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PubMed2004

Liver segmentation in living liver transplant donors: comparison of semiautomatic and manual methods.

PURPOSE: To compare the accuracy and repeatability of a semiautomatic segmentation algorithm with those of manual segmentation for determining liver volume in living liver transplant donors at magnetic resonance (MR) imaging. MATERIALS AND METHODS: The institutional review board approved this retrospective study and waived the requirement for informed consent. The semiautomatic segmentation algorithm is based on geometric deformable models and the level-set technique. It entails (a) placing initialization circle(s) on each image section, (b) running the algorithm, (c) inspecting and possibly manually modifying the contours obtained with the segmentation algorithm, and (d) placing lines to separate the liver segments. For 18 living donors (eight men and 10 women; mean age, 34 years; age range, 25-46 years), two observers each performed two semiautomatic and two manual segmentations on contrast material-enhanced T1-weighted MR images. Each measurement was timed. Actual graft weight was measured during surgery. The time needed for manual and that needed for semiautomatic segmentation were compared. Accuracy and repeatability were evaluated with the Bland-Altman method. RESULTS: Mean interaction time was reduced from 25 minutes with manual segmentation to 5 minutes with semiautomatic segmentation. The mean total time for the semiautomatic process was 7 minutes 20 seconds. Differences between the actual volume and the estimated volume ranged from -223 to +123 mL for manual segmentation and from -214 to +86 mL for semiautomatic segmentation. The 95% limits of agreement for the ratio of actual graft volume to estimated graft volume were 0.686 and 1.601 for semiautomatic segmentation and 0.651 and 1.957 for manual segmentation. Semiautomatic segmentation improved estimation in 15 of 18 cases. Inter- and intraobserver repeatability was higher with semiautomatic segmentation. CONCLUSION: Use of the semiautomatic segmentation algorithm substantially reduces the time needed for volumetric measurement of liver segments while improving both accuracy and repeatability.

Adult↗
PubMed2006

Higher serum triglyceride level in patients with acute ischemic stroke is associated with lower infarct volume on CT brain scans.

We investigated the relationship between serum triglyceride level and acute ischemic stroke severity using infarct volume on CT brain scans as a marker. A total of 121 consecutive acute ischemic stroke patients (53 males and 68 females, age 47-93 years) with anterior circulation (75%), posterior circulation (9%) or lacunar infarcts (16%) were examined. All patients were admitted within 24 h of the symptom onset, and CT scans were taken over the subsequent 24-72 h. With adjustment for the infarct type, age, sex, timing of CT imaging (24-36, >36-48 or >48-72 h since admission), atrial fibrillation, hypertension, fasting cholesterol and glucose levels, a higher (> or =1.70 mmol/l) fasting serum triglyceride level (within 24 h after admission) was associated with a lower infarct volume (p = 0.014). In line with a recent report on milder clinical symptoms in acute ischemic stroke patients with higher triglycerides, the results suggest an independent association between serum triglyceride level and stroke severity.

Aged↗
PubMed2006

Fatal respiratory depression after multiple intravenous morphine injections.

A 26-year-old female was treated with morphine within the first 2 hours after knee surgery, in an attempt to titrate analgesia. The patient received a total of four intravenous injections of morphine 35 mg in total. Soon after the last injection the patient had adequate pain relief, was in a good clinical state and had adequate blood oxygenation. However, 40 minutes later, the patient had a deep respiratory depression followed by a fatal cardiac arrest. Solving the case in a medico-legal context was possible by applying results of clinical pharmacokinetic research on opioid analgesics, most importantly morphine, to this particular clinical case. This knowledge made it possible to estimate the probable concentrations of morphine at the site of its effect, the brain, during the time of the fatal event, and to show that these concentrations could have produced respiratory depression. We mainly attribute the fatal intoxication of morphine to the lag period needed for the transfer of morphine across the blood-brain barrier. Because of its slow transfer between plasma and the effect site, the CNS effects of morphine are delayed from its plasma concentrations to a clinically relevant degree. Successive injections at short intervals of relatively high amounts of morphine increase the clinical relevance of this delay. The present report demonstrates an important application of clinical pharmacokinetics for explaining clinical observations at a scientific level and transferring theoretical knowledge from clinical pharmacokinetics into daily clinical practice as a basis for rational opioid selection.

Adult↗
PubMed2005

A PDA-based system for online recording and analysis of concurrent events in complex behavioral processes.

This article outlines how a Palm- or Newton-based PDA (personal digital assistant) system for online event recording was used to record and analyze concurrent events. We describe the features of this PDA-based system, called the FIT-System (flexible interface technique), and its application to the analysis of concurrent events in complex behavioral processes--in this case, anesthesia work processes. The patented FIT-System has a unique user interface design allowing the user to design an interface template with a pencil and paper or using a transparency film. The template usually consists of a drawing or sketch that includes icons or symbols that depict the observer's representation of the situation to be observed. In this study, the FIT-System allowed us to create a design for fast, intuitive online recording of concurrent events using a set of 41 observation codes. An analysis of concurrent events leads to a description of action density, and our results revealed a characteristic distribution of action density during the administration of anesthesia in the operating room. This distribution indicated the central role of the overlapping operations in the action sequences of medical professionals as they deal with the varying requirements of this complex task. We believe that the FIT-System for online recording of concurrent events in complex behavioral processes has the potential to be useful across a broad spectrum of research areas.

Adult↗
PubMed2002

Creating a statistical atlas of the cranium.

Normative data is very important for simulation procedures in craniofacial surgery. While treating e.g. a malformed skull the surgeon seeks to reconstruct its natural and harmonic shape. Atlas or normative data of the skull could support the surgeon in this effort, as it would provide a standard model of the skull which gives an idea of the natural shape. We create a standard skull by averaging regularly formed skulls in a shape space spanned by spherical harmonics. While state-of-the-art methods use landmarks to define the shape and mean shapes, this method is deterministic, i.e. it manages averaging without landmarks and it provides a complete description of the shape. In addition the shape space can be used to classify shapes to identify different types of an anatomy.

Cephalometry↗
PubMed2002

Multimodal simulation of laparoscopic Heller myotomy using a meshless technique.

In this work we focus our attention on developing a surgical simulator for performing laparoscopic Heller myotomy using force feedback. A meshless numerical technique, the method of finite spheres, is used for the purpose of physically based, real time haptic and graphical rendering of soft tissues. Localized discretization allows display of deformations in the vicinity of the tool tip as well as interaction forces at high update rates (kHz). Novel cutting algorithms are implemented using point-based representation of anatomical models. Graphical rendering is accomplished by using a recently developed volumetric rendering technique known as splatting.

Computer Graphics↗
PubMed2002

Atlas-based segmentation of pathological knee joints.

Efficiency, comparability and simplicity are key aspects for user acceptance of surgical planning systems in the long term. Automatic segmentation and identification of geometric reference systems of the anatomical structures are essential to fulfill these requirements. A statistical motivated shape atlas of the knee joint, based on 235 normal and abnormal MR and CT volume sets, is constructed for automatic segmentation of CT image data. In the first step of the atlas construction, the bony structures of the knee were segmented semi-automatically and processed into a dense and a sparse triangulated surface mesh to obtain training data sets. To establish an inter-individual correspondence, a skeleton-based registration method is used. The registered sparse surface meshes are retriangulated to estimate a pointwise inter-individual correspondence. The shape atlas is build upon these correspondences and integrated into a segmentation algorithm. An iterative segmentation scheme is proposed, which consists of a combination of the iterative-closest-point algorithm for spatial registration and of a downhill-simplex optimization procedure for deformation of the statistical motivated shape atlas to the image data. We expect the statistical shape model to be a robust and image modality independent method for the segmentation of pathological knee joints in CT image data.

Arthroplasty, Replacement, Knee↗
PubMed1990

[An attempt to quantify myocardial ischemia by selective coronary arteriography: determination of a new score. An initial study].

An original model for estimating myocardial ischaemia from coronary arteriography is proposed. Four parameters are taken into consideration: anatomical variations, the myocardial mass perfused, the degree of reduction of basal flow across the stenosis, the eventual summation of several successive stenotic lesions. This scoring system was tested by simulation on a computer and evaluated in 100 anginal patients. Analysis of our preliminary results shows statistically significant differences in the score between the following groups of patients: patients with normal and those with abnormal LV wall motion; patients with and those without previous myocardial infarction; patients with Class II stable angina and those with other forms (III, IV and unstable angina).

Adult↗
PubMedDate not supplied

A Gaussian method to improve work-of-breathing calculations.

The work of breathing is a calculated index of pulmonary function in ventilated patients that may be useful in deciding when to wean and when to extubate. However, the accuracy of the calculated work of breathing of the patient (WOBp) can suffer from artifacts introduced by coughing, swallowing, and other non-breathing maneuvers. The WOBp in this case will include not only the usual work of inspiration, but also the work of performing these non-breathing maneuvers. The authors developed a method to objectively eliminate the calculated work of these movements from the work of breathing, based on fitting to a Gaussian curve the variable P, which is obtained from the difference between the esophageal pressure change and the airway pressure change during each breath. In spontaneously breathing adults the normal breaths fit the Gaussian curve, while breaths that contain non-breathing maneuvers do not. In this Gaussian breath-elimination method (GM), breaths that are two standard deviations from that mean obtained by the fit are eliminated. For normally breathing control adult subjects, GM had little effect on WOBp, reducing it from 0.49 to 0.47 J/L (n = 8), while there was a 40% reduction in the coefficient of variation. Non-breathing maneuvers were simulated by coughing, which increased WOBp to 0.88 (n = 6); with the GM correction, WOBp was 0.50 J/L, a value not significantly different from that of normal breathing. Occlusion also increased WOBp to 0.60 J/L, but GM-corrected WOBp was 0.51 J/L, a normal value. As predicted, doubling the respiratory rate did not change the WOBp before or after the GM correction.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Strategic exploration and analysis using interactive visualization of health care databases.

Effective analysis of health care information is a central component in formulating strategies for improvement initiatives. These initiatives involve the analysis of episodes of care, quality measure comparisons, resource utilization, and investigation of temporal relationships between various factors and outcomes. The ability to efficiently recognize the principal patterns and their variations presents special challenges. This paper describes the design issues and application of the Interactive Visual-Exploratory Data Analysis (IV/EDA) system. IV/EDA is a graphical approach to exploratory analysis of health care information designed to rapidly find and communicate relationships essential to formulating and evaluating strategies that address health care improvement.

Computer Graphics↗
PubMed1997

[The computer as an assistant to the physician].

BACKGROUND: The possibilities of using computer in physician's research work are presented as an example of statistical analysis of axial eyeball length in relation to the age in myopic children with low birthweight. MATERIAL AND METHODS: The study group consisted of 100 children aged from 3 to 15 years, with birthweight from 580 to 2450 g, where in 180 eyes myopia ranging from -1.5 to -22.0 Dsph and axial length of the eye from 20.0 to 30.9 mm were present. The dynamics of eyeball's axial length increase was compared between two groups: one-in which no symptoms of retinopathy of prematurity were present (no-RROP), and the second--in which signs of regressed retinopathy of prematurity were observed (RROP). RESULTS: The results of the analysis are shown in analytical and graphical modes. Statistically significant differences were shown between axial lengths of eyeball's in the analysed groups of mean 9-year-old premature children (no-RROP: 25.19 mm and RROP: 24.33 mm). It was shown that the use of a computer reduces the time of performing statistical analysis of large amount of data.

Adolescent↗
PubMedDate not supplied

Drug redistribution and mean transit time concepts for nonlinear pharmacokinetic systems.

Equations for the mean number of cycles through the peripheral system (R) and the mean transit time through the central compartment (MTTc) are derived for intravenous drugs with linear distribution and linear or nonlinear central elimination. This R is a function of distribution clearance (CLD), dose, and area under the plasma concentration-time curve (AUC). The MTTc is a function of the central volume of distribution, CLD, dose, and AUC. The application of the proposed calculations of R and MTTc was illustrated by computer simulations.

Dose-Response Relationship, Drug↗
PubMed1991

Global tracking of the ocular fundus pattern imaged by scanning laser ophthalmoscopy.

This paper presents an algorithm for the automatic global tracking of ocular fundus landmarks in video image sequences generated by scanning laser ophthalmoscopy (SLO). The tracking algorithm is based on the computation of the discrete unnormalized cross-correlation of an interactively preselected small template and respective images in time sequences of fundus patterns. The correlation is executed with binary images derived from an automatical threshold limitation of the grey-value images. Due to the [+1/-1] representation of the binary images the unnormalized correlation functions directly relate to the Hamming distance of the template and the objects in the images. Experiments show that even templates with features distorted by noise are accurately recognized at any position. The accuracy of position detection is better than 0.4%. Possible hardware implementations of the algorithm which would reduce computation time are briefly mentioned.

Algorithms↗
PubMed1990

Brain maps and parallel computers.

It is well known that neural responses in many brain regions are organized in characteristic spatial patterns referred to as brain maps. It is likely that these patterns in some way reflect aspects of the neural computations being performed, but to date there are no general guiding principles for relating the structure of a brain map to the properties of the associated computation. In the field of parallel computing, maps similar to brain maps arise when computations are distributed across the multiple processors of a parallel computer. In this case, the relationship between maps and computations is well understood and general principles for optimally mapping computations onto parallel computers have been developed. In this paper we discuss how these principles may help illuminate the relationship between maps and computations in the nervous system.

Brain↗
PubMed1997

Solid state NMR sideband shape simulations for any spinning angle and speed. First order calculation of residual dipolar coupling to quadrupolar nuclei.

A simple procedure is described which can be used to simulate solid state NMR sideband shapes for samples rotating at any angle and speed, when a combination of chemical shift anisotropy and dipolar coupling between spin-1/2 and quadrupolar nuclei occurs. The use of Herzfeld-Berger equations for computing individual sideband intensities is coupled to first order perturbation calculation of dipolar coupling effects. The present method can be easily and efficiently implemented on a desktop computer (source code is provided).

Chemical Phenomena↗
PubMed1991

An APL procedure to estimate genotype by environment interaction when two environments are considered.

Genotype by environment interaction (GEI) is a relevant topic in many fields of applied biology. Normal parametric approaches following analysis of variance are not suitable when large differences between error variances within environments are present. We illustrate an APL program following Yamada's approach to estimate GEIs and ancillary statistics when two environments are considered. The choice of APL environment is based on its value as a useful tool in algorithm implementation and problem-solving. Its use is suggested in biological applications where matrix algebra is involved and an understanding of the computing complexity of problems is generally not required.

Algorithms↗
PubMed2004

Rapid calculations of time-harmonic nearfield pressures produced by rectangular pistons.

A rapid method for calculating the nearfield pressure distribution generated by a rectangular piston is derived for time-harmonic excitations. This rapid approach improves the numerical performance relative to the impulse response with an equivalent integral expression that removes the numerical singularities caused by inverse trigonometric functions. The resulting errors are demonstrated in pressure field calculations using the time-harmonic impulse response solution for a rectangular source 5 wavelengths wide by 7.5 wavelengths high. Simulations using this source geometry show that the rapid method eliminates the singularities introduced by the impulse response. The results of pressure field computations are then evaluated in terms of relative errors and computational speeds. The results show that, when the same number of Gauss abscissas are applied to both approaches for time-harmonic pressure field calculations, the rapid method is consistently faster than the impulse response, and the rapid method consistently produces smaller maximum errors than the impulse response. For specified maximum error values of 10% and 1%, the rapid method is 2.6 times faster than the impulse response for pressure field calculations performed on a 61 by 101 point grid. The rapid approach achieves even greater reductions in the computation time for smaller errors and larger grids.

Acoustics↗
PubMedDate not supplied

Contrast media in abdominal computed tomography: optimization of delivery methods.

OBJECTIVE: To provide a systematic overview of the effects of various parameters on contrast enhancement within the same population, an animal experiment as well as a computer-aided simulation study was performed. MATERIALS AND METHODS: In an animal experiment, single-level dynamic CT through the liver was performed at 5-second intervals just after the injection of contrast medium for 3 minutes. Combinations of three different amounts (1, 2, 3 mL/kg), concentrations (150, 200, 300 mgI/mL), and injection rates (0.5, 1, 2 mL/sec) were used. The CT number of the aorta (A), portal vein (P) and liver (L) was measured in each image, and time-attenuation curves for A, P and L were thus obtained. The degree of maximum enhancement (Imax) and time to reach peak enhancement (Tmax) of A, P and L were determined, and times to equilibrium (Teq) were analyzed. In the computed-aided simulation model, a program based on the amount, flow, and diffusion coefficient of body fluid in various compartments of the human body was designed. The input variables were the concentrations, volumes and injection rates of the contrast media used. The program generated the time-attenuation curves of A, P and L, as well as liver-to-hepatocellular carcinoma (HCC) contrast curves. On each curve, we calculated and plotted the optimal temporal window (time period above the lower threshold, which in this experiment was 10 Hounsfield units), the total area under the curve above the lower threshold, and the area within the optimal range. RESULTS: A. Animal Experiment: At a given concentration and injection rate, an increased volume of contrast medium led to increases in Imax A, P and L. In addition, Tmax A, P, L and Teq were prolonged in parallel with increases in injection time The time-attenuation curve shifted upward and to the right. For a given volume and injection rate, an increased concentration of contrast medium increased the degree of aortic, portal and hepatic enhancement, though Tmax A, P and L remained the same. The time-attenuation curve shifted upward. For a given volume and concentration of contrast medium, changes in the injection rate had a prominent effect on aortic enhancement, and that of the portal vein and hepatic parenchyma also showed some increase, though the effect was less prominent. A increased in the rate of contrast injection led to shifting of the time enhancement curve to the left and upward. B. Computer Simulation: At a faster injection rate, there was minimal change in the degree of hepatic attenuation, though the duration of the optimal temporal window decreased. The area between 10 and 30 HU was greatest when contrast media was delivered at a rate of 2-3 mL/sec. Although the total area under the curve increased in proportion to the injection rate, most of this increase was above the upper threshold and thus the temporal window was narrow and the optimal area decreased. CONCLUSION: Increases in volume, concentration and injection rate all resulted in improved arterial enhancement. If cost was disregarded, increasing the injection volume was the most reliable way of obtaining good quality enhancement. The optimal way of delivering a given amount of contrast medium can be calculated using a computer-based mathematical model.

Animals↗