Evaluation of volumetric changes in differential diagnosis of brain atrophy and active hydrocephalus.

Despite a variety of diagnostic methods, differentiation of symptoms of normal pressure hydrocephalus from those of atrophic processes of the brain is still a difficult task. In the present study an attempt of non-invasive differential diagnosis of normal pressure hydrocephalus (NPH) and brain atrophy (BA) was presented using volumetric analysis of CT images of the head by means of VisNow proprietary software. The analysis was based on the number of voxels converted to the amount of cerebrospinal fluid (CSF) in the subarachnoid space, skull base casters, and the ventricular system. The results demonstrate that the mean volumes of CSF in these compartments in patients with NPH differed significantly from those in BA. Similarly, the mean volumes of CSF in the subarachnoid space and skull base casters in patients with BA differed significantly from those in NPH. Volumetric assessment presented in the paper by application of VisNow software seems useful in the evaluation of NPH and brain BA.

Physical and computer modelling of blood flow in a systemic-to-pulmonary shunt.

UNLABELLED: The aim of this work was the application of computer and physical in vitro simulation methods for estimating surgery procedure hemodynamics. The modified Blalock-Taussig (mB-T) palliative surgical procedure is performed to increase the pulmonary blood flow in children with congenital heart defects. Such a systemic-to-pulmonary shunt yields substantial modification in the blood flow within the large blood vessels. The objective of the present study was to investigate basic characteristics of the flow, flow pattern and pressure-flow efficiency, before and after opening of the mB-T graft. METHODS: The model was based on the vessel geometry obtained from the Visible Human Project and included the arch of aorta, the three arteries branching from the arch, the pulmonary trunck, and the left and right pulmonary arteries. The graft was added between the left subclavian artery and the left pulmonary artery. The glass model of the vessels was produced and investigated in a physical model of the cardiovascular system with an artificial ventricular device as the blood pump. Flow rate and hydrostatic pressure were measured at the inlet to and outlets from the glass model and in a few points within the system. Laser flow visualization was also performed. Computer simulations were done using the boundary conditions from the physical model. RESULTS: The opening of the mB-T graft changed flow distribution in all branches (including inflow). A complex flow pattern with large eddies and channelling of the flow in the vicinity of the graft and within it was observed in flow visualization and in computer simulations. Because of that complexity the local measurements of hydrostatic pressure at the vessel wall could not predict the average flow rate. The reversed flow in the graft was observed during the systole. CONCLUSIONS: The complex flow pattern developed in the physical model of the mB-T graft. The channelling of the flow and the formation of large eddies may yield high shear stress and modify blood properties. The rigid wall model can describe only some flow characteristics observed in vivo. Computer simulation is a very fast and accurate method which permits earlier qualification of cardiac surgeons on how to change cardiac vascular blood flow after operations.

Automatic alignment of EEG/MEG and MRI data sets.

OBJECTIVES: We developed a new technique of fully automatic alignment of brain data acquired with scalp sensors (e.g. electroencephalography/evoked potential (EP) electrodes, magnetoencephalography sensors) with a magnetic resonance imaging (MRI) volume of the head. METHODS: The method uses geometrical features (two sets of head points: digitized from the subject and extracted from MRI) to guide the alignment. It combines matching on 3 dimensional (3D) geometrical moments that perform the initial alignment, and 3D distance-based alignment that provides the final tuning. To reduce errors of the initial guessed computation resulting from digitization of the head surface points we introduced weights to compute geometrical moments, and a procedure to remove outliers to eliminate incorrectly digitized points. RESULTS: The method was tested on simulated (Monte Carlo trials) and on real data sets. The simulations demonstrated that for the number of test points within the range of 0.1-1% of the total number of head surface points and for the digitization error in the range of -2-2 mm the average map error was between 0.7 and 2.1 mm. The average distance error was less than 1 mm. Tests on real data gave the average distance error between 2.1 and 2.5 mm. CONCLUSIONS: The developed technique is fast, robust and comfortable for the patient and for medical personnel. It registers scalp sensor positions with MRI head volume with accuracy that is satisfactory for localization of biological processes examined with a commonly used number of scalp sensors (32, 64, or 128).

Quantum-dynamical picture of a multistep enzymatic process: reaction catalyzed by phospholipase A(2).

A quantum-classical molecular dynamics model (QCMD), applying explicit integration of the time-dependent Schrödinger equation (QD) and Newtonian equations of motion (MD), is presented. The model is capable of describing quantum dynamical processes in complex biomolecular systems. It has been applied in simulations of a multistep catalytic process carried out by phospholipase A(2) in its active site. The process includes quantum-dynamical proton transfer from a water molecule to histidine localized in the active site, followed by a nucleophilic attack of the resulting OH(-) group on a carbonyl carbon atom of a phospholipid substrate, leading to cleavage of an adjacent ester bond. The process has been simulated using a parallel version of the QCMD code. The potential energy function for the active site is computed using an approximate valence bond (AVB) method. The dynamics of the key proton is described either by QD or classical MD. The coupling between the quantum proton and the classical atoms is accomplished via Hellmann-Feynman forces, as well as the time dependence of the potential energy function in the Schrödinger equation (QCMD/AVB model). Analysis of the simulation results with an Advanced Visualization System revealed a correlated rather than a stepwise picture of the enzymatic process. It is shown that an sp(2)--> sp(3) configurational change at the substrate carbonyl carbon is mostly responsible for triggering the activation process.

Changes in ventricular repolarization during percutaneous transluminal coronary angioplasty in humans assessed by QT interval, QT dispersion and T vector loop morphology.

OBJECTIVES: Based on clinical, epidemiological, and experimental data, transient cardiac ischaemia is one of the major triggering factors of malignant ventricular arrhythmia. According to animal studies, increased dispersion of repolarization is of pathophysiological relevance in this context. Therefore we explored the impact of myocardial ischaemia during single vessel coronary angioplasty on the change in ventricular repolarization, measured by QT and JT intervals and their dispersion in the 12-lead electrocardiogram. We also assessed a novel method, the 3-dimensional T vector loop, to find out whether it was sensitive to changes in ventricular repolarization during ischaemia, and whether there was any correlation with changes in the dispersion of the QT and/or JT intervals. DESIGN: This study was prospective with consecutive patients. Only patients in sinus rhythm and without bundle branch block were included. SETTING: All coronary angioplasties were performed at Norrlands University Hospital, Umeå. The analysis of the material was performed at the Karolinska Hospital, Stockholm. SUBJECTS: Twenty-nine consecutive patients went through 30 elective one-vessel percutaneous transluminal coronary angioplasty (PTCA) procedures. PTCA was performed in 10 stenoses of the left anterior descending, 10 of the left circumflex, and 10 of the right coronary artery. INTERVENTIONS: A 12-lead electrocardiogram was recorded continuously as part of routine monitoring of the patient during PTCA and the T vector loop was calculated from the simultaneously recorded. X, Y, Z leads. MAIN OUTCOME MEASURES: Repolarization was assessed by the QRS, QT and JT intervals as well as by the T vector loop parameters (Tarea, Tavplan, and Teigenv) before and at the end of the first occlusion during PTCA. RESULTS: PTCA, with an average occlusion time of 171 +/- 60 s (mean +/- SD), induced ischaemia on the 12-lead electrocardiogram in 73% of cases. The overall response for the 30 procedures was a significantly increased dispersion of ventricular repolarization, both corrected and uncorrected for heart rate. QT dispersion increased by, on average, 19% from 74 +/- 35 to 88 +/- 36 ms, QTc dispersion by 27% from 71 +/- 39 to 90 +/- 42 ms, and JTc dispersion by 19% from 78 +/- 32 to 94 +/- 43 ms (P < 0.05). The T vector loop became more circular and bulgy during occlusion (all three parameters changed by between 33% and 59%). There was a significant correlation between changes in one of the T vector loop parameters (Teigenv), and changes in JT and QT dispersion in the left anterior descending group. CONCLUSIONS: Transient ischaemia during PTCA induced significant changes in ventricular repolarization, especially during occlusion of the left anterior descending artery and resulted in a significant increase in both QT and QTc dispersion. The degree of QT dispersion was such that several patients were at risk of ventricular arrhythmia, if a proper triggering extrasystole had occurred. In addition, and as an original observation, the 3-dimensional T vector loop morphology seemed even more sensitive to coronary occlusion than QT dispersion.

Presentation of brain electrical activity distribution on its cortex surface derived from MR images.

Analysis of scalp-recorded potentials (EEG or evoked potential examination) is of great importance for studying bioelectrical processes in the human brain both in normal and pathological cases. Investigating potential distributions in the relation to individual topography of the cortex is helpful in treatment and surgery planning. We developed a method providing visual presentation of electrical potentials measured in EEG examination superimposed on a patient's cortex surface computed from MRI data. Analysis of such images contributes into diagnostics of common neurological disorders (for example: epilepsy, Parkinson's disease, any mechanical damage). Integration of EEG and MRI data sets requires their alignment. This paper focuses on applying a new registration technique for the alignment of these two data sets. The method does not require any external fiducial markers to be fixed on a patient's head, what makes it convenient for numerous examinations performed in clinic. Alignment bases on geometrical features derived from intrinsic data of an image or an object. To show the example of usage of the technique for assisting in neurological diagnostics we present results of SEP (sensory evoked potential) examinations performed for one pathological case and a control group.

"Normal" response of the QT interval and QT dispersion following intravenous injection of the sodium channel blocker disopyramide: methodological aspects.

Measurement of the QT dispersion (the maximal interlead difference) on the surface electrocardiogram has been suggested for assessing the risk for ventricular arrhythmias and for examining drug effects and their proarrhythmic potential. The acute response of QT dispersion was assessed in 10 healthy subjects receiving disopyramide, which is known to delay repolarization and to prolong global measures thereof. The QRS, JT, and QT intervals and their dispersion were assessed at spontaneous rhythm and at atrial pacing at baseline and after an intravenous injection of disopyramide 2 mg/kg over 5 minutes. The short-term (within 30 minutes) and long-term (> or = 2 weeks) variabilities of the QT interval and the QT dispersion, expressed as the coefficient of variation, were also analyzed. At spontaneous rhythm the group average QT interval was between 369 and 375 msec, and the QT dispersion was between 33 and 37 msec; both were relatively stable over time. All subjects responded homogeneously to disopyramide with a significant QT prolongation (p < 0.001), but no consistent response of the QT dispersion was observed. This discrepancy reflects the significant difference in time-dependent variability with a coefficient of variation of spontaneous, paced, and heart rate-corrected QT dispersion between 25% and 42%, 8-42 times greater than the corresponding values of 1-4% for the QT intervals. The individual response of the QT dispersion to drug challenge should therefore be interpreted with caution. Furthermore and as a consequence, QT dispersion is less sensitive for assessing drug effects on ventricular depolarization and repolarization than the QT interval.