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Research Paper

Study of MRI Susceptibility Artifacts for Nanomedical Applications

[+] Author and Article Information
Tim Wortmann1

Department of Computing Science, Division Microrobotics and Control Engineering, University of Oldenburg–KISUM, D-26129 Oldenburg, Germanywortmann@informatik.uni-oldenburg.de

Christian Dahmen, Sergej Fatikow

Department of Computing Science, Division Microrobotics and Control Engineering, University of Oldenburg–KISUM, D-26129 Oldenburg, Germany

1

Corresponding author.

J. Nanotechnol. Eng. Med 1(4), 041002 (Oct 21, 2010) (5 pages) doi:10.1115/1.4002501 History: Received July 30, 2010; Revised August 26, 2010; Published October 21, 2010; Online October 21, 2010

This article deals with the exploitation of magnetic susceptibility artifacts in magnetic resonance imaging (MRI) for the recognition of metallic delivery capsules. The targeted application is a closed-loop position control of magnetic objects implemented using the components of a clinical MRI scanner. Actuation can be performed by switching the magnetic gradient fields, whereas object locations are detected by an analysis of the MRI scans. A comprehensive investigation of susceptibility artifacts with a total number of 108 experimental setups has been performed in order to study scaling laws and the impact of object properties and imaging parameters. In addition to solid metal objects, a suspension of superparamagnetic nanoparticles has been examined. All 3D scans have been segmented automatically for artifact quantification and location determination. Analysis showed a characteristic shape for all three base types of sequences, which is invariant to the magnetic object shape and material. Imaging parameters such as echo time and flip angle have a moderate impact on the artifact volume but do not modify the characteristic artifact shape. The nanoparticle agglomerates produce imaging artifacts similar to the solid samples. Based on the results, a two-stage recognition/tracking procedure is proposed.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

System overview for MRI-guided drug delivery, two signal paths are shown: case 1 (upper path) is executed one time using a full 3D scan and case 2 is subsequently executed using single slice scans

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Figure 2

Heavy distortions caused by ferrofluid embedded into a 0.5 l container of agar in gradient echo (left) and spin echo (middle), spin-echo scan of agar phantom without ferrofluid (right)

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Figure 3

Agar-filled containers (left) and air channels in an agar container scanned with gradient-echo sequence (right)

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Figure 4

Typical artifacts in sagittal plane for gradient echo (left), spin echo (middle), and single-shot spin echo (right) resulting from a 3 mm steel sphere (upper row) and ferrofluid (lower row); the vertical lines result from the ferrofluid sample preparation and are not an imaging artifact

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Figure 5

Resulting segmentation zones for SSFSE sequence scan

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Figure 6

EM segmentation results for single-shot fast spin echo (top), gradient echo (middle), and spin echo (bottom) for steel spheres; diameter: 3 mm, 2.5 mm, 2.0 mm, 1.5 mm, 1.2 mm, and 1mm (left-right)

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Figure 7

Artifact volume comparison of all sequences used for the 2 mm steel sphere with varying echo time (TE), flip angle (FA), and voxel size in frequency encoding direction (FM)

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Figure 8

Artifact volume comparison for different sequences; the volume is derived by a fixed threshold 3D segmentation

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