Time filter

Source Type

Costagli M.,Imago7 Foundation | Costagli M.,Laboratory of Medical Physics and Biotechnologies for Magnetic Resonance | Symms M.R.,GE Applied Science Laboratory | Angeli L.,University of Pisa | And 12 more authors.
European Radiology | Year: 2015

Objectives: This study aimed to assess the performance of a “Silent” zero time of echo (ZTE) sequence for T1-weighted brain imaging using a 7 T MRI system. Methods: The Silent sequence was evaluated qualitatively by two neuroradiologists, as well as quantitatively in terms of tissue contrast, homogeneity, signal-to-noise ratio (SNR) and acoustic noise. It was compared to conventional T1-weighted imaging (FSPGR). Adequacy for automated segmentation was evaluated in comparison with FSPGR acquired at 7 T and 1.5 T. Specific absorption rate (SAR) was also measured. Results: Tissue contrast and homogeneity in Silent were remarkable in deep brain structures and in the occipital and temporal lobes. Mean tissue contrast was significantly (p < 0.002) higher in Silent (0.25) than in FSPGR (0.11), which favoured automated tissue segmentation. On the other hand, Silent images had lower SNR with respect to conventional imaging: average SNR of FSPGR was 2.66 times that of Silent. Silent images were affected by artefacts related to projection reconstruction, which nevertheless did not compromise the depiction of brain tissues. Silent acquisition was 35 dB(A) quieter than FSPGR and less than 2.5 dB(A) louder than ambient noise. Six-minute average SAR was <2 W/kg. Conclusions: The ZTE Silent sequence provides high-contrast T1-weighted imaging with low acoustic noise at 7 T. Key Points: • “Silent” is an MRI technique allowing zero time of echo acquisition• Its feasibility and performance were assessed on a 7 T MRI system• Image quality in several regions was higher than in conventional techniques• Imaging acoustic noise was dramatically reduced compared with conventional imaging• “Silent” is suitable for T1-weighted head imaging at 7 T © 2015 European Society of Radiology

Giovannetti G.,National Research Council Italy | Giovannetti G.,CNR Institute of Neuroscience | Tiberi G.,Laboratory of Medical Physics and Biotechnologies for Magnetic Resonance
Applied Magnetic Resonance | Year: 2016

The design and development of dedicated radiofrequency (RF) coils is a fundamental task to maximize the signal-to-noise ratio (SNR) in nuclear magnetic resonance (NMR) applications. Coil resistance reduces the SNR and should be minimized by employing conductors of appropriate shape and cross section. At RF, the conductor resistance is increased due to the skin effect, which distributes the current primarily on the surface of the conductor instead of uniformly over the cross section. In particular, in rectangular shape conductors the current density is concentrated in the high-curvature area and increases the conductor resistance, while rounded conductors present lower resistance and demonstrate improvements in performance especially in low-frequency tuned coils. This paper summarizes the different methods for estimating conductor losses in RF coils for NMR applications, whose performance strongly affect quality data. Because the impact to coil loss from conductors with different cross-sectional area is not something generally recognized and nor addressed in many other coil design works, we believe the review could be interesting for researchers working in the field of NMR coil design and development. © 2016, Springer-Verlag Wien.

Stara R.,University of Pisa | Stara R.,National Institute of Nuclear Physics, Italy | Tiberi G.,Laboratory of Medical Physics and Biotechnologies for Magnetic Resonance | Gabrieli M.,University of Pisa | And 10 more authors.
Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering | Year: 2015

High static magnetic field magnetic resonance imaging (MRI) is commonly used for preclinical studies in rodents. In this context, minimization of coil losses is mandatory to scan samples that are small compared to the radiofrequency wavelength in the medium. In this study we construct a radiofrequency (RF) birdcage probe with distributed capacitors, operating in quadrature, tailored for 7.0T 1H MRI of small animals. The design eliminates the need for extra electrical components on the probe structure and affords a high SNR, a uniform B1+ field (homogeneity of 93% in the axial plain of the phantom) and a coil sensitivity of 9.8 μT/W. Feasibility experiments of mouse imaging are conducted and the competitive capability of a 7.0 T human system equipped with the proposed coil is demonstrated in both body and brain preclinical imaging. © 2015 Wiley Periodicals, Inc.

Tiberi G.,Imago7 Foundation | Tiberi G.,Laboratory of Medical Physics and Biotechnologies for Magnetic Resonance | Fontana N.,University of Pisa | Fontana N.,National Institute of Nuclear Physics, Italy | And 12 more authors.
Bioelectromagnetics | Year: 2015

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 7.0T 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. Bioelectromagnetics. 36:358-366, 2015. © 2015 Wiley Periodicals, Inc.

Costagli M.,Imago7 Research Foundation | Costagli M.,Laboratory of Medical Physics and Biotechnologies for Magnetic Resonance | Donatelli G.,University of Pisa | Biagi L.,Laboratory of Medical Physics and Biotechnologies for Magnetic Resonance | And 6 more authors.
NeuroImage: Clinical | Year: 2016

Amyotrophic Lateral Sclerosis (ALS) is a progressive neurological disorder that entails degeneration of both upper and lower motor neurons. The primary motor cortex (M1) in patients with upper motor neuron (UMN) impairment is pronouncedly hypointense in Magnetic Resonance (MR) T2* contrast. In the present study, 3D gradient-recalled multi-echo sequences were used on a 7. Tesla MR system to acquire T2*-weighted images targeting M1 at high spatial resolution. MR raw data were used for Quantitative Susceptibility Mapping (QSM). Measures of magnetic susceptibility correlated with the expected concentration of non-heme iron in different regions of the cerebral cortex in healthy subjects. In ALS patients, significant increases in magnetic susceptibility co-localized with the T2* hypointensity observed in the middle and deep layers of M1. The magnetic susceptibility, hence iron concentration, of the deep cortical layers of patients' M1 subregions corresponding to Penfield's areas of the hand and foot in both hemispheres significantly correlated with the clinical scores of UMN impairment of the corresponding limbs. QSM therefore reflects the presence of iron deposits related to neuroinflammatory reaction and cortical microgliosis, and might prove useful in estimating M1 iron concentration, as a possible radiological sign of severe UMN burden in ALS patients. © 2016 The Authors.

Discover hidden collaborations