A new phantom to assess and correct geometrical distortions for Magnetic Resonance Imaging: Design and preliminary experiments

Abstract

Purpose: Nowadays, many focal therapies use Magnetic Resonance (MR) imaging for treatment planning purpose. In this context, geometric distortions should be as low as possible. In this paper, we present a new device to assess image distortions in MRI.Methods: The phantom consists of a stack of plates made of Polymethyl Methacrylate (PMMA). The detection elements are balls forming MRI capsules and delimiting an internal volume filled with paraffin oil. When imaged, this system enables having a regular pattern with the same distance in the three space directions between each capsule center of mass.Correction of the distortions is done using a registration of the detected balls pattern with the theoretical pattern. Iterative Closest Points (ICP) algorithm is used for thus purpose.Results: Preliminary evaluations on different MR sequences have been conducted, the combination of device and ICP-based correction method shows the feasibility of the approach.Conclusion: From the promising preliminary results obtained, future developments will include an upgrade of the phantom and the implementation of more sophisticated correction algorithms.

Measuring geometric accuracy in magnetic resonance imaging with 3D-printed phantom and nonrigid image registration

“…Studying the geometric accuracy of MRI has been a subject of great interest in recent decades, especially from the aspect of quality assurance (QA) [3][4][5][6], radiotherapy treatment planning (RTP) [7][8][9][10][11][12][13][14][15][16], and stereotactic operations [17][18][19]. Most MRI QA protocols include at least a limited investigation of the geometric accuracy, often reporting deviations from known phantom structure lengths.…”

“…Generally, the phantoms have a regular structure; either a hyposignal grid in a signal-producing background medium [3,[6][7][8][9][10], or a pattern of signal-producing markers in a hyposignal medium [4,5,[11][12][13]17]. Typically, the signal-producing material is either water-salt solution [3,5,7,19], paraffin oil [6,[8][9][10]17] or fat-soluble vitamin capsules [11,12]. For example, Wang et al [3] built a phantom from grid sheets, where the interfaces of the water-solution medium and the crosses in the grid sheet served as control points (CP).…”

“…Many of the existing phantoms, especially those developed for RTP purposes, are large field-of-view phantoms [4,[10][11][12] and, consequently, scanned with table-integrated spine coils. Not many phantoms are designed for head coils: the phantom of Vermandel and Betrouni [17] can be modified to fit into both head and body coils; Zhang et al [18] and Pappas et al [19] used Leksell Stereotactic frame (Elekta Instruments AB, Stockholm, Sweden) that stabilizes their phantoms but inflicts distortions, too.…”