Search or add a thesis

Advanced Search (Beta)
Home > Scattering of the Magnetic Resonance Imaging Radiofrequency Field by Implanted Medical Devices

Scattering of the Magnetic Resonance Imaging Radiofrequency Field by Implanted Medical Devices

Thesis Info

Access Option

External Link

Author

Mohsin, Syed Ali

Program

PhD

Institute

University of Engineering and Technology

City

Lahore

Province

Punjab

Country

Pakistan

Thesis Completing Year

2008

Thesis Completion Status

Completed

Subject

Applied Sciences

Language

English

Link

http://prr.hec.gov.pk/jspui/handle/123456789/188

Added

2021-02-17 19:49:13

Modified

2024-03-24 20:25:49

ARI ID

1676727136448

Asian Research Index Whatsapp Chanel
Asian Research Index Whatsapp Chanel

Join our Whatsapp Channel to get regular updates.

Similar


The radiofrequency field used in Magnetic Resonance Imaging is scattered by implanted medical devices. The scattered field is concentrated in the tissue surrounding the implant and conduction currents will flow in the tissue resulting in potentially hazardous heating. Patients with medical implants can undergo diagnostic or interventional MRI procedures and thus the scattering of the MRI RF field by medical implants merits a detailed investigation. In this thesis, scattering by various types of implants has been investigated. The scattered field of a deep brain stimulation lead can be very intense near the electrodes stimulating the brain. The lead is just like an antenna excited by an incident electromagnetic field in a dissipative medium. The greatest concern regarding MRI induced heating is when the lead length approaches the resonant length. The factors that determine the resonant length of a lead are examined. The finite element method is used to find the near field for the lead immersed in nonhomogeneous tissue and connected to an implantable pulse generator as well as for varying distances of the connecting portion of the lead from the air-tissue interface. Electric field, SAR, dissipated powers and induced temperature rise distributions have been obtained in the brain tissue surrounding the electrodes. It is shown that the presence of the IPG can significantly change the induced temperature rise and that the near proximity of the air-tissue interface results in a reduction in the induced temperature rise. The computed values are in good agreement with in-vitro measurements made in the laboratory. Similar analyses and computations have been carried out for an implanted vagus nerve stimulation lead device. Current distributions in the twin-strand lead have been computed. SAR and temperature rise distributions have been obtained around the twin electrodes which are placed on the left vagus nerve. A model implant embedded in nonhomogeneous tissue has been investigated. The nature of the embedding tissue is varied and the current distribution in the implant, the scattered field, and the temperature rise distributions in the tissue surrounding the electrodes has been computed. It has been found that the induced temperature rise is significantly lower for tissue with a lower conductivity and permittivity such as fat than for tissue with a higher conductivity and permittivity such as muscle. The interaction of the MRI RF field with orthopedic implants is investigated. As specific case studies, the scattered fields due to a bone support frame implant and a hip joint implant are computed. It is found that the greatest MRI- induced heating occurs at the tips of long metal parts where the length and thickness of a metal part and its tips determine the amount of induced heating. For the bone support frame, the induced surface current density distributions on the steel pins and the spatial electric field distributions in the surrounding tissue have been obtained. For the hip joint, the maximum temperature rise is at the elliptical tip of the long cylindrical limb of the joint where it joins the femur. The spatial electric field and temperature rise distributions around intravascular stents of various lengths have also been obtained. The maximum temperature rise occurs in the tissue surrounding the tips of a stent. The induced heating effect increases with increasing length.
Loading...
Loading...

Similar Books

Loading...

Similar Chapters

Loading...

Similar News

Loading...

Similar Articles

Loading...

Similar Article Headings

Loading...

ڈاکٹر بھگوان داس

ڈاکٹر بھگوان داس
اسی مہینہ ہندوستان کی ایک اور نامور شخصیت ڈاکٹر بھگوان داس نے انتقال کیا، وہ اپنے دور کے مشہور صاحب علم و قلم اور درویش صفت صوفی مشرب فلسفی تھے، فلسفہ اور تصوف پر ان کی بڑی گہری نظر تھی، اس پر انگریزی میں ان کی کئی تصانیف ہیں، اسلام سے پوری طرح واقف اور اسلامی تصوف سے خاص ذوق رکھتے تھے، عقیدۃً موحد اور اپنی تہذیب و معاشرت میں پرانی تہذیب و شرافت و وضعداری کا نمونہ تھے، اپنے مسلمان دوستوں کو جب خطوط لکھتے تھے تو اپنا نام عبدالقادر لکھتے تھے اور کہتے تھے کہ بھگوان داس اور عبدالقادر کے معنی ایک ہیں، بمبئی کے گورنر سری پرکاش صاحب کے والد تھے، ان کو شرافت و وضعداری اپنے والد ہی سے ترکہ میں ملی ہے،ڈاکٹر بھگوان داس کی موت سے ہندوستان کی ایک بڑی علمی و تہذیبی یادگار مٹ گئی۔ (شاہ معین الدین ندوی، اکتوبر ۱۹۵۸ء)

 

اسلامی علوم و فنون میں ضلع ہری پور کی دینی شخصیات کی کتب کا تحقیقی جائزہ

In this article, twelve scholars of District Haripur have been discussed for their significant contribution in Islamic sciences and various religious issues. The fact remains that District Haripur has remained the center for Islamic education wherein almost every school of thought has existed. In this article, those scholars are provided expression who despite been a part of some particular school of thought, have always encouraged intra-faith harmony. For example, "Al Ribat li Rad Hiyla al Isqat" by Maulana Mohammad Azam contains plenty of updated information on this issue. Similarly, another book called as "Mu'in-ul-'Aqaid” by Maulana Mohammad Hassan, provides grounds for rejecting the hypocrisy of society in a befitting manner. Before writing this article, a session was held with those scholars who are still alive whereas details of those dead were collected from their family members.

Propofol Anesthesia Regulation of Hypnosis Using Nonlinear Control Techniques

Advance technologies and engineering applications have played a significant role in the design and improvement of clinical procedures during the last few decades. Control of drug infusion for patients health and safety is one of the most important step during surgeries. The main objective of safe anesthesia delivery is to achieve the optimum dosage during surgery and simultaneously taking into account the patient clinical parameters and drug requirements. Continuous administration of drug infusion during surgical procedures is essential but increases the undue load of an anesthetist in operating room working in a multi-tasking setup.Manual and target controlled infusion (TCI) systems are not good at handling disturbances or instabilities arising due to inter-patient variability. Patient safety, large inter-individual variability and less post-operative effects are the main factors to motivate automation in anesthesia. The idea of automated system for drug (Propofol) infusion excites the control engineers to come up with a more sophisticated and safe system that handles optimum delivery of drug during surgery and avoid post-operative effects. While most of the work done in anesthesia infusion systems are with linear control strategies, like PID (Proportional Integral derivative), IMC (Internal Model Control) and LMPC (Linear Model Predictive Control) or their improved variants but these linear control methods are not good at handling disturbances and uncertainties related to the system dynamics. These disturbances, which includes, heart rate variability, blood pressure changes and muscular movement, are the main issues causing complexities during surgical activities. The novelty and originality of this research work lies in employing nonlinear control techniques i.e., Sliding Mode Control (SMC) and Backstepping, to regulate the desired hypnosis level of patients undergoing surgery. These two methods, in our knowledge, are not yet applied on anesthesia infusion systems for hypnosis regulation. Both of these control strategies are capable of handling uncertainties and inter-patient variability arising due to the differences in patients clinical data. Simulation results from these methods are analyzed in detail for hypnosis level of the patients and for plasma-drug concentration as well. This effort is envisioned to unleash the true potentials of these nonlinear control techniques for anesthesia systems used today in biomedical field. Results obtained from these non-linear control methods, in terms ofhypnosis level of patients are better than linear control methods. A non-linear control strategy, Sliding Mode Control (SMC), possesses outstanding characteristics related to robustness, accuracy and implementation. Control of non-linear processes with different types of external disturbances and model uncertainties is one of the practical advantage of this method. This non-linear control method can be applied to a wide class of non-linear systems however, their application is limited to single input systems. For the sake of research and analysis, we expand this work to more advanced control technique i.e., backstepping, for hypnosis level tracking. It is a recursive design procedure used for designing stabilizing control for the class of nonlinear dynamical systems. The performance of the designed control laws are studied on the real dataset of(8 for SMC and 5 for backstepping) patients undergoing surgery with different clinical parameters. Despite large patient variability (which includes inter-patient and intra-patient variability), the controller regulates the desired hypnosis level of all patient within the acceptable range as specified by BIS (Bi-spectral Index Scale) without overdose for smooth conduction of surgery.