Maria Filomena Santarelli

Fondazione Toscana Gabriele Monasterio, Pisa, Tuscany, Italy

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Publications (124)206.42 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Hyperpolarized 13C Magnetic Resonance represents a promising modality for in vivo spectroscopy.•13C Magnetic Resonance experiments require dedicated coil design.•This work presents details for simulating and comparing coils with different geometries.•Theoretical SNR-vs-depth profiles were calculated for each coil configuration.
    Measurement. 01/2015; 60.
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    ABSTRACT: T2(⁎) maps obtained by the processing of multiecho MR sequences can be useful in several clinical applications. T2(⁎) map generation procedures should join a processing time compatible with on-line image analysis with a good precision in the entire T2(⁎) range of clinical interest. Fast generation of T2(⁎) maps can be achieved by the estimation of the T2(⁎) values by the weighted linear fitting of the logarithm of the signal (WLSL) method. This approach fails if the signal decay diverges from a pure exponential decay, as happens at low T2((⁎)) values where the rapid decay in the signal intensity leads to a plateau in the later echo times (TE). The proposed method implements the automatic truncation of the signal decay curves to be fitted in order to compensate for the signal collapse at low T2(⁎) values, allowing the extension of the WLSL method through the entire clinical range of T2(⁎) values. Validation was performed on synthetic images and on 60 thalassemia major patients with different levels of myocardial iron overload. Phantom experiments showed that a 5% fitting error threshold represented the best compromise between T2(⁎) value measurement precision and processing time. A good agreement was found between T2(⁎) map pixel-wise measurements and ROI-based measurements performed by expert readers (CoV=1.84% in global heart T2(⁎), CoV=5.8% in segmental analysis). In conclusion, the developed procedure was effective in generating correct T2(⁎) maps for the entire T2(⁎) clinical range. Copyright © 2014 Elsevier Ltd. All rights reserved.
    Computers in biology and medicine. 11/2014; 56C:200-210.
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    ABSTRACT: Dissolution-dynamic nuclear polarization (dissolution-DNP) for magnetic resonance (MR) spectroscopic imaging has recently emerged as a novel technique for noninvasive studies of the metabolic fate of biomolecules in vivo. Since acetate is the most abundant extra- and intracellular short-chain fatty acid, we focused on [1-13C]acetate as a promising candidate for a chemical probe to study the myocardial metabolism of a beating heart. The dissolution-DNP procedure of Na[1-13C]acetate for in vivo cardiac applications with a 3 T MR scanner was optimized in pigs during bolus injection of doses of up to 3 mmol. The Na[1-13C]acetate formulation was characterized by a liquid-state polarization of 14.2% and a T1Effin vivo of 17.6 ± 1.7 s. In vivo Na[1-13C]acetate kinetics displayed a bimodal shape: [1-13C]acetyl carnitine (AcC) was detected in a slice covering the cardiac volume, and the signal of 13C-acetate and 13C-AcC was modeled using the total area under the curve (AUC) for kinetic analysis. A good correlation was found between the ratio AUC(AcC)/AUC(acetate) and the apparent kinetic constant of metabolic conversion, from [1-13C]acetate to [1-13C]AcC (kAcC), divided by the AcC longitudinal relaxation rate (r1). Our study proved the feasibility and the limitations of administration of large doses of hyperpolarized [1-13C]acetate to study the myocardial conversion of [1-13C]acetate in [1-13C]acetyl-carnitine generated by acetyltransferase in healthy pigs. Copyright © 2014 John Wiley & Sons, Ltd.
    Contrast Media & Molecular Imaging 09/2014; · 2.87 Impact Factor
  • M F Santarelli, N Martini, P Positano, L Landini
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    ABSTRACT: Cardiac health depends on the heart's ability to utilize different substrates to support overall oxidative metabolism. To characterize a variety of cardiac diseases, there is an ever-growing demand for an accurate non-invasive approach to evaluating myocardial substrate metabolism. Data obtained from quantitative metabolic imaging modalities add functional information to the anatomic imaging modalities and can aid patient management. The goal of this review is to emphasize the role of non-invasive imaging techniques (such as PET, SPECT, MR spectroscopy and spectroscopic imaging) to detect the metabolic footprints of heart disease. The advancement of models and methods to estimate kinetic parameters of dynamic processes using data acquired from cardiac imaging modalities is discussed.
    Current pharmaceutical design 04/2014; · 4.41 Impact Factor
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    ABSTRACT: Sodium MRI is a powerful tool for providing biochemical information on the tissue viability, cell integrity and function in quantitative and noninvasive manner and it has already been applied in vivo in most human tissues. Although it could provide useful and new information not available with classic proton MRI, the low detectable sodium signal gives rise to technological limitations in terms of data quality when using clinical scanners. The design of dedicated coils capable of providing large field of view with high Signal-to-Noise Ratio (SNR) data is of fundamental importance. This work presents magnetostatic simulation, test and application of a transmit/receive circular coil designed for 23Na MR experiments in phantoms and humans with a clinical 3T scanner. In particular, the paper provides details of the design, modeling and construction of the coil. Such coil prototype was tested at workbench by using a dual-loop probe and a network analyzer, for quality factors and Q ratios measurements. Finally, the coil was employed in MR experiments to acquire phantom and in vivo data on different human organs (heart, kidney, calf and brain).
    Measurement 04/2014; 50:285–292. · 1.13 Impact Factor
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    ABSTRACT: Reconstruction methods for Non-Cartesian magnetic resonance imaging have often been analyzed using the root mean square error (RMSE). However, RMSE is not able to measure the level of structured error associated with the reconstruction process. An index for geometric information loss was presented using the 2D autocorrelation function. The performances of Least Squares Non Uniform Fast Fourier Transform (LS-NUFFT) and gridding reconstruction (GR) methods were compared. The Direct Summation method (DS) was used as reference. For both methods, RMSE and the loss in geometric information were calculated using a digital phantom and a hyperpolarized (13)C dataset. The performance of the geometric information loss index was analyzed in the presence of noise. Comparing to GR, LS-NUFFT obtained a lower RMSE, but its error image appeared more structured. This was observed in both phantom and in vivo experiments. The evaluation of geometric information loss together with the reconstruction error was important for an appropriate performance analysis of the reconstruction methods. The use of geometric information loss was helpful to determine that LS-NUFFT loses relevant information in the reconstruction process, despite the low RMSE.
    Computers in biology and medicine 12/2013; 43(12):2256-62. · 1.27 Impact Factor
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    ABSTRACT: Radiofrequency coils in Magnetic Resonance systems are used to produce a homogeneous B1 field for exciting the nuclei and to pick up the signals emitted by the nuclei with high signal-to-noise ratio. Accordingly, coil performance affects strongly the quality of the obtained data and images.Coil efficiency, defined as the B1 magnetic field induced at a given point on the square root of supplied power P, is an important parameter that characterizes coil performance, since by maximizing efficiency will also maximize the signal-to-noise ratio.This work describes and compares four methods for coil efficiency estimation, based on different theoretical approaches. Three methods allow efficiency measurement by using “probe techniques” (perturbing loop, perturbing sphere and pick-up coil), which can be used both on the bench and inside the scanner, while an “NMR technique” has been employed for comparison purpose.Methods were tested on a 13C birdcage coil tuned at 32.13 MHz.
    Measurement. 08/2013; 46(7):2201–2205.
  • JACC. Cardiovascular imaging 06/2013; 6(6):743-4. · 14.29 Impact Factor
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    ABSTRACT: This work describes the design of a quadrature surface coil constituted by a circular loop and a butterfly coil, employed in transmit/receive (TX/RX) mode for hyperpolarized 13C studies of pig heart with a clinical 3T scanner. The coil characterization is performed by developing an SNR model for coil performance evaluation in terms of coil resistance, sample-induced resistance and magnetic field pattern. Experimental SNR-vs.-depth profiles, extracted from the [1–13C]acetate phantom chemical shift image (CSI), showed good agreement with the theoretical SNR-vs.-depth profiles. Moreover, the performance of the quadrature coil was compared with the single TX/RX circular and TX/RX butterfly coil, in order to verify the advantage of the proposed configuration over the single coils throughout the volume of interest for cardiac imaging in pig. Finally, the quadrature surface coil was tested by acquiring metabolic maps with hyperpolarized [1–13C]pyruvate injected i.v. in a pig. © 2013 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 43B: 69–77, 2013
    Concepts in Magnetic Resonance Part B Magnetic Resonance Engineering 03/2013; 43B(2):69-77. · 0.71 Impact Factor
  • Fabio Gibiino, Vincenzo Positano, Luigi Landini, Maria Filomena Santarelli
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    ABSTRACT: Non-Cartesian acquisition strategies are widely used in MRI to dramatically reduce the acquisition time while at the same time preserving the image quality. Among non-Cartesian reconstruction methods, the least squares non-uniform fast Fourier transform (LS_NUFFT) is a gridding method based on a local data interpolation kernel that minimizes the worst-case approximation error. The interpolator is chosen using a pseudoinverse matrix. As the size of the interpolation kernel increases, the inversion problem may become ill-conditioned. Regularization methods can be adopted to solve this issue. In this study, we compared three regularization methods applied to LS_NUFFT. We used truncated singular value decomposition (TSVD), Tikhonov regularization and L(1) -regularization. Reconstruction performance was evaluated using the direct summation method as reference on both simulated and experimental data. We also evaluated the processing time required to calculate the interpolator. First, we defined the value of the interpolator size after which regularization is needed. Above this value, TSVD obtained the best reconstruction. However, for large interpolator size, the processing time becomes an important constraint, so an appropriate compromise between processing time and reconstruction quality should be adopted.Copyright © 2013 John Wiley & Sons, Ltd.
    International journal for numerical methods in biomedical engineering. 02/2013;
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    ABSTRACT: Magnetic resonance imaging (MRI) using high static field (>3T) generates high-quality images, thanks to high homogeneity in transmission as well as high signal-to-noise ratio (SNR) in reception. On the other hand, biological effects are proportional to the magnetic field strength and moreover the diagnostic accuracy is not always linked to high-quality imaging. For these reasons, the interest in low-field imaging becomes greater, also because of cheaper setting, greater patients comfort and more safety profile. In simple cases, as for surface coil, the coil performance is evaluated using classical electromagnetic theory, but for more complex geometry and in presence of a sample, is more difficult to evaluate the solution and often is necessary to follow a trial-and-error approach. Numerical methods represent a solution to this problem. In this work, we performed numerical simulation on a two-channel knee coil for low-field (0.5 T) MRI scanner. We are interested in seeing the effect of a sample placed inside the coil on the sample-induced resistance and decoupling between channels. In particular, we observe how the position of the sample inside the channel influences the resistance value and for performing this we compared an innovative method based on the exponential fitting on voltage oscillation damping with a validated method (estimation using quality factor). Finally, for the complete coil, the scatter parameters were calculated in loaded and unloaded conditions.
    Applied Magnetic Resonance 01/2013; · 0.83 Impact Factor
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    Journal of Cardiovascular Magnetic Resonance 01/2013; 15(1). · 4.44 Impact Factor
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    Journal of Cardiovascular Magnetic Resonance 01/2013; 15(1). · 4.44 Impact Factor
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    ABSTRACT: Significant technical advances in small animal molecular imaging techniques and in imaging probes with high specificity for various molecular targets have been produced in the last ten years. Notwithstanding, the clinical applicability of molecular imaging proceeds slowly. In animal experiments, multimodality molecular imaging techniques based on hybrid scanners are increasing, providing more insight into path physiologic phenomena associated with cardiovascular disease. In parallel, we assisted in the development of a new generation of multi-imaging probes, such as PET/MRI probes, particularly effective in hybrid scanners. More recently, in order to gain in inherently low sensitivity of MRI, hyperpolarized magnetic resonance spectroscopy using hyperpolarized 13C was proposed. Preliminary results obtained in experimental animal studies seem to confirm the potentialities of hyperpolarized 13C magnetic resonance to monitor myocardial energetics. In this review the preclinical cardiovascular applications and the potential for clinical translation are discussed.
    Current pharmaceutical design 11/2012; · 4.41 Impact Factor
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    ABSTRACT: Coil efficiency, defined as the B1 magnetic field induced at a given point on the square root of supplied power P, is an important parameter that characterizes both the transmit and receive performance of the radiofrequency (RF) coil. Maximizing coil efficiency will maximize also the signal-to-noise ratio. In this work, we propose a novel method for RF coil efficiency estimation based on the use of a perturbing loop. The proposed method consists of loading the coil with a known resistor by inductive coupling and measuring the quality factor with and without the load. We tested the method by measuring the efficiency of a 13C birdcage coil tuned at 32.13 MHz and verified its accuracy by comparing the results with the nuclear magnetic resonance nutation experiment. The method allows coil performance characterization in a short time and with great accuracy, and it can be used both on the bench and inside the scanner. © 2012 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 41B: 139–143, 2012
    Concepts in Magnetic Resonance Part B Magnetic Resonance Engineering 10/2012; 41B(4). · 0.71 Impact Factor
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    ABSTRACT: The objective of this study was to develop an automatic image registration technique capable of compensating for kidney motion in renal perfusion MRI, to assess the effect of renal artery stenosis on the kidney parenchyma. MATERIALS AND METHODS: Images from 20 patients scheduled for a renal perfusion study were acquired using a 1.5 T scanner. A free-breathing 3D-FSPGR sequence was used to acquire coronal views encompassing both kidneys following the infusion of Gd-BOPTA. A two-step registration algorithm was developed, including a preliminary registration minimising the quadratic difference and a fine registration maximising the mutual information (MI) between consecutive image frames. The starting point for the MI-based registration procedure was provided by an adaptive predictor that was able to predict kidney motion using a respiratory movement model. The algorithm was validated against manual registration performed by an expert user. RESULTS: The mean distance between the automatically and manually defined contours was 2.95 ± 0.81 mm, which was not significantly different from the interobserver variability of the manual registration procedure (2.86 ± 0.80 mm, P = 0.80). The perfusion indices evaluated on the manually and automatically extracted perfusion curves were not significantly different. CONCLUSIONS: The developed method is able to automatically compensate for kidney motion in perfusion studies, which prevents the need for time-consuming manual image registration.
    MAGMA Magnetic Resonance Materials in Physics Biology and Medicine 09/2012; · 1.86 Impact Factor
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    ABSTRACT: Receiver coils in magnetic resonance (MR) systems are used to acquire the signals emitted by the nuclei. Surface coils provide a high signal-to-noise ratio due to their small sensitive region but the usable field of view is also limited to the size of the sensitive region. The use of array coils permits to increase the sensitive region. The outputs from the receiver channels are combined to construct a single composite image from the data of many coils. The image reconstruction is usually performed by using root sum-of-squares (RSS) method, which combines data without the knowledge of the coils sensitivity but it is known to introduce bias in low-signal regions. SUPER reconstruction permits to yield a composite image with higher contrast between high- and low-signal regions than RSS algorithm, by preliminary estimating coil sensitivities using low-pass filtering of original images. The purpose of this work is to introduce a theory for obtaining estimated coil sensitivity maps from the individual coil images and successively combining data from array elements using SUPER algorithm. Performance evaluation and comparison with RSS reconstruction were carried out with MR acquisitions performed using a 32-elements cardiac phased-array coil in a 3 T scanner. © 2012 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 41B: 85–93, 2012
    Concepts in Magnetic Resonance Part B Magnetic Resonance Engineering 08/2012; 41B(3). · 0.71 Impact Factor
  • Giulio Giovannetti, Valentina Hartwig, Luigi Landini, Maria Filomena Santarelli
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    ABSTRACT: Radiofrequency (RF) transmitter and receiver coils in magnetic resonance imaging systems are used, respectively, to excite the nuclei in the object to be imaged and to pick up the signals emitted by the nuclei. The quality of obtained images strongly depends upon the correct choice of the coils geometry and typology. For low-field magnetic resonance imaging systems, the dominant power dissipation mechanisms are mainly due to conductor losses and the coils performance are affected by cross-sectional shape of RF coil conductors. This work proposes a method for the estimation of the different skin effects contribution to the total conductor resistance for coil built using strip conductor. The evaluation of coil resistance was performed at different tuning frequencies usually used in clinical scanner (21–128 MHz). © 2012 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 41B: 57–61, 2012
    Concepts in Magnetic Resonance Part B Magnetic Resonance Engineering 04/2012; 41B(2). · 0.71 Impact Factor
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    ABSTRACT: Magnetic resonance imaging (MRI) is essential for the diagnosis and treatment of musculoskeletal conditions. Low-field (<0.5T) imaging is a cost-effective alternative to more expensive high-field strength imaging due to the inexpensive setting, greater patient comfort and better safety profile. On the other hand, if compared with high-field body scanners, the low-field scanners produce poor-quality images with lower signal-to-noise ratio. Especially in low-field MR, receiver coil performance plays a significant role in image quality. Coil performance is generally evaluated using classical electromagnetic theory, but when the coil is loaded with a sample, an analytical solution is extremely difficult to derive, so that a trial-and-error approach is often followed. Numerical methods have been proposed in literature as good alternatives to predict MRI coil performance. In this study the performance of a knee coil for low-field (0.5 T) MR scanners is analyzed using workbench tests and numerical simulation with a software program based on the finite difference time domain method. Parameter performances measured using the classical workbench test are compared with those obtained using numerical simulations. Finally, the knee coil performance is validated with images acquired in a commercial low-field MR system.
    Applied Magnetic Resonance 03/2012; 44(3). · 0.83 Impact Factor
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    Journal of Cardiovascular Magnetic Resonance 02/2012; 14 Suppl 1:P56. · 4.44 Impact Factor

Publication Stats

654 Citations
206.42 Total Impact Points

Institutions

  • 2008–2014
    • Fondazione Toscana Gabriele Monasterio
      Pisa, Tuscany, Italy
    • Clinical and Experimental Center for Functional Magnetic Resonance Imaging
      Torino, Piedmont, Italy
  • 1999–2013
    • National Research Council
      • Institute of Clinical Physiology IFC
      Roma, Latium, Italy
  • 1991–2013
    • Università di Pisa
      • • Department of Information Engineering
      • • Department of Clinical and Experimental Medicine
      Pisa, Tuscany, Italy
  • 2007
    • Institute of Electrical and Electronics Engineers
      Washington, Washington, D.C., United States