The measurement of BMD by dual-energy X-ray absorptiometry (DXA) is the ''gold standard'' for diagnosing osteoporosis but does not directly reflect deterioration in bone microarchitecture. The trabecular bone score (TBS), a novel gray-level texture measurement that can be extracted from DXA images, correlates with 3D parameters of bone microarchitecture. Our aim was to evaluate the ability of lumbar spine TBS to predict future clinical osteoporotic fractures. A total of 29,407 women 50 years of age or older at the time of baseline hip and spine DXA were identified from a database containing all clinical results for the Province of Manitoba, Canada. Health service records were assessed for the incidence of nontraumatic osteoporotic fracture codes subsequent to BMD testing (mean follow-up 4.7 years). Lumbar spine TBS was derived for each spine DXA examination blinded to clinical parameters and outcomes. Osteoporotic fractures were identified in 1668 (5.7%) women, including 439 (1.5%) spine and 293 (1.0%) hip fractures. Significantly lower spine TBS and BMD were identified in women with major osteoporotic, spine, and hip fractures (all p < 0.0001). Spine TBS and BMD predicted fractures equally well, and the combination was superior to either measurement alone ( p < 0.001). Spine TBS predicts osteoporotic fractures and provides information that is independent of spine and hip BMD. Combining the TBS trabecular texture index with BMD incrementally improves fracture prediction in postmenopausal women. ß

The National Electrical Manufacturers Association (NEMA) standard NU 4-2008 for performance measurements of small-animal tomographs was recently published. Before this standard, there were no standard testing procedures for preclinical PET systems, and manufacturers could not provide clear specifications similar to those available for clinical systems under NEMA NU 2-1994 and 2-2001. Consequently, performance evaluation papers used methods that were modified ad hoc from the clinical PET NEMA standard, thus making comparisons between systems difficult. Methods We acquired NEMA NU 4-2008 performance data for a collection of commercial animal PET systems manufactured since 2000: micro- PET P4, microPET R4, microPET Focus 120, microPET Focus 220, Inveon, ClearPET, Mosaic HP, Argus (formerly eXplore Vista), VrPET, LabPET 8, and LabPET 12. The data included spatial resolution, counting-rate performance, scatter fraction, sensitivity, and image quality and were acquired using settings for routine PET. Results The data showed a steady improvement in system performance for newer systems as compared with first-generation systems, with notable improvements in spatial resolution and sensitivity. Conclusion Variation in system design makes direct comparisons between systems from different vendors difficult. When considering the results from NEMA testing, one must also consider the suitability of the PET system for the specific imaging task at hand.

We extend the multiple-scattering theory for elastic waves by taking into account the full vector character. The formalism for both the band structure calculation and the reflection and transmission calculations for finite slabs is presented. The latter is based on a double-layer scheme which obtains the reflection and transmission matrix elements for the multilayer slab from those of a single layer. As a demonstration of applications of the formalism, we calculate the band structures of elastic waves propagating in a three-dimensional periodic arrangement of spherical particles and voids, as well as the transmission coefficients through finite slabs. In contrast with the plane-wave method, the multiple-scattering approach exhibits advantages in handling specialized geometries ͑spherical geometry in the present case͒. We also present a comparison between theory and ultrasound experiment for a hexagonal-close-packed array of steel balls immersed in water. Excellent agreement is obtained.

Utilizing the publicly available neuroimaging database enabled by Alzheimer’s disease Neuroimaging Initiative (ADNI; http://adni.loni.usc.edu/), we have compared the performance of automated classification algorithms that differentiate AD vs. normal subjects using Positron Emission Tomography (PET) with fluorodeoxyglucose (FDG). General linear model, scaled subprofile modeling and support vector machines were examined. Among the tested classification methods, support vector machine with Iterative Single Data Algorithm produced the best performance, i.e., sensitivity (0.84) × specificity (0.95), by 10-fold cross-validation. We have applied the same classification algorithm to four different datasets from ADNI, Health Science Centre (Winnipeg, Canada), Dong-A University Hospital (Busan, S. Korea) and Asan Medical Centre (Seoul, S. Korea). Our data analyses confirmed that the support vector machine with Iterative Single Data Algorithm showed the best performance in prediction of future development of AD from the prodromal stage (mild cognitive impairment), and that it was also sensitive to other types of dementia such as Parkinson’s Disease Dementia and Dementia with Lewy Bodies, and that perfusion imaging using single photon emission computed tomography may achieve a similar accuracy to that of FDG-PET.

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Non-invasive imaging technologies are opening up new windows into mouse biology. We have developed a mouse imaging system that integrates positron emission tomography (PET) with x-ray computed tomography (CT), allowing simultaneous anatomic and molecular imaging in vivo with the potential for precise registration of the two image volumes. The x-ray system consists of a compact mini-focal x-ray tube and an amorphous selenium flat panel x-ray detector with a low-noise CMOS readout. The PET system uses planar arrays of lutetium oxyorthosilicate scintillator coupled to position-sensitive photomultiplier tubes. We describe the design of this dual-modality imaging system and show, for the first time, simultaneously acquired PET and CT images in a phantom and in mice.

We characterize a compact MR-compatible PET insert for simultaneous preclinical PET/MRI. Although specifically designed with the strict size constraint to fit inside the 114-mm inner diameter of the BGA-12S gradient coil used in the BioSpec 70/20 and 94/20 series of small-animal MRI systems, the insert can easily be installed in any appropriate MRI scanner or used as a stand-alone PET system. The insert consists of a ring of 16 detector-blocks each made from depth-of-interaction-capable dual-layer-offset arrays of cerium-doped lutetium-yttrium oxyorthosilicate crystals read out by silicon photomultiplier arrays. Scintillator crystal arrays are made from 22 × 10 and 21 × 9 crystals in the bottom and top layers, respectively, with respective layer thicknesses of 6 and 4 mm, arranged with a 1.27-mm pitch, resulting in a useable field of view 28 mm long and about 55 mm wide. Spatial resolution ranged from 1.17 to 1.86 mm full width at half maximum in the radial direction from a radial offset of 0-15 mm. With a 300- to 800-keV energy window, peak sensitivity was 2.2% and noise-equivalent count rate from a mouse-sized phantom at 3.7 MBq was 11.1 kcps and peaked at 20.8 kcps at 14.5 MBq. Phantom imaging showed that features as small as 0.7 mm could be resolved. F-FDG PET/MR images of mouse and rat brains showed no signs of intermodality interference and could excellently resolve substructures within the brain. Because of excellent spatial resolvability and lack of intermodality interference, this PET insert will serve as a useful tool for preclinical PET/MR.

Lutetium oxyorthosilicate (LSO)-or lutetium-yttrium oxyorthosilicate (LYSO)-based PET scanners have intrinsic radioactivity in the scintillator crystals due to the presence of 176 Lu, which decays by b-emission followed by one or more prompt g-ray emissions. This leads to intrinsic true counts that can influence the image when scanning low levels of activity. An evaluation of the effects of this intrinsic activity for low levels of activity and different energy windows is performed on an LSO-based small-animal PET scanner. Methods: Intrinsic count rate and sensitivity were measured for a range of lower-level discriminators (LLDs) ranging from 100 to 750 keV. The noise equivalent count rate (NECR) as a function of LLD for activity levels from 100 Bq to 100 kBq was estimated using a combination of measurement and previously published data for this scanner. Phantom imaging was performed using three 68 Ge sources of strength 55, 220, and 940 Bq and LLD levels of 250, 350, and 400 keV. The images were assessed using a contrast-to-noise ratio (CNR) analysis and by comparing the observed ratio of source activities to the true ratio value. Results: The intrinsic true count rate is reduced from 940 counts per second (cps) for a 250-to 750-keV energy window to ,2 cps for a 400-to 750-keV window. There is a corresponding 2-fold drop in sensitivity for detected true events for external positron sources for these 2 energy windows. The NECR versus LLD curves showed a highly peaked shape, with the optimum LLD being approximately 425 keV. The phantom image results were dominated by the intrinsic true counts when an energy window of 250-750 keV was used. The intrinsic true counts were almost completely removed by raising the LLD to 400 keV. The CNR for each of the sources was higher for the narrow energy window and the 55 Bq could be easily visualized in images acquired with LLD levels of 350 and 400 keV but not when the 250-keV LLD was used. Images acquired with an LLD of 400 keV and reconstructed with 2-dimensional filtered backprojection were the most quantitatively accurate. Conclusion: It is possible to visualize sources of ,1 kBq in LSO-based animal PET systems by raising the LLD to 400 keV to exclude the majority of the counts due to the intrinsic activity present in the LSO. PET scanner performance is usually optimized for a specific imaging task based on the results of noise equivalent count rate (NECR) measurements (1-4). The usual measure reported is the peak NECR value and the activity at which the peak occurs and, in general, the energy window is chosen to maximize the value of the peak NECR. When the imaging task involves very low levels of injected activity, such as cell trafficking studies (5) or gene expression imaging (6), the scanner is operating at a count rate far less than the peak NECR value.When low activity levels are being imaged, there is a very limited number of true counts that can be acquired so that one would consider using a wider energy window to increase the sensitivity (7). However, the choice...