We present the development of high-performance polarized 3 He targets for use in electron scattering experiments that utilize the technique of alkali-hybrid spin-exchange optical pumping. We include data obtained during the characterization of 24 separate target cells, each of which was constructed while preparing for one of four experiments at Jefferson Laboratory in Newport News, Virginia. The results presented here document dramatic improvement in the performance of polarized 3 He targets, as well as the target properties and operating parameters that made those improvements possible. Included in our measurements were determinations of the so-called X-factors that quantify a temperature-dependent and as-yet poorly understood spin-relaxation mechanism that limits the maximum achievable 3 He polarization to well under 100%. The presence of this spinrelaxation mechanism was clearly evident in our data. We also present results from a simulation of the alkali-hydrid spin-exchange optical pumping process that was developed to provide guidance in the design of these targets. Good agreement with actual performance was obtained by including details such as off-resonant optical pumping. Now benchmarked against experimental data, the simulation is useful for the design of future targets. Included in our results is a measurement of the K-3 He spin-exchange rate coefficient k K se = (7.46 ± 0.62)×10 −20 cm 3 /s over the temperature range 503 K to 563 K.

Results from this study indicate that the performance of template matching is comparable with or better than that of manual tumor localization. This study serves as preliminary investigations towards developing online motion tracking techniques for hybrid MRI-Linac systems. Accuracy of template matching makes it a suitable candidate to replace the labor intensive manual tumor localization for obtaining the ground truth when testing other motion management techniques.

The dynamics of the movement of gas is discussed for two-chambered polarized 3 He target cells of the sort that have been used successfully for many electron scattering experiments. A detailed analysis is presented showing that diffusion is a limiting factor in target performance, particularly as these targets are run at increasingly high luminosities. Measurements are presented on a new prototype polarized 3 He target cell in which the movement of gas is due largely to convection instead of diffusion. NMR tagging techniques have been used to visualize the gas flow, showing velocities along a cylindrically-shaped target of between 5 − 80 cm/min. The new target design addresses one of the principle obstacles to running polarized 3 He targets at substantially higher luminosities while simultaneously providing new flexibility in target geometry.

This is the first examination of Cherenkov-generated pPDDs and pCBPs in an MR-IGRT system. Cherenkov imaging measurements were fast to acquire, and minimal error was observed overall. Cherenkov imaging also provided novel real-time data for IMRT QA. The strengths of this imaging are the rapid data capture ability providing real-time, high spatial resolution data, combined with the remote, noncontact nature of imaging. The biggest limitation of this method is the two-dimensional (2D) projection-based imaging of three-dimensional (3D) dose distributions through the transparent water tank.

We have used an ultrafast laser pulse shaper in conjunction with a genetic algorithm to investigate dynamic alignment in room temperature CO. We find, in experiment and simulation, non-transform-limited laser pulse shapes that interact nonimpulsively with the molecules, yet are just as effective for transient alignment as shorter transform-limited pulses with the same energy. We use principal control analysis to determine which pulse characteristics, in experiment and simulation, are most important for the alignment control we observe. The analysis results suggest that in spite of the fact that the aligning laser intensities ͑ϳ10 14 W/cm 2 ͒ are sufficiently large to induce ionization, a simple rigid-rotor model with constant polarizabilities accurately describes the laser-driven molecular dynamics.

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Purpose To evaluate T2, T2* and signal-to-noise ratio (SNR) for hyperpolarized helium-3 (3He) MRI of the human lung at three magnetic field strengths ranging from 0.43T and 1.5T. Methods Sixteen healthy volunteers were imaged using a commercial whole-body scanner at 0.43T, 0.79T, and 1.5T. Whole-lung T2 values were calculated from a Carr-Purcell-Meiboom-Gill spin-echo-train acquisition. T2* maps and SNR were determined from dual-echo and single-echo gradient-echo images, respectively. Mean whole-lung SNR values were normalized by ventilated lung volume and administered 3He dose. Results As expected, T2 and T2* values demonstrated a significant inverse relationship to field strength. Hyperpolarized 3He images acquired at all three field strengths had comparable SNR values and thus appeared visually very similar. Nonetheless, the relatively small SNR differences among field strengths were statistically significant. Conclusions Hyperpolarized 3He images of the human lung with similar image quality were obtained at three field strengths ranging from 0.43T and 1.5T. The decrease in susceptibility effects at lower field that are reflected in longer T2 and T2* values may be advantageous for optimizing pulse sequences inherently sensitive to such effects. The three-fold increase in T2* at lower field strength would allow lower receiver bandwidths, providing a concomitant decrease in noise and relative increase in SNR.

An updated Cherenkov imaging method identified asymmetric, machine-dependent TSET field angle pairs that provided much larger 90% isodose areas than the commonly adopted symmetric geometry suggested by Task Group 30 Report 23. A novel demonstration of scatter dose Cherenkov imaging in the TSET field was established.