Simultaneous super-resolution estimation of single-molecule position and orientation with minimal photon fluxes.

The orientation of a single molecule provides valuable information on fundamental biological processes. We report a technique for the simultaneous estimation of single-molecule 2D position and 2D orientation with ultra-high localization precision (∼2-nm precision with ∼500 photons under a typical 100-nm diameter of excitation beam pattern), which is also compatible with tracking in living cells. In the proposed method, the theoretical precision limits are calculated, and the localization and orientation performance along with potential applications are explored using numerical simulations. Compared to other camera-based orientation measurement methods, it is confirmed that the proposed method can obtain reasonable estimates even under very weak signals (∼15 photons). Moreover, the maximum likelihood estimator (MLE) is found to converge to the theoretical limit when the total number of photons is less than 100.

Timing of preemptive vascular access placement: do we understand the natural history of advanced CKD?: an observational study.

BACKGROUND: Little is known about the targets and expectations of practicing nephrologists with regard to timing of preemptive AV access surgery and how these relate to actual observed practice patterns in clinical care. METHODS: We administered a 8-question survey to assess nephrologists' expectations for preemptive vascular access placement to 53 practicing nephrologists in California. We performed a retrospective chart review of 116 patients who underwent preemptive vascular access placement at a large academic medical center and examined progression to ESRD. RESULTS: According to our survey of nephrologists, most aimed to have preemptive vascular access created about 6 months prior to start of ESRD or when the chances of ESRD within the next year is two-thirds or greater. The estimated GFR level at which they believe match these conditions is approximately 18 ml/min/1.73 m2. Among the 116 patients with CKD who underwent preemptive vascular access creation, the mean estimated GFR at the time of access creation was 16.1 (6.8) ml/min/1.73 m2. Only 57 out of the 116 patients (49.1%) patients initiated maintenance HD within 1 year after surgery. CONCLUSIONS: In our study, most nephrologists aim for preemptive vascular access surgery approximately 6 months prior to the start of HD. However in fact, only approximately 50% of patients who underwent preemptive vascular access surgery started HD within 1 year. Better tools are needed to predict the natural history of advanced CKD.