Abstracts in subsequent orders for other testing (i.e., proteinuria) were not significant. Conclusions: Following implementation of eGFR reporting, the likelihood of referral to nephrologists increased though the number of nephrology clinic visits did not. Clinicians who were younger, family medicine, and worked full time were more likely to increase referrals after eGFR. Background/Aims: The substantia nigra (SN) selectively degenerates in Parkinson's disease (PD). Prior MRI studies of SN have

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... used manual segmentation to make quantitative measurements, an approach with inherently limited accuracy. Here we used an in-house optimized neuromelanin MRI (NM-MRI) protocol, and a novel semi-automated segmentation method to investigate changes in SN associated with PD. The relationship between MRI measures and orthostatic hypotension, a phenotypic feature of PD, was also examined. Methods: Eight controls and 10 PD patients were scanned on a 3.0 Tesla Siemens MRI scanner using our optimized NM-MRI sequence (2D gradient echo sequence with magnetization transfer contrast preparation pulse) and processing protocol. A contrast to noise ratio (CNR) binary map was generated, identifying voxels with intensity >3 SD above the mean intensity. SN ROIs were defined on the binary map based on the location of the high intensity voxels, which defined its borders discretely. Mean CNR and number of voxels (volume) were then obtained for the SN. Statistical analysis was performed with SPSS. Results: Comparison of means revealed that both CNR and volume of the SN were significantly lower in the PD group than in controls (CNR: P = 0.044; volume: P = 0.028). Each of the two MRI measures were significantly correlated with the orthostatic blood pressure drop (Pearson's correlation, CNR: r = -0.725, P = 0.001; volume: r = -0.661, P = 0.003). Conclusions: As hypothesized, both CNR and volume of SN were significantly lower in the PD group than in controls. Since SN degenerates in PD, this NM-MRI approach appears to detect PD-associated degeneration of SN in vivo. Also as hypothesized, the MRI measures had a significant negative association with orthostatic blood pressure drop, a phenotypic characteristic of PD. These results indicate that the MRI measures presented here represent promising candidate PD biomarkers. Longitudinal studies are warranted to test this approach as part of an early diagnosis strategy and as a potential clinical trial outcome measure.