Katsumi Takami

Positologica: A Positron ECT Device with a Continuously Rotating Detector Ring

A rotary positron emission computed tomography device is developed for human brain and animal studies. The device utilizes 64 rectangular BGO detectors arranged at unequal spacing on a circular ring. The detector ring is continuously rotated at a constant speed of 60 rpm or less. This single continuous motion of the ring with the detector array provides excellent sampling characteristics and high detector redundancy. The device has a field of view 24 cm in diameter with a slice thickness adjustable from 1 cm to 2 cm. Measured width of system response to a 2 mm diameter line source is 5.8 mm FWHM at the center and less than 9 mm FWHM within a circle 16 cm in diameter. Measured sensitivity including scattered coincidence events is about 17 kcps/pCi/ml for a 20 cm diameter water phantom and 2 cm thick slice.

Characteristics of a gamma-ray detector using a bismuth germanate scintillator

Characteristics of a gamma‐ray detector that utilizes a 24×24×15‐mm3 bismuth germanate (BGO) scintillator are measured. Fluorescent light output measured with a BGO crystal coupled to a R1306 photomultiplier (Hamamatsu TV) is found to be 15% that of a NaI(T1) scintillator for incident photons of a given energy. The FWHM of the time spectrum, measured with two BGO crystals coupled to R329‐2 photomultipliers, is equal to 2.0 ns for a 68Ge–68Ga source at room temperature.

Performance Study of Whole-Body, Multislice Positron Computed Tomograph POSITOLOGICA-II

A 3-detector ring, 5-slice whole-body positron CT has been developed and is being tested. The PCT, POSITOLOGICA-II, has a total of 480 BGOs (160/ring), and employs continuous rotation scan (0.5rps). By using a 15mm wide BGO, a 9.2mm FWHM spatial resolution for reconstructed image is obtained at the center of FOV. Measured phantom diameter dependence of the true count rate shows good agreement with theoretically anticipated characteristics, including maximum sensitivity at around 30cm dia. Sensitivities for 20cm dia. phantom are 28 and 38 kcps/¿Ci/ml for in-plane and cross-plane, respectively, including scattered coincidences. Relative system detection efficiency measured with a line source at FOV center is 96% at 15ns time window (90% at 12ns), basing on 100% efficiency in 20-24ns.

Thickness measurement method for thin photoresist film on transparent material

A photoresist‐film thickness measurement method based on absorbance measurement is described. In this case, a 1‐μm‐thick photoresist film is coated on transparent glass, e.g., a Color Picture Tube panel having a 10–12‐mm thickness and a spherical, rough surface. To measure the absorbance, which corresponds to photoresist‐film thickness, the developed method employs a two‐dimensional scan of a 2‐mm‐diam light beam spot having two wavelengths, 365 nm (measuring wavelength) and 546 nm (reference). By switching wavelengths alternately at 25 Hz, total absorbance of the photoresist film and glass is measured with a ‘‘Dynode feedback’’ circuit system, but only the film thickness is displayed through simple signal processing. As experimental results, a minimum detectable thickness change of 0.001 μm (resolution) was obtained. The only remaining thing to be considered for practical use is a zero‐level discrepancy, due to different panel lots, for which the value was approximately equal to a 0.1‐μm thickness change.

Evaluation of Slice Shield Collimators for Multi-Layer Positron Emission Computed Tomographs

Evaluation of slice shield collimators is carried out using theoretical event rate formulas. This approach permits calculation of system performance in terms of sensitivity, scatter fraction, and high-counting rate characteristics. Electronics counting efficiency is also taken into account. A rational approach to optimal design is presented along with design examples. Effectiveness of collimator replacement is suggested. A system using sub-collimator with relatively small detector ring radius is proposed. It achieves a level of performance similar to that of a conventional collimator system with large ring radius.

Photoresist thickness measurement using laser-induced fluorescence.

A technique is proposed to measure the thickness of a small area of photoresist film on a substrate. This technique uses the fluorescence (peak wavelength, ~600 nm) induced in the film by a focused laser beam (wavelength, 497 nm). An initial calibration line is obtained by comparing several thicknesses and their related fluorescence. The films thickness is then determined from its fluorescence signal. The laser spot size and the accuracy of this measurement have also been estimated.

Performance criteria and evaluation of surface scanners

Abstract Performance criteria and testing methods for two types of laser surface scanners (bare wafer scanner and patterned wafer scanner) are discussed along with the experimental results. A Practically Detectable particle Size (PDS) using Polystyrene Latex (PSL) spheres is introduced on the basis of a signal to noise ratio of three. The PDS was approx. 0.16 μm diameter for the bare wafer scanner examined. The counting efficiency test near the lower detection limit is replaced by a measurement of reproducibility from scan to scan giving about 97–98% at the PDS with low particle density. The normalized full width at half maximum (FWHM) of a Pulse Height Analyzer (PHA) histogram (size resolution power) was about 100% at the PDS. To estimate the overall performance of the scanner, a figure of merit is defined by combining scan rate, PDS and normalized FWHM. For the patterned wafer scanner, it is shown that the PDS and the reproducibility should be measured individually for every specific pattern. A counting efficiency test was carried out by measuring the appearance frequency of particle signals on a map with each dot individually identified as a particle, by a photomicroscope. The counting efficiency varied from 30 to 90% for 2.02 μm PSL spheres on a specific Poly-Si patterned wafer depending on the location of particles with respect to the substrate pattern.

Capacitance Thermometer for Rotator

An LC resonant circuit containing a temperature sensitive capacitor of a ferroelectric material such as barium strontium titanate has been utilized above its Curie temperature as a sensing element in a thermometer, by measuring its resonant frequency without any direct connection. This light weight, small size, and connection‐free sensing circuit is especially suited to multipoint thermometry for a high speed rotator. Check of the accuracy of this thermometer was carried out under the operating condition of the rotator using a thermometer, and it was found that accuracy of 1 to 2°C was obtainable in the range from 15 to 200°C. Application of this thermometer to the turbogenerator was examined, and usefulness of this method was demonstrated.