Showing papers by "Enrico De Vita published in 2005"

Depth of delayed cooling alters neuroprotection pattern after hypoxia-ischemia

Abstract: Hypothermia after perinatal hypoxia-ischemia (HI) is neuroprotective; the precise brain temperature that provides optimal protection is unknown. To assess the pattern of brain injury with 3 different rectal temperatures, we randomized 42 newborn piglets: (Group i) sham-normothermia (38.5-39 degrees C); (Group ii) sham-33 degrees C; (Group iii) HI-normothermia; (Group iv) HI-35 degrees C; and (Group v) HI-33 degrees C. Groups iii through v were subjected to transient HI insult. Groups ii, iv, and v were cooled to their target rectal temperatures between 2 and 26 hours after resuscitation. Experiments were terminated at 48 hours. Compared with normothermia, hypothermia at 35 degrees C led to 25 and 39% increases in neuronal viability in cortical gray matter (GM) and deep GM, respectively (both p < 0.05); hypothermia at 33 degrees C resulted in a 55% increase in neuronal viability in cortical GM (p < 0.01) but no significant increase in neuronal viability in deep GM. Comparing hypothermia at 35 and 33 degrees C, 35 degrees C resulted in more viable neurons in deep GM, whereas 33 degrees C resulted in more viable neurons in cortical GM (both p < 0.05). These results suggest that optimal neuroprotection by delayed hypothermia may occur at different temperatures in the cortical and deep GM. To obtain maximum benefit, you may need to design patient-specific hypothermia protocols by combining systemic and selective cooling.

3D MDEFT imaging of the human brain at 4.7 T with reduced sensitivity to radiofrequency inhomogeneity

Abstract: A modification to the 3D modified driven equilibrium Fourier transform (MDEFT) imaging technique is proposed that reduces its sensitivity to RF inhomogeneity. This is especially important at high field strengths where RF focusing effects exacerbate B-1 inhomogeneity, causing significant signal nonuniformity in the images. The adiabatic inversion pulse used during the preparation period of the MDEFT sequence is replaced by a hard (nonadiabatic) pulse with a nominal flip angle of 130 degrees. The spatial inhomogeneity of the hard pulse preparation compensates for the inhomogeneity of the excitation pulses. Uniform signal intensity is obtained for a wide range of B-1 amplitudes and the high CNR characteristic of MDEFT is retained. The new approach was validated by numerical simulations and successfully applied to human brain imaging at 4.7 T, resulting in high-quality T-1-weighted images of the whole human brain at high field strength with uniform signal intensity and contrast, despite the presence of significant RF inhomogeneity. (c) 2005 Wiley-Liss, Inc.

Common SENSE (sensitivity encoding using hardware common to all MR scanners): a new method for single-shot segmented echo planar imaging.

Abstract: A new method is presented that enables image acquisition to be segmented into two readouts. This is achieved using a new pulse sequence that creates two components of magnetization with different spatial profiles. Each component of the magnetization is measured in one of the readouts. This produces two images with complimentary "sensitivity profiles" and near identical contrast. The images can be acquired with a reduced data matrix that corresponds to shorter periods of data acquisition. The reduced matrix images are then combined to produce a full matrix image using reconstruction methods previously applied to images from multiple RF coils in the sensitivity encoding (SENSE) technique.The most promising application for this technique is in improving the performance of echo planar imaging (EPI) at high field. In this application, common SENSE obtains two segments of data in a single excitation of the magnetization (i.e., two readouts are performed per shot). The combination of these segments in image space avoids the difficulties normally associated with segmented EPI methods, namely, increased ghosting from discontinuities in the k-space data. The main advantages are a reduction in distortion and blurring. Common SENSE is compatible with parallel imaging and partial Fourier methods.

Localized 4.7 T Proton Magnetic Resonance Spectroscopy in Neonatal Encephalopathy: Implementation, Safety and Preliminary Interpretation of Results

Abstract: Summary Magnetic resonance (MR) techniques have revolutionized the assessment of brain development and injury in the newborn. MR studies at 3 T or above are becoming widespread; however, given the high cost and complexity of high-field MR systems, it is important to assess their benefits and limitations for clinical practice. MR spectroscopy (MRS) studies at high field carry potential benefits such as improved signal-to-noise ratio (SNR) and chemical shift dispersion compared with 1.5 T. However, safety is a very important consideration as radiofrequency (RF) tissue heating and acoustic noise also increase with field strength. Furthermore, increased chemical-shift dependence of the position of the volume of interest (VOI), shorter transverse and longer longitudinal relaxation times constitute additional challenges. We describe the first in-vivo, proton MRS studies of newborn human brain at 4.7 T. Nine infants with neonatal encephalopathy, all ventilated and with continuous physiological monitoring, were studied. We used L-FOCI localization, mostly with a VOI centred on the thalami. The absence of 4.7 T results from healthy infants made it impossible to interpret pathological metabolite peak-area ratios. However, concentration ratios and concentrations should be field-strength independent and interpretable using control values acquired at lower field. Of eight infants with concentration-ratio measurements, seven had low [N-acetylaspartate (NAA)]/[choline (Cho)] and three increased [lactate]/[NAA]. Of the two infants with ‘concentration’ measurements both had low [NAA] and one reduced [creatine]. We used an adult coil and consequent RF power restrictions had repercussions for the minimum magnetization recovery time (TR). A smaller, neonatal coil should improve SNR and, with less RF power, relax TR constraints thereby enabling fuller exploitation of the potential of high-field MRS.