A. Motta

An integrated PET-SPECT small animal imager: preliminary results

The authors have successfully built and characterised a small animal PET based on 4 rotating detectors with a spatial resolution <2 mm over its field of view and a sensitivity of 640 cps//spl mu/Ci at the centre. The scanner is based on four matrices of 400 YAP:Ce finger crystals (2/spl times/2/spl times/30 mm/sup 3/ each) coupled to Position Sensitive PhotoMultipliers (Hamamatsu R2486-06.) The authors have now applied two high resolution collimators to two opposite detectors, hence realising an integrated PET-SPECT scanner for small animals. The collimators are made of lead with 20 mm long, 0.6 mm hexagonal holes with 0.15 mm septa. The read-out and data acquisition system are handled by NIM-CAMAC standard electronics. The Field Of View (FOV) of the tomograph has a diameter of 4 cm and an axial length of 4 cm in both PET and SPECT configuration which is appropriate for mice and rat studies.

Custom breast phantom for an accurate tumor SNR analysis

The capability of the scintimammography to diagnose subcentimeters sized tumors was increased by the employment of a dedicated gamma camera. The introduction of small field of view camera, based on pixellated scintillation array and position sensitive photomultiplier, allowed to enhance the geometric spatial resolution and contrast of the images due to reduced collimator-tumor distance. The aim of this paper is to investigate the realistic possibility of T1a tumors detection (/spl sim/5 mm size) by comparing the signal-to-noise ratio (SNR) values obtained by different imagers. To this end, we have utilized a self-designed solid breast phantom with different sized hot spots (tumors). The phantom consists of seven disks with different thickness, molded from resin epoxy activated with Co/sup 57/ isotope. The overlapped disks represent a pendula breast with about 800 cc volume. Hot spots have not wall. One disk has holes to fit the hot spots representing the different sized lesions. The imagers utilized were: a standard Anger Camera and three different cameras based on scintillator array, CsI(Tl) or NaI(Tl), coupled to position sensitive photomultiplier with different technologies, to make detectors with field of view of 3 and 5 inch. The experimental results are supported by Monte Carlo simulation. It was highlighted how spatial resolution is a predominant element in tumor visibility and how background causes a reduction of the image contrast. All gamma cameras show close results at SNR values less than 10 and a full detectability of 8 mm tumor size. However, the results show the 5 mm tumor size is lower detection limit for all cameras.

YAP-(S)PET small animal scanner: Quantitative results

The University of Ferrara YAP-(S)PET scanner is currently being employed in small animal SPECT studies, with /sup 99m/Tc labeled radiotracers, with the goal of obtaining quantitative activity measurements from region of interest (ROI) analysis of reconstructed images of rats. The measurements will be compared directly with traditional ex vivo measurement of activity with gamma counters. To achieve this goal, the scanner was calibrated relative to a standard Isodose dose calibrator which was calibrated with various certified activity sources. The calibration factor K was defined as the ratio of the activity measured with the Isodose (MBq) and the image count rate (cps). We find K = 0.1346 /spl plusmn/ 0.0008 MBq/cps, with good linearity over a wide range of activities (9-88 MBq). With the calibrated scanner we compared results of activity measurements from images of whole-rat heart acquisitions versus excised hearts. We found good agreement between the two measurements.

First in vivo studies on rats with the YAPPET scanner

At Ferrara University the authors have built a dedicated 3-D PET scanner (YAPPET) with a very high spatial resolution and sensitivity as necessary for radiopharmaceutical studies on rats and mice. In collaboration with the Institute H.S. Raffaele in Milano the authors have performed both distribution and dynamical uptake studies of various radioactive tracers in rats. They have performed tomographic studies after injecting live rats with FDG and FESP labeled with /sup 18/F, with FE-CIT and Flumazenil labeled with /sup 11/C, and with /sup 18/F. The /sup 18/F-FDG, /sup 18/F-FESP and /sup 11/C-FE-CIT images show the different distribution of the various tracers in the rat brain. The /sup 18/F was injected for imaging the rat skeleton. In addition, the authors studied the uptake and washout curve of /sup 11/C Flumazenil in the rat brain from tomographic images.

A small-animal PET design using SiPMs and Anger logic with intrinsic DOI

In this study a miniature, high-resolution detector head for a small-animal PET imaging system that has intrinsic depth of interaction (DOI) information is proposed. The design is hased upon the classic Anger camera principle, i.e. one detector module layer consists of a continuous slab of scintillator, viewed by a new type of compact silicon photodetector. The photodetector is the recently developed Silicon Photomultiplier (SiPM) that as well as being very compact has many other attractive properties: high gain at low bias voltage, excellent single-photoelectron resolution and fast timing. A detector head of 4/spl times/4 cm/sup 2/ in area is proposed, constructed from three module layers of the continuous detector described above. Here, a simulation study is carried out, using the Monte Carlo simulation package GEANT4. The simulation results are used to determine the performance of a single detector head and to optimize the geometry of the detector, resulting in a spatial resolution of up to /spl sim/0.6 mm full-width at half maximum (FWHM).

Latest achievements in PET techniques

Positron emission tomography (PET) has moved from a distinguished research tool in physiology, cardiology and neurology to become a major tool for clinical investigation in oncology, in cardiac applications and in neurological disorders. Much of the PET accomplishments is due to the remarkable improvements in the last 10 years both in hardware and software aspects. Nowadays a similar effort is made by many research groups towards the construction of dedicated PET apparatus in new emerging fields such as molecular medicine, gene therapy, breast cancer imaging and combined modalities. This paper reports on some recent results we have obtained in small animal imaging and positron emission mammography, based on the use of advanced technology in the field of scintillators and photodetectors, such as Position-Sensitive Detectors coupled to crystal matrices, combined use of scintillating fibers and Hybrid-Photo-Diodes readout, and Hamamatsu flat panels. New ideas and future developments are discussed.

Monte Carlo study and experimental measurements of breast tumor detectability with the YAP-PEM prototype

A prototype for positron emission mammography is under development within a collaboration of the Italian Universities of Pisa, Ferrara, Bologna and Roma. The device is composed of two stationary detection heads, each with an active area of 6 cm /spl times/ 6 cm, made of 30/spl times/30 YAP:Ce finger crystals of 2 mm /spl times/ 2 mm /spl times/ 30 mm. The EGSnrc Monte Carlo code has been used to perform a complete simulation of this camera. We have used a fast three-dimensional iterative algorithm (30 s per iteration on a PC-Pentium III 800 MHz processor) for image reconstruction. The performed study indicates that tumors of 5 mm diameter, i.e., 0.065 cm/sup 3/ volume, with 37 kBq/cm/sup 3/ (1 /spl mu/Ci/cm/sup 3/) specific activity embedded in a breast active phantom, are detectable in 10 minutes for a 10:1 tumor/background ratio with an 8.7 Signal-to-Noise Ratio value. Experimental measurements with the small animal tomograph YAP-PET have validated the Monte Carlo predictions.

Calibration and Performance of the Fully Engineered YAP-(S)PET Scanner for Small Rodents

Functional imaging of small animals,such as mice and rats,using high-performance positron emission tomography (PET)and single-photon emission tomography (SPECT), is becoming a valuable tool for studying animal models of human disease. The possibility to use either PET or SPECT allows the scientist to exploit the advantages of both techniques, e.g., the wide range of easily accessible single-photon radiotracers for SPECT and the exquisite performance of PET. The combination of PET and SPECT techniques for small-animal studies could offer the unique possibility of developing new and interesting protocols for the investigation of many biological phenomena more effectively than with PET or SPECT modality alone.

Quantitative YAP-(S)PET small animal scanner: preliminary results

We have successfully built and characterized small animal PET scanner based on 4 rotating planar detector heads. Each detector module is composed of a matrix of 400 YAP:Ce finger crystals (2/spl times/2/spl times/30 mm/sup 3/ each) directly coupled to position sensitive photomultipliers (Hamamatsu R2486-06). By applying two high resolution collimators to two opposite detectors we realised an integrated PET-SPECT scanner for small animals. At present, at the Department of Experimental and Clinical Medicine of the University of Ferrara, the scanner is employed in small animal SPECT studies with /sup 99m/Tc labeled radiotracers dedicated to obtain quantitative activity measurement in region of interest (ROI) directly from a reconstructed image of a in-vivo rat, with respect to the traditional ex-vivo measurement of activity with gamma counters. To achieve this goal, the scanner was calibrated referring it to a Isodose dose calibrator based on Geiger-Muller counters which previously underwent an absolute calibration with a known activity source. Preliminary results on quantitative tomographic heart perfusion and planar heart biokinetics studies are reported.