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Background: Flow altering angiographic procedures suffer from ill‐defined, qualitative endpoints. Quantitative digital subtraction angiography (qDSA) is an emerging technology that aims to address this issue by providing intra‐procedural blood velocity measurements from time‐resolved, 2D angiograms. To date, qDSA has used 30 frame/s DSA imaging, which is associated with high radiation dose rate compared to clinical diagnostic DSA (up to 4 frame/s). Purpose: The purpose of this study is to demonstrate an interleaved x‐ray imaging method which decreases the radiation dose rate associated with high frame rate qDSA while simultaneously providing low frame rate diagnostic DSA images, enabling the acquisition of both datasets in a single image sequence with a single injection of contrast agent. Methods: Interleaved x‐ray imaging combines low radiation dose image frames acquired at a high rate with high radiation dose image frames acquired at a low rate. The feasibility of this approach was evaluated on an x‐ray system equipped with research prototype software for x‐ray tube control. qDSA blood velocity quantification was evaluated in a flow phantom study for two lower dose interleaving protocols (LD1: 3.7±0.02mGy/s$3.7 \pm 0.02\ {\mathrm{mGy}}/{\mathrm{s}}$ and LD2: 1.7±0.04mGy/s$1.7 \pm 0.04{\mathrm{\ mGy}}/{\mathrm{s}}$) and one conventional (full dose) protocol (11.4±0.04mGy/s)$11.4 \pm 0.04{\mathrm{\ mGy}}/{\mathrm{s}})$. Dose was measured at the interventional reference point. Fluid velocities ranging from 24 to 45 cm/s were investigated. Gold standard velocities were measured using an ultrasound flow probe. Linear regression and Bland‐Altman analysis were used to compare ultrasound and qDSA. Results: The LD1 and LD2 interleaved protocols resulted in dose rate reductions of −67.7% and −85.5%, compared to the full dose qDSA scan. For the full dose protocol, the Bland‐Altman limits of agreement (LOA) between qDSA and ultrasound velocities were [0.7, 6.7] cm/s with a mean difference of 3.7 cm/s. The LD1 interleaved protocol results were similar (LOA: [0.3, 6.9] cm/s, bias: 3.6 cm/s). The LD2 interleaved protocol resulted in slightly larger LOA: [−2.5, 5.5] cm/s with a decrease in the bias: 1.5 cm/s. Linear regression analysis showed a strong correlation between ultrasound and qDSA derived velocities using the LD1 protocol, with a R2${R}^2$ of 0.96$0.96$, a slope of 1.05$1.05$ and an offset of 1.9$1.9$ cm/s. Similar values were also found for the LD2 protocol, with a R2${R}^2$ of 0.93$0.93$, a slope of 0.98$0.98$ and an offset of 2.0$2.0$ cm/s. Conclusions: The interleaved method enables simultaneous acquisition of low‐dose high‐rate images for intra‐procedural blood velocity quantification (qDSA) and high‐dose low‐rate images for vessel morphology evaluation (diagnostic DSA). [ABSTRACT FROM AUTHOR]

Background: Currently, 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. Purpose: To 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. Methods: The 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. Results: At 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%$99\%$. This was significantly higher (p<0.0001$p < 0.0001$) than corresponding correlation results between ultrasound and the previously published SLS and PHS approaches (91$\hskip.001pt 91$ and 93%$93\%$, respectively). In the in vivo study, a reduction in velocity was observed in 85.7%$85.7\%$ of cases after injection of 1 mL, 96.4%$96.4\%$ after 3 mL, and 100.0%$100.0\%$ after 4 mL of embolic particles. Conclusions: The 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. [ABSTRACT FROM AUTHOR]