETs) that are connected by a coil that includes an LC (inductance-capacitance) leg. The apparatus includes a controller that inputs a digital signal to the FETs to control the production of an output analog radio frequency (RF) signal. The LC leg is to selectively alter the output analog RF signal and the analog RF signal is used in parallel magnetic resonance imaging (MRI) transmission.