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An Introductory Odyssey Through Spin Physics

A Wolbarst1*, N Yanasak2*, (1) University Kentucky, Versailles, KY, (2) Augusta University, Augusta, GA


(Monday, 7/13/2020) 2:00 PM - 3:00 PM [Eastern Time (GMT-4)]

Room: Track 4

Magnetic resonance imaging as a clinical imaging modality is highly versatile, providing not only information on anatomy but also physiological information such as tissue perfusion, fat content, and organ stiffness, often at a resolution on the order of a mm. To achieve this, MRI utilizes the nuclear dipole of hydrogen to interrogate the magnetic properties of tissue, which in turn provides insight into biochemistry of the patient. Unfortunately, the technical description of MRI involves complicated quantum mechanical and mathematical concepts that can deter the student new to the study of the subject. This session consists of two presenters who endeavor to describe the essential principles of MRI as simply as possible.

The first talk of this session describes basic MRI physics with complexity stripped away as thoroughly as possible. Although the examples are simplified, starting with magnetization and relaxation processes along a 1D strip of tissue, the concepts behind the discussion are valid within the clinical environment and should serve as a suitable introduction for those not familiar with MRI. Finally, this talk concludes with the concepts of spin- and gradient-echo imaging and how they manipulate tissue contrast, paying close attention to the relationship between contrast and MR scanning parameters such as echo and repetition times.

The second talk of this session picks up with how to convert the various signals from within a 2D volume of interest into an image with clinically useful contrast. Beginning with an overview of spin-warp imaging and its relationship to the formalism of k-space, the talk will cover the use of magnetic gradients to encode signal from different spatial regions. Once this formalism for conventional imaging has been introduced, the remainder of the talk will discuss various methods for speeding up imaging procedures, including multi-slice and multi-echo imaging, and various strategies involving the under-sampling of data in k-space.

Learning Objectives:
1. To describe how NMR signal arises and relaxation of magnetization modifies that signal within a voxel.
2. To distinguish between how spin-echo and gradient-echo sequences generate an NMR echo.
3. To outline the use of gradient magnetic fields to encode spatial information as a temporal modulation of the NMR signal.
4. To enumerate imaging factors that control the time to acquire an MRI image, to explore ways of increasing imaging speed.



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