Ségolène M. Tarte

Computer-assisted fracture reduction of pelvic ring fractures: an in vitro study.

A newly developed software module for computer-assisted surgery based on a commercially available navigation system allows simultaneous, independent registration of two fragments and real-time navigation of both fragments while reduction occurs. To evaluate the accuracy three fracture models were used: geometric foam blocks, a pelvic ring injury with disruption of the symphysis and the sacroiliac joint, and a pelvic ring fracture with symphysis disruption and a transforaminal sacral fracture. One examiner did visual and navigated reduction and in all experiments the end point was defined as anatomic reduction. Residual displacement was measured with a magnetic motion tracking device. The results revealed a significantly increased residual displacement with navigated reduction compared with visual control. The differences were low, averaging 1 mm for residual translation and 0.7° for the residual rotation, respectively. Residual displacement was small in both set-ups and may not be clinically relevant. Additional development of the software prototype with integration of surface registration may lead to improved handling and facilitated multifragment tracking. Use in the clinical setting should be possible within a short time.

Assessment of two novel ventilatory surrogates for use in the delivery of gated/tracked radiotherapy for non-small cell lung cancer

BACKGROUND In selected patients with NSCLC the therapeutic index of radical radiotherapy can be improved with gating/tracking technology. Both techniques require real-time information on target location. This is often derived from a surrogate ventilatory signal. We assessed the correlation of two novel surrogate ventilatory signals with a spirometer-derived signal. The novel signals were obtained using the VisionRT stereoscopic camera system. The VisionRT-Tracked-Point (VRT-TP) signal was derived from tracking a point located midway between the umbilicus and xiphisternum. The VisionRT-Surface-Derived-Volume (VRT-SDV) signal was derived from 3D body surface imaging of the torso. Both have potential advantages over the current surrogate signals. METHODS Eleven subjects with NSCLC were recruited. Each was positioned as for radiotherapy treatment, and then instructed to breathe in five different modes: normal, abdominal, thoracic, deep and shallow breathing. Synchronous ventilatory signals were recorded for later analysis. The signals were analysed for correlation across all modes of breathing, and phase shifts. The VRT-SDV was also assessed for its ability to determine the mode of breathing. RESULTS Both novel respiratory signals showed good correlation (r>0.80) with spirometry in 9 of 11 subjects. For all subjects the correlation with spirometry was better for the VRT-SDV signal than for the VRT-TP signal. Only one subject displayed a phase shift between the VisionRT-derived signals and spirometry. The VRT-SDV signal could also differentiate between different modes of breathing. Unlike the spirometer-derived signal, neither VisionRT-derived signal was subject to drift. CONCLUSION Both the VRT-TP and VRT-SDV signals have potential applications in ventilatory-gated and tracked radiotherapy. They can also be used as a signal for sorting 4DCT images, and to drive 4DCT single- and multiple-parameter motion models.

A comparison of internal target volume definition by limited four-dimensional computed tomography, the addition of patient-specific margins, or the addition of generic margins when planning radical radiotherapy for lymph node-positive non-small cell lung cancer

AIMS Radical radiotherapy for stage II/III non-small cell lung cancer (NSCLC) includes the primary tumour and positive mediastinal lymph nodes in the clinical target volume (CTV). These move independently of each other in magnitude and direction during respiration. To prevent a geographical miss, a generic margin is usually added to the CTV to create an internal target volume (ITV). Previous studies have investigated the use of additional breath-hold computed tomography to generate patient-specific ITVs for primary tumours alone. We used a similar technique to investigate the generation of patient-specific and generic ITVs for CTVs that include mediastinal lymph nodes. MATERIALS AND METHODS Thirteen patients with node-positive NSCLC had two limited end-tidal breath-hold computed tomography scans in addition to their planning computed tomography. The CTV was segmented in each scan and a rigid registration was carried out on the vertebral columns to align them. Different methods for generating an ITV were then analysed. RESULTS Generic margins provided >95% mean coverage of the reference ITV. However, with the exception of 1cm expansion margins, there were cases of inadequate coverage (<95%) for each ITV. With increasing ITV margins there was a small increase in reference ITV coverage, but at the expense of a large increase in the volume of normal tissue within the ITV. DISCUSSION For stage II/III NSCLC, ITV generation by the addition of a generic margin is not optimal. It can result in both geographical miss and excessive irradiation of normal tissue in the same treatment plan. A simple method for producing a patient-specific ITV is to co-register end-tidal breath-hold computed tomography scans to the planning scan. CONCLUSIONS Further work is required to determine whether end-tidal breath-hold scans are representative of the anatomy at the limits of tidal respiration. Planning strategies are also needed to account for breathing cycle variation during a course of radiotherapy.

Validation of the use of photogrammetry to register pre- procedure MR images to intra-procedure patient position for image-guided cardiac catheterization procedures

A hybrid X-ray and magnetic resonance imaging system (XMR) has been proposed as an interventional guidance for cardiovascular catheterisation procedure. However, very few hospitals can benefit from the XMR system because of its limited availability. In this paper we describe a new guidance strategy for cardiovascular catheterisation procedure. In our technique, intra-operative patient position is estimated by using a chest surface reconstructed from a photogrammetry system. The chest surface is then registered with the same surface derived from pre-procedure magnetic resonance (MR) images. The catheterisation procedure can therefore be guided by a roadmap derived from the MR images. Patients were required to hold the breath at end expiration during MRI acquisition. The surface matching accuracy is improved by using a robust trimmed iterative closest point (ICP) matching algorithm, which is especially designed for incomplete surface matching. Compared to the XMR system, the proposed guidance strategy is low cost and easy to set up. Experimental data were acquired from 6 volunteers and 1 patient. The patient data were collected during an electrophysiology procedure. In 6 out of 7 subjects, the experimental results show our method is accurate in term of reciprocal residual error (range from 1.66m to 3.75mm) and constant (closed-loop TREs range from 1.49mm to 3.55mm). For one subject, trimmed ICP failed to find the optimal transform matrix (residual = 4.89, TRE = 9.32) due to the poor quality of the photogrammetry-reconstructed surface. More studies are being carried on in clinical trials.

MO-D-L100J-04: Non-Rigid Registration Based Respiratory Motion Models of the Lung Using Two Parameters

Purpose: Single parameter motion models based on the phase of a respiratory signal can model the motion over an average respiratory cycle. Two parameter models based on amplitude and gradient may also be able to model some of the inter‐cycle variation. We present a method of constructing two parameter motion models and evaluate different functions for the model. Method and Materials: A reference CT volume is non‐rigidly registered to free breathing CT data. A function is then fitted to each of the control point displacements that define the registrations, relating them to the respiratory parameter(s). Three different functions were evaluated on data from an example patient: a 1D cyclic b‐spline function relating the displacements to phase, a 2D linear function, and a 2D 3rd order polynomial function, both relating the displacements to amplitude and gradient. Models built from each of the functions were used to produce transformations at the same parameter values as the registration results. Models were built both leaving out the target registration and including it. Sample points covering the entire region of interest were deformed using the model results and the registration results, and the differences in the displacements of the points were calculated. Results: The mean differences, when using all registrations and when leaving out the target respectively, were 0.53 mm and 0.67 mm for the 1D cyclic b‐spline function, 0.59 mm and 0.71 mm for the 2D linear function, and 0.43 mm and 0.96 mm for the 2D polynomial function. Conclusion: These results suggest that the performance of the 2D linear function is comparable to the 1D b‐spline function. The 2D polynomial function models the data more accurately but would appear to ‘over‐fit’ the data.

Archetypal Narratives in Social Machines: Approaching Sociality through Prosopography

Introducing Social Machines as web-enabled entities integrating social energies and computational powers into a socio-technical system (whether purposeful or not) where social dynamics animate communities, this paper proposes a theoretical framework in which to observe them. Attempting to strike a balance between the roles of humans and non-humans, and aware of the difficulties that this heterogeneity presents, we propose to approach the questions of capturing the social dynamics of a social machine through prosopography. Prosopography is a method, used in particular by historians, that allows to systematically study a collection of biographies, be they of persons, artefacts, infrastructures of groups thereof. Systematization is achieved through designing an appropriate questionnaire to gather homogeneous data across the biographies. Our questionnaire design relies on the identification of five archetypal elements in biographical narratives. Illustrating our method with three examples, we demonstrate how our archetypal narratives have the potential to describe at least aspects of the social dynamics in social machines.

TH‐D‐332‐07: Removing Artifacts From 4DCT Volumes Acquired in Cine Mode Using B‐Spline Non‐Rigid Registrations

Purpose: To remove artefacts that occur between adjacent couch positions in 4DCT volumes acquired in Cine mode. Method and Materials: separate B‐spline non‐rigid registration is performed between an artefact free reference volume and the data from each individual couch position in the 4DCT volume. The registration is performed using an extended control point grid that covers all of the couch positions and is common to all of the registrations. Therefore the result of each registration defines a transformation over all couch positions but was only constrained by data from one couch position. The registration results from all couch position are then combined into a single B‐spline transformation. The control point displacements in the combined transformation are a weighted average of the displacements in the individual registrations. The weight for each registration is different for each row in the control point grid, and depends on the contribution that the control points make to the transformation in the region of the couch position that was registered. The combined transformation is continuous across all the couch positions, and when used to deform the reference volume will produce an artefact free prediction of the anatomy in the same respiratory state as the original 4DCT volume. Results: This method has been applied to 4DCT data from five patients that were subject to artefacts between couch positions. In all cases our method produced volumes that resembled the original 4DCT data but were free of artefacts between adjacent couch positions. Conclusion: We have presented a novel method based on B‐spline non‐rigid registration that can remove the artefacts that occur between adjacent couch positions in 4DCT volumes acquired in Cine model, and have successfully demonstrated this method on data from five patients.

On Wayfaring in Social Machines

In this paper, we concern ourselves with the ways in which humans inhabit social machines: the structures and techniques which allow the enmeshing of multiple life traces within the flow of online interaction. In particular, we explore the distinction between transport and journeying, between networks and meshworks, and the different attitudes and modes of being appropriate to each. By doing this, we hope to capture a part of the sociality of social machines, to build an understanding of the ways in which lived lives relate to digital structures, and the emergence of the communality of shared work. In order to illustrate these ideas, we look at several aspects of existing social machines, and tease apart the qualities which relate to the different modes of being. The distinctions and concepts outlined here provide another element in both the analysis and development of social machines, understanding how people may joyfully and directedly engage with collective activities on the web.

An Image Processing Portal and Web-Service for the Study of Ancient Documents

Linking up two projects that are dedicated to facilitate the work of documentary scholars, this paper presents image processing algorithms tailored to the study of ancient documents and how they have been made available to the users through a portal that calls upon a web-service exploiting grid computational power. To that end, image processing algorithms were wrapped to fit into the National Grid Service (NGS) Uniform Execution Environment; the data model of an existing Virtual Research Environment (VRE-SDM) was extended; JSR-168 compliant portlets were developed to facilitate secure and seamless distributed image analysis; and a GridSAM interface between the portal and the NGS-installed algorithms was developed. The outcomes of the project include: a web-based application, a proof of concept for the usability of the VRE-SDM platform, an opportunity for wider dissemination for the image processing algorithms, and a proof of feasibility for the use of the NGS for Humanities applications.

MOTION AND BIOMECHANICAL MODELS FOR IMAGE-GUIDED INTERVENTIONS

This paper describes recent progress in developing motion and biomechanical models for image guided interventions. The challenge is to provide navigational support for interventions and image directed therapies on soft or mobile structures. We describe our recent progress in generating and testing models of respiratory motion for image directed radiotherapy and focal ablation in the lung and liver, and the development of biomechanical models for image guided local excision in breast surgery.