Zsolt Marton

Bright Lu2O3:Eu Thin-Film Scintillators for High-Resolution Radioluminescence Microscopy

The performance of a new thin-film Lu2 O3 :Eu scintillator for single-cell radionuclide imaging is investigated. Imaging the metabolic properties of heterogeneous cell populations in real time is an important challenge with clinical implications. An innovative technique called radioluminescence microscopy has been developed to quantitatively and sensitively measure radionuclide uptake in single cells. The most important component of this technique is the scintillator, which converts the energy released during radioactive decay into luminescent signals. The sensitivity and spatial resolution of the imaging system depend critically on the characteristics of the scintillator, that is, the material used and its geometrical configuration. Scintillators fabricated using conventional methods are relatively thick and therefore do not provide optimal spatial resolution. A thin-film Lu2 O3 :Eu scintillator is compared to a conventional 500 μm thick CdWO4 scintillator for radioluminescence imaging. Despite its thinness, the unique scintillation properties of the Lu2 O3 :Eu scintillator allow us to capture single-positron decays with fourfold higher sensitivity, which is a significant achievement. The thin-film Lu2 O3 :Eu scintillators also yield radioluminescence images where individual cells appear smaller and better resolved on average than with the CdWO4 scintillators. Coupled with the thin-film scintillator technology, radioluminescence microscopy can yield valuable and clinically relevant data on the metabolism of single cells.

Novel High Efficiency Microcolumnar LuI3:Ce for Hard X-ray Imaging

We report on the development of microcolumnar films of an extremely fast and bright cerium-doped lutetium iodide (LuI3:Ce) scintillator that can resolve the 153 ns bunch structure of the Advanced Photon Source (APS) at Argonne National Laboratory (ANL). Due to the fast, afterglow-free decay, and high efficiency of LuI3:Ce, during the experiments performed at the 1-ID hard X-ray beamline at the APS, single 65 keV X-ray photons could be resolved with high signal-to-noise ratio and with temporal resolution better than 20 ns, revealing the 153 ns bunch structure of the APS. LuI3:Ce has high density (~5.6 g/cm3), high effective atomic number (59.7), bright green emission (540 nm range, well matched to commercial optics and CCD sensors), light yield exceeding 115,000 ph/MeV, and rapid, afterglow-free decay (~28 ns). We have developed the scintillator using a vacuum deposition technique that is suitable for manufacturing large area scintillators in a microcolumnar form which provides high absorption efficiency and allows high temporal and spatial resolution imaging. Details of the scintillator fabrication and characterization, and imaging experiments performed at the Sector 1-ID hard X-ray beamline at the APS will be presented in the paper.

Fabrication of High-Resolution Lu[subscript 2]O[subscript 3]:Eu X-Ray Scintillator by Physical Vapor Deposition

A new structured scintillator was developed that will stop significantly more of the incident X-rays without sacrificing spatial resolution. We have recently demonstrated that it is possible to deposit Lu2O3:Eu in a microcolumnar form using electron beam (e-beam) physical vapor deposition (EBPVD) technique. This new structured Lu2O3:Eu scintillator can have a huge impact on X-ray imaging applications including medical imaging, nondestructive testing and hard X-ray microtomography (XMT). Thin film fabrication of Lu2O3 doped with 5% europium was carried out by means of EBPVD. Uniform and stoichiometrically balanced films several microns thick were grown on various kinds of substrates. Their morphology was studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Scintillation decay, afterglow, spatial resolution and light conversion efficiency were analyzed. A selected set of films was integrated into position-sensitive detection systems to determine their efficacy for synchrotron and laboratory X-ray source-based high-resolution microtomography.

Laser pixelation of thick scintillators for medical imaging applications: x-ray studies

To achieve high spatial resolution required in nuclear imaging, scintillation light spread has to be controlled. This has been traditionally achieved by introducing structures in the bulk of scintillation materials; typically by mechanical pixelation of scintillators and fill the resultant inter-pixel gaps by reflecting materials. Mechanical pixelation however, is accompanied by various cost and complexity issues especially for hard, brittle and hygroscopic materials. For example LSO and LYSO, hard and brittle scintillators of interest to medical imaging community, are known to crack under thermal and mechanical stress; the material yield drops quickly with large arrays with high aspect ratio pixels and therefore the pixelation process cost increases. We are utilizing a novel technique named Laser Induced Optical Barriers (LIOB) for pixelation of scintillators that overcomes the issues associated with mechanical pixelation. In this technique, we can introduce optical barriers within the bulk of scintillator crystals to form pixelated arrays with small pixel size and large thickness. We applied LIOB to LYSO using a high-frequency solid-state laser. Arrays with different crystal thickness (5 to 20 mm thick), and pixel size (0.8×0.8 to 1.5×1.5 mm2) were fabricated and tested. The width of the optical barriers were controlled by fine-tuning key parameters such as lens focal spot size and laser energy density. Here we report on LIOB process, its optimization, and the optical crosstalk measurements using X-rays. There are many applications that can potentially benefit from LIOB including but not limited to clinical/pre-clinical PET and SPECT systems, and photon counting CT detectors.

Ultra-fast LuI3:Ce scintillators for hard x-ray imaging

We have developed ultra-fast cerium-coped lutetium-iodide (LuI3:Ce) films thermally evaporated as polycrystalline, structured scintillator using hot wall epitaxy (HWE) method. The films have shown a 13u2005ns decay compared to the 28u2005ns reported for crystals. The fast speed coupled with its high density (∼5.6u2005g/cm3), high effective atomic number (59.7), and the fact that it can be vapor deposited in a columnar form makes LuI3:Ce an attractive candidate for high frame rate, high-resolution, hard X-ray imaging. In crystal form, LuI3:Ce has demonstrated bright (>100,000 photons/MeV) green (540u2005nm) emission, which is well matched to commercial CCD/CMOS sensors and is critical for maintaining high signal to noise ratio in light starved applications. Here, we report on the scintillation properties of films and those for corresponding crystalline material. The vapor grown films were integrated into a high-speed CMOS imager to demonstrate high-speed radiography capability. The films were also tested at Advanced Photo...

Efficient high-resolution hard x-ray imaging with transparent Lu2O3:Eu scintillator thin films

We have developed microstructured Lu2O3:Eu scintillator films that provide spatial resolution on the order of micrometers for hard X-ray imaging. In addition to their outstanding resolution, Lu2O3:Eu films also exhibits both high absorption efficiency for 20 to 100 keV X-rays, and bright 610 nm emission whose intensity rivals that of the brightest known scintillators. At present, high spatial resolution of such a magnitude is achieved using ultra-thin scintillators measuring only about 1 to 5 μm in thickness, which limits absorption efficiency to ~3% for 12 keV X-rays and less than 0.1% for 20 to 100 keV X-rays; this results in excessive measurement time and exposure to the specimen. But the absorption efficiency of Lu2O3:Eu (99.9% @12 keV and 30% @ 70 keV) is much greater, significantly decreasing measurement time and radiation exposure. Our Lu2O3:Eu scintillator material, fabricated by our electron-beam physical vapor deposition (EB-PVD) process, combines superior density of 9.5 g/cm3, a microcolumnar structure for higher spatial resolution, and a bright emission (48000 photons/MeV) whose wavelength is an ideal match for the underlying CCD detector array. We grew thin films of this material on a variety of matching substrates, measuring some 5–10μm in thickness and covering areas up to 1 x 1 cm2, which can be a suitable basis for microtomography, digital radiography as well as CT and hard X-ray Micro-Tomography (XMT). The microstructure and optical transparency of such screens was optimized, and their imaging performance was evaluated in the Argonne National Laboratory’s Advanced Photon Source. Spatial resolution and efficiency were also characterized.

Lithium alkali halides - New thermal neutron detectors with n-γ discrimination

We are investigating two promising new families of materials derived from proven, low-cost, well-understood, versatile scintillator hosts CsI and NaI. These are modified by incorporating Li ions to achieve the desired spectroscopic properties, producing high quality, combined n/γ sensors. Specifically we report on the synthesis and characterization of Li3Cs2I5 (LCI) and LixNa1-xI (LNI), both of which demonstrate pulse shape discrimination (PSD) and pulse height discrimination (PHD) for effective suppression of gamma background from neutron signals. In the case of LCI, the primary decay time for thermal neutron interactions is faster than for gamma interactions, and is on the order of 250 ns for neutrons and 500 ns for gamma rays. LNI is opposite to LCI in this respect, which shows slower, 210 ns, decay for neutron interactions and relatively faster, 180 ns, decay for gammas. The measured light yield for LCI is ~40,000 to 55,000 photons/neutron, which corresponds to an electron equivalent energy of 2.1 to 2.8 MeV. Whereas LNI demonstrates a much brighter yield of over 100,000 photons/neutron and electron equivalent energy per neutron interaction of over 4.5 MeV, very close to the 6Li(n,α) Q value of 4.7 MeV. Relatively narrow emission bands with a peak at 450 nm for LCI:Eu and at 420 nm for LNI:Tl make these sensors well matched to the quantum efficiency of conventional photodetectors such as PMTs. Our data show that significant red shift in emission can be achieved by doping LCI with Tl and LNI with Eu, making these materials well suited for use with such sensors as solid state photomultipliers (SSPMs). In addition to their excellent scintillation properties, the use of widely available, proven host materials, and a possible vapor deposition method for their synthesis, are promising features of this development. This combination allows mass production of large-area, high-performance neutron sensors in a uniquely time efficient manner.

High performance microstructured Lu2O3:Eu thin film scintillator for X-ray computed tomography

Large penetration depth and weak interaction of high energy X-rays in living organisms provide a non-destructive way to study entire volumes of organs without the need for sophisticated preparation (injection of contrast material, radiotracer labels etc.). X-ray computed tomography (CT) is a powerful diagnostic tool allowing 3D image reconstruction of the complete structure. Using hard X-rays in medical imaging leads to reduced dose received by the patient. At higher energies, however, the conventional scintillators quickly become the limiting factor. They must be thin in order to provide reasonable spatial resolution and preserve image quality. Nevertheless, insufficient thickness introduces the need for long acquisition times due to low stopping power. To address these issues, we synthesized a new structured scintillator to be integrated into CCD- or photodiode-based CT systems. Europiumdoped Lu2O3 (Lu2O3:Eu) has the highest density among all known scintillators, very high absorption coefficient for X-rays and a bright red emission matching well to the quantum efficiency of the underlying CCD- and photodiode arrays. When coupled to a suitable detector, this microcolumnar scintillator significantly improves the overall detective quantum efficiency of the detector. For the first time ever, structured and scintillating film of Lu2O3:Eu was grown by electron-beam physical vapor deposition. A prototype sensor was produced and evaluated using both laboratory X-ray sources as well as synchrotron radiation. Comparative performance evaluations of the newly developed sensor versus commercial grade scintillators were conducted. Such synthesis of high density, microstructured, scintillating coatings enables the development of high sensitivity X-ray detectors for CT applications.

Development and characterization of a scintillating cell imaging dish for radioluminescence microscopy

Radioluminescence microscopy is an emerging modality that can be used to image radionuclide probes with micron-scale resolution. This technique is particularly useful as a way to probe the metabolic behavior of single cells and to screen and characterize radiopharmaceuticals, but the quality of the images is critically dependent on the scintillator material used to image the cells. In this paper, we detail the development of a microscopy dish made of a thin-film scintillating material, Lu2O3:Eu, that could be used as the blueprint for a future consumable product. After developing a simple quality control method based on long-lived alpha and beta sources, we characterize the radioluminescence properties of various thin-film scintillator samples. We find consistent performance for most samples, but also identify a few samples that do not meet the specifications, thus stressing the need for routine quality control prior to biological experiments. In addition, we test and quantify the transparency of the material, and demonstrate that transparency correlates with thickness. Finally, we evaluate the biocompatibility of the material and show that the microscopy dish can produce radioluminescent images of live single cells.

Multilayer coated gratings for phase-contrast computed tomography (CT)

By using the principle of grating interferometry, X-ray phase contrast imaging can now be performed with incoherent radiation from standard X-ray tube. This approach is in stark contrast with imaging methods using coherent synchrotron X-ray sources or micro-focus sources to improve contrast. The gratings interferometer imaging technique is capable of measuring the phase shift of hard X-rays travelling through a sample, which greatly enhances the contrast of low absorbing specimen compared to conventional amplitude contrast images. The key components in this approach are the gratings which consists of alternating layers of high and low Z (atomic number) materials fabricated with high aspect ratios. Here we report on a novel method of fabricating the grating structures using the technique of electron-beam (ebeam) thin film deposition. Alternating layers of silicon (Z=14) and tungsten (Z=74) were deposited, each measuring 100 nm each, on a specially designed echelle substrate, which resulted in an aspect ratio of ~100:1. Fabrication parameters related to the thin film deposition such as geometry, directionality, film adhesion, stress and the resulting scanning electron micrographs will be discussed in detail. Using e-beam method large-area gratings with precise multilayer coating thicknesses can be fabricated economically circumventing the expensive lithography steps.