http://hdl.handle.net/10016/9274 2013-05-26T07:51:13Z http://hdl.handle.net/10016/12582 Title: Imagen molecular Author(s): Vaquero, Juan José 2002-12-31T23:00:00Z http://hdl.handle.net/10016/12241 Title: Design and development of a high performance micro-CT system for small-animal imaging Author(s): Lage, Eduardo; Vaquero, Juan José; Redondo, Santiago; Abella, Mónica; Tapias, Gustavo; Udías, Ángel; Desco, Manuel Abstract: The goal of this work was the development of a lowcost micro-CT scanner, which could be used as an add-on in our previously developed PET systems for small-animals. The scanner design consists of a single-processor computer controlling a micro-focus X-ray tube and a flat panel detector, assembled in a common rotating gantry. The geometrical configuration was selected to achieve a spatial resolution of about 12 lp/mm with a field of view appropriate for small animals such as mice and rats. The radiated dose is controlled during the acquisition by two different elements: an aluminium filter and a tungsten shutter, attached to the X-ray source. The shutter is controlled by the computer in synchronism with the gantry rotation and the detector image integration. In order to achieve high performance with regards to per-animal screening time and cost, the acquisition protocol is able to take advantage from the highest frame rate of the detector also performing onthe-fly corrections for the detector raw data. These corrections include geometrical misalignments, sensor non-uniformities and defective elements, as well as conversion to attenuation images. An FDK reconstruction algorithm adapted to the specific conebeam geometry has been implemented. Symmetries are exploited to accelerate the algorithm and fast back-projection techniques have been developed for those protocols where high resolution is not a requirement. Description: Proceeding of: 2006 IEEE Nuclear Science Symposium Conference Record, San Diego, CA, Oct. 29 - Nov. 1, 2006 2005-12-31T23:00:00Z http://hdl.handle.net/10016/12240 Title: Effects of sinogram filtering in the quality of PET reconstructions: preliminary results Author(s): Abella, Mónica; Redondo, Santiago; Vaquero, Juan José; Sanchez-Gonzalez, J.; Desco, Manuel Abstract: Low-pass filtering sinograms prior to reconstruction is a general practice to reduce noise. Sinograms are generally filtered in the radial direction, although other filtering schemes have been proposed. It is known that the Fourier transform of a sinogram shows a particular shape of the spectral energy distribution (“bow-tie”). In this work, this property has been exploited to perform an adapted filter, whose performance has been compared with previously reported methods: angular, axial and stackgram domain filtering. Stackgram and angular filtering degraded resolution (~16 and ~5.7 % respectively) while no significant enhancement in contrast to noise ratio (CNR) was achieved. Angular filtering resulted in a circle blurring artifact dependant on the distance to the center of the FOV. Bow-tie filtering showed the best results (enhancement of ~26% in resolution and of ~12% in CNR). Axial filtering degraded resolution but enhanced CNR (~14 %), appearing as a good strategy to reduce radial filtering. Experiments on rodent images showed a noticeable image quality enhancement achieved when using bow-tie filtering combined with radial and axial filters. Description: Proceeding of: 2006 IEEE Nuclear Science Symposium Conference Record, San Diego, CA, Oct. 29 - Nov. 1, 2006 2005-12-31T23:00:00Z http://hdl.handle.net/10016/12239 Title: Normalization in 3D PET: dependence on the activity distribution of the source Author(s): Vicente, Esther; Vaquero, Juan José; España, Samuel; Herraiz, J. L.; Udías, José Manuel; Desco, Manuel Abstract: In this communication we show the dependence of the normalization of 3D small animal PET scanners on the calibrating source geometry and non-uniformity of the activity distribution inside it. The potential impact on the reconstructed images of deviations from the ideal activity is discussed. Results from simulated and real data for a pair of block detectors suggest that planar or annular sources can be equally suitable for a normalization procedure if their geometry and their intersections with the system lines-of-response (LORs) are properly taken into account. When comparing an annulus with a centered planar source, both filled with the same total activity, the planar source produces twice the count rate with a 92% of trues versus 66% of trues for the annulus. Scatter and randoms are lower by factors of 3 and 4 respectively in the planar case. We conclude that, although planar and annular sources can be suitable for a normalization procedure if their geometries are properly taken into account, planar source normalization results are better than those of an annulus, particularly if the normalization does not consider the effect of scatter correction, more significant for the annulus source than for the planar one Description: Proceeding of: 2006 IEEE Nuclear Science Symposium Conference Record, San Diego, CA, Oct. 29 - Nov. 1, 2006 2006-12-31T23:00:00Z