6,492 research outputs found
A Multi-modal Brain Image Registration Framework for US-guided Neuronavigation Systems - Integrating MR and US for Minimally Invasive Neuroimaging
US-guided neuronavigation exploits the simplicity of use and minimal invasiveness of Ultrasound (US) imaging and the high tissue resolution and signal-to-noise ratio of Magnetic Resonance Imaging (MRI) to guide brain surgeries. More specifically, the intra-operative 3D US images are combined with pre-operative MR images to accurately localise the course of instruments in the operative field with minimal invasiveness. Multi-modal image registration of 3D US and MR images is an essential part of such system. In this paper, we present a complete software framework that enables the registration US and MR brain scans based on a multi resolution deformable transform, tackling elastic deformations (i.e. brain shifts) possibly occurring during the surgical procedure. The framework supports also simpler and faster registration techniques, based on rigid or affine transforms, and enables the interactive visualisation and rendering of the overlaid US and MRI volumes. The registration was experimentally validated on a public dataset of realistic brain phantom images, at different levels of artificially induced deformations
Medical image computing and computer-aided medical interventions applied to soft tissues. Work in progress in urology
Until recently, Computer-Aided Medical Interventions (CAMI) and Medical
Robotics have focused on rigid and non deformable anatomical structures.
Nowadays, special attention is paid to soft tissues, raising complex issues due
to their mobility and deformation. Mini-invasive digestive surgery was probably
one of the first fields where soft tissues were handled through the development
of simulators, tracking of anatomical structures and specific assistance
robots. However, other clinical domains, for instance urology, are concerned.
Indeed, laparoscopic surgery, new tumour destruction techniques (e.g. HIFU,
radiofrequency, or cryoablation), increasingly early detection of cancer, and
use of interventional and diagnostic imaging modalities, recently opened new
challenges to the urologist and scientists involved in CAMI. This resulted in
the last five years in a very significant increase of research and developments
of computer-aided urology systems. In this paper, we propose a description of
the main problems related to computer-aided diagnostic and therapy of soft
tissues and give a survey of the different types of assistance offered to the
urologist: robotization, image fusion, surgical navigation. Both research
projects and operational industrial systems are discussed
Prostate Biopsy Assistance System with Gland Deformation Estimation for Enhanced Precision
Computer-assisted prostate biopsies became a very active research area during
the last years. Prostate tracking makes it possi- ble to overcome several
drawbacks of the current standard transrectal ultrasound (TRUS) biopsy
procedure, namely the insufficient targeting accuracy which may lead to a
biopsy distribution of poor quality, the very approximate knowledge about the
actual location of the sampled tissues which makes it difficult to implement
focal therapy strategies based on biopsy results, and finally the difficulty to
precisely reach non-ultrasound (US) targets stemming from different modalities,
statistical atlases or previous biopsy series. The prostate tracking systems
presented so far are limited to rigid transformation tracking. However, the
gland can get considerably deformed during the intervention because of US probe
pres- sure and patient movements. We propose to use 3D US combined with
image-based elastic registration to estimate these deformations. A fast elastic
registration algorithm that copes with the frequently occurring US shadows is
presented. A patient cohort study was performed, which yielded a statistically
significant in-vivo accuracy of 0.83+-0.54mm.Comment: This version of the paper integrates a correction concerning the
local similarity measure w.r.t. the proceedings (this typing error could not
be corrected before editing the proceedings
Atlas-Based Prostate Segmentation Using an Hybrid Registration
Purpose: This paper presents the preliminary results of a semi-automatic
method for prostate segmentation of Magnetic Resonance Images (MRI) which aims
to be incorporated in a navigation system for prostate brachytherapy. Methods:
The method is based on the registration of an anatomical atlas computed from a
population of 18 MRI exams onto a patient image. An hybrid registration
framework which couples an intensity-based registration with a robust
point-matching algorithm is used for both atlas building and atlas
registration. Results: The method has been validated on the same dataset that
the one used to construct the atlas using the "leave-one-out method". Results
gives a mean error of 3.39 mm and a standard deviation of 1.95 mm with respect
to expert segmentations. Conclusions: We think that this segmentation tool may
be a very valuable help to the clinician for routine quantitative image
exploitation.Comment: International Journal of Computer Assisted Radiology and Surgery
(2008) 000-99
MRI/TRUS data fusion for brachytherapy
BACKGROUND: Prostate brachytherapy consists in placing radioactive seeds for
tumour destruction under transrectal ultrasound imaging (TRUS) control. It
requires prostate delineation from the images for dose planning. Because
ultrasound imaging is patient- and operator-dependent, we have proposed to fuse
MRI data to TRUS data to make image processing more reliable. The technical
accuracy of this approach has already been evaluated. METHODS: We present work
in progress concerning the evaluation of the approach from the dosimetry
viewpoint. The objective is to determine what impact this system may have on
the treatment of the patient. Dose planning is performed from initial TRUS
prostate contours and evaluated on contours modified by data fusion. RESULTS:
For the eight patients included, we demonstrate that TRUS prostate volume is
most often underestimated and that dose is overestimated in a correlated way.
However, dose constraints are still verified for those eight patients.
CONCLUSIONS: This confirms our initial hypothesis
Framework for a low-cost intra-operative image-guided neuronavigator including brain shift compensation
In this paper we present a methodology to address the problem of brain tissue
deformation referred to as 'brain-shift'. This deformation occurs throughout a
neurosurgery intervention and strongly alters the accuracy of the
neuronavigation systems used to date in clinical routine which rely solely on
pre-operative patient imaging to locate the surgical target, such as a tumour
or a functional area. After a general description of the framework of our
intra-operative image-guided system, we describe a procedure to generate
patient specific finite element meshes of the brain and propose a biomechanical
model which can take into account tissue deformations and surgical procedures
that modify the brain structure, like tumour or tissue resection
Robust Cardiac Motion Estimation using Ultrafast Ultrasound Data: A Low-Rank-Topology-Preserving Approach
Cardiac motion estimation is an important diagnostic tool to detect heart
diseases and it has been explored with modalities such as MRI and conventional
ultrasound (US) sequences. US cardiac motion estimation still presents
challenges because of the complex motion patterns and the presence of noise. In
this work, we propose a novel approach to estimate the cardiac motion using
ultrafast ultrasound data. -- Our solution is based on a variational
formulation characterized by the L2-regularized class. The displacement is
represented by a lattice of b-splines and we ensure robustness by applying a
maximum likelihood type estimator. While this is an important part of our
solution, the main highlight of this paper is to combine a low-rank data
representation with topology preservation. Low-rank data representation
(achieved by finding the k-dominant singular values of a Casorati Matrix
arranged from the data sequence) speeds up the global solution and achieves
noise reduction. On the other hand, topology preservation (achieved by
monitoring the Jacobian determinant) allows to radically rule out distortions
while carefully controlling the size of allowed expansions and contractions.
Our variational approach is carried out on a realistic dataset as well as on a
simulated one. We demonstrate how our proposed variational solution deals with
complex deformations through careful numerical experiments. While maintaining
the accuracy of the solution, the low-rank preprocessing is shown to speed up
the convergence of the variational problem. Beyond cardiac motion estimation,
our approach is promising for the analysis of other organs that experience
motion.Comment: 15 pages, 10 figures, Physics in Medicine and Biology, 201
Prosper: image and robot-guided prostate brachytherapy
Brachytherapy for localized prostate cancer consists in destroying cancer by
introducing iodine radioactive seeds into the gland through hollow needles. The
planning of the position of the seeds and their introduction into the prostate
is based on intra-operative ultrasound (US) imaging. We propose to optimize the
global quality of the procedure by: i) using 3D US; ii) enhancing US data with
MRI registration; iii) using a specially designed needle-insertion robot,
connected to the imaging data. The imaging methods have been successfully
tested on patient data while the robot accuracy has been evaluated on a
realistic deformable phantom
Three-dimensional myocardial strain estimation from volumetric ultrasound: experimental validation in an animal model
Although real-time three-dimensional echocardiography has the potential to allow for more accurate assessment of global and regional ventricular dynamics compared to the more traditional two-dimensional ultrasound examinations, it still requires rigorous testing and validation against other accepted techniques should it breakthrough as a standard examination in routine clinical practice. Very few studies have looked at a validation of regional functional indices in an in-vivo context. The aim of the present study therefore was to validate a previously proposed 3D strain estimation-method based on elastic registration of subsequent volumes on a segmental level in an animal model. Volumetric images were acquired with a GE Vivid7 ultrasound system in five open-chest sheep instrumented with ultrasonic microcrystals. Radial (epsilon(RR)), longitudinal (epsilon(LL)) and circumferential strain (epsilon(CC)) were estimated during four stages: at rest, during esmolol and dobutamine infusion, and during acute ischemia. Moderate correlations for epsilon(LL) (r=0.63; p<0.01) and epsilon(CC) (r=0.60; p=0.01) were obtained, whereas no significant radial correlation was found. These findings are comparable to the performance of the current state-of-the-art commercial 3D speckle tracking methods
Prostate biopsy tracking with deformation estimation
Transrectal biopsies under 2D ultrasound (US) control are the current
clinical standard for prostate cancer diagnosis. The isoechogenic nature of
prostate carcinoma makes it necessary to sample the gland systematically,
resulting in a low sensitivity. Also, it is difficult for the clinician to
follow the sampling protocol accurately under 2D US control and the exact
anatomical location of the biopsy cores is unknown after the intervention.
Tracking systems for prostate biopsies make it possible to generate biopsy
distribution maps for intra- and post-interventional quality control and 3D
visualisation of histological results for diagnosis and treatment planning.
They can also guide the clinician toward non-ultrasound targets. In this paper,
a volume-swept 3D US based tracking system for fast and accurate estimation of
prostate tissue motion is proposed. The entirely image-based system solves the
patient motion problem with an a priori model of rectal probe kinematics.
Prostate deformations are estimated with elastic registration to maximize
accuracy. The system is robust with only 17 registration failures out of 786
(2%) biopsy volumes acquired from 47 patients during biopsy sessions. Accuracy
was evaluated to 0.760.52mm using manually segmented fiducials on 687
registered volumes stemming from 40 patients. A clinical protocol for assisted
biopsy acquisition was designed and implemented as a biopsy assistance system,
which allows to overcome the draw-backs of the standard biopsy procedure.Comment: Medical Image Analysis (2011) epub ahead of prin
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