Philippe C. Cattin

Medical Imaging and Augmented Reality

Orthognathic surgery is a surgical procedure to correct jaw deformities. It requires extensive presurgical planning. We developed a novel computeraided surgical simulation (CASS) system, the AnatomicAligner, for doctors planning the entire orthognathic surgical procedure in computer following our streamlined clinical protocol. The computerized plan can be transferred to the patient at the time of surgery using digitally designed surgical splints. The system includes six modules: image segmentation and three-dimensional (3D) model reconstruction; registration and reorientation of the models to neutral head posture (NHP) space, 3D cephalometric analysis, virtual osteotomy, surgical simulation, and surgical splint designing. The system has been validated using the 5 sets of patient’s datasets. The AnatomicAligner system will be soon available freely to the broader clinical and research communities.

Choosing the optimal wall shear parameter for the prediction of plaque location—A patient-specific computational study in human right coronary arteries

OBJECTIVEnWhile the correlation of atherosclerotic plaque locations with local wall shear stress magnitude has been evaluated previously by other investigators in both right (RCA) and left coronary arteries (LCA), the relative performance of average wall shear stress (AWSS), average wall shear stress gradient (AWSSG), oscillatory shear index (OSI) and relative residence time (RRT) as indicators of potential atherosclerotic plaque locations has not been studied for the LCA. Here we determine the performance of said wall shear parameters in the LCA for the prediction of plaque development locations and compare these results to those previously found in the RCA.nnnMETHODSnWe obtained 30 patient-specific geometries (mean age 67.1 (± 9.2) years, all with stable angina) of the LCA using dual-source computed tomography and virtually removed any plaque present. We then performed computational fluid dynamics simulations to calculate the wall shear parameters.nnnRESULTSnFor the 96 total plaques, AWSS had a higher sensitivity for the prediction of plaque locations (86 ± 25%) than AWSSG (65 ± 37%, p<0.05), OSI (67 ± 32%, p<0.01) or RRT (48 ± 38%, p<0.001). RRT had a higher PPV (49 ± 36%) than AWSS (31 ± 20%, p<0.05) or AWSSG (16 ± 12%, p<0.001). Segment 5 of the LCA presented with overall low values for sensitivity and PPV. Parameter performance in the remainder of the LCA was comparable to that in the RCA.nnnCONCLUSIONSnAWSS features remarkably high sensitivity, but does not reach the PPV of RRT. This may indicate that while low wall shear stress is necessary for plaque formation, its presence alone is not sufficient to predict future plaque locations. Time dependent factors have to be taken into account as well.

Systematic errors in respiratory gating due to intrafraction deformations of the liver

This article shows the limitations of respiratory gating due to intrafraction deformations of the right liver lobe. The variability of organ shape and motion over tens of minutes was taken into account for this evaluation, which closes the gap between short-term analysis of a few regular cycles, as it is possible with 4DCT, and long-term analysis of interfraction motion. Time resolved MR volumes (4D MR sequences) were reconstructed for 12 volunteers and subsequent non-rigid registration provided estimates of the 3D trajectories of points within the liver over time. The full motion during free breathing and its distribution over the liver were quantified and respiratory gating was simulated to determine the gating accuracy for different gating signals, duty cycles, and different intervals between patient setup and treatment. Gating effectively compensated for the respiratory motion within short sequences (3 min), but deformations, mainly in the anterior inferior part (Couinaud segments IVb and V), led to systematic deviations from the setup position of more than 5 mm in 7 of 12 subjects after 20 min. We conclude that measurements over a few breathing cycles should not be used as a proof of accurate reproducibility of motion, not even within the same fraction, if it is longer than a few minutes. Although the diaphragm shows the largest magnitude of motion, it should not be used to assess the gating accuracy over the entire liver because the reproducibility is typically much more limited in inferior parts. Simple gating signals, such as the trajectory of skin motion, can detect the exhalation phase, but do not allow for an absolute localization of the complete liver over longer periods because the drift of these signals does not necessarily correlate with the internal drift.

Retina mosaicing using local features

Laser photocoagulation is a proven procedure to treat various pathologies of the retina. Challenges such as motion compensation, correct energy dosage, and avoiding incidental damage are responsible for the still low success rate. They can be overcome with improved instrumentation, such as a fully automatic laser photocoagulation system. In this paper, we present a core image processing element of such a system, namely a novel approach for retina mosaicing. Our method relies on recent developments in region detection and feature description to automatically fuse retina images. In contrast to the state-of-the-art the proposed approach works even for retina images with no discernable vascularity. Moreover, an efficient scheme to determine the blending masks of arbitrarily overlapping images for multi-band blending is presented.

Fully Automatic Endoscope Calibration for Intraoperative Use

As of today endoscopes have been only used as a keyhole to look inside the human body. Our goal is to enhance the endoscope to a full imaging device providing better quantitative and qualitative data. Possible applications for such an enhanced endoscope are referencing, navigation and 3D visualization during endoscopic surgery. To obtain accurate results, a reliable and fully automatic calibration method for the endoscopic camera has been developed which can be used within the operating room (OR). Special care has been taken to ensure robustness against inevitable distortions and inhomogeneous illumination.

Mitral annular shape, size, and motion in normals and in patients with cardiomyopathy: evaluation with computed tomography

Objective:To assess prospectively, in healthy subjects and in patients with dilated cardiomyopathy (DCM) and hypertrophic obstructive cardiomyopathy (HOCM), the 3-dimensional (3D) shape, size, and motion of the mitral annulus (MA) using computed tomography (CT). Materials and Methods:Twenty patients with no cardiac abnormalities (referred to as normals), 15 with DCM, and 15 with HOCM as determined by echocardiography underwent contrast-enhanced, retrospectively electrocardiography (ECG)-gated 64-slice CT of the heart. The MA was manually segmented in 10% steps of the RR interval with dedicated 3D software employing the point-wrap algorithm. The MA shape, area size, change of the MA area, and apicobasal MA motion throughout the cardiac cycle was determined and compared between the groups. Intercommissural distances were measured with CT and compared with findings during surgery in 9 patients undergoing ring annuloplasty. Results:The MA was nonplanar in all phases and subjects, being largest in diastole and smallest in systole. The MA area was significantly (P < 0.001) larger in patients with DCM (11.5 ± 4.1 cm2/m2) as compared with normals (5.5 ± 0.9 cm2/m2) and HOCM (4.7 ± 0.9 cm2/m2). The change of MA area throughout the cardiac cycle was significantly (P < 0.017) smaller in patients with DCM (12.2 ± 3.3%/m2) as compared with normals (20.0 ± 7.9%/m2) and HOCM (20.5 ± 7.7%/m2). The mean apicobasal motion was significantly (P < 0.017) smaller in patients with DCM (2.2 ± 1.0 mm/m2) as compared with normals (3.6 ± 0.8 mm/m2) and HOCM (2.7 ± 0.7 mm/m2). Intercommissural distances as determined by CT showed a good correlation (r = 0.68, P < 0.05) with intraoperative measurements (mean difference, 0.44 mm; limits of agreement, −2.73–3.62 mm). Conclusion:Our study provides in vivo human data on the 3D shape, size, and motion of the MA in healthy subjects. Significant changes in size and motion of the MA were noted in patients with HOCM.

Markerless endoscopic registration and referencing

Accurate patient registration and referencing is a key element in navigated surgery. Unfortunately all existing methods are either invasive or very time consuming. We propose a fully non-invasive optical approach using a tracked monocular endoscope to reconstruct the surgical scene in 3D using photogrammetric methods. The 3D reconstruction can then be used for matching the pre-operative data to the intra-operative scene. In order to cope with the near real-time requirements for referencing, we use a novel, efficient 3D point management method during 3D model reconstruction. The presented prototype system provides a reconstruction accuracy of 0.1 mm and a tracking accuracy of 0.5 mm on phantom data. The ability to cope with real data is demonstrated by cadaver experiments.

Inter-subject modelling of liver deformation during radiation therapy

This paper presents a statistical model of the liver deformation that occurs in addition to the quasi-periodic respiratory motion. Having an elastic but still compact model of this variability is an important step towards reliable targeting in radiation therapy. To build this model, the deformation of the liver at exhalation was determined for 12 volunteers over roughly one hour using 4DMRI and subsequent non-rigid registration. The correspondence between subjects was established based on mechanically relevant landmarks on the liver surface. Leave-one-out experiments were performed to evaluate the accuracy in predicting the liver deformation from partial information, such as a point tracked by ultrasound imaging. Already predictions from a single point strongly reduced the localisation errors, whilst the method is robust with respect to the exact choice of the measured predictor.

Automatic segmentation of the aortic dissection membrane from 3d CTA images

Acute aortic dissection is a life-threatening condition and must be diagnosed and treated promptly. For treatment planning the reliable identification of the true and false lumen is crucial. However, a fully automatic Computer Aided Diagnosis system capable to display the different lumens in an easily comprehensible and timely manner is still not available. n nIn this paper we present a method that segments the entire aorta and then identifies the two lumens separated by the dissection membrane. The algorithm misdetected part of the membrane in only one of the 15 cases tested, where the aorta has not been significantly altered by the presence of aneurisms.

Automatic Ascending Aorta Detection in CTA Datasets

The assessment of coronary arteries is an essential step when diagnosing coronary heart diseases. There exists a wide range of specialized algorithms for the segmentation of the coronary arteries in Computed Tomography Angiography datasets. In general, these algorithms have to be initialized by manually placing a seed point at the origins of the coronary arteries or within the ascending aorta. In this paper we present a fast and robust algorithm for the automatic detection of the ascending aorta in Computed Tomography Angiography datasets using a two-level threshold ray propagation approach. We further combine this method with an aorta segmentation and coronary artery tree detection algorithm to achieve a fully automatic coronary artery segmentation.