BACKGROUND AND PURPOSE: Diffusion tensor imaging (DTI) may be a useful index of microstructural changes implicated in diffuse axonal injury (DAI) linked to persistent postconcussive symptoms, especially in mild traumatic brain injury (TBI), for which conventional MR imaging techniques may lack sensitivity. We hypothesized that for mild TBI, DTI measures of DAI would correlate with impairments in reaction time, whereas the number of focal lesions on conventional 3T MR imaging would not.

Memory and attentional control impairments are the two most common forms of dysfunction following mild traumatic brain injury (TBI) and lead to significant morbidity in patients, yet these functions are thought to be supported by different brain networks. This 3 T magnetic resonance diffusion tensor imaging (DTI) study investigates whether microstructural integrity of white matter, as measured by fractional anisotropy (FA) within a small set of individually localized regions of interest (ROIs), is associated with these cognitive domains in normal adults and adults with mild TBI. Results in a sample of 23 normal controls reveal a significant correlation between attentional control and FA within a ROI in the left hemisphere anterior corona radiata. Furthermore, the controls demonstrate a correlation between memory performance and FA in a ROI placed in the uncinate fasciculus. Next, to examine whether these relationships are found in the pathological ranges of attention, memory and microstructural white matter integrity associated with mild TBI, these analyses were applied to a group of 43 mild TBI patients. Results, which generally demonstrated a wider range of attention, memory and FA scores, replicated the correlation between attentional control and FA in left hemisphere anterior corona radiata, as well as the correlation between memory performance and FA in the uncinate fasciculus. These two sets of brain-behaviour relationships were highly specific, as shown by a lack of correlation between attention and uncinate fasciculus FA and the lack of correlation between memory performance and anterior corona radiata FA. Furthermore, a 'correlational double dissociation' was demonstrated to exist between two distinct frontal structures independently associated with attention and memory, respectively, via a series of multiple regression analyses in both normal controls and adults with mild TBI. The results of the multiple regression analyses provide direct evidence that tract-specific variation in microstructural white matter integrity among normal controls and among mild TBI patients can account for much of the variation in performance in specific cognitive domains. More generally, such findings suggest that diffusion anisotropy measurement can be used as a quantitative biomarker for neurocognitive function and dysfunction.

The paper presents an analysis of a variety of laboratory experiments substantiating the fact that caustic waterflooding can significantly improve waterflood recovery of certain low-gravity viscous crude oils. Success of the process depends on the presence of naturally occurring organic acids. Experiments show that caustic waterflooding can significantly increase oil recovery obtained before water breakthrough. Introduction Caustic injection as a method for improving waterflood oil recovery is not a new idea. U. S. Patent 1,651,311, covering waterflooding with sodium Patent 1,651,311, covering waterflooding with sodium hydroxide, was issued to H. Atkinson in Nov. 1927. There is no record of successful field application of the method described, however. In 1962 Leach et al. showed that caustic injection water could alter wettability and improve oil recovery in laboratory experiments, but the results of a small field trial were somewhat inconclusive. In 1970 Emery et al. showed that caustic injection could cause wettability reversal and improve the waterflood recovery of crude oil from the Singleton field, Nebraska, in laboratory experiments. A field trial of the process proved to be disappointing, however. The experiments described here show that there is an alternative to the wettability reversal mechanism by which caustic injection can significantly improve the recovery of certain crude oils. The mechanism involves the drastic reduction of oil-water interfacial tension by the caustic activation of potentially surface-active organic acids naturally occurring in the crude oil. The reduction of interfacial tension causes emulsification of crude oil in situ that tends to lower injected water mobility, damp the tendency toward viscous fingering, slow water channeling caused by reservoir stratification, and improve volumetric conformance or sweep efficiency. The laboratory caustic floods of viscous, lowgravity crude oils containing sufficient natural organic acids are characterized by improved recovery at water breakthrough and lower producing water-oil ratios (WOR). The mechanism involving lowered interfacial tension, in-situ emulsification, and water mobility reduction is supported by correlation of interfacial tension with recovery efficiency, observation of in-situ emulsification in thin, transparent glass bead packs accompanied by changes in areal sweep efficiency, and evidence that ultimate residual oil saturation or microscopic conformance in reservoir core material is not significantly affected by caustic injection. The process appears to have good economic potential for suitable crude oils. Sodium hydroxide is potential for suitable crude oils. Sodium hydroxide is an inexpensive material and most required concentrations for in-situ emusification range between 0.05 and 0.50 weight percent, about one-fifth the concentration usually specified for wettability reversal. Furthermore, slug injection of about 0.15 PV can sometimes be as effective as continuous injection in laboratory tests. Core Floods: Interfacial Tension and Caustic Concentration Core floods were carried out on preserved core samples using crude oil at reservoir temperature. Core samples were typically 3 in. long and 1 1/2 in. in diameter. Oil viscosity was adjusted to its reservoir value by addition of a few percent kerosene to compensate for loss of volatile components when necessary. JPT P. 1344

Proposals for caustic injection to improve waterflood oil recovery, have a Proposals for caustic injection to improve waterflood oil recovery, have a long history. Early work and a recent resurgence of research interest now present four fundamentally different mechanisms by which caustic can present four fundamentally different mechanisms by which caustic can operate, along with many process variations. Introduction The first patent on caustic for improved oil recovery was issued in the United States in 1927. Since then, an extensive published record of research and field testing has accumulated. There are now several proposed mechanisms by which caustic waterflooding may improve oil recovery. These include (1) emulsification and entrainment, (2) wettability reversal (oil-wet to waterwet), (3) wettability reversal (water-wet to oil-wet), and (4) emulsification and entrapment. Each mechanism requires somewhat different initial conditions with respect to reservoir oil, rock, and injection water properties, and each process is designed to improve oil recovery in a somewhat different manner. Oil-in-water emulsion injection as a means for improving waterflood efficiency is related to caustic flooding, but its development and field application is less advanced. The proposed mechanisms by which these oil recovery processes operate, the conditions required for successful application, recommended laboratory screening methods, and the published results of field testing are reviewed. Background Even before the issuance of Atkinson's patent on flooding oil-bearing sands with water containing caustic alkali, the benefits of alkaline flood water were well known. In 1917, Squires disclosed that "The displacement of oil may be made more complete by introducing an alkali into the water...." In 1925, Nutting described the use of alkaline salts such as sodium carbonate and sodium silicate for improving waterflood performance. Nutting dismissed stronger bases, such performance. Nutting dismissed stronger bases, such as sodium hydroxide, for field use because they were too reactive with crude oil and would be used up before they could be effective. Nevertheless, Atkinson's patent described the benefits of just such solutions of patent described the benefits of just such solutions of strong bases, including both sodium and potassium hydroxides. In 1927 Beckstrom and Van Tuyl also reported improvements in oil recovery using solutions of alkaline compounds. Although they preferred sodium carbonate, dilute solutions of sodium and potassium hydroxides also were shown to increase the yield of oil. In 1942, Subkow patented the injection of aqueous emulsifying agents for recovering heavy oil or bitumen. Sodium hydroxide was among the suitable emulsifying agents. Mechanisms The early workers were often vague about the mechanism by which caustic acted to increase waterflood oil recovery. Squires gave no reason for his statement that alkaline solutions were beneficial. Nutting believed that alkaline solutions released residual oil from adherence to sand surfaces. essentially a wettability change. He also noted that alkali prevented formation of semisolid, crude oil-water interfacial films, but he discounted the importance of this property in improving recovery. JPT P. 85

BACKGROUND AND PURPOSE In recent years, the role of CTA and CTP for vasospasm diagnosis in the setting of ASAH has been the subject of many research studies. The purpose of this study was to perform a meta-analysis of the diagnostic performance of CTA and CTP for vasospasm in patients with ASAH by using DSA as the criterion standard. MATERIALS AND METHODS The search strategy for research studies was based on the Cochrane Handbook for Systematic Reviews, including literature data bases (PubMed, Embase, Cochrane Database of Systematic Reviews, and the Web of Science) and reference lists of manuscripts published from January 1996 to February 2009. The inclusion criteria were the following: 1) published manuscripts, 2) original research studies with prospective or retrospective data, 3) patients with ASAH, 4) CTA or CTP as the index test, and 5) DSA as the reference standard. Three reviewers independently assessed the quality of these research studies by using the QUADAS tool. Pooled estimates of sensitivity, specificity, LR+, LR−, DOR, and the SROC curve were determined. RESULTS CTA and CTP searches yielded 505 and 214 manuscripts, respectively. Ten research studies met inclusion criteria for each CTA and CTP search. Six CTA and 3 CTP studies had sufficient data for statistical analysis. CTA pooled estimates had 79.6% sensitivity (95% CI, 74.9%–83.8%), 93.1% specificity (95% CI, 91.7%–94.3%), 18.1 LR+ (95% CI, 7.3–45.0), and 0.2 LR− (95% CI, 0.1–0.4); and CTP pooled estimates had 74.1% sensitivity (95% CI, 58.7%–86.2%), 93.0% specificity (95% CI, 79.6%–98.7%), 9.3 LR+ (95% CI, 3.4–25.9), and 0.2 LR− (95% CI, 0.04–1.2). Overall DORs were 124.5 (95% CI, 28.4–546.4) for CTA and 43.0 (95% CI, 6.5–287.1) for CTP. Area under the SROC curve was 98 ± 2.0% for CTA and 97 ± 3.0% for CTP. CONCLUSIONS The high diagnostic accuracy determined for both CTA and CTP in this meta-analysis suggests that they are potentially valuable techniques for vasospasm diagnosis in ASAH. Awareness of these results may impact patient care by providing supportive evidence for more effective use of CTA and CTP imaging in ASAH.

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Background and Purpose To prospectively evaluate the diagnostic accuracy of CT perfusion (CTP) and determine a quantitative threshold for delayed cerebral ischemia (DCI) in aneurysmal subarachnoid hemorrhage (SAH). Methods SAH patients were prospectively enrolled in an IRB approved protocol. CTP was performed during the typical time-period for DCI, between days 6–8 following SAH. Quantitative cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT) values were obtained using standard region-of-interest placement sampling gray matter. The reference standard for DCI is controversial and consisted of clinical and imaging criteria in this study. In a subanalysis of vasospasm, digital subtraction angiography was used as the reference standard. Receiver operating characteristic curves determined diagnostic accuracy using area under the curve. Optimal threshold values were calculated using patient population utility method. Results Ninety-seven patients were included; 41% (40/97) had DCI. Overall diagnostic accuracy was 93% CBF, 88% MTT and 72% CBV. Optimal threshold values were 35mL/100gm/min (90% sensitivity,68% specificity) for CBF and 5.5sec (73% sensitivity,79% specificity) for MTT. In the subanalysis (n=57), 63% (36/57) had vasospasm. Overall diagnostic accuracy was 94% CBF, 85% MTT and 72% CBV. Optimal threshold values were 36.5 mL/100gm/min (95% sensitivity,70% specificity) for CBF and 5.4 sec (78% sensitivity,70% specificity) for MTT. Conclusion CBF and MTT have the highest overall diagnostic accuracy. Threshold values of 35mL/100gm/min CBF and 5.5sec MTT are suggested for DCI based on patient population utility method. Absolute threshold values may not be generalizable due to differences in scanner equipment and post-processing methods.

A system composed of two immiscible fluid layers and heated from below is analyzed to determine its stability to convective motions. The model is applicable to the mantle if some fraction of the density increase with depth results from changes in chemical composition. For different parameter ranges, three modes of instability are possible: (1) convection of the entire depth of the fluid, (2) separate convection within each layer, and (3) overstability in the form of standing waves on the interface between layers. Earth models that include an increase in density due to iron enrichment below 650 km suggest that mantle convection can exist above and below but not through the 650‐km level. The model results are combined with a prior understanding of mineralogical phase changes to suggest a possible mechanism for the deepest earthquakes.