In this study, we assess the impact of the reference tissue (frontal cortex, parietal cortex, cerebellum) on the magnitude of the binding potential obtained for the D2 receptor ligands [18F]N-methyl-benperidol and [123I]iodobenzamide in the rat striatum using dedicated small animal PET (“TierPET”), small animal SPECT (“TierSPECT”) or a conventional dual-head SPECT camera upgraded with multipinhole-collimators (“HiSPECT”). With all 3 cameras employed in our investigation, striatum-to-cerebellum ratios were consistently higher compared to striatum-to-cortex ratios. Moreover, frontal-cortex-to-cerebellum ratios tended to exceeded parietal-cortex-tocerebellum. Findings are in line with previous in vitro results, and show that quantitation of both striatal and cortical D2 receptor binding is feasible using small animal imaging devices including the novel HiSPECT. With HiSPECT, both striatum-to-cortex and striatum-to-cerebellum ratios of IBZM were higher compared to TierSPECT, which underlines the greater suitability of the higher resolving camera. Findings, moreover, imply that the reference tissue should be carefully chosen with respect to the intended investigation.

Purpose There is growing interest in the human sodium/iodide symporter (NIS) gene both as a molecular imaging reporter gene and as a therapeutic gene. Here, we show the feasibility of radioisotope therapy of neuroendocrine tumors. As a separate application of NIS gene transfer, we image NIS-expressing tumors with pinhole SPECT in living subjects. Methods Biodistribution studies and in vivo therapy experiments were performed in nude mice carrying stably NIS-expressing neuroendocrine tumor xenografts following i.v. injection of 131 I and 99m Tc pertechnetate. To show the usefulness of NIS as an imaging reporter gene, 99m Tc pertechnetate uptake was imaged in vivo using a clinical gamma camera in combination with a custom-made single pinhole collimator, followed by SPECT/small animal MRI data coregistration. Results NIS-expressing neuroendocrine tumors strongly accumulated 131 I and 99m Tc pertechnetate, as did thyroid, stomach, and salivary gland. The volume of NIS-expressing neuroendocrine tumors decreased significantly after therapeutic administration of 131 I or 99m Tc pertechnetate, whereas control tumors continued to grow. NIS-mediated uptake of 99m Tc pertechnetate could be imaged in vivo at high resolution with a clinical gamma camera equipped with a custom-made single pinhole collimator. High-resolution functional and morphologic information could be combined in a single three-dimensional data set by coregistration of SPECT and small animal MRI data. Lastly, we demonstrated a therapeutic effect of 99m Tc pertechnetate on NIS-expressing neuroendocrine tumors in cell culture and, for the first time, in vivo, thought to be due to emitted Auger and conversion electrons. Conclusions NIS-expressing neuroendocrine tumors efficiently concentrate radioisotopes, allowing for in vivo high-resolution small animal SPECT imaging as well as rendering possible successful radioisotope therapy of neuroendocrine tumors.

The list-mode format is particularly suitable for high-resolution tomographic systems, where the precision of the data have not to be compromised, but also claims new demands on data processing and image reconstruction. We apply a ray-tracing algorithm to calculate the three-dimensional coincidence response function. The algorithm is embedded in a list-mode reconstruction framework and has been previously assessed with data from the small-animal ClearPETtrade Neuro scanner. In order to compare and verify our algorithm, exemplary response functions are simulated using GATE. Long reconstruction time has been overcome by implementing a reconstruction framework for distributed computing. The implementation uses the message passing interface for communication and a simple master/slave model with dynamical load balancing of the slaves.

667 Objectives: Multi-Pinhole SPECT has become a proven modality in small-animal molecular imaging. Although the spatial-resolution capabilities of SPECT are greater than those of PET, the latter is generally considered the gold-standard nuclear imaging modality due to high-sensitivities. In this work, we present a high-throughput SPECT system that achieves submillimeter reconstructed resolutions while simultaneously approaching the sensitivity of PET. This increase in sensitivity combined with existing advantages of SPECT, e.g. tracer chemistry, cost and dual isotope capabilities, improves the standing of SPECT as a molecular imager. Methods: This camera, the NanoSPECT, consists of four detectors (215x230mm NaI, 33 PMTs, 2mm intrinsic resolution at 140keV) mounted on a high-precision gantry. Each detector is outfitted with an interchangeable 9-pinhole aperture for a total of 36 pinholes surrounding the field of view (FOV). Pinhole diameter and FOV are chosen in accordance with the prescribed application, e.g., mouse or rat imaging. The axial FOV is extended using helical scanning (user-selectable range from 20 to 290mm). Additionally, helical orbits provide an increase in the angular sampling. All told, this increase in sensitivity and sampling greatly improves image quality both for detection and estimation (quantification) as compared to standard SPECT acquisition techniques. Results: We will present a detailed description of the NanoSPECT along with numerous phantom studies and small-animal scans performed with an array of Tc-99m, I-123 and In-111 tracers. The results will address resolution, sensitivity, imaging times, injected dose and quantification results as well as multi-isotope and dynamic SPECT capabilities. Conclusions: We have developed a system with high resolution (submillimeter), high sensitivity (> 2000cps/MBq) and fast acquisition times (down to 1 minute) with quantification and dynamic scanning capabilities.

Die vorliegende Arbeit stellt die Leistungsparameter einer neuen Kleintierkamera (TierSPECT) vor, konstruiert zur In-vivo-Messung von Labortieren mit radioaktiv markierten Substanzen. Die Kamera besitzt im Streumedium eine tomographische Ortsauflösung von 2,7 mm und eine Sensitivität von 22 cps/MBq in einem nutzbaren Messfeld von 82 mm im Durchmesser. Die planare Homogenität beträgt 3,3%, die tomographische abstandsabhängig zwischen 3,2% und 3,5%. Die Abweichungen zwischen eingefüllter und gemessener Aktivitätskonzentration in einem zylindrischen 4-Kammer-Phantom waren geringer als 2,6%. Mittels eines neuartigen Rattenkopfphantoms mit Kammervolumina in der Größenordnung der Ortsauflösung (zwischen 0,065 ml und 0,19 ml) konnte demonstriert werden, dass mit dem TierSPECT unter Beachtung physiologischer Randbedingungen Studien am neostriatalen dopaminergen System der Ratte möglich sind. In-vivo-Studien mit [99mTc]diphosphonato-1,2-propandicarbonsäure (99mTc-DPD) und [123I]N-ω-fluorpropyl-2β-carbomethoxy-3β-(4-iodphenyl)-nortropan (123I-FP-CIT) zeigten, dass Knochenstoffwechsel und Dopamintransporterbindung mit dem TierSPECT visualisiert werden können. Dabei ermöglichte die Fusion von 99mTc-DPD- und 123I-FP-CIT-Bildern die eindeutige Differenzierung zwischen intra- und extrazerebralen Strukturen. Nach Gabe von Methylphenidat war eine deutliche Blockade des Dopamintransporters feststellbar.

This paper presents the performance of a new small-animal camera (TierSPECT) devised for the in vivo measurements of radiolabeled substances in small laboratory animals such as mice and rats. In a scatter medium, the camera has a tomographic spatial resolution of 2.87 mm and a sensitivity of 22 cps/MBq in a usable Field-of-View (FOV) with a diameter of 82 mm. The planar homogeneity amounts to 3.3%, the tomographic homogeneity lies between 3.2% and 3.5%. The deviation between filled and measured concentration of activity in a cylindrical 4-chamber-phantom was smaller than 2.6%. Using a novel rat head phantom with chamber volumes in the order of magnitude of the spatial resolution (between 0.065 ml and 0.19 ml) it could be demonstrated that studies of the rat neostriatal dopaminergic system are feasible under observance of physiological conditions. In vivo studies using [99mTc]diphosphonato-1,2-propandicarbonic acid (99mTc-DPD) and [123I]N-omega-fluoropropyl-2beta-carbomethoxy-3beta-(4-iodophenyl)-nortropane (123I-FP-CIT) proved that bone metabolism and dopamine transporter binding can be visualized with the TierSPECT. The fusion of 99mTc-DPD and 123I-FP-CIT images allowed the differentiation between intra- and extracerebral structures. Pretreatment with methylphenidate resulted in blockade of striatal dopamine transporter binding.

Conventionally, positron emission tomography data are sorted into sinograms prior to image reconstruction. This leads to a loss of spatial and temporal resolution due to histogramming of events. An alternative data representation is the so-called list-mode format which allows to store more attributes of each individual event, like involved detectors, energy, time, gantry state or even the depth of interaction. The format has the advantage, that it keeps the data in their highest possible temporal and spatial resolution. The additional number of attributes, if considered in the system model, can lead to a significant improvement in image quality. We develop a subsetized list-mode expectation-maximization image reconstruction with a ray-tracing technique to compute an enhanced system model. The algorithm approximates the three-dimensional coincidence response function for two arbitrarily oriented cubic detector elements, incorporated into crystal matrices. The geometry of the involved detector modules is evaluated at event time, tracing the ray paths of gamma quanta from one detector to the other through the field of view. The algorithm has been assessed using list-mode data for the ClearPET/spl trade/ Neuro, and is compared to a standard ordered-subset expectation-maximization reconstruction method for projections.

This study assessed [123I]iodobenzamide binding to the rat dopamine D2 receptor in competition with haloperidol and endogenous dopamine using a high-resolution small animal SPECT.

The aim of this study was to investigate the feasibility of assessing dopamine transporter binding after treatment with methylphenidate in the rat using a recently developed high-resolution small animal single-photon emission computed tomograph (TierSPECT) and [123I]FP-CIT.

Small field-of-view PET and SPECT cameras for e.g. animal measurements gained an important role in the development of new camera techniques. In order to achieve both a good spatial and energy resolution a high number of scintillation photons have to reach the photocathode of a photomultiplier tube. This paper deals with the light output of different surface treatments and reflectors at CsJ(Na) crystal needles by simulations and measurements.The measurements using different geometries and surfaces of CsJ(Na) needles showed a high influence of the surface treatment and choice of the external reflector on the photoelectron output and energy resolution of crystal-matrix based camera system. The simulation program DETECT produces probable unreliable results with most of the possible surface models, but seem to work in a proper range when using the PAINT or the GROUND model.