Atlas-based segmentation of brain tumor images using a Markov random field-based tumor growth model and non-rigid registration.

We propose a new and clinically oriented approach to perform atlas-based segmentation of brain tumor images. A mesh-free method is used to model tumor-induced soft tissue deformations in a healthy brain atlas image with subsequent registration of the modified atlas to a pathologic patient image. The atlas is seeded with a tumor position prior and tumor growth simulating the tumor mass effect is performed with the aim of improving the registration accuracy in case of patients with space-occupying lesions. We perform tests on 2D axial slices of five different patient data sets and show that the approach gives good results for the segmentation of white matter, grey matter, cerebrospinal fluid and the tumor.

Development and in-vitro characterization of an implantable flow sensing transducer for hydrocephalus.

An implantable transducer for monitoring the flow of Cerebrospinal fluid (CSF) for the treatment of hydrocephalus has been developed which is based on measuring the heat dissipation of a local thermal source. The transducer uses passive telemetry at 13.56 MHz for power supply and read out of the measured flow rate. The in vitro performance of the transducer has been characterized using artificial Cerebrospinal Fluid (CSF) with increased protein concentration and artificial CSF with 10% fresh blood. After fresh blood was added to the artificial CSF a reduction of flow rate has been observed in case that the sensitive surface of the flow sensor is close to the sedimented erythrocytes. An increase of flow rate has been observed in case that the sensitive surface is in contact with the remaining plasma/artificial CSF mix above the sediment which can be explained by an asymmetric flow profile caused by the sedimentation of erythrocytes having increased viscosity compared to artificial CSF. After removal of blood from artificial CSF, no drift could be observed in the transducer measurement which could be associated to a deposition of proteins at the sensitive surface walls of the packaged flow transducer. The flow sensor specification requirement of +-10% for a flow range between 2 ml/h and 40 ml/h. could be confirmed at test conditions of 37 degrees C.

Prediction of dental implant torque with a fast and automatic finite element analysis: a pilot study.

OBJECTIVES: Despite its importance, implant removal torque can be assessed at present only after implantation. This paper presents a new technique to help clinicians preoperatively evaluate implant stability. STUDY DESIGN: Planning software has been combined with an in-house finite element solver. Once the clinician has chosen the implant position on the planner, a finite element analysis automatically calculates the primary stability. The process was designed to be as simple and fast as possible for clinical use. This paper describes application of the method to the prediction of removal torque. A preliminary validation has been performed in both polyurethane foam and sheep bone. RESULTS: The predicted torque is quantitatively equivalent to experimental values with correlation coefficients of >0.7 in both materials. CONCLUSIONS: This preliminary study is a first step toward the introduction of finite element models in computer-assisted surgery. The fact that the process is fast and automatic makes it suitable for a clinical use.

Quantifying the influence of bone density and thickness on resonance frequency analysis: an in vitro study of biomechanical test materials.

PURPOSE: Resonance frequency analysis (RFA) offers the opportunity to monitor the osseointegration of an implant in a simple, noninvasive way. A better comprehension of the relationship between RFA and parameters related to bone quality would therefore help clinicians improve diagnoses. In this study, a bone analog made from polyurethane foam was used to isolate the influences of bone density and cortical thickness in RFA. MATERIALS AND METHODS: Straumann standard implants were inserted in polyurethane foam blocks, and primary implant stability was measured with RFA. The blocks were composed of two superimposed layers with different densities. The top layer was dense to mimic cortical bone, whereas the bottom layer had a lower density to represent trabecular bone. Different densities for both layers and different thicknesses for the simulated cortical layer were tested, resulting in eight different block combinations. RFA was compared with two other mechanical evaluations of primary stability: removal torque and axial loading response. RESULTS: The primary stability measured with RFA did not correlate with the two other methods, but there was a significant correlation between removal torque and the axial loading response (P < .005). Statistical analysis revealed that each method was sensitive to different aspects of bone quality. RFA was the only method able to detect changes in both bone density and cortical thickness. However, changes in trabecular bone density were easier to distinguish with removal torque and axial loading than with RFA. CONCLUSIONS: This study shows that RFA, removal torque, and axial loading are sensitive to different aspects of the bone-implant interface. This explains the absence of correlation among the methods and proves that no standard procedure exists for the evaluation of primary stability.

Cardiovascular changes after pulmonary embolism from injecting calcium phosphate cement.

Concerns have been raised that the use of calcium phosphate (CaP) cements for the augmentation of fractured, osteoporotic bones may aggravate cardiovascular deterioration in the event of pulmonary cement embolism by stimulating coagulation. The aim of the present study was therefore to investigate the cardiovascular changes after pulmonary embolism of CaP cement using an animal model. In 14 sheep, 2.0 mL CaP or polymethylmethacrylate cement were injected intravenously. Cardiovascular parameters and antithrombin levels were monitored until 60 min postinjection. Postmortem, lungs were subjected to CT scanning, and 3D reconstruction of the cement was performed. Intravenous injection of CaP cement resulted in a more severe increase in pulmonary arterial pressure and decrease in arterial blood pressure. Disintegration of the CaP cement seemed to be the reason for the more severe reaction. There was no evidence of thromboembolism. Disintegration of CaP cement in circulating blood does not only compromise the mechanical properties, but also represents a risk of cardiovascular complications. Reliable cohesion of CaP cements in an aqueous environment is essential for clinical applications such as osteoporotic bone augmentation.