Quantitative blood flow estimation error due to the in-plane component of the flow with intravascular ultrasound

Previously we presented the flow estimation error introduced by in-plane flow using a slow-time FIR (finite impulse response) filter-bank method to quantitatively measure blood flow decorrelation through the image plane of an intravascular ultrasound (IVUS) imaging system. There exists a monotonic relationship between blood flow velocity and the normalized second moment of the slow-time spectrum for flow orthogonal to the imaging plane of a side-looking catheter array. However, in the presence of an in-plane flow component, this monotonic relationship changes due to a shift and spread of slow-time spectra. These two effects cause the normalized second moment to increase, resulting in flow overestimates. Applying appropriate tilts to slow-time signals, however. the slow-time spectrum shifts back to DC and the orthogonal estimation method can be used. We present a method to correct this overestimation and accurately estimate blood flow through the image plane in real-time. Independent simulations show that for blood flowing at angles between +/- 6 degrees and +/- 15 degrees at a speed of 30 cm/sec. flow would be overestimated by as much as 14.82% and 72.24% respectively using the direct filter-bank approach. However, this overestimation error can be corrected using the modified method presented here, reducing the estimation error by a factor of 29.9 and 34.64 for those angles respectively.