Design of a MR Phantom for the Simulation of Lumbar Intervertebral Disks Team Members: Missy Haehn, Can Pi, Ben Sprague, Andrea Zelisko Client: Dr. Victor Haughton Advisor: Prof. Kristyn Masters December 7, 20052Table of Contents Item Page Number(s) Abstract 4 Executive Summary 4 1 Introduction 4-5 1.1 Problem Statement 5 1.2 Medical Background 5 1.2.1 Intervertebral Disks 5 1.2.2 MR Scanner 5-6 1.2.3 Phantoms 6-7 1.3 Client Information and Motivation 7 1.4 Client and Design Requirements 7-8 2 Current Practices 8 2.1 Commercial Phantoms 8-9 2.2 Phantoms for Research Purposes 9 3 Design from Spring 2005 9 3.1 Fixed vs Modular Construction 10 3.2 Hydrogels vs Aqueous disk samples 10-11 3.3 Decision Matrices 11-12 3.4 Spring 2005 Final Design 12-13 4 Testing Results from Spring 2005 13 4.1 Testing of Gadolinium Samples 13 4.2 Disk Sample Testing 13-14 4.3 Testing Results of Tubes and Prototype 14-15 5 Client Feedback 15 5.1 Improvements, Enhancements, and Changes 16 6 Design for Fall 2005 16 6.1 Gadolinium Samples 16 6.2 Hydrogel Disk Samples 17 6.3 Phantom Construction 17-18 7 Progress and Testing in Fall 2005 18 7.1 Gadolinium Sample Testing 18-19 7.2 Hydrogel Sample Testing 19-21 7.3 Phantom Construction 21 8 Future Work/Potential Problems 21 8.1 Phantom Construction 2138.2 Additional Testing 21 8.3 Other Future Work/Potential Problems 22 8.5 Future Work Summarized 23 9 References4Abstract A phantom was designed for use in an MR imager to assess the accuracy of the scanner using T2 relaxation values. The phantom can also be used to determine how certain variables such as distance from coil and loading affect the scanner’s accuracy. The phantom holds Gadolinium (Gd) doped water samples and artificial intervertebral disk samples to assess accuracy and research the relationship between disk composition and resulting MR T2 data. The final design for the phantom consists of an acrylic container with tubes running through to hold glass vials. The glass vials contain the Gd and disk mimicking samples. This design allows variation in sample placement throughout the phantom and encompasses adequate loading for the MR scans. Executive Summary A phantom was designed for use in an MR imager to assess the accuracy of the scanner using T2 relaxation values. The phantom can also be used to determine how certain variables such as distance from coil and loading affect the scanner’s accuracy. The phantom holds Gadolinium (Gd) doped water samples and artificial intervertebral disk samples to assess accuracy and research the relationship between disk composition and resulting MR T2 data. The final design for the phantom consists of an acrylic container with tubes running through to suspend glass vials. The glass vials hold the Gd and disk mimicking samples. This design allows variation in sample placement throughout the phantom and encompasses adequate loading for the MR scans. Validation of the design in the relaxometer and MR imager is currently in progress. From the data taken on the relaxometer, a correlation between Gd concentration and T2 values was determined. This information was used in determining theoretical T2 values of Gd samples tested on the MR scanner. Values measured on the scanner were compared to the theoretical values and varied by approximately +/- 5 ms. Future work will help improve the accuracy. Disk samples were also prepared by using hydrogels as a matrix to suspend the intervertebral disk components. Thus far, gelatin has been chosen as the most appropriate hydrogel for this task and experiments have been performed to include another disk component, glycoaminoglycans (GAGs), in the hydrogels as well. Future work with the disk samples includes MR testing with GAGs and later with collagen added as well. The phantom has not yet been tested as a single entity. The current prototype constructed is non-functional and the design team is working to have the design fabricated by an outside company. Once this step is completed, all elements of the design (disk samples, Gd water samples, and phantom container) can be combined and tested as one. This final validation will be completed by May 2006. 1 Introduction Magnetic resonance (MR) imaging uses magnetic fields with the strength up to 7 Tesla, which is 140,000 times stronger than the earth’s magnetic field, for diagnosing and researching diseases and is a growing modality in medical imaging. During the spring semester of the 2004-2005 school year, a team in the Biomedical Engineering program at UW-Madison started working on a design project that incorporates this imaging5modality. Work has been done on designing, testing, and constructing a phantom to calibrate a MR scanner and hold samples that mimic the intervertebral disks in the spine. 1.1 Problem Statement The phantom is needed to assess the accuracy of an MR scanner by comparing known T2 values to that which the MR scanner measures. Measurements made with the phantom will help assess which variables affect the accuracy of the MR scanner, such as the distance between the spinal coil and the patient’s spine, the size of the patient, and the sensitivity of the MR scanner to very similar solutions. The phantom will also hold artificial samples which have a composition of water, collagen, and proteoglycans and a T2 value comparable to that of lumbar intervertebral disk tissue. Research will be done using the phantom examining the relationship between disk water content, T2 value, collagen, and proteoglycan content in order to better assess the integrity of intervertebral disk tissue using MR technology. 1.2 Medical Background To better understand the problem general background research was completed on intervertebral disks, MR technology, phantoms, and the project’s client, Dr. Haughton, a professor of Neuroradiology from the UW Hospital. 1.2.1 Intervertebral Disks Millions of people suffer from back pain due to degeneration of the intervertebral disks in their spine. The spine consists of many vertebra and cushioning disks between to act as shock absorbers. As people grow older the stress on their back begins to add up, resulting in deterioration of the intervertebral disks. This deterioration
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