An efficient approach for limited-data chemical species tomography and its error bounds.

We present a computationally efficient reconstruction method for the limited-data chemical species tomography problem that incorporates projection of the unknown gas concentration function onto a low-dimensional subspace, and regularization using prior information obtained from a simple flow model. In this context, the contribution of this work is on the analysis of the projection-induced data errors and the calculation of bounds for the overall image error incorporating the impact of projection and regularization errors as well as measurement noise. As an extension to this methodology, we present a variant algorithm that preserves the positivity of the concentration image.

Assessment of clinical occupational dose reduction effect of a new interventional cardiology shield for radial access combined with a scatter reducing drape.

OBJECTIVES: To assess the occupational dose reduction effect of a new interventional cardiology shield for radial access combined with a scatter reducing drape. BACKGROUND: Transradial access for catheterization has been shown to increase occupational radiation dose. Current shielding techniques are primarily based on the femoral access. This article looks at the clinical occupational combined dose reduction effect of a commercially available shield and drape which is specific to access type. METHODS: The evaluation took place in a busy interventional cardiology laboratory, with a single plane 30×40 cm flat panel detector (Siemens Artis Zee, Germany). Radiation exposure to staff was measured using electronic personal dosimeters (Unfors RaysafeAB, Sweden) placed at the collar. Patient radiation exposure was assessed using screening time and dose area product per case. Both staff and patient radiation exposure were monitored for a number of case types and operators before, during, and after deployment of the new shield and drapes. RESULTS: The cardiologists' overall median collar badge reading per case reduced from 15.4 µSv per case without the shield/drape combination to 7.3 µSv per case with the shield drape combination in situ (P<0.001). The radiographers badge reading was reduced from 4.2 µSv per case without to 2.5 µSv per case with the shield drape combination in situ (P<0.001). There was no statistical difference in the cardiac technician's badge reading. Patient's dose area product was not significantly affected by the placement of the shield and drape combination. CONCLUSIONS: The shield/drape combination can significantly reduce operator exposure in a cardiac catheterization laboratory.

Spatially resolved and observer-free experimental quantification of spatial resolution in tomographic images.

We present a novel framework and experimental method for the quantification of spatial resolution of a tomography system. The framework adopts the "black box" view of an imaging system, considering only its input and output. The tomography system is locally stimulated with a step input, viz., a sharp edge. The output, viz., the reconstructed images, is analysed by Fourier decomposition of their spatial frequency components, and the local limiting spatial resolution is determined using a cut-off threshold. At no point is an observer involved in the process. The framework also includes a means of translating the quantification region in the imaging space, thus creating a spatially resolved map of objectively quantified spatial resolution. As a case-study, the framework is experimentally applied using a gaseous propane phantom measured by a well-established chemical species tomography system. A spatial resolution map consisting of 28 regions is produced. In isolated regions, the indicated performance is 4-times better than that suggested in the literature and varies by 57% across the imaging space. A mechanism based on adjacent but non-interacting beams is hypothesised to explain the observed behaviour. The mechanism suggests that, as also independently concluded by other methods, a geometrically regular beam array maintains maximum objectivity in reconstructions. We believe that the proposed framework, methodology, and findings will be of value in the design and performance evaluation of tomographic imaging arrays and systems.

Mutual information as a measure of image quality for 3D dynamic lung imaging with EIT.

We report on a pilot study of dynamic lung electrical impedance tomography (EIT) at the University of Manchester. Low-noise EIT data at 100 frames per second were obtained from healthy male subjects during controlled breathing, followed by magnetic resonance imaging (MRI) subsequently used for spatial validation of the EIT reconstruction. The torso surface in the MR image and electrode positions obtained using MRI fiducial markers informed the construction of a 3D finite element model extruded along the caudal-distal axis of the subject. Small changes in the boundary that occur during respiration were accounted for by incorporating the sensitivity with respect to boundary shape into a robust temporal difference reconstruction algorithm. EIT and MRI images were co-registered using the open source medical imaging software, 3D Slicer. A quantitative comparison of quality of different EIT reconstructions was achieved through calculation of the mutual information with a lung-segmented MR image. EIT reconstructions using a linear shape correction algorithm reduced boundary image artefacts, yielding better contrast of the lungs, and had 10% greater mutual information compared with a standard linear EIT reconstruction.

A multicentre analysis of troponin use in clinical practice.

BACKGROUND: The role of troponin quantification in evaluation of patients with suspected acute coronary syndrome is established, but with cost implications. Emerging high-sensitivity troponin and novel multi-marker assays herald further resource implications. AIMS: The objective of this study was to quantify recent trends in troponin usage and costs in a cross-section of hospitals. METHODS: A cross-sectional survey seeking data on troponin usage and costs from six tertiary referral, public access teaching hospitals for consecutive years between 2003 and 2009 was carried out. RESULTS: A median annual increase in the volume of troponin assays requested was identified in all six hospitals, with an average median annual increase of 6.9 % across hospitals (interquartile range 3.4, 10.1 %). This annual increase was not accompanied by a corresponding increase in volume of patients presenting to the Emergency Department (ED) with chest pain. The majority (44-67 %) of troponin requests originated in the ED of hospitals. The median annual spend on troponins per hospital was 115,612 (interquartile range 80,452, 140,918). An analysis of results of assays performed in one centre found that the majority (91 %) of troponin assays performed were in the normal range. CONCLUSIONS: An annual increase in troponin requests without a corresponding increase in patient activity raises the possibility of increasingly indiscriminate troponin testing. The cumulative direct and indirect costs of inappropriate testing are significant. Corrective strategies are necessary to improve patient selection and testing protocols, particularly in the advent of the high-sensitivity troponin assays and novel multi-marker strategies.

Increasing cardiac interventions among the aged.

Ireland's over 65 year population is growing. As incidence of coronary events rises with age, there is a growing population of elderly patients with cardiac disease. The changing age profile of patients treated by a tertiary hospital's Cardiology service was quantified using Hospital Inpatient Enquiry data. 53% of CCU admissions were aged > or = 65 years, with admissions aged > or = 85 years in 2008 four times greater than in 2002. Percentages of patients undergoing diagnostic coronary angiography and percutaneous coronary interventions in 1997 aged > or = 70 years were 19% and 18% respectively. By 2007, these percentages had risen to 31% and 34% respectively--greatest increases were in the very elderly age categories. The proportion of ICD recipients aged > 70 years increased from 8% in 2003 to 25% by 2008. The proportion of elderly patients receiving advanced cardiac care is increasing. This trend will continue and has clear resource implications. Outcomes of interventions in the very old need further investigation, since the 'old old' are under-represented in clinical trials.

Low-noise current excitation sub-system for medical EIT.

Electrical impedance tomography (EIT) has many potential applications in medicine. The sensitivity and spatial resolution of EIT can be enhanced significantly by increasing the measurement signal-to-noise ratio (SNR), to which a significant contribution is made by the SNR of the current excitation sub-system. In this paper we present a prototype EIT current excitation sub-system with 80 dB SNR, exploiting both digital and analogue techniques. It uses digital waveform synthesis, a 16-bit DAC and subsequent reconstruction filter, to drive an enhanced Howland current source. Detailed analysis and testing of the current sub-system are presented. Its output impedance is 10 MOmega for different load impedances, varying slowly over the frequency range from 10 kHz up to 4 MHz.

A study of composite electrode-tissue impedance.

Electrical impedance tomography has been used in the medical environment for many years. Recently it has been used for brain function imaging. This type of technology uses a large number of electrodes on the scalp, examples in the literature ranging from 8 to 64. In this paper, the composite impedance of the electrode in contact with tissue is investigated. An experimental method has been developed to enable the use of a commercial impedance analyzer in compliance with medical safety standards. The magnitude and long-term stability of the composite impedance of the electrode-tissue system is found to be greatly dependent on the type of electrodes used.

Sub-second functional imaging by electrical impedance tomography.

Functional imaging of the human brain using electrical impedance tomography (EIT) is reported, where the measurement data were collected over a period of 308 ms. Initiation of the measurement sequence occurred at times ranging from 70 to 740 ms after administration of visual or auditory stimuli to two volunteers. The reconstructed images of conductivity change due to individual visual stimulus events correspond with anatomical regions known to be involved in visual sensory processing and the processing of cognitive reflexes. We propose that the mechanism enabling this EIT imaging capability is concerned with synaptic effects upon local conductivity of bulk brain tissue, which is supported by the observations of Klivington and Galambos. In turn, the sensitivity of EIT to this effect is much greater than previously expected, due to the high conductivity of in-vivo skull.

Subsecond observations of EIT voltage changes on the human scalp due to brain stimulus.

A pilot study has investigated the feasibility of imaging human brain function using an electrical impedance tomography (EIT) system time-locked to an evoked response (ER) system. A sixteen-electrode planar EIT configuration was used with polar current injection. We report here measurements on two volunteer patients who were fully awake in all tests. Reference data (with no applied stimulus) yield EIT nearest-neighbour voltage differences over the range 5-28 mV. In comparison with forward calculations [C.M. Towers et al. (2000)], these data suggest a value of skull conductivity of the order of 0.05 S/m. Visual and auditory stimuli were applied as single discrete events to evoke neural responses (VER and AER respectively). In each case, EIT data acquisition commenced at a time between 70 and 740 ms later, taking 308 ms to complete. Average values of voltage pair data over many frames are presented here, with the emphasis on the VER data. When comparing data taken under stimulus conditions against the reference data, voltage differences of up to approximately 3 mV are observed in both AER and VER cases. We attribute these voltage changes to synaptic activity. Preliminary reconstructed images of conductivity are discussed.

Isolated chylopericardium.

A 25-year-old male was discovered to have an asymptomatic pericardial effusion during routine pre-employment medical evaluation. During pericardiocentesis 1200 ml of milky-white fluid was obtained; subsequent biochemical evaluation confirmed the chylous nature of this fluid. Following thorough evaluation a diagnosis of isolated chylopericardium was made. Following several recurrences he underwent thoracotomy with ligation of the thoracic duct and creation of a pericardial window. There are relatively few published reports of true isolated chylopericardium and the aetiology and pathogenesis remain unknown. A primary abnormality of the thoracic lymphatic valve system is postulated. The most effective treatment is surgical with ligation of the thoracic duct above the diaphragm and creation of a pericardial window

Corticobasal syndrome with tau pathology.

Six cases with a clinical corticobasal syndrome (progressive asymmetric apraxia and parkinsonism unresponsive to levodopa) and tau pathology were selected from 97 brain donors with parkinsonism. Postmortem volumetric measures of regional brain atrophy (compared with age/sex-matched controls) were correlated with clinical features and the degree of underlying cortical and subcortical histopathology. At death, no significant asymmetry of pathology was detected. All cases had prominent bilateral atrophy of the precentral gyrus (reduced by 22-54%) with other cortical regions variably affected. Subcortical atrophy was less severe and variable. Two cases demonstrated widespread atrophy of basal ganglia structures (44-60% atrophy of the internal globus pallidus) and substantial subcortical pathology consistent with a diagnosis of progressive supranuclear palsy (PSP). The remaining four cases had typical pathology of corticobasal degeneration. In all cases, neuronal loss and gliosis corresponded with subcortical atrophy, while the density of cortical swollen neurons correlated with cortical volume loss. Atrophy of the internal globus pallidus was associated with postural instability, while widespread basal ganglia histopathology was found in cases with gaze palsy. This study confirms the involvement of the precentral gyrus in the corticobasal syndrome and highlights the variable underlying pathology in these patients.

Neurofilament-immunoreactive neurons are not selectively vulnerable in Alzheimer's disease.

Abnormal neurofilament protein distribution and phosphorylation contributes to the cytoskeletal pathology of Alzheimer's disease. Anatomical studies suggest that cortical neurons immunoreactive for nonphosphorylated 200-kDa neurofilament are most vulnerable. We repeated these studies in formalin-fixed temporal lobe tissue from five Alzheimer's disease cases with tissue volume loss compared to five controls without tissue loss. Immunohistochemistry for nonphosphorylated and phosphorylated forms of the neurofilament protein was counterstained for Nissl substance and immuno-positive and -negative pyramidal neurons quantified using areal fraction counts. Compared with controls, cases with Alzheimer's disease had similar numbers of neurons expressing the nonphosphorylated neurofilament protein, suggesting these neurons are largely spared by the disease process. In Alzheimer's disease there was a significant increase in neurons containing phosphorylated neurofilament and tau proteins and a decrease in neurons devoid of neurofilament protein. Our results challenge the theory that neurons containing 200 kDa neurofilament are selectively vulnerable in Alzheimer's disease.

Cortical inflammation in Alzheimer disease but not dementia with Lewy bodies.

BACKGROUND: There have been no previous studies on the role of inflammation in the brain for the second most common dementing disorder, dementia with Lewy bodies. OBJECTIVE: To investigate the degree of cortical inflammation in dementia with Lewy bodies (DLB) compared with Alzheimer disease (AD) and control brains. DESIGN AND MAIN OUTCOME MEASURES: Post-mortem tissue collection from a brain donor program using standardized diagnostic criteria. Brains collected from January 1, 1993, through December 31, 1996, were screened and selected only for the presence or absence of tau neuritic plaques. Results of immunohistochemistry for HLA-DR were quantified using area fraction counts. Counts were performed by investigators who were unaware of the diagnosis. Results were compared across groups using analysis of variance and posthoc testing. SETTING: A medical research institute in Sydney, Australia. PATIENTS: Eight brains with DLB and without the tau neuritic plaques typical of AD, 10 brains with AD and no Lewy bodies, and 11 nondemented controls without significant neuropathological features were selected from a consecutive sample. RESULTS: Compared with AD, DLB demonstrated significantly less inflammation in the form of HLA-DR-reactive microglia in all cortical regions (P<.001, posthoc). The level of inflammation in DLB was comparable to that seen in controls (P=.54, post hoc). CONCLUSIONS: Inflammation appears related to the tau neuritic plaques of AD. Despite similar clinical presentations, therapeutic anti-inflammatory strategies are not likely to be effective for pure DLB. Arch Neurol. 2000.

Effect of anti-inflammatory medications on neuropathological findings in Alzheimer disease.

BACKGROUND: There has been no analysis of brain tissue from longitudinally observed, cognitively tested patients to validate whether anti-inflammatory medications protect against the pathological changes of Alzheimer disease. OBJECTIVE: To investigate the role of anti-inflammatory medications in alleviating the pathological features of Alzheimer disease. DESIGN AND MAIN OUTCOME MEASURES: A 5-year postmortem tissue collection was performed after a case-control study of Alzheimer disease (approximately 90 [30%] of patients died during follow-up, of whom consent for autopsy was obtained in 44 [50%]). Cases were selected on the basis of (1) adequate clinical histories of nonsteroidal anti-inflammatory drug usage, (2) no neuropathological findings other than Alzheimer disease, and (3) no generalized sepsis at death. Variables analyzed included neuropsychological test scores and amount of tissue inflammation and Alzheimer-type pathological changes. Two-way analysis of variance was used to determine whether drug usage significantly affected these variables. SETTING: The Centre for Education and Research on Ageing and the Prince of Wales Medical Research Institute, Sydney, Australia. PATIENTS: Twelve patients with Alzheimer disease (5 taking anti-inflammatory drugs) and 10 nondemented controls (3 taking anti-inflammatory drugs) were selected (50% of available sample). RESULTS: Of the patients with Alzheimer disease, anti-inflammatory drug users performed better on neuropsychological test scores than did nonusers. However, there were no significant differences in the amount of inflammatory glia, plaques, or tangles in either diagnostic group. CONCLUSION: Long-term anti-inflammatory medications in patients with Alzheimer disease enhanced cognitive performance but did not alleviate the progression of the pathological changes. Arch Neurol. 2000.

Gender differences in the management and outcome of acute myocardial infarction in unselected patients in the thrombolytic era.

This study compares the clinical features, management, and outcome in men and women from a consecutive, unselected series of patients with acute myocardial infarction (AMI) who were admitted to a university cardiac center over a 3-year period. It is a retrospective observational study of 1,059 admissions with AMI identified through the Hospital In-Patient Enquiry (HIPE) registry, validated according to Minnesota Manual criteria, and followed for a period of up to 5 years (median 36 months). Women comprised 40% of all admissions, had a higher hospital mortality (24% vs. 16%, p<0.001), and were less likely to receive thrombolysis (23% vs. 33%, p<0.01), admission to coronary care (65% vs. 77%, p<0.001), or subsequent invasive or noninvasive investigations (55% vs. 63%, p<0.01). However, women with AMI were older than men with AMI (71 vs. 65 years, p<0.001). After adjusting for age, differences that remained significant were prevalence of hypertension (odds ratio [OR] 2.12, 95% confidence intervals [CI] 1.56 to 2.88) and cigarette smoking (OR 0.47, 95% CI 0.35 to 0.65), management in coronary care (OR 0.66, 95% CI 0.49 to 0.88), and hospital mortality (OR 1.48, 95% CI 1.07 to 2.04). Excess mortality occurred predominantly in women <65 years old (18% vs. 8%, OR [multivariate] 2.35, 95% CI 1.19 to 4.56), among whom multivariate analysis demonstrated a significantly lower thrombolysis rate (OR 0.48, 95% CI 0.27 to 0.86). In this group, lack of thrombolysis independently predicted hospital mortality (OR 5.37, 95% CI 1.45 to 19.82). Female gender was not an independent predictor of mortality following AMI (OR 1.42, 95% CI 0.90 to 2.26). Thus, among unselected patients, female gender is associated with, but not an independent predictor of, reduced survival after AMI. Gender differences in mortality are greatest in younger patients, who are less likely to receive thrombolysis and in whom lack of thrombolysis is independently associated with mortality after AMI.

3D simulation of EIT for monitoring impedance variations within the human head.

A preliminary analysis is presented concerning the use of EIT for detecting impedance inhomogeneities within the human brain. The work to date is centred around the monitoring of two distinct impedance variations: those associated with the application of a carotid clamp during surgery and changes caused by the redistribution of blood flow during auditory stimuli. Using the commercially available Ansoft Maxwell package, a 3D finite element model of the human head has been developed to solve the forward problem. The model is hemispherical in shape and comprises regions of brain, cerebrospinal fluid, skull and skin and includes 16 scalp electrodes each of area 1 cm2. Results from simulations using the model suggest that an EIT system, incorporating diametric current excitation, would require a voltage measurement sensitivity of 100-120 dB in order to detect the impedance variations in the above cases.

Characteristics and outcomes in patients with acute myocardial infarction with ST-segment depression on initial electrocardiogram.

BACKGROUND: Acute myocardial infarction (AMI) with nonreciprocal ST-segment depression is said to have a poor prognosis, and early diagnosis and treatment are problematic. The aim of this study was to determine the proportion of unselected consecutive patients admitted to a university center with AMI with nonreciprocal ST-segment depression and to characterize these patients in terms of clinical features, treatment, and short- and long-term prognoses. METHODS AND RESULTS: Admission electrocardiographic data on 852 consecutive admissions with AMI were analyzed. Nonreciprocal ST-depression was an admitting feature in 95 (11%) patients, the majority of whom had ST depression >3 mm. These were older (70.3 vs 66.8 years, P <.05), more likely to have had myocardial infarction (40% vs 25%, P <.01), and to have left ventricular failure (56% vs 42%, P <.5), cardiogenic shock (15% vs 9% P =.06), and atrial fibrillation (34% vs 19%, P <.01). Hospital mortality rate was significantly higher (31% vs 17%, P <.01). Patients were less likely to undergo thrombolysis (17% vs 31%, P <.01), angiography (22% vs 35%, P <.05), or percutaneous revascularization (5% vs 9%, P <.01). Patients with ST depression undergoing coronary angiography were more likely to have 3-vessel disease (71% vs 47%, P <.05). Mortality rate at follow-up (median 36 months) was significantly higher in patients with ST depression (56% vs 32%, P <.001). Analysis by individual electrocardiography demonstrated ST-segment depression to be the third most frequent presentation after ST elevation (n = 327) and T-wave changes (n = 258), in whom hospital mortality rates were 24% and 9%, respectively. In multivariate analysis, previous myocardial infarction was an independent predictor of nonreciprocal ST depression at initial examination (odds ratio 2.04 [1.25 to 3.34], P <.005). No electrocardiographic presentation was an independent predictor of death in the hospital after AMI. CONCLUSIONS: In unselected cases of AMI, patients with ST-segment depression make up a significant minority (11%), who are likely to be older with a high prevalence of previous myocardial infarction and multivessel disease, and who have a poor prognosis.