Simulation of mechanical misalignments in a cone-beam micro-CT system

Proceeding of: 2008 IEEE Nuclear Science Symposium Conference Record (NSS '08), Dresden, Germany, 19-25 October 2008X-ray CT images usually show artefacts due not only to physical effects -e.g., beam hardening-, but also to misalignments that remain after mechanical calibration. These artefacts become particularly noticeable in the case of high spatial resolution systems and in hybrid systems, such as PETCT, SPECT-CT scanners, which rely on a correct registration of emission and CT data. Hence, slight mechanical misalignments affect the quality of the CT images and any attenuation correction methods or further quantification based on them. We implemented a computer simulator of these artefacts on a conebeam, flat-panel based micro-CT scanner. Using this simulator, we studied the effect of these different misalignments (pitch and roll tilts, skew and shifts) on reconstructed images.This work is partially funded by the CD-TEAM Project, CENIT Program, Spanish Ministerio de Industria, and with grants from the Ministerio de Educaci6n y Ciencia, projects TEC200764731 and TEC2008-06715-C02-01

Expanding the dynamic range of flat-panel detectors used in small-animal cone-beam CT: an automated dual-exponsure technique

[Poster] 4th European Molecular Imaging Meeting, Barcelona, Spain, May 27 - 30, 2009This work is supported in part by Ministerio de Ciencia e Innovación (TEC2008-06715 and TEC2007-64731), EU-FP7 project FMTXCT-201792 and CD-TEAM project (CENIT program).Publicad

Software architecture for multi-bed FDK-based reconstruction in X-ray CT scanners

Most small-animal X-ray computed tomography (CT) scanners are based on cone-beam geometry with a flat-panel detector orbiting in a circular trajectory. Image reconstruction in these systems is usually performed by approximate methods based on the algorithm proposed by Feldkamp et al. (FDK). Besides the implementation of the reconstruction algorithm itself, in order to design a real system it is necessary to take into account numerous issues so as to obtain the best quality images from the acquired data. This work presents a comprehensive, novel software architecture for small-animal CT scanners based on cone-beam geometry with circular scanning trajectory. The proposed architecture covers all the steps from the system calibration to the volume reconstruction and conversion into Hounsfield units. It includes an efficient implementation of an FDK-based reconstruction algorithm that takes advantage of system symmetries and allows for parallel reconstruction using a multiprocessor computer. Strategies for calibration and artifact correction are discussed to justify the strategies adopted. New procedures for multi-bed misalignment, beam-hardening, and Housfield units calibration are proposed. Experiments with phantoms and real data showed the suitability of the proposed software architecture for an X-ray small animal CT based on cone-beam geometry.This work was partially funded by AMIT project from the CDTI CENIT program, TEC2007-64731, TEC2008-06715- C02-01, RD07/0014/2009, TRA2009 0175, RECAVA-RETIC, and RD09/0077/00087 (Ministerio de Ciencia e Inovación), and ARTEMIS S2009/DPI-1802 (Comunidad de Madrid).Publicad

Development and performance of the small-animal R-SPECT prototype

[Poster] 4th European Molecular Imaging Meeting, Barcelona, Spain, May 27 - 30, 2009In vivo molecular imaging of small animals has become an essential technique in biomedical research since the introduction of dedicated PeT and SPeCT scanners. however, the capabilities of these typically very expensive machines often exceed the requirements to accomplish common protocols encountered in practice. accordingly, we have developed a simple and compact small-animal SPeCT system, addressed to be used either as an add-on for existing small-animal CT or PeT scanners, or as a stand-alone single photon imagerThis work is supported by Ministerio de Ciencia e innovación (TeC2008-06715-C02-01 and TeC2007-64731/TCM), Ministerio de industria (CdTeaM, Programa CeniT), and the reCaVa-reTiC network.Publicad

rSPECT: a compact gamma camera based SPECT system for small-animal imaging

Proceeding of: 2009 IEEE Nuclear Science Symposium Conference Record (NSS/MIC), Orlando, Florida, 25-31 October 2009We have developed a compact and modular gamma camera system and assessed its performance when used on a small-animal SPECT prototype (rSPECT). Each camera consists of a Hamamatsu H-8500 position sensitive photomultiplier tube coupled to a 30 x 30 NaI (Tl) scintillator array (1.4mm x 1.4mm x 6mm crystal size) and electronics for pre-processing and matching the detector signals to an in-house developed data acquisition system. The camera components are enclosed in a lead-shielded case with a receptacle to insert the collimators (parallel-hole or pinhole with different tungsten apertures). System performance has been assessed for a low energy high resolution parallel-hole collimator (LEHR), and for a 0.75 mm pinhole collimator with 60º aperture angle. In this paper we present details on the system implementation and results of performance measurements, as well as first tomographic images on phantoms and animals. This SPECT was conceived for compactness and cost-effective routine small-animal imaging, and acquisitions of living mice and rats carried out with the system demonstrate its ability to provide useful high-resolution images for in vivo research.This work is partially funded by the CD TEAM project, CENIT Program, Spanish Ministerio de Industria and with grants from the Ministerio de Educación y Ciencia, Projects TEC2007 64731/TCM, TEC2008 06715 C02 01, SAF2009 08076 and the RECAVA RETIC Network

Automated dual-exposure technique to extend the dynamic range of flat-panel detectors used in small-animal cone-beam micro-CT

Proceeding: 2009 IEEE Nuclear Science Symposium Conference Record (NSS/MIC), Orlando, Florida, 25-31 October 2009This work presents an approach to extend the dynamic range of X ray flat panel detectors for cone beam micro CT by using two different acquisitions of the same sample, taken at two different X ray photon fluxes with the same X ray beam peak energy and filtration. Photon flux for the first scan is chosen as the maximum possible value not saturating the detector in the low attenuation areas. The second exposure level is calculated from the data acquired in the first exposure, assuming that the detector response to the incoming radiation is linear. To combine both datasets, we model the response of a detector pixel, as well as the overall gain of the detector. Each pixel of each dataset is weighted according to its value. Pixels whose value lies within the high gain region of the detector receive the higher weights. The weighted Joint Probability Density Function (JPDF) is obtained by assuming that each dataset follows an independent Gaussian distribution. The final pixel value is calculated by means of a maximum likelihood estimation performed on the JPDF. The algorithm has been tested imaging two different phantoms on a small animal cone beam CT. We have performed comparative experiments using the proposed dual exposure technique and a regular single exposure acquisition, following a fully automated procedure. In both cases the dose delivered to the sample was the same. Image quality was assessed from the image noise level and the presence of artifacts on the reconstructed slices, at different dose levels. The dual exposure data show higher signal to noise ratio. Also, image artifacts are noticeably reduced in the dual exposure dataset. Since the proposed technique enhance the quality of the data extending the dynamic range of the detector without increasing the delivered dose, it is particularly suitable to image samples which contain both low and high attenuating regions. Furthermore, the extension of the technique to use more than two exposure levels is straightforward.This work is partially funded by the CD-TEAM Project, (CEN1T, Ministerio de Industrial, projects TEC2007-64731 and TEC2008-06715-C02-01, RETICRECAVA network and European Project FP7-201792

Grasp Exploration for 3D Object Shape Representation using Probabilistic Map

Abstract. In this work it is shown the representation of 3D object shape acquired from grasp exploration. Electromagnetic motion tracking sensors are used on the fingers for object contour following to acquire the 3D points to represent its shape using a probabilistic volumetric map. The object frame of reference is used for its representation. For that, the center of mass of the 3D object is found through the moments to define it. The occupancy of each individual voxel in the map is assumed to be independent from the other voxels occupancy. The posteriori achieved from Bayes ’ rule is the probability distribution on the occupations percentage for each voxel. The probabilistic map in a Cartesian system is converted to the spherical coordinate system for visualization with more details on its surface