Mathematically aggregating experts' predictions of possible futures.

Structured protocols offer a transparent and systematic way to elicit and combine/aggregate, probabilistic predictions from multiple experts. These judgements can be aggregated behaviourally or mathematically to derive a final group prediction. Mathematical rules (e.g., weighted linear combinations of judgments) provide an objective approach to aggregation. The quality of this aggregation can be defined in terms of accuracy, calibration and informativeness. These measures can be used to compare different aggregation approaches and help decide on which aggregation produces the "best" final prediction. When experts' performance can be scored on similar questions ahead of time, these scores can be translated into performance-based weights, and a performance-based weighted aggregation can then be used. When this is not possible though, several other aggregation methods, informed by measurable proxies for good performance, can be formulated and compared. Here, we develop a suite of aggregation methods, informed by previous experience and the available literature. We differentially weight our experts' estimates by measures of reasoning, engagement, openness to changing their mind, informativeness, prior knowledge, and extremity, asymmetry or granularity of estimates. Next, we investigate the relative performance of these aggregation methods using three datasets. The main goal of this research is to explore how measures of knowledge and behaviour of individuals can be leveraged to produce a better performing combined group judgment. Although the accuracy, calibration, and informativeness of the majority of methods are very similar, a couple of the aggregation methods consistently distinguish themselves as among the best or worst. Moreover, the majority of methods outperform the usual benchmarks provided by the simple average or the median of estimates.

[Avoidable visual impairment among residents in care institutions: lessons from an intervention project in the Den Bosch region]. / Onnodige slechtziendheid onder ouderen in zorginstellingen: lessen uit een interventieproject in de regio Den Bosch.

INTRODUCTION: Many elderly in care institutions in The Netherlands are visually impaired (visual acuity < 0.3). They fall more frequently, are more depressed and require more care. In this project visually impaired residents were identified and referred for adequate eye care. The aim of this study is to evaluate the intervention, including validation of the screening, assessment of the prevalence and causes of visual impairment as well as the outcome of the treatment. The effectiveness of the care chain is also evaluated. MATERIALS AND METHODS: 640 residents were offered a basic eye examination and 210 of them were referred, via their general practitioner, to an optometrist (10), ophthalmologist (98), or centre for visually impaired persons (1). RESULTS: Compliance in this study was poor. The prevalence of visual impairment (24%) was lower than in comparable studies. Cataract was the main cause in 51%. Overall 17 (8.1%) residents were treated by ophthalmologists and nine (4.3%) were referred to optical shops. Constraints in the care chain are identified. DISCUSSION: Vision screening in care institutions for elderly is feasible and useful. The care chain should be shorter and simpler. That will increase the effectiveness of this intervention, and thereby the quality of life for many residents.

Central trigeminal involvement in multiple sclerosis using high-resolution MRI at 3 T.

Trigeminal neuralgia and sensory disturbance is common in multiple sclerosis (MS). Recent literature suggests that signal abnormalities in the cisternal trigeminal nerve and pontine root entry zone are seen in approximately 3% of MS patients, using conventional diagnostic MRI. The objective of this study was to determine the prevalence of trigeminal lesions using high-resolution MRI at 3T. Forty-seven patients with clinically definite MS, chosen at random from the outpatient population of a neuroscience centre underwent MRI on a Siemens 3T Trio machine. Three 3D sequences of T2 TSE (turbo spin echo), T2 FLAIR (fluid attenuated inversion recovery) and T1 IR (inversion recovery) were acquired in the coronal plane. The sequences were of contiguous 1 mm slices with in-plane resolution of up to 0.5 mm by 0.5 mm. Images were read by both a neurologist and a neuroradiologist. Any clinical history of trigeminal symptoms was determined for all subjects. The results showed that 11 patients (23%) had high signal in the trigeminal root entry zone and either the trans-cisternal nerve or pontine nucleus; example images are given. MRI changes did not correspond to clinical symptoms (chi square probability 1.000). The study concludes that high-resolution MRI at 3T yielded a high prevalence of detectable trigeminal abnormality in the MS sample studied. MRI involvement did not correspond to trigeminal symptoms.

Magnetic resonance image findings in the early post-operative period after anterior cervical discectomy.

If early neurological deterioration occurs following anterior cervical discectomy, the patient should be evaluated by urgent MRI scanning. In order to interpret such a scan it is essential to know what the normal post-operative MRI appearance is following an uncomplicated procedure. In the lumbar spine it is well recognized that early post-operative imaging following discectomy is difficult to interpret with a high rate of false positive scans. The normal appearance of MRI in the early post-operative period was evaluated prospectively in 15 patients undergoing anterior cervical discectomy without fusion for either cervical radiculopathy or myelopathy. MRI was performed on the first post-operative day, at 6 weeks and 6 months. The successful outcome of the procedure was validated by uniform improvement of Visual Analogue Scale measurement for neck and arm pain, the Neck Disability Index and European Myelopathy Score as appropriate. In contrast to the established findings following lumbar discectomy, only two cases showed a persistent epidural mass in the first post-operative scan and this had completely resolved at 6 months. All patients had foraminal narrowing and root or cord compression pre-operatively. Sixty six percent of cases showed persistent foraminal narrowing on sequential imaging up to 6 months despite showing good symptomatic improvement. All cases demonstrated high signal in the operated disc space on T2 weighted imaging on the first post-operative day and this finding persisted in 13 of 15 scans performed at 6 weeks. Post contrast imaging demonstrated no enhancement of operated disc space and adjacent vertebral body on the first post-operative day, whereas all scans at 6 weeks showed enhancement and such enhancement persisted at 6 months in 50%. Persistent epidural filling defects are uncommon following successful anterior cervical discectomy but persistence of foraminal narrowing is common despite successful outcome. Enhancement of the disc space is also common and does not in itself imply infection.

3D MRI in multiple sclerosis: a study of three sequences at 3 T.

The objective of this study was to assess the feasibility of using 3D acquisition at 3 T for imaging patients with multiple sclerosis (MS). Feasibility was assessed by three criteria based on acquisition time, specific absorption rate (SAR) and image quality. 47 patients with clinically definite MS underwent imaging in a Siemens 3T Trio MR scanner. Patient safety data were obtained following the scan sessions. The study had local ethics approval. The following three-dimensional (3D) sequences, all acquired coronally, were used: T2 fluid attenuated inversion recovery (FLAIR) (repetition time (TR) 6000 ms, echo time (TE) 353 ms, inversion time (TI) 2200 ms), 0.5x0.5x1 mm voxels, acquisition time 10 min 38 s; T2 turbo spin echo (TSE) (TR 3000 ms, TE 354 ms), 1x1x1 mm voxels, acquisition time 8 min 29 s; T1 inversion recovery (IR) (TR 2040 ms, TE 5.56 ms, TI 1100 ms), matrix 512x448 (0.5x0.5 mm pixels), 0.5x0.5x1 mm voxels, acquisition time 7 min 38 s. Total acquisition time was 26 min 45 s. Example images are presented. 3D scanning at 3 T provides highly detailed, high quality images with acquisition times tolerated by MS patients, even by those with severe disability. The volumetric data are suitable for a wide variety of post-processing techniques; the authors suggest that 3D studies at 3 T should be considered as the possible brain imaging protocol for either cross-sectional or longitudinal studies in MS and that the 3D T2 FLAIR sequence should be considered for the purposes of radiological diagnosis.

Imaging abnormalities in sporadic hemiplegic migraine on conventional MRI, diffusion and perfusion MRI and MRS.

Prolonged hemiparetic migraine aura can cause diagnostic confusion and be mistaken for ischaemic stroke occurring during the course of a migraine--'migrainous infarction'. We report a case of prolonged hemiparesis occurring during the course of a migraine attack. Though initially confused with migrainous infarction, we suggest with sequential magnetic resonance imaging, magnetic resonance angiography, diffusion, perfusion images and magnetic resonance spectroscopy that the hemiplegia was not of vascular origin and that the patient had sporadic hemiplegic migraine. We hypothesize that the mechanisms of sporadic hemiplegic migraine probably lie at a cellular level, similiar to familial hemiplegic migraine.

An aerial netting study of insects migrating at high altitude over England.

Day and night sampling of windborne arthropods at a height of 200 m above ground was undertaken at Cardington, Bedfordshire, UK, during July 1999, 2000 and 2002, using a net supported by a tethered balloon. The results from this study are compared with those from the classic aerial sampling programmes carried out by Hardy, Freeman and colleagues over the UK and North Sea in the 1930s. In the present study, aerial netting was undertaken at night as well as daytime, and so the diel periodicity of migration could be investigated, and comparisons made with the results from Lewis and Taylor's extensive survey of flight periodicity near ground level. In some taxa with day-time emigration, quite large populations could continue in high-altitude flight after dark, perhaps to a previously underrated extent, and this would greatly increase their potential migratory range. Any trend towards increases in night temperatures, associated with global warming, would facilitate movements of this type in the UK. Observations on the windborne migration of a variety of species, particularly those of economic significance or of radar-detectable size, are briefly discussed.

A new technique in nasal-tip reduction surgery.

This article presents a technique for the reduction of the overprojected nasal tip with a proportional reduction of the nostril-margin circumference. To achieve these reductions, a modified open rhinoplasty technique is used, which is unique in that it involves the total transection of the columella through the medial crura of the alar cartilage. The alar cartilage is raised with the flap. The technique was first developed and introduced by the senior author (R.A.S.) 25 years ago and has since been refined through the execution of several thousand rhinoplasties. The results continue to be consistent and pleasing from both the patients' and the surgeon's points of view.

Purification and characterization of an iron-nickel hydrogenase from Thermococcus celer.

Thermococcus celer cells contain a single hydrogenase located in the cytoplasm, which has been purified to apparent homogeneity using three chromatographic steps: Q-Sepharose, DEAE-Fast Flow, and Sephacryl S-200. In vitro assays demonstrated that this enzyme was able to catalyze the oxidation as well as the evolution of H2. T. celer hydrogenase had an apparent MW of 155,000+/-30,000 by gel filtration. When analyzed by SDS polyacrylamide gel electrophoresis a single band of 41,000+/-2,000 was detected. Hydrogenase activity was also detected in situ in a SDS polyacrylamide gel followed by an activity staining procedure revealing a single band corresponding to a protein of apparent Mr 84,000+/-3,000. Measurements of iron and acid-labile sulfide in different preparations of T. celer hydrogenase gave values ranging from 24 to 30 g-atoms Fe/mole of protein and 24 to 36 g-atoms of acid-labile sulfide per mole of protein. Nickel is present in 1.9-2.3 atoms per mole of protein. Copper, tungsten, and molybdenum were detected in amounts lower than 0.5 g-atoms per mole of protein. T. celer hydrogenase was inactive at ambient temperature, exhibited a dramatic increase in activity above 70 degrees C, and had an optimal activity above 90 degrees C. This enzyme showed no loss of activity after incubation at 80 degrees C for 28 h, but lost 50% of its initial activity after incubation at 96 degrees C for 20 h. Hydrogenase exhibited a half-life of approximately 25 min in air. However, after treating the air-exposed sample with sodium dithionite, more than 95% of the original activity was recovered. Copper sulfate, magnesium chloride and nitrite were also inactivators of this enzyme.

Direct electrochemical characterization of hyperthermophilic Thermococcus celer metalloenzymes involved in hydrogen production from pyruvate.

The reduction potentials of the metalloproteins pyruvate ferredoxin oxidoreductase (POR), ferredoxin, and hydrogenase isolated from hyperthermophilic Thermococcus celer (Topt = 88 degrees C) were determined as a function of temperature from 10 to 85 degrees C. Square-wave voltammetry experiments were carried out on 15 microL samples directly at an unmodified "edge-polished" pyrolytic graphite electrode using MgCl2 as an electrode promoter. POR exhibited two voltammetric waves with peaks at -280 and -403 mV at room temperature, indicating multiple redox centers, and a single wave at -420 mV at 85 degrees C. These waves displayed different temperature-dependent peak positions and peak heights, indicating that these redox centers have different thermodynamic and kinetic properties. Ferredoxin displayed a single linear temperature-dependent voltammetric wave at -280 mV at room temperature and -327 mV at 85 degrees C. Hydrogenase displayed a single biphasic temperature-dependent voltammetric wave at -197 mV at room temperature and -211 mV at 85 degrees C. Thermodynamic parameters associated with electron transfer, namely standard enthalpies and entropies for the redox centers in the various proteins, are reported.

A national survey of attitudes towards the use of MRI in patients known to have intracranial aneurysm clips.

The objective of this study was to determine the attitudes and practice of neuroradiology centres across the UK regarding the use of MRI in patients known to have intracranial aneurysm clips. A postal survey comprising three questions and a comments section was sent to 35 neuroradiology centres across the UK. There were 32 (91%) respondents to the single questionnaire. 16 (50%) respondents said that they would not consider performing MRI on a patient with an intracranial aneurysm clip. Of the remaining 50%, all said that identification of the clip type and assurance of its safety would be needed prior to scanning the patient. The magnetic strength of the system did not appear to affect the decision regarding whether or not to perform MRI on such patients. There was a variation in attitude towards the use of MRI in such patients between different regions. Neuroradiology centres are equally divided in their attitude and practice about whether it is safe to use MR to image a patient known to have an intracranial aneurysm clip. This is most probably due to the conflicting literature, as well as uncertainty about the identification and ferromagnetic properties of individual clips.

Modulation of the redox potential of the [Fe(SCys)(4)] site in rubredoxin by the orientation of a peptide dipole.

Rubredoxins (Rds) may be separated into two classes based upon the correlation of their reduction potentials with the identity of residue 44; those with Ala44 have reduction potentials that are approximately 50 mV higher than those with Val44. The smaller side chain volume occupied by Ala44 relative to that occupied by Val44 has been proposed to explain the increase in the reduction potential, based upon changes in the Gly43-Ala44 peptide bond orientation and the distance to the [Fe(SCys)(4)] center in the Pyrococcus furiosus (Pf) Rd crystal structure compared to those of Gly43-Val44 in the Clostridium pasteurianum (Cp) Rd crystal structure. As an experimental test of this hypothesis, single-site Val44 <--> Ala44 exchange mutants, [V44A]Cp and [A44V]Pf Rds, have been cloned and expressed. Reduction potentials of these residue 44 variants and pertinent features of the X-ray crystal structure of [V44A]Cp Rd are reported. Relative to those of wild-type Cp and Pf Rds, the V44A mutation in Cp Rd results in an 86 mV increase in midpoint reduction potential and the [A44V] mutation in Pf Rd results in a 95 mV decrease in midpoint reduction potential, respectively. In the crystal structure of [V44A]Cp Rd, the peptide bond between residues 43 and 44 is approximately 0.3 A closer to the Fe center and the hydrogen bond distance between the residue 44 peptide nitrogen and the Cys42 gamma-sulfur decreases by 0.32 A compared to the analogous distances in the wild-type Cp Rd crystal structure. The results described herein support the prediction that the identity of residue 44 alone determines whether a Rd reduction potential of about -50 or 0 mV is observed.

The value of MR imaging in differentiating between hard and soft cervical disc disease: a comparison with intraoperative findings.

The aim of this study is to assess the accuracy of MRI alone in the differentiation of soft cervical disc protrusion from osteophytic compression in cervical disc disease. In a retrospective study, the MRI scans of 41 patients with cervical disc disease, who had previously undergone surgery, were presented to three independent observers, randomly on two different occasions, to identify the accuracy of the diagnosis of the presence of hard or soft disc or both as a cause of compression. The observers (two neurosurgeons and one neuroradiologist) were not involved with the treatment of the cases at any stage and were unaware of the surgical findings. Their observations were compared with those of the surgeon recorded at operation. The intra-observer agreement was poor for diagnosis into three categories as hard or soft disc or both. In distinguishing between the presence or absence of hard disc, there was moderate to good (Kappa = 0.6) intra observer and fair to moderate (Kappa = 0.4) interobserver agreement. The sensitivity of diagnosis of a hard disc was high (87%) but specificity was low (44%), due to the overestimation of the presence of hard disc. There was a significantly higher incidence of hard disc in the elderly age group (76% over the fifth decade, P = 0.0073). It is concluded that MRI alone is not a very efficient diagnostic tool in distinguishing between hard and soft disc in the cervical disc disease.

Redox properties of mesophilic and hyperthermophilic rubredoxins as a function of pressure and temperature.

The formal equilibrium reduction potentials of recombinant electron transport protein, rubredoxin (MW = 7500 Da), from both the mesophilic Clostridium pasteurianum (Topt = 37 degrees C) and hyperthermophilic Pyrococcus furiosus (Topt = 95 degrees C) were recorded as a function of pressure and temperature. Measurements were made utilizing a specially designed stainless steel electrochemical cell that easily maintains pressures between 1 and 600 atm and a temperature-controlled cell that maintains temperatures between 4 and 100 degrees C. The reduction potential of P. furiosus rubredoxin was determined to be 31 mV at 25 degrees C and 1 atm, -93 mV at 95 degrees C and 1 atm, and 44 mV at 25 degrees C and 400 atm. Thus, the reduction potential of P. furiosus rubredoxin obtained under standard conditions is likely to be dramatically different from the reduction potential obtained under its normal operating conditions. Thermodynamic parameters associated with electron transfer were determined for both rubredoxins (for C. pasteurianum, DeltaV degrees = -27 mL/mol, DeltaS degrees = -36 cal K-1 mol-1, and DeltaH degrees = -10 kcal/mol, and for P. furiosus, DeltaV degrees = -31 mL/mol, DeltaS degrees = -41 cal K-1 mol-1, and DeltaH degrees = -13 kcal/mol) from its pressure- and temperature-reduction potential profiles. The thermodynamic parameters for electron transfer (DeltaV degrees, DeltaS degrees, and DeltaH degrees ) for both proteins were very similar, which is not surprising considering their structural similarities and sequence homology. Despite the fact that these two proteins exhibit dramatic differences in thermostability, it appears that structural changes that confer dramatic differences in thermostability do not significantly alter electron transfer reactivity. The experimental changes in reduction potential as a function of pressure and temperature were simulated using a continuum dielectric electrostatic model (DELPHI). A reasonable estimate of the protein dielectric constant (epsilonprotein) of 6 for both rubredoxins was determined from these simulations. A discussion is presented regarding the analysis of electrostatic interaction energies of biomolecules through pressure- and temperature-controlled electrochemical studies.

Direct electrochemistry of the flavin domain of assimilatory nitrate reductase: effects of NAD+ and NAD+ analogs.

Direct electrochemical studies, utilizing two voltammetric methods-square-wave voltammetry (SWV) and cyclic voltammetry (CV)-have been performed on recombinant forms of the flavin domain of spinach assimilatory nitrate reductase in the presence of NAD+ analogs. The reduction potentials (E degrees ') of the flavin domains have been determined at an edge pyrolytic graphite electrode utilizing MgCl2 as a redox-inactive promoter. Under identical experimental conditions (pH 7.0, 25 degrees C), the two-electron reduction potential for the FAD/FADH2 couple has been determined to be -274 and -257 mV by SWV and CV, respectively. In contrast, the reduction potentials of free FAD have been determined to be -234 and -227 mV by SWV and CV, respectively. The reduction potentials of the complex formed between the FAD prosthetic group in the recombinant flavin domain and various NAD+ analogs have been determined to be as follows: NAD+ (E degrees ' = -192 mV), 5'-ADP ribose (E degrees ' = -199 mV), ADP (E degrees ' = -154 mV), AMP (E degrees ' = -196 mV), adenosine (E degrees ' = -192 mV), adenine (E degrees ' = -220 mV), and NMN (E degrees ' = -208 mV). In contrast to these positive shifts in reduction potential, nicotinamide (E degrees ' = -268 mV) had very little effect on the reduction potential of this flavin complex. Moreover, addition of NAD+ to the FAD prosthetic group in a variety of mutant forms of the recombinant flavin domain resulted in positive shifts in the reduction potential of the complex, although the magnitude of the shifts varied from a minimum of 6 mV obtained for the C240A mutant to a maximum of 79 mV obtained for the C62S mutant. These results represent the first extensive application of direct electrochemistry to examine the redox properties of assimilatory nitrate reductase and indicate that complex formation with NAD+, or various NAD+ analogs, results in a positive shift in the flavin reduction potential, with the magnitude of the shift correlating well with the efficiency of the inhibitor.

Sudden cardiac death associated with hypoplasia of the coronary arteries and conduction system alteration.

We present a case of sudden cardiac death in a 24-year-old woman with evidence of hypoplasia of the left anterior descending (LAD) and posterior descending (PDA) coronary arteries. These vessels averaged 0.7 mm in internal diameter combined, in contrast to an average of 2.4 mm in control coronary arteries (p < 0.001). The myocardium exhibited areas of acute and chronic ischemic change. Also, the cardiac conduction system (CCS) had diffuse cellular enlargement, believed to be secondary to ischemia. The cells of the sinoatrial node (SAN) and the Purkinje cells of the proximal right bundle branch (RBB) averaged 28.5 and 25.6 microns, respectively. These were significantly larger than the SAN cells (21.6 microns, p = 0.002) and larger than the Purkinje cells (15.9 microns, p = 0.012) of control cases. We report that hypoplastic coronary artery disease is a cause of sudden death, is associated with varying degrees of ischemic change in the heart, and can be associated with condition system alteration.

Physical characterization of a totally synthetic rubredoxin.

The entire polypeptide of hyperthermophilic Pyrococcus furiosus rubredoxin was synthesized in order to specifically probe structural determinants of protein thermostability. The uv-visible, circular dichroic, electron paramagnetic, and nuclear magnetic resonance spectra, and electrochemical properties, of the native and synthetic proteins were essentially identical. The synthetic protein had a half-life for denaturation of 24 hr at 80 degrees C. The synthetic protein is considerably more thermostable than nonhyperthermophilic rubredoxins, but not as stable as the native protein. Based on the spectroscopic evidence, it appears that the synthetic protein is incorporating iron properly to form holoprotein, but the peptide still may not be folded correctly.

Thiol modification and site directed mutagenesis of the flavin domain of spinach NADH:nitrate reductase.

Incubation of either Chlorella nitrate reductase or the recombinant flavin domain of spinach nitrate reductase with reagents specific for modification of cysteine residues, such as N-ethylmaleimide, resulted in a time-dependent inactivation of NADH:ferricyanide reductase activity which could be prevented by incubation in the presence of NADH. At 25 degrees C and employing a fixed enzyme:modifier ratio, the rate of inactivation for both the Chlorella and spinach enzymes followed the order p-chloromercuribenzoate > methyl methanethiosulfonate > 2-(4'-maleimidylanilino)naphthalene-6-sulfonic acid > N-ethylmaleimide. For the spinach flavin domain, inactivation by methyl methanethiosulfonate or p-chloromercuribenzoate was found to be concentration independent suggesting the absence of nonspecific modifications. Initial rate studies of the methyl methanethiosulfonate-modified flavin domain indicated a reduction in NADH:ferricyanide activity (Vmax) from 85 to 44 micromol NADH consumed/min/nmol FAD and an increase in the Km for NADH from 12 to 35 microM when compared to the native enzyme, confirming a role for cysteine residue(s) in maintaining diaphorase activity. Site-directed mutagenesis of the four individual cysteines (residues 17, 54, 62, and 240) in the recombinant spinach flavin domain resulted in mutant proteins with visible and CD spectra very similar to those of the wild-type domain. Initial rate studies indicated that only substitutions of serine for cysteine 240 decreased diaphorase activity with maximal NADH:ferricyanide activity for the C240S mutant corresponding to 51 micromol NADH consumed/min/nmol FAD with a Km for NADH of 14 microM. Mutation of C240 to Ala or Gly resulted in greater loss of activity. The thermal stability of the four serine mutants was slightly decreased compared to the wild-type domain with the C62S mutant exhibiting the greatest instability. In contrast to the effects on diaphorase activity, square wave voltammetric studies indicated changes in the oxidation-reduction midpoint potential for the FAD/FADH2 couple in the C54S (E0'= -197 mV), C62S (E0' = -226 mV), and C240S (E0' = -219 mV) mutants compared to the wild-type domain (E0' = -268 mV). These results indicate that of the four cysteine residues in the spinach nitrate reductase flavin domain, only C240 plays a role in maintaining diaphorase activity, while C54 has the greatest influence on flavin redox potential and that no correlation between changes in catalytic activity and flavin redox potential was observed.

Variability in measurement of extracranial internal carotid artery stenosis as displayed by both digital subtraction and magnetic resonance angiography: an assessment of three caliper techniques and visual impression of stenosis.

BACKGROUND AND PURPOSE: The degree of stenosis in the extracranial internal carotid artery helps predict the risk of an individual suffering subsequent cerebrovascular ischemic events. Different techniques have evolved to measure stenosis from angiograms, leading to some confusion and a call for the adoption of a single technique. To help choose the most reliable technique, this study assessed observer variability in reporting carotid stenosis for four different techniques, from both digital subtraction (DSA) and MR angiograms (MRA). Three of the techniques used caliper measurements; the fourth was the visual impression of stenosis. METHODS: From a total of 137 angiograms, caliper measurements were possible on 105 DSAs and 74 MRAs. Measurements from these angiograms were made by two independent observers on two separate occasions to assess interobserver and intraobserver variation in reporting. RESULTS: For DSA, the variability in reporting and the number of clinically significant differences arising as a result were similar for each of the four techniques. While the typical measurement errors for each of the techniques studied were on the order of +/- 5%, each technique produced some sizable individual differences for the same angiogram, with resultant wide 95% limits of agreement. Observer variability for reporting MRA was generally a little greater than for DSA. Compared with the caliper techniques, the visual impression of stenosis technique performed well, particularly for MRA. CONCLUSIONS: Although observer variability in reporting can be considerable, no important differences were found among the different techniques widely used for measuring carotid stenosis.