MPI Safety in the View of MRI Safety Standards

Schmale, Ingo; Gleich, Bernhard; Rahmer, Jürgen; Bontus, Claas; Schmidt, J.; Borgert, J.

doi:10.1109/tmag.2014.2322940

Cited by 40 publications

(32 citation statements)

References 4 publications

(12 reference statements)

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“…Without reducing the relevance of the maximal sensitivity values for each imager, all findings must be related to scanner parameters and the experimental protocol. For the extrapolation to human use, scan times, drive field strength and the used frequencies have a direct impact on the specific absorption rate and the peripheral nerve stimulation limits [23][24][25][26] . Addressing these relations will make the results more comparable and easier to relate.…”

Section: Introductionmentioning

confidence: 99%

Towards Picogram Detection of Superparamagnetic Iron-Oxide Particles Using a Gradiometric Receive Coil

Graeser

Knopp

Szwargulski

et al. 2017

Sci Rep

114

107

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Superparamagnetic iron-oxide nanoparticles can be used in medical applications like vascular or targeted imaging. Magnetic particle imaging (MPI) is a promising tomographic imaging technique that allows visualizing the 3D nanoparticle distribution concentration in a non-invasive manner. The two main strengths of MPI are high temporal resolution and high sensitivity. While the first has been proven in the assessment of dynamic processes like cardiac imaging, it is unknown how far the detection limit of MPI can be lowered. Within this work, we will present a highly sensitive gradiometric receive-coil unit combined with a noise-matching network tailored for the imaging of mice. The setup is capable of detecting 5 ng of iron in-vitro with an acquisition time of 2.14 sec. In terms of iron concentration we are able to detect 156 μg/L marking the lowest value that has been reported for an MPI scanner so far. In-vivo MPI mouse images of a 512 ng bolus and a 21.5 ms acquisition time allow for capturing the flow of an intravenously injected tracer through the heart of a mouse. Since it has been rather difficult to compare detection limits across MPI publications we propose guidelines to improve the comparability of future MPI studies.

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Section: Introductionmentioning

confidence: 99%

Towards Picogram Detection of Superparamagnetic Iron-Oxide Particles Using a Gradiometric Receive Coil

Graeser

Knopp

Szwargulski

et al. 2017

Sci Rep

114

107

View full text Add to dashboard Cite

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“…Moreover, the selection field can be rapidly and continuously scanned over the region of interest (ROI) for real-time imaging of SPIO distribution 4 . In short, MPI promises a biomedical imaging modality with the speed of x-ray computed tomography (CT), the safety of Magnetic Resonance Imaging (MRI) 5,6 and the sensitivity of Positron-Emission Tomography (PET).…”

Section: Introductionmentioning

confidence: 99%

Evaluation of PEG-coated iron oxide nanoparticles as blood pool tracers for preclinical magnetic particle imaging

et al. 2017

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Superparamagnetic iron oxide (SPIO) nanoparticles with optimized and well-characterized properties are critical for Magnetic Particle Imaging (MPI). MPI is a novel in vivo imaging modality that promises to integrate the speed of CT, safety of MRI and sensitivity of PET. Since SPIOs are the source of MPI signal, both the core and surface properties must be optimized to enable efficient in vivo imaging with pharmacokinetics tailored for specific imaging applications. Existing SPIOs like Resovist (ferucarbotran) provide suboptimal MPI signal, and further limit MPI's in vivo utility due to rapid systemic clearance. An SPIO agent with a long blood half-life (t1/2) would be a versatile MPI tracer with widespread applications. Here we show a long circulating polyethylene glycol (PEG)-coated SPIO tracer, LS-008, provides excellent colloidal stability and persistent intravascular MPI signal, showing potential as the first blood pool tracer optimized for MPI. We evaluated variations of the PEG coating and found that colloidal stability of tracers improved with increasing PEG molecular weight (keeping PEG loading constant). Blood circulation in mice, evaluated using Magnetic Particle Spectrometry (MPS), showed that t1/2 of SPIO tracers varied with both PEG molecular weight and loading. LS-008, coated with 20 kDa PEG at 18.8% loading capacity, provided the most promising long-term colloidal stability with a t1/2 of about 105 minutes in mice. In vivo MPI imaging with LS-008 in a 7 T/m/μ0 3D x-space MPI mouse scanner revealed a prolonged intravascular signal (3-5 hours) post-injection. Our results show the optimized magnetic properties a nd long systemic retention of LS-008 make it a promising blood pool MPI tracer, with potential to enable MPI imaging in cardio - and cerebrovascular disease models, and solid tumor quantification and imaging via enhanced permeation and retention.

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“…Recent studies indicate that magnetostimulation is the main safety constraint on the drive field in MPI. [11][12][13] Magnetostimulation thresholds have been shown to decrease in a hyperbolic fashion as a function of frequency, 11 to decrease with increasing pulse duration and stabilize for pulses longer than 20 ms, 14 and to first decrease then increase with increasing duty cycle, reaching a peak value at 100% duty cycle. 15 Beyond MPI sequence parameters, thresholds have also been reported to strongly correlate with the inverse of the body part size that is exposed to the magnetic field.…”

Section: Introductionmentioning

confidence: 99%

Anatomical measurements correlate with individual magnetostimulation thresholds for kHz‐range homogeneous magnetic fields

et al. 2020

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Purpose: Magnetostimulation, also known as peripheral nerve stimulation (PNS), is the dominant safety constraint in magnetic resonance imaging (MRI) for the gradient magnetic fields that operate around 0.1-1 kHz, and for the homogeneous drive field in magnetic particle imaging (MPI) that operates around 10-150 kHz. Previous studies did not report correlations between anatomical measures and magnetostimulation thresholds for the gradient magnetic fields in MRI. In contrast, a strong linear correlation was shown between the thresholds and the inverse of body part size in MPI. Yet, the effects of other anatomical measures on the thresholds for the drive field remain unexplored. Here, we investigate the effects of fat percentage on magnetostimulation thresholds for kHz-range homogeneous magnetic fields such as the drive field in MPI, with the ultimate goal of predicting subject-specific thresholds based on simple anatomical measures. Methods: Human subject experiments were performed on the upper arms of 10 healthy male subjects (age: 26 AE 2 yr) to determine magnetostimulation thresholds. Experiments were repeated three times for each subject, with brief resting periods between repetitions. Using a solenoidal magnetostimulation coil, a homogeneous magnetic field at 25 kHz with 100 ms pulse duration was applied at 4-s intervals, while the subject reported stimulation via a mouse click. To determine the thresholds, individual subject responses were fitted to a cumulative distribution function modeled by a sigmoid curve. Next, anatomical images of the upper arms of the subjects were acquired on a 3 T MRI scanner. A two-point Dixon method was used to obtain separate images of water and fat tissues, from which several anatomical measures were derived: the effective outer radius of the upper arm, the effective inner radius (i.e., the muscle radius), and fat percentage. Pearson's correlation coefficient was used to assess the relationship between the threshold and anatomical measures. This statistical analysis was repeated after factoring out the expected effects of body part size. An updated model for threshold prediction is provided, where in addition to scaling in proportion with the inverse of the outer radius, the threshold has an affine dependence on fat percentage. Results: A strong linear correlation (r = 0.783, P < 0.008) was found between magnetostimulation threshold and fat percentage, and the correlation became stronger after factoring out the effects of outer radius (r = 0.839, P < 0.003). While considering body part size alone did not explain any significant variance in measured thresholds (P > 0.398), the updated model that also incorporates fat percentage yielded substantially improved threshold predictions with R 2 = 0.654 (P < 0.001). Conclusions: This work shows for the first time that fat percentage strongly correlates with magnetostimulation thresholds for kHz-range homogenous magnetic fields such as the drive field in MPI, and that the correlations get even stronger after factoring out the effects of b...

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MPI Safety in the View of MRI Safety Standards

Cited by 40 publications

References 4 publications

Towards Picogram Detection of Superparamagnetic Iron-Oxide Particles Using a Gradiometric Receive Coil

Towards Picogram Detection of Superparamagnetic Iron-Oxide Particles Using a Gradiometric Receive Coil

Evaluation of PEG-coated iron oxide nanoparticles as blood pool tracers for preclinical magnetic particle imaging

Anatomical measurements correlate with individual magnetostimulation thresholds for kHz‐range homogeneous magnetic fields

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