True coincidence count (TCC) and noise equivalent count (NEC) curves were measured with a standardized 20-cm-diameter nylon cylinder for five different CTI/Siemens PET (positron emission tomography) scanners with several scanner-collimator combinations: (1) 831/08-12 with 1-mm collimator septa; (2) 933/08-12 and 933/08-16 with 3 to 1-mm tapered collimator septa; and (3) 931/08-12 with 3 to 1-mm tapered and a 1-mm collimator septa and the 931/08-16 with 3 to 1-mm tapered collimator septa In addition, TCC and NEC curves on the 933/08-12 were compared with those from an Alderson brain phantom In general, it is found that the TCC curves indicated peak count rates and activity levels that were as much as 50% higher than the corresponding values from NEC curves The primary factor causing this difference is the noise effect of the randoms component It is demonstrated that, compared to the Alderson brain phantom, the standard 20-cm cylinder is a poor predictor of count rate performance for PET brain imaging >

Measuring PET scanner sensitivity: relating countrates to image signal-to-noise ratios using noise equivalents counts

Coded aperture imaging in high energy astronomy represents an important technical advance in instrumentation over the full energy range from X- to γ-rays and is playing a unique role in those spectral ranges where other techniques become ineffective or impracticable due to limitations connected to the physics of interactions of photons with matter. The theory underlying this method of indirect imaging is of strong relevance both in design optimization of new instruments and in the data analysis process. The coded aperture imaging method is herein reviewed with emphasis on topics of mainly practical interest along with a description of already developed and forthcoming implementations.

Coded aperture imaging in X- and gamma-ray astronomy

Cerium‐activated phosphors are characterized by their fast luminescence decay. Gadolinium orthosilicate (Gd2SiO5) is a material possessing a high atomic number, and can also play host to the cerium activator. Cerium‐doped Gd2SiO5 single crystals were grown by the Czochralski technique, and their luminescence properties were examined. The light output was 1.3 times larger than that of the best Bi4Ge3O12, and the decay constant was 60 ns at room temperature.

Cerium‐activated Gd2SiO5 single crystal scintillator

Non-invasive method of forming prostheses of skeletal structures internal to a body for use in reconstructive surgery. The selected internal skeletal structure is measured by subjecting the body to radiant energy to produce radiant energy responses that are detected to obtain representations delineating the skeletal structure. Three dimensional coordinate data defining the skeletal structure is generated from the obtained representations. The coordinate data is employed to control a sculpting tool to form the prosthesis.

Method of forming implantable prostheses for reconstructive surgery

The trend in the design of scanners for positron emission computed tomography has traditionally been to improve the transverse spatial resolution to several millimeters while maintaining relatively coarse axial resolution (1-2 cm). Several scanners are being built with fine sampling in the axial as well as transverse directions, leading to the possibility of the true volume imaging. The number of possible coincidence pairs in these scanners is quite large. The usual methods of image reconstruction cannot handle these data without making approximations. It is computationally most efficient to reduce the size of this large, sparsely populated array by back-projecting the coincidence data prior to reconstruction. While analytic reconstruction techniques exist for back-projected data, an iterative algorithm may be necessary for those cases where the point spread function is spatially variant. A modification of the maximum likelihood algorithm is proposed to reconstruct these back-projected data. The method, the iterative image space reconstruction algorithm (ISRA), is able to reconstruct data from a scanner with a spatially variant point spread function in less time than other proposed algorithms. Results are presented for single-slice data, simulated and actual, from the PENN-PET scanner.

An Iterative Image Space Reconstruction Algorthm Suitable for Volume ECT

PURPOSE:To improve the resolution of positions without increasing radiation detectors by providing a movalbe member consisting of a radiation shielding material between an object to be inspected and the detectors, and providing the apertures of said members at 1/N of the detection areas of the radiation detectors. CONSTITUTION:A detector ring 10 consists of many radiation detectors which are arrayed annularly around an axis O. Each of the radiation detectors themselves consists of, for example, a scintillation crystal 11A and a photoelectron multiplier 11B. A movable member 12 is supported so as to be made rotatable around the axis O on the inner side of the detector ring, and the member itself is constituted of an X-ray shielding material, for example, tungsten. Apertures of the number corresponding to the number of the radiation detectors are provided at equal intervals on the periphery of the movable member, so that radiations can be made incident to the radiation detectors only through these apertures. The apertures have the circumferential length occupying 1/N of the detection areas of the radiation detectors.

Scanner of positron emission ct device

Neutron doses often come dominant in mazes of electron accelerator facilities in which X-rays of energies more than 10 MV are produced. A simple analytical method to calculate neutron doses in such a facility is developed. In the calculation procedure, it is assumed that the irradiation room is spherical in shape and the maze is cylindrical. Multiple reflection of neutrons is also considered using the albedo concept in the calculation. The procedure allows to exist a hanging wall over the entrance of the irradiation room and also multiple legs in the maze. All the parameters used in the calculation are given definitely in the procedure, and any experiment is unnecessary to determine value of the parameters. Comparison of the calculated results with experimental ones will be described in the following report.

https://www.jstage.jst.go.jp/article/radioisotopes1952/39/2/39_2_29/_pdf

Kenji Ishimatsu

Papers

Scanner of positron emission ct device

[Leakage radiations in a medical electron accelerator facility--calculation of neutron doses in the facility].