A system , comprising: a catheter ; an expandable member ; a plurality of sensor modules disposed on an outer surface of the expandable member and circumferentially spaced apart from one another, wherein each of the plurality of sensor modules includes a first emitter configured to emit light of a first wavelength, and a detector configured to detect light; a controller coupled to the plurality of sensor modules , wherein the controller is configured to: from each detector , receive along a first short vector, a measurement of light intensity over time of light, reflected off of body tissue, at the first wavelength and originating from a first emitter from a same sensor module ; from each detector , receive along a first long vector, a measurement of light intensity over time of light, reflected off of body tissue, at the first wavelength and originating from a first emitter from a circumferentially adjacent sensor module , calculate separate perfusion indexes corresponding to measured light intensity over time of each first short vector and each first long vector; and cause the display of the separate perfusion indexes corresponding to measured light intensity over time of each first short vector and each first long vector. a catheter ; an expandable member ; a plurality of sensor modules disposed on an outer surface of the expandable member and circumferentially spaced apart from one another, wherein each of the plurality of sensor modules includes a first emitter configured to emit light of a first wavelength, and a detector configured to detect light; a controller coupled to the plurality of sensor modules , wherein the controller is configured to: from each detector , receive along a first short vector, a measurement of light intensity over time of light, reflected off of body tissue, at the first wavelength and originating from a first emitter from a same sensor module ; from each detector , receive along a first long vector, a measurement of light intensity over time of light, reflected off of body tissue, at the first wavelength and originating from a first emitter from a circumferentially adjacent sensor module , calculate separate perfusion indexes corresponding to measured light intensity over time of each first short vector and each first long vector; and cause the display of the separate perfusion indexes corresponding to measured light intensity over time of each first short vector and each first long vector. from each detector , receive along a first short vector, a measurement of light intensity over time of light, reflected off of body tissue, at the first wavelength and originating from a first emitter from a same sensor module ; from each detector , receive along a first long vector, a measurement of light intensity over time of light, reflected off of body tissue, at the first wavelength and originating from a first emitter from a circumferentially adjacent sensor module , calculate separate perfusion indexes corresponding to measured light intensity over time of each first short vector and each first long vector; and cause the display of the separate perfusion indexes corresponding to measured light intensity over time of each first short vector and each first long vector. <EOS>