Greetings, I am not that familiar with bioimpedance and tetrapolar probes, but I do have experience with NI ELVIS. To me, it seems as if you are looking for something with two current outputs and two voltage inputs. If you have two constant current outputs to excite something (in your case tissue or some other biological agent) and measure the voltage across the resistance in question, you will be able to determin the resistance of the material (using Ohm's Law; V = I*R).
NI ELVIS can definitely measure the two voltages using its analog inputs or the DMM. Unfortunately, NI ELVIS does not have the capability to act as a constant current source, but if you have power supply or another device to supply the current, you could definitely use NI ELVIS and LabVIEW to acquire the voltage and compute the resistance of the material in question (if you are not interested in the phase angle, it seems as if you are only interested in the real component of imedance which is resistance). We do have devices that are capable of supplying a constant current. For example, the PCI-6704 (linked below) has the ability to generate currents between 0 and 20 mA. NI PCI-6704 http://sine.ni.com/apps/we/nioc.vp?cid=10705&lang=US Let me know if you have any additional questions or if I am not making any sense. Have a great day. Regards, Todd D. NI Applications Engineer
