I'm working on a respiration monitor and I was wondering what area of electronics I would need to get familiar with to design the hardware filters that would stop the RF/EMI from frying the system.
The MRI we are working with is actively shielded so stray magnetic fields are not as harsh out side of the magnet but we are still going to run cables to the patient inside of the MRI. The signal distortion is not much of a problem, we have the algorithms that can filter the interference.
Currently we are using a set of BioPac cables on loan to us from another researcher. I deal with DSP and FPGA design so the analog part of this is not my expertise. I'm looking for a nudge in the right direction so I can learn about what needs to be done. Thank you!
Best Answer
The biggest field from an MRI system is DC and therefore not a problem as long as you pay attention to ferromagnetic materials as the previous responder said. The RF field is the one that may annoy electronics connected to the patient. As a first principle, ALWAYS use balanced transmission plus an overall shield -- i.e. 2-core shielded cable for a 2-pin sensor -- and a differential amp as the receiver; NEVER use single-ended (earth referenced) transmission. This will immediately give you big attenuation of the RFI, which of course will be common-mode on the two cores. Given that, a fairly simple RC filter on each core at the point of entry into your equipment is probably all you'll need, unless you're working with microvolt signals! (Anyone for an intra-MRI EEG, perhaps? ). Any small-signal circuitry should also be in a screening can to keep the RF field out, unless the outer casing is very, very well EMC'ed.