Applications of Low Field Magnetic Resonance Imaging
Poster Number
15a
Introduction/Abstract
A major goal of medicine is to measure the integrity of tissues without invasive procedures. Current methods of detecting cancerous or diseased tissue involves rudimentary techniques such as palpation or extensive lab tests and biopsies. Tissue is extracted from the patient and analyzed under a microscope for signs of tumor growth, and therefore, the patient needs to undergo surgery for the tissue extraction. This results in patient discomfort and higher medical costs. Palpation is a clinical examination tool that has been used for centuries to detect abnormalities in parts of the human body that are easily accessible by assessing the changes in the stiffness of tissues. The elasticity of tissues in the human body is well known and therefore, a change in elasticity may indicate the presence of disease. However, it is limited to tissues that are easily accessible to the physicians by hand. Recent advancement of medical technology has allowed for the use of imaging techniques to analyze the tissues that are not easily accessible. X-ray imaging has come to be a significant means of detecting bone damage, CT imaging has allowed for the volumetric imaging of various areas of the body, and MRI has provided enhanced soft-tissue contrast with little radiation. However, these techniques fail to quantify the changes in the mechanical properties of the tissues due to disease. The MRI system can be modified to perform Magnetic Resonance Elastography (MRE) a technique that allows for the noninvasive measurement of local mechanical properties of tissues by analyzing the visual and temporal strains caused by the propagation of mechanical shear waves.
Purpose
The purpose of project is to determine the capability of low field MRI in acquiring high resolution images and to develop and validate a low field MR Elastography system that is capable of non-invasively measuring the mechanical properties of soft samples.
Method
MR imaging was done with a typical spin echo pulse sequence. A pulse sequence is a programmed set of variables that are used to acquire MR images. For MRE, the spin echo pulse sequence was modified to include critical MRE parameters. The MRE system was designed so that the modified pulse sequence controlled an actuator that was synchronized with the MRI system. The actuator, a piezoelectric bending transducer, was driven by a sinusoidal signal generated by a waveform generator. Laser Doppler Vibrometry was used to determine the resonance frequency of actuator. The vibrometer was able to measure the displacement of the actuator by pointing a laser beam on the its surface and measuring the reflected signal. The aim was to obtain a frequency that produced the greatest displacement. This was done by subjecting the actuator to a band limited frequency sweep from 1Hz to 1kHz. The resulting plot was analyzed and once the resonance frequency was found, the actuator was subjected to a sinusoidal wave at that frequency and the displacement was measured. With the above setup, a resonance frequency of 370-420 Hz was found that gave a vibrational amplitude of 145-200 μm. To validate the MRE system, agarose gel samples of two stiffnesses (1 % wt on bottom and 0.5% wt on top) were used. For a novel MRE application, adult human Mesenchymal Stem Cells (hMSC) were cultured and seeded and differentiated onto protein silk scaffolds to produce tissue engineered bone. The development of the bone was measured with MRI and MRE at 3 times points; week 0, week 2, and week 4.
Results
Results obtained from MRE experimentation on agarose gel validated the technique. A map was produced that illustrated the stiffness of the two gel samples on a pixel-by-pixel basis. Tissue engineered bone constructs were imaged at week 0 time point with MRI and MRE. The data obtained illustrated the capability to acquire high resolution MR images with isotropic resolution up to 195 micrometers and the capability to measure the stiffness of the TE bone through MRE. It is expected that as the TE bone develops, the intensity of MR imaging will drop due to bone mineralization. The mineralization will increase the stiffness of the bone which will be measured by MRE.
Significance
Low field MRI and MRE present low-cost tools for assessing the health of tissues. A challenge in tissue engineering is to measure the mechanical integrity of the engineered constructs without harming the living cells they contain. MRI and MRE can safely provide the mechanical properties of the engineered tissues without the need for sample sacrifice.
Location
DeRosa University Center
Format
Poster Presentation
Poster Session
Morning 10am-12pm
Applications of Low Field Magnetic Resonance Imaging
DeRosa University Center
A major goal of medicine is to measure the integrity of tissues without invasive procedures. Current methods of detecting cancerous or diseased tissue involves rudimentary techniques such as palpation or extensive lab tests and biopsies. Tissue is extracted from the patient and analyzed under a microscope for signs of tumor growth, and therefore, the patient needs to undergo surgery for the tissue extraction. This results in patient discomfort and higher medical costs. Palpation is a clinical examination tool that has been used for centuries to detect abnormalities in parts of the human body that are easily accessible by assessing the changes in the stiffness of tissues. The elasticity of tissues in the human body is well known and therefore, a change in elasticity may indicate the presence of disease. However, it is limited to tissues that are easily accessible to the physicians by hand. Recent advancement of medical technology has allowed for the use of imaging techniques to analyze the tissues that are not easily accessible. X-ray imaging has come to be a significant means of detecting bone damage, CT imaging has allowed for the volumetric imaging of various areas of the body, and MRI has provided enhanced soft-tissue contrast with little radiation. However, these techniques fail to quantify the changes in the mechanical properties of the tissues due to disease. The MRI system can be modified to perform Magnetic Resonance Elastography (MRE) a technique that allows for the noninvasive measurement of local mechanical properties of tissues by analyzing the visual and temporal strains caused by the propagation of mechanical shear waves.
