Details of blood flow patterns and rates can provide useful information to physicians when deciding whether to treat diseased vessels and in assessing the effectiveness of treatments. These blood flow details are difficult to see using ‘realtime’ imaging techniques of 30 fps. 1000 fps High-Speed Angiography (HSA) provides the temporal resolution needed to record details of flow within patient vasculature. The Actaeon detector from XCounter is capable of x-ray imaging at 1000 fps providing sufficient temporal and spatial resolution (100 μm pixel pitch) for the quantification of flow details. A new method for experimentally obtaining flow details in patient-specific geometries demonstrates microspheres tracking vascular flow similar to methods used in optical laser-based particle image velocimetry (PIV). The microspheres are prepared by soaking them in iodinated contrast medium to provide radio-opacity and injected into 3D-printed, patient-specific vascular phantoms during x-ray exposure. Images were acquired at 1000 fps for 2.4 seconds using the Actaeon’s High-Sensitivity mode. Changes in particle positions were tracked through consecutive frames and the position data was used to calculate velocities. The velocities were then mapped to the initial position and binned to reduce apparent variation in individual particle paths. This method provides quantitative data regarding the flow details within a vessel and also qualitative information regarding flow at different points in time during the acquisition. These methods could enable new measurements of flow properties in patient-specific vasculature.
While angiography may be considered the gold standard for evaluating diseases of the human vasculature, vascular flow details are unavailable due to the low temporal resolution of flat panel detectors (FPDs) which operate at a maximum of 15 – 30 fps. Higher frame rates are necessary to extract any meaningful flow detail, which may act as additional information that can be used to characterize flow-dependent disease states. These higher rates have become available with recent advances in photon-counting detector (PCD) technology. The XCounter Actaeon was used to perform high frame rate imaging at 1000 fps. The Actaeon also provides superior spatial resolution due to its 100 um pixel size and electronic charge sharing correction, making it a good candidate for small ROI imaging. With this detector, “High Speed Angiography” (HSA) was performed on a variety of 3D printed patient-specific vasculature and interventional devices, using a simulated flow loop and iodinated contrast media. The images, which illustrate pathology-dependent flow detail, were recorded in a sequence of 1 ms frames. In addition, the energy discrimination capabilities of the Actaeon were used such that with a lower energy threshold, instrumentation noise was virtually negligible. The per frame noise quality and overall patient dose were acceptable as compared to standard angiography dose rates using FPDs. The previously unseen flow detail may give new insight into the diagnosis, progression, and treatment of neuro and cardiovascular pathologies.
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