High-resolution Scintillation Research Articles

FlexiSPECT: A SPECT System Consisting of a Compact High-Resolution Scintillation Detector (SPECTatress) and a Lofthole Collimator

This article describes a compact single-photon emission computed tomography (SPECT) system that consists of a high-resolution detector combined with a lofthole collimator. The detector is based on a NaI(Tl) scintillator, a position sensitive photomultiplier (PSPMT), dedicated read-out electronics that digitize all PSPMT anodes and finally, a maximum likelihood algorithm for position estimation. The collimator has a new pinhole geometry, called the lofthole. Our choice of magnification (1.06 for the mouse setup, 0.63 for the rat setup) results in a small system with a footprint of 45 cm × 25 cm. Design and measurements of both the detector and the SPECT system are shown. Detector measurements with a beam source have been done to investigate the spatial and energy resolution of the detector. Two SPECT setups have been made, one that fits rat-size phantoms and one that fits mouse-size phantoms. On both setups we have done measurements of a Derenzo phantom and a uniformity phantom. The results show that the detector resolution is 1.1 mm and energy resolution is 9.3% in the center of the detector. With the tomographic rat setup we are able to distinguish the 2.4 mm hot rods in a Derenzo phantom. The mouse setup allows us to distinguish the 1.6 mm rods. This demonstrates the SPECT capabilities of this compact prototype scanner.

SPEM: a state-of-the-art instrument for high resolution molecular imaging of small animal organs

To describe the Single Photon Emission Microscope (SPEM), a state-of-the-art instrument for small animal SPECT imaging, and characterize its performance presenting typical images of different animal organs. SPEM consists of two independent imaging devices based on high resolution scintillators, high sensitivity and resolution Electron-Multiplying CCDs and multi-pinhole collimators. During image acquisition, the mouse is placed in a rotational vertical holder between the imaging devices. Subsequently, an appropriate software tool based on the Maximum Likelihood algorithm iteratively produces the volumetric image. Radiopharmaceuticals for imaging kidneys, heart, thyroid and brain were used. The mice were injected with 74 to 148 MBq/0,3mL and scanned for 40 to 80 minutes, 30 to 60 minutes afterwards. During this procedure, the animals remained under ketamine/xilazine anesthesia. SPEM images of different mouse organs are presented, attesting the imaging capabilities of the instrument. SPEM is an innovative technology for small animal SPECT imaging providing high resolution images with appropriate sensitivity for pre-clinical research. Its use with appropriate radiotracers will allow translational investigation of several animal models of human diseases, their pharmacological treatment and the development of potential new therapeutic agents.

A novel compensation method for the anode gain non-uniformity of multi-anode photomultiplier tubes

The position-sensitive multi-anode photomultiplier tube (MA-PMT) is widely used in high-resolution scintillation detectors. However, the anode gain non-uniformity of this device is a limiting factor that degrades the intrinsic performance of the detector module. The aim of this work was to develop a gain compensation method for the MA-PMT and evaluate the resulting enhancement in the performance of the detector. The method employs a circuit that is composed only of resistors and is placed between the MA-PMT and a resistive charge division network (RCN) used for position encoding. The goal of the circuit is to divide the output current from each anode, so the same current flows into the RCN regardless of the anode gain. The current division is controlled by the combination of a fixed-value series resistor with an output impedance that is much larger than the input impedance of the RCN, and a parallel resistor, which detours part of the current to ground. PSpice simulations of the compensation circuit and the RCN were performed to determine optimal values for the compensation resistors when used with Hamamatsu H8500 MA-PMTs. The intrinsic characteristics of a detector module consisting of this MA-PMT and a lutetium-gadolinium-oxyorthosilicate (LGSO) crystal array were tested with and without the gain compensation method. In simulation, the average coefficient of variation and max/min ratio decreased from 15.7% to 2.7% and 2.0 to 1.2, respectively. In the flood map of the LGSO-H8500 detector, the uniformity of the photopeak position for individual crystals and the energy resolution were much improved. The feasibility of the method was shown by applying it to an octagonal prototype positron emission tomography scanner.

Three-dimensional X-ray diffraction imaging of process-induced dislocation loops in silicon

In the semiconductor industry, wafer handling introduces micro-cracks at the wafer edge and the causal relationship of these cracks to wafer breakage is a difficult task. By way of understanding the wafer breakage process, a series of nano-indents were introduced both into 20 × 20 mm (100) wafer pieces and into whole wafers as a means of introducing controlled strain. Visualization of the three-dimensional structure of crystal defects has been demonstrated. The silicon samples were then treated by various thermal anneal processes to initiate the formation of dislocation loops around the indents. This article reports the three-dimensional X-ray diffraction imaging and visualization of the structure of these dislocations. A series of X-ray section topographs of both the indents and the dislocation loops were taken at the ANKA Synchrotron, Karlsruhe, Germany. The topographs were recorded on a CCD system combined with a high-resolution scintillator crystal and were measured by repeated cycles of exposure and sample translation along a direction perpendicular to the beam. The resulting images were then rendered into three dimensions utilizing open-source three-dimensional medical tomography algorithms that show the dislocation loops formed. Furthermore this technique allows for the production of a video (avi) file showing the rotation of the rendered topographs around any defined axis. The software also has the capability of splitting the image along a segmentation line and viewing the internal structure of the strain fields.

Design of a high resolution scintillator based SPECT detector (SPECTatress)

SPECT scanners using multi-pinhole collimators benefit from compact detectors having a high spatial resolution. Such detectors can be placed closer to the collimator and perpendicular to the pinhole axis (thereby limiting DOI spatial resolution degradation). Current clinical gamma ray cameras have a large area and a poor spatial resolution. This proceeding describes the architecture of SPECTatress, a compact high resolution gamma camera. The main components (PMT and scintillator) are presented, a brief overview of the read-out electronics is given and a first measurement using the center-of-gravity (COG) event-positioning algorithm is shown. The result of this measurement indicates a good spatial resolution (1.75 mm FWHM) in the center of the detector. Further research has to be done on the event-positioning algorithm to extend the usable detector area and to enhance the spatial resolution.

Porous silicon phantoms for high-resolution scintillation imaging

High resolution radionuclide imaging requires phantoms with precise geometries and known activities using either Anger cameras equipped with pinhole collimators or dedicated small animal devices. Porous silicon samples, having areas of different shape and size, can be made and loaded with a radioactive material, obtaining: (a) precise radio-emitting figures corresponding to the porous areas geometry, (b) a radioactivity of each figure depending on the pore's specifications, and (c) the same emission energy to be used in true exams. To this aim a sample with porous circular areas has been made and loaded with a 99mTcO 4 − solution. Imaging has been obtained using both general purpose and pinhole collimators. This first sample shows some defects that are analyzed and discussed.

High resolution scintimammography helps in differentiating benign from malignant findings in scintigraphic hot spots

Several efforts have been focusing on the development of detectors devoted to high solution 99mTc sestamibi scintimammography to improve sensitivity for non palpable lesions. To this aim new high resolution scintillation gamma camera was developed under the “Integiated Mammographic Imaging” project. The gamma camera, made by CAEN and Pol.Hi.Tech, has an overall dimension of 112×120×75mm3. It consists of an array of 1 in. PSPMTs Hamamatsu H8520-C12 closely packed, a NaI(T1) scintillation array (1.8×1.8×6mm 3 pixel) and a general purpose collimator. By this gamma camera a clinical experience on a few patients with breast cancer suspicion was performed. In this paper we show how high resolution approach allows to better categorize the lesions on the basis of the morphology of the spatial distribution of the radiotracer in the breast tissue. By comparing conventional and high resolution images of a young patient (29 y.o.) with breast cancer suspicion, it appears clear how the Anger, camera images showed a defined hot spot, highly suggestive of malignant lesion; on the contrary, the high resolution scan shown a large and inhomogeneous uptake area with the absence of clear and focal character of the uptake, to be considered as a probably non malignant lesions. This resuh was confirmed by byoptical findings that diagnosed the echographic findings as a benign inflammatory lesion.

Measurement accuracy and Cerenkov removal for high performance, high spatial resolution scintillation dosimetry

With highly conformal radiation therapy techniques such as intensity-modulated radiation therapy, radiosurgery, and tomotherapy becoming more common in clinical practice, the use of these narrow beams requires a higher level of precision in quality assurance and dosimetry. Plastic scintillators with their water equivalence, energy independence, and dose rate linearity have been shown to possess excellent qualities that suit the most complex and demanding radiation therapy treatment plans. The primary disadvantage of plastic scintillators is the presence of Cerenkov radiation generated in the light guide, which results in an undesired stem effect. Several techniques have been proposed to minimize this effect. In this study, we compared three such techniques-background subtraction, simple filtering, and chromatic removal-in terms of reproducibility and dose accuracy as gauges of their ability to remove the Cerenkov stem effect from the dose signal. The dosimeter used in this study comprised a 6-mm(3) plastic scintillating fiber probe, an optical fiber, and a color charge-coupled device camera. The whole system was shown to be linear and the total light collected by the camera was reproducible to within 0.31% for 5-s integration time. Background subtraction and chromatic removal were both found to be suitable for precise dose evaluation, with average absolute dose discrepancies of 0.52% and 0.67%, respectively, from ion chamber values. Background subtraction required two optical fibers, but chromatic removal used only one, thereby preventing possible measurement artifacts when a strong dose gradient was perpendicular to the optical fiber. Our findings showed that a plastic scintillation dosimeter could be made free of the effect of Cerenkov radiation.

Design and simulation of a high-resolution stationary SPECT system for small animals

Exciting new SPECT systems can be created by combining pinhole imaging with compact high-resolution gamma cameras. These new systems are able to solve the problem of the limited sensitivity-resolution trade-off that hampers contemporary small animal SPECT. The design presented here (U-SPECT-III) uses a set of detectors placed in a polygonal configuration and a cylindrical collimator that contains 135 pinholes arranged in nine rings. Each ring contains 15 gold pinhole apertures that focus on the centre of the cylinder. A non-overlapping projection is acquired via each pinhole. Consequently, when a mouse brain is placed in the central field-of-view, each voxel in the cerebrum can be observed via 130 to 135 different pinholes simultaneously. A method for high-resolution scintillation detection is described that eliminates the depth-of-interaction problem encountered with pinhole cameras, and is expected to provide intrinsic detector resolutions better than 150 µm. By means of simulations U-SPECT-III is compared to a simulated dual pinhole SPECT (DP-SPECT) system with a pixelated array consisting of 2.0 × 2.0 mm NaI crystals. Analytic calculations indicate that the proposed U-SPECT-III system yields an almost four times higher linear and about sixty times higher volumetric system resolution than DP-SPECT, when the systems are compared at matching system sensitivity. In addition, it should be possible to achieve a 15 up to 30 times higher sensitivity with U-SPECT-III when the systems are compared at equal resolution. Simulated images of a digital mouse-brain phantom show much more detail with U-SPECT-III than with DP-SPECT. In a resolution phantom, 0.3 mm diameter cold rods are clearly visible with U-SPECT-III, whereas with DP-SPECT the smallest visible rods are about 0.6–0.8 mm. Furthermore, with U-SPECT-III, the image deformations outside the central plane of reconstruction that hamper conventional pinhole SPECT are strongly suppressed. Simulation results indicate that future pinhole SPECT systems are likely to bring about significant improvements in radio-molecular imaging of small animals.

Toward both larger and smaller scintispheres

High-resolution scintillation spectrometers based on the use of large-volume spherical CsI(Tl) spectrometers viewed by conventional 1 cm/sup 2/ PIN diode have been shown to have excellent performance characteristics. In particular, their unique geometry, the small area of contact between the diode and the crystal's surface, and the high reflectivity of the packing material combine to provide a detector in which there is a very small variance in the signal generated by energy deposits in different regions of the crystal. In view of the unique spectral-resolution achieved using the first prototype Scintispheres (S100-PIN and S300-PIN) to be manufactured, it was natural to explore the boundaries within which this technology might be useful. This paper presents the results of a series of modeling exercises and experimental investigations aimed at finding the range of detector volumes that can usefully be constructed based on the use of PIN photodiodes. For a given amplifier performance, the predicted spectra-resolution of a range of Scintisphere volumes has been estimated as a function of energy. This study was made both for the CsI(Tl) material used in the original devices and for other materials which may be important when the speed of operation and stopping power are important design parameters. These studies also considered the performance limits that might be achievable in small volume Scintispheres. This paper also presents the results obtained when our deconvolution algorithm is applied to a wide range of standard scintillation spectrometers. These demonstrate the high spectra-resolution and sensitivity that can be achieved using this technique.

Evaluation of Hamamatsu R5900 series PMTs for readout of high-resolution scintillator arrays

Two types of Hamamatsu R5900 series photomultiplier tubes (PMTs) have been evaluated as position-sensitive photon detectors for reading out arrays of small scintillator elements. Both PMTs have metal-channel dynode structures and compact dimensions of 26×26×20 mm 3 . Model R5900-C12 is a position sensitive PMT (PS-PMT) with photoelectrons shared among 12 plate anodes arranged in a crossed pattern such that there are six anodes each in the X and Y directions. Model R5900-M64 is a multi-channel PMT (MC-PMT) with 64 individual channels and low inter-channel crosstalk. Scintillator arrays can be coupled to these PMTs either directly or by using optical fibers. In this paper, we present measurements of single photoelectron spectra, pulse linearity, positioning response, inter-channel gain variation and pixel-to-pixel crosstalk for these PMTs. We have also measured their positioning response in reading out high-resolution lutetium oxyorthosilicate (LSO) scintillator arrays. Across a sample of 30 R5900-M64 MC-PMTs which were manufactured recently, the maximum gain variation over all channels is less than 3:1, while the difference between any two adjacent channels is less than 2:1. With a tapered voltage divider, the output of the anode signal at a gain of 10 6 remains linear up to 200 photoelectrons for the R5900-M64. For the R5900-C12, the summed anode signal remains linear up to 400 photoelectrons when irradiated through a 2 mm diameter aperture. Images obtained with a Na-22 source irradiating an array of 1×1×10 mm 3 LSO crystals coupled by an optical fiber bundle to the R5900-C12 or the R5900-M64 show excellent crystal identification.

High spatial resolution scintillator screens coupled to CCD detectors for X-ray imaging applications

New generations of X-ray imaging detectors are being developed for X-ray diffraction studies using both conventional sources and synchrotron beam lines. In many cases, these detectors utilise a scintillator screen to convert the X-ray photon energy into scintillation light. However, the spatial resolution is limited due to the diffusion of light that occurs within the scintillator layer. Results are presented for a scintillation screen that improves the spatial resolution through the use of a specially prepared fibre optic surface where the clad glass has been selectively etched away to leave the protruding columns of core glass. When evaporated onto this surface, the scintillator grows as extensions of these pillars forming discrete columns which individually act as light guides for the scintillation light. A calculation of the system DQE is presented and used to predict the performance to 8 keV X-rays. A Monte Carlo simulation of the X-ray interaction in CsI is also used to evaluate the system DQE above the K shell absorption edges (33 and 37 keV) and therefore determine the useful energy range of the scintillator.

A measurement of the cosmic-ray H-2 and He-3 spectra and H-2/He-4 and He-3/He-4 ratios in 1989

The energy spectra of H-2 and H-3 nuclei up to energies of 450 and 800 MeV nucleon, respectively, were measured during a balloon flight of the NASA/NMSU Balloon Borne Magnet Facility on September 5, 1989. These isotopes were cleanly resolved from the more abundant H-1 and He-4 using a measurement of rigidity versus velocity as measured in a high-resolution scintillation counter. After correction for atmospheric secondaries the measured H-2/He-4 and He-3/He-4 ratios are both consistent with the production expected if H-1 and He-4 have the same path length in the galaxy as heavier cosmic-ray nuclei such as C and Fe, to within about 20 percent. Solar modulation effects play an important role in this uncertainty. This result favors a generally similar propagation history, along with similar types of sources for H-1 and He-4 and the heavier cosmic-ray nuclei.

High resolution scintillation spectroscopy with HgI 2 as the photodetector

This report details the progress made in developing mercuric iodide photocells - in particular as the photodetector in scintillation spectrometers where photomultipliers are conventionally used. A spectrometer consisting of an HgI 2 photocell optically coupled with a CsI(Tl) scintillators gave a 137Cs (662 keV) resolution of 5.33% fwhm, the best 137Cs resolution reported to date using a scintillation spectrometer. Relative to photomultiplier tubes, solid state photodetectors are smaller, insensitive to magnetic fields, and have higher quantum efficiencies, HgI 2 photocells offer an unprecedented energy resolution for scintillation spectrometers and push closer to the resolution of scintillation crystals themselves.

Scintigraphic method to quantify the passage from brain parenchyma to the deep cervical lymph nodes in rats

In order to investigate the kinetics of the passage from the brain parenchyma to the lymphatic system in vivo a high resolution scintillation camera technique was developed. Albumin, albumin colloids and dextran labelled with 99mTc were injected into the right side of the thalamus of anesthetized rats. Continuous measurement of the activity distribution in head and neck were performed for 70 min. Rate constants were calculated by means of a computer program for compartment analysis. The animals were killed 10 h postinjection, to measure the activity in tissue samples. For some animals, images were registered up to 24 h after injection. This work presents an in vivo technique to clarify the particle flow paths in the brain and make quantification possible. The method is simple and does not require continuous blood or lymph sampling. Our work shows that there is a substantial flow of injected material from the brain via lamina cribriformis to the lymphatic system. This route is of great interest for the drainage of the interstitial fluid of the brain. We have also shown a difference in flow for dextran particles with different charge.

Analysis of Positron-Emission Tomography Scintillation-Detectors with Wedge Faces and Inter-Crystal Septa

Various high-resolution scintillation detectors are analyzed for resolution and sensitivity. In particular, the effects of using a wedge face and inter-crystal tungsten-septa are studied for both BaF2 and BGO crystals. The results indicate that usage of septa alone causes an improvement in resolution in areas away from the center of the image, but also causes a degradation in sensitivity in those areas, and that usage of a wedge face alone causes no improvement in resolution, while usage of septa and a wedge face in combination causes a similar resolution improvement, but with a lesser degradation in sensitivity.

High resolution scintillation hodoscope using a position sensitive photomultiplier

Using a position sensitive photomultiplier we have realized and tested a prototype of high resolution scintillation hodoscope. A space resolution of ∼ 1 mm (fwhm) has been obtained by a single block of NE102A scintillator, 10 mm thick, with 10 GeV/ c π − particles. An off-line analysis based on the moment method has confirmed the fact that suitable cuts in the second-order moments provide a powerful criterion for improving the image quality.

Scintillation Calorimetry and Readout Techniques

The status and prospects of new scintillation materials for calorimetry applications in high energy physics are reviewed. New readout methods are discussed with emphasis on the operation of high resolution scintillation calorimeters in magnetic fields.

Anticoincidence scintillator spectrometer for photon energies up to 100 MeV

An anticoincidence, high-efficiency, high-resolution scintillation γ spectrometer, designed for photon energies up to 100 MeV, is described. The detector performances, measured during a detailed study of proton capture reactions on light nuclei, are reported.

Application of explosive-driven implosions to fusion

Our explosive-driven implosion facility was used to produce hemispherical implosions in a stoichiometric mixture of deuterium-oxygen. A high-resolution scintillator detection system measured neutrons and γ rays resulting most likely from the fusion of deuterium.