Segmentation is an important problem in various applications. There exist many effective models designed to locate all features and their boundaries in an image. However such global models are not suitable for automatically detecting a single object among many objects of an image, because nearby objects are often selected as well. Several recent works can provide selective segmentation capability but unfortunately when generalized to three dimensions, they are not yet effective or efficient. This paper presents a selective segmentation model which is inherently suited for efficient implementation. With the added solver by a fast nonlinear multigrid method for the inside domain of a zero level set function, the over methodology leads to an effective and efficient algorithm for 3D selective segmentation. Numerical experiments show that our model can produce efficient results in terms of segmentation quality and reliability for a large class of 3D images.

Many effective models are available for segmentation of an image to extract all homogenous objects within it. For applications where segmentation of a single object identifiable by geometric constraints within an image is desired, much less work has been done for this purpose. This paper presents an improved selective segmentation model, without `balloon' force, combining geometrical constraints and local image intensity information around zero level set, aiming to overcome the weakness of getting spurious solutions by Badshah and Chen's model [8]. A key step in our new strategy is an adaptive local band selection algorithm. Numerical experiments show that the new model appears to be able to detect an object possessing highly complex and nonconvex features, and to produce desirable results in terms of segmentation quality and robustness.

Purpose Training in Interventional Radiology currently uses the apprenticeship model, where clinical and technical skills of invasive procedures are learnt during practice in patients. This apprenticeship training method is increasingly limited by regulatory restrictions on working hours, concerns over patient risk through trainees’ inexperience and the variable exposure to case mix and emergencies during training. To address this, we have developed a computer-based simulation of visceral needle puncture procedures. Methods A real-time framework has been built that includes: segmentation, physically based modelling, haptics rendering, pseudo-ultrasound generation and the concept of a physical mannequin. It is the result of a close collaboration between different universities, involving computer scientists, clinicians, clinical engineers and occupational psychologists. Results The technical implementation of the framework is a robust and real-time simulation environment combining a physical platform and an immersive computerized virtual environment. The face, content and construct validation have been previously assessed, showing the reliability and effectiveness of this framework, as well as its potential for teaching visceral needle puncture. Conclusion A simulator for ultrasound-guided liver biopsy has been developed. It includes functionalities and metrics extracted from cognitive task analysis. This framework can be useful during training, particularly given the known difficulties in gaining significant practice of core skills in patients.

In vascular interventional radiology, procedures generally start with the Seldinger technique to access the vasculature, using a needle through which a guidewire is inserted, followed by navigation of catheters within the vessels. Visual and tactile skills are learnt in a patient apprenticeship which is expensive and risky for patients. We propose a training alternative through a new virtual simulator supporting the Seldinger technique: ImaGiNe (imaging guided interventional needle) Seldinger. It is composed of two workstations: (1) a simulated pulse is palpated, in an immersive environment, to guide needle puncture and (2) two haptic devices provide a novel interface where a needle can direct a guidewire and catheter within the vessel lumen, using virtual fluoroscopy. Different complexities are provided by 28 real patient datasets. The feel of the simulation is enhanced by replicating, with the haptics, real force and flexibility measurements. A preliminary validation study has demonstrated training effectiveness for skills transfer.

Recognition of the many limitations of traditional apprenticeship training is driving new approaches to learning medical procedural skills. Among simulation technologies and methods available today, computer-based systems are topical and bring the benefits of automated, repeatable, and reliable performance assessments. Human factors research is central to simulator model development that is relevant to real-world imaging-guided interventional tasks and to the credentialing programs in which it would be used.

Interventional Radiology procedures (e.g., angioplasty, embolization, stent graft placement) provide minimally invasive therapy to treat a wide range of conditions. These procedures involve the use of flexible tipped guidewires to advance diagnostic or therapeutic catheters into a patient's vascular or visceral anatomy. This paper presents a real-time physically based hybrid modeling approach to simulating guidewire insertions. The long, slender body of the guidewire shaft is simulated using nonlinear elastic Cosserat rods, and the shorter flexible tip composed of a straight, curved, or angled design is modeled using a more efficient generalized bending model. Therefore, the proposed approach efficiently computes intrinsic dynamic behaviors of guidewire interactions within vascular structures. The efficacy of the proposed method is demonstrated using detailed numerical simulations inside 3-D blood vessel structures derived from preprocedural volumetric data. A validation study compares positions of four physical guidewires deployed within a vascular phantom, with the co-ordinates of the corresponding simulated guidewires within a virtual model of the phantom. An optimization algorithm is also implemented to further improve the accuracy of the simulation. The presented simulation model is suitable for interactive virtual reality-based training and for treatment planning.

Guidewire manipulation is a core skill in endovascular interventional radiology procedures. Simulation-based training offers a valuable alternative for mastering these skills, but requires a faithful replication of complex guidewire behaviour inside the vasculature. This paper presents the integration of real flexural modulus (FM) measurements into our guidewire model that mimics the flexibility of standard guidewires. The variation of FM along the length of each wire was determined for seven commonly used guidewires using a three-point bending test for the main body and a two-point bending test for the flexible end. Guidewire FM values were then attributed to seven different models, each formed by a series of particles connected by links of variable FM and replicating the flexible end shape. The FM integration was done through a trial and error process matching real FM to virtual bending coefficient. This mass-spring representation captures the required range of behaviour and enables accurate deformation within virtual vasculature.

Training in interventional radiology is slowly shifting towards simulation which allows the repetition of many interventions without putting the patient at risk. Accurate segmentation of anatomical structures is a prerequisite of realistic surgical simulation. Therefore, our aim is to develop a generic approach to provide fast and precise segmentation of various virtual anatomies covering a wide range of pathology, directly from patient CT/MRA images. This paper presents a segmentation framework including two segmentation methods: region model based level set segmentation and hierarchical segmentation. We compare them to an open source application ITK-SNAP which provides similar approaches. The subjective human influence such as inconsistent inter-observer errors and aliasing artifacts etc. are analysed. The proposed segmentation techniques have been successfully applied to create a database of various anatomies with different pathologies, which is used in computer-based simulation for interventional radiology training.

Guidewire insertion is an imperative task of minimally invasive medical procedures. During the procedure, surgeons need to steer long flexible thin wires through patient's blood vessels to reach a clinical target. In this paper, we present a novel approach to model haptics of guidewire insertion process for training simulation. The algorithm also allows for the analysis of the insertion process through subtle physical behaviours of guidewires via force feedbacks. The method includes a 6‐DoF dynamic coupling between a rigid body, i.e. the virtual tool and the deformation of the wire simulated as an elastic rod. Instead of using the frictional contact force or the acceleration of the guidewire tip for haptic feedbacks, we compute constrained forces by directly connecting the virtual tool to the end of the guidewire. Therefore, the coupling scheme transmits haptic interactions through constrained dynamics between the virtual tool and the guidewire. Both positional and rotational control modes are implemented and evaluated with respect to the dynamics of the guidewire, user inputs and feedback forces. Experiments highlight the usability of our algorithm for an insertion procedure simulation with complex blood vessel structures. Copyright © 2011 John Wiley & Sons, Ltd.

This paper presents a virtual environment for training femoral palpation and needle insertion, the opening steps of many interventional radiology procedures. A novel augmented reality simulation called PalpSim has been developed that allows the trainees to feel a virtual patient using their own hands. The palpation step requires both force and tactile feedback. For the palpation haptics effect, two off-the-shelf force feedback devices have been linked together to provide a hybrid device that gives five degrees of force feedback. This is combined with a custom built hydraulic interface to provide a pulse like tactile effect. The needle interface is based on a modified PHANTOM Omni end effector that allows a real interventional radiology needle to be mounted and used during simulation. While using the virtual environment, the haptics hardware is masked from view using chroma-key techniques. The trainee sees a computer generated patient and needle, and interacts using their own hands. This simulation provides a high level of face validity and is one of the first medical simulation devices to integrate haptics with augmented reality.

CardioVascular and Interventional Radiology (CVIR) acknowledges and appreciates all of our contributing reviewers for another successful year. In 2011, more than 500 reviewers provided substantial scientific analysis of manuscripts submitted for publication in CVIR. Several reviewers have emerged as this year’s ‘‘Distinguished Reviewers.’’ These individuals have submitted six or more reviews in the past year (maximum: 29 reviews), and have averaged 10 days or less for review turnaround time (minimum: \24 h). Special recognition is presented to the following individuals. Thank you all, and congratulations for a job very well done!

A SensAble Omni force feedback device has been modified to increase the face validity of a needle insertion simulation. The new end effector uses a real needle hub and shortened needle shaft in place of the Omni's pre-fitted pen shaped end effector. This modification facilitates correct procedural training through the simulation of co-located visual and haptic cues in an augmented reality approach to simulation. The development of the new end effector is described and a pictorial guide to its manufacture and the fitting process is provided. Initial results from face validation studies bode well for the fidelity of this low cost device.

Guidewire and catheter manipulation is a core skill in endovascular interventional radiology. It is usually acquired in an apprenticeship on patients, but this training is expensive and risky. Simulation offers an efficient alternative for core skills training, though the instrument complex behaviour requires accurate replication. This paper reviews the mass-spring model used to simulate seven guidewires and three catheters, and the matching with their real world counterparts by tuning our model's bending coefficient, which allows replication of the instrument flexibility. This coefficient was matched through computed tomography imaging of a vascular phantom in which each instrument was inserted and manipulated. With an average distance of 2.27 mm (standard deviation: 1.54) between real and virtual instruments, our representation showed realistic behaviour.

Endovascular clinicians use guidewires to navigate within vessels during angiography or angioplasty. In mastering this core skill, an alternative to the traditional apprenticeship in patients is provided by virtual training environments though these require a faithful replication of complex guidewire behaviours inside the vasculature. This paper presents the integration of realistic flexibilities into our guidewire model that simulates the stiffness of seven commonly used guidewires. Each virtual instrument is represented as a mass-spring model replicating their flexibility and shape, especially at the flexible end. The bending coefficients were determined by comparing of the behaviour of real guidewires in a transparent silicone rubber vascular phantom to that of virtual guidewires in the virtual representation of the phantom. As a result, our representation captures the required range of behaviour and enables accurate deformation.

To validate a virtual reality simulator suitable for training Interventional Radiology (IR) skills. Task Analysis (TA) was employed to create a detailed description of a Liver Biopsy procedure, from which critical procedure steps (CPS) were identified. Engineers and computer scientists used the TA and CPS to build a simulator capable of measuring performance. Hierarchical and cognitive TA was carried out using interviews (n=12) with subject matter experts, and observation and recording of actual procedures (n=4). CPS were identified through interviews (n=12) and questionnaires (n=8). Engineers and computer scientists used the TA and CPS to build a training simulator capable of measuring performance. The discriminant validity of the simulator was investigated by measuring performance on a simulated Liver Biopsy procedure. The validation study was conducted at three UK clinical centres and participants were a convenience sample recruited on site with varying degrees of experience (consultants n=14, trainees n=26). The Liver Biopsy TA described174 procedural steps and 22 performance metrics were included in the simulator. Independent t-tests revealed significant differences between consultants (n=14) and trainees (n=26) on 4 performance metrics. ANOVA revealed significant differences between three groups with differing levels of experience in IR (< 1 year experience, 1-2 years, or 3+ years) on 7 performance metrics. Significant performance metrics were: no go area touched; targeting; length of session; probe usage time; total needle distance moved; number of skin contacts; total time in no go area. All 22 performance metrics followed the predicted pattern with level of performance consistently reflecting experience. The use of cognitive task analysis when developing training simulators allows the development of metrics that are a valid discriminator of skill between experts and novices. The indication is that simulation could be a useful training tool that can reflect performance levels on numerous procedural steps. Further validation work is needed to demonstrate transfer of training to the real world.

Simulating intrinsic deformation behaviors of guidewire and catheters for interventional radiology (IR) procedures, such as minimally invasive vascular interventions is a challenging task. Especially real-time simulations for interactive training systems require not only the accuracy of guidewire manipulations, but also the efficiency of computations. The insertion of guidewires and catheters is an essential task for IR procedures and the success of these procedures depends on the accurate navigation of guidewires in complex 3D blood vessel structures to a clinical target, whilst avoiding complications or mistakes of damaging vital tissues and blood vessel walls. In this paper, a novel elastic model for modeling guidewires is presented and evaluated. Our interactive guidewire simulator models the medical instrument as thin flexible elastic rods with arbitrary cross sections, treating the centerline as dynamic and the deformation as quasi-static. Constraints are used to enforce inextensibility of guidewires, providing an efficient computation for bending and twisting modes of the physically-based simulation model. We demonstrate the effectiveness of the new model with a number of simulation examples.

Debate on the existence of innate skills has all but evaporated in the light of evidence that it is only the hours spent in deliberate practice that correlate with even the most elite levels of expertise. A range of simple to advanced technologies stands to address some of the many challenges to effective training of 21st century, procedural medicine. Simulation could train and assess behaviours remotely from patients, in complete safety, reducing the risks of inexperienced trainees learning critical tasks in patients while contributing to certification and revalidation. Understanding the strengths and limitations of these devices, determining and improving their effectiveness and identifying their roles, as well as those of individuals and teams, represents a cornerstone of successful adoption into the interventional radiology curriculum. This requires a simulation strategy that includes standards for simulator documentation.

We present an integrated system for training visceral needle puncture procedures. Our aim is to provide a cost effective and validated training tool that uses actual patient data to enable interventional radiology trainees to learn how to carry out image-guided needle puncture. The input data required is a computed tomography scan of the patient that is used to create the patient specific models. Force measurements have been made on real tissue and the resulting data is incorporated into the simulator. Respiration and soft tissue deformations are also carried out to further improve the fidelity of the simulator.