In vivo 3D brain and extremity MRI at 50 mT using a permanent magnet Halbach array

O’Reilly, Thomas; Teeuwisse, Wouter M.; Gans, Danny de; Koolstra, Kirsten; Webb, Andrew

doi:10.1002/mrm.28396

“… 29 , 30 Similarities between MRI, which need a strong homogeneous field and variable magnetic field gradient indicate the principal possibility that such magnet setups cannot only steer SPIONs but also image them. 18 , 31 , 32 Additionally, such magnet systems can also be used to move other super para- or ferromagnetic objects used in micro-fluidics, nano- and micro-robotics 33 or nanoscience. 34 …”

Section: Discussionmentioning

confidence: 99%

Contactless Nanoparticle-Based Guiding of Cells by Controllable Magnetic Fields

Blümler¹,

Friedrich²,

Pereira³

et al. 2021

NSA

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Controlled and contactless movements of magnetic nanoparticles are crucial for fundamental biotechnological and clinical research (eg, cell manipulation and sorting, hyperthermia, and magnetic drug targeting). However, the key technological question, how to generate suitable magnetic fields on various length scales (µm–m), is still unsolved. Here, we present a system of permanent magnets which allows for steering of iron oxide nanoparticles (SPIONs) on arbitrary trajectories observable by microscopy. The movement of the particles is simply controlled by an almost force-free rotation of cylindrical arrangements of permanent magnets. The same instrument can be used to move suspended cells loaded with SPIONs along with predetermined directions. Surprisingly, it also allows for controlled movements of intracellular compartments inside of individual cells. The exclusive use of permanent magnets simplifies scaled up versions for animals or even humans, which would open the door for remotely controlled in vivo guidance of nanoparticles or micro-robots.

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“…For the time being, it remains technically challenging to obtain accurate brain volume measurements in a rapid-enough fashion to guide clinical treatment decisions in most sub-Saharan African settings. We anticipate, however, that with the emergence of available inexpensive low-field MRI technologies 28,29 and continuing development of more automated machine learning segmentation protocols, 30 brain volume could become part of standard hydrocephalus assessment and follow-up in the way that ventricle size is currently.…”

Section: Discussionmentioning

confidence: 99%

Brain growth and neurodevelopment after surgical treatment of infant post-infectious hydrocephalus in sub-Saharan Africa

Kulkarni

¹

,

Mbabazi-Kabachelor

²

,

Mugamba

³

et al. 2020

Preprint

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ImportancePost-infectious hydrocephalus in infants is a major public health burden in sub-Saharan Africa.ObjectiveTo determine long-term brain growth and cognitive outcome after surgical treatment of infant post-infectious hydrocephalus in Uganda.DesignProspective follow-up of a previously randomized cohort.SettingSingle center in Mbale, Uganda.ParticipantsInfants (<180 days old) with post-infectious hydrocephalus.InterventionsEndoscopic or shunt surgery.Main outcomesBayley Scales of Infant Development (BSID-3) and brain volume on computed tomography (raw and normalized for age and sex) at 2 years after treatment.ResultsEighty-nine infants were assessed for 2-year outcome. There were no significant differences between the two surgical treatment arms, so they were analyzed together. Raw brain volumes increased between baseline and 24 months (median change=361 cc, IQR=293 to 443, p<0.001), but almost all of this increase was seen in the first year (median change=381 cc, IQR=310 to 442, p<0.001), with very little change between 12 and 24 months (median change=-5 cc, IQR=-52 to 42, p=0.66). The fraction of those with a normal brain volume increased from 15% at baseline to 50% at 1 year, but then declined to 18% at 2 years. Substantial normalized brain volume loss was seen in 21% between baseline and year 2 and in 77% between years 1 and 2. The extent of brain growth in the first year was not associated with extent of brain volume changes in the second year. There were significant positive correlations between 2-year brain volume and all BSID-3 scores and BSID-3 changes from baseline.Conclusions and RelevanceIn sub-Saharan Africa, even after successful surgical treatment of infant post-infectious hydrocephalus, post-treatment brain growth stagnates in the second year. While the reasons for this are unclear, this emphasizes the importance of primary infection prevention strategies along with optimizing the child’s environment to maximize brain growth potential.Trial RegistrationClinicalTrials.gov number, NCT01936272KEY POINTSQuestionWhat is the brain growth and cognitive trajectory of infants treated for post-infectious hydrocephalus in Uganda?FindingsIn this prospective follow-up of a cohort of 89 infants, early normalization of brain volume after treatment was followed by brain growth stagnation in the second year, with many falling back into the sub-normal range. Poor brain growth was associated with poor cognitive outcome.MeaningSuccessful surgical treatment of hydrocephalus is not sufficient to allow for adequate brain growth and cognitive development. Interventions aimed at primary infection prevention and reducing comorbidities are needed to improve brain growth potential.

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“…The low field system is a k = 1 Halbach magnet, constructed as described in [18], producing an 0.05 T (2.15 MHz) magnetic field at the center of the bore. The main magnetic field was measured in a 225 × 225 × 300 mm 3 field of view (FOV) at 5 × 5 × 5 mm 3 resolution using a gaussmeter (Lake Shore Cryotronics, Westerville, OH) connected to a 3D positioning robot [19].…”

Section: Methodsmentioning

confidence: 99%

Image distortion correction for MRI in low field permanent magnet systems with strong B0 inhomogeneity and gradient field nonlinearities

Koolstra

¹

,

O’Reilly

²

,

Börnert

³

et al. 2021

Magn Reson Mater Phy

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Objective To correct for image distortions produced by standard Fourier reconstruction techniques on low field permanent magnet MRI systems with strong $${B}_{0}$$ B 0 inhomogeneity and gradient field nonlinearities. Materials and methods Conventional image distortion correction algorithms require accurate $${\Delta B}_{0}$$ Δ B 0 maps which are not possible to acquire directly when the $${B}_{0}$$ B 0 inhomogeneities also produce significant image distortions. Here we use a readout gradient time-shift in a TSE sequence to encode the $${B}_{0}$$ B 0 field inhomogeneities in the k-space signals. Using a non-shifted and a shifted acquisition as input, $$\Delta {B}_{0}$$ Δ B 0 maps and images were reconstructed in an iterative manner. In each iteration, $$\Delta {B}_{0}$$ Δ B 0 maps were reconstructed from the phase difference using Tikhonov regularization, while images were reconstructed using either conjugate phase reconstruction (CPR) or model-based (MB) image reconstruction, taking the reconstructed field map into account. MB reconstructions were, furthermore, combined with compressed sensing (CS) to show the flexibility of this approach towards undersampling. These methods were compared to the standard fast Fourier transform (FFT) image reconstruction approach in simulations and measurements. Distortions due to gradient nonlinearities were corrected in CPR and MB using simulated gradient maps. Results Simulation results show that for moderate field inhomogeneities and gradient nonlinearities, $$\Delta {B}_{0}$$ Δ B 0 maps and images reconstructed using iterative CPR result in comparable quality to that for iterative MB reconstructions. However, for stronger inhomogeneities, iterative MB reconstruction outperforms iterative CPR in terms of signal intensity correction. Combining MB with CS, similar image and $$\Delta {B}_{0}$$ Δ B 0 map quality can be obtained without a scan time penalty. These findings were confirmed by experimental results. Discussion In case of $${B}_{0}$$ B 0 inhomogeneities in the order of kHz, iterative MB reconstructions can help to improve both image quality and $$\Delta {B}_{0}$$ Δ B 0 map estimation.

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In vivo 3D brain and extremity MRI at 50 mT using a permanent magnet Halbach array

Abstract: This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Cited by 123 publications

References 43 publications

Contactless Nanoparticle-Based Guiding of Cells by Controllable Magnetic Fields

Contactless Nanoparticle-Based Guiding of Cells by Controllable Magnetic Fields

Brain growth and neurodevelopment after surgical treatment of infant post-infectious hydrocephalus in sub-Saharan Africa

Image distortion correction for MRI in low field permanent magnet systems with strong B0 inhomogeneity and gradient field nonlinearities

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