Beta Camera Research Articles

Development of a compact alpha and beta camera for dismantlement applications

A new method has been developed to image surface contamination on-site by short range radiation emitters (such as alpha or beta particle emitters). The measurement is performed in direct contact with the contaminated surface and uses a solid scintillator coupled with Silicon Photomultiplier arrays. A proof of principle is performed in laboratory using a simple prototype and multiple alpha and beta calibrated sources. The experimental setup used to acquire the data, as well as the analysis procedure, are described and the detection results and the image reconstruction are discussed with regard to dismantling requirements.

Betabox: a beta particle imaging system based on a position sensitive avalanche photodiode

A beta camera has been developed that allows planar imaging of the spatial and temporal distribution of beta particles using a 14 × 14 mm2 position sensitive avalanche photodiode (PSAPD). This camera system, which we call Betabox, can be directly coupled to microfluidic chips designed for cell incubation or other biological applications. Betabox allows for imaging the cellular uptake of molecular imaging probes labeled with charged particle emitters such as 18F inside these chips. In this work, we investigate the quantitative imaging capabilities of Betabox for 18F beta particles, in terms of background rate, efficiency, spatial resolution, and count rate. Measurements of background and spatial resolution are considered both at room temperature (21 °C ± 1 °C) and at an elevated operating temperature (37 °C ± 1 °C), as is often required for biological assays. The background rate measured with a 4 keV energy cutoff is below 2 cph mm−2 at both 21 and 37 °C. The absolute efficiency of Betabox for the detection of 18F positron sources in contact with a PSAPD with the surface passivated from ambient light and damage is 46% ± 1%. The lower detection limit is estimated using the Rose Criterion to be 0.2 cps mm−2 for 1 min acquisitions and a 62 × 62 µm2 pixel size. The upper detection limit is approximately 21 000 cps. The spatial resolution at both 21 and 37 °C ranges from 0.4 mm FWHM at the center of the field of view (FOV), and degrades to 1 mm at a distance of 5 mm away from center yielding a useful FOV of approximately 10 × 10 mm2. We also investigate the effects on spatial resolution and sensitivity that result from the use of a polymer based microfluidic chip. For these studies we place varying layers of low-density polyethylene (LDPE) between the detector and the source and find that the spatial resolution degrades by ∼180 µm for every 100 µm of LDPE film. Sensitivity is reduced by half with the inclusion of ∼200 µm of additional LDPE film. Lastly, we demonstrate the practical utilization of Betabox, with an imaging test of its linearity, when coupled to a polydimethylsiloxane microfluidic chip designed for cell based assays.

Development of a DSP-based real-time position calculation circuit for a beta camera

A digital signal processor (DSP)-based position calculation circuit was developed and tested for a beta camera. The previous position calculation circuit which employed flash analog-to-digital (A-D) converters for A-D conversion and ratio calculation produced significant line artifacts in the image due to the differential non-linearity of the A-D converters. The new position calculation circuit uses four A-D converters for A-D conversion of the analog signals from the position sensitive photomultiplier tube (PSPMT). The DSP reads the A-D signals and calculates the ratio of X a/( X a+ X b) and Y a/( Y a+ Y b) on an event-by-event basis. The DSP also magnifies the image to fit the useful field of view (FOV) and rejects the events out of the FOV. The line artifacts in the image were almost eliminated.

Imaging of an artery from skin surface using beta camera

Dynamic images of positron distribution in artery was measured from the skin surface of human subject using beta camera for noninvasive measurement of the input function. After estimating the possibility of the method by some phantom studies, the beta camera was attached from the skin surface on the artery of wrist during the PET measurement using the O-15 water injection method. After injection of O-15 water, dynamic images of the artery were measured. Regions of interest (ROIs) were set on the artery and on the adjacent area of the artery. From the ROIs analysis, a time activity curve similar to that measured by the invasive technique was noninvasively obtained.

Development of a high resolution beta camera for a direct measurement of positron distribution on brain surface

We have developed and tested a high resolution beta camera for a direct measurement of positron distribution on the brain surface of animals. The beta camera consists of a thin CaF/sub 2/(Eu) scintillator, a tapered fiber optic plate (tapered fiber) and a position sensitive photomultiplier tube (PSPMT). The tapered fiber is the key component of the camera. We have developed two different sizes of beta cameras. One is 20 mm diameter field of view camera for imaging the brain surface of cats. The other is 10 mm diameter camera for that of rats. Spatial resolutions of the beta camera for cats and rats were 0.8 mm FWHM and 0.5 mm FWHM, respectively. We demonstrated that developed beta cameras may overcome the limitation of the spatial resolution of positron emission tomography (PET).

Gamma and beta intra-operative imaging probes

Small area (∼1.5 cm 2) scintillation cameras for imaging gammas and betas using inter-changeable detector front ends were built and characterized. Components common to both emission imaging cameras include: (1) fiber optic bundles 2–3 m long, comprised of multi-clad fibers which connect the scintillation detector to (2) an MC-PMT; (3) parallel MC-PMT outputs feed a resistive positioning network and i- V converter/line driver network which produce balanced + X, − X, + Y, and − Y outputs; and (4) four ADCs and a Macintosh PC for system control and image display. The beta and gamma devices used distinct scintillation detectors which were characterized by both simulation and measurement. The beta camera utilized a 0.5 mm by 1.25 cm φ CaF 2(Eu) scintillation crystal coupled, through a diffusing light guide, to 19 2-mm φ optical fibers. These front-end fibers are in turn coupled by a more flexible fiber bundle to the MC-PMT. CaF 2(Eu) has high light output, high beta sensitivity, and low gamma sensitivity. Image signals are histogrammed and displayed after Anger logic computations are performed on digitized signals. The beta camera has <0.6 mm FWHM intrinsic resolution. The gamma camera concept was tested with matrices of discrete 1 × 1 mm 2 and 2 × 2 mm 2 CsI(Tl) and NaI(Tl) crystals of various lengths, and 3 mm thick continuous crystals. Configurations using 4 × 4 element matrices with one-to-one coupling between crystals and fiber channels, and light diffusers between each crystal matrix and fibers were evaluated. The continuous crystals were coupled directly to the fiber optics with signal and data processing analogous to the beta camera. Coupling of discrete crystals to fiber optics by both methods gave essentially perfect identification of the crystal of interaction, allowing spatial resolution to be defined by the crystal size and collimator. The continuous crystal gamma camera gave intrinsic resolution of ∼1.4 mm FWHM.

Development of a high-resolution alpha camera

We have developed and tested a high-resolution alpha camera. The alpha camera consists of a thin CaF 2(Eu) scintillator, a tapered fiber optics plate (tapered fiber), a position-sensitive photomultiplier tube (PSPMT) and a position calculation circuit. Though this configuration was originally planned as a high-resolution beta camera for direct measurement of positron distribution over brain surface of animals, we found that, with some modifications, it could also image alpha particles. The scintillator is covered by a thin aluminized mylar to protect it from light while allowing the transmission of alpha particles. The tapered fiber is a key component of the camera. The alpha-induced scintillation image is magnified by the tapered fiber with little light loss. Resolution of the alpha camera can be improved by approximately the magnification factor of the tapered fiber, though the field of view of the camera is decreased. We developed a 20 mm diameter field of view alpha camera. Energy resolution of the camera was 30% full-width at half-maximum (FWHM) for 241Am alpha particles (5.5 MeV). Spatial resolution for 241Am alpha particles was better than 0.6 mm. We confirmed that this alpha camera can be used for high-resolution alpha autoradiography or other alpha imaging applications.

Annihilation /spl gamma/-ray background characterization and rejection for a small beta camera used for tumor localization during surgery

The authors have developed a miniature (1.2 cm/sup 2/) beta-ray camera prototype to assist a surgeon in locating the margins of a resected tumor. With this technique, one directly detects betas emitted from exposed radio-labeled tissue. When imaging positron emitting radiopharmaceuticals, annihilation gamma ray interactions in the detector can mimic those of the betas. The extent of the background contamination depends on the detector, geometry and the tumor specificity of the radiopharmaceutical. The authors have characterized the effects that annihilation gamma rays have on positron imaging with their small camera. They studied beta and gamma ray detection rates and imaging using small positron or electron sources directly exposed to the detector to simulate hot tumor remnants, and a cylinder filled with /sup 18/F to simulate annihilation background from the brain. For various ratios of phantom head/tumor activity, a background gamma rate of 2.0 cts/sec//spl mu/Ci was measured in the CaF/sub 2/(Eu) detector. The authors present two gamma-ray background rejection schemes that require a /spl beta/-/spl gamma/ coincidence. The first configuration uses a high efficiency scintillator coincidence "shield", the second, a "phoswich". Results show that these coincidence methods work with /spl sim/99% gamma ray rejection efficiency.

An ISPA camera for beta radiography

We have developed a new type of beta camera based on an imaging silicon pixel array (ISPA) tube combined with planar plastic scintillators or with SiY/sub 2/O/sub 5/:Ce scintillating powder. The ISPA tube consists of a photocathode viewed at 3 cm distance by a silicon anode divided into 1024 rectangular (75 /spl mu/m/spl times/500 /spl mu/m) detector pixels, each bump-bonded to its equally sized electronic pixel. Depending on the beta detector thickness we achieved spatial resolutions (FWHM) between 105-/spl mu/m (/sup 63/Ni source and 30-/spl mu/m-thick plastic scintillator) and 240-/spl mu/m (/sup 90/Sr-/sup 90/Y source and 120-/spl mu/m-thick plastic scintillator) by covering the detectors with brass templates. With their four 60-/spl mu/m-wide slits oriented parallel to the long pixel edges, we simulated small-sized beta strips. The impact of detector thickness is explained by multiple scattering, angular aperture of the template slits, and scintillating light distribution at the ISPA photocathode. Beta detection sensitivities were measured with calibrated /sup 3/H (tritium)- and /sup 14/C-Amersham microscale sources. They amount to 0.1 Bq (/sup 3/H) with 150 min counting time and to 0.025 Bq (/sup 14/C) with 180 min counting time.

Reduction of noise in the Beta camera for low activity applications

The "Beta-camera" used in the past in the authors' laboratory for imaging of biomedical samples, has a noise level of about 50 counts per second. It is desirable to reduce this noise, in order to improve the detectability in the biological samples. Accordingly, here the authors report on a coincidence technique that reduces the noise level to almost zero.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Beta Camera Low Activity Tumor Imaging

A new technique, the beta camera, to complement film autoradiography, with fast quantitative imaging of beta particle-emitting radionuclides has been developed. It consists of a thin plastic scintillator and a light-sensitive microchannel plate detector. The thin tissue sample is mounted on the scintillator. Our first system had a high background and a moderate spatial resolution of 900 microns. We now report an improved system with a photomultiplier tube mounted on the scintillator of the microchannel plate detector. Only events registered by both detectors are accepted. A fast coincidence unit processes the signals, and if a time overlap exists, an event is generated in the beta camera. In the coincidence mode, images with low activity distribution of 201Tl (count rate 1 s-1) in 50 microns-thick slices of a human glioma tumor could be recorded with a spatial resolution of 500 microns.

Imaging detector for static and dynamic studies in biological samples

Biomedical applications of a previously described beta camera are reported here for static imaging of tumor slices with negatron and positron emitting radionuclides. Also applications for dosimetry and dynamic imaging are reported.

Analysis of proliferative compartments in human tumors. I. Renal adenocarcinoma.

Vascular perfusion of 16 renal adenocarcinomas with radioactive DNA precursors provides a possibility of characterize proliferative compartments of this tumor type. Immediately after resection of the tumor-bearing kidney, the organ is perfused via renal artery with dextran-diluted, heparinized oxygenated blood at physiological temperature, pH, flow, and pressure in a recirculation system. DNA synthetizing cells are labeled by addition of 3H- or 14C-thymidine or both isotopes at different intervals. Beta camera scans and whole-tumor autoradiograms disclose a striking proliferative heterogeneity of the tumor. Cell proliferation depends on intratumoral localization, cellular differentiation, histological structure and vascular supply. Subpopulations of high proliferative activity are found at the invasive borderline near normal kidney, focally in subcapsular areas and in intrarenal metastases, but also immediately adjacent to necrotic areas in the tumor center. Quantitative evaluation of autoradiograms yields, at the cellular level, a significantly higher labeling index in granular cells (3.21%) than in clear cells (0.65%), with a large variability dependent on the histological structure. The highest number of DNA synthetizing cells is seen in papillary and mixed solid-tubular zones and at peripheral parts of solid areas, whereas in central parts of solid tumor cords and in highly differentiated tubular areas lower labeling indices are observed. The labeling index decreases exponentially as a function of the distance from the supporting blood vessel. In solid cords, no labeled cells are seen at a distance of more than 200 micron from the capillary. The ts determined by 3H/14C-thymidine double labeling is between 9.9 and 16.8 hr for granular cells and about 9.2 hr for clear cells. Potential population doubling time calculated for various subpopulations yields values between 4 and 50 days. It is concluded that cell loss is high, for granular cells in particular. Besides cell loss, a large nonproliferating compartment contributes to a delay of the tumor volume doubling time. Proliferative heterogeneity of advanced human tumors, as exemplified by the renal adenocarcinoma, bears important implications for therapy and prognosis.