SAR prediction in adults and children by combining measured B1+ maps and simulations at 7.0 Tesla

Tiberi, Gianluigi; Costagli, Mauro; Biagi, Laura; Ciantis, Alessio De; Fontana, Nunzia; Stara, Riccardo; Symms, Mark Roger; Cosottini, Mirco; Guerrini, Renzo; Tosetti, Michela

doi:10.1002/jmri.25241

Cited by 12 publications

(12 citation statements)

References 22 publications

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“…[3][4][5][6] Additional intrinsic sequence properties include rapid imaging times, silent scanning, high-resolution isotropic datasets, and resistance to artifacts. [7][8][9] The applicability of ZTE for bone imaging has been successfully demonstrated in small clinical case series and ex vivo studies of the cranial vault, face, jaw, and spine. [12][13][14][15][16][17][18][19] Because MR imaging already provides superior soft-tissue detail, the addition of a ZTE bone sequence would enable highly efficient and radiation-free evaluation in several pediatric neuroimaging, head/neck imaging, and musculoskeletal imaging scenarios.…”

Section: Discussionmentioning

confidence: 99%

“…The technique uses lower changes in amplitude over time (dB/dt) than conventional sequences; low flip angles and built-in scanner safety measures counter the short RF pulse duration that would otherwise raise concern for a high specific absorption rate (SAR). 9…”

Section: Technical Considerationsmentioning

confidence: 99%

“…[3][4][5][6] The ZTE sequence is rapid, high-resolution, silent, and resilient to artifacts caused by motion and B 0 inhomogeneitycharacteristics that are well-suited to pediatric use. [7][8][9] Raw images demonstrate relative signal void compared with surrounding soft tissues, colloquially known as a "black-bone" display. There is computational potential for "bright-bone" reconstructions that are visually analogous to CT (Figure ).…”

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confidence: 99%

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Zero TE MRI for Craniofacial Bone Imaging

Gorny

2019

AJNR Am J Neuroradiol

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Zero TE MR imaging is a novel technique that achieves a near-zero time interval between radiofrequency excitation and data acquisition, enabling visualization of short-T2 materials such as cortical bone. Zero TE offers a promising radiation-free alternative to CT with rapid, high-resolution, silent, and artifact-resistant imaging, as well as the potential for "pseudoCT" reconstructions. In this report, we will discuss our preliminary experience with zero TE, including technical principles and a clinical case series demonstrating emerging applications in neuroradiology. ABBREVIATIONS: RFCT examinations per year. For certain indications (eg, acute screening and cortical bone assessment), CT remains a first-line technique. However, adverse effects from radiation are of great concern and include both deterministic (developmental disruption, skin damage, cataracts, sterility, radiation sickness) and stochastic effects (cancer, hereditary defects, growth impairment). These effects are magnified in children due to the increased sensitivity of developing tissues/organs, predisposing conditions that increase susceptibility, and greater cumulative lifetime risk of radiation exposure. 1 Concerns regarding the adverse effects of radiation in the pediatric population have prompted the "Image Gently" campaign. 2

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Section: Discussionmentioning

confidence: 99%

Section: Technical Considerationsmentioning

confidence: 99%

mentioning

confidence: 99%

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Zero TE MRI for Craniofacial Bone Imaging

Gorny

2019

AJNR Am J Neuroradiol

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“…[49][50][51][52][53][54][55][56] A more direct and potentially more accurate approach to estimate SAR is to use actual MRI images; for example, obtaining B 1 maps that may then be used to estimate the E field and derive the SAR distribution. [57][58][59][60] It is important to note that, for the purposes of safety monitoring, SAR is merely used as a surrogate measure for the potential to cause tissue damage. The real problem is heating.…”

Section: Rf Heating Of Biological Tissuementioning

confidence: 99%

“…Attempts have been made to develop human body models that, when used with numerical simulation techniques, may give accurate estimates of SAR . A more direct and potentially more accurate approach to estimate SAR is to use actual MRI images; for example, obtaining

B_{1}

maps that may then be used to estimate the

bold-italicE

field and derive the SAR distribution …”

Section: The Rf Fieldmentioning

confidence: 99%

The physics of MRI safety

Panych

Madore

2017

Magnetic Resonance Imaging

133

150

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The main risks associated with magnetic resonance imaging (MRI) have been extensively reported and studied; for example, everyday objects may turn into projectiles, energy deposition can cause burns, varying fields can induce nerve stimulation, and loud noises can lead to auditory loss. The present review article is geared toward providing intuition about the physical mechanisms that give rise to these risks. On the one hand, excellent literature already exists on the practical aspect of risk management, with clinical workflow and recommendations. On the other hand, excellent technical articles also exist that explain these risks from basic principles of electromagnetism. We felt that an underserved niche might be found between the two, ie, somewhere between basic science and practical advice, to help develop intuition about electromagnetism that might prove of practical value when working around MR scanners. Following a wide‐ranging introduction, risks originating from the main magnetic field, the excitation RF electromagnetic field, and switching of the imaging gradients will be presented in turn. Level of Evidence: 5 Technical Efficacy: 1 J. Magn. Reson. Imaging 2018;47:28–43.

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A pathway towards a two‐dimensional, bore‐mounted, volume body coil concept for ultra high‐field magnetic resonance imaging

Voss

Taracila²,

Robb³

et al. 2022

NMR in Biomedicine

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Lack of a body‐sized, bore‐mounted, radiofrequency (RF) body coil for ultrahigh field (UHF) magnetic resonance imaging (MRI) is one of the major drawbacks of UHF, hampering the clinical potential of the technology. Transmit field (B1) nonuniformity and low specific absorption rate (SAR) efficiencies in UHF MRI are two challenges to be overcome. To address these problems, and ultimately provide a pathway for the full clinical potential of the modality, we have designed and simulated two‐dimensional cylindrical high‐pass ladder (2D c‐HPL) architectures for clinical bore‐size dimensions, and demonstrated a simplified proof of concept with a head‐sized prototype at 7 T. A new dispersion relation has been derived and electromagnetic simulations were used to verify coil modes. The coefficient of variation (CV) for brain, cerebellum, heart, and prostate tissues after B1+ shimming in silico is reported and compared with previous works. Three prototypes were designed in simulation: a head‐sized, body‐sized, and long body‐sized coil. The head‐sized coil showed a CV of 12.3%, a B1+ efficiency of 1.33 μT/√W, and a SAR efficiency of 2.14 μT/√(W/kg) for brain simulations. The body‐sized 2D c‐HPL coil was compared with same‐sized transverse electromagnetic (TEM) and birdcage coils in silico with a four‐port circularly polarized mode excitation. Improved B1+ uniformity (26.9%) and SAR efficiency (16% and 50% better than birdcage and TEM coils, respectively) in spherical phantoms was observed. We achieved a CV of 12.3%, 4.9%, 16.7%, and 2.8% for the brain, cerebellum, heart, and prostate, respectively. Preliminary imaging results for the head‐sized coil show good agreement between simulation and experiment. Extending the 1D birdcage coil concept to 2D c‐HPLs provides improved B1+ uniformity and SAR efficiency.

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SAR prediction in adults and children by combining measured B1+ maps and simulations at 7.0 Tesla

Abstract: For ZTE and FLAIR, limits on maximum local and global SAR were met in all subjects, both adults and children. To enhance safety in adults and children with 7.0 Tesla MR systems, we suggest the possibility of using SAR prediction. J. MAGN. RESON. IMAGING 2016;44:1048-1055.

Cited by 12 publications

References 22 publications

Zero TE MRI for Craniofacial Bone Imaging

Zero TE MRI for Craniofacial Bone Imaging

The physics of MRI safety

A pathway towards a two‐dimensional, bore‐mounted, volume body coil concept for ultra high‐field magnetic resonance imaging

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