Search

A fast and precise algorithm for wavefront reconstruction by the registration of wavefront segments is presented. If the wavefront exceeds the sensor aperture or the dynamic range of the sensor, a Shack–Hartmann sensor can measure only segments of an optical wavefront. The algorithm registers the wavefront segments in parallel, where they are simultaneously transformed to minimize their overlap mismatch for precise reconstruction of the entire wavefront. The original nonlinear optimization problem is approximated by a convex optimization problem that can be solved more efficiently. A simulation-based analysis of the algorithm and a comparison to a previously proposed parallel registration (PR) algorithm as well as to the iterative closest point (ICP) algorithm are presented. It is shown that despite measurement noise, the algorithm can precisely register plane as well as divergent wavefronts with root mean square registration errors smaller than 10 nm. Particularly for the divergent wavefront, this enables a reduction of the registration error by a factor of up to 750 as compared to the established algorithms. Analysis and comparison to the ICP and PR algorithm also show that the computation time of the proposed algorithm can be from one to three orders of magnitude smaller.

This paper presents a robust registration algorithm for wavefront reconstruction from multiple partial measurements. Wavefronts exceeding the dynamic range or size of the Shack–Hartmann sensor can be measured as a set of segments. The wavefront is reconstructed by parallel registration of these wavefront segments, enabling compensation for sensor misalignment as well as for phase differences. For registration, a global mismatch metric is minimized by rigid body transformations and propagation of the wavefront segments. Apart from the description of the algorithm, a simulation-based evaluation and comparison to the iterative closest point (ICP) algorithm is performed. It is shown that in the case of a noisy data set, the parallel approach enables reconstruction errors that are a factor of 10 smaller than the result obtained with the ICP algorithm.

This paper deals with the characterization of freeform optics by means of a wavefront sensor. Freeform optics show an increasing demand since they have the potential to improve optical system performance while reducing size, weight and complexity. To directly measure the performance of a freeform optical part, a novel scanning wavefront sensor approach is proposed which is faster than a coordinate measuring machine and more flexible than an interferometer. The challenges lie in the limited dynamic range of a Shack-Hartmann sensor concerning wavefront slope and curvature. Both limits can be overcome by repositioning the sensor and orienting it tangentially to the wavefront. An automatic setup is developed and first measurements are demonstrated on a highly divergent wavefront. It is shown that the dynamic range of the sensor is increased by scanning the sensor along the wavefront and orienting the sensor tangential to the wavefront in each position. Measurements are taken over a range of ±15°, which is an improvement by a factor 5 compared to the typical dynamic range of ±3° for a static Shack-Hartmann sensor.

Purpose Autologous chondrocyte transplantation (ACT) is an established method in cartilage repair. Although long-term results show durable repair of isolated cartilage defects, some problems still remain. Since hypertrophy of the transplanted periosteum is a common problem, alternatives for periosteum are in demand. Periosteal grafts have been reported to stimulate neochondrogenesis via paracrine effects. The objective of this study was to evaluate the modulation of chondrocyte metabolism by periosteal grafts in vitro.Methods Periosteal explants and articular chondrocytes obtained from slaughtered adult cattle were co-cultured in a newly established perfusion system. The experimental groups were: 1. monocultured chondrocytes; 2. chondrocytes cultured with synovial supernatants; 3. chondrocytes cultured with periosteal supernatants; 4. chondrocytes co-cultured with periosteal explants.Results Chondrocyte proliferation, evaluated by measuring total DNA content, was prolongated by periosteal and synovial explants. Immunocytochemical staining of collagen type II was stronger in monoculture than in co-culture. Protein biosynthetic activity estimated by [3H]-proline incorporation, as well as extracellular matrix deposition for collagen type II, were reduced by periosteal and synovial explants. Additionally, co-culturing led to a decrease in aggrecan synthesis and release. The inhibiting effects were significantly stronger when cellular chondrocyte-periosteal cross-talk was made possible via paracrine effects.Conclusions The results of our study suggest a catabolic effect of periosteal explants on isolated chondrocytes in vitro. Further investigations are necessary whether periosteum in ACT is dispensable.

OBJECTIVE: To evaluate longterm results and survival rate of open synovectomy of the elbow joint in patients with rheumatoid arthritis (RA). METHODS: Between 1986 and 2000, synovectomy of the elbow was performed on 103 joints in 92 patients with RA. Eighty-five joints were included in this study. Mean age at time of surgery was 52 years (range 13 to 62 yrs). On 13 elbows with Larsen stage I and II disease, early synovectomy preserving the radial head was performed; in 72 cases with Larsen stage III and IV, late synovectomy with radial head resection was necessary. RESULTS: In early synovectomy, one joint received prosthetic joint replacement and 2 joints underwent resynovectomy a mean of 9 years after primary surgery. The survival rate (no further operations) was 91% after 5 years and 78% after 10 years. In late synovectomy, 16 elbow joints were operated again a mean of 4.6 years after primary surgery (10 prosthetic joint replacements, 2 resection interposition arthroplasties, 4 resynovectomies). Survival rate was 82% after 5 years and 66% after 10 years. Sixty-one elbows were examined clinically at a mean followup period of 8.7 years (range 2.8–17.3 yrs). There was a significant improvement of the Morrey score at followup, especially due to effective relief of pain. Improvement of joint motion was seen in late synovectomy for pronation and supination. The mean preoperative Larsen stage was 3.11, which decreased significantly to 3.66 at followup. CONCLUSION: Our findings suggest that synovectomy is a safe and effective procedure in differential treatment of RA of the elbow.