Browsing by Author "Zulkarnain, Nur Izzati Huda"

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    Deep Brain Stimulation (DBS) and Implant-friendly (IF) Mode Calculator
    (2023-07-20) Sadeghi-Tarakameh, Alireza; DelaBarre, Lance; Zulkarnain, Nur Izzati Huda; Harel, Noam; Eryaman, Yigitcan; sadeg032@umn.edu; Sadeghi-Tarakameh, Alireza; University of Minnesota/CMRR/Safety Lab
    The purpose of this study is to present a strategy to calculate the implant-friendly (IF) excitation modes—which mitigate the radiofrequency (RF) heating at the contacts of deep brain stimulation (DBS) electrodes—of multi-channel RF coils at 7T. Methods: An induced RF current on an implantable electrode generates a scattered magnetic field whose left-handed circularly polarizing component (B1+) is approximated using a -mapping technique and subsequently utilized as a gauge for the electrode’s induced current. Using this approach, the relative induced currents due to each channel of a multi-channel RF coil on the DBS electrode were calculated. The IF modes of the corresponding multi-channel coil were determined by calculating the null space of the relative induced currents. The proposed strategy was tested and validated for unilateral and bilateral commercial DBS electrodes (directional lead, Infinity DBS system, Abbott Laboratories) placed inside a uniform phantom by performing heating and imaging studies on a 7T MRI scanner using a 16-channel transceive RF coil. Results: Individual IF modes nor shim solutions obtained from IF modes did not induce significant temperature increase when used for a high-power Turbo Spin Echo sequence. In contrast, shimming with the scanner’s toolbox (i.e., based on per-channel B1+ fields) resulted in a more than 2°C temperature increase for the same amount of input power. Conclusion: A strategy for calculating the IF modes of a multi-channel RF coil is presented. This strategy was validated using a 16-channel RF coil at 7T for unilateral and bilateral commercial DBS electrodes inside a uniform phantom.
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    On the Feasibility of RTapp™ as a Daily Delivered Dose Evaluation Tool for Adaptive Lung Stereotactic Body Radiation Therapy (SBRT)
    (2020-08) Zulkarnain, Nur Izzati Huda
    RTapp™ is a daily dose evaluation software developed by ©SegAna LLC. It utilizes deformable image registration (DIR) to update patient anatomy based on daily cone-beam CT and assess the dose distribution according to the detected changes. RTapp™ can be a useful tool in lung stereotactic body radiation therapy (SBRT) to avoid underdosing target and overdosing organs at risk (OARs). In this study, the feasibility of RTapp™ to assess the quality of treatment delivered in every fraction was investigated in a retrospective analysis of 20 lung SBRT patients. For each patient, the simulation CT images, treatment structures, plan, and dose from Pinnacle3 treatment planning system, daily CBCT from MOSAIQ record and verify system, and pre-treatment couch alignment information from Varian on-board imaging (OBI) software were imported into the RTapp™ software. Bidirectional DIR was applied to update the planning target volumes and OARs and the dose distribution to the patient's daily anatomy. The ability of RTapp™ to deform structures were validated by evaluating Dice coefficient (DC) and Hausdorff distance (HD) between the deformed RTapp™ ITV (rtITV) and physician-drawn ITV (pITV). The accuracy of dose calculations by RTapp™ was evaluated by recalculating the doses with Pinnacle3 for the target coverage and several dose metrics to lungs, heart, cord, esophagus, and airway. Ten, three, and one out of 20 patients showed more than 5% decrease in PTV V100%, PTV V90%, and both ITV V100% and GTV V100%, respectively. The mean (± standard deviation) values of the DC ranged from 0.75 to 0.81, with a mean of 0.78 ± 0.03, indicating good overlap between the rtITV and pITV. Meanwhile, the average, 95%, and maximum HD had mean values (± standard deviation) 1.44 ± 0.27 mm, 3.61 ±0.62 mm and 6.14 ± 1.24 mm respectively. The difference in the PTV coverage had the largest variation. 97% of the fractions had the ITV and GTV coverage difference within ± 2.5%. The difference in the dose to OARs was the highest in regions with a steep dose gradient, specifically, the dose to lungs. The ability of RTapp™ as a daily dose evaluation tool to maintain the quality of lung SBRT treatment was validated. The fast auto-segmentation and dose distribution updates according to daily anatomical changes provided by the RTappTM software is highly beneficial as a step towards the realization of adaptive radiation therapy without introducing time and resource constraints. However, further studies are necessary to validate the accuracy of RTapp™ DIR for clinical applications.