Unscented Kalman Filtering for Real Time Thermometry During Laser Ablation Interventions.

We present a data-assimilation Bayesian framework in the context of laser ablation for the treatment of cancer. For solving the nonlinear estimation of the tissue temperature evolving during the therapy, the Unscented Kalman Filter (UKF) predicts the next thermal status and controls the ablation process, based on sparse temperature information. The purpose of this paper is to study the outcome of the prediction model based on UKF and to assess the influence of different model settings on the framework performances. In particular, we analyze the effects of the time resolution of the filter and the number and the location of the observations. Clinical Relevance - The application of a data-assimilation approach based on limited temperature information allows to monitor and predict in real-time the thermal effects induced by thermal therapy for tumors.

Model-Based Thermometry for Laser Ablation Procedure Using Kalman Filters and Sparse Temperature Measurements.

OBJECTIVE: We implement a data assimilation Bayesian framework for the reconstruction of the spatiotemporal profile of the tissue temperature during laser irradiation. The predictions of a physical model simulating the heat transfer in the tissue are associated with sparse temperature measurements, using an Unscented Kalman Filter. METHODS: We compare a standard state-estimation filtering procedure with a joint-estimation (state and parameters) approach: whereas in the state-estimation only the temperature is evaluated, in the joint-estimation the filter corrects also uncertain model parameters (i.e., the medium thermal diffusivity, and laser beam properties). We have tested the method on synthetic temperature data, and on the temperature measured on agar-gel phantom and porcine liver with fiber optic sensors. RESULTS: The joint-estimation allows retrieving an accurate estimate of the temperature distribution with a maximal error 1.5 °C in both synthetic and liver 1D data, and 2 °C in phantom 2D data. Our approach allows also suggesting a strategy for optimizing the temperature estimation based on the positions of the sensors. Under the constraint of using only two sensors, optimal temperature estimation is obtained when one sensor is placed in proximity of the source, and the other one is non-symmetrical. CONCLUSION: The joint-estimation significantly improves the predictive capability of the physical model. SIGNIFICANCE: This work opens new perspectives on the benefit of data assimilation frameworks for laser therapy monitoring.

[Connective tissue in non-union and pseudarthrosis of long bones. Part I: Capsule of false joints in dogs (author's transl)]. / Das Bindegewebe in Pseudarthrosen und Nearthrosen langer Röhrenknochen- Teil I: Pseudogelenkkapsel beim Hund.

Animal experiments were carried out on 28 dogs which underwent osteotomy of the femur without postoperative fixation. For systematic light- and transmission electron microscopy tissue from this area of 7 dogs was prepared. Result was a functional morphology of connective tissue. Instability of bone fragments is regarded as the most important factor in pathogenesis of pseudarthrosis. Pathologic mobility in the osteotomy area caused specific altered differentiation of local connective tissue cells, leading to a joint capsule-like formation of connective tissue. "Lining cells" to the pseudarthrotic cavity are fibroblasts and histiocyts, comparable to the "lining cells" of normal stratum synoviale. These cells are surrounded by some collagenous fibres and large amounts of amorphous ground substances. They derive means of numerous transitional forms. The capsule-like tissue formation aside the pseudarthrotic cavity is comparable to stratum synoviale of normal joints. In some of these capsule-like areas there are degenerative alterations similar to those of joint capsules in osteoarthritis.

[Connective tissue in non-union and pseudarthrosis of long bones. Part II: cavity of false joints in dogs (author's transl)]. / Das Bindegewebe in Pseudarthrosen und Nearthrosen langer Röhrenknochen-Teil II: Pseudogelenkspalt beim Hund.

Pseudarthrotic cavity is surrounded by joint capsule-like connective tissue as well as by the locked-up bone ends. Macroscopic and microscopic examinations indicate instability as a traumatic factor to the surrounding tissues, leading to tears and clefts covered by fibrin and erythrocyte deposits. Below, cell-layers consisting of fibroblasts and histiocytes are formed, which become comparable to stratum synoviale of normal joint especially in areas with constant mechanical stimulus like sliding and little pressure without considerable traumatic effect. Where bone ends reach like lever-arms far into the peripseudarthrotic tissue and mechanical stress of abnormal mobility is of adequate permanent traumatic effect, vascularisation is not visible and regressive, necrobiotic alterations are predominant. In areas with presumable more pressure, with little or no vascularisation, woven cartilage-like partially calcified tissues are formed. Where osteotomized bones are pressed upon each other with instability an intensive remodeling with resorption and rebuilding of bone trabeculae is visible. Muscle interposits degenerate within the continuously injured and scarcely vasculated osteotomized area, and are replaced by tight connective tissues as well as walled-in by bone trabeculae. By reforming abundant collagenous fibres the pseudarthrosis becomes more and more tight. In this way there is a reduction of the functional stimulus abnormal mobility, which induces the local connective tissue to differentiate into joint-like structures, comparable to a mechanism of "self-limitation". One animal was observed up to 48 months after osteotomy. Without therapeutic immobilisation bony consolidation and corticalisation was present in the former pseudarthrotic region, joint capsule-like tissues were no more demonstrable.

[Connective tissue in non-union and pseudarthrosis of long bones. Part III: comparative examination of human false joints (author's transl)]. / Das Bindegewebe in Pseudarthrosen und Nearthrosen langer Röhrenknochen- Teil III: Vergleichende Untersuchung am Patienten.

Nontreatment of far dislocated fractures of long bones is seldom, fortunately. In comparison to our animal experiments tissue samples from only one patient with similar conditions could be examined by light- and transmission electron microscopy. Microscopic findings are similar to those of animal experiments. Pathologic pseudarthrotic conditions caused by abnormal mobility can be taken as a model for observing reformation of connective tissue. In general tissue dynamics are the same as those known from the ontogeny of connective tissue. The influence of abnormal mobility to pseudarthrosis formation is discussed.

[Regional anesthesia in geriatric surgery. Possibilities and limitations: (author's transl)]. / Regionalanästhesie in der geriatrischen Chirurgie. Möglichkeiten und Grenzen

Modern anesthetic techniques are superior to regional anesthesia for most operative procedures. Yet because of new advances in techniques and methods and sound pathophysiological knowledge, there are some operations for which regional anesthesia has distinct advantages over general anesthesia. This is the case, for example, in geriatric surgery. Here, the technical simplicity and short amount of time required give spinal anesthesia marked advantages over general anesthesia. Post-spinal headaches and slight falls in blood pressure have become rarer due to technical innovations and can reasonably be accepted.