P-038 MRI SYSTEM TRACKING AND CORRECTION USING THE ADNI PHANTOM Jeff L. Gunter 1 , Matt A. Bernstein 1 , Paula J. Britson 1 , Joel P. Felmlee 1 , Norbert Schuff 2 , Michael Weiner 2 , Clifford R. Jack, Jr. 1 , 1 Mayo Clinic and Foundation, Rochester, MN, USA; 2 VA Med Center, San Francisco, CA, USA. Contact e-mail: gunter.jeffrey@mayo.edu Background: MRI systems used primarily for clinical practice are also used in clinical imaging research. Clinical considerations typically drive scanner maintenance schedules. The Alzheimer’s Disease Neuroimaging Initiative (ADNI) is a large multi-center natural history study. Approximately 800 subjects will be tracked longitudinally. Employing 80 different scanners over five years, upgrades and recalibrations will be unavoidable. Objective(s): To track and compensate for scanner upgrades in serial image data using a phantom. Methods: As part of the ADNI MRI scanning protocol a phantom is scanned immediately after each human study. Comparison of the phantom as imaged to the physically constructed phantom allows the determination of dimensional scale factors in 3D which may be used to track scanner perfor- mance. The same scalings may be applied to the human images. Results: For each phantom scan on a single representative 1.5T scanner, the linear scale factors are plotted versus scan date (Figure 1). Ideal scale factors are unity. Dashed lines indicate maintenance or upgrade dates. Slow drifts are observed as well as discrete changes associated with upgrade/maintenance. If the phan- tom is capturing scanner drift then application of the scaling factors to human images should improve the spatial consistency of the images. Co-registration (including scaling) of pairs of scans for individual subjects with and without phantom-based scaling was carried out. For each subject, pairs of images were acquired on a single scanner. Data from 19 pairs of images acquired on multiple 1.5T scanners from a single MRI vendor are shown in histograms of co-registration scaling factors in the logical X (R/L) direction for pairs of images with (without) phantom scaling correction (Figure 2). The distribution of scale factors after phantom-based correction is narrower and centered closer to unity than the uncorrected distribution. Similar results (not shown) are found for the remaining two cardinal directions. Phantom based correction reduces the width (RMS) of the co-registration scale factor distributions by one quarter to one half. Conclusions: The ADNI phantom may be used to capture longi- tudinal changes in scanner performance. Our findings suggest that the phantom reduces measurement error, and thus may be expected to reduce variance in clinical trials and increase power. P-039 TELOMERE SHORTENING AND/OR “ABSENCE” MAY INDICATE DEMENTIA/AD STATUS IN OLDER INDIVIDUALS WITH DOWN SYNDROME Edmund C. Jenkins 1 , Lingling Ye 1 , Hong Gu 1 , Samantha A. Ni 1 , Milen Velinov 1 , Deborah Pang 1 , Darlynne A. Devenny 1 , Warren B. Zigman 1 , Nicole Schupf 2 , Wayne P. Silverman 3 , 1 New York State Institute for Basic Research in Developmental Disabilities (NYS IBRDD), Staten Island, NY, USA; 2 The Taub Institute for Research on Alzheimer’s Disease and the Aging Brain, Columbia University, New York, NY, USA; 3 The Kennedy Krieger Institute and Johns Hopkins University School of Medicine, Baltimore, MD, USA. Contact e-mail: ecjenkins@erols.com Background: We have previously reported that cultured T-lymphocytes from women with Down syndrome (DS) and Alzheimer’s Disease (AD)/ dementia have shorter telomeres, chromosome ends consisting of highly conserved TTAGGG repeats, than their peers without AD/dementia (Neu- robiol Aging 2006;27:942). Objective: To extend our previous findings and to determine if any measures of telomere length could provide diag- nostically useful information regarding AD status. Methods: Adults with Down syndrome were classified with respect to dementia status based upon recommended criteria (Amer J Ment Retard 2004;109:111). Cases were age- and sex-matched such that one individual within each pair had either AD/dementia or a status comparable (in many respects) to mild cognitive impairment (MCI) in the general population, abbreviated here as MCI-DS, and the other did not. Forty T-lymphocyte metaphases (20) and interphases (20) per individual were analyzed to detect shorter or absent telomeres as indicated by fluorescent light intensity differences after FISH with a pep- tide nucleic acid (PNA) probe. All chromosomes, as well as some single chromosomes, were examined. Results: Significantly shorter telomeres were found in a total of 15 people (our original sample plus six new cases) with AD/dementia and were also observed in four females with MCI-DS. Interestingly, we have also found that a simple count of the total number of signals from all telomeres is reduced in people with AD/Dementia. Finally, we found that single chromosomes, especially chromosome 21, have shorter telomeres in people with DS/AD/Dementia and MCI-DS and, most importantly, there was no overlap in some measures between people with DS/AD/Dementia or MCI-DS versus peers classified as “not de- mented.” Conclusions: Findings that telomere length can distinguish among groups with and without dementia/MCI-DS suggest that we may have found a biomarker for AD. However, we need to confirm and extend these results before making firm conclusions. Should replication be suc- cessful, it could provide a basis for development of a diagnostic procedure with both high sensitivity and specificity, permitting future treatments to be targeted most effectively. S109 Posters: P-038