Background: High-resolution Impedance Manometry (HRIM) is used to detect complete versus incomplete bolus transit. Three-Dimensional Volume of Inverted Impedance (VII) was developed to measure the remnant impedance volume between each swallow. However, its clinical usefulness and meaning were not fully evaluated. Radionuclide esophageal transit scintigraphy (RETS) has been used to determine bolus transit in esophageal motor disorders. Here we aimed to investigate the absolute measurement of bolus transit based on the 3-D volume of impedance and its clinical meaning by assessing its relationship with RETS. Methods: Thirty-one patients who underwent both HRIM and RETS were enrolled in this study. Twenty-nine of these patients were diagnosed with achalasia and two patients were normal. Each patient underwent HRIM using a catheter with 32 circumferential pressure and 16 impedance sensors. The impedance profi les were converted to ASCII fi les and analyzed with the MATLAB program. VII was plotted after transforming the data to a cubic spline interpolation followed by resampling the manometry position at 0.2-cm intervals. The VII between swallows was categorized into four different 5-second frames. RETS was performed by using 99mTc-DTPA, and remnant radionuclide in the lumen of esophageal body was measured at 1,5,10,15,and 20 minutes ofinterval after swallowing. Results: A total of 40 HRIM and RETS procedures were analyzed (nine patients with achalasia underwent both tests twice before and after treatment). The mean VII value of the later 15 second frames from each swallow showed a signifi cant positive correlation to the 20-minute RETS (r=0.31, P=0.04). Moreover, the mean VII value of the later 10-second frames also showed a signifi cant positive correlation to 20-minute RETS (r=0.32, P=0.04). Conclusions: The newly developed VII method may have a close relationship with the currently using RETS despite different protocols.