Search for γ-Ray Line Signals from Dark Matter Annihilations in the Inner Galactic Halo from 10 Years of Observations with H.E.S.S

Spectral lines are among the most powerful signatures for dark matter (DM) annihilation searches in very-high-energy γ rays. The central region of the Milky Way halo is one of the most promising targets given its large amount of DM and proximity to Earth. We report on a search for a monoenergetic spectral line from self-annihilations of DM particles in the energy range from 300 GeV to 70 TeV using a two-dimensional maximum likelihood method taking advantage of both the spectral and spatial features of the signal versus background. The analysis makes use of Galactic center observations accumulated over ten years (2004-2014) with the H.E.S.S. array of ground-based Cherenkov telescopes. No significant γ-ray excess above the background is found. We derive upper limits on the annihilation cross section ⟨σv⟩ for monoenergetic DM lines at the level of 4×10^{-28}  cm^{3} s^{-1} at 1 TeV, assuming an Einasto DM profile for the Milky Way halo. For a DM mass of 1 TeV, they improve over the previous ones by a factor of 6. The present constraints are the strongest obtained so far for DM particles in the mass range 300 GeV-70 TeV. Ground-based γ-ray observations have reached sufficient sensitivity to explore relevant velocity-averaged cross sections for DM annihilation into two γ-ray photons at the level expected from the thermal relic density for TeV DM particles.

H.E.S.S. Limits on Linelike Dark Matter Signatures in the 100 GeV to 2 TeV Energy Range Close to the Galactic Center

A search for dark matter linelike signals iss performed in the vicinity of the Galactic Center by the H.E.S.S. experiment on observational data taken in 2014. An unbinned likelihood analysis iss developed to improve the sensitivity to linelike signals. The upgraded analysis along with newer data extend the energy coverage of the previous measurement down to 100 GeV. The 18 h of data collected with the H.E.S.S. array allow one to rule out at 95% C.L. the presence of a 130 GeV line (at l=-1.5°, b=0° and for a dark matter profile centered at this location) previously reported in Fermi-LAT data. This new analysis overlaps significantly in energy with previous Fermi-LAT and H.E.S.S.

RESULTS

No significant excess associated with dark matter annihilations was found in the energy range of 100 GeV to 2 TeV and upper limits on the gamma-ray flux and the velocity weighted annihilation cross section are derived adopting an Einasto dark matter halo profile. Expected limits for present and future large statistics H.E.S.S. observations are also given.

Search for Dark Matter Annihilations towards the Inner Galactic Halo from 10 Years of Observations with H.E.S.S

The inner region of the Milky Way halo harbors a large amount of dark matter (DM). Given its proximity, it is one of the most promising targets to look for DM. We report on a search for the annihilations of DM particles using γ-ray observations towards the inner 300 pc of the Milky Way, with the H.E.S.S. array of ground-based Cherenkov telescopes. The analysis is based on a 2D maximum likelihood method using Galactic Center (GC) data accumulated by H.E.S.S. over the last 10 years (2004-2014), and does not show any significant γ-ray signal above background. Assuming Einasto and Navarro-Frenk-White DM density profiles at the GC, we derive upper limits on the annihilation cross section ⟨σv⟩. These constraints are the strongest obtained so far in the TeV DM mass range and improve upon previous limits by a factor 5. For the Einasto profile, the constraints reach ⟨σv⟩ values of 6×10^{-26}  cm^{3} s^{-1} in the W^{+}W^{-} channel for a DM particle mass of 1.5 TeV, and 2×10^{-26}  cm^{3} s^{-1} in the τ^{+}τ^{-} channel for a 1 TeV mass. For the first time, ground-based γ-ray observations have reached sufficient sensitivity to probe ⟨σv⟩ values expected from the thermal relic density for TeV DM particles.

A three-dimensional finite element model of maximal grip loading in the human wrist

The aim of this work was to create an anatomically accurate three-dimensional finite element model of the wrist, applying subject-specific loading and quantifying the internal load transfer through the joint during maximal grip. For three subjects, representing the anatomical variation at the wrist, loading on each digit was measured during a maximal grip strength test with simultaneous motion capture. The internal metacarpophalangeal joint load was calculated using a biomechanical model. High-resolution magnetic resonance scans were acquired to quantify bone geometry. Finite element analysis was performed, with ligaments and tendons added, to calculate the internal load distribution. It was found that for the maximal grip the thumb carried the highest load, an average of 72.2 +/- 20.1 N in the neutral position. Results from the finite element model suggested that the highest regions of stress were located at the radial aspect of the carpus. Most of the load was transmitted through the radius, 87.5 per cent, as opposed to 12.5 per cent through the ulna with the wrist in a neutral position. A fully three-dimensional finite element analysis of the wrist using subject-specific anatomy and loading conditions was performed. The study emphasizes the importance of modelling a large ensemble of subjects in order to capture the spectrum of the load transfer through the wrist due to anatomical variation.

The relation between MRI neuroactivation changes and response rate on a word-fluency task

This study investigated the functional magnetic resonance imaging response of the left premotor cortex activated during a word-fluency task. We hypothesized that a cortical region crossing the boundary between Brodmann's areas 44 and 6 would show bias toward output during word generation (i.e., the more words generated the greater the activation), supporting the view that this region is involved in the motor planning of speech rather than the search component of word generation. Ten participants were shown letters with different word-generational frequencies, and these were correlated with magnetic resonance signal changes over the region. Significant differences (p = .05) were found in the neuroactivation changes between groups of letters associated with high and low overt frequencies. This finding supports our hypothesis concerning the role of areas 44 and 6 in word-generation tasks.

The ferromagnetic pillow: a potential MR hazard not detectable by a hand-held magnet

This paper describes an incident in which an apparently normal hospital pillow became a ferromagnetic missile when brought into the proximity of a 1.5 T MR system owing to a fine internal spring system within the pillow. Measurements revealed that the 1 kg pillow reached a maximum velocity of 33.7 km h(-1) after undergoing a maximum acceleration of 9.9g. Non-pathological cervical spines should sustain the measured forces and torques without significant injury. However, the effect could be injurious or even fatal to patients suffering from an existing cervical instability, for example due to rheumatoid arthritis. Of more general concern is the fact that the use of a powerful hand-held magnet did not reveal the presence of ferromagnetic components in this instance. Large objects containing sparsely distributed ferromagnetic materials may not be deflected by such a magnet but could still represent a hazard in the MR environment.

Method of determination of three dimensional index finger moment arms and tendon lines of action using high resolution MRI scans

High-resolution MRI scans, in conjunction with CAD software, were used to determine the three-dimensional moment arms and force vector direction cosines for 11 structures passing the interphalangeal and metacarpophalangeal joints of the index finger. The results are presented for five different angles of joint flexion for a single subject. The moment arm data obtained differ from previous studies, where results have been derived from tendon excursion techniques or geometrical models. These dissimilarities have been accounted for by the differences in experimental techniques.

Thermal injuries associated with MRI

Most physicians are aware of the absolute contraindications to magnetic resonance imaging (MRI). However, less familiar is the potential for an MRI-induced thermal or electrical burn associated with electrical monitoring devices. Although detailed studies concerning the burn hazard in MRI have not been reported, it is widely believed that direct electromagnetic induction in looped cables associated with the patient is responsible for the excessive heating and it is on this theory that present guidelines are based. Recent reports have however indicated that other mechanisms may cause the heating of metal, either in or on the patient. This document reviews numerous reported burn injuries sustained during MRI and addresses the underlying heating mechanisms possibly causing these events.

Investigation of the factors responsible for burns during MRI

Numerous reported burn injuries have been sustained during clinical MRI procedures. The aim of this study was to investigate the possible factors that may be responsible for such burns. Experiments were performed to investigate three possible mechanisms for causing heating in copper wire during MRI: direct electromagnetic induction in a conductive loop, induction in a resonant conducting loop, and electric field resonant coupling with a wire (the antenna effect). Maximum recorded temperature rises were 0.6 degrees C for the loop, 61.1 degrees C for the resonant loop, and 63.5 degrees C for the resonant antenna. These experimental findings suggest that, contrary to common belief, it is unlikely that direct induction in a conductive loop will result in thermal injury. Burn incidents are more likely to occur due to the formation of resonant conducting loops and from extended wires forming resonant antenna. The characteristics of resonance should be considered when formulating safety guidelines.

Estimation of torque on mechanical heart valves due to magnetic resonance imaging including an estimation of the significance of the Lenz effect using a computational model

Mitral and aortic valve replacement is a procedure which is common in cardiac surgery. Some of these replacement valves are mechanical and contain moving metal parts. Should the patient in whom such a valve has been implanted be involved in magnetic resonance imaging, there is a possible dangerous interaction between the moving metal parts and the static magnetic field due to the Lenz effect. Mathematical models of two relatively common forms of single-leaflet valves have been derived and the magnitude of the torque which opposes the motion of the valve leaflet has been calculated for a valve disc of solid metal. In addition, a differential model of a ring-strengthener valve type has been considered to determine the likely significance of the Lenz effect in the context of the human heart. For common magnetic field strengths at present, i.e. 1 to 2 T, the effect is not particularly significant. However, there is a marked increase in back pressure as static magnetic field strength increases. There are concerns that, since field strengths in the range 3 to 4 T are increasingly being used, the Lenz effect could become significant. At 5 to 10 T the malfunction of the mechanical heart valve could cause the heart to behave as though it is diseased. For unhealthy or old patients this could possibly prove fatal.

Potential MR hazard to patients with metallic heart valves: the Lenz effect

The Lenz effect on the motion of metal containing moving parts of artificial heart valves has not been considered to date. In this paper the basic theory is outlined and a simple model applied to estimate worst-case forces on such valves. The results indicate a potential for forces over 100 times greater than for the more widely recognized ferromagnetic interation. Resistive pressure effects comparable to cardiac pressure differences may occur for such valves in the mitral position even at fields as low as 1.5 T. The effect will increase linearly with field strength. Additional monitoring and perhaps even exclusion of such patients may be prudent, even at 1.5 T.

Early 1H magnetic resonance spectroscopy of acute head injury: four cases

In an attempt to examine in vivo the early metabolic consequences of severe acute head injury, 1H MRS was performed in four patients from 8 to 25 h (mean 15 h) following trauma. In three of these patients, decompressive surgery was performed 4-5 h prior to the MRS. High levels of lactate (area of lactate peak >50% of the mean areas of the NAA, choline-containing, and creatine-containing compound peaks) were found at 8 h posttrauma in the one patient who was not operated on and at 10 h posttrauma in one of the patients who underwent surgery. In the other two postoperative patients, at 18 and 25 h after trauma, lactate levels were found to be low (lactate peak <20% of the mean area of the other three peaks). In the one patient who had a follow-up at 6 days and who had the largest initial lactate levels, these remained high. These findings suggest that high levels of lactate may not be an inevitable consequence of severe head injury and that similar MRS studies should be performed on each individual patient before therapies to reduce lactate are considered. There appeared to be no correlation between the relative amounts of lactate and outcome.

Structure and functional relationships in human pur H

1. The human pur H (ATIC) gene encoding a bifunctional protein, hPurH, which carries the penultimate and final enzymatic activities of the purine nucleotide synthesis pathway, AICARFT & IMPCH, has been cloned and sequenced. The gene product, hPurH has been overexpressed in E. coli, purified to homogeneity and crystallized. 2. The human pur H gene lies on chromosome 2, between band q34 and q35. There is at least one intron of 278 bp near the 5' end. 3. Truncation mutant studies demonstrate two non-overlapping functional domains in the protein arranged as indicated in Figure 5. The existence of a linker or interaction region between the catalytic domains remains to be established. 4. Cleland-type kinetic inhibition experiments indicate that the AICARFT reaction is of the ordered, sequential type with the reduced folate cofactor binding first. 5. The reaction has a broad pH optimum in the alkaline range, with a maximum at about pH 8.2. 6. Preliminary transient phase kinetic studies show the presence of a "burst" indicating that a late step in the reaction sequence is rate limiting. 7. A PurH crystal structure is that of a dimer, with a putative single binding site for the reduced folate cofactor formed using elements from each of the monomer subunits. Probable binding sites for AICAR and FAICAR can be identified on each monomer. 8. Equilibrium sedimentation studies show hPurH apoprotein to be a monomer:dimer equilibrium mixture with a kD of 0.55 uM. 9. The crystal structure has permitted identification of a number of candidate amino acid residues likely to be involved in catalysis and/or substrate binding. Among these, we have thus far completed studies on two, Lysine 265 and Histidine 266. These appear to be critically involved in the AICARFT reaction, although whether their role(s) are in catalysis or binding remains to be determined.

Errors in MR stereotaxy due to undetected extraneous metal objects

MR stereotaxic procedures are being increasingly used, particularly in functional neurosurgery where very high levels of localization accuracy are required. Whilst many studies have investigated intrinsic causes of non-linearity, potential errors due to an extrinsic cause are not generally appreciated. It is not uncommon to find objects such as hair clips, paper clips and pins inside high-field magnets. They can remain undetected for long periods because they can reach positions not open to visual inspection and because they often do not produce observable deterioration in routine image quality. In this study we measured the maximum absolute positional shifts caused by such objects and found that these can be significant (> 1 mm, even up to 200 mm from one such object). Additional measurements were performed using an MR compatible Leksell stereotaxic frame to calculate actual stereotaxic coordinate errors. The encompassing nature of the frame is such that some degree of compensation for such nonlinearities is inherent, and so errors for areas of the brain more proximal to the object are found to be reduced but not eliminated. Stereotaxic coordinate errors will not be reduced in nonencompassing designs and in frameless stereotaxy. The prevalence of such objects in clinical systems and the measures required to detect their presence are discussed. The need for quality control testing before each stereotaxic procedure is highlighted.

Early changes in peritumorous oedema and contralateral white matter after dexamethasone: a study using proton magnetic resonance spectroscopy

AIMS

To study the mechanism of action of steroids in patients with peritumorous oedema.

METHODS

To investigate early cerebral metabolic changes proton magnetic resonance spectroscopy (1H-MRS) was used before and 11 to 14 hours after treatment with dexamethasone (12 mg oral loading and 4 mg four times daily maintenance). Nine patients (two men, seven women, mean age 54) with pronounced oedema associated with various intracranial tumours (two astrocytomas, three meningiomas, two glioblastoma, and two metastases) were examined using MRI and MRS. SE1500/135 volume selected MRS (mean volume 21 ml) were performed on an oedematous region and a contralateral region. All spectra were acquired with and without water suppression. Metabolite peak area ratios were determined.

RESULTS

Regions of oedema had significantly (P < 0.01) higher unsuppressed water than the contralateral regions, as expected. There was no change at this early time point after dexamethasone. The ratio of the area of choline containing compounds to that creatine and phosphocreatine compounds was determined after which the serial ratios of these before and after were calculated (a serial ratio of 1.0 would indicate no change in the choline to creatine ratios after steroid administration). The mean serial ratios for the area of oedema were 1.02 (SEM 0.08) and 1.10 (0.08) for the contralateral volume of interest, indicating no significant changes. However, significant changes (P < 0.02) were found in the N-acetyl-aspartate (NAA)/choline serial ratios (0.86 (0.06) in the area of oedema, 1.20 (0.10) in contralateral brain) and the NAA/creatine serial ratios (0.86 (0.08) for the oedema, 1.25 (0.11) in contralateral brain).

CONCLUSIONS

Such rapid changes may be explained either by relatively large alterations in the relaxation characteristics of NAA or, more controversially, by actual changes in the amounts of NAA. It is proposed that steroids act primarily by causing early metabolic changes that are later expressed in improvements in intracranial volume relations.

Habituation-like effects cause a significant decrease in response in MRI neuroactivation during visual stimulation

A wide range of rest/stimulus cycle durations (40-360 sec) is reported to have been used by various groups for MRI neuroactivation studies of the visual cortex. In this paper we demonstrate a clear habituation-like response for longer cycle durations which results in a halving of apparent activation between cycle durations of 138 and 276 sec. This has important implications, not only in terms of optimizing the technique, but also in providing an insight into the underlying physiological mechanisms.

Single-chain recombinant human cytomegalovirus protease. Activity against its natural protein substrate and fluorogenic peptide substrates

We report here the production of active recombinant single-chain human cytomegalovirus protease in Escherichia coli and development of a continuous assay for this protease. In order to produce the human cytomegalovirus (HCMV) protease for structural studies and accurate kinetic analysis, mutation of alanine 143 at an internal cleavage site was introduced to prevent auto-proteolysis. The resulting soluble 29-kDa A143Q protease was purified to homogeneity as a stable single-chain protein by hydrophobic interaction and ionic-exchange chromatography. The in vivo protein substrate, assembly protein precursor, was also expressed and purified for activity studies. To develop a continuous protease assay, fluorescent synthetic peptide substrates similar to the cleavage sequence P5 to P5' of the maturation site containing anthranilic acid and nitrotyrosine as a resonance energy transfer donor-acceptor pair were designed. Purified HCMV A143Q protease cleaved the recombinant assembly protein precursor with Km and kcat values of 3.0 +/- 1.0 microM and 13.3 +/- 1.6 min-1. The Km for peptide substrates is at least 45-fold higher than for the natural protein substrate, but the kcat values are similar. A sensitive assay was developed using fluorescent peptide substrates, which can detect nM HCMV protease activity.

Characterization of the Phe-81 and Val-82 human fibroblast collagenase catalytic domain purified from Escherichia coli

Soluble recombinant human fibroblast collagenase catalytic domain was highly expressed and purified from Escherichia coli. The expression construct utilized the T7 gene 10 promoter for transcription of a two-cistron messenger RNA which encoded the ubiquitin-collagenase catalytic domain fusion protein as the second cistron. The ubiquitin domain was attached to the collagenase catalytic domain with the linker sequences Gly-Gly-Thr-Gly-Asp-Val-Ala-Gln (wild type) or Gly-Gly-Thr-Gly-Asp-Val-Gly-His (mutant) which served as cleavage sites for in vitro activation. The last four residues of the linker were included based on the crystal structure of human prostromelysin-1 catalytic domain. Soluble fusion proteins purified from E. coli retained the proteolytic activity of the collagenase catalytic domain. The collagenase catalytic domain was released by either autoproteolytic or stromelysin-1-catalyzed cleavage, purified to homogeneity, and separately possess Phe-81, Val-82, or Leu-83 as the amino-terminal residue. Very similar kcat/Km values were determined for the Phe-81 and Val-82 forms using continuous fluorogenic and chromogenic peptide cleavage assays.

Structure of human rhinovirus 3C protease reveals a trypsin-like polypeptide fold, RNA-binding site, and means for cleaving precursor polyprotein

The structure of human rhinovirus-14 3C protease (3Cpro) has been determined at 2.3 A resolution and refined to an R factor of 0.22. This cysteine protease folds into two topologically equivalent six-stranded beta barrels and in this sense is similar to trypsin-like serine proteases. However, there are differences in the lengths and positioning of individual beta strands as well as in loops connecting elements of secondary structure. The catalytic residues Cys-146, His-40, and Glu-71 are positioned as in serine proteases, but the oxyanion hole is moved 1-1.2 A away. Residues that bind to the 5' noncoding region of rhinovirus genomic RNA are located on the opposite side of the molecule from the active site. Interactions between individual 3Cpro molecules in the crystal lattice suggest a model for intermolecular proteolytic cleavage of the 3CD polyprotein.

Short communication: acoustic noise levels during magnetic resonance imaging scanning at 1.5 T

Although much has been published concerning the various safety risks associated with magnetic resonance (MR) imaging, little mention is made of the acoustic noise generated during scanning. The existing data are now out of date with regard to currently used imaging protocols and technology. Out of concern for patient safety, measurements were made of the acoustic noise generated during various scan protocols on a high field (1.5 T) Siemens MR imager. These data were compared with published data. The data show that for certain protocols, the exposure to acoustic noise falls outside safety guidelines unless ear protection is used.

Intracranial deformation caused by brain tumors: assessment of 3-D surface by magnetic resonance imaging

A shape analysis technique has been developed to quantify intracranial deformation as a means of objectively assessing treatment for brain tumor. Conventional measurements of tumor volume are prone to ambiguity and error, so instead the authors are investigating the secondary space occupying effects of tumor, namely the deformation of structures within the brain. In order to avoid surface segmentation problems in MR images and to facilitate computation, the B-splines method has been introduced to approximate digital 3-D image surfaces. Using the mean curvature and the Gaussian curvature the authors classify a surface into 4 basic types: planar, parabolic, elliptic, and hyperbolic. The deformation of a surface can be described by measuring the geometric changes in these basic types. The method is independent of size, domain (translation), and viewpoint (rotation). These invariance properties are important as they overcome problems caused by wide variations in brain size within the normal population as well as small differences in patient orientation during acquisition. Experimental results show the potential of the technique in objectively monitoring patient response to treatment.

Changes in intracranial CSF volume after lumbar puncture and their relationship to post-LP headache

Post-lumbar puncture (LP) headache may be due to "low CSF pressure", leading to stretching of pain sensitive intracranial structures. The low intracranial pressure is secondary to net loss of intracranial CSF. It has, however, not been possible to measure intracranial CSF volume accurately during life until recently. Intracranial CSF volume can now be measured non-invasively by a MRI technique. The changes in intracranial CSF volume were studied in 20 patients who had LP. Total intracranial CSF volume was reduced in 19 of the 20 patients 24 hours after LP (range -1.8 mls to -158.6 mls). Most of the CSF was lost from the cortical sulci. Very large reductions in intracranial CSF volume were frequently related to post-LP headache but some patients developed headache with relatively little alteration in the intracranial CSF volume. There was not a measurable change in position of the intracranial structures following LP.

Comparison of magnetic resonance imaging and computed tomography in suspected lesions in the posterior cranial fossa

OBJECTIVE

To compare computed tomography and magnetic resonance imaging in investigating patients suspected of having a lesion in the posterior cranial fossa.

DESIGN

Randomised allocation of newly referred patients to undergo either computed tomography or magnetic resonance imaging; the alternative investigation was performed subsequently only in response to a request from the referring doctor.

SETTING

A regional neuroscience centre serving 2.7 million.

PATIENTS

1020 Patients recruited between April 1986 and December 1987, all suspected by neurologists, neurosurgeons, or other specialists of having a lesion in the posterior fossa and referred for neuroradiology. The groups allocated to undergo computed tomography or magnetic resonance imaging were well matched in distributions of age, sex, specialty of referring doctor, investigation as an inpatient or an outpatient, suspected site of lesion, and presumed disease process; the referring doctor's confidence in the initial clinical diagnosis was also similar.

INTERVENTIONS

After the patients had been imaged by either computed tomography or magnetic resonance (using a resistive magnet of 0.15 T) doctors were given the radiologist's report and a form asking if they considered that imaging with the alternative technique was necessary and, if so, why; it also asked for their current diagnoses and their confidence in them.

MAIN OUTCOME MEASURES

Number of requests for the alternative method of investigation. Assessment of characteristics of patients for whom further imaging was requested and lesions that were suspected initially and how the results of the second imaging affected clinicians' and radiologists' opinions.

RESULTS

Ninety three of the 501 patients who initially underwent computed tomography were referred subsequently for magnetic resonance imaging whereas only 28 of the 493 patients who initially underwent magnetic resonance imaging were referred subsequently for computed tomography. Over the study the number of patients referred for magnetic resonance imaging after computed tomography increased but requests for computed tomography after magnetic resonance imaging decreased. The reason that clinicians gave most commonly for requesting further imaging by magnetic resonance was that the results of the initial computed tomography failed to exclude their suspected diagnosis (64 patients). This was less common in patients investigated initially by magnetic resonance imaging (eight patients). Management of 28 patients (6%) imaged initially with computed tomography and 12 patients (2%) imaged initially with magnetic resonance was changed on the basis of the results of the alternative imaging.

CONCLUSIONS

Magnetic resonance imaging provided doctors with the information required to manage patients suspected of having a lesion in the posterior fossa more commonly than computed tomography, but computed tomography alone was satisfactory in 80% of cases...

Changes in cranial CSF volume during hypercapnia and hypocapnia

Magnetic resonance imaging was used to measure the effect of inhalation of 7% CO2 and hyperventilation with 60% O2 on human cranial cerebrospinal fluid volume. During CO2 inhalation there was a reduction in the cranial CSF volume ranging from 0.7-23.7 ml (mean 9.36 ml). The degree of reduction in cranial CSF volume was independent of the individual subject's increase in end-expiratory pCO2 or mean arterial blood pressure, in response to hypercapnia. During hyperventilation with high concentration oxygen the cranial CSF volume increased in all subjects (range 0.7-26.7 ml, mean 12.7 ml). The mean changes in cranial CSF volume, induced by hypercapnia and hypocapnia, were very similar to the expected reciprocal changes in cerebral blood volume.

Brain and intracranial cavity volumes: in vivo determination by MRI

Brain volume is altered by pathological processes such as swelling or atrophy yet until now this is a parameter which could only be determined at post mortem. This paper describes a non-invasive technique using MRI which permits the in vivo determination of brain volume (BV), intracranial cavity volume (ICV), ventricular, cortical sulcal and total intracranial CSF volumes. The technique was applied to 40 normal volunteers (20 males, 20 females) to investigate the variation of these parameters with age and sex after normalisation with respect to ICV. There was found to be a significant decrease in normalised brain volume between the ages of 20 and 60 years in males by 1.6% per decade. In females the decrease was less (0.5%) but was not statistically significant. This technique will make it possible, for the first time, to investigate prospectively the correlation between mental function and brain volume in illness and ageing.

Catheter infection. A comparison of two catheter maintenance techniques

Incidence of catheter-related infections was studied using two techniques: changing catheters over a guide-wire or placing a new catheter at a new site every 3 days. Patients were randomized into two groups: Group 1 (new site) and Group 2 (guide-wire). Of the 105 catheterization sites (20 arterial and 85 central lines) in patients of Group 1, none were considered infected (i.e., having 15 or more colonies at the time of semi-quantitative microbiology analysis and clinical signs of infection at the catheter site). Of the 274 catheterization sites (56 arterial and 218 central) of patients of Group 2, eight (2.9%) were infected (chi 2 = 1.89, p greater than 0.05). Colonization (15 or more cultures without clinical signs of infection) occurred in three of 105 (2.9%) and in four of 274 (1.5%) of the catheterization sites of Groups 1 and 2, respectively (chi 2 = 0.23, p greater than 0.05). Study results indicate no significant difference in infection or colonization rates between the two methods of catheter replacement.

Magnetic resonance imaging of acute subarachnoid hemorrhage

The feasibility, safety, and diagnostic value of magnetic resonance (MR) imaging versus computerized tomography (CT) scanning were compared in 30 patients with clinical evidence of subarachnoid hemorrhage. Subarachnoid blood was identified more often and more information was available about the site and source of the hemorrhage on MR imaging than on CT. Magnetic resonance imaging could be used safely both before and after the operation, provided that nonferromagnetic clips were used and that comprehensive monitoring and cardiorespiratory support were available. Postoperative studies showed that artifacts from metallic implants and from patient movement caused less image degradation on MR images than on CT scans.

Temporal physiochemical changes during in vitro relaxation time measurements: the cerebrospinal fluid

Documented relaxation time measurements of body fluids such as cerebrospinal fluid (CSF) vary considerably. This may be largely due to lack of an appropriate method of maintaining the in vivo physiological and biochemical characteristics of the fluid. We have developed an in vitro technique that maintains the in vivo characteristics of body fluid samples for a sufficiently long period to establish the true relaxation times. To illustrate this we studied changes in CSF pH, pO2, and pCO2, first as it equilibrated with air and then under anaerobic conditions as found in vivo. Relaxation times of CSF were then studied under aerobic and anaerobic conditions. Under the particular aerobic conditions used the pH and pO2 of CSF increased quickly and pCO2 fell within the first 30 min. By 3-4 h equilibration with air was complete. The T1 and T2 relaxation times of CSF decreased by 14 and 16%, respectively, as a result of these physicochemical changes. It is important that such changes be considered when relaxation measurements of any body fluid are performed in vitro and efforts to maintain the in vivo milieu should not be neglected.

Magnetic resonance imaging in acute head injury

Using cardiorespiratory monitoring and support equipment compatible with a low field (0.15 T) system, magnetic resonance imaging (MRI) of patients suffering acute head injuries proved to be both feasible and safe. An abnormality was demonstrated by magnetic resonance imaging in 46 of 50 patients examined within 7 days of head injury using T2 weighted (SE2200/80) and T1 weighted (IR2000/600/40) multislice sequences. IN contrast, computed tomography (CT) demonstrated abnormalities in only 31 of the 50 patients. Intracranial extracerebral space-occupying collections of blood were well shown by magnetic resonance imaging which provided especially clear definition in the posterior fossa, subtemporal and subfrontal regions. Magnetic resonance imaging was more sensitive to cerebral abnormalities associated with traumatic unconsciousness and detected parenchymal lesions both in patients in coma and in those who had lost consciousness for only a few minutes. Lesions seen with MRI but not with CT included non-haemorrhagic contusions and abnormalities thought to reflect shearing injuries of white matter and intracerebral vessels. Magnetic resonance imaging is an effective alternative to CT; the additional information it can provide should be valuable in increasing the understanding of the early effects and late consequences of a head injury.

Early and late magnetic resonance imaging and neuropsychological outcome after head injury

Twenty five adults with closed head injury who had early magnetic resonance imaging (MRI) and computed tomography (CT) were followed up 5 to 18 months after injury. Patients were given a repeat MRI and performed a series of neuropsychological tests. They were classified by the deepest abnormality detectable on scanning. Classifications derived from early and late MRI scanning were significantly correlated. However, measures of neuropsychological outcome showed a strong correlation only with late MRI, and little or no relationship with either early MRI or early CT. Deeper abnormalities detected by late MRI were associated with poorer neuropsychological test performance; late ventricular enlargement was particularly associated with poor outcome. It is concluded that the lesions visualised by MRI are important for neuropsychological outcome, and that functionally significant abnormalities may only be fully apparent on late scanning.

Magnetic resonance imaging of renal transplants: initial experience

Magnetic resonance imaging (MRI) was used in 45 renal transplant investigations (38 patients) using a Picker 0.15 T resistive system and a localized surface coil. An attempt was made to define optimal sequences in the evaluation of both normal and pathological transplants. Three sequences were found to be of value; a T1 weighted sequence (IR2180/700/40) to assess corticomedullary differentiation and its loss in acute rejection and acute tubular necrosis, a T2 weighted sequence (SE2000/80) for assessment of renal vessels and disturbances in blood supply, and a STIR (short tau inversion recovery) sequence (IR800/100/40) to define further the distended collecting system in obstruction and the presence of any perirenal collection. Encouraging results have been obtained, particularly in cases of acute rejection. It is suggested that the MRI scan is a useful screening test in cases of clinical doubt and may even obviate biopsy in some cases.

Is cranial CSF volume under hormonal influence? An MR study

We used magnetic resonance to investigate the hypothesis that premenstrual neurological symptoms are due to cerebral oedema and brain swelling. Total cranial and lateral ventricular CSF volumes were measured midcycle and premenstrually in 20 women with a normal menstrual cycle, and similar measurements were made 2 weeks apart in 10 postmenopausal women and 10 men. Total cranial CSF volume increased premenstrually in 19 women. The mean premenstrual increase was by 11.5 ml. There was not a significant difference between those women who were taking an oral contraceptive and those who were not. The CSF volume did not change significantly on repeat measurement in men and postmenopausal women. The CSF changes observed reflect a reduction in brain volume and do not support cerebral swelling as the cause of premenstrual neurological symptoms.

Intracranial CSF volumes: natural variations and physiological changes measured by MRI

Cranial CSF volumes, for the first time including CSF in the subarachnoid space, can be measured by Magnetic Resonance Imaging (MRI). The MRI sequence causes signal from the grey matter and white matter to cancel producing a contrast of 200: 1 between a unit of CSF and a unit of brain. We have assessed the variations between normal individuals and investigated some of the physiological factors that might influence cranial CSF volumes. Total CSF volumes were measured in 64 normal subjects, aged from 18-64 years (mean 38 years). Ventricular, cortical sulcal and posterior fossa volumes were also calculated separately. In 20 females with a normal menstrual cycle, CSF volumes were measured mid cycle and premenstrually; 10 post menopausal females and 10 males were rescanned after an interval of 2 weeks. Total cranial CSF volume were calculated before and during inhalation of 7% CO2 and before and during hyperventilation while breathing 60% O2, in 12 normal subjects. Total intracranial CSF volume ranged from 57.1-286.5 ml. Total intracranial and cortical sulcal CSF volumes increased more steeply with age than ventricular or posterior fossa CSF volumes. Males had more cranial CSF than females. Total CSF volume increased premenstrually in 19 females. Males and post-menopausal females did not have a significant change in CSF volume, on repeat examination. CO2 inhalation produced a mean increase of paCO2 of 17.2 mmHg and CSF volume decreased in all subjects (mean 9.4 ml). Cranial CSF volume increased in 11 subjects during O2 inhalation (range -0.5 to +26.7 ml mean 10.9 ml).(ABSTRACT TRUNCATED AT 250 WORDS)

MRI measurement of syrinx size before and after operation

When patients with syringomyelia fail to improve after operation, factors such as incomplete cyst decompression or type of operation are often implicated. MRI has been used to confirm adequate syrinx decompression post-operatively and to compare the degree of collapse with the type of operation. Foramen magnum decompression was at least as effective in reducing cyst size as syringo-subarachnoid shunting. MRI may also provide a better classification of syringomyelia.

Magnetic resonance imaging in the management of resistant focal epilepsy: pathological case report and experience of 12 cases

Clinical improvement in epilepsy following temporal lobectomy is more often obtained when an abnormality is found on subsequent histological examination. Pre-operative MRI demonstrated an abnormal signal in the temporal lobe of a patient with pathologically proven mesial temporal sclerosis with microvascular anomaly. MRI may therefore be helpful in the selection of patients for temporal lobectomy. MRI findings of 12 patients with resistant focal epilepsy are reviewed. A wide range of T1 and T2 weighting is suggested to maximise selection of patients.

Syringomyelia: cyst measurement by magnetic resonance imaging and comparison with symptoms, signs and disability

The severity and distribution of symptoms and signs in patients with syringomyelia is considered to be dependent on the longitudinal and transverse dimensions of the syrinx and it is thought that clinical examination can identify the extent of the cyst. Magnetic resonance imaging has made the anatomical localisation of intramedullary spinal lesions more exact and probably more specific than previous methods of investigation. Syrinx length, diameters, cyst:cord and cord:canal ratios have been studied in 12 patients with syringomyelia to assess whether the dimensions of the syrinx relate to the clinical findings. The length of syrinx appeared to be related to cyst diameter, cyst:cord and cord:canal ratios. Patients with a small syrinx tended to have a small cyst diameter, and small cyst:cord and cord:canal ratios. No significant relationship was found between muscle wasting or weakness, distribution of sensory loss, degree of disability or distress and the dimensions of the syrinx. These findings should be borne in mind when surgical management is being considered.

MR relaxation times of cerebrospinal fluid

A review of 15 recent publications purporting to provide the relaxation times of CSF reveals a considerable disparity in the quoted results, by a factor of five in terms of T1 (range 1,000 to 5,500 ms) and by a factor of 16 for T2 (range 166 to 2,640 ms). In this article measurements are performed independently on both a spectrometer and an imager. The results indicate that for CSF T1 is greater than 3,000 ms and T2 is approximately 2,000 ms at 6 MHz. The vast differences in relaxation behaviour between CSF and other body tissues have considerable clinical implications and present profound diagnostic opportunities. The application of this knowledge to ventriculography, myelography, and image contrast methodology is discussed.

Human cranial CSF volumes measured by MRI: sex and age influences

Accurate measurements of CSF volumes would assist in the diagnosis of several important neurological conditions. Using Magnetic Resonance Imaging (MRI) we have devised a method to measure both total intracranial CSF volume and ventricular volume. This initial study, in normal humans, provides an answer to two longstanding questions: first, do these volumes differ between the sexes; second, do both total and ventricular CSF volumes increase with normal aging? We found that the total cranial CSF volume and skull size of males were significantly greater than those of females, but that there was not a statistically significant difference between the ventricular volumes of the sexes. Total cranial CSF volume increased steeply with age in both sexes but although there was an increase in ventricular volume with age in males, no significant increase with age could be demonstrated in females.

Digital mapping of multi-parameter contrast functions in magnetic resonance (MR) imaging using a standard MR computer system and digital display

A technique is described which utilises the full analysis and display capabilities of a commercial MRI system to produce digital maps of multi-parameter functions produced by MR contrast theory. The technique is utilised to determine the effects of nominating specific overall scan times on the optimum solutions as produced by the theory and it is shown that different solutions are obtained when the theory is applied using typical clinical constraints. The digital mapping approach is potentially of great value in prospectively determining pulse timing parameters to produce optimum contrast images, in producing contrast maps to aid retrospective image interpretation, and as a training aid for clinicians inexperienced in the interpretation MR images.