Intravascular ultrasound radiofrequency signal analysis of blood speckles: Physiological assessment of intermediate coronary artery stenosis

Background This study aimed to systematically investigate feasibility of radiofrequency intravascular ultrasound (RF-IVUS) analysis of blood signals for assessing functionally significant coronary stenosis. Methods First, in-vivo human study was performed to evaluate 83 intermediate coronary lesions from 75 patients, using 40-MHz RF-IVUS, fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR). Average blood integrated-backscatter (IB) values within lumen were measured at proximal and distal segments to the stenosis; Delta IB values between the two sites were calculated. Second, bench-test was performed to assess relationships of blood IB values to blood flow velocity and hematocrit using 40 and 60-MHz RF-IVUS. Results In in-vivo study, Delta IB values across the stenosis significantly correlated with both FFR (r = -.85, p < .0001) and iFR (r = -.65, p < .0001), which was confirmed in small minimum lumen area (MLA) lesions (MLA <2.0 mm(2)). Receiver operating characteristic curve analyses identified the best cut-off value as 10.06 of Delta IB values for predicting FFR <= 0.8 and iFR <= 0.89 (sensitivity 76.2 and 95.5%, specificity 100 and 82.0%, positive predictive value 100 and 65.6%, negative predictive value 80.4 and 98.0%, accuracy 92.9 and 92.8% for FFR and iFR). Bench-test study also identified that blood IB values exponentially changed as a function of blood flow velocity at any given hematocrit in both 40 and 60-MHz RF-IVUS. Conclusions This study supports the potential utility of RF-IVUS analysis of blood signals to estimate functional ischemia, demonstrating relationships of blood Delta IB values to FFR and iFR, as well as relationships between blood IB values and flow velocity.