A Model for Research on the Blood–Brain Barrier Disruption Induced by Unsaturated Fatty Acid Emulsion

Unsaturated free fatty acid emulsion infusion into carotid artery enhances drug delivery to the rat brain

AIMS

To determine whether the blood-brain barrier (BBB) opens to enhance drug delivery during the acute stage of unsaturated fat embolism.

METHODS

We infused oleic, linoleic, and linolenic acid emulsions through the right common carotid artery of rats, followed by trypan blue for gross and lanthanum for electron microscopic (EM) examination. Doxorubicin and temozolomide were also administered, and then the rats were euthanized at 30 min, 1 h, and 2 h. Trypan blue hue was analyzed to semiquantitatively measure BBB opening. Desorption electrospray ionization-mass spectrometry (DESI-MS) imaging was used to evaluate drug delivery.

RESULTS

Trypan blue staining observed in each group 30 min after emulsion infusion increased at 1 h and decreased after 2 h in the oleic acid group. The linoleic and linolenic acid groups showed weak staining over time. The hue and trypan blue analysis results were corroborative. EM showed tight junction opening, whereas DESI-MS imaging showed increased doxorubicin and temozolomide signal intensities in ipsilateral hemispheres of all three groups.

CONCLUSION

We demonstrated that oleic, linoleic, and linolenic acid emulsions opened the BBB, promoting drug delivery to the brain. Hue analysis and DESI-MS imaging are appropriate for analysis of doxorubicin and temozolomide concentrations in brain tissue.

Is Oral Lipid-Based Delivery for Drug Targeting to the Brain Feasible?

This review outlines the feasibility of oral lipid-based targeted delivery of drugs to the brain, including permeation of the central nervous system's (CNS) protective blood-brain barrier (BBB). The structure of the BBB and disruption caused by varying disease states highlights the need for disease-specific approaches to alter permeation. Disruption during disease state, and the effects of certain molecules on the barrier, demonstrate the possibility of exploiting such BBB disruption for drug delivery. Many administration methods can be used to target the brain, but oral administration is considered ideal for chronic, long-term illnesses. Several lipids that have been shown to facilitate drug delivery into the brain after systemic administration, but could also be delivered orally are discussed, including oleic acid, triolein, alkylglycerol, and conjugates of linoleic and myristic acids. Current data reveal the potential for the use of such lipids as part of oral formulations for delivery to the brain by reaching sufficient plasma levels after administration to increase the permeability of the BBB. However, gaps in the literature remain regarding the concentrations and form of most lipids required to produce the desired effects. The use of lipids via oral delivery for brain targeting has not been investigated thoroughly enough to determine with certainty if similar permeability-enhancing effects would be observed as for parenteral administration. In conclusion, further research to fill research gaps is needed, but the limited evidence suggests that oral lipid-based drug delivery for brain targeting is potentially feasible.

Modulation of the Blood-Brain Barrier for Drug Delivery to Brain

The blood-brain barrier (BBB) precisely controls brain microenvironment and neural activity by regulating substance transport into and out of the brain. However, it severely hinders drug entry into the brain, and the efficiency of various systemic therapies against brain diseases. Modulation of the BBB via opening tight junctions, inhibiting active efflux and/or enhancing transcytosis, possesses the potential to increase BBB permeability and improve intracranial drug concentrations and systemic therapeutic efficiency. Various strategies of BBB modulation have been reported and investigated preclinically and/or clinically. This review describes conventional and emerging BBB modulation strategies and related mechanisms, and safety issues according to BBB structures and functions, to try to give more promising directions for designing more reasonable preclinical and clinical studies.

Myocardial Viability Imaging using Manganese-Enhanced MRI in the First Hours after Myocardial Infarction

Early measurements of tissue viability after myocardial infarction (MI) are essential for accurate diagnosis and treatment planning but are challenging to obtain. Here, manganese, a calcium analogue and clinically approved magnetic resonance imaging (MRI) contrast agent, is used as an imaging biomarker of myocardial viability in the first hours after experimental MI. Safe Mn2+ dosing is confirmed by measuring in vitro beating rates, calcium transients, and action potentials in cardiomyocytes, and in vivo heart rates and cardiac contractility in mice. Quantitative T1 mapping-manganese-enhanced MRI (MEMRI) reveals elevated and increasing Mn2+ uptake in viable myocardium remote from the infarct, suggesting MEMRI offers a quantitative biomarker of cardiac inotropy. MEMRI evaluation of infarct size at 1 h, 1 and 14 days after MI quantifies myocardial viability earlier than the current gold-standard technique, late-gadolinium-enhanced MRI. These data, coupled with the re-emergence of clinical Mn2+ -based contrast agents open the possibility of using MEMRI for direct evaluation of myocardial viability early after ischemic onset in patients.

Structure, Function, and Regulation of the Blood-Brain Barrier Tight Junction in Central Nervous System Disorders

The blood-brain barrier (BBB) allows the brain to selectively import nutrients and energy critical to neuronal function while simultaneously excluding neurotoxic substances from the peripheral circulation. In contrast to the highly permeable vasculature present in most organs that reside outside of the central nervous system (CNS), the BBB exhibits a high transendothelial electrical resistance (TEER) along with a low rate of transcytosis and greatly restricted paracellular permeability. The property of low paracellular permeability is controlled by tight junction (TJ) protein complexes that seal the paracellular route between apposing brain microvascular endothelial cells. Although tight junction protein complexes are principal contributors to physical barrier properties, they are not static in nature. Rather, tight junction protein complexes are highly dynamic structures, where expression and/or localization of individual constituent proteins can be modified in response to pathophysiological stressors. These stressors induce modifications to tight junction protein complexes that involve de novo synthesis of new protein or discrete trafficking mechanisms. Such responsiveness of BBB tight junctions to diseases indicates that these protein complexes are critical for maintenance of CNS homeostasis. In fulfillment of this vital role, BBB tight junctions are also a major obstacle to therapeutic drug delivery to the brain. There is an opportunity to overcome this substantial obstacle and optimize neuropharmacology via acquisition of a detailed understanding of BBB tight junction structure, function, and regulation. In this review, we discuss physiological characteristics of tight junction protein complexes and how these properties regulate delivery of therapeutics to the CNS for treatment of neurological diseases. Specifically, we will discuss modulation of tight junction structure, function, and regulation both in the context of disease states and in the setting of pharmacotherapy. In particular, we will highlight how these properties can be potentially manipulated at the molecular level to increase CNS drug levels via paracellular transport to the brain.

Doxorubicin concentration in brain remains high for one day after triolein emulsion infusion induced BBB opening

Aim: The purpose of this study was to assess changes in doxorubicin concentration in rabbit brain with respect to time after BBB opening induced by triolein emulsion infusion via a carotid artery and the mechanism of BBB opening.Materials and Methods: Doxorubicin (2.4 mg/kg) was infused immediately after triolein emulsion (1%) into rabbit carotid arteries. Bilateral hemispheres were harvested 2, 4, 6 12 and 24 h later and doxorubicin concentrations were measured fluorometrically. Doxorubicin concentration ratios of ipsilateral versus contralateral hemispheres were calculated, and a TEM study was performed to investigate the mechanism responsible for the increased vascular permeability induced by triolein.Results: Doxorubicin concentrations were higher in ipsilateral hemispheres at all time points, and peaked at 2 h after treatment. Doxorubicin was still detected in ipsilateral hemispheres at 24 h after treatment. TEM showed tight junction opening by triolein emulsion with lanthanum tracer spillage into neural interstitium and transcytotic vesicles.Conclusion: Doxorubicin was delivered into neural interstitium because of the increased vascular permeability of the BBB induced by triolein emulsion. Doxorubicin concentrations in brain peaked within 2 h of triolein and doxorubicin administration and remained high for 24 h. The study shows increased vascular permeability induced by triolein emulsion may involve paracellular and transcellular pathways.

Morphologic mechanisms of increased vascular permeability of triolein emulsion to the blood-brain barrier

Triolein emulsion has been known to increase vascular permeability in the brain when it is infused into the carotid artery. The purpose of this study was to identify the morphologic mechanism of increased vascular permeability in brain induced by infusion of emulsified triolein into the carotid artery by transmission electron microscopy (TEM). Triolein emulsion was infused into the carotid artery of rats. TEM using lanthanum tracer was used to evaluate morphologic changes in endothelium with a focus on transcytotic vesicles and tight junction opening. The treat group showed multiple transcytotic vesicles containing lanthanum tracer within endothelium on TEM. TEM also revealed that lanthanum tracer entered neural interstitium through tight junctions between capillary endothelial cells infrequently in the treat group. No evidence of transcytotic vesicles containing lanthanum tracer or lanthanum leakage through tight junctions was observed in the control group. Transcytosis and the opening of tight junctions appears the pathway for vascular permeability enhancement by triolein. This result could be utilized in studies on the blood-brain barrier and by those searching for chemotherapeutic methods that deliver anti-tumor agents to normally drug inaccessible organs.

Triolein Emulsion Infusion Into the Carotid Artery Increases Brain Permeability to Anticancer Agents

BACKGROUND

Triolein emulsion infusion into the carotid artery has been reported to induce temporary and reversible opening of the blood-brain barrier by increasing vascular permeability.

OBJECTIVE

To evaluate the effect of triolein emulsion infusion on brain permeance by anticancer agents.

METHODS

In the doxorubicin study. 2.4 mg/kg doxorubicin was injected immediately after triolein emulsion (1%, 1.5%, and 2%) infusion into rabbit carotid arteries. Two hours later, bilateral hemispheres and eyeballs were harvested, and doxorubicin concentrations were measured fluorometrically. Doxorubicin ratios of ipsilateral/contralateral hemispheres were compared with those of doxorubicin controls by use of the Kruskal-Wallis test followed by the Dunn test. In the cisplatin study, 10 mg/kg cisplatin was injected immediately after 2% triolein emulsion infusion into rat carotid arteries. Ipsilateral hemispheres were harvested 2, 6, 12, 24, and 36 hours after treatment. Time-dependent cisplatin concentrations were determined by liquid chromatography/electrospray ionization-tandem mass spectrometry/mass spectrometry.

RESULTS

Doxorubicin concentrations were significantly higher in ipsilateral hemispheres and eyeballs in all 3 triolein treatment groups than in doxorubicin controls. In the cisplatin study, cisplatin concentrations in the ipsilateral hemispheres peaked at 6 hours after infusion of cisplatin.

CONCLUSION

Brain permeance to anticancer agents was increased by triolein emulsion infusion, which suggests that triolein infusion might be a useful adjuvant treatment for brain tumors.

Hemorrhage in cerebral fat embolisms in a cat model using triolein dependent on the physical properties of triolein

PURPOSE

Hemorrhage is a finding of clinical fat embolism syndrome. The purpose of the present study was to evaluate the occurrence of hemorrhage in the cat brain by SW MR imaging after infusion of triolein as a bolus or as an emulsion into the carotid artery.

MATERIALS AND METHODS

Twenty-two cats were divided into two groups according to the type of triolein infused: group 1 (n = 11) was infused with a 0.1 ml triolein bolus, group 2 (n = 11) with triolein emulsion containing 0.1 ml triolein in 20 ml saline. SW imaging was performed before and after triolein infusion (at 2 h, 1 and 4 days). After MR imaging on day 4, cats were sacrificed and brains were immediately excised. Hemorrhage was evaluated using H&E staining.

RESULTS

Hemorrhage was observed in eight cats in group 1, in no cats in group 2. Hemorrhage on SW images was found to correspond with light microscopy.

CONCLUSIONS

SW images revealed hemorrhage in lesion hemispheres infused with triolein bolus. However, there was no evidence of hemorrhage infused with emulsified triolein. Thus, the occurrence of hemorrhage in cerebral fat embolism may depend on fat status.

Evaluation of a fibrin-binding gadolinium chelate peptide tetramer in a brain glioma model

PURPOSE

To compare a fibrin-targeted, high relaxivity gadolinium tetramer, EP-2104R, in terms of magnitude of contrast enhancement (CE) and temporal time course, to a conventional extracellular gadolinium chelate, in a brain glioma model at 1.5-T magnetic resonance imaging.

METHODS

Six rats were evaluated, with each animal receiving (for separate studies) 0.05 mmol/kg gadopentetate dimeglumine (Gd DTPA or Magnevist) and 0.0125 mmol/kg of EP-2104R, with the 2 magnetic resonance examinations separated in each animal by 24 hours. The compound (EP-2104R) was synthesized using published methodology, being comprised of an 11 amino acid peptide derivatized at both the C- and N-termini with Gd-DOTA-like (Dotarem-like) moieties. T1-weighted scans were acquired precontrast and for 5 consecutive 2-minute intervals postcontrast, and subsequently at 15 and 20 minutes postcontrast.

RESULTS

Maximum tumor contrast-to-noise and CE both occurred at 1 minute versus at 5 minutes following administration of Gd DTPA versus EP-2104R, respectively. Utilizing an equivalent dose on a Gd ion per body weight basis, signal-to-noise, contrast-to-noise, and CE were greater for EP-2104R at all time points postcontrast, yielding overall statistically significantly greater levels of all 3 parameters with the latter. With EP-2104R, improvements in CE ranged between 87% and 391%, increasing at each measured time postcontrast with the exception of a slight decrease from 15 to 20 minutes postadministration. Histopathology confirmed, using immunofluorescence technique, abnormally increased fibrin within the tumor.

CONCLUSIONS

Statistically significantly greater brain tumor enhancement was noted with greater lesion enhancement at all observed time points postcontrast for EP-2104R utilizing an equivalent concentration to Gd DTPA on a per gadolinium ion basis. These findings together with the prolonged time course of enhancement suggest possible fibrin-binding and altered distribution kinetics.

Blood-brain barrier experiments with clinical magnetic resonance imaging and an immunohistochemical study

OBJECTIVE

The purpose of study was to evaluate the feasibility of brain magnetic resonance (MR) images of the rat obtained using a 1.5T MR machine in several blood-brain barrier (BBB) experiments.

METHODS

Male Sprague-Dawley rats were used. MR images were obtained using a clinical 1.5T MR machine. A microcatheter was introduced via the femoral artery to the carotid artery. Normal saline (group 1, n = 4), clotted autologous blood (group 2, n = 4), triolein emulsion (group 3, n = 4), and oleic acid emulsion (group 4, n = 4) were infused into the carotid artery through a microcatheter. Conventional and diffusion-weighted images, the apparent coefficient map, perfusion-weighted images, and contrast-enhanced MR images were obtained. Brain tissue was obtained and triphenyltetrazolium chloride (TTC) staining was performed in group 2. Fluorescein isothiocyanate (FITC)-labeled dextran images and endothelial barrier antigen (EBA) studies were performed in group 4.

RESULTS

The MR images in group 1 were of good quality. The MR images in group 2 revealed typical findings of acute cerebral infarction. Perfusion defects were noted on the perfusion-weighted images. The MR images in group 3 showed vasogenic edema and contrast enhancement, representing vascular damage. The rats in group 4 had vasogenic edema on the MR images and leakage of dextran on the FITC-labeled dextran image, representing increased vascular permeability. The immune reaction was decreased on the EBA study.

CONCLUSION

Clinical 1.5T MR images using a rat depicted many informative results in the present study. These results can be used in further researches of the BBB using combined clinical MR machines and immunohistochemical examinations.

Intra-arterial delivery of triolein emulsion increases vascular permeability in skeletal muscles of rabbits

Background

To test the hypothesis that triolein emulsion will increase vascular permeability of skeletal muscle.

Methods

Triolein emulsion was infused into the superficial femoral artery in rabbits (triolein group, n = 12). As a control, saline was infused (saline group, n = 18). Pre- and post-contrast T1-weighted MR images were obtained two hours after infusion. The MR images were qualitatively and quantitatively evaluated by assessing the contrast enhancement of the ipsilateral muscles. Histologic examination was performed in all rabbits.

Results

The ipsilateral muscles of the rabbits in the triolein group showed contrast enhancement, as opposed to in the ipsilateral muscles of the rabbits in the saline group. The contrast enhancement of the lesions was statistically significant (p < 0.001). Histologic findings showed that most examination areas of the triolein and saline groups had a normal appearance.

Conclusion

Rabbit thigh muscle revealed significantly increased vascular permeability with triolein emulsion; this was clearly demonstrated on the postcontrast MR images.

Brain tumor enhancement in magnetic resonance imaging at 3 tesla: intraindividual comparison of two high relaxivity macromolecular contrast media with a standard extracellular gd-chelate in a rat brain tumor model

OBJECTIVES

The aim of this study was to evaluate lesion enhancement (LE) and contrast-to-noise ratio (CNR) properties of P846, a new intermediate sized, high relaxivity Gd-based contrast agent at 3 Tesla in a rat brain glioma model, and to compare this contrast agent with a high relaxivity, macromolecular compound (P792), and a standard extracellular Gd-chelate (Gd-DOTA).

MATERIALS AND METHODS

Seven rats with experimental induced brain glioma were evaluated using 3 different contrast agents, with each MR examination separated by at least 24 hours. The time between injections assured sufficient clearance of the agent from the tumor, before the next examination. P792 (Gadomelitol, Guerbet, France) and P846 (a new compound from Guerbet Research) are macromolecular and high relaxivity contrast agents with no protein binding, and were compared with the extracellular agent Gd-DOTA (Dotarem, Guerbet, France). T1w gradient echo sequences (TR/TE 200 milliseconds/7.38 milliseconds, flip angle = 90 degrees , acquisition time: 1:42 minutes:sec, voxel size: 0.2 x 0.2 x 2.0 mm, FOV = 40 mm, acquisition matrix: 256 x 256) were acquired before and at 5 consecutive time points after each intravenous contrast injection in the identical slice orientation, using a dedicated 4-channel head array animal coil. The order of contrast media injection was randomized, with however Gd-DOTA used either as the first or second contrast agent. Contrast agent dose was adjusted to compensate for the different T1 relaxivities of the 3 agents. Signal-to-noise ratio, CNR, and LE were evaluated using region-of-interest analysis. A veterinary histopathologist confirmed the presence of a glioma in each subject, after completion of the imaging study.

RESULTS

P792 showed significantly less LE as compared with Gd-DOTA within the first 7 minutes after contrast agent injection (P < 0.05) with, however, reaching comparable LE values at 9 minutes after injection (P = 0.07). However, P792 provided significantly less CNR as compared with Gd-DOTA (P < 0.05) for all examination time points. P846 provided comparable but persistent LE as compared with Gd-DOTA (P < 0.05) and demonstrated significantly greater LE and CNR when compared with P792 (P < 0.05). No statistically significant differences between CNR values for Gd-DOTA and P846 were noted for all examination time points (P < 0.05), with P846 administered at one-fourth the dose as compared with Gd-DOTA.

CONCLUSION

The intravascular contrast medium P792 showed significantly less LE and CNR in comparison to Gd-DOTA and P846, suggesting that it does not show marked extravasation from tumor neocapillaries and does not significantly cross the disrupted blood brain-barrier in this rat glioma model. In distinction, P846 provides comparable enhancement properties at a field strength of 3 Tesla to the extracellular contrast agent Gd-DOTA, using the adjusted dose, suggesting that it crosses the disrupted blood-brain-barrier and tumor capillaries, most likely based on the decreased molecular weight as compared with P792. At the same time, the high relaxivity of this compound allows for decreasing the injected gadolinium dose by a factor of 4 whereas providing comparable enhancement properties when compared with a standard extracellular Gd-chelate (Gd-DOTA) at a dose of 0.1 mmol/kg body weight.

In vivo myocardial infarct area at risk assessment in the rat using manganese enhanced magnetic resonance imaging (MEMRI) at 1.5T

The aim of this study was to measure the myocardial area at risk in rat, using MRI and manganese injection during a coronary occlusion/reperfusion model at 1.5T. A sequential protocol with occlusion and MnCl2 injection immediately followed by MRI was used with the assumption that MnCl2-induced contrast persistence is enough to accurately image the area at risk 90 min after occlusion. A total of 15 adult rats underwent a single 30-min episode of coronary occlusion followed by reperfusion. MnCl2 was injected (25 micromol/kg) at the beginning of the occlusion for 11 rats (group 1) and 6 h after reperfusion for four animals (group 2). A deficit of signal enhancement was observed in all rats. Hypoenhancement area in group 1 was correlated to the area at risk delineated by methylene blue (r=0.96, P<0.0001) whereas in group 2 it was correlated to the infarct area given by triphenyltetrazolium chloride (TTC) solution (r=0.98, P=0.003). The area at risk size was significantly correlated with left ventricle ejection fraction (LVEF), end-systolic volume and anterolateral wall thickening. This work demonstrates that hypoenhanced zone obtained after manganese injection during occlusion represents the area at risk and not only the infarct zone.

An apparent unidirectional influx constant for manganese as a measure of myocardial calcium channel activity

PURPOSE

To develop an in vivo MR method for evaluation of myocardial calcium channel activity through quantification of apparent unidirectional manganese influx constants following manganese dipyridoxyl-diphosphate (MnDPDP) infusions.

MATERIALS AND METHODS

A total of 10 healthy volunteers were divided in two groups, and received 5 micromol of MnDPDP per kg of body weight intravenously in a 1.5 Tesla scanner over five or 30 minutes, respectively. A fast inversion recovery gradient echo sequence was used to estimate pre- and postcontrast R1 values and to measure signal changes following infusions. By assuming equal longitudinal relaxivity (r1) of the contrast in all tissue compartments, signal changes in blood and myocardial tissue yielded temporal input and tissue contrast concentrations respectively. Through a two-tissue compartment model, apparent unidirectional influx constants (Ki) for myocardial manganese accumulation were estimated.

RESULTS

Consistent values for Ki in left ventricular wall were found, with a mean value of 5.96 mL/100 g/minute (SD=0.49; N=10). No statistical significant differences in Ki were found between the two infusion groups.

CONCLUSION

Since unidirectional manganese accumulation depends upon intact myocyte membranes with functioning calcium channels, the use of unidirectional manganese influx rates may be a valuable research tool for in vivo studies of myocyte functioning in myocardial disease.

Manganese dipyridoxyl-diphosphate (MnDPDP) as a viability marker in patients with myocardial infarction

PURPOSE

To evaluate contrast accumulation in left ventricular (LV) myocardium after manganese dipyridoxyl-diphosphate (MnDPDP) administration in patients with recent first time myocardial infarction.

MATERIALS AND METHODS

MnDPDP (5 micromol/kg) was administered to 10 patients with recent myocardial infarction (three to 12 weeks). One slice of interest (SOI) likely to traverse the infarction was chosen, and sectorial pre- and postcontrast longitudinal relaxivity rates (R(1)) and signal changes during infusion were estimated with a fast gradient echo sequence. LV volume and wall thickening were measured in short-axis cine recordings. Infarct localization from R(1) and wall thickening data were compared by vector analyses.

RESULTS

Reduced wall thickening was associated with reduced precontrast R(1) and reduced contrast enhancement. Both remote and infarcted regions showed rapid initial contrast accumulation. In remote regions, this was followed by a continuing slow increase. Mean precontrast R(1) was 0.87 +/- 0.06 second(-1) in infarcted regions and 0.96 +/- 0.03 second(-1) in remote regions (P < 0.001). Mean R(1) change over one hour was 0.24 +/- 0.07 second(-1) in infarcted regions and 0.38 +/- 0.03 second(-1) in remote regions (P < 0.0001).

CONCLUSION

Remote regions showed larger increases in R(1) than infarcted regions. This is most likely due to selective and slow Mn accumulation in viable myocytes.

Advances in Magnetic Resonance (2006)

Advances in the field of magnetic resonance (MR) as it pertains to clinical diagnostic radiology are examined in this review on the basis of publications in Investigative Radiology over the past 2 years (2005-2006). The articles published during that timeframe are discussed, organizationally wise, by anatomic region with an additional focus on studies involving MR contrast media.

Brain Tumor Enhancement in Magnetic Resonance Imaging

OBJECTIVE

The objective of this study was to compare the difference in lesion enhancement between 1.5 and 3 T using an extracellular gadolinium chelate in a rat brain glioma model.

METHODS

Five rats (CDF Fischer 344) with implanted C6/LacZ brain gliomas were evaluated using matched T1-weighted spin echo techniques and hardware configurations at 1.5 and 3 T. Serial imaging over 10 minutes after gadoteridol (ProHance) administration was performed. Contrast enhancement (CE), signal-to-noise ratios (SNR) for brain and tumor, as well as contrast-to-noise ratios (CNR) were evaluated using region-of-interest (ROI) analysis at both field strengths. All gliomas were also evaluated by histopathology.

RESULTS

CE at 3 T increased by 106% to 137% (all P<0.05) with maximum CE occurring at 5 minutes for both 1.5 and 3 T (9.8+/-2.2 vs 21.1+/-3.5; P=0.0004). At 3 T, SNR increased for normal brain by 66% to 76% (P<0.01) and SNR for tumor increased by 70% to 89% (P<0.01). CNR increased by 101% to 137% (P<0.05) depending on the time postcontrast. The highest CNR for both 1.5 T and 3 T occurred 5 minutes after contrast (1.5 T: 9.4+/-1.1 vs 3 T: 20.3+/-2.4; P<0.0004).

CONCLUSION

Using a standardized animal model and matched scan techniques, this study shows a significant benefit of 3 T compared with 1.5 T in contrast-enhanced brain tumor magnetic resonance imaging.

Essential fatty acids and the brain: from infancy to aging

The major effects of essential fatty acids (EFA) on brain structure and functions are reviewed. EFA determine the fluidity of neuronal membrane and control the physiological functions of the brain. EFA is also involved in synthesis and functions of brain neurotransmitters, and in the molecules of the immune system. Since they must be supplied from the diet, a decreased bioavailability is bound to induce major disturbances. While the brain needs a continuous supply during the life span, there are two particularly sensitive periods-infancy and aging. EFA deficiency during infancy delays brain development, and in aging will accelerate deterioration of brain functions. In discussing the role of EFA two issues must be considered-the blood-brain barrier, which determines the bioavailability, and the myelination process, which determines the efficiency of brain and retinal functions.