[Show abstract][Hide abstract] 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
[Show abstract][Hide abstract] 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).
[Show abstract][Hide abstract] 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
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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
[Show abstract][Hide abstract] 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
[Show abstract][Hide abstract] 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
[Show abstract][Hide abstract] ABSTRACT: Hyperpolarization of ¹³C-labeled energy substrates enables the noninvasive detection and mapping of metabolic activity, in vivo, with magnetic resonance spectroscopy (MRS). Therefore, hyperpolarization and ¹³C MRS can potentially become a powerful tool to study the physiology of organs such as the heart, through the quantification of kinetic patterns under both normal and pathological conditions. In this study we assessed myocardial uptake and metabolism of hyperpolarized [1-¹³C]pyruvate in anesthetized pigs. Pyruvate metabolism was studied at baseline and during dobutamine-induced stimulation. We applied a numerical approach for spectral analysis and kinetic fitting (LSFIT/KIMOfit), making a comparison with a well-known jMRUI/AMARES analysis and γ-variate function, and we estimated the apparent conversion rate of hyperpolarized [1-¹³C]pyruvate into its downstream metabolites [1-¹³C]lactate, [1-¹³C]alanine and [¹³C]bicarbonate in a 3 T MR scanner. We detected an increase in the apparent kinetic constants (k(PX) ) for bicarbonate and lactate of two-fold during dobutamine infusion. These data correlate with the double product (rate-pressure product), an indirect parameter of cardiac oxygen consumption: we observed an increase in value by 46 ± 11% during inotropic stress. The proposed approach might be applied to future studies in models of cardiac disease and/or for the assessment of the pharmacokinetic properties of suitable ¹³C-enriched tracers for MRS.