Simultaneous compression and opacity data from time-series radiography with a Lagrangian marker.

Time-resolved radiography can be used to obtain absolute shock Hugoniot states by simultaneously measuring at least two mechanical parameters of the shock, and this technique is particularly suitable for one-dimensional converging shocks where a single experiment probes a range of pressures as the converging shock strengthens. However, at sufficiently high pressures, the shocked material becomes hot enough that the x-ray opacity falls significantly. If the system includes a Lagrangian marker such that the mass within the marker is known, this additional information can be used to constrain the opacity as well as the Hugoniot state. In the limit that the opacity changes only on shock heating, and not significantly on subsequent isentropic compression, the opacity of the shocked material can be determined uniquely. More generally, it is necessary to assume the form of the variation of opacity with isentropic compression or to introduce multiple marker layers. Alternatively, assuming either the equation of state or the opacity, the presence of a marker layer in such experiments enables the non-assumed property to be deduced more accurately than from the radiographic density reconstruction alone. An example analysis is shown for measurements of a converging shock wave in polystyrene at the National Ignition Facility.

Absolute Hugoniot measurements from a spherically convergent shock using x-ray radiography.

The canonical high pressure equation of state measurement is to induce a shock wave in the sample material and measure two mechanical properties of the shocked material or shock wave. For accurate measurements, the experiment is normally designed to generate a planar shock which is as steady as possible in space and time, and a single state is measured. A converging shock strengthens as it propagates, so a range of shock pressures is induced in a single experiment. However, equation of state measurements must then account for spatial and temporal gradients. We have used x-ray radiography of spherically converging shocks to determine states along the shock Hugoniot. The radius-time history of the shock, and thus its speed, was measured by radiographing the position of the shock front as a function of time using an x-ray streak camera. The density profile of the shock was then inferred from the x-ray transmission at each instant of time. Simultaneous measurement of the density at the shock front and the shock speed determines an absolute mechanical Hugoniot state. The density profile was reconstructed using the known, unshocked density which strongly constrains the density jump at the shock front. The radiographic configuration and streak camera behavior were treated in detail to reduce systematic errors. Measurements were performed on the Omega and National Ignition Facility lasers, using a hohlraum to induce a spatially uniform drive over the outside of a solid, spherical sample and a laser-heated thermal plasma as an x-ray source for radiography. Absolute shock Hugoniot measurements were demonstrated for carbon-containing samples of different composition and initial density, up to temperatures at which K-shell ionization reduced the opacity behind the shock. Here we present the experimental method using measurements of polystyrene as an example.

Lumbar disc nomenclature: version 2.0: Recommendations of the combined task forces of the North American Spine Society, the American Society of Spine Radiology and the American Society of Neuroradiology.

BACKGROUND CONTEXT: The paper ''Nomenclature and classification of lumbar disc pathology, recommendations of the combined task forces of the North American Spine Society, the American Society of Spine Radiology and the American Society of Neuroradiology,'' was published in 2001 in Spine (© Lippincott, Williams & Wilkins). It was authored by David Fardon, MD, and Pierre Milette, MD, and formally endorsed by the American Society of Spine Radiology (ASSR), American Society of Neuroradiology (ASNR), and North American Spine Society (NASS). Its purpose was to promote greater clarity and consistency of usage of spinal terminology, and it has served this purpose well for over a decade. Since 2001, there has been sufficient evolution in our understanding of the lumbar disc to suggest the need for revision and updating of the original document. The revised document is presented here, and it represents the consensus recommendations of contemporary combined task forces of the ASSR, ASNR, and NASS. This article reflects changes consistent with current concepts in radiologic and clinical care. PURPOSE: To provide a resource that promotes a clear understanding of lumbar disc terminology amongst clinicians, radiologists, and researchers. All the concerned need standard terms for the normal and pathologic conditions of lumbar discs that can be used accurately and consistently and thus best serve patients with disc disorders. STUDY DESIGN: This article comprises a review of the literature. METHODS: A PubMed search was performed for literature pertaining to the lumbar disc. The task force members individually and collectively reviewed the literature and revised the 2001 document. The revised document was then submitted for review to the governing boards of the ASSR, ASNR, and NASS. After further revision based on the feedback from the governing boards, the article was approved for publication by the governing boards of the three societies, as representative of the consensus recommendations of the societies. RESULTS: The article provides a discussion of the recommended diagnostic categories pertaining to the lumbar disc: normal; congenital/developmental variation; degeneration; trauma; infection/inflammation; neoplasia; and/or morphologic variant of uncertain significance. The article provides a glossary of terms pertaining to the lumbar disc, a detailed discussion of these terms, and their recommended usage. Terms are described as preferred, nonpreferred, nonstandard, and colloquial. Updated illustrations pictorially portray certain key terms. Literature references that provided the basis for the task force recommendations are included. CONCLUSIONS: We have revised and updated a document that, since 2001, has provided a widely acceptable nomenclature that helps maintain consistency and accuracy in the description of the anatomic and physiologic properties of the normal and abnormal lumbar disc and that serves as a system for classification and reporting built upon that nomenclature.

Lumbar disc nomenclature: version 2.0: recommendations of the combined task forces of the North American Spine Society, the American Society of Spine Radiology, and the American Society of Neuroradiology.

STUDY DESIGN: This article comprises a review of the literature pertaining to the normal and pathological lumbar disc and the compilation of a standardized nomenclature. OBJECTIVE: To provide a resource that promotes a clear understanding of lumbar disc terminology among clinicians, radiologists, and researchers. SUMMARY OF BACKGROUND DATA: The article "Nomenclature and Classification of Lumbar Disc Pathology. Recommendations of the Combined Task Forces of the North American Spine Society, American Society of Spine Radiology and American Society of Neuroradiology" was published in 2001 in Spine © Lippincott, Williams and Wilkins and formally endorsed by the 3 boards. Its purpose, which it served for well over a decade, was to promote greater clarity and consistency of usage of spine terminology. Since 2001, there has been sufficient evolution in our understanding of the lumbar disc to suggest the need for revision and updating. The document represents the consensus recommendations of the current combined task forces and reflects changes consistent with current concepts in radiological and clinical care. METHODS: A PubMed search was performed for literature pertaining to the lumbar disc. The task force members individually and collectively reviewed the literature and revised the 2001 document. It was then reviewed by the governing boards of the American Society of Spine Radiology, the American Society of Neuroradiology, and the North American Spine Society. After further revision based on their feedback, the paper was approved for publication. RESULTS: The article provides a discussion of the recommended diagnostic categories and a glossary of terms pertaining to the lumbar disc, a detailed discussion of the terms and their recommended usage, as well as updated illustrations and literature references. CONCLUSION: We have revised and updated a document that, since 2001, has provided a widely accepted nomenclature that helps maintain consistency and accuracy in the description of the properties of the normal and abnormal lumbar discs and that serves as a system for classification and reporting built upon that nomenclature.

Spine infections.

Infections of the spine represent a rare but potentially debilitating and neurologically devastating condition for patients. Early diagnosis, imaging, and intervention may prevent some of the more critical complications that may ensue from this disease process, including alignment abnormalities, central canal compromise, nerve root impingement, vascular complications, and spinal cord injury. This article reviews the underlying pathophysiologic basis of infection, clinical manifestations, and imaging modalities used to diagnose infections of the spine and spinal cord.

How is the balance between protein synthesis and degradation achieved?

Unlike most substances that cells manufacture, proteins are not produced and broken down by a common series of chemical reactions, but by completely different (independent and disconnected) mechanisms that possess no intrinsic means of making the rates of the two processes equal and attaining steady state concentrations. Balance between them is achieved extrinsically and is often imagined today to be the result of the actions of chemical feedback agents. But however instantiated, chemical feedback or any similar mechanism can only rectify induced imbalances in a system previously balanced by other means. Those "other means" necessarily involve reversible mass action or equilibrium-based interactions between native and altered forms of protein molecules somewhere in time and space between their synthesis and degradation.

The incoherence of the vesicle theory of protein secretion.

The rates at which cells secrete peptides and proteins must on average equal their rate of synthesis. This basic equality has unanticipated and seemingly categorical negative consequences for the vesicle theory of protein secretion. This is because the transport mechanisms it proposes, such as the budding and fusion of small vesicles and secretion by exocytosis, are not capable of balancing forces. What follows is an account of the analysis that leads to this conclusion.

The constancy of the internal environment: proteins in plasma.

The simple fact that there are normal concentrations of various proteins and peptides in blood has broad and surprising implications for how these molecules are released into and removed from the bloodstream by the cells of the body. If, as widely accepted, vesicle transport mechanisms such as exocytosis and endocytosis account for these events, then complex, presently unknown and seemingly unlikely mechanisms must exist to coordinate the rates of separate transport processes. The basis for this conclusion as well as the sole alternative method of transport, movement across permeable membranes, are discussed.

Oral gene therapy: a novel method for the manufacture and delivery of protein drugs.

Despite the great promise of a broadly based protein pharmaceutics, the use of protein drugs remains limited by drug availability due to the complexity and cost of manufacture, and patient compliance because of the need for needle injection. In this article we present proof of principle for a concept that avoids these difficulties and offers the prospect of greatly expanding the use and utility of protein drugs. Rather than the protein itself, the drug is a DNA plasmid that codes for it, that is swallowed, not injected. The protein is manufactured by the body in cells of the small intestine and is delivered by them into the bloodstream. The drug has a short-lived action and like other oral medications must be taken frequently (every day or two) to be effective. The short term of action is an advantage that provides for safe, easily managed treatment, unlike most gene-based therapies in use today. The dose of the drug can be altered from day to day, and treatment can be stopped quickly if untoward side effects are observed.

The Gene Pill and its therapeutic applications.

Gene delivery represents a revolutionary therapeutic approach with the potential for sustained protein production by the human body, leading to a convenient and effective method for systemic delivery of protein drugs. In this review, advantages of an orally administered DNA formulation, Gene Pill, are presented. Unlike previously described DNA delivery approaches, the Gene Pill enables DNA delivery in a non-invasive manner, leading to the secretion of therapeutic proteins into a patient's blood, supplanting the need for injection of therapeutic protein products. The Gene Pill also has potential for the development of oral DNA vaccination through expression of protein antigens in the gut lymphoid tissue. This approach limits the biodistribution of the delivered DNA to the gut and retains all of the safety advantages of non-viral gene delivery, including repeat dosing. Development of an oral DNA formulation involves overcoming several challenges, including depurination by low pH in the stomach, enzymatic degradation by DNases in the gut, crossing the physical barrier imposed by the mucus layer, cell entry, intracellular trafficking and nuclear uptake. The advantages of the Gene Pill technology, as well as challenges for its development, are presented in this review.

Conservation of digestive enzymes.

The traditional understanding is that an entirely new complement of digestive enzymes is secreted by the pancreas into the small intestines with each meal. This is thought to be necessary because, like food itself, these enzymes are degraded during digestion. In this review we discuss experiments that bring this point of view into question. They suggest that digestive enzymes can be absorbed into blood, reaccumulated by the pancreas, and reutilized, instead of being reduced to their constituent amino acids in the intestines. This is called an enteropancreatic circulation of digestive enzymes.