unobstructed coronary arteries -- keywords

The following is an initial stab at this search.  It would be far more specific if the "AND" could be replaced by a proximity indicator.  Alas, this option is not available in PubMed.  

((normal OR negative OR "no stenosis" OR stenosis-free OR astenotic  OR patent OR unblocked OR unobstructed OR clear ) AND (MRA OR CTA OR angiograph* OR "coronary artery" OR "coronary arteries" ))