Take a look he http://zone.ni.com/devzone/cda/tut/p/id/5448 for
the difference between a FB and shunt ammeter. The output of the op
amp is -I*Rf . In practical designs there is a capacitor across the
feedback resistor. The OP amps needs a low Vos and needs to be unity
gain stable. You can use two 9V batteries which I have done or use a
rail splitter. I've built plenty of them.

It is important to get a handle on the operating current.