Block Diagram (SBD) - Magnetic Resonance Imaging (MRI)

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Design Considerations

Magnetic Resonance Imaging (MRI) is a non-invasive diagnostic technology that produces physiologic images based on the use of magnetic and radio frequency (RF) fields. The MRI system uses powerful magnets to create a magnetic field which forces hydrogen atoms in the body into a particular alignment (resonance). Radio frequency energy is then distributed over the patient, which is disrupted by body tissue. The disruptions correspond to varying return signals which, when processed, create the image.

The accurate processing of these signals is key to obtaining high quality images. A key system consideration for the receive channel is high SNR. The return signals have narrow bandwidths with an IF location directly dependent on the main magnet s strength. Some systems use high-speed pipeline ADCs with wideband amplifiers to directly sample the IF, leaving large headroom for post-processing gain by a digital down converter or FPGA. Other systems mix the IF to baseband where lower-speed, higher-resolution SAR and delta-sigma ADCs can be used.

For controlling the magnetic and RF energy in the MRI, high-resolution, high-speed DACs are needed. High resolution is required to accurately define the area of the patient to be scanned. High-speed is necessary to match the high IFs being generated by the main magnet. DSPs can be used to provide gradient processor control used for properly controlling the magnets in the MRI system. A DSP can also take care of preprocessing the signal before it reaches the image reconstruction engine.

A wide variety of TI products are available for MRI systems and equipment manufacturers, including op amps, DSPs, multi-channel high- and low-speed data converters, clocking distribution, interface, and power management.