Colour Doppler Study in Infertilityn

Uterine arteries supply blood to the uterus (from the internal iliac) they further divide into radial, arcuate, spiral arteries. By colour Doppler flow, we are able to assess the exact blood flow to the uterus, myometrium and endometrium. The various Doppler indices like Resistance index (RI), Pulsatility index, peak systolic velocity (PSV), end diastolic velocity (EDV), S/D ratio, gives us an idea of blood flow to endometrium and ovarian follicles. Mature follicles have high vascularity which can help in timing of hCG injection by the IVF specialist.

Fibroids, adenomas, adenomyosis, endometrial hyperplasia, endometrial polyps, ovarian tumours, ovarian masses, cervical malignancy, ovarian cancer, endometrial malignancy, all these gynace pathologies have varied vascularity patterns which are easily discernable on colour Doppler flow.

Doppler Velocimetry

Ultrasound technologies has evolved from only producing images of the pregnancy to now include methods for measurement of both maternal and fetal circulatory functions the phenomenon of Doppler shift of ultrasonic echoes forms the technical basis for acquisition of information on the maternal-fetal hemodynamic circulations.

Johann Christian Doppler was an Austrian physicist who taught in Prague during the mid-1800s (white 1982) He suggested that a sound source (for example red blood cells in fetal umbilical circulation) is moving relative to an observer (for example, an ultrasound transducer), the perceived pitch will vary from the true pitch. In accordance with the Doppler shift principal, echoes returning from moving structures are altered in frequency and the amount of shift is directly proportional to the velocity of the moving structure. The frequencies of echoes returning from structure moving toward the transducer. In contrast, the frequencies of echoes returning from structure moving any from the transducer are lower. The primary uses of those Doppler echo shifts in obstetrics have been to detect and measure blood flow. The sound of moving blood cells within the vasculature generates and effective Doppler shift, which serves has the basis of Doppler Velocimetry studies of maternal and fetal circulations. There are two methods of estimating circulatory homodynamics.

• Direct measurement of the volume of blood flow
• Indirect estimation of flow velocity using waveform analysis

Determination of blood volume flow

Doppler shifted sound frequencies depend on a number of factors In this equations, fo is original frequency of the ultrasound beam (in obstetrical imagine this is usually 3 to 5 MHz), v is the velocity of blood cells in the vessel studied, 0is the incident angel (angel of insonance ) between the ultrasound beam and the vessel, and C is the speed of sound (in tissue, equal to 1540 m/sec). the cosine remains close to 1 as long as the angel is kept low, but at higher angels of insonance, especially those more than 60 degrees, considerable error in measurement is introduced.

The equation in figure includes a factor (v) for the velocity of blood in the vessel studies. To solve for v, and to thus estimate the velocity of red blood cells, the following equation is used:

Because volume flow (mL/min) is simply velocity times cross-sectional area of the blood vessel (area equals pi time the square of the radius), it is possible to calculate volume flow by measuring the bllod vessel diameter using ultrasound. However there are several techniques difficulties with measurement of vessel diameters. for example, the vessel are dynamic with changing diameters during the cardiac cycle. The many technical difficulties inherent in Doppler blood volume flow measurement result in high error rates for this methodology. Estimates of error up to 50 percent have been reported with the most careful attention to methodology (gill, 1985) and up to 50 percent are not uncommon (burns, 1987), because of these mythological problems, blood volume flow measurement have been largely abandoned in clinical applications (low, 1991).

Waveform analysis of blood velocity

From the foregoing, the errors encountered in volume flow estimation may be profound. Thus indirect indices of flow have been developed that might provide useful information about flow without engendering excessive errors. These indices are independent of the angel of insonation and do not require measurement of the diameter of the vessel.

Perhaps the most simple of these indices to compute is the systolic-diastolic ratio, or S-D ratio (fig.44-14). The maximal systolic shift is divided by the enddiastolic shift. This may be measured from the maternal uterine or fetal umbilical artery. In both vessels, the index gradually decreases as gestation progresses. Because of the low diastolic velocities seen in more central fetal vessel, such as the descending aorta, the S-D ratios not useful elsewhere in the fetal circulation.

Similar in ease of calculation is the pourcelot index, or the resistance index (fig. 44-14). To calculate this index, the difference in systolic and diastolic shifts is divided by the systolic value ([D - S]/S, also expressed as 1 - [D/S]). This ratio is also applicable only to the umbilical and the uterine, and low diastolic value limit its usefulness in the fetal aorta or other central vessel Of the widely used indices, the most complicated to measure is the Pulsatility index (fig. 44-14). It requires a digitized waveform for calculating the mean of the maximal frequencies represented. Because of the mean value in the denominator, this index can be computed using flow data from the fetal descending aorta without encountering excessive variation caused with division by small numbers as with the other two indices. Doppler arterial waveform in nonpregnant humans are characterized by high systolic velocity and little or no diastolic velocity. Exceptions are the carotid and cerebral vessels, which have continuous diastolic blood flow seen on waveform analysis. During pregnancy, maternal and fetal vessels perfusing the placenta assume waveform indicative of continuous diastolic flow.

Doppler waveforms of vessels have been described in a variety of ways, but all are based upon the relationship between systole and diastole. The most common measurement are some variation of the S-D ratio. These measurements are intended to relate peak flow at systole to that at end-diastole, and the ratio us calculated from the highest of the systole and diastole peaks.

Waveform with a high flow in diastole accompany low downstream vessel impedance. In contrast, waveforms with little diastole flow, or reversed flow, are seen when vascular impedance downstream is abnormally high (e.g. placental insufficiency). Figure 44-15 illustrates several of the several of the vessels in which S-D ratio have been studied, as well as the corresponding S-D waveforms for blood velocity in these vessels. Blood flow velocity has also been studied in the umbilical vein and fetal cerebral circulation.