Toward individualized SAR models and in vivo validation

Abstract

The specific absorption rate (SAR) is a limiting constraint in sequence design for high-field MRI. SAR estimation is typically performed by numerical simulations using generic human body models. This entails an intrinsic uncertainty in present SAR prediction. This study first investigates the required detail of human body models in terms of spatial resolution and the number of soft tissue classes required, based on finite-differences timedomain simulations of a 3 T body coil. The numerical results indicate that a resolution of 5 mm is sufficient for local SAR estimation. Moreover, a differentiation between fatty tissues, water-rich tissues, and the lungs was found to be essential to represent eddy current paths inside the human body. This study then proposes a novel approach for generating individualized body models from whole-body water-fat-separated MR data and applies it to volunteers. The SAR hotspots consistently occurred in the arms due to proximity to the body coil as well as

Local SAR management by RF Shimming: a simulation study with multiple human body models

“…1a. A differentiation between these tissue types has been shown to be essential for accurate representation of the eddy current pathways in the human body [26].…”

“…In this study, model generation was performed based on whole-body 3D water-fat separated images as described in [26]. Nine healthy male volunteers (34-55 years) were scanned in a 1.5 T MR scanner (Philips Achieva, Philips Medical Systems, Best, The Netherlands) in compliance with the regulations of the institution.…”

“…After water-fat separation, a segmentation into three tissue classes according to [26] was performed, representing low conductive fatty tissue, highly conductive water-rich tissue, and lung tissue as illustrated in Fig. 1a.…”

“…To investigate the patient-dependency of the SAR, simulations were performed using human body models of nine volunteers, representing a relatively broad range of male adults. These models were generated from water-fat separated whole-body MR images as described in [26].…”

Safety considerations for magnetic fields of 10 mT to 100 mT amplitude in the frequency range of 10 kHz to 100 kHz for magnetic particle imaging

“…Homann et al [10] report on the importance of using patient-specific models for SAR estimation in MRI that at least distinguish between fat-like tissue, muscle-like tissue, bone, and lung.…”