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This paper proposes an inverse strategy for relocation of structural natural frequencies using first order formulation and solution algorithm. In the proposed method a sensitivity analysis of the systems eigenvalues with respect to material or geometrical parameters of the structure is conducted initially. The required parameter variation to achieve a desired frequency shift for the structure is then computed. The proposed technique incorporates the design constraints or objective functions in the system equations in such a way that a square system of equations is always preserved. The formulations are general and applicable to all finite element structures because the sensitivity analysis is based on the stiffness and mass matrices regardless of the type of elements used. An algorithm suitable for implementation of the technique for practical purposes is developed. The accuracies of the proposed methods are tested conducting several case studies and the results are validated against exact solutions.

This paper presents formulations for inverse optimisation of vibration behaviour of finite element models of both truss and continuous structures. The proposed algorithms determine the required modifications on truss and continuous structures to achieve specified natural frequencies. The modification can be carried out globally or locally on the structures stiffness and matrices and the formulation can also be used to add new structural members to achieve the desired response. Numerical examples and finite element implementation of the developed method are provided to demonstrate the feasibility of the formulations.

Purpose: MRI-guided focused ultrasound (MRgFUS) has many potential and realized applications including controlled heating and localized drug delivery. The development of many of these applications requires extensive preclinical work, much of it in small animal models. The goal of this study is to characterize the spatial targeting accuracy and reproducibility of a preclinical high field MRgFUS system for thermal ablation and drug delivery applications. Methods: The RK300 (FUS Instruments, Toronto, Canada) is a motorized, 2-axis FUS positioning system suitable for small bore (72 mm), high-field MRI systems. The accuracy of the system was assessed in three ways. First, the precision of the system was assessed by sonicating regular grids of 5 mm squares on polystyrene plates and comparing the resulting focal dimples to the intended pattern, thereby assessing the reproducibility and precision of the motion control alone. Second, the targeting accuracy was assessed by imaging a polystyrene plate with randomly drilled holes and replicating the hole pattern by sonicating the observed hole locations on intact polystyrene plates and comparing the results. Third, the practicallyrealizable accuracy and precision were assessed by comparing the locations of transcranial, FUS-induced blood-brain-barrier disruption (BBBD) (observed through Gadolinium enhancement) to the intended targets in a retrospectivemore » analysis of animals sonicated for other experiments. Results: The evenly-spaced grids indicated that the precision was 0.11 +/− 0.05 mm. When image-guidance was included by targeting random locations, the accuracy was 0.5 +/− 0.2 mm. The effective accuracy in the four rodent brains assessed was 0.8 +/− 0.6 mm. In all cases, the error appeared normally distributed (p

Although the histologic anatomy of the lower eyelid retractors is well defined, the physiology of the lower retractors has been determined only by interference based on anatomic and clinical findings. In this study, in five normal subjects we investigated the physiology of the lower eyelid retractors utilizing dynamic high resolution magnetic resonance imaging (MRI) with a custom designed surface coil. Measurements of the excursion of the cornea, lower eyelid margin, and anterior edge of the inferior oblique muscle were made from scans taken in upgaze and downgaze. We found that the corneal movement was substantially greater than the movement of the eyelid margin, a finding that can readily be made clinically. A more important result was that the movement of the eyelid margin and the movement of the inferior oblique margin were similar in all cases. Thus, the length of the anterior capsulopalpebral fascia between the tarsus and inferior oblique muscle remains constant in downgaze, and the source of the stretch in the lower eyelid retractors lies in the posterior capsulopalpebral system, at the capsulopalpebral head. High resolution eyelid MR has great potential to allow investigation of essential aspects of normal and pathologic eyelid anatomy and physiology.

More and more emphasis is being made on alternatives to invasive surgery and the use of ionizing radiation to treat various diseases including cancer. Novel screening, diagnosis, treatment and monitoring of response to treatment are also hot areas of research and new clinical technologies. Ultrasound(US) has gained traction in all of the aforementioned areas of focus. Especially with recent advances in the use of ultrasound to noninvasively treat various diseases/organ systems. This session will focus on covering MR-guided focused ultrasound and the state of the art clinical applications, and the second speaker will survey the more cutting edge technologies e.g. Focused Ultrasound (FUS) mediated drug delivery, principles of cavitation and US guided FUS. Learning Objectives: 1. Fundamental physics and physical limitations of US interaction with tissue and nanoparticles 2. The alteration of tissue transport using focused ultrasound 3. US control of nanoparticle drug carriers for targeted release 4. The basic principles of MRI-guided focused ultrasound (MRgFUS) surgery and therapy 5. the current state of the art clinical applications of MRgFUS 6. requirements for quality assurance and treatment planning

There are compelling reasons for merging high-resolution anatomical information from magnetic resonance (MR) imaging with the functional images attainable with positron emission tomography (PET). The ideal solution to this intermodality image registration is to acquire PET and MR scans simultaneously with imaging systems that are fixed relative to each other, which will permit near-perfect image registration. This is particularly important for studies of small brain structures or in animal studies. A prototype PET system has been developed that permits PET and MR images to be acquired simultaneously. It consists of seventy-two 2 × 2 × 5-mm lutetium oxyorthosilicate crystals coupled by 2-mm-diameter, 4-m-long double-clad optical fibers to three multichannel photomultiplier tubes shielded inside an aluminum enclosure. The detector ring diameter is 56 mm. The scanner provides a single-image plane with a transaxial field of view of 28 mm and 1-mm full-width-at-half-maximum slice thickness. The reconstructed resolution is 2 mm. This PET system is shown to be compatible with a clinical 1.5-T MR scanner. Possible image degradation caused by simultaneous imaging has been measured. The PET and MR phantom images show no noticeable image artifacts or distortions resulting from dual modality image acquisition. The first in vivo simultaneous PET and MR images have also been obtained from a rat brain, demonstrating the feasibility of simultaneous PET and MR studies of in vivo systems.

Despite significant advances made over the past decade in ultrasound (US) and magnetic resonance imaging (MRI) for guidance and assessment of high intensity focused ultrasound (HIFU) treatments many challenges remain. Recent developments address clinically relevant barriers to image guidance of therapeutic ultrasound. This session will feature invited presentations on (1) the use of MRI temperature mapping in presence of fat, within bone, and moving tissues, (2) dual mode ultrasound array (DMUA) systems for imaging and therapy with the advantage of inherent registration between the image‐guidance and therapeutic coordinate systems, (3) echo decorrelation imaging, providing real‐time feedback about cumulative heat‐induced tissue changes, (4) laparoscopic US imaging and HIFU treatments with special emphasis on the use of US to assess temperature change as well as tissue characteristics; and (5) opportunities for medical physicists to participate in the development, treatment planning, and quality control aspects of image‐guided HIFU therapy. Learning Objectives: 1. To understand the role of various MRI and US technologies in guidance and monitoring of HIFU therapy, including MR temperature mapping, dual mode ultrasound array systems, echo decorrelation imaging for ablation assessment, and laparoscopic US‐guided HIFU 2. To identify opportunities for medical physicists in assessment and deployment of technologies in image‐guided therapeutic ultrasound Dr. Carol is the Chief Development Officer for US HIFU, LLC

Oncologic surgery relies strongly on the hand‐eye coordination of surgeons and their ability to correctly determine surgical margins, distinguishing cancerous from healthy tissues. In recent years a variety of innovative intra‐operative imaging technologies have been developed that allow for more accurate identification of tumor and its boundaries and they help bring quantitative measures to the surgical theater. This symposium will present some of the latest developments in intra‐operative imaging technologies, including cone beam computed tomography,mass spectrometry and optical spectroscopy. Each offers to overcome the limitations of conventional surgical navigation (i.e., tracking in the context of preoperative images) and allow intraoperative assessment of the quality of tumor resection and the avoidance of adjacent, normal anatomy. Such technological advances are key to safer, more precise, and more minimally invasive interventions. In addition, we will discuss the role of medical physicists in the assessment and validation of technologies in image‐guidedoncologic interventions. Learning Objectives: 1. To identify emerging imaging technologies in image‐guidedoncologic surgery 2. To better understand the role of various technologies toward reaching the surgical end point 3. To identify opportunities for medical physicists in assessment of technologies in image‐guidedoncologic interventions