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We developed a cost-effective SPECT scanner prototype (rSPECT) for in vivo imaging of rodents based on small-area gamma cameras. Each detector consists of a position-sensitive photomultiplier tube (PS-PMT) coupled to a 30 30 NaI(Tl) scintillator array and electronics attached to the PS-PMT sockets for adapting the detector signals to an in-house developed data acquisition system. The detector components are enclosed in a leadshielded case with a receptacle to insert the collimators. System performance was assessed using 􀀀􀀀 􀀀 for a high-resolution parallel- hole collimator, and for a 0.75-mm pinhole collimator with a 60 aperture angle and a 42-mm collimator length. The energy resolution is about 10.7% of the photopeak energy. The overall system sensitivity is about and planar spatial resolution ranges from 2.4 mm at 1 cm source-to-collimator distance to 4.1 mm at 4.5 cm with parallel-hole collimators. With pinhole collimators planar spatial resolution ranges from 1.2 mm at 1 cm source-to-collimator distance to 2.4 mm at 4.5 cm; sensitivity at these distances ranges from 2.8 to . Tomographic hot-rod phantom images are presented together with images of bone, myocardium and brain of living rodents to demonstrate the feasibility of preclinical small-animal studies with the rSPECT. This work was supported in part 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, program ARTEMIS S2009/DPI-1802, Comunidad de Madrid, and the RECAVA-RETIC Network Publicado

Proceeding of: 2008 IEEE Nuclear Science Symposium Conference Record (NSS '08), Dresden, Germany, 19-25 October 2008 We propose a retrospective respiratory gating algorithm to generate dynamic CT studies. To this end, we compared three different methods of extracting the respiratory signal from the projections of small-animal cone-beam computed tomography (CBCT) scanners. Given a set of frames acquired from a certain axial angle, subtraction of their average image from each individual frame produces a set of difference images. The respiratory signals were extracted by analyzing the shape of the histogram of these difference images: we calculated the first four central and non-central moments. However, only odd-order moments produced the desired breathing signal, as the even-order moments lacked information about the phase. Each of these curves was compared to a reference signal recorded by means of a pneumatic pillow. Given the similar correlation coefficients yielded by all of them, we selected the mean to implement our retrospective protocol. Respiratory phase bins were separated, reconstructed independently and included in a dynamic sequence, suitable for cine playback. We validated our method in 5 adult rat studies by comparing profiles drawn across the diaphragm dome, with and without retrospective respiratory gating. Results showed a sharper transition in the gated reconstruction, with an average slope improvement of 60.7%. This project was supported by the CENIT Programme (Ministerio de Industria), CIBER CB07/09/0031 and RETICRECAVA (Ministerio de Sanidad y Consumo), and TEC2007-64731 TCM (Ministerio de Educaci6n y Ciencia).

Proceeding of: 2007 IEEE Nuclear Science Symposium Conference Record (NSS'07), Honolulu, Hawaii, USA, Oct. 27 - Nov. 3, 2007 The potential of PET imaging for pre-clinical studies will be fully realized only if repeatable, reliable and accurate quantitative analysis can be performed. The characteristic blurring of PET images due to positron range and non co-linearity, as well as random, pile-up and scatter contributions, that may be significant for fully 3D PET acquisitions of small animal, make it difficult their quantitative analysis. In this work specific activity versus specific counts in the image calibration curves for 3D-OSEM reconstructions from a commercially available small animal PET scanner are determined. Both linear and non-linear calibration curves are compared and the effect of corrections for random and scatter contributions are studied. To assess the improvement in the calibration procedure when scatter and random corrections are considered, actual data from a rat tumor pre- and postcancer therapy are analyzed. The results show that correcting for random and scatter corrections can increase the sensitivity of PET images to changes in the biological response of tumors by more than 15%, compared to uncorrected reconstructions. This work has been partially funded by projects TEC2004-07052-C02 of Ministerio de Educación y Ciencia and CD-TEAM, program CENIT, Ministerio de Industria, Spain. Part of the computations of this work were done at the '`High capacity cluster for physical techniques'' of the Faculty for Physical Sciences of the UCM, funded in part by the UE under the FEDER program and in part by the UCM.