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Regression models have been widely studied to investigate whether multimodal neuroimaging measures can be used as effective biomarkers for predicting cognitive outcomes in the study of Alzheimer's Disease (AD). Most existing models overlook the interrelated structures either within neuroimaging measures or between cognitive outcomes, and thus may have limited power to yield optimal solutions. To address this issue, we propose to incorporate an L21 norm and/or a group L21 norm (G21 norm) in the regression models. Using ADNI-1 and ADNI-GO/2 data, we apply these models to examining the ability of structural MRI and AV-45 PET scans for predicting cognitive measures including ADAS and RAVLT scores. We focus our analyses on the participants with mild cognitive impairment (MCI), a prodromal stage of AD, in order to identify useful patterns for early detection. Compared with traditional linear and ridge regression methods, these new models not only demonstrate superior and more stable predictive performances, but also identify a small set of imaging markers that are biologically meaningful.

Background It is not known if the loads and motions reported for instrumented knees are generalizable to a larger population of total knee replacement (TKR) patients. The purpose of this study is to: 1) report axial implant force data for chair and stair activities for a population of cruciate-retaining TKR patients and 2) compare the population forces to those measured with instrumented TKRs. Methods Twenty-three subjects with a cruciate-retaining TKR underwent motion analysis during stair ascending, stair descending, chair sitting, and chair rising activities after informed consent in this IRB approved study. Axial TKR forces were calculated using a previously validated computational model. Differences between the mean and variability of population instrumented TKR peak forces and force impulses were tested using t-tests and Levene’s test. Results Peak axial forces were 3.06, 2.74, 2.65, and 2.60 kN for stair ascent, stair descent, chair rising, and chair sitting, respectively. Force impulses were 123.3, 123.4, 153.5, and 154.0 kN*% activity cycle for stair ascent, stair descent, chair sitting, and chair rising, respectively. Population TKR and instrumented TKR peak forces were different for stair ascent (p=0.03) and stair descent (p=0.03) in the second half of the activity cycles. The variability of the peak forces and impulses were not different (p=0.106 to p=0.99) Conclusion The forces and motions presented in this study represent cruciate-retaining TKR patients and could be used for displacement-driven knee wear testing. The forces are similar to those in the literature from instrumented prostheses of an ultra-congruent cruciate-sacrificing TKR.

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