Spatiotemporal frequency domain analysis for blood velocity measurement during embolization procedures

Abstract

BackgroundCurrently, determining procedural endpoints and treatment efficacy of vascular interventions is largely qualitative and relies on subjective visual assessment of digital subtraction angiography (DSA) images leading to large interobserver variabilities and poor reproducibility. Quantitative metrics such as the residual blood velocity in embolized vessel branches could help establish objective and reproducible endpoints. Recently, velocity quantification techniques based on a contrast enhanced X‐ray sequence such as qDSA and 4D DSA have been proposed. These techniques must be robust, and, to avoid radiation dose concerns, they should be compatible with low dose per frame image acquisition.PurposeTo develop and evaluate a technique for robust blood velocity quantification from low dose contrast enhanced X‐ray image sequences that leverages the oscillating signal created by pulsatile blood flow.MethodsThe proposed spatiotemporal frequency domain (STF) approach quantifies velocities from time attenuation maps (TAMs) representing the oscillating signal over time for all points along a vessel centerline. Due to the time it takes a contrast bolus to travel along the vessel centerline, the resulting TAM resembles a sheared sine wave. The shear angle is related to the velocity and can be determined in the spatiotemporal frequency domain after applying the 2D Fourier transform to the TAM. The approach was evaluated in a straight tube phantom using three different radiation dose levels and compared to ultrasound transit‐time‐based measurements. The STF velocity results were also compared to previously published approaches for the measurement of blood velocity from contrast enhanced X‐ray sequences including shifted least squared (SLS) and phase shift (PHS). Additionally, an in vivo porcine study (n = 8) was performed where increasing amounts of embolic particles were injected into a hepatic or splenic artery with intermittent velocity measurements after each injection to monitor the resulting reduction in velocity.ResultsAt the lowest evaluated dose level (average air kerma rate 1.3 mGy/s at the interventional reference point), the Pearson correlation between ultrasound and STF velocity measurements was 99%. This was significantly higher () than corresponding correlation results between ultrasound and the previously published SLS and PHS approaches (91 and 93%, respectively). In the in vivo study, a reduction in velocity was observed in 85.7% of cases after injection of 1 mL, 96.4% after 3 mL, and 100.0% after 4 mL of embolic particles.ConclusionsThe results show good agreement of the spatiotemporal frequency domain approach with ultrasound even in low dose per frame image sequences. Additionally, the in vivo study demonstrates the ability to monitor the physiological changes due to embolization. This could provide quantitative metrics during vascular procedures to establish objective and reproducible endpoints.

Motion-compensation approach for quantitative digital subtraction angiography and its effect on in-vivo blood velocity measurement

“…49 As these frequency ranges do not overlap, the influence of contrast changes caused by respiratory motion on the blood velocity analysis conducted in the spatiotemporal frequency domain is reduced. These results further confirm the findings of Wagner et al 33 where no significant difference was found between blood velocity measurements performed on DSA images and images with no background subtraction.…”

“…Among the various qDSA techniques reported, [31][32][33] the velocity quantification algorithm proposed by Wagner et al 33 was used throughout this study. This algorithm was preferred due to its global, non-iterative approach for blood velocity quantification from a TAM.…”

“…The qDSA velocity quantification algorithm used throughout this study was proposed by Wagner et al 33 and provided a global, non-iterative solution using a spatiotemporal frequency domain analysis. In a TAM, the contrast traveling along a vessel centerline during each cardiac cycle results in sheared lines (Fig.…”

“…The two static centerlines were used for comparison with a previous, uncompensated qDSA approach. 33 The best-case static centerline was chosen from the set of manually annotated centerlines that minimized d e .…”

“…This work has two main purposes, to investigate in-vivo the effects of vessel motion on the measurement of time-attenuation maps and the subsequent effects on blood velocity analysis using quantitative digital subtraction angiography (qDSA). [31][32][33] The second purpose of this work was to provide an in-vivo motion-compensated approach to determine time-attenuation maps from vessels with motion for subsequent blood velocity analysis using qDSA.…”