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At least 937 records · Page 52Linked to original sources
PubMed1997

Rapid saccular aneurysm induction by elastase application in vitro.

OBJECTIVE: To develop a new saccular aneurysm model in vitro using elastase to study aneurysm initiation, growth, and rupture and to create a new in vivo aneurysm model to test endovascular therapies. METHODS: Seventeen common carotid arteries excised from freshly killed pigs and sheep were treated with seven different methods of elastase delivery. The arteries were mounted in a saline-filled flow chamber. They received pulsatile flow for 48 hours, or until the resulting aneurysms ruptured. Changes were continuously monitored with video camera recordings and validated with histological sections. RESULTS: All eight arteries treated topically, either on the intimal or on the adventitial surface, with elastase concentrations greater than 1 U/mm2, developed saccular aneurysms; five of them ruptured within 48 hours. All four arteries treated with surface concentrations of 0.1 U/mm2 via microcatheter infusion into the lumen developed fusiform aneurysms. None of the arteries that received surface concentrations less than 0.1 U/mm2 developed aneurysms. Histological sections revealed a reduced number of cellular element in a stretched collagen matrix at the dome of the saccular aneurysms. CONCLUSION: After empirically testing several methods of elastase delivery, we were able to induce saccular, bifurcation-type aneurysms in animal arterial specimens. These aneurysms are histologically similar and more authentic than surgical models. The procedure is easy and reproducible. Our results suggest a possible enzymatic role in aneurysm formation and highlight the dramatic effects of selective arterial elastic damage. Also, the rapid growth of our experimental aneurysms may reflect the speed of the natural process.

Aneurysm, Ruptured↗
PubMed2003

Regularization of flow streamlines in multislice phase-contrast MR imaging.

Magnetic resonance angiography (MRA) has become an important tool for the clinical evaluation of vascular disease. Flow measurement with phase-contrast (PC) magnetic resonance (MR) imaging provides a powerful method for evaluation of blood velocity information inside vessels. However, image artifacts from complex flow patterns including slow flow, recirculation zone, and pulsatile flow can adversely affect accuracy of results. In this paper, we introduce a new numerical formulation for improving the accuracy of PC velocity fields and corresponding streamlines, based on a physical constraint from fluid dynamics, within a regularization framework. The formulation which makes use of a stream function, automatically enforces continuity constraint of incompressible flow and reconstructs the flow streamlines from PC images. We applied the algorithm to complex MR imaging flow velocities obtained in a flow phantom of an axisymmetric abdominal aortic aneurysm. The algorithm significantly improved streamline results especially inside the recirculation zone, where artifacts are more pronounced. A velocity reconstruction method in primitive variable form is also presented and results are compared with the stream function method. In order to validate flow characteristics derived from PC MR images, we used the FLUENT computational fluid dynamics software package, to simulate flow patterns within the same geometry as our phantom. There was a good agreement between the numerical simulations and recovered PC streamline results. Processed streamlines, in both stream function and primitive variable methods, were more realistic and provided more precise flow patterns than unprocessed PC data. Additionally, the feasibility of the method was demonstrated in the aorta of a normal volunteer.

Algorithms↗
PubMed1994

Influence of abdominal aortic curvature and resting versus exercise conditions on velocity fields in the normal abdominal aortic bifurcation.

Local hemodynamics are considered an important atherogenetic factor in the abdominal aortic bifurcation. This study addresses the quantitative flow fields in a pulsatile flow model of a normal abdominal aortic bifurcation when encountering realistic upstream anatomy, realistic inlet flow conditions and different physiologic flow conditions (rest vs. exercise). Two-dimensional laser Doppler anemometry measurements gave axial as well as radial velocities. The localization and magnitude of peak velocities, retrograde flow and secondary velocity patterns were found to be determined to a great extent by the curvature of the abdominal aorta, the triphasic flow wave form and the inlet velocity profile. Significant changes were also seen when simulating different physiologic flow conditions. Thus retrograde velocities were present at both the flow divider and the lateral vessel wall for the rest condition but not for the exercise flow conditions, and the location of low and retrograde velocities during diastole were as much determined by abdominal aortic curvature as by the bifurcation for nearly all flow conditions and locations. In conclusion, the anatomy and hemodynamics in the abdominal aorta cannot be neglected when studying the hemodynamics in the abdominal aortic bifurcation.

Aorta, Abdominal↗
PubMedDate not supplied

Digital signal processor-based real-time optical Doppler tomography system.

We present a real-time data-processing and display unit based on a custom-designed digital signal processor (DSP) module for imaging tissue structure and Doppler blood flow. The DSP module is incorporated into a conventional optical coherence tomography system. We also demonstrate the flexibility of embedding advanced Doppler processing algorithms in the DSP module. Two advanced velocity estimation algorithms previously introduced by us are incorporated in this DSP module. Experiments on Intralipid flow demonstrate that a pulsatile flow of several hundred pulses per minute can be faithfully captured in M-scan mode by this DSP system. In vivo imaging of a rat's abdominal blood flow is also presented.

Abdomen↗
PubMed1992

Color Doppler sonography of hepatocellular carcinoma before and after treatment by transcatheter arterial embolization.

Color Doppler sonographic findings on 38 lesions in 31 patients who had primary hepatocellular carcinoma were evaluated before and after transcatheter arterial embolization and compared with dynamic CT and hepatic arteriographic findings. All lesions that were observed with dynamic CT or arteriography were correctly identified on color Doppler sonography. Peritumoral pulsatile flow was the predominant color Doppler flow seen in all lesions. Mixed pulsatile and continuous flow were noted in larger tumors and in tumors with a higher degree of vascularity, as determined by arteriography. Two weeks after treatment, color Doppler flow was still identified in 18 lesions (47%), corresponding to dynamic CT or arteriographic findings documenting residual tumor. Histopathologic examination, performed in 10 other lesions, showed that the tumor was completely necrotic in five. These five necrotic tumors were not visible on color Doppler flow images after treatment. Viable tumor was observed in the five remaining lesions, all of which were shown on color Doppler flow images after treatment. During the 6- to 16-month follow-up period, color Doppler flow images showed recurrence of 13 (50%) of 26 lesions, corresponding to tumor recurrence as shown by CT and arteriography. We conclude that color Doppler sonography is useful for imaging hepatocellular carcinoma, for evaluating residual tumor after treatment, and for imaging tumor recurrence during follow-up.

Aged↗