S.T.G. Fetal

Bio: S.T.G. Fetal is an academic researcher from University of Coimbra. The author has contributed to research in topics: Scintillation & Gas electron multiplier. The author has an hindex of 13, co-authored 20 publications receiving 502 citations.

CCD readout of GEM-based neutron detectors

Abstract: We report on the optical readout of the gas electron multiplier (GEM) operated with a gaseous mixture suitable for the detection of thermal neutrons: 3 He–CF4. A CCD system operating in the 400–1000 nm band was used to collect the light. Spectroscopic data on the visible and NIR scintillation of He–CF4 are presented. Images of the tracks of the proton and triton recorded with a triple GEM detector are also shown. r 2002 Elsevier Science B.V. All rights reserved. PACS: 29.40.Gx

The GEM scintillation in He–CF4, Ar–CF4, Ar–TEA and Xe–TEA mixtures

Abstract: Light emitted during the development of electron avalanches in a gas electron multiplier (GEM) can be efficiently used for optical readout of the detector. We report on measurements of total light yields in Ar/CF 4 , He/CF 4 , Ar/TEA and Xe/TEA mixtures. Information on the energy resolution obtained with low-energy X-ray photons is also presented. The spectral distribution of the light produced in the GEM is analysed and the mechanisms associated with the process of light production are considered.

Advances in detectors for single crystal neutron diffraction

Abstract: Parallax error severely limits the use of gas detectors for neutron and X-ray single-crystal diffractometry. This is particularly the case in Neutron Macromolecule Crystallography (NMC), where a large solid angle is needed. High-resolution cylindrical detectors based on Neutron Image Plates provide a large angular coverage but they are gamma sensitive and do not allow time-resolved measurements. We describe the principle of a gas counter, the multi-blade Microstrip Gas Chamber (MSGC), which has the potential to design parallax-free cylindrical detectors. It contains radial MSGC plates, providing a partitioning of the gas volume and a segmentation of the signal readout. The axial coordinate is measured by reading out the charge signal on the anodes and the trans-axial coordinate is deduced from the electron drift distance measured optically using the time difference between the primary and the avalanche light. Expected characteristics are a sub-millimeter position resolution, a sub-microsecond time resolution, and a global counting rate greater than 10 7 s - 1 .

Luminescence and imaging with gas electron multipliers

Abstract: Although the GEM has been mainly used as a gaseous preamplifier device, it has been shown that using suitable gaseous mixtures the avalanches emit a large number of photons, in the UV, visible and/or NIR bands. This scintillation, readout by CCDs, has been used recently for the development of imaging detectors to be used with X-rays, alpha particles and neutrons. The luminescence process in the GEM and a summary of its applications will be presented. The latest developments, including the operation of the GEMs in photon counting mode, will also be referred.

Performance of an optical readout GEM-based TPC

Abstract: We report on the operation of a GEM-based small TPC using an optical readout. The detector was operated with a mixture of Ar+CF4 using 5.48 MeV alpha particles obtained from a 241 Am source and the GEM scintillation was concurrently read by a CCD camera and a photomultiplier. Precision collimators were used to define the track orientation. Qualitative results on the accuracy of the track angle, length and charge deposition measurements are presented.

The gas electron multiplier (GEM): Operating principles and applications

Abstract: Introduced by the author in 1997, The Gas Electron Multiplier (GEM) constitutes a powerful addition to the family of fast radiation detectors; originally developed for particle physics experiments, the device and has spawned a large number of developments and applications; a web search yields more than 400 articles on the subject. This note is an attempt to summarize the status of the design, developments and applications of the new detector.

The positron emission mammography/tomography breast imaging and biopsy system (PEM/PET): design, construction and phantom-based measurements.

Abstract: Tomographic breast imaging techniques can potentially improve detection and diagnosis of cancer in women with radiodense and/or fibrocystic breasts. We have developed a high-resolution positron emission mammography/tomography imaging and biopsy device (called PEM/PET) to detect and guide the biopsy of suspicious breast lesions. PET images are acquired to detect suspicious focal uptake of the radiotracer and guide biopsy of the area. Limited-angle PEM images could then be used to verify the biopsy needle position prior to tissue sampling. The PEM/PET scanner consists of two sets of rotating planar detector heads. Each detector consists of a 4 x 3 array of Hamamatsu H8500 flat panel position sensitive photomultipliers (PSPMTs) coupled to a 96 x 72 array of 2 x 2 x 15 mm(3) LYSO detector elements (pitch = 2.1 mm). Image reconstruction is performed with a three-dimensional, ordered set expectation maximization (OSEM) algorithm parallelized to run on a multi-processor computer system. The reconstructed field of view (FOV) is 15 x 15 x 15 cm(3). Initial phantom-based testing of the device is focusing upon its PET imaging capabilities. Specifically, spatial resolution and detection sensitivity were assessed. The results from these measurements yielded a spatial resolution at the center of the FOV of 2.01 +/- 0.09 mm (radial), 2.04 +/- 0.08 mm (tangential) and 1.84 +/- 0.07 mm (axial). At a radius of 7 cm from the center of the scanner, the results were 2.11 +/- 0.08 mm (radial), 2.16 +/- 0.07 mm (tangential) and 1.87 +/- 0.08 mm (axial). Maximum system detection sensitivity of the scanner is 488.9 kcps microCi(-1) ml(-1) (6.88%). These promising findings indicate that PEM/PET may be an effective system for the detection and diagnosis of breast cancer.

Raman imaging at biological interfaces: applications in breast cancer diagnosis

Abstract: Background One of the most important areas of Raman medical diagnostics is identification and characterization of cancerous and noncancerous tissues. The methods based on Raman scattering has shown significant potential for probing human breast tissue to provide valuable information for early diagnosis of breast cancer. A vibrational fingerprint from the biological tissue provides information which can be used to identify, characterize and discriminate structures in breast tissue, both in the normal and cancerous environment.

Molecular breast imaging: use of a dual-head dedicated gamma camera to detect small breast tumors.

Abstract: OBJECTIVE. Molecular breast imaging with a single-head cadmium zinc telluride (CZT) gamma camera has previously been shown to have good sensitivity for the detection of small lesions. To further improve sensitivity, we developed a dual-head molecular breast imaging system using two CZT detectors to simultaneously acquire opposing breast views and reduce lesion-to-detector distance. We determined the incremental gain in sensitivity of molecular breast imaging with dual detectors.SUBJECTS AND METHODS. Patients with BI-RADS category 4 or 5 lesions < 2 cm that were identified on mammography or sonography and scheduled for biopsy underwent molecular breast imaging as follows: After injection of 740 MBq of technetium-99m (99mTc) sestamibi, 10-minute craniocaudal and mediolateral oblique views of each breast were acquired. Blinded reviews were performed using images from both detectors 1 and 2 and images from detector 1 only (simulating a single-head system). Lesions were scored on a scale of 1–5; 2 or higher wa...