Mark R. Symms

7T MRI in focal epilepsy with unrevealing conventional field strength imaging

To assess the diagnostic yield of 7T magnetic resonance imaging (MRI) in detecting and characterizing structural lesions in patients with intractable focal epilepsy and unrevealing conventional (1.5 or 3T) MRI.

Tissue Border Enhancement by inversion recovery MRI at 7.0 Tesla.

IntroductionThis contribution presents a magnetic resonance imaging (MRI) acquisition technique named Tissue Border Enhancement (TBE), whose purpose is to produce images with enhanced visualization of borders between two tissues of interest without any post-processing.MethodsThe technique is based on an inversion recovery sequence that employs an appropriate inversion time to produce images where the interface between two tissues of interest is hypo-intense; therefore, tissue borders are clearly represented by dark lines. This effect is achieved by setting imaging parameters such that two neighboring tissues of interest have magnetization with equal magnitude but opposite sign; therefore, the voxels containing a mixture of each tissue (that is, the tissue interface) possess minimal net signal. The technique was implemented on a 7.0 T MRI system.ResultsThis approach can assist the definition of tissue borders, such as that between cortical gray matter and white matter; therefore, it could facilitate segmentation procedures, which are often challenging on ultra-high-field systems due to inhomogeneous radiofrequency distribution. TBE allows delineating the contours of structural abnormalities, and its capabilities were demonstrated with patients with focal cortical dysplasia, gray matter heterotopia, and polymicrogyria.ConclusionThis technique provides a new type of image contrast and has several possible applications in basic neuroscience, neurogenetic research, and clinical practice, as it could improve the detection power of MRI in the characterization of cortical malformations, enhance the contour of small anatomical structures of interest, and facilitate cortical segmentation.

Investigation of maximum local specific absorption rate in 7 T magnetic resonance with respect to load size by use of electromagnetic simulations

Local specific absorption rate (SAR) evaluation in ultra high field (UHF) magnetic resonance (MR) systems is a major concern. In fact, at UHF, radiofrequency (RF) field inhomogeneity generates hot-spots that could cause localized tissue heating. Unfortunately, local SAR measurements are not available in present MR systems; thus, electromagnetic simulations must be performed for RF fields and SAR analysis. In this study, we used three-dimensional full-wave numerical electromagnetic simulations to investigate the dependence of local SAR at 7.0 T with respect to subject size in two different scenarios: surface coil loaded by adult and child calves and quadrature volume coil loaded by adult and child heads. In the surface coil scenario, maximum local SAR decreased with decreasing load size, provided that the RF magnetic fields for the different load sizes were scaled to achieve the same slice average value. On the contrary, in the volume coil scenario, maximum local SAR was up to 15% higher in children than in adults.

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

To predict local and global specific absorption rate (SAR) in individual subjects.

Evaluation of temperature increase during Magnetic Resonance examinations by combining electromagnetic/thermal simulations and B1 maps

The purpose of the present study is to evaluate the temperature increase due to radio-frequency (RF) exposure in Magnetic Resonance (MR) examinations, by combining electromagnetic/thermal simulations and B1 maps.

Magnetic Resonance Imaging at 7 Tesla with Dedicated Radiofrequency Coils - Application to Cervical Cord and Knee

Magnetic Resonance (MR) Imaging is a valuable tool in the diagnosis and monitoring of various musculoskeletal pathologies. New Ultra-High Field (UHF) 7 T MRI systems, with their enhanced Signal-toNoise Ratio, may offer increased image quality in terms of spatial resolution and/or shorter scanning time compared to lower field systems. However, these benefits can be difficult to obtain because of increased radio-frequency (RF) inhomogeneity, increased Specific Absorption Rate (SAR) and the relative lack of specialized and commercially available RF coils compared to lower field systems. This study reports the feasibility of imaging in bones and cartilages at UHF with a 7 T MR scanner available at the IMAGO7 Foundation (Pisa, Italy). Dedicated radio-frequency coils for proton imaging have been designed, developed, optimized for different anatomical regions and validated in vivo, and are now ready for clinical research studies. The performance of the RF coil prototypes in targeting different anatomical regions are also demonstrated, obtaining images of the neck (the cervical cord) and of the knee (trabecular bone and