<prompt> Investigation to diagnose the Laryngo pharyngeal refluxEsophageal pH monitoringDual Probe Impedance pH monitoringBarium EsophagogramScintigraphy  <response>: Ans. b Dual Probe Impedance pH MonitoringRef: Shackelford Page 2228th Edition pH monitoring at the level of Pharynx is not helpful because the acid refluxed is neutralized by the Pharyngeal secretions. Hence a Dual Bifurcated catheter measuring both pH and Impedance is used across Upper esophageal sphincter, thereby permitting detection of Pharyngeal reflux 