3D modeling of leg veins from MRI slices: interest of volume quantification to assess the effects of compression therapy

Abstract

Introduction: Direct mechanical compression of the veins seems to be the main mechanism of action of compression therapy in venous disease. New imaging techniques allow a quantitative evaluation of the biophysical impact of compression on the 3D anatomy of the leg, particularly on the venous system The aim is to use 3D modeling and volume quantification in order to better understand the anatomical effects of compression therapy on the venous system [1,2]. Material and methods: A total of 13 individuals were studied by T2 weighted MRI of the calf or thigh in different body position: supine, prone, upright (6 cases) before and after application of different stockings and bandages. In every case the interface pressure was measured by the use of Picopress® pressure transducer. Compression devices producing different pressures and stifness were assessed. 3D vectorial models were built with Winsurf® software from cross sectional pictures by manual segmentation of all important anatomical structures (bone, muscles, skin, superficial and deep veins). A realistic interactive 3D vectorial model of the extremity was obtained for each leg showing the influence of compression on the leg’s anatomy not only in a single cross-sectional slice but for the whole calf. Results: Surprisingly, even low external pressure (22 mm Hg) is able to induce changes of venous caliber in the deep veins, while there is no compression of the superficial veins. The quantification of each vein volume was done If we increase the external pressure, a compression could be obtained with a pressure of 80 mm Hg Similar results could be obtained in supine position at rest and during contraction of the calf muscles with a compression stocking. The reduction in the venous volume is more important in the deep system, and this effect is enhanced by the compression of the calf with a stocking. And finally, without any compression stocking, the superficial system is dilated in standing position, and the deep system reduced by the muscular contraction of the Soleus. Discussion and conclusion: Limitations of this MRI technique: A long acquisition time is necessary (2-3 minutes) making it difficult to remain in standing position or muscular contraction with no move. For the same reason, the number of slices/thickness are limited. As a result, the acquisition is limited to a segment of the calf 12-25 cm). The 3D modeling technique has also limits and pitfalls: It is mandatory to take landmarks on the skin before acquisition to scan exactly the same zone. Manual drawed boundaries of the anatomical structures are tedious and the interval between slices is large causing partial volume effect (hazy limits). Nevertheless, acurate 3D models can be obtained making possible a quantification of the venous volume. 3D modeling and volume quantification renders clear images of the anatomical structures of the leg demonstrating the effect of different kinds of venous compression.