OBJECTIVETo determine regional cerebral water content in vivo by magnetic resonance imaging (MRI) after the administration of 7.5% saline in brain-lesioned rabbits.
DESIGNRandomized, controlled, ...intervention trial.
SETTINGUniversity animal laboratory.
SUBJECTSEighteen male New Zealand white rabbits, randomly assigned to one of three groups.
INTERVENTIONSThe animals were anesthetized (1% halothane), intubated, and mechanically ventilated to maintain end-tidal CO2 tension between 30 and 35 mm Hg (4 and 4.7 kPa). Arterial and central venous catheters were inserted and arterial blood samples were serially obtained during the experiment. Serum osmolality was measured. A cryogenic cerebral lesion was produced by pouring liquid nitrogen for 1 min into a funnel placed on the intact skull over the right hemisphere. One group of animals received 20 mL of 7.5% saline intravenously 150 mins after the cerebral lesion was generated (7.5% saline group, n = 7). A second group of animals received the same volume of 0.9% saline intravenously (0.9% saline group, n = 7). In a third group of animals (control group, n = 4) no lesion was created and no fluid administered.
MEASUREMENTS AND MAIN RESULTSFive spin-echo T2-weighted MRIs of the brain were acquired at 90 mins (Baseline 1), 120 mins (Baseline 2), 150 mins (Infusion), 180 mins (Infusion + 30 mins), and 210 mins (Infusion + 60 mins) after the generation of the cerebral lesion. In the control group, two scans separated by a time interval of 120 mins were performed. The percent changes in signal intensity between the first and the four following scans of a coronal slice of the central region were determined. Analysis of variance and the Mann-Whitney U test were used for statistical analysis. Data are presented as mean +/- SD; p < .05 was considered significant. Serum osmolality increased significantly from 308 +/- 13 mosm/L to 349 +/- 19 mosm/L after the infusion of 20 mL of 7.5% saline, but did not change after the administration of 0.9% saline. Signal intensity in the area between the caudal edge of the core of the lesion and the basal ganglia was 9 +/- 8% higher on the injured side than in the corresponding area on the contralateral side (p < .05). Compared with Baseline 1, signal intensity at Infusion + 60 mins decreased by 26.3 +/- 13.7% in the 7.5% saline group, whereas it decreased by 10.4 +/- 8.6% in the 0.9% saline group (p < .05 between groups). Signal intensity decreased only slightly and nonsignificantly by 0.6 +/- 4.4% between the two scans in the control group.
CONCLUSIONSThe administration of a 7.5% saline solution causes a prompt and substantial decrease in cerebral water content as assessed by spin-echo T2-weighted MRI. Magnetic resonance imaging offers the opportunity for repeated, noninvasive in vivo determinations of cerebral water content. (Crit Care Med 1998; 26:108-114)
The early evolution of ischemic brain injury under normoglycemic and streptozotocin-induced hyperglycemic plasma conditions was studied using magnetic resonance imaging (MRI). Male Sprague-Dawley ...rats were subjected to either permanent middle cerebral artery occlusion (MCAO), or 1-h MCAO followed by reperfusion using the intraluminal suture insertion method. The animals were divided into four groups each with eight rats: normoglycemia with permanent MCAO, normoglycemia with 1-h MCAO, hyperglycemia with permanent MCAO, and hyperglycemia with 1-h MCAO. Diffusion-weighted images (DWIs) and T2-weighted images (T2WIs) were aquired every 1 h from 20 min until 6 h after MCAO, at which time cerebral plasma volume images (PVIs) were acquired. Tissue infarction was determined by triphenyltetrazolium chloride staining at 7 h after MCAO. The ischemic damage, measured as the area of DWI and T2WI hyperintensity and tissue infarction, increased significantly in hyperglycemic rats in both permanent and transient MCAO models. In the permanent MCAO model, the maximal apparent water diffusion coefficient (ADC) decline under either normo- or hyperglycemia was about 40%, but the speed of ADC drop was faster in hyperlgycemic rats than in normoglycemic rats. Reperfusion after 1 h of MCAO in normoglycemic rats partly reversed the decline in ADC, whereas the low ADC area continued to expand after reperfusion in the hyperglycemic group. Between the two hyperglycemic groups with either permanent MCAO or reperfusion, no significant difference was found in the infarct volume measured at 7 h after MCAO. However, reperfusion dramatically increased the extent and accelerated the development rate of vasogenic edema. ADC in the hyperglycemic reperfusion group also dropped to a lower level. A large "no-reflow" zone was found in the ischemic hemisphere in the hyperglycemic reperfusion group. This study provides strong evidence to support that preischemic hyperglycemia exacerbates ischemic damage in both transient and permanent MCAO models and demonstrates, using MRI, that reperfusion under preischemic hyperglycemia accelerates the evolution of early ischemic injury.
FLASHForward D’Arcy, R.; Aschikhin, A.; Bohlen, S. ...
Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences,
08/2019, Letnik:
377, Številka:
2151
Journal Article
Recenzirano
The FLASHForward experimental facility is a high-performance test-bed for precision plasma wakefield research, aiming to accelerate high-quality electron beams to GeV-levels in a few centimetres of ...ionized gas. The plasma is created by ionizing gas in a gas cell either by a high-voltage discharge or a high-intensity laser pulse. The electrons to be accelerated will either be injected internally from the plasma background or externally from the FLASH superconducting RF front end. In both cases, the wakefield will be driven by electron beams provided by the FLASH gun and linac modules operating with a 10Hz macro-pulse structure, generating 1.25 GeV, 1 nC electron bunches at up to 3 MHz micro-pulse repetition rates. At full capacity, this FLASH bunch-train structure corresponds to 30 kW of average power, orders of magnitude higher than drivers available to other state-of-the-art LWFA and PWFA experiments. This high-power functionality means FLASHForward is the only plasma wakefield facility in the world with the immediate capability to develop, explore and benchmark high-average-power plasma wakefield research essential for next-generation facilities. The operational parameters and technical highlights of the experiment are discussed, as well as the scientific goals and high-average-power outlook.
This article is part of the Theo Murphy meeting issue ‘Directions in particle beam-driven plasma wakefield acceleration’.
When surgically removing a spinal nerve schwannoma, preservation of the involved root is attempted and may be feasible. However, in large tumors, sacrifice of the nerve root is often required to ...achieve total removal of the tumor, and the resection does not always result in postoperative neurological deficit. The present study was designed to determine the incidence and extent of neurological deficit as correlated with resection of the root, performed between 1976 and 1987 in 86 cases at the time of total removal of spinal schwannoma. Thirty-one patients underwent sacrifice of a root critical for the function of the upper (C5-T1, 14 cases) or the lower extremities (L3-S1, 17 cases). This report is limited to these 31 cases. Only seven patients (23%) developed detachable motor or sensory deficits postoperatively. All deficits were no more than partial loss of strength or sensation. Fifteen of the 31 patients had large tumors with extradural components, which necessitated sacrifice of the entire motor and sensory radix; however, 11 (76%) of these 15 did not develop any deficits referrable to the involved myotome or dermatome. Six cases showed histological characteristics of "neurofibroma," with axons intermingled in the tumor, and none developed a postoperative deficit. Preoperative electromyography was performed in 23 cases. Of 13 patients with findings of denervation, five developed deficits after surgery; the other 10 patients showed no evidence of denervation, and none had deficits after surgery. These results indicate that the spinal roots giving origin to schwannoma are frequently nonfunctional at the time of surgery, and risks of causing disabling neurological deficit after sacrificing these roots are small.
The medical records and histological specimens from 26 patients with choroid plexus papillomas operated on at one institution were reviewed retrospectively. Four patients died perioperatively, and 21 ...of the remaining 22 patients were followed through March, 1986; the patient lost to follow-up review was last seen 14 years postoperatively. Of the 14 patients who underwent gross total removal of their tumor, one had a recurrence at 11 years postoperatively and two died in the perioperative period. Of the 12 patients who underwent subtotal removal of their tumor, two died in the perioperative period. The two patients who did not have radiation therapy postoperatively are free of apparent disease at 6 and 8 years after their operation. Eight patients underwent radiation therapy after subtotal removal of their tumor; four of these remain alive and well, and four have died of progressive disease. The role of irradiation in the treatment of subtotally resected lesion remains controversial, but this therapy is thought to be indicated for recurrent disease after a surgical excision that is as complete as possible. Histopathologically, the presence of occasional mitotic figures, microscopic infiltration, ependymal differentiation, or mild to moderate atypia was not correlated with likelihood of complete resectability or tendency to recurrence.
A comprehensive review of the literature has shown that the treatment of choice for cerebellar astrocytomas has primarily been gross-total resection of the mass and gross-total resection of the ...enhancing portion of pilocytic astrocytomas. Most large scale studies of postresection survival rates of patients with cerebellar astrocytomas were conducted when computerized tomography (CT) and magnetic resonance (MR) imaging were not readily available. It has been shown that postoperative CT scans or MR images are more reliable than the surgeon's estimate of the degree of tumor resection at the time of surgery. It is not possible, therefore, to make an accurate determination regarding a postresection prognosis based on the degree of suspected tumor resection without the availability of appropriate radiographic imaging. In this study, the authors retrospectively evaluated the treatment of 54 patients with cerebellar astrocytoma who underwent surgery at the Mayo Clinic in Rochester, Minnesota, from 1978 through 1990. Preoperative and postoperative CT scans or MR images were available in all 54 patients.
The AO Universal Spine System thoracic pedicle hook design includes a fixation screw that passes obliquely through the inferior facet into the pedicle to engage in the posterior portion of the ...superior vertebral body endplate. This endplate screw provides additional purchase at the hook-bone interface. To determine the safety of this fixation system the authors reviewed the operative notes, radiographs, and outcomes of patients who underwent placement of endplate screws.
Thirty-six patients (16 male and 20 female patients) who required posterior thoracic instrumentation for spinal deformity (11 cases), neoplasm (15 cases), and traumatic injury (10 cases) were included in this study. One hundred sixty-four endplate screws were placed (mean 4.3/patient) to augment pedicle hooks for posterior thoracic instrumentation. The number of instrumented levels ranged from seven to 16. The positions of the screws in relation to the pedicle, neural foramen, spinal canal, and endplate were evaluated by assessing plain radiographs and computerized tomography scans (10 cases). Eighty-two screws (56%) were in ideal position. Lateral pedicle wall perforation occurred with 51 screws (35%). Three screws violated the medial wall and nine screws violated the superior or inferior walls of the pedicle. There were no clinical sequelae associated with any of the malpositioned screws. Adequate follow-up radiographic data were not available in five patients. The mean follow-up duration was 19.8 months (range 3-61 months). Two patients required revision surgery at 3 months and 18 months, respectively, because of hook/endplate screw displacement. There was also one case of an endplate screw fracture without hook displacement that was discovered during subsequent revision surgery. The remainder of the endplate screws and associated pedicles hooks maintained their original positions. There was no case of spinal cord, nerve root, pulmonary, or vascular injury.
The placement of supplemental endplate screws in conjunction with thoracic pedicle hooks can be conducted safely.
Preexisting hyperglycemia is associated with enhanced reperfusion injury in the postischemic rat brain. The goal of this study was to evaluate whether the hyperglycemic exacerbation of brain injury ...is associated with enhanced generation of hydroxyl radicals in rats subjected to middle cerebral artery occlusion (2 h), followed by reperfusion (2 h). Magnetic resonance images revealed the exacerbation of focal brain injury in hyperglycemic rats. The salicylate trapping method was used in conjunction with microdialysis to continuously estimate hydroxyl radical production by measurement of the stable adducts 2,3- and 2,5-dihydroxybenzoic acid (DHBA) during ischemia/reperfusion. In normoglycemic rats, from a mean baseline level of 130 nmol/l, 2,3-DHBA levels surged to peak levels of 194 nmol/l 45 min into ischemia and to 197 nmol/l 15–30 min into the reperfusion period, returning to baseline by 2 h into reperfusion. A similar temporal profile was observed in hyperglycemic rats, except that absolute 2,3-DHBA levels were higher (165 nmol/l at baseline, 317 nmol/l peak during ischemia, 333 nmol/l peak during reperfusion), and levels remained significantly high (
p < .05) throughout the reperfusion period. These results suggest that hydroxyl radical is an important contributor to the exacerbation of neuronal and cerebrovascular injury after focal ischemia/reperfusion in hyperglycemic rats.
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