We report on the operation and performance tests of a preclinical head scanner developed for proton computed tomography (pCT). After extensive preclinical testing, pCT is intended to be employed in support of proton therapy treatment planning and pre-treatment verification in patients undergoing particle-beam therapy. In order to assess the performance of the scanner, we have performed CT scans with 200 MeV protons from both the synchrotron of the Loma Linda University Medical Center (LLUMC) and the cyclotron of the Northwestern Medicine Chicago Proton Center (NMCPC). The very high sustained rate of data acquisition, exceeding one million protons per second, allowed a full 360° scan to be completed in less than 7 minutes. The reconstruction of various phantoms verified accurate reconstruction of the proton relative stopping power (RSP) and the spatial resolution in a variety of materials. The dose for an image with better than 1% uncertainty in the RSP is found to be close to 1 mGy.

While CTA is an established clinical gold standard for imaging large cerebral arteries and veins, an important challenge that currently remains for CTA is its limited performance in imaging small perforating arteries with diameters below 0.5 mm. The purpose of this work was to theoretically and experimentally study the potential benefits of using photon counting detector (PCD)-based CT (PCCT) to improve the performance of CTA in imaging these small arteries. In particular, the study focused on an important component of the CTA image package known as the maximum intensity projection (MIP) image. To help understand how the physical properties of a detector quantitatively influence the MIP image quality, a theoretical model on the statistical properties of MIP images was developed. After validating this model, it was used to explore the individual and joint contribution of the following detector properties to the MIP signal-to-noise ratio (SNR): inter-slice noise covariance, spatial resolution along the z direction, and native pixel pitch along z. The model demonstrated that superior slice sensitivity, reduced inter-slice noise correlation, and smaller native pixel pitch along z provided by PCDs lead to improved vessel SNR in MIP images. Finally, experiments were performed by scanning an anthropomorphic cerebral angiographic phantom using a benchtop PCCT system and a commercial MDCT system. The experimental MIP results consistently demonstrated that compared with MDCT, PCCT provides superior vessel conspicuity and reduced artifactual stenosis.

BACKGROUND AND PURPOSE: Quantification of blood flow using a 4D-DSA would be useful in the diagnosis and treatment of cerebrovascular diseases. A protocol optimizing identification of density variations in the time-density curves of a 4D-DSA has not been defined. Our purpose was to determine the contrast injection protocol most likely to result in the optimal pulsatility signal strength. MATERIALS AND METHODS: Two 3D-printed patient-specific models were used and connected to a pulsatile pump and flow system, which delivered 250-260 mL/min to the model. Contrast medium (Isovue, 370 mg I/mL, 75% dilution) was injected through a 6F catheter positioned upstream from the inlet of the model. 4D-DSA acquisitions were performed for the following injection rates: 1.5, 2.0, 2.5, 3.0 and 3.5 mL/s for 8 seconds. To determine pulsatility, we analyzed the time-density curve at the inlets using the oscillation amplitude and a previously described numeric metric, the sideband ratio. Vascular geometry from 4D-DSA reconstructions was compared with ground truth and micro-CT measurements of the model. Dimensionless numbers that characterize hemodynamics, Reynolds and Craya-Curtet, were calculated for each injection rate. RESULTS: The strongest pulsatility signal occurred with the 2.5 mL/s injections. The largest oscillation amplitudes were found with 2.0-and 2.5-mL/s injections. Geometric accuracy was best preserved with injection rates of .1.5 mL/s. CONCLUSIONS: An injection rate of 2.5 mL/s provided the strongest pulsatility signal in the 4D-DSA time-density curve. Geometric accuracy was best preserved with injection rates above 1.5 mL/s. These results may be useful in future in vivo studies of blood flow quantification.

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positive correlation between TCBF and CVO (r=0.81 and P<0.001) was seen. The TCBF (20.21 ±4.58 ml/s versus 11.78±2.03 ml/s; P<0.001) and CVO (12.80 ± 3.82 ml/s versus 9.03 ±2.31 ml/s; P=0.010) were significantly higher in children compared to adult volunteers. The CVO/TCBF ratio was significantly lower in children versus adult volunteers (0.63 ± 0.01 versus 0.76 ± 0.02, P=0.025). In adults, the correlation of TCBF with age remains strong (rho =-0.69, t-stat =-4.5, P=0.00018). However, CVO (rho =-0.29, t-stat =-1.42, P=0.171) and CVO/TCBF ratio (r=0.16, P=0.446) were not significantly associated with age in the adult cohort. The ratio of cerebral arterial inflow to systemic aortic outflow was significantly higher in children compared to adults (0.45±0.08 versus 0.15 ±0.02, P<0.001). Conclusions Both TCBF and CVO decrease with age, however unlike TCBF, there is no correlation between the decrease in CVO through the Transverse sinuses and age, which could suggest the early development of alternative venous drainage pathways through the emissary and extracranial veins. This could also explain the differential ratio of CVO to TCBF, which suggests that more than 20% of cerebral venous outflow in adults and more than 35% of outflow in Children are not through the Transverse sinuses in the supine position. Understanding the quantitative differences between TCBF and CVO in healthy volunteers could help identify and manage changes related to venous outflow abnormalities.