ISMRM23 - Artifacts & Correction Strategies

ISMRM & ISMRT Annual Meeting & Exhibition • 03-08 June 2023 • Toronto, ON, Canada

Artifacts & Correction Strategies

Weekend Course

ORGANIZERS: Mark Chiew, Andrew Scott

Sunday, 04 June 2023

718B

07:45 - 11:45

Moderators: Yoshitaka Bito & Tevfik Ismail

Skill Level: Basic to Intermediate

Session Number: WE-22

CME Credit

Session Number: WE-22

Overview
This 4-hour course will cover the main artifacts commonly encountered in MRI and introduce some of the methods used to remove, avoid, or mitigate them. The first portion of the course covers general artifacts found in many situations, while the second part covers more specific artifacts, including flow-related artifacts and artifacts induced by image reconstruction, finishing with a tutorial on methods for correcting for distortion in EPI.

Target Audience
Clinicians and technologists with an interest in the source and mitigation of the artefacts they see everyday, and engineers/physicists starting out in MRI.

Educational Objectives
As a result of attending this course, participants should be able to:
- Identify the key sources of artefacts in commonly appearing in MRI;
- Explain methods available for correcting common artefacts; and
- Apply techniques to correct for distortion artefacts in EPI data.

07:45		Basic Artifacts View Presentation Video Martin Graves Keywords: Image acquisition: Artefacts Image artifacts can arise from one or more of the following: MR physics, MR system hardware, and the patient. Given the wide range of possible MR artifacts this presentation will be limited to the main relationships between data corruptions during image acquisition, i.e., in raw data or k-space, and their appearance in the reconstructed image after Fourier transformation. The cause and effect of artifacts including Gibbs ringing, phase encode direction aliasing/foldover, zippers, spikes and motion during image acquisition will be discussed, together with failures in fat suppression and the effect of receiver bandwidth on chemical shift artifact.
08:15		B0-Related Artifacts View Presentation Video Catherine Morgan Keywords: Image acquisition: Artefacts, Physics & Engineering: Physics Inhomogeneity of the main magnetic field, B0, can cause a number of artefacts. In this educational session, causes of B0 inhomogeneity will be described, with a focus on magnetic susceptibility related artefacts. For example at air-tissue interfaces or around metal implants. The effects on different sequences e.g. spin-echo, gradient-echo and echo-planar imaging will be described. Lastly correction strategies for B0 artefacts will be presented, grouped by approach: acquisition, specialised sequences and post-processing.
08:45		B1-Related Artifacts View Presentation Video Laura Schreiber
09:15		Gradient-Related Artifacts View Presentation Video Corey Baron Keywords: Image acquisition: Artefacts This educational session will describe the mechanisms behind artifacts that stem from gradient non-linearity, eddy currents, and concomitant gradient fields. Attendees will learn to identify each type of gradient-related artifact, and will learn about methods to mitigate, correct, or avoid them. Distinction will be made between artifacts stemming from gradients used for contrast generation and gradients used for image encoding. For example, diffusion MRI is especially sensitive to gradient-related artefacts due to the use of extremely large gradient amplitudes to sensitize the signal to diffusion.
09:45		Break & Meet the Teachers
10:15		Flow-Related Artifacts View Presentation Video Julio Garcia Flores Keywords: Cardiovascular: Blood, Cardiovascular: Hemodynamics, Image acquisition: Artefacts This educational session will introduce most common technique to measure flow. In particular phase-contrast magnetic resonance imaging and its applications. Blood flow acquisition and quantification can be affected by image artifacts from multiple sources. This lecture will discuss the most common sources of artifacts impacting blood flow measurements in 2D and 4D and strategies to correct them.
10:45		Image Reconstruction Artifacts View Presentation Video Gastao Cruz Keywords: Image acquisition: Reconstruction Artifacts arise in MR reconstruction from a variety of sources: the discrete (and band-limited) sampling of the signal, noise amplification, parallel imaging, regularization strategies like compressed sensing, motion, and many others. In this talk we'll look at some of the underlying mechanics that cause these artifacts, and how they can impact clinical images.
11:15		Tutorial: EPI Distortion Correction View Presentation Video Barbara Dymerska Keywords: Image acquisition: Artefacts, Contrast mechanisms: fMRI, Neuro: Brain EPI is sensitive to inhomogeneities in the static magnetic field that arise from the interfaces between tissues with different magnetic susceptibilities. Field inhomogeneities cause geometric distortions in EPI in the phase-encoding direction leading to mislocalization of activation and difficulty coregistering functional results to anatomical scans. We will learn how to correct distortions using a field map calculated from the phase change between images acquired at different echo times. A single field map does not capture dynamic field changes occurring due to motion or respiration. We will thus also expand our capabilities to perform dynamic distortion correction.