Design trade-off and proof of concept for LOUPE, the Lunar Observatory for Unresolved Polarimetry of Earth.

We provide a proof of the technical feasibility of LOUPE, the first integral-field snapshot spectropolarimeter, designed to monitor the reflected flux and polarization spectrum of Earth. These are to be used as benchmark data for the retrieval of biomarkers and atmospheric and surface characteristics from future direct observations of exoplanets. We perform a design trade-off for an implementation in which LOUPE performs snapshot integral-field spectropolarimetry at visible wavelengths. We used off-the-shelf optics to construct a polarization modulator, in which polarization information is encoded into the spectrum as a wavelength-dependent modulation, while spatial resolution is maintained using a micro-lens array. The performance of this design concept is validated in a laboratory setup. Our proof-of-concept is capable of measuring a grid of 50 × 50 polarization spectra between 610 and 780 nm of a mock target planet - proving the merit of this design. The measurements are affected by systematic noise on the percent level, and we discuss how to mitigate this in future iterations. We conclude that LOUPE can be small and robust while meeting the science goals of this particular space application, and note the many potential applications that may benefit from our concept for doing snapshot integral-field spectropolarimetry.

Data-driven directions for effective footwear provision for the high-risk diabetic foot.

AIMS: Custom-made footwear is used to offload the diabetic foot to prevent plantar foot ulcers. This prospective study evaluates the offloading effects of modifying custom-made footwear and aims to provide data-driven directions for the provision of effectively offloading footwear in clinical practice. METHODS: Eighty-five people with diabetic neuropathy and a recently healed plantar foot ulcer, who participated in a clinical trial on footwear effectiveness, had their custom-made footwear evaluated with in-shoe plantar pressure measurements at three-monthly intervals. Footwear was modified when peak pressure was ≥ 200 kPa. The effect of single and combined footwear modifications on in-shoe peak pressure at these high-pressure target locations was assessed. RESULTS: All footwear modifications significantly reduced peak pressure at the target locations compared with pre-modification levels (range -6.7% to -24.0%, P < 0.001). The metatarsal heads were most frequently targeted. Repositioning an existing (trans-)metatarsal pad in the shoe insole (-15.9% peak pressure relief), applying local cushioning to the insole (-15.0%) and replacing the insole top cover with Plastazote (-14.2%) were the most effective single modifications. Combining a new Plastazote top cover with a trans-metatarsal bar (-24.0% peak pressure relief) or with local cushioning (-22.0%) were the most effective combined modifications. CONCLUSIONS: In people with diabetic neuropathy and a recently healed plantar foot ulcer, significant offloading can be achieved at high-risk foot regions by modifying custom-made footwear. These results provide data-driven directions for the design and evaluation of custom-made footwear for high-risk people with diabetes, and essentially mean that each shoe prescribed should incorporate those design features that effectively offload the foot.

Offloading effect of therapeutic footwear in patients with diabetic neuropathy at high risk for plantar foot ulceration.

AIMS: Custom-made therapeutic footwear is often prescribed to patients with diabetic neuropathy, foot deformity and a healed plantar foot ulcer. Offloading these feet is important to prevent ulcer recurrence. The aim was to evaluate the offloading effect of custom-made footwear in these patients. METHODS: In 171 patients with diabetic neuropathy (336 feet) with foot deformity and a recently healed plantar foot ulcer, plantar pressures walking barefoot and inside new custom-made footwear were measured. At the previous ulcer location and at locations of highest barefoot pressure attributable to the deformity, in-shoe pressures were compared with non-deformed feet. The footwear was considered effective in offloading when in-shoe peak pressure at these locations was < 200 kPa. RESULTS: Mean in-shoe peak pressures ranged between 211 and 308 kPa in feet with forefoot deformity (vs. 191-222 kPa in non-deformed feet) and between 140 and 187 kPa in feet with midfoot deformity (vs. 112 kPa in non-deformed feet). Offloading was effective in 61% of all feet with deformity, 81% of feet with midfoot deformity, 44% of feet with forefoot deformity and 62% of previous ulcer locations. Inter-subject variability in measured in-shoe plantar pressure was large. CONCLUSIONS: Offloading in custom-made footwear is often not sufficiently achieved in high-risk diabetic feet with deformity. Highest offloading success rates were seen at known high-risk locations such as previous ulcer locations and Charcot feet, the lowest success rates in forefoot deformities. Together with the large inter-subject variability in pressure outcomes, this emphasizes the need for evidence-based prescription and evaluation procedures to assure adequate offloading.

Pressure-reduction and preservation in custom-made footwear of patients with diabetes and a history of plantar ulceration.

AIMS: To assess the value of using in-shoe plantar pressure analysis to improve and preserve the offloading properties of custom-made footwear in patients with diabetes. METHODS: Dynamic in-shoe plantar pressures were measured in new custom-made footwear of 117 patients with diabetes, neuropathy, and a healed plantar foot ulcer. In 85 of these patients, high peak pressure locations (peak pressure > 200 kPa) were targeted for pressure reduction (goal: > 25% relief or below an absolute level of 200 kPa) by modifying the footwear. After each of a maximum three rounds of modifications, pressures were measured. In a subgroup of 32 patients, pressures were measured and, if needed, footwear was modified at 3-monthly visits for 1 year. Pressures were compared with those measured in 32 control patients who had no footwear modifications based on pressure analysis. RESULTS: At the previous ulcer location and the highest and second highest pressure locations, peak pressures were significantly reduced by 23%, 21% and 15%, respectively, after modification of footwear. These lowered pressures were maintained or further reduced over time and were significantly lower, by 24-28%, compared with pressures in the control group. CONCLUSION: The offloading capacity of custom-made footwear for high-risk patients can be effectively improved and preserved using in-shoe plantar pressure analysis as guidance tool for footwear modification. This provides a useful approach to obtain better offloading footwear that may reduce the risk for pressure-related diabetic foot ulcers.

Twelve steps per foot are recommended for valid and reliable in-shoe plantar pressure data in neuropathic diabetic patients wearing custom made footwear.

BACKGROUND: Dynamic in-shoe plantar pressure assessment is used both in research and clinical practice to evaluate therapeutic footwear interventions in neuropathic diabetic patients. The aim was to determine the required number of footsteps for reliable and valid in-shoe plantar pressure data in these patients. METHODS: In 30 neuropathic diabetic patients wearing custom-made therapeutic footwear, in-shoe plantar pressures were measured for a minimum of 20 midgait walking steps per foot. For each incremental number of steps and for each of six anatomical regions per foot, peak pressure, pressure-time integral, contact area, contact time, and force-time integral were calculated. Reliability was assessed by calculating intraclass correlation coefficients. Validity was assessed by calculating the coefficient of variation between each n-step protocol and the 20-step reference protocol based on Limits of Agreement analysis. Data was considered reliable with intraclass correlation coefficients >0.90 and valid with coefficients of variation <10%. FINDINGS: Three steps per foot were required to obtain reliable data for each foot region and parameter. Depending on the parameter, between 7 and 17 steps per foot were required to obtain valid data. With the exception of deviant outcomes in three forefoot regions for force-time integral, overall 12 steps per foot were required for valid data. INTERPRETATION: For neuropathic diabetic patients wearing custom-made therapeutic footwear, 12 midgait steps per foot are required to obtain valid and reliable in-shoe plantar pressure data. This provides directions for the use of in-shoe plantar pressure analysis in research and clinical practice in this patient group.