On the Assessment of Image Inhomogeneity Using T2 Magnetic Resonance Imaging in Head Phantom for Radiotherapy Treatment Planning: Preliminary Study

Dwihapsari, Yanurita; Asdiantoro, E.; Maulidiyah, Nurul

doi:10.1007/s00723-019-01177-x

Cited by 7 publications

(6 citation statements)

References 38 publications

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“…When different pulse sequences were introduced, variation in R2* measurements increased slightly on average across the four 1.5 T systems and increased considerably across the three 3 T systems. The levels of variation seen here are slightly beyond the range of 1.4–7% that has been reported previously 6,16 . is most likely due pulse sequences that will be discussed later in this section.…”

Section: Discussionsupporting

confidence: 48%

“…When considering quantitative imaging using MRI, a clear parameter of concern is the homogeneity of the static magnetic field used for image acquisition. It has been shown that inhomogeneous magnetic fields lead to incorrect evaluation of signal intensity in MR images, 15 which could ultimately lead to improper characterization of R2*, thus LIC. However, since the magnetic field homogeneity of all MRI scanners at our institution are evaluated annually by qualified medical physicists, as per ACR recommendations, magnetic field inhomogeneity is not expected to account for a substantial portion of the R2* variability measured in this study.…”

Section: Discussionmentioning

confidence: 99%

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Reproducibility of liver iron concentration estimates in MRI through R2* measurement determined by least‐squares curve fitting

Headley

Pickens

2020

J Applied Clin Med Phys

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Measuring transverse relaxation rate (R2* = 1/T2*) via MRI allows for noninvasive evaluation of multiple clinical parameters, including liver iron concentration (LIC) and fat fraction. Both fat and iron contribute to diffuse liver disease when stored in excess in the liver. This liver damage leads to fibrosis and cirrhosis with an increased risk of developing hepatocellular carcinoma. Liver iron concentration is linearly related to R2* measurements using MRI. A phantom was constructed to assess R2* quantification variability on 1.5 and 3 T MRI systems. Quantification was executed using least-squares curve fitting techniques. The phantom was created using readily available, low-cost materials. It contains four vials with R2* values that cover a clinically relevant range (100 to 420 Hz at 1.5 T). Iron content was achieved using ferric chloride solutions contained in glass vials, each affixed in a three-dimensional (3D)printed polylactide (PLA) structure, surrounded by distilled water, all housed in a sealed acrylic cylinder. Multiple phantom stands were also 3D-printed using PLA for precise orientation of the phantom with respect to the direction of the static magnetic field. Acquisitions at different phantom angles, across multiple MRI systems, and with different pulse sequence parameters were evaluated. The variability between any two R2* measurements, taken in the same vial under these various acquisition conditions, on a 1.5 T MRI system, was <7% for each of the four vials. For 3 T MRI systems, variability was less than 14% in all cases. Variability was <6% for both 1.5 and 3 T acquisitions when unchanged pulse sequence parameters were used. The phantom can be used to mimic a range of clinically relevant levels of R2* relaxation rates, as measured using MRI. These measurements were found to be reproducible relative to the gold-standard method, liver biopsy, across several different image acquisition conditions.

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Section: Discussionsupporting

confidence: 48%

Section: Discussionmentioning

confidence: 99%

Reproducibility of liver iron concentration estimates in MRI through R2* measurement determined by least‐squares curve fitting

Headley

Pickens

2020

J Applied Clin Med Phys

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“…Image inhomogeneity can diminish SNR, induce geometrical distortion, and impact image uniformity. 4 Magnetic field homogeneity in its simplest term is how the magnetic field (B 0 ) of the main magnet is uniformly distributed when no patient is within the magnetic field, and measured in parts per million (ppm) 1 from the isocenter. 5 In general, field inhomogeneity is classified under three groups: static magnetic field (B 0 ), chemical shift, and susceptibility-induced inhomogeneities.…”

Section: Introductionmentioning

confidence: 99%

“…design. 4 A steady homogenous magnetic field with the best homogeneity in the entire measuring object volume is ideal for MRI. However, since no practical magnet can ever produce a perfect homogenous magnetic field, generating a static homogeneous field is nearly impossible.…”

mentioning

confidence: 99%

Impact of Magnetic Field Inhomogeneity on the Quality of Magnetic Resonance Images and Compensation Techniques: A Review

Manson¹,

Inkoom²,

Mumuni³

2022

RMI

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Background: Magnetic field inhomogeneity in magnetic resonance imaging (MRI) is caused by the inherent properties of the main magnet, external ferromagnetic components surrounding the magnet, and the patient itself. Significant deviations from magnetic field inhomogeneity can create artifacts in MRI images, thereby compromising image quality. Optimizing magnetic field homogeneity improves image quality and helps to reduce artifacts. The goal of this article therefore is to help radiographers and operators of MRI understand the clinical basis of magnetic field inhomogeneity and its effects on MR images. This would assist them to appreciate the trade-offs between sequence parameters and image quality metrics towards optimizing magnetic field inhomogeneity. Methods: A narrative literature review was conducted from relevant databases using search terms such as MRI, magnetic field inhomogeneity, optimization, magnetic field inhomogeneity artifacts, and MRI shimming. Results: Minimizing field inhomogeneities in MRI is not straightforward but involves a multitude of factors and steps. Magnetic field homogeneity could be optimized to improve MR image quality by choosing the most appropriate pulse sequence/imaging parameters that could best minimize distortion and increase SNR based on the anatomical region of interest (or tissue types) while complementing it with shimming and use of dielectric pads. Conclusion: Future works to investigate the association between the MRI pulse sequence parameters and measurements of MR image quality metrics, based on individual tissue densities, could provide a new window for reducing magnetic field inhomogeneity due to susceptibility and chemical shift effects.

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“…As agar is a hydrogel and consists of water molecules, it can be used in diffusion MRI measurement to observe the diffusion pattern of water molecules in the agar [2]. Agarose gel phantoms also aid in MRI-based radiotherapy treatment planning by providing more accurate quantitative features of disease and healthy tissue rather than depending solely on qualitative assessment [9]. Furthermore, as the resting-state fMRI depends on transversal relaxation of tissue (T2*), the usage of agar as phantom materials can result in local inhomogeneity of the magnetic field which will further reduce the T2* value.…”

Section: Introductionmentioning

confidence: 99%

Signal-to-noise ratio uniformity and stability of agar gel phantom with iron (III) oxide as relaxation modifier

Lim

Dwihapsari

et al. 2021

Beni-Suef Univ J Basic Appl Sci

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Background Agar has been commonly used as one of the materials to fabricate magnetic resonance imaging phantoms in the past few decades. In this study, eleven agar gel phantoms with different iron (III) oxide (Fe2O3) masses were prepared. This study was aimed to evaluate the signal-to-noise ratio (SNR) uniformity and stability of agar gel phantoms with and without the addition of Fe2O3 at two different time points (TPs). Fe2O3 powder was used as a relaxation modifier to manipulate and produce various SNR, T1 and T2 values. These phantoms were scanned using turbo spin echo pulse sequence to produce T1- and T2-measurement images. The SNR was then computed by plotting 1, 3 and 25 regions of interest on the images using ImageJ software. The T1 and T2 relaxation equations were then fitted to the experimental results of SNR versus TR and SNR versus TE curves for the determination of saturation (SNRo), T1 and T2 values. Results The results demonstrated that the agar gel phantoms were able to maintain SNR uniformity but not SNR stability after 4 weeks of phantom preparation. The change in the water content and microstructure of the phantoms have no significant effect on T2 relaxation but on T1 relaxation. The T1 and T2 of the agar gel phantoms were minimally affected although there was a systemic increase in the content of the Fe2O3 powder. Conclusions It can be concluded that the agar gel phantoms exhibited the characteristics of SNR uniformity, but they showed instability of SNR at TP2. The Fe2O3 in powder form is not an effective relaxation modifier to reduce the T1 and T2 when it is introduced into the agar gel phantoms. Dissolved nanosized particles should be the focus of future studies.

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On the Assessment of Image Inhomogeneity Using T2 Magnetic Resonance Imaging in Head Phantom for Radiotherapy Treatment Planning: Preliminary Study

Cited by 7 publications

References 38 publications

Reproducibility of liver iron concentration estimates in MRI through R2* measurement determined by least‐squares curve fitting

Reproducibility of liver iron concentration estimates in MRI through R2* measurement determined by least‐squares curve fitting

Impact of Magnetic Field Inhomogeneity on the Quality of Magnetic Resonance Images and Compensation Techniques: A Review

Signal-to-noise ratio uniformity and stability of agar gel phantom with iron (III) oxide as relaxation modifier

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