For every patient, nowadays, dentists use a software to generate the dental scheme. The dental scheme is basically a diagram representing the whole dentition of the patient. On this diagram, each tooth is represented along with the various operations the patient underwent. The dental scheme for instance shows whether some teeth are missing, or if any treatment was ever performed on the dental roots, it also represents the dental fillings, removable prosthesis, dental crowns or tooth bridges. Filling up the dental scheme may be tedious for dentists, as for every new patient, they would have to carefully make an inventory of every dental care the patient underwent. In this work, we intend to study the feasibility of automatically generating the dental scheme from radiographs. Indeed, we aim to propose an image processing method that would automatically detect missing teeth, as well as any dental care in the dentition, this may save a significant amount of time during the dental consultation. In a first step, our method extracts the relevant portion of the scanner image, i.e. we automatically crop the dentition and thus remove the jaws and chin. The bending of the jaw (dentition curvature) is also estimated, and allows to distinguish the upper and lower jaws. A local minimum/maximum computation coupled with the Hough transform, and a fit with Gaussian Mixture Models helps us to segment the teeth despite strong luminance irregularities due to the imaged spine.
KEYWORDS: Bone, 3D modeling, Anisotropy, Physiology, 3D image processing, Reconstruction algorithms, Tomography, 3D acquisition, Data acquisition, Wavelets, 3D image reconstruction, 3D microstructuring
Trabecular bone and its microarchitecture are of prime importance for health. This paper focuses onto the relationship between bone microarchitecture and the texture found on micro CT projections. From a small animal study, 5 mice legs were studied by microCT at a resolution of 6μm. The 3D reconstructions are only used as ground truth for their microarchitecture parameters. The study uses 2 different sets of tomographic data : 3 volumes acquired at ANU in Canberra and 2 volumes acquired in Nantes. For each projection set, we determine the texture orientation onto a ROI region of both medial epiphysis and diaphisys using a local variance computed onto Mojette projections from the ROI.
Carotid surgery is a frequent act corresponding to 15 to 20 thousands operations per year in France. Cerebral perfusion has to be tracked before and after carotid surgery. In this paper, a diagnosis support using quality metrics is proposed to detect vascular lesions on MR images. Our key stake is to provide a detection tool mimicking the human visual system behavior during the visual inspection. Relevant Human Visual System (HVS) properties should be integrated in our lesion detection method, which must be robust to common distortions in medical images. Our goal is twofold: to help the neuroradiologist to perform its task better and faster but also to provide a way to reduce the risk of bias in image analysis. Objective quality metrics (OQM) are methods whose goal is to predict the perceived quality. In this work, we use Objective Quality Metrics to detect perceivable differences between pairs of images.
The Mojette transform is a discrete and exact Radon transform, based on the discrete geometry of the projection
and reconstruction lattice. The specific sampling scheme of the Mojette transform results in theoretical exact
image reconstruction. In this paper, we compare the reconstructions obtained with the Mojette transform to
the ones obtained with several usual projection/backprojection digitized Radon transform. These experiments
validate and demonstrate the performance of the Mojette transform sampling over classical implementations
based on continuous space.
Trabecular bone and its micro-architecture are of prime importance for health. Changes of bone micro-architecture are linked to different pathological situations like osteoporosis and begin now to be understood. In a previous paper, we started to investigate the relationships between bone and vessels and we also proposed to build a Bone Atlas. This study describes how to proceed for the elaboration and use of such an atlas. Here, we restricted the Atlas to legs (tibia, femur) of rats in order to work with well known geometry of the bone micro-architecture. From only 6 acquired bone, 132 trabecular bone volumes were generated using simple mathematical morphology tools. The variety and veracity of the created micro-architecture volumes is presented in this paper. Medical application and final goal would be to determinate bone micro-architecture with some angulated radiographs (3 or 4) and to easily diagnose the bone status (healthy, pathological or healing bone...).
Trabecular bone and its micro-architecture are of prime importance for health. Changes of bone micro-architecture are linked to different pathological situations like osteoporosis and begin now to be understood. In a previous paper [12], we started to investigate the relationships between bone and vessels and proposed some indices of characterization for the vessels issued from those used for the bone. Our main objective in this paper is to qualify the classical values used for bone as well as those we proposed for vessels according to different acquisition parameters and for several thresholding methods used to separate bone vessels and background. This study is also based on vessels perfusion by a contrast agent (barium sulfate mixed with gelatin) before euthanasia on rats. Femurs and tibias as well as mandibles were removed after rat’s death and were imaged by microCT (Skyscan 1272, Bruker, Belgium) with a resolution ranging from 18 to 3μm. The so obtained images were analyzed with various softwares (NRecon Reconstruction, CtAn, and CtVox from Bruker) in order to calculate bone and vessels micro-architecture parameters (density of bone/blood within the volume), and to know if the results both for bone and vascular micro-architecture are constant along the chosen pixel resolution. The result is clearly negative. We found a very different characterization both for bone and vessels with the 3μm acquisition. Tibia and mandibles bones were also used to show results that can be visually assessed. The largest portions of the vascular tree are orthogonal to the obtained slices of the bone. Therefore, the contrast agent appears as cylinders of various sizes.
Micro-CT represents a modality where the quality of CT reconstruction is very high thanks to the acquisition properties.
The goal of this paper is to challenge our proposed Mojette discrete reconstruction scheme from real micro-CT data. A
first study was done to analyze bone image degradations by lowering the number of projections. A second study analyzes
trabecular bone and vessels tree through an animal study. Small vessels are filling trabecular holes with almost the same
grey levels as the bone. Therefore vessel detectability that can be achieved from the reconstruction algorithm according
to the number of projections is a major issue.
Trabecular bone and its microarchitecture are of prime importance for health. Studying vascularization helps to better know the relationship between bone and vascular microarchitecture. This research is an animal study (nine Lewis rats), based on the perfusion of vascularization by a contrast agent (a mixture of 50% barium sulfate with 1.5% of gelatin) before euthanasia. The samples were studied by micro CT at a resolution of 9μm. Softwares were used to show 3D volumes of bone and vessels, to calculate bone and vessels microarchitecture parameters. This study aims to understand simultaneously the bone microarchitecture and its vascular microarchitecture.
Pauline Bléry, Yves Amouriq, Jeanpierre Guédon, Paul Pilet, Nicolas Normand, Nicolas Durand, Florent Espitalier, Aurore Arlicot, Olivier Malard, Pierre Weiss
The squamous cell carcinomas of the upper aero-digestive tract represent about ten percent of cancers. External
radiation therapy leads to esthetic and functional consequences, and to a decrease of the bone mechanical
abilities. For these patients, the oral prosthetic rehabilitation, including possibilities of dental implant placement,
is difficult. The effects of radiotherapy on bone microarchitecture parameters are not well known. Thus, the
purpose of this study is to assess the effects of external radiation on bone micro architecture in an experimental
model of 25 rats using micro CT. 15 rats were irradiated on the hind limbs by a single dose of 20 Grays, and 10
rats were non irradiated. Images of irradiated and healthy bone were compared. Bone microarchitecture
parameters (including trabecular thickness, trabecular number, trabecular separation, connectivity density and
tissue and bone volume) between irradiated and non-irradiated bones were calculated and compared using a
Mann and Whitney test. After 7 and 12 weeks, images of irradiated and healthy bone are different. Differences on
the irradiated and the healthy bone populations exhibit a statistical significance. Trabecular number, connectivity
density and closed porosity are less important on irradiated bone. Trabecular thickness and separation increase
for irradiated bone. These parameters indicate a decrease of irradiated bone properties. Finally, the external
irradiation induces changes on the bone micro architecture. This knowledge is of prime importance for better oral
prosthetic rehabilitation, including implant placement.
Bone microarchitecture is the predictor of bone quality or bone disease. It can only be measured on a bone biopsy, which
is invasive and not available for all clinical situations. Texture analysis on radiographs is a common way to investigate
bone microarchitecture. But relationships between three-dimension histomorphometric parameters and two-dimension
texture parameters are not always well known, with poor results. The aim of this paper is twofold : to study one classical
parameter namely the fractal dimension which is easily computed on the 2D binary texture and to explore its
relationships with the microarchitecture. We performed several experiments in order to check from ground truth the
different possible values and their possible explanations. The results show great variations of the fractal dimension
according to the size of the window and its location. These variations can be explained both by a misuse of the algorithm
and by the number of trabecular and their characteristics inside the window where the fractal dimension is computed.
This study also shows a specific interest to work with dual fractal dimension of the bone-spongious tissues.
KEYWORDS: Clouds, Data storage, Picture Archiving and Communication System, Image storage, Medicine, Distributed computing, Medical imaging, Computer security, Multimedia, Web services
Dicom images of patients will necessarily been stored in Clouds. However, ethical constraints must apply. In this paper,
a method which provides the two following conditions is presented:
1) the medical information is not readable by the cloud owner since it is distributed along several clouds
2) the medical information can be retrieved from any sufficient subset of clouds
In order to obtain this result in a real time processing, the Mojette transform is used.
This paper reviews the interesting features of the Mojette transform in terms of information theory. Since only portions
of the original Dicom files are stored into each cloud, their contents are not reachable. For instance, we use 4 different
public clouds to save 4 different projections of each file, with the additional condition that any 3 over 4 projections are
enough to reconstruct the original file. Thus, even if a cloud is unavailable when the user wants to load a Dicom file, the
other 3 are giving enough information for real time reconstruction. The paper presents an implementation on 3 actual
clouds. For ethical reasons, we use a Dicom image spreaded over 3 public clouds to show the obtained confidentiality
and possible real time recovery.
The precision of a medical LINear ACcelerator (LINAC) gantry rotation angle is crucial for the radiation therapy process,
especially in stereotactic radio surgery, given the expected precision of the treatment and in Image Guided Radiation Therapy
(IGRT) where the mechanical stability is disturbed due to the additional weight of the kV x-ray tube and detector.
We present in this paper an extension of the Winston and Lutz test initially dedicated to control the size and the position
of the isocenter of the LINAC and here adapted to test the gantry rotation angle with no additional portal images.
This new method uses a test-object patented by QualiFormeD5 and is integrated in the QUALIMAGIQ software platform
developed to automatically analyze images acquired for quality control of medical devices.
KEYWORDS: Monte Carlo methods, Bone, Control systems, Radiotherapy, Bladder, Optical simulations, Data modeling, Prostate, Computer simulations, Photon transport
Last year, we demonstrated the feasibility of a new method to perform dosimetric quality control of Treatment Planning
Systems in radiotherapy, this method is based on Monte-Carlo simulations and uses anatomical Digital Test Objects
(DTOs). The pelvic DTO was used in order to assess this new method on an ECLIPSE VARIAN Treatment Planning
System. Large dose variations were observed particularly in air and bone equivalent material.
In this current work, we discuss the results of the previous paper and provide an explanation for observed dose
differences, the VARIAN Eclipse (Anisotropic Analytical) algorithm was investigated. Monte Carlo simulations (MC)
were performed with a PENELOPE code version 2003. To increase efficiency of MC simulations, we have used our
parallelized version based on the standard MPI (Message Passing Interface). The parallel code has been run on a 32-
processor SGI cluster. The study was carried out using pelvic DTOs and was performed for low- and high-energy photon
beams (6 and 18MV) on 2100CD VARIAN linear accelerator. A square field (10x10 cm2) was used. Assuming the MC
data as reference, χ index analyze was carried out. For this study, a distance to agreement (DTA) was set to 7mm
while the dose difference was set to 5% as recommended in the TRS-430 and TG-53 (on the beam axis in 3-D
inhomogeneities). When using Monte Carlo PENELOPE, the absorbed dose is computed to the medium, however
the TPS computes dose to water. We have used the method described by Siebers et al. based on Bragg-Gray
cavity theory to convert MC simulated dose to medium to dose to water. Results show a strong consistency between
ECLIPSE and MC calculations on the beam axis.
Bone microarchitecture is the predictor of bone quality or bone disease. It can only be measured on a bone biopsy,
which is invasive and not available for all clinical situations. Texture analysis on radiographs is a common way to
investigate bone microarchitecture. But relationship between three-dimension histomorphometric parameters and two-dimension
texture parameters is not always well known, with poor results. The aim of this study is to performed
angulated radiographs of the same region of interest and see if a better relationship between texture analysis on several
radiographs and histomorphometric parameters can be developed. Computed radiography images of dog (Beagle)
mandible section in molar regions were compared with high-resolution micro-CT (Computed-Tomograph) volumes.
Four radiographs with 27° angle (up, down, left, right, using Rinn ring and customized arm positioning system) were
performed from initial radiograph position. Bone texture parameters were calculated on all images. Texture parameters
were also computed from new images obtained by difference between angulated images. Results of fractal values in
different trabecular areas give some caracterisation of bone microarchitecture.
In this paper, we deepen the R&D program named DTO-DC (Digital Object Test and Dosimetric Console),
which goal is to develop an efficient, accurate and full method to achieve dosimetric quality control (QC) of radiotherapy
treatment planning system (TPS). This method is mainly based on Digital Test Objects (DTOs) and on Monte Carlo
(MC) simulation using the PENELOPE code [1]. These benchmark simulations can advantageously replace experimental
measures typically used as reference for comparison with TPS calculated dose. Indeed, the MC simulations rather than
dosimetric measurements allow contemplating QC without tying treatment devices and offer in many situations (i.p.
heterogeneous medium, lack of scattering volume...) better accuracy compared to dose measurements with classical
dosimetry equipment of a radiation therapy department. Furthermore using MC simulations and DTOs, i.e. a totally
numerical QC tools, will also simplify QC implementation, and enable process automation; this allows radiotherapy
centers to have a more complete and thorough QC. The program DTO-DC was established primarily on ELEKTA
accelerator (photons mode) using non-anatomical DTOs [2]. Today our aim is to complete and apply this program on
VARIAN accelerator (photons and electrons mode) using anatomical DTOs.
First, we developed, modeled and created three anatomical DTOs in DICOM format: 'Head and Neck', Thorax
and Pelvis. We parallelized the PENELOPE code using MPI libraries to accelerate their calculation, we have modeled in
PENELOPE geometry Clinac head of Varian Clinac 2100CD (photons mode). Then, to implement this method, we
calculated the dose distributions in Pelvis DTO using PENELOPE and ECLIPSE TPS. Finally we compared simulated
and calculated dose distributions employing the relative difference proposed by Venselaar [3].
The results of this work demonstrate the feasibility of this method that provides a more accurate and easily achievable
QC. Nonetheless, this method, implemented on ECLIPSE TPS version 8.6.15, has revealed large discrepancies (11%)
between Monte Carlo simulations and the AAA algorithm calculations especially in equivalent air and equivalent bone
areas. Our work will be completed by dose measurement (with film) in the presence of heterogeneous environment to
validate MC simulations.
Mechanical stability of a medical LINear ACcelerator (LINAC), particularly the quality of the gantry, collimator and table rotations and the accuracy of the isocenter position, are crucial for the radiation therapy process, especially in stereotactic radio surgery and in Image Guided Radiation Therapy (IGRT) where this mechanical stability is perturbed due to the additional weight the kV x-ray tube and detector.
In this paper, we present a new method to evaluate a software which is used to perform an automatic measurement of the "size" (flex map) and the location of the kV and the MV isocenters of the linear accelerator. The method consists of developing a complete numerical 3D simulation of a LINAC and physical phantoms in order to produce Electronic Portal Imaging Device (EPID) images including calibrated distortions of the mechanical movement of the gantry and isocenter misalignments.
Shape description is an important step in image analysis. The skeleton is used as a simple, compact representation of a
shape. A skeleton represents the line centered in the shape and must be homotopic and one point wide. Current skeletonization
algorithms compute the skeleton over several image scans, using either thinning algorithms or distance transforms.
The principle of thinning is to delete points as one goes along, preserving the topology of the shape. On the other hand,
the maxima of the local distance transform identifies the skeleton and is an equivalent way to calculate the medial axis.
However, with this method, the skeleton obtained is disconnected so it is required to connect all the points of the medial
axis to produce the skeleton. In this study we introduce a translated distance transform and adapt an existing distance driven
homotopic algorithm to perform skeletonization with a single scan and thus allow the processing of unbounded images.
This method is applied, in our study, on micro scanner images of trabecular bones. We wish to characterize the bone micro
architecture in order to quantify bone integrity.
For some authors trabecular bone is highly visible in intraoral radiographs. For other authors, the observed intrabony
trabecular pattern is a representation of only the endosteal surface of cortical bone, not of intermedullary striae. The
purpose of this preliminary study was to investigate the true anatomical structures that are visible in routine dental
radiographs and classically denoted trabecular bone. This is a major point for bone texture analysis on radiographs.
Computed radiography (CR) images of dog mandible section in molar region were compared with simulations calculated
from high-resolution micro-CT volumes. Calculated simulations were obtained using the Mojette Transform. By
digitally editing the CT volume, the simulations were separated into trabecular and cortical components into a region of
interest. Different images were compared and correlated, some bone micro-architecture parameters calculated. A high
correlation was found between computed radiographs and calculated simulations from micro-CT. The Mojette transform
was successful to obtain high quality images. Cortical bone did not contribute to change in a major way simulated
images. These first results imply that intrabony trabecular pattern observed on radiographs can not only be a
representation of the cortical bone endosteal surface and that trabecular bone is highly visible in intraoral radiographs.
The Radon transform and its inversion are the mathematical keys that enable tomography. Radon transforms are defined for continuous objects with continuous projections at all angles in [0,π). In practice, however, we pre-filter discrete projections taken at a discrete set of angles and reconstruct a discrete object. Since we
are approximating a continuous transform, it would seem that acquiring more projections at finer projection resolutions is the path to providing better reconstructions. Alternatively, a discrete Radon transform (DRT) and its inversion can be implemented. Then the angle set and the projection resolution are discrete having been predefined by the required resolution of the tomogram. DRT projections are not necessarily evenly spaced in [0, π),
but are concentrated in directions which require more information due to the discrete square [or cubic] grid of the reconstruction space. A DRT, by design, removes the need for interpolation, speeding up the reconstruction process and gives the minimum number of projections required, reducing the acquisition time and minimizing
the required radiation dose. This paper reviews the concept of a DRT and demonstrates how they can be used to reconstruct objects from
X-ray projections more efficiently in terms of the number of projections and to enable speedier reconstruction. This idea has been studied as early as 1977 by Myron Katz. The work begun by Katz has continued and many methods using different DRT versions have been proposed for tomographic image reconstruction. Here, results using several of the prominent DRT formalisms are included to demonstrate the different techniques involved. The quality and artifact structure of the reconstructed images are compared and contrasted with that obtained using standard filtered back projection.
Quality control of external conformal radiotherapy treatment planning systems softwares is a crucial issue. The treatment quality depends directly on the quality of treatment planning systems (TPS). Radiotherapists need to be sure that softwares compute accurately each parameter of the treatment. This paper focuses on the quality control of geometrical tools of the treatment planning systems, i.e. the virtual simulation software. These TPS compute the geometrical part of the treatment. They define the targets and shapes of the irradiation beams. Four operations done by these TPS are examined in this work. The quality control of the auto-contouring, auto-margin, isocenter computation and collimator conformation tools is treated with a new method based on Digital Test Objects (DTO). Standard methods for this quality control have been set up from the development of some Physical Test Objects (PTO). These methods are time-consuming, incomplete and inaccurate. Results are biased by the CT-scanner acquisition of PTOs and error evaluation is done with the graphic tools of the TPS. Our method uses DTOs and allows for an automated qualitative error evaluation. DTOs present many advantages for TPS quality control. They lead to a fast, accurate, complete and automatic quality assessment. Special DTOs have been developed to control the TPS tools mentioned previously as well as their automatic result analysis methods. A TPS has been controlled with these test objects. The quality assessment shows some errors and highlights some particularities in the TPS tools functioning. This quality control was then compared with the standard quality control.
Tomographic acquisition uses projection angles evenly distributed around 2π. The Mojette transform and the discrete
Finite Radon Transform (FRT) both use discrete geometry to overcome the ill-posedeness of the inverse Radon
transform. This paper focuses on the transformation of acquired tomographic projections into suitable discrete projection
forms. Discrete Mojette and FRT algorithms can then be used for image reconstruction. The impact of physical
acquisition parameters (which produce uncertainties in the detected projection data) is also analysed to determine the
possible useful interpolations according to the choice of angle acquisitions and the null space of the transform. The mean
square error (MSE) reconstruction results obtained for data from analytical phantoms consistently shows the superiority
of these discrete approaches when compared to the classical "continuous space" FBP reconstruction.
Accurate isocentre positioning of the treatment machine is essential for the radiation therapy process, especially in
stereotactic radio surgery and in image guided radiation therapy.
We present in this paper a new method to evaluate a software which is used to perform an automatic analysis of the
Winston-Lutz test used in order to determine position and size of the isocentre. The method consists of developing
digital phantoms that simulate mechanical distortions of the treatment machine as well as misalignments of the
positioning laser targeting the isocentre. These Digital Test Objects (DTOs) offer a detailed and profound evaluation of
the software and allow determining necessary adjustments which lead to high precision and therefore contributes to a
better treatment targeting.
This paper deals with the CT scanner images quality control, which is an important part of the quality control process of the CT scanner, which consists of making measurement in images of dedicated phantoms.
Standard methods consist of scan explorations of phantoms that contain different specific patterns1, 2. These methods rely on manual measurements with graphics tools in corresponding images (density, position, length...) or automatic measurements developed in softwares3, 4 that use some masks to determine the region of interest (ROI). The problem of these masks is that they may produce wrong results in case of misalignment of the phantom.
We propose a new method that consists, firstly of developing software tools that are capable of performing an automated analysis of CT images of three standard phantoms, LAP5 , GEMS6 and CATPHAN6007, in terms of slice thickness, spatial resolution, low and high level contrast, noise and uniformity. The method we have developed is completely automatic because it uses some protocols and special treatments in the images to automatically detect the position and the size of the ROI. Secondly, to test the performances of our software tools, we develop two digital phantoms which reproduce the exact geometry and composition of the physical phantoms, i.e. some perfect CT images of the real phantoms, and a complete set of distorted digital phantoms which represent the "perfect" phantom distorted by noise and blur calibrated functions to test the performances of our automated analysis software.
Conformal radiotherapy helps to deliver an accurate and effective cancer treatment by exactly targeting the
tumor. In this purpose, softwares of the treatment planning system (TPS) compute every geometric parameters
of the treatment. It is essential to control the quality of them because the TPS performances are directly
connected with the precision on the treated region. The standard method to control them is to use physical
test objects (PTOs).1, 2 The use of PTOs introduces uncertainties in the quality assessment because of the CT
scan. Another method to assess the quality of these softwares is to use digital test objects (DTOs).3-5 DTOs
are exactly known in a continuous and a discrete way. Thus the assessment of the TPS quality can be more
accurate and faster. The fact that the DTO characteristics are well known allows to calculate a theoretical result.
The comparison of the TPS and this theoretical results leads to a quantitative assessment of the TPS softwares
quality. This work presents the control of major quality criteria of digitally reconstructed radiograph (DRR)
computation: ray divergence, ray incidence and spatial resolution. Fully automated methods to control these
points have been developed. The same criteria have been tested with PTO and the quality assessments by the
two methods have been compared. The DTO methods appeared to be much more accurate because computable.
Wireless technology based on the IEEE 802.11 standard is widely deployed. This technology is used to support multiple types of communication services (data, voice, image) with different QoS requirements. MANET (Mobile Adhoc NETwork) does not require a fixed infrastructure. Mobile nodes communicate through multihop paths. The wireless communication medium has variable and unpredictable characteristics. Furthermore, node mobility creates a continuously changing communication topology in which paths break and new one form dynamically. The routing table of each router in an adhoc network must be kept up-to-date. MANET uses Distance Vector or Link State algorithms which insure that the route to every host is always known. However, this approach must take into account the adhoc networks specific characteristics: dynamic topologies, limited bandwidth, energy constraints, limited physical security, ... Two main routing protocols categories are studied in this paper: proactive protocols (e.g. Optimised Link State Routing - OLSR) and reactive protocols (e.g. Ad hoc On Demand Distance Vector - AODV, Dynamic Source Routing - DSR). The proactive protocols are based on periodic exchanges that update the routing tables to all possible destinations, even if no traffic goes through. The reactive protocols are based on on-demand route discoveries that update routing tables only for the destination that has traffic going through. The present paper focuses on study and performance evaluation of these categories using NS2 simulations. We have considered qualitative and quantitative criteria. The first one concerns distributed operation, loop-freedom, security, sleep period operation. The second are used to assess performance of different routing protocols presented in this paper. We can list end-to-end data delay, jitter, packet delivery ratio, routing load, activity distribution. Comparative study will be presented with number of networking context consideration and the results show the appropriate routing protocol for two kinds of communication services (data and voice).
Quality Control (QC) procedures are mandatory to achieve accuracy in radiotherapy treatments. For that purpose, classical methods generally use physical phantoms that are acquired by the system in place of the patient. In this paper, the use of digital test objects (DTO) replace the actual acquisition1. A DTO is a 3D scene description composed of simple and complex shapes from which discrete descriptions can be obtained. For QC needs, both the DICOM format (for Treatment Planning System (TPS) inputs) as well as continuous descriptions are required. The aim of this work is to define an equivalence model between a continuous description of the three dimensional (3D) scene used to define the DTO, and the DTO characteristics. The purpose is to have an XML- DTO description in order to compute discrete calculations from a continuous description. The defined structure allows also to obtain the three dimensional matrix of the DTO and then the series of slices stored in the DICOM format. Thus, it is shown how possibly design DTO for quality control in CT simulation and dosimetry.
The Mojette transform is an exact discrete version of the Radon transform that can be exactly implemented from the discrete object with its associated geometry. This exact method requires a very large set of projections that will not be acquired. Then, the goal of this paper is to show how the Mojette projections
set can be interpolated to enlarge the set of projections. The second part of the paper is devoted to recall the sampling geometry both of the reconstructed image and the projections. The third part of the paper presents two Mojette reconstruction algorithms: an exact backprojection filtering Mojette scheme which needs a
(large) finite number of projections and its equivalent FBP-Mojette method. The fourth section presents an angular interpolation method used to generate a suitable set of projections from the known information. The reconstruction results given by this new set of angles used with the two reconstruction methods presented are given and discussed. The quality assessement of the reconstruction algoritms in the case of an insufficient number of projections is done using synthetic phantoms.
The goal of this paper is to characterize the noise properties of a spline Filtered BackProjection (denoted as FBP) reconstruction scheme. More specifically, the paper focuses on angular and radial sampling of projection data and on assumed local properties of the function to be reconstructed. This new method is visually and quantitatively compared to standard sampling used for FBP scheme. In the second section, we recall the sampling geometry adapted to the discrete geometry of the reconstructed image. Properties of the discrete zero order Spline Ramp filter for classic angles and discrete angles generated from Farey’s series reconstruction are used to generate their equivalent representations for first order Spline filters. Digital phantoms are used to assess the results and the correctness of the linearity and shift-invariantness assumption for the discrete reconstructions. The filter gain has been studied in the Mojette case since the number of projections can be very
different from one angle to another. In the third section, we describe the Spline filter implementation and the continuous/discrete correspondence. In section 4, Poisson noise is added to noise-free onto the projections. The reconstructions between classic angle distribution and Mojette acquisition geometry are compared. Even if the number of bins per projections is fixed for classic FBP while it varies for the Mojette geometry (leading to very different noise behavior per bin) the results of both algorithms are very close. The discussion allows for a general comparison between classic FBP reconstruction and Mojette FBP. The very encouraging results obtained for the Mojette case conclude for the developments of future acquisition devices modeled with the Mojette geometry.
Iterative methods are now recognized as powerful tools to solve inverse problems such as tomographic reconstruction. In this paper, the main goal is to present a new reconstruction algorithm made from two components. An iterative algorithm, namely the Conjugate Gradient (CG) method, is used to solve the tomographic problem in the least square (LS) sense for our specific discrete Mojette geometry. The results are compared (with the same geometry) to the corresponding Mojette Filtered Back Projection (FBP) method. In the fist part of the paper, we recall the discrete geometry used to define the projection M and backprojection M* operators. In the second part, the CG algorithm is presented within the context of the Mojette geometry. Noise is then added onto these Mojette projections with respect to the sampling and reconstructions are performed. Finally the Toeplitz block Toeplitz (TBT) character of M*M is demonstrated.
Nowadays, most of treatments for external radiotherapy are prepared with Treatment Planning Systems (TPS) which uses a virtual patient generated by a set of transverse slices acquired with a CT scanner of the patient in treatment position 1 2 3. In the first step of virtual simulation, the TPS is used to define a ballistic allowing a good target covering and the lowest irradiation for normal tissues. This parameters optimisation of the treatment with the TPS is realised with particular graphic tools allowing to: •Contour the target, •Expand the limit of the target in order to take into account contouring uncertainties, patient set up errors, movements of the target during the treatment (internal movement of the target and external movement of the patient), and beam's penumbra, •Determine beams orientation and define dimensions and forms of the beams, •Visualize beams on the patient's skin and calculate some characteristic points which will be tattooed on the patient to assist the patient set up before treating, •Calculate for each beam a Digital Reconstructed Radiography (DRR) consisting in projecting the 3D CT virtual patient and beam limits with a cone beam geometry onto a plane. These DRR allow one for insuring the patient positioning during the treatment, essentially bone structures alignment by comparison with real radiography realized with the treatment X-ray source in the same geometric conditions (portal imaging).
Then DRR are preponderant to insure the geometric accuracy of the treatment. For this reason quality control of its computation is mandatory4 . Until now, this control is realised with real test objects including some special inclusions4 5 . This paper proposes to use some numerical test objects to control the quality DRR calculation in terms of computation time, beam angle, divergence and magnification precision, spatial and contrast resolutions. The main advantage of this proposed method is to avoid a real test object CT acquisition allowing for a drastic time reduction of the control as well as its automatic control. This method has been used to test a new method to compute DRR6 and is here presented to control a standard DRR calculation algorithm7 .
Within the framework of telemedicine, the amount of images leads first to use efficient lossless compression methods for the aim of storing information. Furthermore, multiresolution scheme including Region of Interest processing is an important feature for a remote access to medical images. Moreover, the securization of sensitive data (e.g. metadata from DICOM images) constitutes one more expected functionality: indeed the lost of IP packets could have tragic effects on a given diagnosis. For this purpose, we present in this paper an original scalable image compression technique (LAR method) used in association with a channel coding method based on the Mojette Transform, so that a hierarchical priority encoding system is elaborated.
The LAR (Locally Adaptive Resolution) coder, based on an non-uniform subsampling of the image, is a multi-layered scheme that provides just as well lossless representation of data as very low-bit rates encoded images. The Mojette transform technique realizes multiple description of information elements in a very low order of complexity. These descriptions are transmitted without adding any specific mechanism for regulating flows purpose. This global system provides a solution for secured transmission of medical images through low-bandwidth networks such as the Internet.
The Filtered BackProjection is still questionable since
many discrete versions have been derived from the continuous Radon formalism.
From a continuous point of view, a previous work has made a link between continuous and discrete FBP versions
denoted as Spline 0-FBP model leading to a regularization of the infinite Ramp filter by the Fourier transform of a
trapezoidal shape. However, projections have to be oversampled (compared to the pixel
size) to retrieve the theoretical properties of Sobolev and Spline spaces. Here we obtain a novel version of the Spline 0 FBP
algorithm with a complete continuous/discrete correspondence using a specific discrete Radon transform, the Mojette transform.
From a discrete point of view, the links toward the FBP algorithm are shaped with the morphological
description and the extended use of discrete projection angles. The resulting equivalent FBP scheme uses a selected set of angles
which covers all the possible discrete Katz's directions issued from the pixels of the (square) shape under reconstruction: this is
implemented using the corresponding Farey's series. We present a new version of a discrete FBP method using a finite number
of projections derived from discrete geometry considerations.
This paper makes links between these two approaches.
In this paper, we propose to perform a novel discrete implementation of the filtered back projection algorithm. For this, we use a version of the discrete exact Radon transform called the Mojette transform that has been developed in our team for few years. The initial questioning was centered about the angular distribution needed for the continuous Radon reconstruction. Because of the discrete set of angles used in the FBP algorithm, discrete angles issued from Farey's series were used. Our version of the FBP algorithm is compared with the classical FBP algorithm. The choice of the set of projection angles is discussed in order to produce a good and efficient angular sampling. Finally, the very different behaviors between the classical FBP and our algorithm justify our study.
Presently most Nuclear Medicine physicians are well trained to report PET FDG studies. However, only a very limited number of them are able to diagnose difficult, unusual cases. For this reason, we developed an electronic lightbox called POSITOSCOPE onto which PET studies can be downloaded, displayed, reported and sent to remote sites for expert advice. To promote its use, we emphasized user-friendliness which is a keypoint of the prototype: the POSITOSCOPE looks like a classical lightbox equipped with a small touchscreen and a digital sound recorder. It is connected to local PET scanners and long distance high speed networks. Difficult studies can thus be sent to remote experts. The request consists of the whole image data set and a soundtrack explaining its nature. It may be sent to one or more experts. At this stage, only the local physician is responsible for reporting even though (s)he makes use of remote expertise. The prototype is being tested in two hospitals and the clinical evaluation involving four University hospitals and one private practice Nuclear Medicine center, started last September. Our goal is not to have PET studies acquired in a local center and to have them reported in a remote reference center, but to provide remote expertise when necessary to improve daily reporting of PET studies and to improve the expertise of local Nuclear Medicine physicians. The concept may be easily extended to unusual single photon studies for which local expertise is not always available, and to multimodality studies.
This paper describes a new kind of use for image watermarking. A stream watermarking method is presented, in which a key allows the authorized users to recover the original image. Our algorithm exploits the redundancy properties of the Mojette Transform. This transform is based on a specific discrete version of the Radon transform with an exact inversion. Anyone whom knows the watermark key will be able to decode the original image whereas only a marked image can be decoded without this key. The presented algorithm is suitable for different applications when fragile and reversible watermarks are mandatory such as medical image watermarking, and it could also be used for a data access scheme (cryptography). A multiscale watermark variation is presented and can be used when different user profile levels are encountered.
To meet QoS for multimedia transmission over packet-lossy network such as IP networks, two ways can be followed, either the source scalability is extended to packets, or multiple description schemes are used. In this case, equivalence between packets is assumed and forward error correction is needed. In this paper the proposed solution allows multiple description of a scalable bitstream source using a backprojection operator. This operator belongs to the class of the Mojette transforms, already presented in ITCom2001. In this scheme a redundant projections set is firstly computed for different angles. In a second step only few projections are selected to check the reconstructibility (quantization step). Third an entropic coding on remaining projections is applied. The Mojette transform is an exact discrete Radon transform generating bins from
ixels (information elements) computed as XOR or standard additions. This transform is linear (in number of pixels and number of projections) both for coding and decoding. In this new scheme we propose, sub flows (when assuming source scalability) issued from the application output bitstreams are mapped into buffers. The projections issued from these buffers meet both the compression of the bitstreams and the
multiple descriptions constraints.
In this paper, the notion of multimedia ship area network is developed. The review of possible multimedia services, the possible physical layers, the different IP architectures as well as different levels of service, and finally the resulting simulations for hundreds of end-users are presented and commented.
This paper describes a new methodology for image watermarking which is suitable both for copyright protection and for data hiding. The two presented algorithms are based upon the morphological mathematics properties of the Mojette Transform (denoted as MT in the following). The main properties of the Mojette transform are roughly recalled and the linked concept of phantom which depicts the null space of the operator is presented. Theses phantoms are implemented in the spatial domain giving the added watermarks. Then, two algorithms are presented based on this type of marks, the first one is devoted to the copyright embedding process and the second describes the steganographic scheme. Corresponding extractions of either the mark or the hidden message are then described. Finally, results are given in the last section for the two above schemes and robustness characteristics for the first scheme in terms of geometric attacks as well as the data hiding capacity for the second algorithm are discussed.
The Mojette transform is a discrete projector generating bins from ixels (information elements) values. The initial bitstream is first rearranged into a 2D or n-dimensional box of ixels. Each bin value (belonging to a (n-1)-dimensional projection) is computed as the XOR addition of ixels belonging to a discrete line which fix the projection direction. The major advantage of this transform is the linear complexity (both in the number of ixels and the number of projections) for encoding and decoding. Each packet contains a projection, and additional projections can be computed without slowing the network flow. The size of this n-dimensional buffer is tuned according to the real- time constraints and to the desired packet size.
Video (and other multimedia sources) distribution starts to implement industrial solutions that supposes no quality of service (QoS) properties for the network. To overcome congestion problems in the core of a worldwide Internet network, mirrors sites at the edges of the network are dispatched. Thus the QoS problem is only relevant for the network extremities. Nevertheless, this strategy implies to replicate the multimedia database (denoted at MDB) at multiple edge points to meet the real-time constraints and to establish specific mechanisms between mirror sites to satisfy customer needs as for video distribution. For each of both kind of constraints, we propose a unique data/network representation.
A new method for data integrity on ATM protocol is proposed. The algorithm represents image data via a new transform called the Mojette. The transform and its inverse are in order of complexity of the fast Fourier transform. An object oriented model for image and sequence are presented. The method is tested on videoendoscopic sequences. This source- channel coding avoids any additional protocol over ATM to secure data and provide real-time possibilities.
In this paper, we present a multimedia, ATM network based approach to generating and transmitting imaging procedure multimedia (MmR) reports in emergency situations. This approach was applied to V/P lung scintigrams in our institution. The architecture of our multimedia reporting system consists of a (gamma) -camera providing V/P lung scintigram as Interfile formatted data, a workstation in which MmRs can be generated and from which they can be accessed, a set of low cost workstations where MmR can be displayed, and an ATM network running throughout our hospital and connecting the above stations. The main features of the MmR are detailed in the paper and are assessed from a physician point of view.
In this paper, we present different theoretical results linked with the Mojette transform that has been defined in VCIP '96. Direct and inverse transforms are extended to different implementations and the choice of the set of projections is deeply analyzed. Applications for image coding and image analysis are sketched to see the links between the Mojette transform with other tools: block/wavelet decomposition for coding and segmentation/texture for analysis.
The asynchronous transfer mode (ATM) appears as the standard protocol for image and video transmission. There is virtually no bandwidth limitations neither a restricted size of operating area. However, the main problem stands in the non-secured transmission when ATM native applications are implemented. This induced a new way of encoding images where the redundancy is generated into the CoDec. In this paper, we present the Mojette transform that generates the redundancy at the higher level of the coder in order to safely transmit image data. BLock and wavelet implementations associated with the Mojette transform are presented and compared not only from the coder point of view but for the source and the channel characteristics. For this specific case we also present the asynchronous Mojette reconstruction. An adapted object oriented model has been developed accordingly.
The goal of this paper is to describe a new fully reversible image transform specifically designed for image coding and transmission in a context of possible loss of information as encountered in ATM networks. The so-called Mojette transform, is based on a discrete exact radon transform which allows for a natural redundancy of the initial image information. The inverse Mojette transform is particularly flexible and efficient: any portion of the coded image can be replaced by another one if transmission problems occur. Furthermore, the transform is also well suited to the two-layers paradigm used for video transmission on ATM networks by using a multiscale and/or quadtree decomposition into the transform domain. Finally, we discuss the merits of the transform both for image storage and transmission in order to show its ability to operate as the core representation of digital images.
The goal of this paper is to describe a new fully-reversible image transform specifically designed for an efficient (pseudo-critical) coding while preserving a psychovisual Fourier domain description. There is now strong evidence for the presence of directional and angular sensitivity in the cells of the human visual cortex and the representation proposed here has for main objective to respect this human like filter bank. The decomposition is performed using a discrete Radon transform for the angular patches and by splitting each projection with a 1D spline wavelet for the radial part. Consequently, the whole algorithm is performed in the spatial domain. Finally, we show that the transform is both well-suited for psychovisual quantization and channel adapted coding.
KEYWORDS: Modeling, Statistical analysis, Tomography, Radon, Principal component analysis, Data modeling, Digital filtering, Filtering (signal processing), Data acquisition, Image filtering
The conventional approach to tomographic reconstruction in the presence of noise consists in finding some compromise between the likelihood of the noisy projections and the expected smoothness of the solution, given the ill-posed nature of the reconstruction problem. Modelling noise properties is usually performed in iterative reconstruction schemes. In this paper, an analytical approach to the reconstruction from noisy projections is proposed. A statistical model is used to separate the relevant part of the projections from noise before the reconstruction. As reconstruction of sampled noise-free projections is still an ill- posed problem, a continuity assumption regarding the object to be reconstructed is also formulated. This assumption allows us to derive a spline filtered backprojection in order to invert the Radon operator. Preliminary results show the interest of combining continuity assumptions with noise modelling into an analytical reconstruction procedure.
There are many current trends toward combining diagnostic tests and features in medical imaging. For this reason we have been exploring the stucture of the finite-training-sample bias and variance that one encounters in pilot or feasibility studies within this paradigm. Here we report on the case of the simple linear Bayesian classifier in a space of a few dimensions (two through fifteen). The results argue for the importance of estimating these effects in clinical studies, perhaps through the use of resampling techniques.
KEYWORDS: Signal to noise ratio, Digital imaging, Target detection, Sensors, Medical imaging, Interference (communication), Image processing, Digital image processing, Signal detection, Signal processing
Medical image quality can be defined in terms of observer performances in detecting image abnormalities, since diagnosis is essentially based on visual inspection of medical images. There exists a large body of theoretical and experimental work specifying it in terms of signal to noise ratio, area under the ROC curve, and detectability index. However, the comparison between the theoretical and experimental figures of merit (FOMs) is made difficult because FOMs do operate on different signals and observers. In this paper we investigate the relationships between such signals, observers, and FOMs; the soundness of the underlying assumptions; and the possibility of optimizing image display. In section 2 we define three signal-observer pairs for which the main theoretical and experimental results are recalled. We also present the results obtained in our lab to show their consistency with results found in the literature. In section 3 we describe an experiment designed to evaluate the relationships between the three types of signal-observer pairs, and to assess the robustness of the model with respect to the assumptions. We also present in this section the results of this experiment. In section 4 these results and the relevance of FOMs are discussed.
In practical situations, images are discrete and only discrete filtering can be performed, such that the above theory must be adapted accordingly. In this paper, we derive the filter family which must replace the Gaussian kernel, in this case. The result can be understood because the Fourier transform of the second derivative corresponds to the multiplication by the square of the frequency, such that our filter is the discrete version of a Gaussian. In other words, our approach consistently generalizes the continuous theory to the discrete case. When the discrete equivalent of the Laplacian is defined on the basis of n-order B-spline interpolating functions, the image stack exactly verifies the continuous diffusion equation at the spatially sampled points. These results are generalized to any linear partial differential operator corresponding to another requirement on the image stack, just by defining the discrete equivalent operator.
The goal of this paper is to describe a consistent method which permits to define discrete image processing operators in the same way as discrete image formation operators. This is done via the use of the generalized sampling theorem which establishes the relationship between continuous and discrete functions according to the mean-square error in a spline or bandlimited subspace. A discrete operator is defined according to its continuous counterpart operating on continuous functions in the same subspace. Classical medical image acquisition bases often are radial where classical image processing operators are deduced from separable bases. The paper shows the trends between these two imperatives for medical image processing, explains where are the risks for information loss induced by implementing discrete linear operators and presents two methods to partially or totally keep the initial stored information.
KEYWORDS: Image processing, Data modeling, Composites, Medical imaging, Data processing, Lung, Image compression, 3D image processing, Sensors, Image filtering
For the last two years, we have been developing a medical image processing system driven by a knowledge-based system, which has been partially presents at the last SPIE Medical Imaging conference. In short, it consists of three modules: (1) an expert system (ES) which handles generic knowledge about image processing, image sources and medicine, and specific knowledge for every developed application. Consequently, it knows why, under which circumstances and in which environment an image processing tool must be achieved. (2) a relational data base (rDB) on which the ES may perform requests to select image data for an application. (3) an image processing (IP) toolbox which is able to run procedures according to the ES specifications on data pointed to by the rDB. In other words the IP toolbox knows how to run a procedure but not why.
Previous formulations for the noise power spectrum (NPS) of tomographic images have usually been obtained using a radially bandlimited discrete representation of the continuous 2- D function under reconstruction. Also, the same sampling distance is used to represent discrete versions of the function and its projection. In this paper, the expression for the NPS is generalized to spline and bandlimited subspaces of square-integrable functions and to unequal sampling distances for the image and the projection data. The theory was used to predict the NPS obtained using several different sets of basis functions: radially bandlimited (Shepp- Logan) and angular dependent splines, i.e., B-splines of degree 0 (Haar system), degree 1, degree 3, and separable bandlimited. Measurement of the NPS of simulated images was used to confirm the predictions of the theory. The NPS shows different radial and angular dependent characteristics for each set of basis functions, and for oversampling of the projection data. The magnitude of the aliasing in the reconstructed image depends on the choice of basis functions. Thus the basis functions used and the type of object imaged must be considered in any evaluation of the imaging system.
In this paper, a new approach to the Filtered BackProjection (FBP) algorithm is presented. The method is based on the reconstruction stability in Sobolev spaces and B-spline functions which define a Pixel Intensity Distribution Model (PIDM-n) according to the spline degree n of the desired reconstruction. It is shown that PIDM-n reconstructions can be efficiently obtained. Angular sampling is studied and comparison with standard FBP shows the superiority of the algorithm presented. Moreover, simulation studies of noise degradation and blur in the projections show the algorithm to be superior to FBP in this more realistic case.
In this paper, a continuous / discrete projection / backprojection model is presented, from which the validity of
the discrete projection / reconstruction algorithm can be assessed. We mainly focus on projection sampling since angular
sampling has been extensively studied previously. For this purpose a pixel intensity distribution model relating continuous
and discrete original functions is proposed. Sampling of model projections is then studied, and projection filtering analyzed.
Proper implementation of the discrete backprojection operator is derived, such that the resulting reconstructed function can
be compared with the original one, and the overall consistency of the aproach proved. Experimental results are presented to
demonstrate the validity of the theoritical approach. The consequences of properly sampling projections in practical
conditions are fmally discussed.
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