Free-breathing quantification of regional ventilation derived by phase-resolved functional lung (PREFUL) MRI.

PURPOSE: To test the feasibility of regional fully quantitative ventilation measurement in free breathing derived by phase-resolved functional lung (PREFUL) MRI in the supine and prone positions. In addition, the influence of T2 * relaxation time on ventilation quantification is assessed. METHODS: Twelve healthy volunteers underwent functional MRI at 1.5 T using a 2D triple-echo spoiled gradient echo sequence allowing for quantitative measurement of T2 * relaxation time. Minute ventilation (ΔV) was quantified by conventional fractional ventilation (FV) and the newly introduced regional ventilation (VR), which corrects volume errors due to image registration. ΔVFV versus ΔVVR and ΔVVR versus ΔVVR with T2 * correction were compared using Bland-Altman plots and correlation analysis. The repeatability and physiological plausibility of all measurements were tested in the supine and prone positions. RESULTS: On global and regional scales a strong correlation was observed between ΔVFV versus ΔVVR and ΔVVR versus ΔVVRT2* (r > 0.93); however, regional Bland-Altman analysis showed systematic differences (p < 0.0001). Unlike ΔVVRT2* , ΔVVR and ΔVFV showed expected physiologic anterior-posterior gradients, which decreased in the supine but not in the prone position at second measurement during 3 min in the same position. For all quantification methods a moderate repeatability (coefficient of variation <20%) of ventilation was found. CONCLUSION: A fully quantified regional ventilation measurement using ΔVVR in free breathing is feasible and shows physiologically plausible results. In contrast to conventional ΔVFV, volume errors due to image registration are eliminated with the ΔVVR approach. However, correction for the T2 * effect remains challenging.

Some mechanical/hydrodynamical problems of contemporary vascular grafts.

In view of the importance of properly matching vascular grafts and replaced arteries, we measured some mechanical properties of a set of eleven vascular grafts. The deformation response of inflated grafts for a set of Czechoslovak-made warp and weft knitted grafts was also measured on a special experimental device. A simple two-parameter model describing the stress-strain behavior of the grafts is given. Proper pre-elongation of the graft during implantation is important. From the hydrodynamic point of view it is essential to optimize the size and shape of the crimping, especially for small-diameter grafts. Our experiments indicate that the warp knitted grafts are more distensible than the weft knitted ones, but they are all more rigid than the replaced arteries.