Maybe what was actually used was NMR ? equipment looks the same (at least to this layman) and is used to capture things like bloodflow in different parts of the brain …
Eh, I’ve “met” a few women who could comply. 
NMR and MRI are exactly the same thing! However there is a distinction between functional MRI (fMRI) and anatomical MRI. The former more or less shows what bits of the brain are relatively active at a given time. Anatomical MRI just visualises the structure of the brain (or other body part) - this is what was used in the expt. where people were fucking in an MRI machine (the original paper’s in the Lancet IIRC). The OP’s referring to fMRI. Would be quite easy to fuck in some designs of scanner, the problem would be getting the person in the scanner to remaining still, as others have noted. Movement causes all sorts of problems in fMRI data analysis - can be corrected for to some extent, but not if the person in question is banging their head against the scanner bore…
Considering the implications of the experiment in regards to design and equipment, I believe we’re talking about an oral examination, are we not? Dammit! Why don’t they disclose this information?
In my happy(female) experience, there are different levels of orgasm. Some sweet and pleasant, some body-writhing and wrenching, and, the best ones just make me laugh hysterically for a few minutes after in an ecstatic losing my mind sense. I can see this study explaining that last type.
There are different levels, though, because we wimmens are wonderfully complex, so don’t order that high-end orgasmometer just yet. As said here, there is a strong variable of people measured in lab circumstances. Also, according to the OP’s link
He and colleagues took brain scans of 13 women and 11 men, aged 19-49 who had volunteered for the study, while they were being sexually stimulated by their partner and during an orgasm and compared them to images of their brains at rest., it’s a very small sample. Not to say that the inquiry isn’t worthwhile.
Sorry, correcting that quote, from the Op’s link:
“He and colleagues took brain scans of 13 women and 11 men, aged 19-49 who had volunteered for the study, while they were being sexually stimulated by their partner and during an orgasm and compared them to images of their brains at rest”
Very small sample to draw conclusions from.