This article discusses Magnetic Resonance Elastography (MRE), a technique for measuring the viscoelastic properties of tissues. It emphasizes the process of using a gelatin phantom to simulate tissue and capture shear wave propagation through MRI.
Magnetic Resonance Elastography, or MRE, measures the viscoelastic properties of tissues, such as stiffness and elasticity, by analyzing shear wave propagation.
To perform MRE, start with a gelatin phantom designed to mimic tissue and secured in the magnetic resonance imaging or MRI head coil.
The phantom is connected to an electromagnetic actuator through a vibration plate.
Attach the actuator to a function generator to generate the shear waves that are transmitted through the vibration plate and into the phantom.
Simultaneously, initiate the MRI scans.
As the shear waves propagate, the MRI captures their motion as phase images.
Process these images using algorithms to isolate the shear wave propagation patterns, where different colors represent various wave phases.
An expanded wave pattern indicative of slower wave propagation through the gelatin phantom, suggests its soft tissue-like properties.
Whereas, a dense wave pattern indicates faster wave propagation, suggesting stiff tissue-like properties.
Place the gelatin phantom into the head coil. Then, put the vibration plate on top of the gelatin phantom. Ensure that the contact between the phantom and the vibration plate is firm. Put sponges and sandbags around the gelatin phantom to make sure the phantom is firmly placed. Mount an electromagnetic actuator on the head coil and connect the transmission bar to the vibration plate.
Connect the power lines that the actuator with the amplifier, and then connect the control lines with the controller. Set the waveform, vibration frequency, and amplitude in the function generator. Set the desired vibration amplitude by adjusting the power amplifier. Then, set the function generator to work in the trigger mode. Connect the trigger line to the external trigger port of the MRI machine.
Set the MRE scanning frequency the same as that from the function generator, so that the motion encoding gradient is synchronized with the motion of the vibration plate. Next, set the flip angle to 30 degrees, TR and TE to 50 and 31 milliseconds, field of view to 300 millimeters, slice thickness to 5 millimeters, and voxel size to 2.34 by 2.34 square millimeter.
Measure the phase images at four temporal points in one sinusoidal cycle. Apply both positive and negative motion encoding gradients at each time point. Based on the phase image acquired, remove the background phase by subtracting the positive and negative encoded phase images. Unwrap the phase with a reliability sorting-based algorithm.
Extract the principal components of the motion by applying Fast Fourier Transform to the unwrapped phase images. Filter the phase image with a digital bandpass filter and estimate the shear modulus with a 2D direct inversion algorithm to obtain storage modulus G Prime and loss modulus G double prime.
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