Patient compliance limits the efforts of quality improvement initiatives on arteriovenous fistula maturation.

OBJECTIVE: Our institutional quality-improvement (QI) initiative instituted a well-defined office follow-up schedule after arteriovenous fistula (AVF) creation, including an office visit within 30 days, fistulogram within 40 days, if indicated, and a second office visit within 55 days. In addition, a patient liaison contacted patients and dialysis units to improve follow-up. The purpose of this study was to determine the effect of the QI initiative on patient compliance and overall time to AVF permission to cannulate. METHODS: We performed a retrospective review of patients undergoing first-time radiocephalic, brachiocephalic, and basilic vein transposition creation before the QI initiative (pre-QI group: January to April 2012) and during the QI period (QI group: January to April 2013). Categoric data were compared using χ(2) analysis, and nominal data were compared using the Student t-test. RESULTS: We reviewed 198 first-time AVF creations in patients (57% male) with a mean age of 61 years. Demographics and comorbidities between the pre-QI and QI groups were similar. Compliance with the first 30-day postoperative appointment increased significantly after the QI initiative, from 48% in the pre-QI group to 65% in the QI group (P = .015). Yet, the QI initiative did not maintain an effect on the subsequent follow-up checkpoints. No statistical difference was identified for compliance with fistulogram within 40 days of access creation (pre-QI, 12% vs QI, 25%; P = .093) or for compliance with the 55-day postoperative appointment (pre-QI, 33% vs QI, 23%; P = .457). Both checkpoints demonstrated a very high noncompliance rate. Accordingly, the mean time to permission to cannulate was 88 days for both the pre-QI and QI groups, with a failure to mature rate of 22% for the pre-QI group and 21% for the QI group (P = .816). CONCLUSIONS: The QI initiative significantly increased the number of patients complying with the first 30-day follow-up appointment after AVF access creation. However, patient compliance with a timely fistulogram and the second follow-up appointment was poor and not influenced by the QI initiative, limiting the functional effect of the QI initiative on the time to AVF permission to cannulate.

Boosting phase contrast with a grating Bonse-Hart interferometer of 200 nanometre grating period.

We report on a grating Bonse-Hart interferometer for phase-contrast imaging with hard X-rays. The method overcomes limitations in the level of sensitivity that can be achieved with the well-known Talbot grating interferometer, and without the stringent spectral filtering at any given incident angle imposed by the classic Bonse-Hart interferometer. The device operates in the far-field regime, where an incident beam is split by a diffraction grating into two widely separated beams, which are redirected by a second diffraction grating to merge at a third grating, where they coherently interfere. The wide separation of the interfering beams results in large phase contrast, and in some cases absolute phase images are obtained. Imaging experiments were performed using diffraction gratings of 200 nm period, at 22.5 keV and 1.5% spectral bandwidth on a bending-magnetic beamline. Novel design and fabrication process were used to achieve the small grating period. Using a slitted incident beam, we acquired absolute and differential phase images of lightly absorbing samples. An advantage of this method is that it uses only phase modulating gratings, which are easier to fabricate than absorption gratings of the same periods.

Subnanoradian X-ray phase-contrast imaging using a far-field interferometer of nanometric phase gratings.

Hard X-ray phase-contrast imaging characterizes the electron density distribution in an object without the need for radiation absorption. The power of phase contrast to resolve subtle changes, such as those in soft tissue structures, lies in its ability to detect minute refractive bending of X-rays. Here we report a far-field, two-arm interferometer based on the new nanometric phase gratings, which can detect X-ray refraction with subnanoradian sensitivity, and at the same time overcomes the fundamental limitation of ultra-narrow bandwidths (Δλ/λ~10⁻4) of the current, most sensitive methods based on crystal interferometers. On a 1.5% bandwidth synchrotron source, we demonstrate clear visualization of blood vessels in unstained mouse organs in simple projection views, with over an order-of-magnitude higher phase contrast than current near-field grating interferometers.

Low dose hard x-ray contact microscopy assisted by a photoelectric conversion layer.

Hard x-ray contact microscopy provides images of dense samples at resolutions of tens of nanometers. However, the required beam intensity can only be delivered by synchrotron sources. We report on the use of a gold photoelectric conversion layer to lower the exposure dose by a factor of 40 to 50, allowing hard x-ray contact microscopy to be performed with a compact x-ray tube. We demonstrate the method in imaging the transmission pattern of a type of hard x-ray grating that cannot be fitted into conventional x-ray microscopes due to its size and shape. Generally the method is easy to implement and can record images of samples in the hard x-ray region over a large area in a single exposure, without some of the geometric constraints associated with x-ray microscopes based on zone-plate or other magnifying optics.

Interferometric hard x-ray phase contrast imaging at 204 nm grating period.

We report on hard x-ray phase contrast imaging experiments using a grating interferometer of approximately 1/10th the grating period achieved in previous studies. We designed the gratings as a staircase array of multilayer stacks which are fabricated in a single thin film deposition process. We performed the experiments at 19 keV x-ray energy and 0.8 µm pixel resolution. The small grating period resulted in clear separation of different diffraction orders and multiple images on the detector. A slitted beam was used to remove overlap of the images from the different diffraction orders. The phase contrast images showed detailed features as small as 10 µm, and demonstrated the feasibility of high resolution x-ray phase contrast imaging with nanometer scale gratings.

Interpretation of dark-field contrast and particle-size selectivity in grating interferometers.

In grating-based x-ray phase sensitive imaging, dark-field contrast refers to the extinction of the interference fringes due to small-angle scattering. For configurations where the sample is placed before the beamsplitter grating, the dark-field contrast has been quantified with theoretical wave propagation models. Yet when the grating is placed before the sample, the dark-field contrast has only been modeled in the geometric optics regime. Here we attempt to quantify the dark-field effect in the grating-before-sample geometry with first-principle wave calculations and understand the associated particle-size selectivity. We obtain an expression for the dark-field effect in terms of the sample material's complex refractive index, which can be verified experimentally without fitting parameters. A dark-field computed tomography experiment shows that the particle-size selectivity can be used to differentiate materials of identical x-ray absorption.

Grazing angle Mach-Zehnder interferometer using reflective phase gratings and a polychromatic, un-collimated light source.

Normal incidence Talbot-Lau interferometers in x-ray applications have the drawbacks of low fringe visibility with polychromatic sources when the wave propagation distance is increased to achieve higher phase sensitivity, and when fabrication limits the attainable grating density. In contrast, reflective gratings illuminated at grazing angles have dramatically higher effective densities than their physical values. However, new designs are needed for far field interferometers using grazing angle geometry with incoherent light sources. We show that, with the appropriate design and choice of reflective phase gratings, there exist pairs of interfering pathways of exactly equal lengths independent of the incoming beam's incidence angle and wavelength. With a visible light grazing angle Mach-Zehnder interferometer, we show the conditions for achieving near ideal fringe visibility and demonstrate both absolute and differential phase-contrast imaging. We also describe the design parameters of an x-ray interferometer and key factors for its implementation.