Nuclear Imaging Systems Research Articles

Evaluating the radiation detection of the RbGd 2Br 7:Ce scintillator by Monte Carlo methods

The purpose of this study was to investigate the radiation detection efficiency of the recently introduced RbGd 2Br 7:Ce (RGB) scintillator material by a custom developed Monte Carlo simulation code. Considering its fast principal decay constant (45 ns) and its high light yield (56 000 photons/MeV), RbGd 2Br 7:Ce appears to be a quite promising scintillator for applications in nuclear medical imaging systems. In this work, gamma-ray interactions, within the scintillator mass were studied. In addition, the effect of K-characteristic fluorescence radiation emission, re-absorption or escape, as well as the effect of scattering events on the spatial distribution of absorbed energy was examined. Various scintillator crystal thicknesses (5–25 mm), used in positron emission imaging, were considered to be irradiated by 511 keV photons. Similar simulations were performed on the well known Lu 2SiO 5:Ce (LSO) scintillator for comparison purposes. Simulation results allowed the determination of the quantum detection efficiency as well as the fraction of the energy absorbed due to the K-characteristic radiation. Results were obtained as a function of scintillator crystal thickness. The Lu 2SiO 5:Ce scintillator material showed to exhibit better radiation absorption properties in comparison with RbGd 2Br 7:Ce. However, RGB showed to be less affected by the production of K-characteristic radiation. Taking into account its very short decay time and its high light yield, this material could be considered to be employed in positron imaging (PET) detectors.

WE-D-330A-06: Dual Projection Imaging System for Small Animal Research

Purpose: The use of small mammals as models of human diseases has increased in the last several years. These models provide a valuable research tool to characterize these diseases and to evaluate new therapies. Dedicated imagingsystems, with the resolution and sensitivity to allow in vivo studies in small animals, reduce the number of animals required for a given study and offer the possibility of serial studies in the same animal. A dual two‐dimensional imagingsystem has been developed to monitor tumor development in mice and other small animals.Method and Materials: This imagingsystem combines functional information gained from projection nuclear emission imaging with the anatomical context provided by an x‐ray transmission image. The system captures a nuclear image in one side of a single computed radiographydetector(CR plate) and then the plate is moved to acquire an x‐ray image in the opposite side. The nuclear image is formed by using a parallel hole collimator. Four fiducial markers, that are visible in both images, are attached to the system. A transformation algorithm uses the information from the fiducial markers to align the images. The nuclear emission image is color coded and overlaid onto the gray‐scale x‐ray image.Results: For the assessment of the imagingsystem, a tissue‐equivalent phantom was manufactured. Initial investigations used I‐125. The spatial resolution, contrast, and detected scattered photon levels have been measured for both x‐ray and nuclear imaging, and the sensitivity of the nuclear imagingsystem was also measured. Conclusion: The lower radiation levels, faster throughput, and lower cost of this imagingsystem would allow the evaluation of functional activity more frequently in serial studies. This imagingsystem would complement tomographic systems by allowing rapid pre‐screening of animals when a complete 3D volume data set is not necessary.

Incorporation of a fluoroscopic X-ray modality in a small animal imaging system

The authors have developed a multimodality system for imaging the biodistribution of biologically interesting ligands tagged with /sup 125/I. By incorporating a small fluoroscope as an additional modality, they have enhanced their small animal nuclear imaging system to include both X-rays and images from two Hamamatsu R3292 diameter position sensitive photomultiplier tubes (PSPMT) viewing pixelated scintillators with image co-registration of 1.5 mm or better. Collimators placed between the animal and the scintillators can easily be interchanged and include CuBe parallel-hole collimators with a range of resolution and sensitivity combinations. The small X-ray fluoroscope provides 5 cm diameter images, several of which can readily be combined to provide structural anatomical information from the animal under study. The system has been tested by comparing the uptake of /sup 125/I (in NaI) in control mice and mice previously fed a solution of KI (potassium iodide) designed specifically to block uptake of the radiolabeled iodine in the thyroid. This system not only provides an effective approach for the analysis of KI dose and toxicity issues but also allows for detection of individual variation in animals, an important issue in contemporary pharmacology and genomics.

Biomedical imaging in pharmacology with nuclear medical imaging methodologies: positron emission tomography (PET) and single photon emission computed tomography (SPECT)

The nuclear imaging technologies, positron emission tomography (PET) and single photon emission computed tomography (SPECT), have the power to non-invasively obtain dynamic and real-time information on the in vivo behaviors of radiolabeled molecules not only in humans but also in experimental animals. Thus, PET and SPECT can image molecular interactions of biological processes in vivo directly and reveal biological phenomena that are hidden from view. Furthermore, these imaging procedures also can be repeatedly performed before and after interventions, thereby allowing each subject to be used as its own control. In these studies, the radiolabeled compounds used as imaging probes for non-invasive assays of biochemical processes should have defined in vivo behaviors that can provide valuable information on the physiological and pharmacological processes. This paper describes the principle of the nuclear medical imaging systems, rational design of radiolabeled imaging probes, and the application to in vivo investigation of the change of various neurotransmission systems under disease and drug treatment. The efficient utilization of these nuclear medical imaging technologies will accelerate biomedical studies and drug development.

Imaging gene expression and endogenous molecular processes: molecular imaging.

Noninvasive molecular imaging has developed over the past decade and involves nuclear (positron emission tomography [PET], gamma camera), magnetic resonance, and optical imaging systems. Most current molecular imaging strategies are "indirect" and involve the coupling of a "reporter gene" with a complementary "reporter probe." Imaging the level of probe accumulation provides indirect information related to the level of reporter gene expression. Reporter gene constructs are driven by upstream promoter/enhancer elements; reporter gene expression can be leading to continuous transcription and used to identify the site of transduction and to monitor the level and duration of gene (vector) activity. Alternatively, reporter gene expression can be leading to controlled gene expression, or reporter genes can function as a "sensor" to monitor the level of endogenous promoters and transcription factors. The development of versatile and sensitive assays that do require tissue sampling will be of considerable value for monitoring molecular-genetic and cellular processes in animal models of human disease, as well as for studies in human subjects in the future. Noninvasive imaging of molecular-genetic and cellular processes will complement established molecular-biologic assays that require tissue sampling, and will provide a spatial as well as a temporal dimension to our understanding of various diseases. Several examples of imaging endogenous biologic processes in animals using reporter constructs, radiolabeled probes, and PET imaging are reviewed (e.g., p53-dependent gene expression, T-cell receptor-dependent activation of T-lymphocytes, and preliminary studies of endogenous HIF-1alpha expression). Issues related to the translation of noninvasive molecular imaging technology into the clinic are also discussed.

Study of the homogeneity of CdTe-THM monolithic nuclear detector arrays: the role of electron lifetime and leakage current

For nuclear imaging systems, CdTe-THM already has been shown to be an appropriate material. However, the homogeneity in the detector array material is still the main property that has to be improved, especially for thick detectors that are necessary for achieving a high counting rate efficiency. Apart from the standard material defects, i.e., grain boundaries, Te-precipitates, etc., electron lifetime and resistivity seem to be the major electric properties inducing or expressing the heterogeneity. Therefore, detector arrays with noticeable spread detection values have been investigated. Results are compared with energy resolution and counting rate efficiency. As expected, energy resolution is highly dependent on the electron lifetime and, to a lesser extent, on the leakage current. Their homogeneity is also discussed, but no correlation has been found between the electrical properties and the counting rate efficiency. This last parameter seems to be independent of the electrical properties, unlike the structural defects. This fact explains the large difference between pixels and why a pixel can give good /sup 57/Co spectra with poor efficiency, and vice versa.

Pinhole collimator design for nuclear survey system

A conventional knife-edge collimator, which is widely used in gamma camera for medical diagnosis, is not suitable for nuclear imaging system because many scattering radiations near the pinhole aperture happen and blur image. A new pinhole collimator, which shapes a channeled aperture for reducing image degradation induced by the scattering radiations, is introduced and its characteristics are analyzed by Monte Carlo simulation. Resolutions defined as the full-width at half-maximum (FWHM) of point spread function and efficiencies are calculated about several pinhole diameters from 4 to 8 mm and channel heights from 2 to 10 mm. For this calculation, we assumed that 137Cs radiation sources with 662 keV mono-energies enter into our designed collimator at the 1 m distance from the detector plane. The efficiencies and resolutions of the channeled collimator are compared with those of the conventional collimator. By comparison results, it is verified that the new collimator takes advantage more than the conventional collimator. The optimum channel height and diameter of the pinhole collimator from simulation results are also proposed and designed. We finally acquired nuclear image mounting this collimator in the nuclear survey system.

Field Correction of Nuclear Imaging System Ongoing

Field Correction of Nuclear Imaging System Ongoing

A time projection chamber with optical readout for charged particle track structure imaging

We report about a nuclear track imaging system which is designed to study in detail the ionization topology of charged particle tracks in a low-pressure gas. The detection method is based on a time projection chamber (TPC) filled with low-pressure triethylamine (TEA). Ionization electrons produced by energetic charged particles are three-dimensionally imaged by recording light from electron avalanches with an intensified CCD system. The detector permits to investigate the spatial ionization distributions of particle tracks in gas, of equivalent length and resolution in tissue of 4 μm and 40 nm (RMS), respectively. We explain the relevance of this technique for dosimetry, describe the experimental method and the basic operation parameters. First results of the chamber response to protons and alpha particles are presented.

Two quantitative methods for imaging samples in molecular biology.

In this paper, we introduce two autoradiography imaging systems from Packard Instrument Company, that provide unmatched speed, accuracy, sensitivity, and resolving power for radioisotopic imaging in biomedical research. The first system is a direct nuclear imaging system, which provides fast and accurate nuclear counting without intermediate steps. Data are displayed in real time so that counting, imaging and data analysis can be done all at the same time. The second system is a new storage phosphor system that was designed with a unique optical assembly which provides high resolution imaging. With various types of phosphor screens, one can optimize the performance of this storage phosphor system with any radiolabel and any appropriate sample size. With these two systems, quantitative radioisotopic imaging becomes not only faster and easier, but also more consistent and accurate, providing researchers with a higher standard in molecular biology imaging.

Screws In Nuclear Imaging System Patient Table Could Come Loose

Screws In Nuclear Imaging System Patient Table Could Come Loose

Nuclear Imaging System Software Not Validated

Nuclear Imaging System Software Not Validated

Large area real-time system for screening DNA libraries

A nuclear imaging system based on a position-sensitive photomultiplier tube (PSPMT) and scintillating fiber optics is described. A real-time, large-area imaging system has been constructed and tested using realistic phantoms and biological samples. This prototype, which has an active area of 112 cm/sup 2/ was found to be more than 100 times more sensitive for detection of /sup 32/P radiation than film and provided a spatial resolution of approximately 1.7 mm. By choosing suitable fiber dimensions and packing methods on the PSPMT this system is capable of producing images over an area equal to X-ray film and with spatial resolution approaching 0.5 mm. The digital nature of the image allows a great deal of freedom in processing and displaying data, including automatic identification and location of the desired features.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A nuclear survey instrument with imaging capability

A novel nuclear survey instrument with an imaging capability is being developed for remotely locating high-level radioactive sources with minimal operator exposure. It combines an image of the distribution of radioactivity with a video image of the area containing the source, allowing rapid, remote location of the source. The nuclear imaging system is based on a position-sensitive photomultiplier tube and a diverging hole collimator. The design and measured performance of a prototype device are discussed. >

Magnetic fields associated with a nuclear magnetic resonance medical imaging system

Measurements were made of magnetic and electric field levels in and around a nuclear magnetic resonance imaging system undergoing a clinical trial. Magnetic field levels ranged from 0.04 tesla (T) in the imaging volume down to about 0.0006 T at the end of the patient table. The peak radio-frequency magnetic field level was 15 amperes per meter (A/m) in the imaging volume, while the rms value was 4.6 A/m. The specific absorption rate resulting from the radio-frequency magnetic field was calculated to be no more than 0.017 watts per kilogram (W/kg). The radio-frequency electric field was detectable only within a few centimeters of the coil assembly, and does not significantly contribute to the specific absorption rate. These exposure levels were much lower than existing guidelines for clinical NMR procedures.

Functional evaluation of blood pump by using radio isotope and nuclear imaging system

Functional evaluation of blood pump by using radio isotope and nuclear imaging system