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Patricia B. Raksin, Noam Alperin, Anusha Sivaramakrishnan, Sushma Surapaneni and Terry Lichtor

Current techniques for intracranial pressure (ICP) measurement are invasive. All require a surgical procedure for placement of a pressure probe in the central nervous system and, as such, are associated with risk and morbidity. These considerations have driven investigators to develop noninvasive techniques for pressure estimation. A recently developed magnetic resonance (MR) imaging–based method to measure intracranial compliance and pressure is described. In this method the small changes in intracranial volume and ICP that occur naturally with each cardiac cycle are considered. The pressure change during the cardiac cycle is derived from the cerebrospinal fluid (CSF) pressure gradient waveform calculated from the CSF velocities. The intracranial volume change is determined by the instantaneous differences between arterial blood inflow, venous blood outflow, and CSF volumetric flow rates into and out of the cranial vault. Elastance (the inverse of compliance) is derived from the ratio of the measured pressure and volume changes. A mean ICP value is then derived based on a linear relationship that exists between intracranial elastance and ICP. The method has been validated in baboons, flow phantoms, and computer simulations. To date studies in humans demonstrate good measurement reproducibility and reliability. Several other noninvasive approaches for ICP measurement, mostly nonimaging based, are also reviewed. Magnetic resonance imaging–based ICP measurement may prove valuable in the diagnosis and serial evaluation of patients with a variety of disorders associated with alterations in ICP.

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Raghu Raghavan, Martin L. Brady, María Inmaculada Rodríguez-Ponce, Andreas Hartlep, Christoph Pedain and John H. Sampson

✓ Convection-enhanced delivery (CED) is the continuous injection under positive pressure of a fluid containing a therapeutic agent. This technique was proposed and introduced by researchers from the US National Institutes of Health (NIH) by the early 1990s to deliver drugs that would otherwise not cross the blood–brain barrier into the parenchyma and that would be too large to diffuse effectively over the required distances were they simply deposited into the tissue. Despite the many years that have elapsed, this technique remains experimental because of both the absence of approved drugs for intraparenchymal delivery and the difficulty of guaranteed delivery to delineated regions of the brain. During the first decade after the NIH researchers founded this analytical model of drug distribution, the results of several computer simulations that had been conducted according to more realistic assumptions were also published, revealing encouraging results. In the late 1990s, one of the authors of the present paper proposed the development of a computer model that would predict the distribution specific to a particular patient (brain) based on obtainable data from radiological images. Several key developments in imaging technology and, in particular, the relationships between image-obtained quantities and other parameters that enter models of the CED process have been required to implement this model. Note that delivery devices need further development.

In the present paper we review key features of CED as well as modeling of the procedure and indulge in informed speculation on optimizing the direct delivery of therapeutic agents into brain tissue.

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Daniel L. Surdell, Ziad A. Hage, Christopher S. Eddleman, Dhanesh K. Gupta, Bernard R. Bendok and H. Hunt Batjer

against bilateral middle cerebral artery ischemia after carotid artery occlusion: case report . Neurosurgery 45 : 367 – 361 , 1999 9 Bremmer JP , Verweij BH , van der Zwan A , : Sutureless nonocclusive bypass surgery in combination with an expanded polytetrafluoroethylene graft . J Neurosurg 107 : 1190 – 1197 , 2007 10 Brilstra EH , Rinkel GJ , Klijn CJ , : Excimer laser-assisted bypass in aneurysm treatment: short-term outcomes . J Neurosurg 97 : 1029 – 1035 , 2002 11 Charbel FT , Misra M , Clarke ME , : Computer

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W. Jeff Elias, Dibyendu Kumar Ray and John A. Jane Sr.

expert teacher and dissector of the brain. He believed brain dissection to be fundamental to any student of neuroscience as “no book, plastic model, or high-tech computer simulation can replace gross dissections as a vehicle for the study of the human brain.” 15 Only a few basic instruments and simple tissue fixation were required to provide lasting knowledge of the body’s most complex organ. Armed with only a brain knife and a formalin-fixed brain, he captivated audiences for hours and effectively imparted his vast knowledge of brain structure with a gentle and

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John S. Pezaris and Emad N. Eskandar

segregated, it presents the only location where it might be possible to selectively stimulate the 3 pathways, suggesting the possibility of independently controlling luminance and chrominance information. Based on high-fidelity computer simulations of microwire electrodes placed in the LGN, the physical extent of the area allows for the placement of substantial numbers of fine microwire contacts. 63 The most plausible format for implanting large numbers of microwires is to use a mechanism similar to the Ad-Tech Medical Instruments macro-micro system ( http

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Nicole C. H. Keong, Alonso Pena, Stephen J. Price, Marek Czosnyka, Zofia Czosnyka and John D. Pickard

to measure a transmantle pressure gradient have consistently failed to do so, making progressive ventriculomegaly in such conditions somewhat contradictory. In more recent work employing biomechanics, Pena et al. 61 developed a computer simulation model of acute obstructive hydrocephalus using Hakim's theory as a starting point to understand why periventricular edema was most prominent in the anterior and posterior horns of the lateral ventricles. A finite-element mesh was created based on the understanding of deformation mechanics as described by Biot

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Sudhakar Vadivelu, Harold L. Rekate, Debra Esernio-Jenssen, Mark A. Mittler and Steven J. Schneider

HJ , el Sakka W , Ko WH : Ventricular volume regulation: a mathematical model and computer simulation . Pediatr Neurosci 14 : 77 – 84 , 1988 18 Starling SP , Patel S , Burke BL , Sirotnak AP , Stronks S , Rosquist P : Analysis of perpetrator admissions to inflicted traumatic brain injury in children . Arch Pediatr Adolesc Med 158 : 454 – 458 , 2004 19 Stiver SI : Complications of decompressive craniectomy for traumatic brain injury . Neurosurg Focus 26 : 6 E7 , 2009 20 Vadivelu S , Esernio-Jenssen D , Rekate