Subburaj is a medical image analyst in the Musculskeletal Quantitative Imaging Research Group at the Dept. of Radiology and Biomedical Imaging, University of California San Francisco (UCSF). He received his PhD in Mechanical Engg. from Indian Institute of Technology Bombay (IIT Bombay), where he was associated with OrthoCAD Network Research Cell (Aug. 2009). His thesis was focused on developing 3D geometric algorithms for virtual reconstructive surgery planning of tumour knee joint. He continued his research work at IIT Bombay as a Senior Research Fellow (surgery planning & navigation) until Joining UCSF in February 2010. He has obtained his master's (Advanced Manufacturing Techniques) from The Maharaja Sayajirao University of Baroda in 2005. His research interests are in the fields of BioCAD/Graphics, Cartilage Biomechanics, MRI/CT, Physical Exercise, medical imaging, Image processing and analysis, Medical Imaging, Surgery Planning, and Geometric Reasoning.
Abstract: INTRODUCTION: Injury to the anterior cruciate ligament (ACL) is common. While prior studies have shown that surgical reconstruction of the ACL can restore anterior-posterior kinematics, ACL-injured and reconstructed knees have been shown to have significant differences in tibial rotation when compared to uninjured knees. Our laboratory has developed an MR compatible rotational loading device to objectively quantify rotational stability of the knee following ACL injuries and reconstructions. Previous work from our group demonstrated a significant increase in total tibial rotation following ACL injuries. The current study is a prospective study on the same cohort of patients who have now undergone ACL reconstruction. We hypothesize that ACL reconstructed knees will have less tibial rotation relative to the pre-operative ACL deficient condition. We also hypothesize that ACL reconstructed knees will have greater rotational laxity when compared to healthy contralateral knees. METHODS: Patients. Six of the ACL injured patients from our initial study who had subsequently undergone ACL reconstruction were evaluated 8.1±2.9 months after surgery. All patients underwent single-bundle ACL reconstruction using anteromedial portal drilling of the femoral tunnel with identical post-operative regimens. Magnetic Resonance (MR) Imaging. Patients were placed in a supine position in the MR scanner on a custom-built loading device. Once secured in the scanner bore, an internal/external torque was applied to the foot. The tibiae were semi-automatically segmented with in-house software. Tibial rotation comparisons were made within subjects (i.e. side-to-side comparison between reconstructed and contralateral knees) and differences were explored using paired sample t-tests with significance set at p=0.05. RESULTS: Regarding tibial rotation, in the ACL deficient state, these patients experienced an average of 5.9±4.1° difference in tibial rotation between their ACL deficient and contralateral knees. However, there was a -0.2±6.1° difference in tibial rotation of the ACL reconstructed knee when compared to the contralateral uninjured knee. Regarding tibial translation, ACL deficient patients showed a difference of 0.75±1.4mm of anterior tibial translation between injured and healthy knees. After ACL reconstruction, there was a 0.2±1.1mm difference in coupled anterior tibial translation of the ACL reconstructed knee compared to the contralateral knee. No significant differences in contact area between the two time points could be discerned. DISCUSSION: The objective of our study was to assess the rotational laxity present in ACL reconstructed knees using a previously validated MRI-compatible rotational loading device. Our study demonstrated that ACL reconstruction can restore rotational laxity under load. This may speak to the benefit of an anteromedial drilling technique, which allows for a more horizontal and anatomically appropriate graft position.
Abstract: Adolescent idiopathic scoliosis is the most common type of abnormal curvature observed in spine and it progresses rapidly during the puberty period. The most followed clinical way of assessing the spinal deformity is subjective by measuring the characteristic angles of spinal curve from a set of radiographic images. This paper presents a web-based information system (called ScolioMedIS) based on parameterized 3D anatomical models of the spine to quantitatively assess the deformity and to minimize the amount of radiation exposure by reducing the number of radiographs required. The main components of the system are 3D parametric solid model of spine, back surfaces, relevant clinical information and scoliosis ontology. The patient-specific spine model is regenerated from the parametric model and surface data using anatomical information extracted from radiographic images. The system is designed to take inherent advantage of Web for facilitating multi-center data collection and collaborative clinical decisions. The preliminary analysis of patient data showed promising results, which involve improved documentation standard, clinical decision knowledge base record, facilitated exchange and retrieval of medical data between institutions in multi-center clinical studies, 3D visualization of spinal deformity, and permanent monitoring of treatments.
Abstract: Accurate, simple, and quick measurement of anatomical deformities at preoperative stage is clinically important for decision making in surgery planning. The deformities include excessive torsional, angular, and curvature deformation. This paper presents computer-aided methods for automatically measuring anatomical deformities of long bones of the lower limb. A three-dimensional bone model reconstructed from CT scan data of the patient is used as input. Anatomical landmarks on femur and tibia bone models are automatically identified using geometric algorithms. Medial axes of femur and tibia bones, and anatomical landmarks are used to generate functional and reference axes. These methods have been implemented in a software program and tested on a set of CT scan data. Overall, the performance of the computerized methodology was better or similar to the manual method and its results were reproducible.
Abstract: This paper presents a methodology for developing kinematic model of the human scoliosis simulator using 3D models of spinal vertebrae reconstructed from point clouds. The main objectives of the work are (i) to reduce the number of spinal radiographs required for measuring idiopathic spinal deformities, the most common spine deformity (more than 80% of cases) at adolescents and (ii) improve the visualization and measurement for better treatment planning. The reconstructed 3D model is parameterized and used as a reference model for creating patient-specific anatomical models based on dimensions extracted from radiographic images (Cobb angle and dislocation of vertebrae). The methodology has been implemented and demonstrated with a case study.
Abstract: Identification of anatomical landmarks on skeletal tissue reconstructed from CT/MR images is indispensable in patient-specific preoperative planning (tumour referencing, deformity evaluation, resection planning, and implant alignment and anchoring) as well as intra-operative navigation (bone registration and instruments referencing). Interactive localisation of landmarks on patient-specific anatomical models is time-consuming and may lack in repeatability and accuracy. We present a computer graphics-based method for automatic localisation and identification (labelling) of anatomical landmarks on a 3D model of bone reconstructed from CT images of a patient. The model surface is segmented into different landmark regions (peak, ridge, pit and ravine) based on surface curvature. These regions are labelled automatically by an iterative process using a spatial adjacency relationship matrix between the landmarks. The methodology has been implemented in a software program and its results (automatically identified landmarks) are compared with those manually palpated by three experienced orthopaedic surgeons, on three 3D reconstructed bone models. The variability in location of landmarks was found to be in the range of 2.15-5.98 mm by manual method (inter surgeon) and 1.92-4.88 mm by our program. Both methods performed well in identifying sharp features. Overall, the performance of the automated methodology was better or similar to the manual method and its results were reproducible. It is expected to have a variety of applications in surgery planning and intra-operative navigation.
Abstract: Orthopaedic surgeries require identification of anatomical landmarks on skeletal tissue. Manual palpation methods may not be accurate, especially in resecting deceased tissue and positioning custom implants or mega endo-prostheses. This article describes a computer-aided method for automatic identification of anatomical landmarks on a 3D model reconstructed from CT images of the patient. This is based on computing curvature values, identifying different regions of the surface (generated from the segmented volume data), and classifying the regions as peaks, ridges, pits and ravines. The landmarks are identified by walking along all vertices, extracting gradients from curvature map, and checking against a set of rules. The approach has been successfully demonstrated on a pelvis model reconstructed from 443 slices. The locations of the landmarks are determined, useful for dimension measurements and pre-operative planning.
Abstract: Injection mold development lead time has been reduced presently by over 50% by employing rapid prototyping based tooling methods. Rapid tooling methods however, have certain limitations in terms of mold material, accuracy, surface finish, and mold life. The relevant process knowledge, especially for newer routes, is not very well established, resulting inconsistent or inappropriate rapid tooling (RT) process selection and mold design incompatibility. This paper presents a computer aided rapid tooling process selection and manufacturability evaluation methodology for injection molding, supported by mold cost estimation models and RT process capability database. Rapid tooling process selection is based on process capability mapping in quality function deployment (QFD) against a set of tooling requirements that are prioritized through pairwise comparison using analytical hierarchal process (AHP). The mold manufacturability for the selected RT process is carried out using fuzzy-analytic hierarchy process (fuzzy-AHP) to identify problem features, if any. This is followed by estimating the cost of RT mold and comparing it with a conventional mold, using cost models developed based on the concept of cost drivers and cost modifiers. The entire methodology has been implemented in a software program using Visual C++ in Windows environment and demonstrated on an experimental mold as well as industrial cases. The proposed methodology enables selecting an appropriate rapid tooling process for a given injection mold requirement, and identifying critical features that could be modified to improve manufacturability, thereby achieving better quality and lower cost of molded parts along with shorter lead time.
Abstract: External ear defects can be corrected by surgery, but this may not be feasible for personal or medical reasons. Reconstructive solutions are a good alternative, but rely on the artistry and availability of the anaplastologist. A semi-automated methodology using computer-aided design (CAD) and rapid prototyping (RP) technologies was developed for auricular prosthesis development, and demonstrated in a real-life case. The correct geometry and position of the prosthesis were ensured by stacking the computed tomography scan images of the contralateral normal ear in reverse order, and joining them using a medical modelling software program. The CAD model of the remnant portion of the defective ear was subtracted from the model of the mirrored contralateral ear, using a haptic CAD system, to obtain the final geometry of the prosthesis. Polymer models were fabricated in RP systems, and used for making a corresponding mould. Medical grade silicone rubber of the appropriate colour was packed into the mould to fabricate the final ear prosthesis and fitted to the deficient side of the patient using medical grade adhesive. The computer-aided methodology gave a high level of accuracy in terms of shape, size and position of the prosthesis, and a significantly shorter lead time compared to the conventional (manual) technique.
Abstract: Thickness is a commonly used parameter in product design and manufacture. Its intuitive definition as the smallest dimension of a cross-section or the minimum distance between two opposite surfaces is ambiguous for intricate solids, and there is very little reported work in automatic computation of thickness. We present three generic definitions of thickness: interior thickness of points inside an object, exterior thickness for points on the object surface, and radiographic thickness along a view direction. Methods for computing and displaying the respective thickness values are also presented. The internal thickness distribution is obtained by peeling or successive skin removal, eventually revealing the object skeleton (similar to medial axis transformation). Another method involves radiographic scanning normal to a viewing direction, with minimum, maximum and total thickness options, displayed on the surface of the object. The algorithms have been implemented using an efficient voxel based representation that can handle up to one billion voxels (1000 per axis), coupled with a near-real time display scheme that uses a look-up table based on voxel neighborhood configurations. Three different types of intricate objects: industrial (press cylinder casting), sculpture (Ganesha idol), and medical (pelvic bone) were used for successfully testing the algorithms. The results are found to be useful for early evaluation of manufacturability and other lifecycle considerations.
Abstract: The meniscus which is fibrocartilaginous tissue found within the knee joint, is responsible for shock dissipation, load transmission, and stability within the knee joint. The mechanical function of the meniscus largely depends on the structural and molecular integrity of its matrix, composed of a network of collagen fibers (Type I) immobilizing proteoglycans (PG). Recent studies have shown the potential of quantitative MR imaging, including T2 and T1Ï quantifications for studying biochemical composition of meniscus. T1Ï relaxation time, also known as spin-lattice relaxation in the rotating frame, probes the interaction between motion-restricted water molecules and the macromolecular environment. It has been shown in literature that T1Ï relaxation is negatively correlated with PG content and tissue hydration. T2 reflects the energy exchange between free water proton molecules and is related to collagen matrix structure and water content. However, to our knowledge, the effect of acute loading on the meniscal MR relaxation times (T1Ï and T2) values has not been studied. The purpose of this study was to determine the response of PG and collagen, which are responsible for the compressive stiffness and tensile strength of meniscus, respectively, to static- and cyclic loading using magnetic resonance (MR) relaxation times (T1Ï and T2) in young healthy adults.
Abstract: Metabolic abnormalities including obesity and type 2 diabetes have been associated with alterations in the amount and the regional distribution of adipose tissue in the lower extremities, including changes in intermuscular adipose tissue (IMAT) and subcutaneous adipose tissue (SAT) volumes. Chemical shift-based water/fat separation approaches, like Dixon methods and the iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) method, have been recently applied to measure a quantitative proton density fat fraction map in skeletal muscle, enabling an accurate and reliable determination of fat amount in the muscle cross-section. However, a study of fat distribution would require a reproducible extraction of SAT and muscle regions to determine the amounts of SAT and IMAT respectively. A fully automated, accurate and reproducible segmentation technique for identifying the SAT and the muscle region still remains challenging due to severe fatty infiltration of certain muscles in numerous pathologic conditions. The inherent multi-modal imaging (MMI) property of chemical shift-based water/fat separation makes it an ideal candidate for multi-parametric segmentation. Therefore, the purpose of the present study is to introduce and validate a fully automated unsupervised multi-parametric segmentation method of the SAT and muscle region to determine SAT and IMAT volumes based on the images from a quantitative chemical shift-based water/fat separation approach
Abstract: Computer Assisted Orthopedic Surgery (CAOS) employing information and computer graphics technologies for preoperative planning, intraoperative navigation, and for guiding or performing surgical interventions, has received very little attention for bone tumor surgery applications. We have developed a CAOS system called OrthoSYS, driven by geometric reasoning algorithms to visualize tumor size, shape, and plan for resection according to the tumor's spread, starting from a 3D model reconstructed from CT images. Anatomical landmarks on bone are automatically identified and labeled, useful for registering patient model with virtual model during surgery and also as a reference for tumor resection and prosthesis positioning. The thickness of bone stock remaining after tumor resection is automatically analyzed to choose the best modular stem and fix the prosthesis. A method for prosthesis components selection using fuzzy logic has been developed to assist the surgeons. The medial axis of the long bones and anatomical landmarks are used for positioning the prosthesis in virtual planning and verification in the intraoperative stage. A set of anatomical metrics have been developed to measure the effectiveness of the prosthetic replacement of bone.
Abstract: Modular endo-prostheses were introduced in 1980s with the intent of replacing custom made implants, which were criticized for lack of intra-operative flexibility, and high lead time and cost [1]. A typical modular prosthesis set may have as many as 200 components, making it difficult to select the right set of components in intra operative stage. An automated prosthesis selection methodology to limit the choice of prosthesis components with a qualitative tag such as: (1) `most suitable', (2) `probably suitable', and (3) `not suitable', will greatly help the surgeons. This article describes a computer aided decision support system for selecting endo-prosthesis components driven by anatomical data of the patient. The methodology is explained with a case study of distal femur replacement.
Abstract: Bone torsional deformity is excessive anatomical or axial twist of proximal portion with respect to distal. Accurate, simple, and quick measurement of torsional deformities at preoperative stage is clinically important for decision making in prosthesis design and surgery planning. Commonly used 2D methods for assessing excessive torsion use radiographic images or a set of slices of CT/MR images. The slices representing reference axes of distal and proximal portion are superimposed; the angle between the axes provides a measure of torsion. Representing 3D anatomical landmarks and reference axes in a 2D transverse slice or projected radiographic image leads to inaccurate and inconsistent values. Owing to the complex 3D shape of bones (ex. femur and tibia), there is a need for 3D model based assessment methods with little or no human intervention. Excessive torsion in the tibia and femur affects the procedure of total knee replacement. We present an automated methodology for assessing excessive torsional deformation of femur and tibia bone based on 3D anatomical landmarks based referencing. Reconstructed 3D bone model from a set of CT scan images using tissue segmentation and surface fitting is used in this methodology. Anatomical landmarks on femur and tibia bone are automatically identified based their shape and predefined landmarks spatial adjacency matrix. The identified 3D anatomical landmarks and computed functional and reference axes (femur: neck axis, condylar axis, and long axis; tibia: tibial plateau axis, long axis, and malleolus axis) are used for measuring torsional deformation, using 3D shape reasoning algorithms. The methodology has been implemented in a software program and tested on five sets of CT scan images of lower limb. The computerized methodology is found to be fast and efficient, with reproducible results.
Abstract: Limb salvage surgery has replaced amputation as the treatment of choice for sarcomas of the extremities. However, complications such as prosthesis loosening and fracture of bone or prosthesis continue to occur due to poorly aligned prosthesis or unconsidered bone deformities. These can be minimized by detailed implantation planning: intervention, resection, selection, and alignment decisions considering anatomical variations. Previous works employed interactive identification of anatomical landmarks, and prosthesis position planning by superimposing prosthesis drawing on radiographic image, which is cumbersome and error-prone. We present an automated methodology for mega endoprosthesis implantation planning in a 3D computer graphics environment. First, a virtual anatomical model is reconstructed by stacking and segmenting CT scan images. A neighborhood configuration based 3D visualization algorithm has been developed for fast rendering of the volumetric data, enabling a quick understanding of anatomical structures. Key skeletal landmarks used for implantation are automatically localized using curvature analysis of the 3D model and knowledge based rules. Anatomical details (mainly dimensions and reference axes) are extracted based on the landmarks and used in resection planning. A decision support method has been developed for segregating prosthesis components into three sets: âmost suitableâ, âprobably suitableâ, and ânot suitableâ for a particular patient. The geometrical landmarks of the prosthesis components are mapped with respect to the anatomical landmarks of the patientâs model to derive alignment relationships. 3D curved medial axes of both (prosthesis and anatomical models) are used for reference and alignment. A set of selection and positional accuracy measures have been developed to evaluate the anatomical conformity of the prosthesis. The computeraided methodology is illustrated for tumour knee endoprosthetic replacement. It is shown to reduce the time required for implantation planning and improve the quality of outcome. The 3D environment is also more intuitive and easy-to-use than the traditional approach relying on 2D images.
Abstract: Today, a number of direct routes using rapid prototyping (RP) processes (fused deposition modelling (FDM), laminated object manufacturing (LOM), stereolithography apparatus (SLA), selective laser sintering (SLS), etc.), as well as indirect routes (RP coupled with secondary or soft-tooling processes like RTV vacuum casting) are available for rapid fabrication of tooling for sand and investment casting processes. Each route is unique in terms of geometric, material, quality and cost characteristics; no comprehensive database of their capabilities has been reported, especially for metal casting applications. The problem of selecting the optimal rapid tooling (RT) route is a complex multi-criteria decision-making problem. This paper describes a systematic approach for RT route selection and planning. A database of RT process capabilities was generated through benchmarking experiments, covering 20 different widely used RT routes (both direct and indirect: two- and three-step processes) involving an impeller pattern. In this approach, RT process route selection involves translating the tooling requirements specified by the casting engineer into weighted tooling attributes using quality function deployment and analytic network process (QFD-ANP), which along with part specifications is used for RT route selection by calculating the overall process compatibility indices. The routes are ranked as per the value of the overall compatibility index. Once the optimal route is selected, process planning is carried out by retrieving a similar process plan using case-based reasoning (CBR). The methodology has been implemented in a software program using Visual C + + programming language in a Windows environment. The methodology is demonstrated and validated with an industrial example of a separator body casting. It has proved to be a robust evaluation and decision-making tool for selecting appropriate tooling route for a given casting based on customer requirements.
Abstract: The ubiquitous availability of high power' computers has opened up the possibility of handling large (high resolution) volumetric data to accurately represent medical models, and performing geometric reasoning for various applications. In this paper, we present an efficient protocol to reconstruct accurate medical models from CT/MR images having equal or unequal values of slice thickness, inter slice distance, and pixel size. It involves modifying the slice thickness while leaving the in-slice resolution intact; issues such as slice overlap and inter-slice gap are handled using slice based interpolation. Noise reduction and better delineation of object boundaries and segmentation are performed in voxel space. Geometric analysis of reconstructed volumetric data is performed to generate internal thickness mapping, useful for pre-operative planning and custom implant design. A test case of pelvic model reconstruction from CT slices is described to illustrate the algorithms.
