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A Righini

Publications and source records attributed to A Righini.

16 recordsLinked to original sources
PubMed1996

Imaging focal reperfusion injury following global ischemia with diffusion-weighted magnetic resonance imaging and 1H-magnetic resonance spectroscopy.

The purpose of the study was to determine whether diffusion-weighted magnetic resonance imaging (DWI) could identify focal lesions that develop in ischemia-sensitive cerebral tissues during reperfusion following global brain ischemia. Localized 1H-Magnetic Resonance Spectroscopy (1H-MRS) measurements were also obtained to determine whether abnormal spectroscopic markers were associated with focal lesions and to define time correlations between DWI and metabolic changes. Brain diffusion-weighted magnetic resonance imaging measurements were made in a cat model of repetitive global cerebral ischemia and reperfusion. Five animals were exposed to three episodes of 10 min vascular occlusions at hourly intervals. Three animals were evaluated as controls. DWI, T2WI, and 1H-MRS data were acquired for up to 12 h. Transient focal DWI hyperintensity was detected in the hippocampus, basal ganglia, and cortical watershed areas. These focal abnormalities usually appeared during the final reperfusion and eventually spread to encompass all of the gray matter. Spectroscopic measurements demonstrated the expected elevation of the lactate signal intensity during vessel occlusion, which returned to normal during early reperfusion. A subsequent rise in the lactate signal occurred approximately 3-4 h after the beginning of the third reperfusion. This late lactate elevation occurred after focal hyperintensities were identified by DWI. No significant signal changes were seen in spectroscopic metabolites other than lactate. The study illustrates that DWI and 1H-MRS are sensitive to focal cerebral lesions that occur during reperfusion following global cerebral ischemia.

Animals↗
PubMed1996

High temporal resolution diffusion MRI of global cerebral ischemia and reperfusion.

Although brain ischemia has been extensively studied using diffusion-weighted magnetic resonance imaging, most studies performed so far have not had adequate time resolution to follow the temporal changes in the water apparent diffusion coefficient (ADC) in hyperacute ischemia. Using diffusion echo planar imaging, we obtained ADC maps (calculated from measurements made with 8 b-values) with a time resolution of 43 s in a feline model of global brain ischemia and reperfusion. Different protocols were performed: 10-min hypoperfusion, 10- and 22-min ischemia followed by reperfusion, and cardiac arrest. ADC values were obtained from white matter of the internal capsule and from the thalamus. Cortical gray matter measurements were not deemed reliable due to the close proximity of CSF in the cortical sulci. Following occlusion, the ADC declined in the thalamus to < 2 SD of its normal baseline value within 1.5-2.5 min. This decay was exponential with a time constant (tau +/- SD) of 6.0 +/- 2.6 min; no further decrease in the ADC was observed 10 min following ischemia. Following reperfusion, in animals that showed ADC recovery, the ADC began increasing immediately, returning to its preischemic value in approximately 15 min. No significant ADC changes were observed during hypoperfusion. Following cardiac arrest, the decay of ADC was more rapid in the thalamus (tau = 2.6 +/- 0.6 min) than in white matter (tau = 6.6 +/- 1.8 min). We observed that the ADC at 40 min after cardiac arrest was similar to the ADC at 10 min after ischemia. Given that all animals subjected to 10-min ischemic episodes showed ADC recovery with reperfusion, doubt is cast on whether it is possible to define a threshold value of the ADC below which brain tissue is irreversibly damaged. Finally, despite variability in the time constants of the ADC decay induced by ischemia, the ADC values at 10 min were very similar in all the animals. This suggests that when blood flow is diminished sufficiently to induce an ADC reduction, differences in perfusion affect the rapidity of the decrease but not the final asymptotic value reached.

Animals↗
PubMed1995

Cerebral white matter in the centrum semiovale exhibits a larger N-acetyl signal than does gray matter in long echo time 1H-magnetic resonance spectroscopic imaging.

Long echo time (272 ms) 1H magnetic resonance spectroscopic imaging was used to measure the relative magnitudes of the N-acetylaspartate (NAA) signal in a variety of anatomically defined brain structures (centrum semiovale, thalamus, medial frontal cortex, and genu of the corpus callosum) composed primarily of gray matter or white matter. Six normal young adult humans aged 30-40 were studied. With a 95% level of statistical confidence, the white matter in the centrum semiovale (CSO) produced a more intense NAA signal than did the gray matter in the thalamus and the frontal cortex. Differences between the white matter regions were also noted. The CSO white matter's NAA signal yielded a larger NAA signal than did the white matter of the genu of the corpus callosum. Possible reasons for the anatomical variation in the cerebral NAA signal intensity are discussed.

Adult↗
PubMed1995

Blue blood or black blood: R1 effects in gradient-echo echo-planar functional neuroimaging.

Changes in the longitudinal relaxation rate (R1) may play a role in the MRI signal intensity increases that have been associated with physiological brain activation. We used gradient-echo echo-planar MRI (GRE-EPI) to test whether physiological activations associated with hypercapnia in dogs were dependent on the delay (TR) between successive images in a time-series. Our results show that, in addition to activation-induced changes in the R2 (transverse relaxation including inhomogeneity effects), activation-induced changes in R1 are significant under certain pulsing conditions. In our paradigm, the R1 contribution became significant at TR values of 1 s or less.

Animals↗
PubMed1995

Brain regional distribution pattern of metabolite signal intensities in young adults by proton magnetic resonance spectroscopic imaging.

Proton magnetic resonance spectroscopy (1H-MRS) is evolving from single-volume localized acquisitions to multiple-volume acquisitions using magnetic resonance spectroscopic imaging (1H-MRSI). The normal regional patterns of 1H-MRSI-detectable metabolite signal intensities have yet to be established. We studied 13 healthy young adults with a multiple-section 1H-MRSI technique. The metabolite signals measured were N-acetylaspartate (NA), choline-containing compounds (CHO), creatine-phosphocreatine (CRE), and lactate. Ten neuroanatomic regions (nine bilateral) were identified in gray matter, white matter, and basal nuclei. Analysis of the data led to the following conclusions: (1) NA and CHO signals from centrum semiovale (CSO) can be used as a normalizing factor to reduce intersubject variability due to external causes; (2) in normal human brain, there is no left versus right asymmetry in the regions studied; (3) statistically significant patterns of signal distribution of NA, CHO, and CRE can be identified in normal human brain; and (4) CSO-normalized metabolite signal intensities and metabolite ratios complement each other for the detection of significant regional differences.

Adult↗
PubMed1994

Interobserver variability in CT assessment of brain atrophy.

To assess interobserver variability in estimation of brain atrophy based on CT, four neuroradiologists examined CT brain images of 150 consecutive patients without focal lesions. An independent neuroradiologist made the following quantitative measurements: frontal horn index, subarachnoid space area and the ratio between subarachnoid space area and inner skull space area. Level of agreement was fair for the presence (k = 0.24), slight for the degree (mild, moderate, severe) (k = 0.24) and moderate for the type (cortical, subcortical, mixed) of atrophy (k = 0.59). There was a highly significant correlation between the number of observers agreeing and quantitative measurements. We concluded that neuroradiologists' subjective estimation of brain atrophy alone is not reliable. Quantitative measurements would be needed in cases where the presence of brain atrophy might determine clinical decisions.

Adult↗
PubMed1994

Brain parenchyma apparent diffusion coefficient alterations associated with experimental complex partial status epilepticus.

The objective of this study was to evaluate whether water apparent diffusion coefficient (ADC) measurements provide more specific information than T2-weighted MRI about the evolution of brain parenchyma lesions secondary to prolonged complex partial seizures. We measured the ADC in the brain of rats exhibiting prolonged complex partial seizures induced by intraperitoneal injection of kainic acid (KA). The animals were imaged with diffusion and T2-weighted MRI at 2 T from 3 h up to 9 days after KA injection. In the piriform cortex and amygdala, the T2-weighted MRI signal intensity appeared to be uniformly increased from 24 to 72 h after KA injection, and returned to normal by 9 days. In the same regions between 24 and 72 h, the ADC first decreased and then increased. The ADC changes were consistent with the known histopathologic alterations. In this complex partial seizure model, the ADC measurement provides more specific information than T2-weighted MRI about the histopathologic evolution of the lesions. This supports the proposal that diffusion MRI may be valuable for the evaluation of the neuropathologic sequelae in patients with multiple or prolonged seizures.

Animals↗
PubMed1993

Histopathologic correlates of abnormal water diffusion in cerebral ischemia: diffusion-weighted MR imaging and light and electron microscopic study.

PURPOSE: To correlate the findings on diffusion-weighted magnetic resonance (MR) images with the cytologic and histologic findings in ischemic tissue. MATERIALS AND METHODS: A photochemical model of cerebral infarction in rats was studied with diffusion- and T2-weighted MR imaging. The development of lesions was followed from 20 minutes to 5 days after the onset of ischemia. Apparent water diffusion coefficient (ADC) maps were calculated and correlated with light and electron microscopic findings. RESULTS: T2-weighted images clearly showed vasogenic edema but did not enable distinction between areas with cellular damage and the surrounding edematous regions. In contrast, the ADC, which was elevated in nonischemic edematous regions, was diminished in areas with histologic evidence of ischemic damage or necrosis. In the core of the infarct, the ADC became elevated when electron microscopy revealed cellular lysis. CONCLUSION: Diffusion-weighted images may help ascertain the extent of cellular damage and death after stroke.

Animals↗
PubMedDate not supplied

Curved CT reformatted images of head scans.

Attempts have been made to overcome the limited visibility of anatomic structures on axial CT by direct multiplanar sections or multiplanar reformatted views. So as not to be restricted by "planar cuts," we have used curved coronal reformatting to investigate some of the cranial structures, whose tortuous anatomy cannot be visualized entirely with standard CT. In fact, we have provided a "flattened" presentation of the optic nerve and chiasma, facial nerve canal, and jugular foramen, showing them in their entire extension. Despite the geometrical deformation produced by this technique, its potential to depict the anatomy of some structures is noteworthy.

Glomus Tumor↗
PubMedDate not supplied

Functional MRI: primary motor cortex localization in patients with brain tumors.

PURPOSE: Our goal was (a) to test the ability of functional MRI (fMRI) to localize the hand primary motor cortex in patients with brain neoplasms using a conventional scanner and (b) to compare within the same subject the location and morphology of the activated motor areas in the affected hemisphere with the contralateral ones. METHOD: Seventeen right-handed patients with frontoparietal intra- and extraaxial tumors were studied. Hand motor performance ranged from normal to slight impairment of finger dexterity. The fMRI study was based on a series of FLASH images. Two or three contiguous slices parallel to the bicommissural plane were acquired through the level of frontoparietal cortex. Each patient was requested to perform with each hand a finger-tapping task or a simpler repetitive flexion-extension of the last four fingers. Pseudo-color activation maps were then calculated by a Z-score method and superimposed on high resolution images. RESULTS: Five patients were excluded because of gross motion artifacts. In all other patients, areas of significant signal increase were detected on the precentral gyrus. They had a spot-like appearance, and no substantial side-to-side differences in shape or extension could be observed. In the presence of severe compression of the gyri, a displacement of the activated areas in the affected hemisphere with respect to the contralateral ones was noticeable. CONCLUSION: fMRI localization of the primary motor area using a conventional scanner can be obtained also in patients with brain tumors, although with a lower success rate than in normal volunteer studies, mainly because of subject compliance problems. Areas of significantly increased signal are detectable even in cortex where normal anatomical patterns are lost.

Adolescent↗
PubMedDate not supplied

fMRI changes in the brain associated with the carotid compression test.

PURPOSE: The purpose of our investigation was to study in normal volunteers the response to a unilateral common carotid (CC) compression test using dynamic MRI sensitive to variations in blood magnetic susceptibility. METHOD: Nine volunteers, positioned in a 1.5 T MR scanner, performed a unilateral 40 to 45 s CC self-compression during the acquisition of single slice axial T2*-weighted FLASH images. RESULTS: In three subjects, the signal showed a significant 2% drop from baseline in the ipsilateral frontal temporal cortex during the compression. In another three subjects, a significant 1.5-2% signal decrease was observed in both hemispheres. In two subjects whose MR angiography showed abnormalities of the circle of Willis, the bilateral signal drop was more remarkable (3%). In one volunteer, the signal did not change. CONCLUSION: Increased deoxyhemoglobin within the brain microcirculation is the probable explanation for the signal drop. This method could be further tested in view of the widespread use of open interventional MR units.

Adult↗
PubMedDate not supplied

Facial asymmetry in partial epilepsies.

Fifty-six consecutive epileptic patients with partial seizures (30 temporal, 26 extratemporal) and facial asymmetry were studied. Facial asymmetry was compared with EEG, radiologic, and other clinical findings. Thirty patients had a lesional epilepsy whereas 26 were considered cryptogenic. In lesional epilepsies, 60% of patients had EEG foci ipsilateral to the smaller hemiface and only 20% had EEG foci contralaterally. In the cryptogenic group, the EEG focus was ipsilateral in 50% and contralateral to the facial smallness in 46%. No differences were noted between temporal and extratemporal epilepsies. Early acquired cerebral lesions may modify development of the hemisphere involved, leading to a small ipsilateral hemiface and seizures originating from the same side.

Adult↗
PubMedDate not supplied

MR of diffusion slowing in global cerebral ischemia.

PURPOSE: To investigate the causal connections between ischemia and the hyperintensity in diffusion-weighted MR images that has been associated with it. METHODS: Diffusion-weighted and T2-weighted MR imaging were used in a feline global cerebral ischemia/reperfusion model. Single 30-minute vascular occlusions followed by reperfusion were studied. Global occlusions were used to avoid interpretive complications associated with the temporally unstable hemodynamics of the penumbral zones around focal occlusions and the possible growth of the ischemic and penumbral regions with time. RESULTS: Diffusion-weighted hyperintensity and the associated diffusional slowing were not attributable exclusively to the cessation of blood flow because: 1) it does not appear abruptly at the onset of ischemia; 2) it resolves slowly early in reperfusion; and 3) it reappears after prolonged reperfusion. CONCLUSION: The times during which diffusion-weighted hyperintensity is manifested during ischemia, and recovers with reperfusion, point to a role for energy metabolism failure.

Animals↗