MRI compatible mechatronic devices to aid medical diagnosis and intervention

Imperial Users onl

Intraoperative Real-Time Querying of White Matter Tracts During Frameless Stereotactic Neuronavigation

BACKGROUND: Brain surgery faces important challenges when trying to achieve maximum tumor resection while avoiding postoperative neurological deficits. OBJECTIVE: For surgeons to have optimal intraoperative information concerning white matter (WM) anatomy, we developed a platform that allows the intraoperative real-time querying of tractography data sets during frameless stereotactic neuronavigation. METHODS: Structural magnetic resonance imaging, functional magnetic resonance imaging, and diffusion tensor imaging were performed on 5 patients before they underwent lesion resection using neuronavigation. During the procedure, the tracked surgical tool tip position was transferred from the navigation system to the 3-dimensional Slicer software package, which used this position to seed the WM tracts around the tool tip location, rendering a geometric visualization of these tracts on the preoperative images previously loaded onto the navigation system. The clinical feasibility of this approach was evaluated in 5 cases of lesion resection. In addition, system performance was evaluated by measuring the latency between surgical tool tracking and visualization of the seeded WM tracts. RESULTS: Lesion resection was performed successfully in all 5 patients. The seeded WM tracts close to the lesion and other critical structures, as defined by the functional and structural images, were interactively visualized during the intervention to determine their spatial relationships relative to the lesion and critical cortical areas. Latency between tracking and visualization of tracts was less than a second for a fiducial radius size of 4 to 5 mm. CONCLUSION: Interactive tractography can provide an intuitive way to inspect critical WM tracts in the vicinity of the surgical region, allowing the surgeon to have increased intraoperative WM information to execute the planned surgical resection

Multimodality Non-rigid Image Registration for Planning, Targeting and Monitoring During CT-Guided Percutaneous Liver Tumor Cryoablation

Rationale and Objectives: To develop non-rigid image registration between pre-procedure contrast enhanced MR images and intra-procedure unenhanced CT images, to enhance tumor visualization and localization during CT-guided liver tumor cryoablation procedures. Materials and Methods: After IRB approval, a non-rigid registration (NRR) technique was evaluated with different pre-processing steps and algorithm parameters and compared to a standard rigid registration (RR) approach. The Dice Similarity Coefficient (DSC), Target Registration Error (TRE), 95% Hausdorff distance (HD) and total registration time (minutes) were compared using a two-sided Student’s t-test. The entire registration method was then applied during five CT-guided liver cryoablation cases with the intra-procedural CT data transmitted directly from the CT scanner, with both accuracy and registration time evaluated. Results: Selected optimal parameters for registration were section thickness of 5mm, cropping the field of view to 66% of its original size, manual segmentation of the liver, B-spline control grid of 5×5×5 and spatial sampling of 50,000 pixels. Mean 95% HD of 3.3mm (2.5x improvement compared to RR, p<0.05); mean DSC metric of 0.97 (13% increase); and mean TRE of 4.1mm (2.7x reduction) were measured. During the cryoablation procedure registration between the pre-procedure MR and the planning intra-procedure CT took a mean time of 10.6 minutes, the MR to targeting CT image took 4 minutes and MR to monitoring CT took 4.3 minutes. Mean registration accuracy was under 3.4mm. Conclusion: Non-rigid registration allowed improved visualization of the tumor during interventional planning, targeting and evaluation of tumor coverage by the ice ball. Future work is focused on reducing segmentation time to make the method more clinically acceptable

MRI compatible mechatronic devices to aid medical diagnosis and intervention

The excellent soft tissue contrast of Magnetic Resonance Imaging (MRI) makes it an invaluable tool for guiding and monitoring interventional procedures. This has encouraged the development of MR compatible manipulators capable of combining the high precision and repeatability of robotic systems with the image capabilities of MRI. A system capable of performing transrectal prostate biopsy inside a high field 1.5T MRI scanner was developed to improve the pathological diagnosis of prostate cancer. The 5 DOF device is actuated using piezoceramic motors and can position an endorectal probe inside of the rectum in order to align a biopsy needle to a target position in the prostate. A specially developed MR pulse sequence was capable of tracking two passive fiducials in the head of the endorectal probe, and could thus update the image scan planes to always include the biopsy needle. Phantom tests demonstrate the needle target accuracy was always within the \pm3mm limit specified in the requirements. A preliminary clinical trial has been performed with the manipulator showing a very successful outcome. A second system developed was able to position limbs at a desired orientation within the confined space of a closed bore scanner in order to exploit the magic angle effect to aid diagnosis of tendinous and other muskoloskeletal injury. The 3 DOF device can position tendons in the hand, knee and ankle, proving to be very versatile. The system kinematics were derived such that the device can locate the target tissue as close as possible to the isocentre, while avoiding collision between the patient anatomy and the scanner bore. Preliminary clinical trials with healthy volunteers were performed, where the signal at the Achilles tendon was measured as a function of orientation, showing clear magic angle effects in accordance with the theory.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Characterization of upper urinary tract urothelial lesions in patients with gross hematuria using diffusion-weighted MRI: A prospective study

Objective: Our objective was to evaluate the utility of diffusion-weighted MRI (DWI) and apparent diffusion coefficient (ADC) values in differentiation between malignant and non malignant lesions of the upper urinary tract in patients with gross hematuria. Methods: We prospectively evaluated 51 patients with gross hematuria. The MRI sequences included T1, T2 weighted spin echo imaging and DWI with calculating ADC values of each detected lesion. Two radiologists independently reviewed the imaging sequences. The reference standard was established on the basis of histopathology. The agreement between two reviewers was tested by K statistics. Group comparison was completed with the Kruskal–Wallis test for ADC values and the Mann–Whitney U test. Furthermore, the diagnostic performance was evaluated by using the area under the curve (AUC) of receiver operating characteristic (ROC) curve analysis. Results: DWI had higher sensitivity and specificity for both reviewers reviewer 1 [94%, 77%] and reviewer 2 [89% and 77%] over conventional sequences [T1 and T2] reviewer 1 [86%, 77%] and reviewer 2 [84% and 69%], respectively. Interobserver agreement was good (K = 0.79) using DWI. AUC was 89% and ROC curve revealed that a value of 1.5 × 10−3 mm2/s is the most significant cut off value with highest sensitivity and specificity 79% and 82% respectively in differentiation between malignant and non malignant lesions. Conclusion: DWI had high sensitivity and accuracy in detection of upper urinary tract urothelial lesions and could also be used in differentiation between malignant and non malignant lesions of upper urinary tract lesions in patients with gross hematuria. Advances in knowledge: To our knowledge this is the first prospective study that included benign lesions and tried to differentiate between malignant and non malignant lesions of the upper urinary tract

Image Registration of Pre-Procedural MRI and Intra-Procedural CT Images to Aid CT-Guided Percutaneous Cryoablation of Renal Tumors

Purpose: To determine whether a non-rigid registration (NRR) technique was more accurate than a rigid registration (RR) technique when fusing pre-procedural contrast-enhanced MR images to unenhanced CT images during CT-guided percutaneous cryoablation of renal tumors. Methods: Both RR and NRR were applied retrospectively to 11 CT-guided percutaneous cryoablation procedures performed to treat renal tumors (mean diameter; 23 mm). Pre-procedural contrast-enhanced MR images of the upper abdomen were registered to unenhanced intra-procedural CT images obtained just prior to the ablation. RRs were performed manually, and NRRs were performed using an intensity-based approach with affine and Basis-Spline techniques used for modeling displacement. Registration accuracy for each technique was assessed using the 95% Hausdorff distance (HD), Fiducial Registration Error (FRE) and the Dice Similarity Coefficient (DSC). Statistical differences were analyzed using a two-sided Student’s t-test. Time for each registration technique was recorded. Results: Mean 95% HD (1.7 mm), FRE (1.7 mm) and DSC (0.96) using the NRR technique were significantly better than mean 95% HD (6.4 mm), FRE (5.0 mm) and DSC (0.88) using the RR technique (P < 0.05 for each analysis). Mean registration times of NRR and RR techniques were 15.2 and 5.7 min, respectively. Conclusions: The non-rigid registration technique was more accurate than the rigid registration technique when fusing pre-procedural MR images to intra-procedural unenhanced CT images. The non-rigid registration technique can be used to improve visualization of renal tumors during CT-guided cryoablation procedures

Multimodality non-rigid image registration for planning, targeting and monitoring during CT-guided percutaneous liver tumor cryoablation.

RATIONALE AND OBJECTIVES: The aim of this study was to develop non-rigid image registration between preprocedure contrast-enhanced magnetic resonance (MR) images and intraprocedure unenhanced computed tomographic (CT) images, to enhance tumor visualization and localization during CT imaging-guided liver tumor cryoablation procedures. MATERIALS AND METHODS: A non-rigid registration technique was evaluated with different preprocessing steps and algorithm parameters and compared to a standard rigid registration approach. The Dice similarity coefficient, target registration error, 95th-percentile Hausdorff distance, and total registration time (minutes) were compared using a two-sided Student\u27s t test. The entire registration method was then applied during five CT imaging-guided liver cryoablation cases with the intraprocedural CT data transmitted directly from the CT scanner, with both accuracy and registration time evaluated. RESULTS: Selected optimal parameters for registration were a section thickness of 5 mm, cropping the field of view to 66% of its original size, manual segmentation of the liver, B-spline control grid of 5 × 5 × 5, and spatial sampling of 50,000 pixels. A mean 95th-percentile Hausdorff distance of 3.3 mm (a 2.5 times improvement compared to rigid registration, P \u3c .05), a mean Dice similarity coefficient of 0.97 (a 13% increase), and a mean target registration error of 4.1 mm (a 2.7 times reduction) were measured. During the cryoablation procedure, registration between the preprocedure MR and the planning intraprocedure CT imaging took a mean time of 10.6 minutes, MR to targeting CT image took 4 minutes, and MR to monitoring CT imaging took 4.3 minutes. Mean registration accuracy was CONCLUSIONS: Non-rigid registration allowed improved visualization of the tumor during interventional planning, targeting, and evaluation of tumor coverage by the ice ball. Future work is focused on reducing segmentation time to make the method more clinically acceptable

Intra-operative multimodal non-rigid registration of the liver for navigated tumor ablation.

CT guided tumor ablation of the liver often suffers from a lack of visualization of the target tumor and surrounding critical structures. This information is available on pre-operative contrast enhanced MR images and a non-rigid registration technique is desirable. However while registration methods have been successfully tested retrospectively on patient data, very few have been incorporated into clinical procedures. A non-rigid registration technique has been evaluated, optimized and validated to be able to perform registration of the liver between MR to CT images, and between intra-operative CT images. The method requires pre-processing and segmentation of the liver, and presents an accuracy of approximately 2 mm. A clinical feasibility study has been conducted in 5 liver ablation cases. The method helps clinicians enhance interventional planning, confirm ablation probe location with respect to the tumor, and in the case of cryotherapy, evaluate tumor coverage by the ice ball