Magnetic Resonance Tomography Receive Apparatus Digital Down-Conversion
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Solution Overview
Problem
Current magnetic resonance tomography (MRT) systems face challenges in efficiently processing high-frequency magnetic resonance signals due to the need for high sampling rates and long communication links, which result in expensive system manufacturing and interference issues.
Innovation Solution
The MRT system employs a digital mixer and clock reduction device to shift the MR signal from a high-frequency range to an intermediate frequency range before transmission, allowing for a lower transmission bandwidth and simplifying the system design by avoiding direct analog mixing down into baseband, using a simple mixer device and lowpass filters to reduce clock rate and prevent interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high A/D converter sampling rates are used to achieve high decimation gain, then the MR signal can be properly digitized, but the system cost increases significantly and high-frequency interference signals are emitted
Solution Approach 1:
The patent applies preliminary action by performing analog mixing down to an intermediate frequency range (e.g., 0-64 MHz) before A/D conversion. This preprocessing step reduces the frequency band of the MR signal, allowing subsequent use of lower sampling rates in the digital domain while maintaining the required decimation gain for proper signal digitization
Solution Approach 2:
The patent introduces an intermediate frequency range as a mediator between the high-frequency MR signal and the baseband digital signal. By mixing down to this intermediate range first (e.g., using a mixer to shift 64-500 MHz to 0-64 MHz), the system can then apply digital down-conversion and decimation in stages, avoiding the need for extremely high sampling rates while preserving measurement precision
2Ease of operation
If long communication links are used to transmit data from the A/D converter to the evaluation unit, then the system can be spatially separated, but high-frequency interference signals are emitted and shielding costs increase
Solution Approach 1:
The patent performs preliminary frequency reduction by mixing down the MR signal to an intermediate frequency range and then to baseband before data transmission. This reduces the frequency content of the transmitted digital data, thereby minimizing high-frequency electromagnetic emissions from communication links while maintaining spatial separation between the receive apparatus and evaluation unit
Solution Approach 2:
The patent changes the frequency parameter of the transmitted signal by performing digital down-conversion and decimation. This transforms high-frequency digital data into lower-frequency baseband signals for transmission, reducing electromagnetic interference while allowing long communication links and RF shielding to be implemented more cost-effectively
3Device complexity
If digital mixing down into baseband is performed close to the examination magnetic field, then image information can be processed as low-frequency signal, but control signals may couple into the receive coil and disrupt the MR signal
Solution Approach 1:
The patent segments the signal processing into distinct stages: first analog mixing down to intermediate frequency, then digital mixing down to baseband after A/D conversion. This segmentation separates the high-frequency analog processing (done with simple mixers close to the coil) from the low-frequency digital processing (done in the RF-shielded evaluation unit), eliminating control signal coupling issues while maintaining processing efficiency
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 reduces system complexity and cost by enabling efficient processing and transmission of MR image information with lower clock rates, minimizing interference and thermal noise, and allowing for simpler component design and reduced waste heat.
Implementation Method 1
at least one receive coil element (28) that is coupled to an input of an analog/digital converter (34)
Data Source
AI summary
A magnetic resonance tomography (MRT) system has a receive apparatus disposed in a magnetic field, in which a receive coil is coupled to an input of an analog/digital converter. The analog/digital converter is configured for this purpose. A digital output of the analog/digital converter is coupled via a digital mixer device and a clock-rate-reduction device to a data output of the receive apparatus. The mixer device is configured to mix a predetermined frequency band of the MR signal downwards into an intermediate frequency range and create a digital IF signal.