Jorge Uribe

A multi-source inverse-geometry CT system: initial results with an 8 spot x-ray source array

We present initial experimental results of a rotating-gantry multi-source inverse-geometry CT (MS-IGCT) system. The MS-IGCT system was built with a single module of 2 × 4 x-ray sources and a 2D detector array. It produced a 75 mm in-plane field-of-view (FOV) with 160 mm axial coverage in a single gantry rotation. To evaluate system performance, a 2.5 inch diameter uniform PMMA cylinder phantom, a 200 µm diameter tungsten wire, and a euthanized rat were scanned. Each scan acquired 125 views per source and the gantry rotation time was 1 s per revolution. Geometric calibration was performed using a bead phantom. The scanning parameters were 80 kVp, 125 mA, and 5.4 µs pulse per source location per view. A data normalization technique was applied to the acquired projection data, and beam hardening and spectral nonlinearities of each detector channel were corrected. For image reconstruction, the projection data of each source row were rebinned into a full cone beam data set, and the FDK algorithm was used. The reconstructed volumes from upper and lower source rows shared an overlap volume which was combined in image space. The images of the uniform PMMA cylinder phantom showed good uniformity and no apparent artifacts. The measured in-plane MTF showed 13 lp cm(-1) at 10% cutoff, in good agreement with expectations. The rat data were also reconstructed reliably. The initial experimental results from this rotating-gantry MS-IGCT system demonstrated its ability to image a complex anatomical object without any significant image artifacts and to achieve high image resolution and large axial coverage in a single gantry rotation.

Multi-source inverse-geometry CT: From system concept to research prototype

Third-generation CT architectures are approaching fundamental limits. Dose-efficiency is limited by finite detector efficiency and by limited control over the X-ray flux spatial profile. Increasing the volumetric coverage comes with increased scattered radiation, cone-beam artifacts, Heel effect, wasted dose and cost. Spatial resolution is limited by focal spot size and detector cell size. Temporal resolution is limited by mechanical constraints, and alternative geometries such as electron-beam CT and dual-source CT come with severe tradeoffs in terms of image quality, dose-efficiency and complexity. The concept of multi-source inverse-geometry CT (IGCT) breaks through several of the above limitations [1-3], promising a low-dose high image quality volumetric CT architecture. In this paper, we present recent progress with the design and integration efforts of the first gantry-based multi-source CT scanner.

Multisource inverse-geometry CT — Prototype system integration

Todays 3rd generation CT scanners have one or two X-ray tubes, with one focal spot or “source” per vacuum chamber or “tube”. Our first multi-source inverse geometry CT prototype has eight X-ray sources. We have demonstrated multisource imaging with an 8-spot X-ray tube on a stationary gantry and a rotating phantom. We present an update on the development of the gantry-based multi-source CT scanner: we combine the multi-source X-ray tube and gantry rotation producing the first multi-source gantry-based CT scanner prototype. Currently the system is in the process of being upgraded to 32 X-ray sources to provide a larger field-of-view and to demonstrate the concept of virtual bowtie.

Initial results with a multisource inverse-geometry CT system

The multi-source inverse-geometry CT(MS-IGCT) system is composed of multiple sources and a small 2D detector array. An experimental MS-IGCT system was built and we report initial results with 2×4 x-ray sources, a 75 mm inplane field-of-view (FOV) and 160 mm z-coverage in a single gantry rotation. To evaluate the system performance, experimental data were acquired from several phantoms and a post-mortem rat. Before image reconstruction, geometric calibration, data normalization, beam hardening correction and detector spectral calibration were performed. For reconstruction, the projection data were rebinned into two full cone beam data sets, and the FDK algorithm was used. The reconstructed volumes from the upper and lower source rows shared an overlap volume which was combined in image space. The reconstructed images of the uniform cylinder phantom showed good uniformity of the reconstructed values without any artifacts. The rat data were also reconstructed reliably. The initial experimental results from this rotating-gantry MS-IGCT system demonstrated its ability to image a complex anatomical object without any significant image artifacts and to ultimately achieve large volumetric coverage in a single gantry rotation.

FRIDA, the diffraction limited NIR imager and IFS for the Gran Telescopio Canarias: status report

FRIDA is a diffraction limited imager and integral field spectrometer that is being built for the Gran Telescopio Canarias. FRIDA has been designed and is being built as a collaborative project between institutions from México, Spain and the USA. In imaging mode FRIDA will provide scales of 0.010, 0.020 and 0.040 arcsec/pixel and in IFS mode spectral resolutions R ~ 1000, 4,500 and 30,000. FRIDA is starting systems integration and is scheduled to complete fully integrated system tests at the laboratory by the end of 2015 and be delivered to GTC shortly after. In this contribution we present a summary of its design, fabrication, current status and potential scientific applications.

FRIDA INTEGRAL FIELD UNIT OPTO-MECHANICAL DESIGN

FRIDA (inFRared Imager and Dissector for the Adaptive optics system of the Gran Telescopio Canarias) has been designed as a cryogenic and diffraction limited instrument that will offer broad and narrow band imaging and integral field spectroscopy (IFS). Both, the imaging mode and IFS observing modes will use the same Teledyne 2Kx2K detector. This instrument will be installed at Nasmyth B station, behind the GTC Adaptive Optics system. FRIDA will provide the IFS mode using a 30 slices Integral Field Unit (IFU). This IFU design is based on University of Florida FISICA where the mirror block arrays are diamond turned on monolithic metal blocks. FRIDA IFU is conformed mainly by 3 mirror blocks with 30 spherical mirrors each. It also has a Schwarzschild relay based on two off axis spherical mirrors and an afocal system of two parabolic off axis mirrors. Including two insertion mirrors the IFU holds 96 metal mirrors. Each block or individual mirror is attached on its own mechanical mounting. In order to study beam interferences with mechanical parts, ghosts and scattered light, an iterative optical-mechanical modeling was developed. In this work this iterative modeling is described including pictures showing actual ray tracing on the opto-mechanical components.

Electronics and mechanisms control system for FRIDA (inFRared Imager and Dissector for Adaptive optics)

FRIDA will be a common-user near infrared imager and integral field spectrograph covering the wavelength range from 0.9 to 2.5 microns. Primary observing modes driven the instrument design are two: direct imaging and integral field spectroscopy. FRIDA will be installed at the Nasmyth-B platform of the Gran Telescopio Canarias (GTC) behind the GTC Adaptive Optics (GTCAO) system. Instrument will use diffraction-limited optics to avoid degrading the high Strehl ratios derived by the GTCAO system in the near infrared. High-performance astronomical instruments with a high reconfiguration degree as FRIDA, not only depends on optical and mechanical efficient designs but also on the good quality of its electronics and control systems design. In fact, astronomical instruments operating performance on telescope greatly relies on electronics and control system. This paper describes the main design topics for the FRIDA electronics and mechanisms control system, pointing on the development that these areas have reached on the project status. FRIDA Critical Design Review (CDR) was held on September 2011.

Mechanical conceptual design of 6.5 meter telescope: Telescopio San Pedro Mártir (TSPM)

Telescopio San Pedro Mártir (TSPM) project intends to build a 6.5 meters telescope with alt-azimuth design, currently at the conceptual design. The project is an association between Instituto de Astronomía de la Universidad Nacional Autónoma de México (IA-UNAM) and the Instituto Nacional de Astrofísica, Óptica Electrónica (INAOE) in partnership with department of Astronomy and Steward Observatory of University of Arizona and Smithsonian Astrophysical Observatory of Harvard University. Conceptual design of the telescope is lead and developed by the Centro de Ingeniería y Desarrollo Industrial (CIDESI). An overview of the feasibility study and the structural conceptual design are summarized in this paper. The telescope concept is based on telescopes already commissioned such as MMT and the Baade and Clay Magellan telescopes, building up on these proven concepts. The main differences relative to the Magellan pair are; the elevation axis is located 1 meter above the primary mirror vertex, allowing for a similar field of view at the Cassegrain and both Nasmyth focal stations; instead of using a vane ends to position the secondary mirror TSPM considers an Steward platform like MMT; finally TSPM has a larger floor distance to m1 cell than Magellans and MMT. Initially TSPM will operate with an f/5 Cassegrain station, but the design considers further Nasmyth configurations from a Cassegrain f/5 up to a Gregorian f/11. The telescope design includes 7 focal stations: 1 Cassegrain; 2 Nasmyth; and 4 folded-Cassegrain. The telescope will be designed and manufactured in Mexico, will be design in Queretaro by CIDESI and built between Queretaro and Michoacán manufacturing facilities; it will be preassembled in these facilities and disassembled to send it to the San Pedro Mártir Observatory for final integration. The azimuth and altitude structure is planned to be constructed in modules and transported by truck and shipped to Ensenada and finally to the OAN where is going to be finally assembled, verified and tested.

Mechanical preliminary design of the 6.5 meter Telescopio San Pedro Mártir (TSPM)

The Telescopio San Pedro Mártir project intends to build a 6.5 meters telescope with alt-azimuth mount and it has currently finished the preliminary design. The project is an association between Instituto de Astronomía de la Universidad Nacional Autónoma de México and the Instituto Nacional de Astrofísica, Óptica Electrónica in partnership with the University of Arizona and the Smithsonian Astrophysical Observatory. The telescope preliminary design this is lead and developed at Querétaro by the Centro de Ingeniería y Desarrollo Industrial. An overview of the preliminary design and the structural design updates are summarized in this paper.

The Telescopio San Pedro Mártir project

The Telescopio San Pedro Martir project intends to construct a 6.5m telescope to be installed at the Observatorio Astron´omico Nacional in the Sierra San Pedro M´artir in northern Baja California, Mexico. The project is an association of Mexican institutions, lead by the Instituto Nacional de Astrofısica, Optica y Electronica and UNAM’s Instituto de Astronomia, in partnership with the Smithsonian Astrophysical Observatory and the University of Arizona’s Department of Astronomy and Steward Observatory. The project is advancing through the design stage, having completed five design reviews of different subsystems in 2016 and 2017 (enclosure and services: PDR, CDR; optical design: PDR; optics: progress review; telescope: PDR). Once completed, the partners plan to operate the MMT and TSPM as a binational astrophysical observatory.