Purpose: The Aries x-ray photon-counting detector (Direct Conversion Inc.) can image at 1000 fps and is being investigated to observe details of vascular blood flow. This study considers the input-exposure requirements of the imager and the radiation dose implications for clinical use.
Methods: The Aries image receptor has 100-micron pixels and a 5x7.5 cm FOV. Image frames were captured using one millisecond acquisition times, an RQA5 phantom placed in the beam and technique parameters set to 70 kVp and 100 mA. A 6-cc PTW ionization chamber was used to measure exposure at the detector input. An idealized ICA saccular-aneurysm model was placed over the phantom and images of contrast flow taken at 1000 fps were evaluated. The image signal-to-noise ratio and the vessel contrast-to-noise ratio were calculated from the counts per pixel. The integrated input detector exposure was determined over the transit time of a contrast bolus through the vasculature of interest.
Results: The RQA5 phantom images had a detector input-exposure-per-frame (EPF) of 38 µR, with a signal-to-noise ratio (SNR) of 7.2 and contrast-to-noise ratio (CNR) for the aneurysm of 2.4. At this dose level, flow details could be clearly seen in images of the aneurysm model. Contrast-bolus transit times are typically under 200 ms, requiring less than 200 1-ms frames. The integrated detector exposure for the RQA5 phantom run would correspond to about 7.5 seconds of DSA (300 µR/frame) at 3fps.
Conclusion: The Aries imager has been shown to give high temporal and spatial resolution, providing visualization of detailed blood-flow patterns in vascular pathology previously unseen. Estimated exposure for HSA runs appear to be comparable to present DSA runs.
Funding Support, Disclosures, and Conflict of Interest: This work was supported in part by NIH Grant 1R01EB030092.