[annie123 (OP)]

if one is undergoing an MRI can one's thoughts or feelings make a difference to the diagnosis? If one cultivated a miserable attitude, or an angry feeling, would this skew the diagnosis? or if one falls asleep in the machine does that register on the screen?

[RD]

if one is undergoing an MRI can one's thoughts or feelings make a difference ...

Only if it's functional Magnetic Resonance Imaging : fMRI
as that shows brain activity. Regular MRI just shows anatomy.

[alancalverd]

We sometimes have a problem with patients falling asleep in my "upright MRI" units www.uprightmri.co.uk because they twitch and wriggle. It is less of a problem if they are lying down in a narrow tunnel but we sometimes have to wake them up to keep them still, so we generally show an interesting (but neither calming nor exciting) TV documentary to keep them focussed.