This response is a little too long for a comment, so here's a more complete explanation. Besides, there's some real fun stuff here...
First, the paper is available online
here.
The MR study was actual anatomical imaging. It used a very high speed sequence (single-shot) that allowed 11 1-cm slices in the axial (i.e. head-foot) direction to be acquired in 14 seconds. They acquired the images by asking the couple to pause. Make your own joke. It really was just a "feasibility study", so there's no real technical commentary.
Now, fMRI of the participants neurological activity during coitus might be interesting. Actually, it would be very interesting--I'm pretty sure that's an unknown area of research. Plus, it's would be easier to restrain the head during the act than the entire body.
A few closing observations:
*My mental state was way to clinical during this. I didn't even make a joke about cine imaging...
*The paper quotes Leonardo da Vinci and includes Queen Elizabeth II as an acknowledgement. Honest.
*The study was done without external funding. I wonder why.
*I still love the comment about the amateur street acrobats.
*Yes, the paper was done in Amsterdam.