The microPET Focus 120 scanner is a third-generation animal PET scanner dedicated to rodent imaging. Here, we report the results of scanner performance testing. Methods: A 68 Ge point source was used to measure energy resolution, which was determined for each crystal and averaged. Spatial resolution was measured using a 22 Na point source with a nominal size of 0.25 mm at the system center and various off-center positions. Absolute sensitivity without attenuation was determined by extrapolating the data measured using an 18 F line source and multiple layers of absorbers. Scatter fraction and counting rate performance were measured using 2 different cylindric phantoms simulating rat and mouse bodies. Sensitivity, scatter fraction, and noise equivalent counting rate (NECR) experiments were repeated under 4 different conditions (energy window, 250;750 keV or 350;650 keV; coincidence window, 6 or 10 ns). A performance phantom with hot-rod inserts of various sizes was scanned, and several animal studies were also performed. Results: Energy resolution at a 511-keV photopeak was 18.3% on average. Radial, tangential, and axial resolution of images reconstructed with the Fourier rebinning (FORE) and filtered backprojection (FBP) algorithms were 1.18 (radial), 1.13 (tangential), and 1.45 mm full width at half maximum (FWHM) (axial) at center and 2.35 (radial), 1.66 (tangential), and 2.00 mm FWHM (axial) at a radial offset of 2 cm. Absolute sensitivities at transaxial and axial centers were 7.0% (250;750 keV, 10 ns), 6.7% (250;750 keV, 6 ns), 4.0% (350;650 keV, 10 ns), and 3.8% (350;650 keV, 6 ns). Scatter fractions were 15.9% (mouse phantom) and 35.0% (rat phantom) for 250;750 keV and 6 ns. Peak NECR was 869 kcps at 3,242 kBq/mL (mouse phantom) and 228 kcps at 290 kBq/mL (rat phantom) at 250;750 keV and 6 ns. Hot-rod inserts of 1.6-mm diameter were clearly identified, and animal studies illustrated the feasibility of this system for studies of whole rodents and mid-sized animal brains. Conclusion: The results of this independent field test showed the improved physical characteristics of the F120 scanner over the previous microPET series systems. This system will be useful for imaging studies on small rodents and brains of larger animals.Key Words: small-animal PET; performance measurement; instrumentation; molecular imaging; small-animal imaging PETi s a noninvasive, diagnostic imaging technique that produces functional or biochemical images of a body (1-4). Although PET is regarded as a powerful translational research tool between animal models and human clinical applications (5-8), clinical PET scanners used for human studies do not have satisfactory spatial resolution or sensitivity for studies of small animals, such as rats and mice (9-11). Because the linear dimensions of organs in these animals are 10 or more times smaller in each dimension than in human subjects, the spatial resolution of a suitable PET scanner must be similarly higher and the voxel size should also be reduced according to sampling theory (9,10). T...

Purpose: To evaluate the usefulness of 3 ¶-deoxy-3 ¶-[18 F]fluorothymidine (FLT)-positron emission tomography (PET) for predicting response and patient outcome of gefitinib therapy in patients with adenocarcinoma of the lung. Experimental Design: Nonsmokers with advanced or recurrent adenocarcinoma of the lung were eligible. FLT-PET images of the thorax were obtained before and 7 days after the start of gefitinib (250 mg/d) therapy, the maximum standardized uptake values (SUVmax) of primary tumors were measured, and the percent changes in SUVmax were calculated. After 6 weeks of therapy, the responses were assessed by computed tomography of the chest. Results: Among 31 patients who were enrolled, we analyzed 28 patients for whom we had complete data. Chest computed tomography revealed partial response in 14 (50%), stable disease in 4 (14%), and progressive disease in 10 (36%) after 6 weeks of treatment. Pretreatment SUVmax of the tumors did not differ between responders and nonresponders. At 7 days after the initiation of therapy, the percent changes in SUVmax were significantly different (-36.0 F 15.4% versus 10.1 F 19.5%; P < 0.001). Decrease of >10.9% in SUVmax was used as the criterion for predicting response. The positive and negative predictive values were both 92.9%. The time to progression was significantly longer in FLT-PET responders than nonresponders (median, 7.9 versus 1.2 months; P = 0.0041). Conclusion: FLT-PETcan predict response to gefitinib 7 days after treatment in nonsmokers with advanced adenocarcinoma of the lung.The change in tumor SUVmax obtained by FLT-PETseems to be a promising predictive variable.Morphologic imaging techniques such as computed tomography (CT) have been standard methods for assessing tumor response to treatment. Changes in size, however, are often delayed; hence, morphologic imaging is usually repeated after at least 6 weeks of therapy. This causes difficulties in assessing the early treatment response and hinders rapid decisions by clinicians regarding a change in therapy for nonresponders. Moreover, in the case of cytostatic agents, tumors may not regress radiologically despite effective treatment. These limitations could be overcome by using functional imaging techniques such as positron emission tomography (PET), because metabolic and physiologic changes in the tumor are likely to precede changes in size (1). The most widely used PET tracer is [18 F]fluorodeoxyglucose (FDG), which reflects cell metabolism. However, FDG is not highly tumor specific and is also taken up by inflammatory cells such as macrophages (2).Recently, 3 ¶-deoxy-3 ¶-[ 18 F]fluorothymidine (FLT) was introduced as a PET tracer for imaging tumor proliferation. FLT is phosphorylated by thymidine kinase 1, the key enzyme of the salvage pathway of DNA synthesis, and then trapped in the cell with little further metabolism (3). Thymidine kinase 1 is selectively up-regulated during the S phase of the cell cycle (4). Therefore, FLT uptake is dependent on cell proliferation. In lung tumors, FLT up...

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