Sébastien Muller

FEASIBILITY OF ULTRASOUND IMAGING OF OSTEOCHONDRAL DEFECTS IN THE ANKLE: A CLINICAL PILOT STUDY

Talar osteochondral defects (OCDs) are imaged using magnetic resonance imaging (MRI) or computed tomography (CT). For extensive follow-up, ultrasound might be a fast, non-invasive alternative that images both bone and cartilage. In this study the potential of ultrasound, as compared with CT, in the imaging and grading of OCDs is explored. On the basis of prior CT scans, nine ankles of patients without OCDs and nine ankles of patients with anterocentral OCDs were selected and classified using the Loomer CT classification. A blinded expert skeletal radiologist imaged all ankles with ultrasound and recorded the presence of OCDs. Similarly to CT, ultrasound revealed typical morphologic OCD features, for example, cortex irregularities and loose fragments. Cartilage disruptions, Loomer grades IV (displaced fragment) and V (cyst with fibrous roof), were visible as well. This study encourages further research on the use of ultrasound as a follow-up imaging modality for OCDs located anteriorly or centrally on the talar dome.

Simulation Model for Assessing Quality of Ultrasound Strain Estimation in Abdominal Aortic Aneurysm

The purpose of this study was to develop a simulation model for evaluating methods for ultrasound strain estimation in abdominal aortic aneurysms. Wall geometry was obtained from a real ultrasound image and wall motion was simulated applying realistic blood pressures to a nonlinear viscoelastic wall model. The ultrasound simulation included speckle, absorption and angle dependent reflection. Gaussian white noise was added to simulate various noise levels. Despite not fully replicating real ultrasound images, the model simulated realistic circumferential variations in intensity and realistic speckle patterns and has potential for initial evaluation of strain estimation methods.

Degree of Adhesions After Repair of Incisional Hernia

Results of this study suggest that ultrasound can be used to quantitatively estimate the degree of adhesions between intestine and the abdominal wall.

Real-time phase recognition in novel needle-based intervention: a multi-operator feasibility study

Purpose. One of the goals of new navigation systems in the operating room and in outpatient clinics is to support the surgeons decision making while minimizing the additional load on surrounding health personnel. To do so, the system needs to rely on context-awareness providing the surgeon with the most relevant visualization at all times. Such a system could also provide support for surgical training. The objective of this work is to assess the feasibility of an automatic surgical phase recognition using tracking data from a novel instrument for injections and biopsies. Methods. An injection into the sphenopalatine ganglion planned with MRI and CT images is carried out using optical tracking of the instrument. In the context of a feasibility study, the intervention was performed by 5 operators, each 5 times, on a specially designed phantom. The coordinate information is processed into 7 features characterizing the intervention. Three classifiers, Hidden Markov Model (HMM), a Support Vector Machine (SVM), and a combination of these (SVM+HMM) are trained on manually annotated data and cross-validated for intra- and inter-operator variability. Standard test metrics are used to compare the performance of each classifier. Results. HMM alone and SVM alone are comparable classifiers, but feeding the output of the SVM into an HMM results in significantly better classifications: accuracy of 97.8%, sensitivity of 93.1% and specificity of 98.4%. Conclusion. The use of trajectory information can provide a robust real-time phase recognition of surgical phases for needle-based interventions.

Application of eigen-spaced beamformers for imaging lamina of vertebral arch

Ultrasound (US) has been proposed as a guidance tool for spinal intervention. However, bone structures are often visualized poorly in the standard US images which is based on the delay and sum beamforming method (DAS). In this study, we investigate combination of an eigenspace based beamformer (ESMV) with the phase symmetry (PS) post-processing technique to extract the lamina surface from ultrasound images. Thereby, in simulation, and in-vivo studies we show that an ESMV beamformer with a rank-1 signal subspace, can keep the bone structure and improve the edges, despite some distortion of the speckle pattern. The PS images obtained from this beamformer setup have sharper bone boundaries compared with the DAS ones.