ViewRay (United States)

Abstract. In this work, we describe the development of the Carbon monOxide Measurement from Ames (COMA) instrument for measurement of carbon monoxide (CO) and nitrous oxide (N2O) aboard NASA's WB-57 high-altitude research aircraft. While COMA has previously flown in the cabin of the NASA P3 platform, here the instrument was modified to operate in a significantly different environment – an unpressurized pallet flying primarily above 12 km (40 000 ft). Modifications were made to the laser to allow for detection of CO and N2O, ruggedization and thermal management were addressed, and a calibration system was designed to quantify the measurement stability in-flight. Testing was conducted in a thermal vacuum chamber to mimic anticipated ambient conditions experienced inside the WB-57 pallet bay and found that the electronic components remained within the thermal limits. COMA was operated successfully during 9 unattended transit flights to and from South Korea and 15 research flights during NASA's Asian summer monsoon Chemical & CLImate Project (ACCLIP) 2022 campaign, which was focused on studying the Asian summer monsoon anticyclone in the western Pacific. The CO measurement has an overall uncertainty ranging between 4.1 ppb (at 50 ppb CO) and 5.6 ppb (at 200 ppb CO). N2O has an overall uncertainty of 2.7 ppb (at 320 ppb N2O). In addition, COMA observations were compared with two other in situ CO instruments co-located on the WB-57: the Carbon Monoxide Laser Detector 2 (COLD2) and the Airborne Carbonic Oxides and Sulfide Spectrometer (ACOS). Comparisons for the 15 flights during the ACCLIP campaign indicate ranges in slope of 1.10–1.15 for COLD2 vs. COMA and 0.94–1.10 for ACOS vs. COMA.

<strong class="journal-contentHeaderColor">Abstract.</strong> In this work, we describe development of the Carbon monOxide Measurement from Ames (COMA) instrument for measurement of carbon monoxide (CO) and nitrous oxide (N₂O) aboard NASA's WB-57 high altitude research aircraft. While COMA has previously flown in the cabin of the NASA P-3 platform, here the instrument was modified to operate in a significantly different environment- an unpressurized pallet flying primarily above 12 km (40,000 ft). Modifications were made to the laser to allow for detection of CO and N₂O, ruggedization and thermal management were addressed, and a calibration system was designed to quantify the measurement stability in-flight. Testing was conducted in a thermal vacuum chamber to mimic anticipated ambient conditions experienced inside the WB-57 pallet bay and found electronic components remained within thermal limits. COMA successfully operated during nine unattended transit flights to and from South Korea and fifteen research flights during NASA&rsquo;s Asian summer monsoon Chemical &amp; CLImate Project (ACCLIP) 2022 campaign, which was focused on studying the Asian summer monsoon anticyclone in the Western Pacific. The CO measurement has an overall uncertainty ranging between 4.1 ppb (at 50 ppb CO) and 5.9 ppb (at 200 ppb CO). N₂O has an overall uncertainty of 2.7 ppb (at 320 ppb N₂O). In addition, COMA observations were compared with two other in-situ CO instruments co-located on the WB-57: Carbon Monoxide Laser Detector (COLD) 2 and Airborne Carbonic Oxides and Sulfide Spectrometer (ACOS). Comparisons for 15 flights during the ACCLIP campaign indicate a range in slope of 1.10&ndash;1.15 for COLD2 vs. COMA and 0.94&ndash;1.10 for ACOS vs COMA.

<strong class="journal-contentHeaderColor">Abstract.</strong> In this work, we describe development of the Carbon monOxide Measurement from Ames (COMA) instrument for measurement of carbon monoxide (CO) and nitrous oxide (N₂O) aboard NASA's WB-57 high altitude research aircraft. While COMA has previously flown in the cabin of the NASA P-3 platform, here the instrument was modified to operate in a significantly different environment- an unpressurized pallet flying primarily above 12 km (40,000 ft). Modifications were made to the laser to allow for detection of CO and N₂O, ruggedization and thermal management were addressed, and a calibration system was designed to quantify the measurement stability in-flight. Testing was conducted in a thermal vacuum chamber to mimic anticipated ambient conditions experienced inside the WB-57 pallet bay and found electronic components remained within thermal limits. COMA successfully operated during nine unattended transit flights to and from South Korea and fifteen research flights during NASA&rsquo;s Asian summer monsoon Chemical &amp; CLImate Project (ACCLIP) 2022 campaign, which was focused on studying the Asian summer monsoon anticyclone in the Western Pacific. The CO measurement has an overall uncertainty ranging between 4.1 ppb (at 50 ppb CO) and 5.9 ppb (at 200 ppb CO). N₂O has an overall uncertainty of 2.7 ppb (at 320 ppb N₂O). In addition, COMA observations were compared with two other in-situ CO instruments co-located on the WB-57: Carbon Monoxide Laser Detector (COLD) 2 and Airborne Carbonic Oxides and Sulfide Spectrometer (ACOS). Comparisons for 15 flights during the ACCLIP campaign indicate a range in slope of 1.10&ndash;1.15 for COLD2 vs. COMA and 0.94&ndash;1.10 for ACOS vs COMA.

This paper presents the design, prototype engineering, and initial testing of a relatively low-voltage, high aspect ratio electron gun for versatile pulsed power applications. The sheet beam, diode electron gun is designed for (23–25) kV voltage and 6 µA/V1.5, as is required for x-band klystron, as a part of a compact Klylac delivering electron beam energy in the MeV range. The gun prototype was engineered, built, and tested using a Scandinova M1-0.5 modulator. Beam loss on the anode aperture is evaluated from transient waveforms and equivalent circuit modeling.

To modify and evaluate an automatic American College of Radiology (ACR) phantom analysis toolbox for ACR quality assurance (QA) on a low-field MR-guided radiotherapy system (ViewRay). An open-source toolbox was modified for ACR QA of a 0.35T MRI system (ViewRay MRIdian). A total of 17 ACR datasets were evaluated, including 10 datasets acquired from different systems across the world, and seven datasets acquired at our center between 2014 and 2020. All required ACR tests, geometric accuracy (GA), high-contrast spatial resolution (HCSR), slice thickness accuracy (ST), slice position accuracy (SP), percent integral uniformity (PIU), percentage signal ghosting (PSG), and low-contrast object detectability (LCOD), were assessed manually and using the toolbox automatically. Measurements between manual and automatic analysis were compared. Precision, recall, and accuracy were calculated, where the manual results were used as the ground truth. The software took less than 2min to complete all seven tests, which usually requires 40min or more if analyzed manually. Overall, the automatic measurement was consistent with the manual result. The absolute differences between the two measurements were 0.72±0.66 (mm), 0.01±0.03, 0.50±0.60 (mm), 0.39±0.41 (mm), 1.01±1.00 (%), 0.0016±0.0019, and 2.79±2.29 for the seven tests. The precision of the automatic toolbox was 100% for all tests, indicating that a test would 100% pass a manual analysis if it had passed the automatic analysis. Recall and accuracy were≥96% for GA, HCSR, SP, PIU, PSG, and LCOD tests, and 91% for the ST test. An automatic ACR QA tool was adopted and evaluated for the low-field MR-guided radiotherapy (MRgRT) system. Overall, the toolbox provided comparable results as manual analysis, and reduced the processing time from over 40min to <2min. This toolbox holds the potential to be widely adopted either as a second check tool or partially replace human measurement for MRgRT programs using the same system.

Purpose:To describe the physical and dosimetric properties of a novel double‐stack multileaf collimator (MLC).Methods:One of the compromises made in the MLC design has been to employ linear‐motion singly‐divergent shapes. Because the MLC leading edge moves linearly, it is rounded to provide a consistent, albeit compromised penumbra. The MLC employed in the new linac‐based MR‐IGRT unit is designed to be doubly focused in that each leaf moves in an arc centered at the source, and the sides of the leaves are machined such that they lie parallel to a line between the leaf edge and the source. The curvature of the MLC keeps motors and encoders in lower magnetic field. However, high spatial‐resolution leaves are difficult to manufacture to sufficiently tight tolerances and difficult to move due to restricted space on the gantry. Wider leaves alleviate this problem with less moving parts but the coarse resolution disallows treating very small lesions. This compromise has been overcome by splitting the MLC leaf bank into two sets, stacked one upon the other and offset half of a leaf width. The dosimetry has been simulated using Monte‐Carlo and a 6 MV linac in a 0.35 T magnetic field.Results:The combined MLC leaf set has a spatial resolution of effectively half of the leaf width, 4mm here. The dosimetry resolution and conformality are consistent with 4mm wide MLC assisted by inverse fluence modulation. Also, because each leaf junction is backed up by the stacked leaf that lies over the junction, the problem of tongue‐and‐groove dosimetry has been greatly reduced. The novel MLC design allows the use of more powerful leaf motors than would be otherwise possible if a single MLC bank is employed.Conclusions:The stacked MLC will provide highly conformal dose distributions suitable for stereotactic radiation therapy of small lesions.The research was funded by ViewRay, Inc.

Head motion during PET brain imaging can cause significant degradation of image quality. Several authors have proposed ways to compensate for PET brain motion to restore image quality and improve quantitation. Head restraints can reduce movement but are unreliable; thus the need for alternative strategies such as data-driven motion estimation or external motion tracking. Herein, the authors present a data-driven motion estimation method using a preprocessing technique that allows the usage of very short duration frames, thus reducing the intraframe motion problem commonly observed in the multiple frame acquisition method. The list mode data for PET acquisition is uniformly divided into 5-s frames and images are reconstructed without attenuation correction. Interframe motion is estimated using a 3D multiresolution registration algorithm and subsequently compensated for. For this study, the authors used 8 PET brain studies that used F-18 FDG as the tracer and contained minor or no initial motion. After reconstruction and prior to motion estimation, known motion was introduced to each frame to simulate head motion during a PET acquisition. To investigate the trade-off in motion estimation and compensation with respect to frames of different length, the authors summed 5-s frames accordingly to produce 10 and 60 s frames. Summed images generated from the motion-compensated reconstructed frames were then compared to the original PET image reconstruction without motion compensation. The authors found that our method is able to compensate for both gradual and step-like motions using frame times as short as 5 s with a spatial accuracy of 0.2 mm on average. Complex volunteer motion involving all six degrees of freedom was estimated with lower accuracy (0.3 mm on average) than the other types investigated. Preprocessing of 5-s images was necessary for successful image registration. Since their method utilizes nonattenuation corrected frames, it is not susceptible to motion introduced between CT and PET acquisitions. The authors have shown that they can estimate motion for frames with time intervals as short as 5 s using nonattenuation corrected reconstructed FDG PET brain images. Intraframe motion in 60-s frames causes degradation of accuracy to about 2 mm based on the motion type.