Count Rate Linearity Research Articles

Characteristics of a new system for monitoring the leakage factor during regional hyperthermic isolated limb perfusion

A new system is presented and evaluated for real-time monitoring of blood leakage during hyperthermic isolated limb perfusion (HILP) surgery, the Veenstra HILP system. This system incorporates two software models to determine blood leakage: a single-nuclide algorithm and a newly developed dual-nuclide algorithm. The latter algorithm has the advantage that, in principle, it is independent of system sensitivity and thus independent of changes in geometrical efficiency. A physical description of the system is given, together with the required hardware and software specifications. In-vitro measurements, corresponding to the intended clinical use, are presented to investigate the relevant performance characteristics of the system: count rate linearity, measurement uncertainty, response time, and accuracy. As the Veenstra HILP system provides the opportunity to use different filter settings and averaging time, the influence of these settings on the time response and measurement uncertainty is described. Count rate linearity was better than 1% for the count rate domain typically observed during HILP procedures. The response time of the system degrades with increasing total averaging time. In contrast, measurement uncertainty in the blood leakage factor improves with increasing radiotracer count rates and increasing total averaging time. For both blood leakage algorithms, measurement accuracy is better than 1.0 and 1.5%, respectively. Measurements have shown that the system is well suited for the real-time monitoring of blood leakage during HILP surgery. Furthermore, a good agreement was observed between the theoretical and measured response time and measurement uncertainty.

MONICA: a compact, portable dual gamma camera system for mouse whole-body imaging.

We describe a compact, portable dual-gamma camera system (named "MONICA" for MObile Nuclear Imaging CAmeras) for visualizing and analyzing the whole-body biodistribution of putative diagnostic and therapeutic single photon emitting radiotracers in animals the size of mice. Two identical, miniature pixelated NaI(Tl) gamma cameras were fabricated and installed "looking up" through the tabletop of a compact portable cart. Mice are placed directly on the tabletop for imaging. Camera imaging performance was evaluated with phantoms and field performance was evaluated in a weeklong In-111 imaging study performed in a mouse tumor xenograft model. Tc-99m performance measurements, using a photopeak energy window of 140 keV+/-10%, yielded the following results: spatial resolution (FWHM at 1 cm), 2.2 mm; sensitivity, 149 cps (counts per seconds)/MBq (5.5 cps/microCi); energy resolution (FWHM, full width at half maximum), 10.8%; count rate linearity (count rate vs. activity), r(2)=0.99 for 0-185 MBq (0-5 mCi) in the field of view (FOV); spatial uniformity, <3% count rate variation across the FOV. Tumor and whole-body distributions of the In-111 agent were well visualized in all animals in 5-min images acquired throughout the 168-h study period. Performance measurements indicate that MONICA is well suited to whole-body single photon mouse imaging. The field study suggests that inter-device communications and user-oriented interfaces included in the MONICA design facilitate use of the system in practice. We believe that MONICA may be particularly useful early in the (cancer) drug development cycle where basic whole-body biodistribution data can direct future development of the agent under study and where logistical factors, e.g., limited imaging space, portability and, potentially, cost are important.

R&D status of 64-channel photon-counting imaging module

A high speed photon-counting imaging module that utilizes the previously developed GaAsP-photocathode 64-channel Hybrid Photo-Detector (HPD) has been developed. This photon-counting imaging module was designed in use for application fields such as bio-imaging, where it is necessary to detect ultra-low-level light signals with a relatively high count rate and to visualize the biological activity of the specimen. The basic operation of the module, which demonstrates its concept, has been confirmed. The fundamental characteristics were evaluated and we observed a dark rate per channel of 300–500s−1, count rate linearity of up to 1.2MHz for light pulse of a steady repetition, and maximum crosstalk ratio between channels of 2.7%. The current frame transfer rate of 50fps is limited by the un-optimized algorithm of the computer software.

Evaluating performance of a pixel array semiconductor SPECT system for small animal imaging

Small animal imaging has recently been focused on basic nuclear medicine. We have designed and built a small animal SPECT imaging system using a semiconductor camera and a newly designed collimator. We assess the performance of this system for small object imaging. We employed an MGC 1500 (Acrorad Co.) camera including a CdTe semiconductor. The pixel size was 1.4 mm/pixel. We designed and produced a parallel-hole collimator with 20-mm hole length. Our SPECT system consisted of a semiconductor camera with the subject holder set on an electric rotating stage controlled by a computer. We compared this system with a conventional small animal SPECT system comprising a SPECT-2000H scanner with four Anger type cameras and pinhole collimators. The count rate linearity for estimation of the scatter was evaluated for a pie-chart phantom containing different concentrations of 99mTc. We measured the FWHM of the 99mTc SPECT line source along with scatter. The system volume sensitivity was examined using a flood source phantom which was 35 mm long with a 32-mm inside diameter. Additionally, an in vivo myocardial perfusion SPECT study was performed with a rat. With regards to energy resolution, the semiconductor camera (5.6%) was superior to the conventional Anger type camera (9.8%). In the count rate linearity evaluation, the regression lines of the SPECT values were y = 0.019x + 0.031 (r2 = 0.999) for our system and y = 0.018x + 0.060 (r2 = 0.997) for the conventional system. Thus, the scatter count using the semiconductor camera was less than that using the conventional camera. FWHMs of our system and the conventional system were 2.9 +/- 0.1 and 2.0 +/- 0.1 mm, respectively. Moreover, the system volume sensitivity of our system [0.51 kcps/(MBq/ ml)/cm] was superior to that of the conventional system [0.44 kcps/(MBq/ml)/cm]. Our system provided clear images of the rat myocardium, sufficient for practical use in small animal imaging. Our SPECT system, utilizing a semiconductor camera, permits high quantitative analysis by virtue of its low scatter radiation and high sensitivity. Therefore, this system may contribute to molecular imaging of small animals and basic medical research.

Micro-pocket fission detectors (MPFD) for in-core neutron flux monitoring

Micro-pocket fission detectors (MPFD) have been fabricated and tested as in-core flux monitors in the 250 kW TRIGA nuclear reactor at Kansas State University. The prototype devices have been coated with a natural uranyl-nitrate to provide a neutron reactive coating. The devices are composed of alumina substrates sealed together to form a miniature gas pocket 3 mm in diameter and 1 mm wide. The devices are radiation hard and can operate in pulse mode in a neutron flux exceeding 10 12 cm −2 s −1. Placed in the central thimble of the reactor core, the MPFDs have shown count rate linearity from low to high power. Dead time losses become apparent at power levels exceeding 100 kW, yet are still low enough to allow for pulse mode operation.

Performance measurements of a high-spatial-resolution YAP camera

Physical properties of a position-sensitive camera for the analysis of biodistributions of gamma- and beta-emitting radiopharmaceuticals in small animals have been studied, in order to achieve optimal operating conditions. The camera consisted of a highly segmented yttrium-aluminate perovskite (YAP) scintillator, coupled to a position-sensitive photomultiplier. The energy resolution, the detection efficiency, the spatial resolution, the spatial linearity and the count-rate linearity of the YAP camera have been determined. Images related to initial activity levels and successive biodistribution evolution in mice organs are presented as an illustration of the camera performance.

A next generation, high speed detector for synchrotron radiation research

A high-speed, one-dimensional detector array for electrons and UV/X-ray photons has been developed. The detector is capable of handling the high countrates encountered in at third generation synchrotron radiation sources and is free from nonlinearity problems present in charge coupled device (CCD) detectors. Electrons are counted by a configuration of microchannel plates, an array of charge collection electrodes, and custom-designed integrated circuits (IC) assembled on a ceramic hybrid. The charges are collected on 768 strips with a 48 /spl mu/m pitch that are wire-bonded to 6 pairs of signal processing ICs. Each front-end IC has 128 channels of amplifiers (peaking time 25 ns) and discriminators. The pulse-pair resolution is 50 ns leading to a maximum linear countrate/channel of 2 MHz. The second, custom-designed IC features 24-b buffered counters and a serial link for the transfer of commands and data. A possible deadtime-less readout of all channels in 150 /spl mu/s opens the door to time resolved experiments. The complete detector system includes the high-voltage power supply, a field programmable gate array (FPGA)-based data acquisition system, and supporting software. Special care has been taken to insure reliable operation in an ultra-high vacuum environment. The detector architecture and design is described and measured performance characteristics such as spatial resolution and count-rate linearity are presented.

Quantitative imaging and correction for cascade gamma radiation of 76Br with 2D and 3D PET

Several positron emitting nuclides with applications in PET, such as 76Br, 124I, 110mIn and 86Y, also emit gamma radiation in their decays. Measured coincidences between annihilation photons and this cascade gamma radiation are essentially true coincidences and the standard PET corrections do not account for them. We investigated the performance of 76Br in 2D and 3D PET, the effect of the gamma radiation emitted by 76Br on quantitative accuracy and the distribution of cascade gamma radiation coincidences in 2D and 3D PET sinograms. A correction method for cascade gamma radiation coincidences was implemented and evaluated. Count rate linearity was affected by the gamma radiation from the 76Br decay. Spatial resolution and sphere recovery were slightly worse for 76Br compared to 18F. Correction for cascade gamma radiation coincidences by subtraction of a linear projection tail fit improved total correction accuracy to similar values as for positron-only emitters such as 18F, and improved image contrast significantly.

An External-Sample Liquid Scintillation Counting for &lt;sup&gt;75&lt;/sup&gt;Se and Its Application to Selenoprotein Detection

An external-sample liquid scintillation (LS) counting for the gamma emitter 75Se has been developed. An expressly designed well-type LS vial and a 2,5-diphenyoxazole-1,4-bis(5-phenyl-2-oxazoyl)-benzene-xylene solution containing 35% tertrabutylzinn allow 75Se to be counted in a standard LS counter with counting efficiency up to 43.2%, much higher than that of conventional LS counting method. This external sample LS has a good count rate linearity and exhibits low background count rates. After in vivo labeling with [75Se]selenite, 75Se distributions and the Se-containing proteins present in tissues of male rat were investigated by means of sodium dodecyl sulfate-polyacrylamide gel electrophoresis, external-sample LS and gamma-detector. Eight Se-containing proteins or protein subunits were detected to be Se-containing proteins or protein subunits in arterial wall, and their apparent molecular masses (Mr) were 76.4, 67.0, 57.4, 30.3, 25.4, 22.7, 21.7, and 15.1 kDa, respectively. In addition, eight 75Se-labeled proteins (Mr: 66.8, 57.0, 43.1, 30.0, 24.8, 19.8, 18.0, and 14.8 kDa) were found in brain homogenates, and nine 75Se-labeled proteins (Mr: 117.0, 78.0, 66.6, 57.2, 43.0, 38.1, 25.0, 20.1, and 18.0 kDa) were detected in testis homogenates. Some of them should be new biologically important selenoproteins that have not been identified so far.

An investigation of the physical characteristics of 66Ga as an isotope for PET imaging and quantification.

Isotopes commonly used for PET imaging and quantification have a straightforward decay scheme involving "pure" positron (beta +) emission, i.e., 95%-100% beta + abundance, with no additional gamma rays. 66Ga (Emax = 4.2 MeV, T1/2 = 9.5 h) is a member of a category of isotopes with a lower abundance of beta +'s (57%) and a more complicated spectrum involving combinations of gamma rays that are emitted in cascade. These additional gamma rays tend to cause a higher singles rate, resulting in more random coincidence events. The most abundant positron (51.5%) in the spectrum has one of the highest energies considered for PET imaging. For the purpose of monoclonal antibody dosimetry using 66Ga, it is important to verify the quantification in phantoms prior to initiating human studies. A series of quantitative phantom measurements were performed on the PC4600, a head-optimized BGO based scanner with multiple detector rings. Count rate linearity was verified over concentrations ranging from 4.0 kBq/cc to 37 kBq/cc (0.11-1.0 microCi/cc); resolution averaged 16 mm full width half-maximum in the x and y directions in both the direct and cross planes. Axial resolution was 14 mm. The range of the energetic positrons (up to 4.153 MeV, range 7.6 mm in tissue) was verified as a primary source of resolution degradation. Within the limits outlined above, 66Ga is a suitable isotope for use as 66Ga citrate or with monoclonal antibodies in the detection and staging of tumors and other lesions. In addition, the energetic positrons have possible therapeutic applications when used as a monoclonal antibody label.

Evaluation of the Karolinska new positron camera system; the Scanditronix PC2048-15B

The PC2048-15B is the brain version of the new generation of Scanditronix positron camera systems, now being installed at the Karolinska Hospital in Stockholm, Sweden. The system has eight rings with 256 BGO crystals per ring. The dimensions of the crystals are 6*12*30 mm. Data corresponding to 15 image slices are simultaneously recorded. The detector rings are based on block-detector units, each with 16 scintillation crystals mounted on two dual photomultiplier tubes. The system is described, and test results including spatial resolution, sensitivity to true and random coincidences, scatter correction, count rate linearity, spatial independence, and reproducibility are presented. Clinical results are discussed, including rCBF studies and receptor studies, to cover the two most extreme situations met in brain PET (positron emission tomography) studies, i.e. high count rate and high resolution requirements.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A preliminary evaluation of the Scanditronix PC2048-15B brain scanner.

The PC2048-15B is the brain version of the new generation of Scanditronix positron camera systems. It is based on a detection unit with 16 scintillating crystals mounted on 2 dual photomultiplier tubes. A system description is given and preliminary test results including spatial resolution, sensitivity to true and random coincidences, scatter correction, and count rate linearity are presented.

A preliminary evaluation of a positron camera system using weighted decoding of individual crystals

The whole-body positron camera PC4096-15WB is based on a detection unit with 16 scintillating crystals mounted on two dual photomultiplier tubes. The design ideas are specified and a system description is given. Preliminary test results including spatial resolution, sensitivity to true and random coincidences, scatter correction, and count-rate linearity are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Physical performance of the latest generation of commercial positron scanner

A study of some of the basic physical performance characteristics of an advanced commercial positron-emission tomograph (PET) is reported. It consists of eight rings of BGO (bismuth germanate) detectors (512/ring) with removable interring septa and retractable transmission ring sources for each ring. The (transaxial) detector width is 5.6 mm, and the lower limit of the spatial resolution in the reconstructed image is about 5 mm. Investigations were carried out of count-rate linearity, image count recovery with object size, the effect of attenuation correction on quantitation, and scatter fraction.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A preliminary evaluation of a dual crystal positron camera.

The whole-body positron camera PC2048-7WB, manufactured by Scanditronix AB, is based on a detection unit with two scintillating crystals on each photomultiplier tube. The design ideas are specified and a system description is given. Preliminary test results including spatial resolution, time resolution, scatter correction, homogeneity, sensitivity, and count rate linearity are presented.

Design and evaluation of a positron emission tomograph: HEADTOME III.

A high performance positron emission tomograph, HEADTOME III, with 480 bismuth germanate oxide detectors (13.4 X 25.0 X 40.0 mm), arranged in three rings of 750 mm diameter, with independent shadow masks and septa, is described. Image plane resolution at the center of the field of view (FOV) is 7.9 and 6.5 mm full width at half maximum (FWHM) in low resolution (LR) and high resolution (HR) mode, respectively. Axial resolution is 13.1, 11.3, and 9.1 mm FWHM at the center of FOV for direct planes of low quantitation (LQ), cross planes of LQ, and high quantitation (HQ) mode, respectively. Sensitivities evaluated by true events for a 68Ga 20 cm diameter cyclindrical pool were 34.5 (56.7), 16.4 (27.5), 19.4 and 9.5 kcps (muCi/ml)-1 with the direct (cross) planes of LQLR, direct (cross) planes of LQHR, and direct planes of HQLR and HQHR, respectively. The fraction of scattered coincidence in a cold spot phantom after software correction is 2.5% in LRLQ mode. Count rate linearity after software correction is within 1% up to 50 X 10(3) true events per second per plane with LRLQ mode.

High efficiency gamma radiation detection in clinical radioimmunoassays by liquid scintillation counting with “LSC gamma vials”

A polycrystalline sodium iodide detector (LSC Gamma Vial) has been developed which allows high efficiency counting of gamma emitting radioisotopes in liquid scintillation counters. The adaptor will fit any standard liquid scintillation counter. The LSC Gamma Vials allow I-125 and Co-57 to be detected in a standard liquid scintillation counter with counting efficiencies of 74% and 54% respectively, as compared to that of conventional gamma counting equipment. Even higher comparative efficiencies (> 100%) were obtained when the standard LSC coincidence circuitry was negated. This detector offers counting efficiency that is relatively independent of volume, has good count rate linearity, and exhibits low background count rates.