Feasibility of Laser Doppler Vibrometry as potential diagnostic tool for patients with abdominal aortic aneurysms.

The application of laser measurements in medical applications makes it possible to measure even very small vibrations without contacting the skin surface. In the present work we investigate the use of a scanning vibrometer to measure the mechanical wave of the abdominal wall caused by the heart beat and blood pressure pulse. A Laser Doppler Vibrometer, triggered by cardiac signals, is used to scan points on a grid positioned on the abdomen of human subjects. The proposed procedure is intended for detecting anomalies in the abdominal cavity such as aortic aneurysms. Here, we outline the technical setup used in our preliminary in vivo experiments and present some preliminary results. This feasibility study shows that the proposed measurement procedure allows for measuring the skin motion, that the skin motion measured is related to the heart activity, and that there are indication that the presence of an abdominal aortic aneurysm significantly modifies the relation between blood pressure pulsations and skin motion on the abdomen.

Vibration testing of a fresh-frozen human pelvis: the role of the pelvic ligaments.

A biodynamic model of the human pelvis is being developed in the frame of a research project on low back pain. In order to validate such model, the dynamic behaviour of the human pelvis needs to be investigated. In this study, a human fresh-frozen specimen comprising the three bones of the pelvic girdle and its ligamentous system has been used to perform vibration testing. In such test the response of the system to vibrations is measured at various points on the structure for frequencies between 10 and 340 Hz. The vibration testing is performed a first time on the specimen with intact ligamentous system. The measurements are taken two more times after subsequent bilateral resection of both the sacrotuberous and the sacrospinous ligaments first, and the iliolumbar ligaments afterwards. A comparison between the system response obtained in the three configurations provides information on the role of the resected ligaments in the dynamics of the system, thus on their relevance in the model. Results indicate that the sacrospinous, the sacrotuberous and the iliolumbar ligaments do not play a role in the pelvis dynamics as measured in this study, and will therefore not be represented in the biodynamic model.

Development of fibrinous thrombus analogue for in-vitro abdominal aortic aneurysm studies.

PURPOSE: To develop different thrombus analogues, with mechanical properties similar to those of human fibrinous thrombus, for in-vitro aneurysm sac pressure studies. METHODS: Using dynamic mechanical analysis we determined the E-modulus (/E(*)/) at 0.8, 1.0, 1.5 and 3.9 Hz of ten different human fibrinous thrombus samples. We also determined loss and storage modulus to quantify the visco-elastic properties. For comparison, we measured the E-modulus (|E(*)|), loss and storage modulus of gelatin, Novalyse ST8, ST14 and ST20 with and without contrast agent. RESULTS: Mean E-modulus of the thrombus samples (SD) at 0.8, 1.0, 1.5 and 3.9 Hz was 39 (16), 37 (15), 37 (15) and 38 (14)kPa, respectively. Median (SD) storage and loss modulus were 35 (12) and 8 (4)kPa, respectively. Median (SD) tandelta was 0.25 (0.06). The E-modulus of gelatin, Novalyse ST8, ST14 and ST20 was 4, 27, 48 and 60 kPa, respectively. The E-modulus of Novalyse ST8, ST14 and ST20 mixed with contrast agent was 18, 23 and 33 kPa, respectively. Median (SD) storage, loss modulus and tan delta of the six Novalyse samples were 30 (15), 3 (1) and 0.087 (0.04), respectively. CONCLUSION: All the thrombus analogues, except gelatin, had an E-modulus in the range of human fibrinous thrombi. Novalyse samples are validated thrombus analogues for in-vitro aneurysm sac pressure studies. Gelatin is not appropriate to simulate fibrinous thrombus.