Volume Ultrasound in Uterine and Tubal Evaluation Fig. 7: Endometrial vascularization and midcycle-the radial and spiral arteries. Power Doppler is used to visualize the low velocity flow in small vessels penetrating the endometrium. In this case, the flow reaches the inner half of the endometrium (type III) arteries are responsible for the endometrial vascularization with a very high impact on early embryonic development. Doppler mapping of the subendometrial flow7 depicted four types of endometrial flow during early luteal phase, as follows: Type 0: vascularization far from subendometrial region Type 1: peripheral-vessels reaching the outer echogenic layer of the endometrium Type 2: intermediate-flow within the middle hypoechogenic layer Type 3: central-blood flow on the entire endometrial thickness. The evaluation should be performed with power Doppler in order to visualize even low-flow vessels and to avoid loss of signal with increasing insonation angle (Fig. 7). The vascularity type may be predictor of ovulation and implantation, therefore, it is important to be assessed in infertile patients. Usually, there is poor vascularity in anovulatory cycles. Each type correlates with a different implantation prognosis which varies from 0% for type 0 to 37.9% for type 3. Using the three-dimensional techniques, endometrial vascularization may be quantified in a semiautomatic manner. The volume organ computer aided analysis (VOCAL) provided three indices: Vascularization index (VI) represents total number of color voxels or total number of voxels from region of interest and reflects the number of vessels in the tissue. Flow index (FI) represents total intensity of color voxels or total number of color voxels in the volume and reflects the total blood volume. Vascularization/flow index (VFI) represents total intensity of color voxels or total number of voxels (color and grey) in the volume and combines information about the quality and quantity of vascularization. It also offers a general view of both subendometrial and endometrial blood flow along with the measurement of endometrial volume (Fig. 2). Changes in endometrial and subendometrial flow were investigated in 27 healthy, fertile volunteers with regular menstrual periods, using 3D power Doppler on alternate days, starting on cycle day 3 until ovulation, and then every 4 days afterward until initiation of menses.8 With the use of the VOCAL, the vascular indexes were calculated for each time point. For the subendometrial vascular index, an arbitrary limit of 5 mm was established, and the inner third of the endometrium and the area irrigated by the radial arteries. Both endometrial and subendometrial vascular flow increased to a maximum 3 days prior to ovulation, then decreased until postovulatory day 5, and finally begun a gradual increase during the rest of the luteal phase. The proliferative phase increment was related to estradiol levels and its vasodilating effects, while the luteal phase increase was related to serum progesterone. Interestingly, the flow indexes continued to increase during menstruation regardless of a drastic drop in progesterone levels; this might be explained by the high endometrial vascular density due to progressive compaction of the spiral arteries. The reduction in the postovulatory vascular indexes is explained by vasodilatation of the subepitelial capillary plexus, which induces the required stromal edema to allow embryo implantation. Another study found that the lowest vascularization index occurred 2 days after ovulation and progressively increased during the luteal phase.9 Thus, 3D US is a reliable technique for investigating cyclic, physiological changes in endometrial vascularization, showing that there are maximum values 2 to 3 days prior to ovulation, decreasing to minimal values 2 to 5 days postovulation and increasing thereafter. Vascular flow is delicately orchestrated in order to provide human embryos a favorable microenviroment for implantation, although the amount of oxygen the embryo needs from the endometrium during the implantation process is still controversial. More studies are needed to definitively establish the role of endometrial/subendometrial vascular oscillations in embryo implantation. The question at this moment is, when there are so many sonographic tools, which one is better and more predictive in evaluating endometrial receptivity and a potential pregnancy outcome. The most reproducible measurement seems to be the endometrial volume, but in similar stimulated cycles the 2D and 3D endometrial parameters are similar.10 A recent study11 evaluating the predictive value of power Doppler angiography and three-dimensional endometrial parameters for endometrial receptivity in IVF cycles, found a very good correlation between endometrial volume, VI, FI, VFI and pregnancy outcome. Moreover, the indices are even better predictive when one grade I embryo or one no grade embryo are transfered with an important role in management of single embryo transfer politics. On the other hand, endometrial pattern (triple line aspect) and endometrial thickness were of less predictive value. Measuring endometrial volume by 3D US is the latest acquisition in gynecological ultrasound and offers extended data based on all three acquisition planes. The endometrium has a variable thickness, normal < 13 ml in menopause. This may be calculated automatically or semiautomatically (VOCAL II).
Posted on: Thu, 24 Oct 2013 21:17:34 +0000
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