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关键词： Aspiration   Cerebral venous sinus   Mechanical thrombectomy   Thrombosis  

摘要： BACKGROUND: Cerebral venous sinus thrombosis is a rare cause of acute stroke. It may lead to hemorrhagic venous infarctions, brain swelling, or raised intracranial pressure and can be associated with significant mortality and morbidity. Low-molecular-weight heparin is the mainstay of treatment. Endovascular treatment is reserved for patients who deteriorate despite medical management. METHODS: Retrospective evaluation of our institutional databases from 2018-2019 revealed 7 patients who underwent aspiration thrombectomy using large-bore aspiration catheters for recanalization of the dural sinuses with or without intrasinus thrombolysis during the procedure. Their clinical, imaging findings, endovascular technique, and outcome are discussed. RESULTS: We treated 7 patients who did not respond to best medical management. Aspiration thrombectomy was the primary mode of endovascular treatment. Adjuvant low-dose (10 mg recombinant tissue plasminogen activator), short-duration (20-minute) intrasinus thrombolysis was used in 4 patients only during the procedure. Headache was the most common symptom, followed by seizures, focal neurologic deficits, and vomiting. There was improvement in clinical condition within 24 hours of procedure in all patients. The 30-day modified Rankin Scale score was 0 in 6 patients. One patient had residual hemiparesis and aphasia. There were no procedure-related complications. CONCLUSIONS: The described technique appears to be simple, safe, and effective and results in a relatively short procedure time in achieving complete or partial recanalization of the dural sinuses in patients who deteriorate despite clinical management. Endovascular thrombectomy along with conventional medical management restores the final drainage pathway of the brain with good clinical outcome.

关键词： Clipping   Lone Star retractor system   Sphenoid ridge keyhole approach   Unruptured MCA aneurysms  

摘要： BACKGROUND: We report a technique for the sphenoid ridge keyhole approach using the Lone Star (LS) retractor system as an extracranial tissue retractor in microsurgical clipping of unruptured middle cerebral artery aneurysms. METHODS: The LS retractor system is used as the extracranial tissue retractor. A skin incision (50-60 mm) without shaving is made. The temporal fascia is cut, and skin and fascia flap are reflected anteriorly. On the temporal muscle, keyhole craniotomy is registered using the navigation system such that the lateral edge of the sphenoid ridge is the center of the craniotomy. After the temporal muscle is split in the direction of the muscle fiber, keyhole craniotomy of approximately 30 mm in diameter is created. After dural incision, the Sylvian fissure is dissected by a standard microsurgical technique using brain retractors, and the target aneurysm is clipped. RESULTS: By precise registration of the sphenoid ridge keyhole craniotomy, the Sylvian fissure emerged in the center of the keyhole. Using the LS retractor system, a flat and shallow operative field was obtained. There were no complications using this method. CONCLUSIONS: We optimized the craniotomy, manipulating the target aneurysm in the center of the keyhole. It did not interfere with conventional microsurgical techniques.

关键词： anthroporphic phantom   deep brain stimulation   magnetic resonance imaging   radiofrequency   safety   thermal effects  

摘要： Purpose The objective of this work was to design and construct an improved anthropomorphic phantom for use in studying magnetic resonance imaging (MRI) radiofrequency (RF) safety at 3 T related to deep brain stimulation (DBS), and especially the role of DBS lead trajectories. Method Based on a computer-aided design including reasonable representation of human features, the phantom was fabricated by three-dimensional (3D) printing and then fully assembled with a human skull, a commercial DBS device implanted using the surgical standard at our institution, and fiber-optic temperature sensors embedded in two tissue mimicking solutions (e.g., the heterogeneous setup). Preliminary MRI safety experiments were conducted using turbo spin-echo (TSE) imaging with the device powered on and powered off. These results were then compared to analogous results for a homogeneous phantom setup that filled the structure with a standard body average solution. Result Both phantom setups produced temperature increases of similar to 1.0 degrees C, with a maximum increase of 1.1 +/- 0.2 degrees C recorded during imaging of the heterogeneous phantom setup. The preliminary experimental results suggest that improved phantom structures capable of replicating actual DBS lead trajectories may be advisable when conducting DBS-related MRI safety studies. Conclusion An anthropomorphic phantom was constructed with promising initial results indicating different DBS lead trajectories and phantom setups may impact temperature elevations along an implanted DBS lead. Although additional work will be necessary to validate its efficacy over conventional phantoms, the anthropomorphic phantom can likely be used in the future to assess different procedures for DBS lead placement, the RF power deposition of MRI protocols applicable to DBS patients, and to validate novel methods to reduce localized heating effects associated with DBS devices, such as parallel RF transmission.

关键词： dose profile   flattening filter free beam   halcyon  

摘要： Introduction The use of flattening filter free (FFF) beams generated by standard linear accelerators is increasing in the clinical practice. The radiation intensity peaked toward the beam central axis is properly managed in the optimization process of treatment planning through intensity modulation. Specific FFF parameters for profile analysis, as unflatness and slope for FFF beams, based on the renormalization factor concept has been introduced for quality assurance purposes. Recently, Halcyon, an O-ring based linear accelerator equipped with a 6 MV FFF beam only has been introduced by Varian. Methods Renormalization factors and related fit parameters according to Fogliata et al. ["Definition of parameters for quality assurance of FFF photon beams in radiation therapy," Med. Phys. 39, 6455-6464 (2012)] have been evaluated for the 6 MV FFF beam generated by Halcyon units. The Halcyon representative beam data provided by Varian were used. Dose fall-off at the field edges was matched with an unflattened beam generated by a 6 MV from a TrueBeam linac. Consistency of the results was evaluated against measurements on a clinical Halcyon unit, as well as a TrueBeam 6 MV FFF for comparison. Results The five parameters in the analytical equation for estimating the renormalization factor were determined with an R-2 of 0.997. The comparison of the unflatness parameters between the Halcyon representative and hospital beam data was consistent within a range of 0.6%. Consistently with the computed parameters, the Halcyon profiles resulted in a less pronounced peak than TrueBeam. Conclusion Renormalization factors and related fit parameters from the 6 MV FFF beam generated by the Varian Halcyon unit are provided.

关键词： brain phantom   PET  

摘要： Purpose To introduce a method that allows the generation of ultra high-resolution (submillimeter) heterogeneous digital PET brain phantoms and to provide a new publicly available [18F]FDG phantom as an example. Method The radiotracer distribution of the phantom is estimated by minimizing the Kullback-Leibler distance between the parameterized unknown phantom distribution and a radiotracer-specific template used as a reference. The phantom is modelled using the histological and tissue classified volumes of the BigBrain atlas to provide both high resolution and heterogeneity. The Hammersmith brain atlas is also included to allow the estimation of different activity values in different anatomical regions of the brain. Using this method, a realistic [18F]FDG phantom was produced, where a single real [18F]FDG scan was used as the reference to match. An MRI T1-weighted image, obtained from the BigBrain atlas, and a pseudo-CT are included to complete the dataset. A full PET-MRI dataset was simulated and reconstructed with MR-guided methods for the new [18F]FDG phantom. Results An ultra high-resolution (400 mu m voxel size) and heterogeneous phantom for [18F]FDG was obtained. The radiotracer activity follows the patterns observed in the scan used as a reference. The simulated PET-MRI dataset provided a realistic simulation that was able to be reconstructed with MR-guided methods. By visual inspection, the reconstructed images showed similar patterns to the real data and the improvements in contrast and noise with respect to the standard MLEM reconstruction were more modest compared to simulations done with a simpler phantom, which was created from the same MRI image used to assist the reconstruction. Conclusions A method to create high-resolution heterogeneous digital brain phantoms for different PET radiotracers has been presented and successfully employed to create a new publicly available [18F]FDG phantom. The generated phantom is of high resolution, is heterogeneous, an

关键词： Crouzon's syndrome   Distraction osteogenesis   Le fort III osteotomy   Midface hypoplasia   Rigid external device   3D surgery simulation  

摘要： Introduction/Background Distraction osteogenesis (DO) with an external distraction device such as the rigid external distraction frame has become an established method for treating midface hypoplasia in faciocraniosynostosis. It allows for greater advancement of the midface in comparison with traditional Le Fort III osteotomies, associated or not with fronto-orbital osteotomies (Le Fort IV). However, the forward movement of the bone segments may not always be performed obeying an ideal distraction vector, resulting in asymmetries, anterior open bite, and loosening of screws. In addition, the cost of the distraction devices is significant and may preclude their routine use in developing countries. Method We present an alternative device and method for craniofacial advancement in a clinical case of Crouzon's syndrome. Results A 3D virtual simulation of the distraction vector and a modified external device were used in the current case. Conclusion The alternative external device in this case proved to be safe, effective, and reliable.

摘要： Background: The digital footprint of vascular residency and fellowship programs may have an impact on an applicant's likelihood of selecting a given program. This may include content and accessibility of a particular program's website as well as its social media presence. The goal of this study is to evaluate the online presence of all accredited vascular surgery training programs in the United States and Canada. Methods: A list of accredited vascular surgery training programs in the United States was ob-tained from the Accreditation Council for Graduate Medical Education and the Society for Vascular Surgery websites. Canadian program websites were sourced from the Canadian Soci-ety for Vascular Surgery website. Each program website was individually queried. A systematic Google search of each program was carried out to determine website accessibility. Thirty-one individual content and quality metrics were used to appraise the websites. Three major social media platforms (Twitter, Facebook, and Instagram) were individually searched for program profiles. Results: A total of 105 independent vascular surgery fellowship programs in the 5 + 2 paradigm and 55 integrated vascular surgery residency programs in the 0 + 5 paradigm were identified in the United States. An additional 10 Canadian programs were also identified, including 10 inte-grated residency programs and 4 independent fellowships. Ninety-nine percent of integrated residency and fellowship programs were accessible through Google search. Program descrip-tion was also almost universally available. Significant differences between US and Canadian programs were observed including the mention of salary information (43% vs. 10%, P = 0.039), clinic responsibilities (38% vs. 90%, P = 0.001), teaching responsibilities (34% vs. 100%, P < 0.0001), program director contact information (47% vs. 80%, P = 0.045), mention of journal club (52% vs. 100%, P = 0.003), research requirements (50% vs. 90%, P = 0.014), and past and cur

关键词： dynamic pricing and learning   Kiefer-Wolfowitz algorithm   nonparametric pricing policy   revenue management   stochastic approximation  

摘要： We consider the problem of nonparametric multi-product dynamic pricing with unknown demand and show that the problem may be formulated as an online model-free stochastic program, which can be solved by the classical Kiefer-Wolfowitz stochastic approximation (KWSA) algorithm. We prove that the expected cumulative regret of the KWSA algorithm is bounded above by kappa 1T+kappa 2 where kappa(1), kappa(2) are positive constants and T is the number of periods for any T = 1, 2, horizontal ellipsis . Therefore, the regret of the KWSA algorithm grows in the order of T, which achieves the lower bounds known for parametric dynamic pricing problems and shows that the nonparametric problems are not necessarily more difficult to solve than the parametric ones. Numerical experiments further demonstrate the effectiveness and efficiency of our proposed KW pricing policy by comparing with some pricing policies in the literature.

关键词： cardiac radiosurgery   stereotactic arrhythmia radioablation   ventricular tachycardia  

摘要： Purpose Ventricular tachycardia (VT) is a rapid, abnormal heart rhythm that can lead to sudden cardiac death. Current treatment options include antiarrhythmic drug therapy and catheter ablation, both of which have only modest efficacy and have potential complications. Cardiac radiosurgery has the potential to be a noninvasive and efficient treatment option for VT. Cardiac motion, however, must be accounted for to ensure accurate dose delivery to the target region. Cardiac synchronized volumetric modulated arc therapy (CSVMAT) aims to minimize the dose delivered to normal tissues by synchronizing beam delivery with a cardiac signal, irradiating only during the quiescent intervals of the cardiac cycle (when heart motion is minimal) and adjusting the beam delivery speed in response to heart rate changes. Methods A CSVMAT plan was adapted from a conventional VMAT plan and delivered on a Varian TrueBeam linear accelerator. The original VMAT plan was divided into three interleaved CSVMAT phases, each consisting of alternating beam-on and beam-off segments synchronized to a sample heart rate. Trajectory log files were collected for the original VMAT and CSVMAT deliveries and the dose distributions were measured with Gafchromic EBT-XD film. Results Analysis of the trajectory log files showed successful synchronization with the sample cardiac signal. Film analysis comparing the original VMAT and CSVMAT dose distributions returned a gamma passing rate of 99.14% (2%/2 mm tolerance). Conclusions The film results indicated excellent agreement between the dose distributions of the original and cardiac synchronized beam deliveries. This study demonstrates a proof of principle cardiac synchronization strategy for precise radiation treatment plan delivery and adjustment to a variable heart rate. The cardiac synchronized technique may be advantageous in radioablation for VT.