A percutaneous transluminal angioplasty catheter (100, 250, 1000, 2000, 3300) comprising: an expandable dilatation chamber (120, 1200, 2200, 3320) sized and configured to exert a force when expanded sufficiently to expand a narrowed or obstructed vessel lumen portion (NR1, NR2, NR3, NR) to a size larger than nominal size of said vessel lumen portion; an elongated shaft (110, 1100, 2100, 3310) comprising a proximal end, a distal end, and a sidewall, said elongated shaft is connected at a distal region to said expandable dilatation chamber; an inflation lumen (126, 1320, 2124) defined at least in part by said sidewall and intercommunicating a proximal inflation inlet port (128, 1120, 2122) and a distal inflation exit port (124, 1150); and an infusion lumen (134, 1310, 2114), sealed to said inflation lumen, defined at least in part by said sidewall of said elongated shaft and intercommunicating a proximal infusion inlet port (136, 1110, 2112) and a distal infusion exit port (132, 1140, 2116, 3330); characterised in that said expandable dilatation chamber (120, 1200, 2200, 3320) comprises an inflatable balloon that also forms an occlusion balloon, wherein said distal inflation exit port (124, 1150) is disposed within an interior of said occlusion balloon, and said distal infusion exit port (132, 1140, 2116, 3330) is positioned proximal to said occlusion balloon, such that said occlusion balloon is expandable to an occluding state that fills a cross-section of said vessel lumen portion (NR1, NR2, NR3, NR) and is configured to maintain said occluding state for a period of time to image a vascular region of said vessel lumen portion. an expandable dilatation chamber (120, 1200, 2200, 3320) sized and configured to exert a force when expanded sufficiently to expand a narrowed or obstructed vessel lumen portion (NR1, NR2, NR3, NR) to a size larger than nominal size of said vessel lumen portion; an elongated shaft (110, 1100, 2100, 3310) comprising a proximal end, a distal end, and a sidewall, said elongated shaft is connected at a distal region to said expandable dilatation chamber; an inflation lumen (126, 1320, 2124) defined at least in part by said sidewall and intercommunicating a proximal inflation inlet port (128, 1120, 2122) and a distal inflation exit port (124, 1150); and an infusion lumen (134, 1310, 2114), sealed to said inflation lumen, defined at least in part by said sidewall of said elongated shaft and intercommunicating a proximal infusion inlet port (136, 1110, 2112) and a distal infusion exit port (132, 1140, 2116, 3330); characterised in that said expandable dilatation chamber (120, 1200, 2200, 3320) comprises an inflatable balloon that also forms an occlusion balloon, wherein said distal inflation exit port (124, 1150) is disposed within an interior of said occlusion balloon, and said distal infusion exit port (132, 1140, 2116, 3330) is positioned proximal to said occlusion balloon, such that said occlusion balloon is expandable to an occluding state that fills a cross-section of said vessel lumen portion (NR1, NR2, NR3, NR) and is configured to maintain said occluding state for a period of time to image a vascular region of said vessel lumen portion.