Search

Synchrotron-based high-pressure x-ray diffraction measurements indicate that compressibility, a fundamental materials property, can have a size-specific minimum value. The bulk modulus of nanocrystalline titania has a maximum at particle size of 15 nm. This can be explained by dislocation behavior because very high dislocation contents can be achieved when shear stress induced within nanoparticles counters the repulsion between dislocations. As particle size decreases, compression increasingly generates dislocation networks hardened by overlap of strain fields that shield intervening regions from external pressure. However, when particles become too small to sustain high dislocation concentrations, elastic stiffening declines. The compressibility has a minimum at intermediate sizes.

Interest in tissue oxygen (PtiO2) monitoring is increasing. However the exact interactions between ptiO2, systemic and cerebral variables are a matter of debate. Particularly, the relationship between ptiO2, cerebral oxygen supply and consumption needs to be clarified. We designed a model to achieve progressive Cerebral Blood Flow (CBF) reduction through 3 steps: 1. baseline, 2. CBF between 50-60% of the baseline, 3. CBF30% of the baseline. In 7 pigs, under general anaesthesia, Cerebral Perfusion Pressure (CPP) and CBF were reduced through the infusion of saline in a lateral ventricle. PtiO2 and CBF were monitored respectively through a Clark electrode (Licox, GMS) and laser doppler (Peri-Flux). Blood from superior sagittal sinus and from an arterial line was simultaneously drawn to calculate the artero-venous difference of oxygen (AVDO2). Brain oxygen supply was calculated by multiplying relative CBF change and arterial oxygen content. PtiO2 reflected CBF reductions, as it was 27.95 (+/- 10.15) mmHg during the first stage of intact CBF, declined to 14.77 (+/- 3.58) mmHg during the first CBF reduction, declined to 3.45 (+/- 2.89) mmHg during the second CBF reduction and finally fell to 0 mmHg when CBF was completely abolished. CBF changes were also followed by a decline in O2 supply and a parallel increase in AVDO2.This model allows stable and reproducible steps of progressive CBF reduction in which ptiO2 changes can be studied together with oxygen supply and consumption.

Arterial hyperoxia improves oxygen tension measured into the cerebral tissue (ptiO2). The extent of this improvement in ameliorating O2 delivery to the cerebral tissue, when cerebral blood flow (CBF) is reduced, is still unclear. The present experiment was developed to investigate the effect of arterial hyperoxia at normal or reduced CBF (baseline, CBF = 50-60%, and CBF = 20-30% of the baseline). CBF reduction was achieved in 7 pigs by saline infusion in a lateral ventricle. PtiO2 was measured by Licox equipment. Arterovenous oxygen difference (AVDO2) was calculated as the difference between arterial oxygen content and superior sagittal sinus oxygen content. Hyperoxia was induced by increasing inspired oxygen fraction to 100%. PtiO2 moved respectively from 27.95 (+/- 10.15) to 45.98 (+/- 15.31), from 14.77 (+/- 3.58) to 30.71 (+/- 12.2), and from 3.45 (+/- 2.89) to 11.1 (+/- 12.6) mmHg at normal CBF, after the first reduction and after the second reduction. O2 supply showed only a negligible increase. AVDO2 decreased during the phases of intact and moderate CBF impairment, while it did not change during the phase of severe CBF impairment.an increase of ptiO2 does not necessarily correspond to an improvement of brain oxygen delivery. The small increase in oxygen delivery due to hyperoxia may cause a slight improvement in the balance between O2 delivery and consumption during mild CBF reduction, but such improvement is negligible when severe CBF reduction occurs.

Endoscopic third ventriculostomy (ETV) is considered the gold standard treatment for obstructive hydrocephalus due to partial or complete obstruction of cerebrospinal fl uid (CSF) ventricular pathways caused by mass lesions. However long-term effi cacy of this procedure remains controversial as treatment of chronic adult hydrocephalus due to stenosis of Sylvian acqueduct [late-onset idiopathic aqueductal stenosis (LIAS)]. The authors describe clinical presentation, diagnostic investigations in patients affected by LIAS, and defi ne their clinical and radiological outcome after ETV. From January 2003 to December 2008, 13 consecutive LIAS patients treated by ETV were retrospectively reviewed. Pre- and post-operative clinical and radiological fi ndings, including conventional and phase-contrast (PC) cine magnetic resonance imaging (MRI) were investigated. ETV was successfully performed in all patients. Patient’s neurological condition improved. No one required a second ETV procedure or shunt implantation. Clinical and radiological results reveal a satisfactory outcome of LIAS patients treated by ETV. At follow-up a clinical improvement could be demonstrated in all cases. Selection criteria of LIAS patients seem to be crucial to obtain satisfactory and long-lasting results. Even in elderly patients with chronic hydrocephalus, ETV can be considered the treatment of choice.

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.