Methods for medical applications

The paper presents an innovative approach totally based on digital data to optimize lower limb socket prosthesis design. This approach is based on a stump's detailed geometric model and provides a substitute to plaster cast obtained through the traditional manual methodology with a physical model, realized with Rapid Prototyping technologies; this physical model will be used for the socket lamination. The paper discusses a methodology to reconstruct a 3D geometric model of the stump able to describe with high accuracy and detail the complete structure subdivided into bones, soft tissues, muscular masses and dermis. Some different technologies are used for stump acquisition: non contact laser technique for external geometry, CT and MRI imaging technologies for the internal structure, the first one dedicated to bones geometrical model, the last for soft tissues and muscles. We discuss problems related to 3D geometric reconstruction: the patient and stump positioning for the different acquisitions, markers' definition on the stump to identify landmarks, alignment's strategies for the different digital models, in order to define a protocol procedure with a requested accuracy for socket's realization. Some case-studies illustrate the methodology and the results obtained. © 2006 SPIE-IS&T.

Keywords: 3D geometrical model , Human body scanning , Lower limb prosthesis , Medical imaging , Rapid prototyping , Reverse engineering

Aim of the work was the definition of an experimental procedure enabling to evaluate the mechanical properties of orthopaedic insoles used in daily and sport activities. Customers and manufacturers can be interested in knowing which is the durability of the insoles for a correct substitution of an exhausted sole together with for product liability. A cyclic test was developed for the measure of stiffness and damping properties of different types of insoles under pulsated compression loads applied by means of a servo hydraulic test machine. Accelerated fatigue tests were performed by applying repeated blocks of compression overloads and measuring periodically the mechanical properties of the insoles to estimate the insole durability. Finally, a group of subjects wearing insoles during daily life was involved in the study and two pairs of identical insoles were prepared for each subject: one pair underwent the fatigue test and the other pair was used by the subject in his daily activity (normal or sport) during a given period of time. Final comparison between the mechanical properties of used and tested insoles enabled to define the number of equivalent damage cycles per month of each type of customer. © 2006 Springer-Verlag New York.

Objectives: The aim of this study was to evaluate the effects of scanning parameters on the precision of the data acquired using a facial laser scanner and to assess the reliability of automatic model recording in humans. Methods: Data were acquired using a laser scanner (Cyberware 3030RGB); analysis and measurements were performed with Rapid Form 2004 software. A mannequin and six volunteers were scanned to investigate the effects of environmental conditions, positioning, head orientation, and software procedures. Precision and accuracy of the data were evaluated comparing six linear measures calculated on scanned data with those obtained directly. Two sessions with different head inclination were performed. The reliability of repeated scans was also assessed measuring the distance between the surfaces reconstructed from two separate scans of the same subject, at 12 anatomical points, in 5 subjects, during two sessions using a different head inclination. Differences were analysed using paired t-tests or analysis of variance (ANOVA). Results: The accuracy of scanning was ±0.65 mm. The development of a specific protocol resulted in a mean scanning error of 1-1.2 mm and a recording error of 0.3-0.4 mm on repeated scans of human subjects. Conclusions: This study indicates that scanning of the human face may be hampered by errors and artefacts, mainly due to movements. While the effect of trembling and involuntary movements during the exam may be minimized using faster scanning devices, comparative observation over time may be affected by unreal differences due to the uncertainty of facial expression. The overall error is, however, in the range useful for most clinical studies. © 2006 The British Institute of Radiology.

Keywords: Anthropometry , Face , Three-dimensional imaging , Validation studies

In the last two decades, medical and engineering specialists developed a more and more close cooperation. Dental and orthodontic sciences represent an excellent example of this synergic view. In particular, detailed information on stress distribution in the implant region may greatly help clinical experts to reduce risk of failures thus preventing the need for re-implantations. Of course, modeling and analysis of biological/medical structures is often based on subjective information that may considerably change from patient to patient. In view of this, the present research aims to set up a framework for building reliable analysis models from geometrical information gathered with medical imaging tools. In order to check the feasibility of the procedure, we considered the case of a human mandible for which a virtual model is reconstructed from Computerized Tomography. This case is very indicative because of the very high complexity of the anatomical district analyzed. The mandible model thus reconstructed has been studied with FEM analyses simulating four different scenarios that may occur during mastication. The experimental part of this research is the processing of CT scan files which actually requires a very accurate study and special cares. The experimental work then prosecuted with the construction of the a stereolithographic model that can be utilized for photoelastic investigations.

Incremental Forming processes have been introduced in the recent past as an alternative to the money consuming stamping technology, when small batches have to be manufactured. Anyway, they introduce some advantages in terms of flexibility and material formability but, also, some problems such as the dimensional accuracy decreasing. In this paper, a particular application is carried out taking into account the development of an innovative technique to produce a customised ankle support. In this way Incremental Forming process has been selected for the sheet profiling, exalting the role that this technology may play when single complex product has to be manufactured. The producing procedure finishes with a measure of the dimensional accuracy that shown a good result for the desired application. © 2005 Elsevier B.V. All rights reserved.

Keywords: Ankle support , Incremental Forming , Reverse engineering

In this paper, the activity aimed at the contact less acquisition, the generation of polygonal descriptive models, the generation of NURBS-based models and the reproduction by means of rapid prototyping tools of pieces of interest in both the heritage and the automotive domains are presented. The work gives an insight of how three-dimensional range cameras and suitable data modeling can be helpful in the reverse engineering and in the virtual representation of complex shapes. In addition, the research represents a valuable example of Computer Support Collaboration Work (CSCW) for the restoration and the rapid prototyping of the objects. © 2005 Taylor & Francis Group.

Computerized Tomography (CT) and Magnetic Resonance Imaging (MRI) are gold standards for cross-sectional images of the human body. Furthermore, several images reformatting softwares have been developed in order to assist pre-operating diagnosis and treatment planning. These softwares offer the possibility to interface scanning equipments with Solid Free-form Fabrication (SFF) systems, to build a custom made replica of the anatomical site. Selective Laser Sintering (SLS) and Sterolitography (SLA) manufacturing techniques are two kinds of SFF processes that produce physical models through a selective solidification of a variety of fine powders and liquids. SLS and SLA technologies are getting a great amount of attention, particularly in oral and maxillofacial surgery. When applying 3-D medical models to clinical cases, model accuracy is a major concern. We investigate the influence of different SFF manufacturing techniques and materials on the shape accuracy of anatomical models, derived from CT acquisition of a dry mandible, using full-field measurement system such as fringe projection techniques. The application of such a method, allows for objective decisions regarding the precise location of bony anatomical landmarks.

Keywords: 3-D Digitizing Techniques , Selective Laser Sintering , Solid Free-form Fabrication , Stereolitography

The purpose of the present work was to develop a tool for preoperatively planning the Total Hip Replacement (THR). Starting from the MR images, the 3D surface model of both the pelvis and the femur was built and the surgical operation was virtually performed. Data coming from gait analysis were added to visualize the physiologic movement of the hip joint. The resulting triangular mesh was sufficiently accurate to allow the building of the stereolithographic model of the joint by means of rapid prototyping technique. The plastic bones allow the user to have an enhanced vision of the surgical procedure to be performed. © 2005 CARS and Elsevier B.V.

Keywords: Magnetic resonance imaging , Rapid prototyping , Surgical planning , Total hip replacement

Many applications in orthopaedic surgery require the creation of personalised design models that can serve as the basis for navigation in computer aided surgery systems or be used to create a personalised model to perform structural analysis during pre-operative planning or post-operative follow-up. The paper introduces a method for developing a three-dimensional (3D) patient-specific model of a femur bone from an antero-posterior radiograph. A generic femur was employed and was altered on the basis of bone boundaries visible on radiographs. Morphological errors were evaluated against 3D models obtained from computed tomography (CT) scans. When only the antero-posterior radiograph was used, the average radius estimation error was 4.8 mm, the average percentage area estimation error was 14%, and the average percentage estimation error for inertial moments was 15%. If both the medial-lateral and the anterior-posterior radiographs were used, these errors were 2.0 mm, 5% and 7%, respectively. The procedure described can be profitably employed whenever CT scans are not available, such as during a retrospective analysis, or when CT scans cannot be justified because of X-ray exposure and cost considerations. © IFMBE: 2005.

Keywords: 3D model , CT , Femur morphing , Radiographs

This article presents the use of stereolithography in oral implantology. Stereolithography is a new technology that can produce physical models by selectively solidifying an ultraviolet-sensitive liquid resin using a laser beam, reproducing the true maxillary and mandibular anatomic dimensions. With these models, it is possible to fabricate surgical guides that can place the implants in vivo in the same places and same directions as those in the planned computer simulation. A 70-year-old woman, in good health, with severe mandibular bone atrophy was rehabilitated with an overdenture supported by 2 Branemark implants. Two different surgical planning methods were considered: 1) the construction of a surgical guide evaluating clinical aspects, and 2) the surgical guide produced by stereolithographic study. The accuracy of surgical planning can reduce the problems related to bone density and dimensions. Furthermore, the stereolithographic study assured the clinicians of a superior location of fixtures in bone. Surgical planning based on stereolithographic technique is a safe procedure and has many advantages. This technologic advance has biologic and therapeutic benefits because it simplifies anatomic surgical management for improved implant placement. Copyright © 2004 by Lippincott Williams & Wilkins.

Keywords: Anatomic models , Jaw atrophy , Rapid prototyping , Surgical planning

The planning of the hip prosthesis surgical operation is usually performed manually by the surgeon, who 'draws' on a patient's X-ray image the outline of the prosthetic stem in order to choose the one most suitable for the case at hand. In an attempt to give some repeatability and objectivity to the planning phase, a procedure has been devised for hip prosthesis' stem selection based on the extraction of the femoral relevant outlines. This work presents a computer aided method aimed at automatically extracting the medulla duct outlines from a human femur radiographic image. The outlines are retrieved by referring to a suitable geometric model of the generic femoral cross-section; the projection function obtained by simulating the radiographic acquisition of such a model is fitted on the grey-level functions corresponding to the rows of the actual digitised radiographic image by means of a least squares algorithm. The resulting outlines are used in a software tool performing the hip prosthesis pre-operational planning. © 2003 Published by Elsevier B.V.

Keywords: Medical images processing , Model-based image processing , Surgery aiding tools

The evolution of Computer Tomography and Rapid Prototyping allows production of accurate replicas of the internal anatomical structures of the specific patient. However, the exploitation of all the possibilities offered by these technologies can be obtained only in a collaborative environment, involving doctors and engineers. This article describes three different methods of surgical planning in maxillo-facial surgery: the first involves only medical competences, the second and the third require the use of engineering instruments and personnel. For every method, we will describe instruments, activities and special attention will be payed to the interaction methods between experts of different fields.

This work presents a procedure aimed at automatically extracting the medulla duct outlines from a human femur radiographic image. The outlines are retrieved by referring to a suitable geometric model of the generic femoral cross section; the projection function deriving from such a model is fitted on the grey level values corresponding to the rows of the digitised radiographic image by means of a least square algorithm. The resulting outlines are used in a software system performing the hip prosthesis pre-operational planning.

This work illustrates a computer program designed to aid surgeons in selecting the hip prosthesis femoral component during the preoperation planning stage of hip replacement surgery. Starting from the processing of the patient's coxo-femoral region X-ray image, the program, called Hippin, interacts with the user to outline the femoral region, including the head and the inner contour of the proximal femur. It automatically examines all possible couplings with the patient's femur outlines from a database containing the outlines of the available prostheses created by digitizing the templates normally used in preoperation planning. The resulting images enable the surgeon to visually compare all the alternatives. In addition, the program provides numerical values for the distances between the physiological rotation and prosthesis centers, helping the surgeon in selecting from among the possibilities. The program has been validated by comparing the computer results with actual surgeon selections. (C) 2000 Elsevier Science Ireland Ltd.

Keywords: Hip prosthesis , Image processing , Preoperation planning

The use of non-cemented prosthetic components in implant surgery is demanding a high quality of bone beds in order to allow for a good level of osseointegration. Two parameters are significant in the evaluation of the quality of the host bone: roughness, which reports on the presence of gaps and peeks, and flatness, which reports on the total percentage of bone which lies in a given interval from the prosthesis. Robot assisted cutting of 32 pig femours and tibiae was performed using various techniques and options. This paper demonstrates roughness and flatness can be taken of the order of the limits necessary for osseointegration, by using a milling cutting tool mounted on a strong support, in this case a robot arm, improving on the results obtained by similar studies referred to hand sawed bones by 10 times.

When a patient undergoes an arthroprosthesis implant, the stresses acting on the bone are redistributed, and correspondingly, the bone density adjacent to the entire prosthesis changes its pattern. In order to study these phenomena an automatic methodology has been developed: this methodology is based on the bone density measured on X-ray. The method is compared to other bone densitometry methods and to more recent bone remodeling pattern recognition methods; it turns out to be cost-effective and it has the advantage of allowing back-dated investigation exploiting the numerous existing radiograph records relative to arthroplastic follow-up. The results of the set-up videodensitometric analysis show the method not only has diagnostic capability, but also can effectively support prostheses designers; moreover, the results obtained offer a capable support to real-time observation of remodeling processes and to the biomechanical assessment of the behavior of bone implant systems. For the clinical practice a risk index has been set up in order to systematize the numerous data collected from the measuring mesh grids and to monitor dangerous situations, which can end in implant failure. © 1997 Academic Press Limited.

Hip joint simulators were developed for predicting, by attempting to duplicate in vitro physiological loads and motion, the wear rate that total hip replacements are likely to show in vivo. From a theoretical point of view, loading and motion cycles of hip joints could be closely reproduced by three rotation actuators and three force actuators. However existing devices have been designed assuming that some of these degrees of freedom are negligible, in order to reduce the complexity of the equipment. The present study singles out some preliminary indications on the design choices regarding the spatial configuration of loading and motion actuators. The aim is to define theoretically a simplified simulator but still able to apply the most physiologically realistic loading cycle to the specimen.

Keywords: Biomechanics , Hip joint simulator , Wear

Video-densitometric analysis has proved useful in the study of bone remodelling, however, for more efficient results, an investigation procedure that enables the comparison of X-rays is needed. In the present research an automated method has been developed which considerably speeds up the entire procedure through the implementation of specially designed C++ software. At present, a sequence of six X-rays can be analysed in about 1 h irrespective of the number of areas to be investigated, which can be arbitrarily increased (200 or more). Analysis is fast as well as more reliable and accurate. In clinical practice, the results offer an effective support to observations on the biomechanical behaviour of bone implant systems.

Keywords: arthroprosthesis implants , Bone remodelling , follow-up assessment , video-densitometric analysis , X-ray analysis