Biomedical subjects

J Troccaz

Publications and source records attributed to J Troccaz.

At least 19 recordsLinked to original sources

PubMed2001

A methodological tool for computer-assisted surgery interface design: its application to computer-assisted pericardial puncture.

Computer Assisted Surgery systems are becoming more and more prevalent. Design processes currently used, pay only a small attention to the surgeon's interaction. To address this lack in design, we propose the OP-a-S notation: OP-a-S modeling of a system adopts an interaction-centered point of view and highlights the links between the real world and the virtual world. Based on an OP-a-S modeling, predictive usability analysis can be performed by considering the ergonomic property. We illustrate our method on the retro-design of a computer assisted surgical application, CASPER.

Computer Simulation↗

PubMed2001

Clinical validation of computer assisted pelvic surgery using ultrasound. A percutaneous safe technique with low radiation exposure.

This study presents early results of the clinical experience of computer assisted surgery (CAS) applied to percutaneous iliosacral screwing. The results of these 10 first cases (4 patients) are compared to an historical series of 51 cases (30 patients). The CAS technique shows better screw placement without outside bone screw and a very low radiation exposure.

Adolescent↗

PubMed2000

Patient set-up using portal images: 2D/2D image registration using mutual information.

OBJECTIVE: Conformal radiation therapy requires accurate patient set-up for each fraction delivery. Electronic portal imaging devices allow the acquisition of portal images just before and even during dose delivery. However, the quantitative interpretation of these images in determining and correcting the patient's position remains uncertain, and automated methods are therefore being developed. Such methods must be usable for the different radiation therapy techniques. They must be robust and as automated as possible for use in clinical routines. This work was undertaken to establish the feasibility of 2D/2D registration for portal/portal and portal/simulator images in radiotherapy. MATERIALS AND METHODS: This paper describes an automated method based on the combination of calibration algorithms and pixel-based registration algorithms. We present experiments with the different imaging techniques, some of which use a phantom with and without a gold standard. Preliminary results obtained using patient data are also presented and discussed. RESULTS: The results obtained with a phantom demonstrated that this automated method for 2D/2D registration is fast, accurate, and robust, even in the case of blurred images for small treatment fields. CONCLUSIONS: Mutual information is a feasible method for 2D/2D portal/portal and portal/simulator image registration in radiotherapy.

Algorithms↗

PubMed2000

Computer-guided pericardiocentesis: experimental results and clinical perspectives.

Percutaneous pericardial puncture is a relatively safe and effective technique in case of large pericardial effusions when practiced under echographic or radiological control. The goal of our project is to improve the performance of this technique, mainly in case of smaller and loculated effusions using an accurate guidance towards a preplanned target, based on a model of the pericardial effusion. This paper presents preclinical results of this new computer-assisted technique used to reach the pericardial cavity. The procedure is divided into 3 steps: 1. acquisition of ultrasound data, using an echocardiographic device connected to a 3-D localizer and to a computer, 2. modeling procedure to define the optimal strategy taking into account the mobility of organs on a digital model, 3. guided puncture with a localized needle to reach the predefined target using a passive guidance system. After validation on a dynamic phantom and a feasibility study on dogs, an accuracy and reliability analysis protocol was realized on pigs with experimental pericardial effusion. Feasibility of the technique is demonstrated on animal study with an accuracy of at least 2.5 mm. Further clinical investigation is in progress using a more ergonomic and less cumbersome system. This study demonstrates the feasibility of computer-assisted pericardiocentesis. Beyond the simple improvement of the current technique, this could be a new way to reach the heart or a new tool for percutaneous access and image-guided puncture of soft tissues.

Animals↗

PubMed2000

Foreword

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Journal Article↗

PubMed2000

[Implantation of iliosacral screws. Simulation of optimal placement by 3-dimensional X-ray computed tomography].

PURPOSE OF THE STUDY: Percutaneous iliosacral screws are used advantageously to fix unstable pelvic girdle avoiding the morbidity of open access for conventional screw fixation. The insertion technique must be precise due to the risk of injury to the lumbosacral nerve trunk, the cauda equina roots, and the first sacral nerve. We undertook a study of the implantation site of iliosacral screws looking for a means of standardizing the drilling procedure on the basis of 3D computed tomography (CT) data. MATERIAL AND METHODS: A CT series with 3D reconstruction was performed on 11 pelvis bones. We retained pelvis parameters and characterized the axis and narrow zone of the sacral wing. The insertion routes of 6.5 mm cancelous bone screws were simulated: two iliosacral routes fixing S1, and two iliosacroiliac routes fixing S1 and S2. The values of the pelvic parameters and the positions of the screws were compared with the Spearman correlation test and graphic regression. RESULTS: The pelvic incidence was a mean 47 degrees. The length of the sacral wing was a mean 73 mm. The narrow zone of the wing was 47 mm from the lateral iliac fossa. In the narrow zone, the wing section showed an oval shape: 22 mm largest diameter, 11 mm smallest diameter. The wing was oriented 84 degrees in the paracoronal plane perpendicular to the plane of the sacral plate, 67 degrees in the para-axial plane parallel to the sacral plate, and 37 degrees in the sagittal plane of the subject. The length of the upper S1 screw was a mean 80 mm. This upper screw was inclined 89 degrees in the para-coronal plant, 61 degrees in the para-axial plane and 28 degrees in the sagittal plane. The length of the lower S1 screw as a mean 80 mm. This lower screw was inclined 74 degrees in the para-coronal plane, 91 degrees in the para-axial plane and 110 degrees in the sagittal plane. The fixation screws could be inserted in 12 out of 22 cases. Correlations were found with height of the subject, length of the wing and the screw, and screw inclination. The inclination of the upper S1 screw in the para-coronal plane was correlated with the larger diameter of the sacral wing. DISCUSSION: The pelvis parameters measured were comparable with data in the literature. The very small dimensions of the narrow zone dictate a very precise drilling for the narrow zone. This narrow zone determines the inclination of the screw insertion. In the sagittal plane the standard deviation was very large making it impossible to interpret the data. The route of the upper screw runs obliquely forward in the plane parallel to the sacral plate. The lower screw runs upwardly in the plane perpendicular to the sacral plate. It does not appear possible to insert fixation screws in a routine procedure. Preoperative assessment would be necessary before percutaneous insertion. CONCLUSION: The 3D CT reconstructions of the sacral wing can be used to determine the precise optimal position of the two iliosacral screws. The principle orientations can be deducted from the plane of the sacral plate. Approximate indications can help reduce operative time and exposure to irradiation (patient and surgeon). Percutaneous iliosacroiliac screw fixation cannot be proposed for all patients.

Adult↗

PubMed2000

[Image fusion methods for the repositioning of the patient in radiotherapy].

Conformal radiotherapy requires the accurate and reproducible setup of the patient for each fraction delivery. Megavoltage imaging could enable this. This requires the development of image processing and data fusion algorithms. We describe an automated method based on the use of mutual information for registration. Such a method does not require any preliminary segmentation of the images. This method has been extensively tested on phantom as well as on some patient data. The obtained results demonstrated that this automated method for 2D/2D registration is rapid, accurate and robust even in the case of blurred images for small treatment fields.

Humans↗

PubMed1999

The use of a semi-customized phantom for verification of conformal plans.

We have developed a technique for inverse treatment planning of prostate therapy designed to improve the degree of conformation between the dose distribution and the target volume. We compared the inverse plan with a "standard" four-field box technique as well as a four-field technique using oblique fields ("cross technique"). We validated the dosimetry of the inverse plan using Fricke gel solution in phantom specifically designed for this purpose. The phantom is a Plexiglas tank with a cross section, which approximates the dimensions of the pelvis. Anatomical data from computed tomography (CT) images of a patient were used to simulate organs in our phantom. This allows us to calculate dose distributions with the external geometry of the phantom and internal anatomy of the patient. Dose-volume histograms (DVHs) for the three different plans were calculated. The phantom containing the Fricke gel was irradiated according to the inverse plan. Magnetic resonance (MR) images was used to determine the dose distribution delivered to the phantom. We observe, on DVHs, that the inverse plan significantly reduces the dose to the rectum and the bladder but slightly increases the inhomogeneity inside the target volume. Correlation is good between isodoses on MR images and calculated isodoses. We conclude that inverse planning software can greatly improve the conformal degree of treatment to the prostate. This technique could be applied to other complex anatomic sites at which dose to organs at risk is a limiting factor and increased dose to the target volume is indicated. Our phantom and the Fricke gel solution are convenient to carry out validation of conformal treatments.

Humans↗

PubMed1999

Accurate guidance for percutaneous access to a specific target in soft tissues: preclinical study of computer-assisted pericardiocentesis.

In the field of percutaneous access to soft tissues, our project was to improve classical pericardiocentesis by performing accurate guidance to a selected target, according to a model of the pericardial effusion acquired through three-dimensional (3D) data recording. Required hardware is an echocardiographic device and a needle, both linked to a 3D localizer, and a computer. After acquiring echographic data, a modeling procedure allows definition of the optimal puncture strategy, taking into consideration the mobility of the heart, by determining a stable region, whatever the period of the cardiac cycle. A passive guidance system is then used to reach the planned target accurately, generally a site in the middle of the stable region. After validation on a dynamic phantom and a feasibility study in dogs, an accuracy and reliability analysis protocol was realized on pigs with experimental pericardial effusion. Ten consecutive successful punctures using various trajectories were performed on eight pigs. Nonbloody liquid was collected from pericardial effusions in the stable region (5 to 9 mm wide) within 10 to 15 minutes from echographic acquisition to drainage. Accuracy of at least 2.5 mm was demonstrated. This study demonstrates the feasibility of computer-assisted pericardiocentesis. Beyond the simple improvement of the current technique, this method could be a new way to reach the heart or a new tool for percutaneous access and image-guided puncture of soft tissues. Further investigation will be necessary before routine human application.

Animals↗

PubMed1998

Computer-assisted spine surgery.

The aim of this study was to improve the reliability of pedicle screw insertion. Transpedicle screw insertion may cause neurological, vascular, and mechanical complications. Previous studies of surgical procedures have shown a significant rate of incorrect placement of the screw ranging from 10 to 40%. A new technique that combines preoperative computed tomography (CT) imaging with intraoperative passive navigation was used to perform 64 pedicle screw insertions in the thoracolumbar region. At the same time, 64 pedicle screw insertions were performed manually in the same region and on the same vertebral levels. Surgery was followed in all cases by postoperative radiographs and computed tomography examination, which allowed measurements of screw position relative to pedicle position to be performed. A comparison between the two groups showed that six screws in 64 vertebra (9%) had incorrect placement with the computer-assisted technique whereas 28 screws in 64 vertebra (44%) had incorrect placement with manual insertion. The intraoperative accuracy provided by the computer after registration was better than 1 mm. The good results obtained are similar to those reported in the literature. The cortex penetration observed with the computer-assisted technique was not imputed to computer failure. Errors by the surgeon in acquiring data in the pre- and perioperative steps may explain the six incorrect screw placements. This clinical experience confirms that the accuracy and the reliability of this computer-assisted technique are good.

Bone Screws↗

PubMed1998

[Computer-assisted surgery: automated screw placement in the vertebral pedicle].

AIM OF THE STUDY: Previous studies of conventional surgical procedures have shown a significant rate of incorrect pedicle screw placement ranging from 10 to 40%. Transpedicle screw insertion may cause three types of complications: neurologic, vascular and mechanical. The aim of this prospective study is to improve the reliability of pedicle screwing with computer assistance. MATERIAL AND METHODS: A new and original technique that combines preoperative computed tomography imaging with intraoperative passive navigation has been used to perform 48 pedicle screwings in the thoracolumbar region. In the same time, 48 pedicle screwings were performed manually in the same region and on the same vertebral levels. With postoperative X-rays and computed tomography examination, screw position related to pedicle position could be assessed and comparison could be made between the two groups (with and without computer assistance). RESULTS: Two screws in 48 vertebra (4%) had incorrect placement with computer assisted technique whereas 18 screws in 48 vertebra (37%) had incorrect placement with manual insertion. The intraoperative accuracy provided by the computer after registration was better than 1 mm. The difference between the two groups was statistically highly significant (P < 0.0001). The cortex penetration observed with the computer assisted technique was not imputed to computer failures. Errors in acquiring data by the surgeon in the pre and peroperative steps may explain the two incorrect placements of the screws. CONCLUSION: This clinical experience confirms that the accuracy and reliability of this computer assisted technique are very good.

Bone Screws↗

PubMed1998

Guiding systems for computer-assisted surgery: introducing synergistic devices and discussing the different approaches.

Computer-assisted surgery (CAS) or computer-assisted therapy (CAT) attempt primarily to optimize the performance of medical tasks. CAS systems include a guiding system to connect the information world of data and plans to the physical world of surgeons, patients and instruments, and to supplement the surgeon's perception and dexterity. Passive, semi-active and active systems have been proposed and implemented in various clinical applications. In this paper we introduce synergistic devices which are an extension of semi-active systems. We also discuss the advantages of the different categories of guiding systems on the basis of a list of task-oriented and user-oriented qualitative factors.

Humans↗

PubMed1997

Computer assisted pericardial puncture: work in progress.

Until now, computer assisted surgery has focused primarily on surgical procedures involving rigid anatomical structures. Because soft tissues can be highly mobile and deformable, they may require specific imaging devices, suitable modeling tools, and guiding systems. Percutaneous pericardial puncture is a good clinical target for computer assisted surgery; this procedure is often performed without direct visualization and is dangerous even though echographic control is used. Computer assistance can greatly improve this technique and will allow accurate puncture of preplanned targets. This paper describes a new approach for computer assisted pericardial punctures (CASPER) and describes a first feasibility analysis of CASPER demonstrated with anesthetized animals. The approach is based on the use of echographic data localized in space, from which an optimal strategy is defined. Because of the specificity of the pericardial effusion, a stable target can be selected despite the heart motions. A passive guiding system is used. We have demonstrated the feasibility of the approach.

Animals↗

PubMed1997

Computer assisted spine surgery.

When inserting screws into a vertebral pedicle, the surgeon usually exposes the back part of the vertebra and uses his or her anatomic knowledge to align the drill in the proper direction. A slight error in direction may result in an important error in the position of the tip of the screw. This is done with no direct visibility of crucial structures (spinal cord, pleura, vessels). Statistical analysis of a series of surgical procedures has shown that 10% to 40% of the screws are not installed correctly. To reduce the risk of complication, a computer assisted method is proposed that enables the surgeon to place a screw at a position preoperatively defined in 3 dimensions using computed tomography images. This allows the surgeon to align a standard surgical drill with the optimal position and direction. The depth of the pilot hole during drilling also is monitored by the system to prevent penetration of the anterior cortex of the vertebral body. Using this procedure, in vitro tests were performed and showed that an accuracy of less than 1 mm can be obtained. Clinical trials were done in 10 patients who suffered severe scoliosis or spondylolisthesis. The trajectory of the holes drilled in L2, L3, L4, and L5 vertebrae were checked for all clinical tests. Postoperative radiographs and computed tomography scans showed that the screws were well inserted in each plane for each pedicle. This technique also can be used to perform osteosynthesis at the thoracic and cervical levels.

Adult↗

PubMed1996

Virtual echography. The simulation of ultrasonographic examination.

We present a Virtual Echographic System. Because this examination is particularly difficult, developing a simulator is very useful to give students some common databases of pathological samples on which they could experiment image acquisition and evaluate their understanding of clinical cases. We have applied our method to the simulation of thigh ultrasonographic examination for thrombosis diagnosis. A preliminary system, focusing on image generation, has been developed. Virtual echographic slices are generated using a particular interpolation technique and a deformation model of significant structures. Resulting images have a visual quality similar to usual ones.

Computer Simulation↗

PubMed1995

Computer-assisted spine surgery: a technique for accurate transpedicular screw fixation using CT data and a 3-D optical localizer.

The computer-assisted spine surgery system presented in this paper follows the basic ideas which have been developed for computer-assisted medical interventions (CAMI) in our lab since 1985. There are three steps to insert a linear tool inside vertebral pedicles. First, the surgeon defines an optimal trajectory on pre-operative computed tomography. Second, this trajectory is reported in the operating room coordinate system using an intra-operative sensor and a registration algorithm. Third, a guiding system helps the surgeon follow the selected trajectory. In this paper, we present an implementation of this method that uses only a 3-dimensional optical localizer. Results on cadaver specimens and on the first seven patients are presented.

Bone Screws↗

PubMed1995

Patient setup optimization for external conformal radiotherapy.

The aim of conformal radiotherapy is to deliver precisely a specific dose of radiation to a planning target volume, concurrently radiating as little healthy tissue and organs as possible. This can be accomplished only with the accurate positioning of the patient with respect to the radiotherapy system. In this paper, we describe a system to achieve a higher overall accuracy in the delivery of a prostatic radiation boost for treatment of carcinoma of the prostate. The system is based on the use of ultrasound images for measuring the actual position of the patient's prostate just before the radiation. Since these images are registered with pretreatment computed tomography or magnetic resonance imaging, the position and orientation of the planning target volume are computed with respect to the radiotherapy system and can be corrected as needed. This system is under clinical evaluation.

Computer Simulation↗

PubMed1995

Building a hybrid patient's model for augmented reality in surgery: a registration problem.

In the field of Augmented Reality in Surgery, building a hybrid patient's model, i.e. merging all the data and systems available for a given application, is a difficult but crucial technical problem. The purpose is to merge all the data that constitute the patient model with the reality of the surgery, i.e. the surgical tools and feedback devices. In this paper, we first develop this concept, we show that this construction comes to a problem of registration between various sensor data, and we detail a general framework of registration. The state of the art in this domain is presented. Finally, we show results that we have obtained using a method which is based on the use of anatomical reference surfaces. We show that in many clinical cases, registration is only possible through the use of internal patient structures.

Algorithms↗