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  • 1
    Keywords: SYSTEM ; liver ; CALIBRATION ; ABLATION ; IMAGING INTERACTION TOOLKIT ; STANDARDIZED ASSESSMENT
    Abstract: PURPOSE: Intra-procedural acquisition of the patient anatomy is a key technique in the context of computer-assisted interventions (CAI). Ultrasound (US) offers major advantages as an interventional imaging modality because it is real time and low cost and does not expose the patient or physician to harmful radiation. To advance US-related research, the purpose of this paper was to develop and evaluate an open-source framework for US-based CAI applications. MATERIALS AND METHODS: We developed the open-source software module MITK-US for acquiring and processing US data as part of the well-known medical imaging interaction toolkit (MITK). To demonstrate its utility, we applied the module to implement a new concept for US-guided needle insertion. Performance of the US module was assessed by determining frame rate and latency for both a simple sample application and a more complex needle guidance system. RESULTS: MITK-US has successfully been used to implement both sample applications. Modern laptops achieve frame rates above 24 frames per second. Latency is measured to be approximately 250 ms or less. CONCLUSION: MITK-US can be considered a viable rapid prototyping environment for US-based CAI applications.
    Type of Publication: Journal article published
    PubMed ID: 24343000
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  • 2
    Keywords: ALGORITHM ; segmentation ; RECONSTRUCTION ; ABLATION ; DEFORMATIONS ; navigation ; GUIDED LIVER SURGERY ; LAPAROSCOPIC PARTIAL NEPHRECTOMY ; PATIENT REGISTRATION ; RANGE IMAGES
    Abstract: One of the main challenges in computer-assisted soft tissue surgery is the registration of multi-modal patient-specific data for enhancing the surgeon's navigation capabilities by observing beyond exposed tissue surfaces. A new approach to marker-less guidance involves capturing the intra-operative patient anatomy with a range image device and doing a shape-based registration. However, as the target organ is only partially visible, typically does not provide salient features and underlies severe non-rigid deformations, surface matching in this context is extremely challenging. Furthermore, the intra-operatively acquired surface data may be subject to severe systematic errors and noise. To address these issues, we propose a new approach to establishing surface correspondences, which can be used to initialize fine surface matching algorithms in the context of intra-operative shape-based registration. Our method does not require any prior knowledge on the relative poses of the input surfaces to each other, does not rely on the detection of prominent surface features, is robust to noise and can be used for overlapping surfaces. It takes into account (1) similarity of feature descriptors, (2) compatibility of multiple correspondence pairs, as well as (3) the spatial configuration of the entire correspondence set. We evaluate the algorithm on time-of-flight (ToF) data from porcine livers in a respiratory liver motion simulator. In all our experiments the alignment computed from the established surface correspondences yields a registration error below 1cm and is thus well suited for initializing fine surface matching algorithms for intra-operative soft-tissue registration.
    Type of Publication: Journal article published
    PubMed ID: 25038492
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  • 3
    Keywords: OPTIMIZATION ; tumor ; Germany ; IN-VIVO ; VIVO ; CT ; imaging ; SUPPORT ; SYSTEM ; liver ; TUMORS ; ACCURACY ; computed tomography ; NUCLEAR-MEDICINE ; TIME ; TARGET ; NO ; TRIAL ; TRIALS ; ACQUISITION ; LESIONS ; EXPERIENCE ; RADIOFREQUENCY ABLATION ; REGISTRATION ; tomography ; COMPUTED-TOMOGRAPHY ; MOTION ; TRACKING ; IMAGE REGISTRATION ; nuclear medicine ; ORGAN MOTION ; radiology ; RE ; GUIDANCE ; ABLATION ; radiation therapy ; NUCLEAR ; USA ; SET ; IMPROVEMENT ; navigation ; MEDICINE ; CHALLENGES ; INSERTION ; HEPATIC-TUMORS ; INTERVENTIONS ; tumours ; NEEDLES ; computerised tomography ; needle insertion ; CLINICAL-EVALUATION ; motion compensation ; patient treatment
    Abstract: Computed tomography (CT)-guided percutaneous radiofrequency ablation (RFA) has become a commonly used procedure in the treatment of liver tumors. One of the main challenges related to the method is the exact placement of the instrument within the lesion. To address this issue, a system was developed for computer-assisted needle placement which uses a set of fiducial needles to compensate for organ motion in real time. The purpose of this study was to assess the accuracy of the system in vivo. Two medical experts with experience in CT-guided interventions and two nonexperts used the navigation system to perform 32 needle insertions into contrasted agar nodules injected into the livers of two ventilated swine. Skin-to-target path planning and real-time needle guidance were based on preinterventional 1 mm CT data slices. The lesions were hit in 97% of all trials with a mean user error of 2.4 +/- 2.1 mm, a mean target registration error (TRE) of 2.1 +/- 1.1 mm, and a mean overall targeting error of 3.7 +/- 2.3 mm. The nonexperts achieved significantly better results than the experts with an overall error of 2.8 +/- 1.4 mm (n=16) compared to 4.5 +/- 2.7 mm (n=16). The mean time for performing four needle insertions based on one preinterventional planning CT was 57 +/- 19 min with a mean setup time of 27 min, which includes the steps fiducial insertion (24 +/- 15 min), planning CT acquisition (1 +/- 0 min), and registration (2 +/- 1 min). The mean time for path planning and targeting was 5 +/- 4 and 2 +/- 1 min, respectively. Apart from the fiducial insertion step, experts and nonexperts performed comparably fast. It is concluded that the system allows for accurate needle placement into hepatic tumors based on one planning CT and could thus enable considerable improvement to the clinical treatment standard for RFA procedures and other CT-guided interventions in the liver. To support clinical application of the method, optimization of individual system modules to reduce intervention time is proposed
    Type of Publication: Journal article published
    PubMed ID: 19175098
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  • 4
    Keywords: tumor ; ACCURACY ; NUMBER ; COMPUTED-TOMOGRAPHY ; COMPLICATIONS ; GUIDANCE ; ABLATION ; phantom ; electromagnetic tracking ; image-guided therapy ; INTERVENTIONS ; motion compensation ; animal studies ; CT-guidance ; HEPATIC-LESIONS ; liver biopsy ; Liver simulator ; navigated biopsy
    Abstract: Rationale and Objectives: The aim of this prospective, randomized animal study was to compare a new computer guided needle based navigation system for liver biopsy with conventional computed tomography (CT)-guided liver biopsy. Computer-navigated interventions provide continuous needle tracking during motion and deformation from patient respiration and movement. Materials and Methods: Twenty artificial tumors of about 5 mm in diameter were injected into the livers of five pigs, each at a different site. Each tumor was targeted by conventional CT-guided and computer navigated intervention. Intervention was considered complete after successful tumor biopsy. Data on procedure time, number of CT scans performed, accuracy, and success rate were recorded. Results: All tumors (100%) were biopsied successfully. Mean procedural time was comparable between the two techniques (20 9 minutes conventional versus 20 8 minutes navigation). Mean number of CT scans were 1.2 +/- 0.4 with navigation and 6.1 +/- 3.8 with the conventional technique (P 〈 .01). The dose-length product in the conventional group was significantly higher (212 +/- 116 mGy x cm) than in the navigated group (78 +/- 22 mGy x cm; P 〈 .001). Mean number of capsule penetrations was 4 +/- 1 with navigation versus 2 +/- 1 with the conventional technique (P 〈 .001). Conclusion: Computer-navigated liver biopsy may provide a promising and innovative device for easy, rapid, and successful liver biopsies with low morbidity. Further technical improvements and clinical studies in humans are required
    Type of Publication: Journal article published
    PubMed ID: 20832025
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  • 5
    Keywords: SYSTEM ; liver ; TRACKING ; CALIBRATION ; ABLATION ; STANDARDIZED ASSESSMENT
    Abstract: Ultrasound (US) guided procedures are frequently performed for diagnosis and treatment of many diseases. However, there are safety and procedure duration limitations in US-guided interventions due to poor image quality and inadequate visibility of medical instruments in the field of view. To address this issue, we propose an interventional imaging system based on a mobile electromagnetic (EM) field generator (FG) attached to a US probe. A standard US probe was integrated with an EM FG to allow combined movement of the FG with real-time imaging to achieve (1) increased tracking accuracy for medical instruments are located near the center of the tracking volume, (2) increased robustness because the FG is distant to large metallic objects, and (3) reduced setup complexity since time-consuming placement of the FG is not required. The new integrated US-FG imaging system was evaluated by assessing tracking and calibration accuracy in a clinical setting. To demonstrate clinical applicability, the prototype US-EMFG probe was tested in needle puncture procedures. The mobile EMFG attached to a US probe yielded sub-millimeter tracking accuracy despite the presence of metal close to the FG. Calibration errors were in the range of 1-2 mm. In an initial phantom study on US-guided needle punctures, targeting errors of about 3 mm were achieved. A combined US-EMFG probe is feasible and effective for tracking medical instruments relative to US images with high accuracy and robustness while keeping hardware complexity low.
    Type of Publication: Journal article published
    PubMed ID: 24664266
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  • 6
    Keywords: IN-VITRO ; tumor ; Germany ; human ; MODEL ; THERAPY ; VITRO ; CT ; SYSTEM ; liver ; ACCURACY ; computed tomography ; SURGERY ; TARGET ; REGISTRATION ; STRATEGIES ; COMPUTED-TOMOGRAPHY ; MOTION ; TRACKING ; BIOPSY ; RE ; THERAPIES ; ABLATION ; THIN-PLATE SPLINES ; RESPIRATORY MOTION ; ENGLAND ; THERMAL ABLATION ; navigation ; respiratory liver motion simulator ; POSITION ; INTERVENTIONS ; NEEDLES ; DEVICE ; deformation model ; image-guided systems ; interventional radiology ; needle insertion ; respiratory motion compensation
    Abstract: Computed tomography (CT) guided minimally invasive procedures in the liver, such as tumor biopsy and thermal ablation therapy, require precise targeting of hepatic structures that are subject to breathing motion. To facilitate needle placement, we introduced a navigation system which uses needle-shaped optically tracked navigation aids and a real-time deformation model to continuously estimate the position of a moving target. In this study, we assessed the target position estimation accuracy of our system in vitro with a custom-designed respiratory liver motion simulator. Several real-time compatible transformations were compared as a basis for the deformation model and were evaluated in a set of experiments using different arrangements of three navigation aids in two porcine and two human livers. Furthermore, we investigated different placement strategies for the case where only two needles are used for motion compensation. Depending on the transformation and the placement of the navigation aids, our system yielded a root mean square (RMS) target position estimation error in the range of 0.7 mm to 2.9 mm throughout the breathing cycle generated by the motion simulator. Affine transformations and spline transformations performed comparably well (overall RMS 〈 2 mm) and were considerably better than rigid transformations. When two navigation aids were used for motion compensation instead of three, a diagonal arrangement of the needles yielded the best results. This study suggests that our navigation system could significantly improve the clinical treatment standard for CT-guided interventions in the liver
    Type of Publication: Journal article published
    PubMed ID: 18432412
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