Rostyslav Boutchko

Design and Implementation of a Facility for Discovering New Scintillator Materials

We describe the design and operation of a high-throughput facility for synthesizing thousands of inorganic crystalline samples per year and evaluating them as potential scintillation detector materials. This facility includes a robotic dispenser, arrays of automated furnaces, a dual-beam X-ray generator for diffractometry and luminescence spectroscopy, a pulsed X-ray generator for time response measurements, computer-controlled sample changers, an optical spectrometer, and a network-accessible database management system that captures all synthesis and measurement data.

Medical applications of shortwave FM radar: remote monitoring of cardiac and respiratory motion.

PURPOSE This article introduces the use of low power continuous wave frequency modulated radar for medical applications, specifically for remote monitoring of vital signs in patients. METHODS Gigahertz frequency radar measures the electromagnetic wave signal reflected from the surface of a human body and from tissue boundaries. Time series analysis of the measured signal provides simultaneous information on range, size, and reflective properties of multiple targets in the field of view of the radar. This information is used to extract the respiratory and cardiac rates of the patient in real time. RESULTS The results from several preliminary human subject experiments are provided. The heart and respiration rate frequencies extracted from the radar signal match those measured independently for all the experiments, including a case when additional targets are simultaneously resolved in the field of view and a case when only the patients extremity is visible to the radar antennas. CONCLUSIONS Micropower continuous wave FM radar is a reliable, robust, inexpensive, and harmless tool for real-time monitoring of the cardiac and respiratory rates. Additionally, it opens a range of new and exciting opportunities in diagnostic and critical care medicine. Differences between the presented approach and other types of radars used for biomedical applications are discussed.

First-principles studies of Ce-doped RE2M2O7 (RE = Y, La; M = Ti, Zr, Hf): A class of nonscintillators

Lanthanum and yttrium compounds with composition RE2 M2 O7 (RE = Y, La; M = Ti, Zr, Hf) have high density and high Z and can be doped with Ce onto the La and Y sites. This makes these compounds good candidates for Ce-activated scintillator γ-ray detectors particularly for the hafnate systems which have a very high density. There is disagreement in the literature concerning La2 Hf2 O7:Ce as it has been reported to show both bright as well as no Ce-activated luminescence by different experimental groups. We have performed first-principles electronic structure calculations of these compounds doped with Ce using the pseudopotential method based on the generalized gradient approximation in density functional theory. The positions of the Ce 4f states relative to the valence band maximum and the position of the Ce 5d states relative to the conduction band minimum (CBM) of the host material are determined. We find, unlike Ce-activated La and Y compounds where the CBM is typically of La 5d or Y 4d character, that ...

First-Principles Studies and Predictions of Scintillation in Ce-Doped Materials

A theoretical approach based on first-principles calculations is used to select candidate Ce activated scintillator materials for synthesis. Our theoretical approach involves the calculation of the ground state band structure of the Ce-doped material as well as the calculation of the (Ce3+)* excited state. From our theoretical studies of known scintillators and non-scintillators we have developed a set of criteria that are necessary characteristics of bright Ce activated scintillators. Applying these criteria to new compounds we were able to successfully predict that Ba2YCl7 : Ce would be a bright scintillator.

Cerium Activated Scintillation in Yttrium Halides: First Principles Theory and Prediction

Recently, scintillation has been observed in Ce-doped YI3, YBr3, and YCl3 crystals. In particular, YI3 has been reported to be among the scintillators with the highest luminosity. In this work, we present a systematic study of scintillation in any of the four YHa3:Ce materials where Ha = F, Cl, Br, I, using ab initio calculations. Last year, our group demonstrated successful application of a method of gauging scintillation properties of Ce-doped crystals based on first-principle calculations using density functional theory. This method has been developed as an integral component of a High Throughput Scintillator Discovery facility based at the Lawrence Berkeley National Lab. By analyzing the energies and spatial localization of the highest occupied band in the ground state and in the lowest excited state, we are able to make qualitative predictions about the possibility of scintillation in Ce-doped compounds. In this paper we present the details of our theoretical approach in application to yttrium halides and compare them with the available experiments. Our results yield a prediction of Ce-based scintillation for all four materials: YF3, YCl3, YBr3 and YI3 and are in correspondence with the available experimental data. We believe that our method is the first use of first-principles calculations to predict some of the factors necessary for the activation of Ce3+ ions in crystals.

Fast direct estimation of the blood input function and myocardial time activity curve from dynamic SPECT projections via reduction in spatial and temporal dimensions

PURPOSE Reconstruction of parametric images from dynamic single photon emission computed tomography (SPECT) data acquired with slow rotating cameras is a challenge because the estimation of the time-activity curves (TACs) may involve fitting data to an inconsistent underdetermined system of equations. This work presents a novel algorithm for the estimation of the blood input function and myocardial TAC with high accuracy and high efficiency directly from these projections. METHODS In the proposed dynamic reconstruction method, the information from the segmentation of functional regions from the static reconstructed image was used as a prior to construct a sparse matrix, through which the spatial distribution of the radioactive tracer was represented. Then the temporal distribution of the radioactive tracer was modeled by nonuniform B-spline basis functions which were determined according to a new selection rule. With reduction in both the spatial and temporal dimensions of the reconstructed image, the blood input function and myocardial TAC were estimated using the 4D maximum likelihood expectation maximization algorithm. The method was validated using data from both digital phantom simulations and an experimental rat study. RESULTS Compared with the conventional dynamic SPECT reconstruction method without the reduction in spatial dimensions, the proposed method provides more accurate TACs with less computation time in both phantom simulation studies and a rat experimental study. CONCLUSIONS The proposed method is promising in both providing more accurate time-activity curves and reducing the computation time, which makes it practical for small animal studies using clinical systems with slow rotating cameras.

Dynamic molecular imaging of cardiac innervation using a dual headpinhole SPECT system

Typically 123I-MIBG is used for the study of innervation and function of the sympathetic nervous system in heart failure. The protocol involves two studies: first a planar or SPECT scan is performed to measure initial uptake of the tracer, followed some 3-4 hours later by another study measuring the wash-out of the tracer from the heart. A fast wash-out is indicative of a compromised heart. In this work, a dual head pinhole SPECT system was used for imaging the distribution and kinetics of 123I-MIBG in the myocardium of spontaneous hypertensive rats (SHR) and normotensive Wistar Kyoto (WKY) rats. The system geometry was calibrated based on a nonlinear point projection fitting method using a three-point source phantom. The angle variation effect of the parameters was modeled with a sinusoidal function. A dynamic acquisition was performed by injecting 123I-MIBG into rats immediately after starting the data acquisition. The detectors rotated continuously performing a 360o data acquisition every 90 seconds. We applied the factor analysis (FA)method and region of interest (ROI) sampling method to obtain time activity curves (TACs)in the blood pool and myocardium and then applied two-compartment modeling to estimate the kinetic parameters. Since the initial injection bolus is too fast for obtaining a consistent tomographic data set in the first few minutes of the study, we applied the FA method directly to projections during the first rotation. Then the time active curves for blood and myocardial tissue were obtained from ROI sampling. The method was applied to determine if there were differences in the kinetics between SHR and WKY rats and requires less time by replacing the delayed scan at 3-4 hours after injection with a dynamic acquisition over 90 to 120 minutes. The results of a faster washout and a smaller distribution volume of 123IMIBG near the end of life in the SHR model of hypertrophic cardiomyopthy may be indicative of a failing heart in late stages of heart failure.

Reconstruction of 4-D dynamic SPECT images from inconsistent projections using a Spline initialized FADS algorithm (SIFADS).

In this paper, we propose and validate an algorithm of extracting voxel-by-voxel time activity curves directly from inconsistent projections applied in dynamic cardiac SPECT. The algorithm was derived based on factor analysis of dynamic structures (FADS) approach and imposes prior information by applying several regularization functions with adaptively changing relative weighting. The anatomical information of the imaged subject was used to apply the proposed regularization functions adaptively in the spatial domain. The algorithm performance is validated by reconstructing dynamic datasets simulated using the NCAT phantom with a range of different input tissue time-activity curves. The results are compared to the spline-based and FADS methods. The validated algorithm is then applied to reconstruct pre-clinical cardiac SPECT data from canine and murine subjects. Images, generated from both simulated and experimentally acquired data confirm the ability of the new algorithm to solve the inverse problem of dynamic SPECT with slow gantry rotation.

A detector response function design in pinhole SPECT including geometrical calibration

Clinical single photon emission computed tomography (SPECT) equipped with pinhole collimators have a magnification factor that results in high spatial resolution images for small animal imaging. Using Monte Carlo simulations to model the acquisition process and the propagation of the photons from their point of emission to their detection point then integrating the model into an iterative reconstruction algorithm improves the signal-to-noise ratio, the contrast and the spatial resolution in the reconstructed images. However, pinhole SPECT systems are known to be very sensitive to geometrical misalignments. Geometrical misalignments are defined as the radial or axial shift of the collimator pinhole and/or twist and tilt of the detector heads and are introduced in the system each time the collimation device is changed (pinhole to parallel holes or vice versa). In this work, we present a flexible detector response function table (DRFT) design that takes into account the geometrical misalignments and avoids performing new Monte Carlo simulations for each exam in order to calculate a geometrical study-dependent system matrix. The utilization of the DRFT for the calculation of the system matrix speeds up its computation time by two orders of magnitude making it acceptable for preclinical and clinical applications.

Monitoring Tc Dynamics in a Bioreduced Sediment: An Investigation with Gamma Camera Imaging of 99mTc-Pertechnetate and 99mTc-DTPA

We demonstrate the utility of nuclear medical imaging technologies and a readily available radiotracer, [(99m)Tc]TcO(4)(-), for the noninvasive monitoring of Fe(II) production in acetate-stimulated sediments from Old Rifle, CO, USA. Microcosms consisting of sediment in artificial groundwater media amended with acetate were probed by repeated injection of radiotracer over three weeks. Gamma camera imaging was used to noninvasively quantify the rate and extent of [(99m)Tc]TcO(4)(-) partitioning from solution to sediment. Aqueous Fe(II) and sediment-associated Fe(II) were also measured and correlated with the observed tracer behavior. For each injection of tracer, curves of (99m)Tc concentration in solution vs time were fitted to an analytic function that accounts for both the observed rate of sedimentation as well as the rate of (99m)Tc association with the sediment. The rate and extent of (99m)Tc association with the biostimulated sediment correlated well with the production of Fe(II), and a mechanism of [(99m)Tc]TcO(4)(-) reduction via reaction with surface-bound Fe(II) to form an immobile Tc(IV) species was inferred. After three weeks of bioreduction, a subset of microcosms was aerated in order to reoxidize the Fe(II) to Fe(III), which also destroyed the affinity of the [(99m)Tc]TcO(4)(-) for the sediments. However, within 3 days postoxidation, the rate of Tc(VII) reduction was faster than immediately before oxidation implying a rapid return to more extensive bioreduction. Furthermore, aeration soon after a tracer injection showed that sediment-bound Tc(IV) is rapidly resolubilized to Tc(VII). In contrast to the [(99m)Tc]TcO(4)(-), a second commercially available tracer, (99m)Tc-DTPA (diethylenetriaminepentaacetic acid), had minimal association with sediment in both controls and biostimulated sediments. These experiments show the promise of [(99m)Tc]TcO(4)(-) and (99m)Tc-DTPA as noninvasive imaging probes for a redox-sensitive radiotracer and a conservative flow tracer, respectively.