Tomas Gustavsson

A New Automated Computerized Analyzing System Simplifies Readings and Reduces the Variability in Ultrasound Measurement of Intima-Media Thickness

BACKGROUND AND PURPOSE A computerized analyzing system with manual tracing of echo interfaces for measurement of intima-media thickness and lumen diameter in carotid and femoral arteries was previously developed by our research group and has been used for many years in several laboratories. However, manual measurements are not only time consuming, but the results from these readings are also dependent on training and subjective judgement. A further problem is the observed drift in measurements over time. A new computerized technique for automatic detection of echo interfaces was therefore developed. The aim of this study was to evaluate the new automated computerized analyzing system. METHODS The new system is based on dynamic programming and includes optional interactive modification by the human operator. Local measurements of vessel echo intensity, intensity gradient, and boundary continuity are extracted by image analysis techniques and included as weighed terms in a cost function. The dynamic programming procedure is used for determining the optimal location of the vessel interfaces in a way that the cost function is minimized. RESULTS With the new automated computerized analyzing system the measurement results were less dependent on the readers experience, and the variability between readers was less compared with the old manual analyzing system. The measurements were also less time consuming. CONCLUSIONS The new automated analyzing system will not only greatly increase the speed of measurements but also reduce the variability between readers. It should also reduce the variability between different laboratories if the same analyzing program is used. Furthermore, the new system will probably prevent the problem with drift in measurements over time.

Aging of silicone rubber under ac or dc voltages in a coastal environment

Material samples of silicone rubber with known differences in their composition, i.e. different filler content and extra silicone oil added, have been aged at the Anneberg field station on the west coast of Sweden. ac or dc voltage supplied to cylindrical samples at stress levels of 50 or 100 V/mm. The work includes laboratory examination of material changes together with on-site, visual observations and leakage current measurements. Material samplings for the laboratory tests were made after 18 months of electrical aging, which went on for one more year in order to gather further information on the long-term electrical performance of the material. The dominant aging factor was the level of the applied stress, independent of ac or dc voltage. The dc stressed samples showed a higher leakage current and exhibited larger surface degradation compared with samples exposed to ac voltage. The material parameter, an addition of extra silicone oil, initially led to an increase in adhesion of pollutants, whereas the overall performance was improved by the higher suppression of the leakage current related to oligomer diffusion. Samples with lower levels of alumina trihydrate (ATH) exhibited a delayed onset of degradation, but once damaged they degraded more rapidly than the specimens with a higher ATH content. Infrared spectroscopy showed that the ATH was completely consumed at the eroded surface regions. The aging of the surfaces was further assessed by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The low molar mass siloxanes present in the pollution layer were extracted and analyzed by size exclusion chromatography and gas chromatography-mass spectroscopy. The results indicated that the main degradation factor was thermal depolymerization activated by electrical discharges. Oxidative crosslinking of the silicone rubber, usually attributed to surface close corona discharges, appeared to have played a minor role.

Combining snakes and active shape models for segmenting the human left ventricle in echocardiographic images

The authors propose a method for segmenting the human left ventricle (LV) in ultrasonic images, which is based on principles from both Active Shape Models (ASM) and Active Contour Models (ACM). Principal Component Analysis (PCA) is applied to a frequency-based shape representation of the LV thus eliminating the need for the difficult determination of corresponding landmarks. The average ventricular shape and the set of most significant shape variation modes are obtained from a training set. The LV boundaries in new images are found by placing an initial ACM (Snake) and allowing it to deform only according to the examined shape variations. A training set of 105 expert-segmented echocardiographic images was used. Improvements in the segmentation results were obtained especially in cases where the ventricular boundary was partly occluded by noise.

Increasing Peripheral Artery Intima Thickness From Childhood to Seniority

Background—Using new, very high-resolution ultrasound biomicroscopy, we examined the thickness of artificial layers of silicone and intima thickness (IT) of radial and anterior tibial arteries in healthy subjects and in patients with vascular disease. Methods and Results—Silicone layers of varying thicknesses and mesenteric artery specimens obtained from 18 patients undergoing colectomy were measured by both ultrasound biomicroscopy (55 MHz) and morphometry. There was high correlation (r>0.9; P<0.0001) between IT and intima area versus ultrasound biomicroscopy. In 90 healthy subjects (aged between 10 and 90 years), radial and anterior tibial arterial IT and intima-media thickness were measured, as was carotid intima-media thickness in 56 of these subjects. Age was strongly related with both media thickness and IT of both peripheral arteries. Correlations were found between carotid intima-media thickness and both radial and anterior tibial IT/intima-media thickness (r=0.44 to 0.53; P<0.0001). The IT-to-lumen diameter ratio increased with age and was larger at all ages in the anterior tibial artery (0.067±0.034) versus the radial artery (0.036±0.012; P<0.0001). A thicker radial intimal layer was found in patients with peripheral artery disease. Conclusion—This study is the first to our knowledge in humans to show the feasibility of measuring IT of the radial and anterior tibial arteries using very high-resolution ultrasound. IT progresses with age, and the IT-to-lumen diameter ratio is largest in the arteries of the foot. Assessment of IT by ultrasound biomicroscopy may aid in detecting early peripheral vascular abnormalities.

A dynamic programming procedure for automated ultrasonic measurement of the carotid artery

Describes a computerized technique for automated ultrasonic measurements of the carotid artery based on dynamic programming. Local measurements vessel echo intensity, edge strength, and continuity were extracted by image analysis techniques and included as weighted terms in a cost function. The dynamic programming procedure was used for determining the locations of the vessel interfaces in a way that the cost function was minimized. Then lumen diameter (LD) and intima-media thickness (IMT) were computed. Inter-method (auto versus manual) variability as well as inter- and intraobserver variability was studied by computing conventional coefficient of variation (CV). Inter-method (n=22), inter-observer (n=50), and intra-observer (n=47) variability of LD measurements were 1.2, 0.90, and 1.0%, respectively. Corresponding values for IMT were 3.2, 4.7, and 3.6%. These results indicate that the carotid artery can be automatically measured with accuracy.<<ETX>>

Implementation and comparison of four different boundary detection algorithms for quantitative ultrasonic measurements of the human carotid artery

In this paper we examine four algorithms for automated ultrasonic boundary detection, and describe the application of these algorithms to the quantification of the intima-media thickness (IMT) in the human carotid artery. The first algorithm uses a dynamic programming approach to identify the boundary that minimizes a certain cost function. The second algorithm is based on finding points of maximum gradient. The third algorithm employs a mathematical model describing the intensity profile perpendicular to the two boundaries defining the IMT. The last algorithm is based on defining a template representing the intensity profile across boundary and applying a matched filter procedure to find the image region that best matches it. The authors also present a quantitative and qualitative comparison between the four algorithms examined. It is shown that the dynamic programming algorithm provides superior performance in terms of accuracy and robustness. The correlation coefficients between automated measurements and manually obtained reference values were 0.96, 0.94, 0.63, and 0.85 for the dynamic programming, the maximum gradient the model-based, and the matched filter algorithm, respectively (n=30).

The Effects of Nitrous Oxide on Left Ventricular Systolic and Diastolic Performance Before and After Cardiopulmonary Bypass: Evaluation by Computer-assisted Two-dimensional and Doppler Echocardiography in Patients Undergoing Coronary Artery Surgery

We investigated the effects of nitrous oxide (N2 O) on central hemodynamics and left ventricular systolic and diastolic function in 25 patients undergoing coronary artery bypass surgery.All patients were receiving beta-blockers and had good left ventricular function. Global and regional systolic left ventricular performance and diastolic function were determined by computer-assisted analysis of transesophageal echocardiographic (TEE) images, and mitral Doppler flow profiles, respectively. The patients were anesthetized with fentanyl and ventilated with oxygen in air. Hemodynamic and TEE measurements were obtained before and after the introduction of N2 O in oxygen (60%/40%), before and after cardiopulmonary bypass (CPB). N2 O reduced mean arterial pressure, heart rate, stroke volume, and cardiac output both before and after CPB. Left ventricular global area ejection fraction (GAEF) was not changed by the introduction of N2 O, either before or after CPB. N2 O induced a significant change in regional wall motion after, but not before CPB, as assessed by the relationship between segmental area ejection fraction (SAEF) and GAEF. Analysis of the mitral flow profile indicated an increase in early diastolic relaxation in the pre-CPB period after introduction of N2 O, that was absent in the post-CPB period. We conclude that N2 O induces regional wall motion abnormalities and possibly diastolic dysfunction post-CPB. (Anesth Analg 1995;81:243-8)

An internet-based videoconferencing system for supporting frail elderly people and their carers

Summary The ACTION project uses information and communication technology to support frail elderly people and their family carers. The aims are to enhance their quality of life, independence and preparedness and to break social isolation. A videoconferencing system, connecting homes and a call centre, was used in a pilot study in 1997–2002. A re-designed system was brought into use in late 2004 and over 60 new units were introduced during the first six months. The new system was evaluated with an interview study and by data logging. Eight family users and four professional carers were interviewed. The family users had used the videophone at least six times and they had had the equipment at home for at least two months. The average number of initiated calls per user was 5.7 per month and the average call time per user was 40 min per month. Seven of the users (88%) reported that the system very much reduced their sense of loneliness and isolation. The results of the evaluation were encouraging. There were several frequent users of videoconferencing. System quality was acceptable although a shorter audio delay would be desirable. The system was used regularly by the participants and it fulfilled its purpose.

Deformable spatio-temporal shape models: extending active shape models to 2D+time

Abstract This paper extends 2D active shape models to 2D+time by presenting a method for modeling and segmenting spatio-temporal shapes (ST-shapes). The modeling part consists of constructing a statistical model of ST-shape parameters. This model describes the principal modes of variation of the ST-shape in addition to constraints on the allowed variations. An active approach is used in segmentation where an initial ST-shape is deformed to better fit the data and the optimal proposed deformation is calculated using dynamic programming. Segmentation results on both synthetic and real data are presented.

Morphometry of the optic nerve and retinal vessels in children by computer-assisted image analysis of fundus photographs.

Abstract• Background: The retinal fundus in childhood has a different morphology than in adulthood. Existing methods are not suitable for evaluation of fundus photographs from children. Therefore, a new method for quantitative analysis of fundus morphology utilizing a personal computer-assisted digital mapping system was developed. • Methods: A CCD flatbed scanner is used to digitize fundus photographs, producing computer images which are analyzed on an IBM/AT computer. Area measurements of the optic disc, excavation and peripapillary crescent are made, as well as determinations of the length, branching, tortuosity and distribution of the retinal vessels on the fundus surface. • Results: Determination of the inter-and intra-observer variability of the computer-assisted image analysis technique demonstrated good reproducibility. The method is demonstrated using fundus photographs of six normal children and six children with the fetal alcohol syndrome. Typical variations in appearance of optic disc and retinal vessels are seen. • Conclusion: The system is unique in measuring both the optic nerve head and the retinal vessels and is therefore especially useful for detailed studies of normal and abnormal development of these structures in children.