Track 14. Cardiovascular Mechanics 14.8. Flow Measurement and Imaging In Vivo and In Vitro with Applications - Ultrasound & Laser Techniques $301

effect of compression on the deformation of veins in different positions (i.e. with varying hydrostatic pressure component). This model is also used to calculate venous compliance curves for the vessels mentioned above in compressed and uncompressed states. This is a first and important step towards a full model of lower limb venous blood flow and optimisation of therapeutic compression.

References [1] Lord R.S.A., Hamilton D. Graduated compression stockings (20-30 mmHg) do

not compress leg veins in the standing position. ANZ J. Surg. 2004; 74: 581- 585.

[2] Partsch B., Partsch H. Calf compression pressure required to achieve venous closure from supine to standing positions. J. Vasc. Surg. 2005; 42: 734-738.

4629 Th, 11:30-11:45 (P42) Character izat ion of t issue components for atherosclerot ic p laques using e x vivo hrMR and synchrot ron tomography

M. Auer 1 , R Schmid 2, R. Stollberger 3, P. Regitnig 4, R.H. Menk 5, L. Rigon 6, G.A. Holzapfel 1,7 . 1Graz University of Technology, Computational Biomechanics, Graz, Austria, 2Austrian Academy of Sciences, Institute of Biophysics and X-ray Structure Research c/o Synchrotron Trieste, Basovizza (TS), Italy, 3Medical University Graz, Department of Radiology, Graz, Austria, 4Medical University Graz, Institute of Pathology, Graz, Austria, 5 Synchrotrone Trieste, S.c.p.A, Basovizza (TS), Italy, 61CTP (International Center for Theoretical Physics), Trieste, Italy, 7 Royal Institute of Technology, School of Engineering Sciences, Stockholm, Sweden

Assessment of the arterial wall structure and morphology is an issue of highest clinical priority. Existing standard imaging modalities such as IVUS or CT provide little or no information on the structures of diseased walls, and hence do not meet the requirements for mechanical investigations used for biomechanical modeling of, e.g., balloon angioplasty [1]. In the present ex vivo study, we examine six human coronary arteries and two human carotid arteries with well-established atherosclerotic lesions. The specimens are first scanned by high-resolution MR imaging, thereafter they are scanned by synchrotron tomography. We compared hrMR, synchrotron to- mography and histological images of corresponding sections. The synchrotron images provide a relatively weak contrast. Nevertheless, synchrotron tomogra- phy provides a high signal-to-noise ratio in a short time, and, consequently, high details of the tissue components, i.e. calcification (I-c), fibrous cap (I-fc) and lipid pool (I-Ip). The identification of these components is of highest importance for meaningful finite element analysis and clinical diagnostics. Acknowledgement: Financial support for this research was partly provided by the Cooperative Research EU-Project DISHEART; Call Identifier: FP6-2002- SME-I.

References [1] Holzapfel G.A., Stadler M., Schulze Bauer C.A.J. A layer-specific 3D model for

the simulation of balloon angioplasty using MR imaging and mechanical testing. Ann Biomed Eng 2002; 30: 753-767.

5533 Th, 11:45-12:00 (P42) Di f ferences in ve loc i ty prof i les between young and elderly healthy volunteers affect wall shear stress assessment with the parabolo id method in the internal carotid artery; a s tudy with ve loc i ty encoded MRI

F.M.A. Box 1 , R.J. van der Geest 1, M.J.P. van Osch 2, J. van der Grond 2, A.J.M. de Craen 3, G.J. Blauw 3, M.A. van Buchem 2, J.H.C. Reiber 1 . 1Division of Image Processing, University Medical Center, Leiden, Netherlands, 2Department of Radiology, University Medical Center, Leiden, Netherlands, 3Department of Gerontology & Geriatrics, University Medical Center, Leiden, Netherlands

Objective: The assessment of Wall Shear Stress (WSS) in blood vessels based on phase-contrast MR imaging requires the determination of flow volume and maximum flow velocity in vessel cross-sections in these images. Low or oscillating WSS in blood vessels is correlated to atherosclerosis and de- creases with age. WSS is normally achieved by assuming a parabolic velocity profile, which is calculated from the measured maximum blood velocity (Vmax) and diameter [1]. The aim of this study was to assess whether differences in velocity profiles exist in the internal carotid artery (ICA) between young and elderly individuals and if these effects could influence WSS determination. Methods: A semi-automatic method to assess WSS in vivo in the internal carotid artery was applied and investigated in healthy young and elderly volunteers. The quantification approach is based on determining the maximum velocity in the region of interest and on fitting a 3D parabolic velocity model to the actual velocity profiles. This is done in cross sections of the ICA 2cm distal to the bifurcation in 16 phases of the cardiac cycle. Materials consisted of MRI data of 20 healthy young volunteers (26.7±7.1 years) and of 16 healthy elderly volunteers (73.9±2.8 years). Results: Velocity profiles differed significantly between the groups. The velocity profile of the elderly was more peaked and of the young more blunted. This

was also seen in a significantly lower Flow/Vmax for elderly. WSS and Flow were significantly lower for elderly compared to young individuals.

Young (N = 40) Elderly (N = 28) Delta (%) p-value Mean ±stdev Mean ±stdev

Flow/Vmax (cm 2) 0.15±0.03 0.11 ±0.02 -26.0 1.3 10 7 Flow (ml/min) 286±51 195±68 -31.8 2.5 10 7 Vmax (cm/s) 32±5 29±9 -9.8 0.096 WSS (Pa) 1.17±0.29 0.96±0.28 -18.3 2.9 10 3 Values are averaged over the cardiac cycle.

Conclusions: Flow and WSS, as well as Flow/Vmax decreased significantly with age. Because velocity profiles change in shape, it is expected that WSS decreases faster with age than can be assessed by paraboloid modeling.

References [1] Gnasso A., et al. Circulation 1996; 94: 3257-62.

14.8.2. Ultrasound and Laser Techniques

7377 Th, 14:00-14:15 (P44) Object ive assessment o f fetal activity K. Kafu±yr~ski 1 , K. Czajkowski 2, T. Kret 1 , J. Sier~ko 2, B. Le~niak 1 , T. Pafko 1 . 1Institute for Precision and Biomedical Engineering, Warsaw University of Technology, Warsaw, Poland, 2 2nd Department of Obstetrics and Gynecology, Medical University of Warsaw, Poland

Fetal activity is an important indicator of fetal well-being. The fetal biophysical profile (BPP) was introduced to improve inferencing on the presence of fetal asphyxia. Three out of five BPP parameters describe fetal motor activity: presence of fetal breathing movements, body movements, and the fetal tone. Another approach is the analysis of the fetal gross body movements (GM). Ultrasonographic examination of a fetus by a specialist (BPP, GM) or software analysis of video recordings of ultrasonographic data (GM) are carried out. Both methods are time-consuming and subjective. Elaborating an objective method to parametrize fetal movements is of interest. The approach proposed employs a 2 MHz Doppler device to obtain information on fetal movement velocity, a laptop and an on-line running LabVIEW software. The distinction between the signals due to different fetal movements is based on their time-frequency structure. The velocities of the movements are com- puted from the phase of the Doppler signal. The accelerations are obtained as smoothed derivatives. The breathing movements are detected in the spectra of the movement velocity. The median, standard deviation, skewness and kurtosis of velocity and acceleration histogram are computed. These parameters and the information on breathing movements form a feature vector, describing the activity pattern of the fetus. The approach was validated on simulated data and data recorded in clinic. Some sequences of ultrasonographic images were videotaped with a concur- rent Doppler signal recording on the audio track. All observed episodes of the fetal pseudobreathing and gross body movements were detected in the Doppler signals. The approach presented here, contrary to the majority of existing de- vices/methods for fetal monitoring, incorporates a detailed analysis of the fetal movement features. The proposed methodology enables automatic detection of the fetal breathing movements, determination of body movement velocity and acceleration. The proposed solution seems to be a promising diagnostic tool for obstetricians.

5064 Th, 14:15-14:30 (P44) Ul t rasound invest igat ion of lower l imb haemodynamics dur ing compress ion using a water-f i l led cuff

G.W. John 1 , J.E Woodcock 1, R.J. Morris 1 , A.J. Narracott 2, D.R. Hose 2, EV. Lawford 2. 1Medical Physics and Bioengineering, Cardiff University, Cardiff,, Wales, UK, 2Medical Physics, University of Sheffield, Sheffield, UK

A new technique has been developed that allows ultrasound imaging and blood flow assessment through a water-filled cuff. The equipment is a closed system of two connected, watertight bladders obtained from commercial air compression cuffs. The system is filled with water and one bladder is placed around the limb to be investigated. Water flows between the bladders depending on their relative position. As water flows into the bladder around the limb, it causes compression. Ultrasound imaging through the water-filled cuff allows investigation of regions directly beneath the compression site as the compression pressure is varied. The compression pressure is measured by a pressure transducer at the inlet to the compression bladder. Initial investigations indicate less than 30 mmHg is sufficient to collapse deep veins in the leg when semi-recumbent. Venous collapse occurs very quickly with almost no intermediate "semi-open" stage. Following initial collapse of the vein, blood flow ceases. However, while compression is maintained, venous blood flow begins to reappear after a short time (42 minutes). The vein