| Zugriffsnummer | 49366 |
| Dokumenttyp | Zeitschriftenartikel |
| Peer Review | mit Peer Review |
| Sprache | Englisch |
| Titel | Towards an integrated radiofrequency safety concept for implant carriers in MRI based on sensor-equipped implants and parallel transmission |
| Autor(in); Institution |
Speck, Oliver; Otto von Guericke Universität Magdeburg, GERMANY
|
| Quelle/Jahr | NMR in Biomedicine:(2023), 20 S. |
| Artikelnummer | e4900 |
| Availability | [online first] |
| ISSN | 1099-1492 (ONLINE) |
| DOI | |
| Verlag | New York, NY: Wiley |
| Freie Schlagworte | body imaging ; B1+ mapping ; FDTD simulation ; parallel transmission (pTx) ; peak spatial SAR ; respiration ; ultrahigh field |
| Zusammenfassung | To protect implant carriers in MRI from excessive radiofrequency (RF) heating it has previously been suggested to assess that hazard via sensors on the implant. Other work recommended parallel transmission (pTx) to actively mitigate implant-related heating. Here, both ideas are integrated into one comprehensive safety concept where native pTx safety (without implant) is ensured by state-of-the-art field simulations and the implant-specific hazard is quantified in situ using physical sensors. The concept is demonstrated by electromagnetic simulations performed on a human voxel model with a simplified spinal-cord implant in an eight-channel pTx body coil at 3T. To integrate implant and native safety, the sensor signal must be calibrated in terms of an established safety metric (e.g., specific absorption rate [SAR]). Virtual experiments show that E-field and implant-current sensors are well suited for this purpose, while temperature sensors require some caution, and B1 probes are inadequate. Based on an implant sensor matrix Qs, constructed in situ from sensor readings, and precomputed native SAR limits, a vector space of safe RF excitations is determined where both global (native) and local (implant-related) safety requirements are satisfied. Within this safe-excitation subspace, the solution with the best image quality in terms of B1+ magnitude and homogeneity is then found by a straightforward optimization algorithm. In the investigated example, the optimized pTx shim provides a 3-fold higher mean(B1+) magnitude compared with circularly polarized excitation for a maximum implant-related temperature increase <1K. To date, sensor-equipped implants interfaced to a pTx scanner exist as demonstrator items in research labs, but commercial devices are not yet within sight. This paper aims to demonstrate the significant benefits of such an approach and how this could impact implant-related RF safety in MRI. Today, the responsibility for safe implant scanning lies with the implant manufacturer and the MRI operator; within the sensor concept, the MRI manufacturer would assume much of the operator's current responsibility. |
| Kostenfreier Zugang | Open Access Hybrid |
| Rechteinformation | CC BY 4.0 ; Creative Commons Attribution 4.0 License |
| Themenbereich der Metrologie | Metrologie in der Medizin |
| Förderinformationen (1) |
Förderername: European Commission (EC)
Förderer ID: 0000 0001 2242 8989 Förderer ID Typ: ISNI Förderprogramm: EMPIR 2017 Industry Titel der Förderung: 17IND01: MIMAS: Procedures allowing medical implant manufacturers to demonstrate compliance with MRI safety regulations Förderungsnummer: 17IND01 |
| Förderinformationen (2) |
Förderername: European Commission (EC)
Förderer ID: 0000 0001 2242 8989 Förderer ID Typ: ISNI Förderprogramm: Metrology Partnership 2021 Normative Titel der Förderung: 21NRM05: STASIS: Standardisation for safe implant scanning in MRI Förderungsnummer: 21NRM05 |
Zitierung
Petzold, J., Schmitter, S., Silemek, B., Winter, L., Speck, O., Ittermann, B., & Seifert, F. (2023). Towards an integrated radiofrequency safety concept for implant carriers in MRI based on sensor-equipped implants and parallel transmission. NMR in Biomedicine, 20 S. https://doi.org/10.1002/nbm.4900