Doppler ultrasound of the vessels of the prostate gland

Ultrasonic dopplerography of the vessels of the prostate gland is an effective tool for non-invasive evaluation of blood flow in the prostate. To assess blood flow in the prostate gland, as a rule, color speed and energy Doppler.

The prostate gland receives blood supply from the branches of the right internal iliac artery that pass along the posterior surface of the bladder and divide into two terminal branches: the prostatic and internal bladder arteries. The prostatic artery branched into the urethral and capsular arteries. The branches of the urethral artery surround the neck of the bladder and, when using color Doppler mapping, are visualized within the preprogressive sphincter.

These blood vessels supply the transitional zone. On the lateral surfaces of the gland, the capsular arteries form a network from which perforating vessels that feed the peripheral zone depart. Capsular arteries are a part of the posterolateral vascular-plexus plexus, which includes capsular veins and erectile nerves. At the base of the gland with transrectal ultrasound examination, the vascular plexus can mimic the nodal formation of a decreased echogony. These structures can easily be differentiated by color dopplerography.

Periurethral vascular plexuses are defined either as a ring around the urethra during transverse scans, or as urethral vascular structures with sagittal scans and with proximity to the prostate base during transverse scans.

Methods of ultrasonic dopplerography of prostatic vessels

In clinical practice, ultrasound examination of the prostate gland uses energy Doppler mapping. This gives a two-dimensional picture of the arrangement and shape of the vessels, singled out in one color on the background of the conventional image in the B-mode.

The method of energy dopplerography indicates the fact of blood flow in the gland, but does not give quantitative information on the average blood flow velocity. In this sense, it is close to the method of radiopaque angiography and allows to observe vessels with low blood flow velocities and small diameter. Color shades give an idea of the intensity of signals reflected by moving blood elements. Advantages of the method are practically complete independence from the angle of Doppler scanning, increased sensitivity (in comparison with other Doppler methods), high frame rate, and lack of ambiguity in spectrum measurement.

For transrectal ultrasound dopplerography high-frequency (5-7.5 MHz or more) rectal sensors are used, which allow obtaining highly informative images of the prostate gland with high resolution.

Transrectal dopplerographic examination of the prostate usually involves:

• color Doppler mapping of the prostate gland and / or investigation in the energy Doppler regime;
• registration and analysis of blood flow characteristics in the spectral Doppler mode,

In the last 5-7 years, such modifications of transrectal dopplerographic research have appeared and entered into clinical practice, such as:

• three-dimensional dopplerographic angiography of the prostate (ZD-dopplerography as a variant of a three-dimensional ultrasound examination of the prostate gland);
• dopplerography of the vessels of the prostate with strengthening (ultrasound contrast agents, other options for improving visualization and vessels).

Colored Doppler mapping of the prostate gland and / or Doppler mode examination follows transrectal ultrasonography in the gray scale mode, and at the end of the study - when the sensor is removed from the rectum. Transrectal ultrasonic dopplerography in color and energy modifications allows to see the vascular pattern of the prostate gland, to assess the degree of its expression and symmetry in various parts of the organ, in connection with which it is sometimes called ultrasonic angiography. A certain complexity lies in the fact that the researcher must interpret the image on the screen in real time in real time, and this assessment is sometimes very subjective.

Each time, individual adjustment of the equipment (filter, power, pulse repetition frequency, etc.) is carried out. The gain of a color signal is set to the maximum, but always below the level of occurrence of flashing color artifacts. With colored Doppler mapping, a color scale with maximum velocities of 0.05-0.06 m / s is usually used to visualize arteries, and for best visualization of veins - with a maximum speed of 0.023 m / s. Assess the presence, severity and symmetry of the blood flow, as well as the diameter, direction of stroke, the nature of the branching of the arteries and veins in the following areas of the prostate:

1. in periurethral vascular plexuses (transitional zone);
2. in the peripheral zone of the prostate (right and left);
3. at the border of the peripheral and transitional or central zone of the prostate (in the interlobar or enveloping vessels on the right and left);
4. in the vessels of the anterior-upper part of the prostate, in the parenchyma of the central or transitional zone of the prostate (right and left);
5. in posterolateral lateral prostatectic vascular plexuses (right and left);
6. in the anterior and antero-lateral near-prostatic vascular plexuses (right and left);
7. in the hemorrhoidal vascular plexus (when removing the sensor).

It should be noted that in the study in the color and energy Doppler mode, the image of the vessels is superimposed in real time on the image of the prostate gland of the gray scale - the so-called duplex scanning, which allows the researcher to clearly determine the localization of the visualized vascular structures.

With color Doppler mapping, the frequency shift of successive ultrasonic pulses is transformed into colors of different shades according to the scale and depending on the direction and degree of shear. As a rule, we use the standard blue-red scale, while the red color maps the blood flow towards the sensor, and the shades of blue from the sensor. A more pronounced frequency shift and, correspondingly, higher speeds are shown in lighter shades.

Energy (power) Doppler is a method based on recording the change in amplitude (strength), rather than the frequency of the ultrasonic signal reflected from the moving object. Energy Doppler, although it does not allow to determine the direction of the blood flow, is more sensitive in the visualization of small vessels, and therefore many researchers of the day of visualization of the vessels of the prostate gland prefer to use this particular modification of the Doppler study. On the monitor screen, the change in the strength of the reflected signal is visualized in accordance with a single-color scale. We usually use the standard orange-yellow scale.

Analysis of blood flow characteristics in the spectral Doppler mode is performed after color Doppler mapping. Blood flow is consistently recorded in the arteries and veins of the above areas of the prostate gland.

With spectral doping, the frequency shift is represented as a curve reflecting the direction and degree of time shift. Deviation of the curve above the isoline indicates the direction of blood flow to the sensor, below the isoline - from the sensor. The degree of deviation of the curve is directly proportional to the degree of Doppler shift and, accordingly, the blood flow velocity.

During the analysis of the Doppler spectrum curve in arteries, the following indices are determined: 

• the maximum linear velocity (V _max or A, m / s); 
• the minimum linear velocity (V _min or V, m / s); 
• the ripple index (Gosling index, PI) = A - B / V; 
• resistance index (Purselo index, RI) = A - B / A; 
• systolodiastolic ratio (Oyuart index, S / D) = A / B.

In the study of intraprostatic veins, only linear flow velocity (VB) is usually recorded, since the blood flow in them is almost always non-pulsative.

Correct registration of blood flow velocities in small parenchymal vessels can be associated with certain difficulties, since these vessels are often visualized as a pulsating point and it is impossible to trace their direction in this case. At the same time, it is known that the absolute speed indices depend directly on the angle between the sensor and the vessel under study, and thus it is errors in determining the direction of the vessel that can lead to an incorrect calculation of the blood flow velocities. It should be noted that the calculated relative indicators (indices of pulsation and resistance, systolodystolic ratio) are not angle-dependent and correctly characterize the blood flow, even in cases when it is impossible to accurately determine the direction of the vessel's progress.

The results of the analysis of the Doppler spectrum are compared with the data of color mapping and ultrasonography in the gray scale, on the basis of which the final interpretation of ultrasonic dopplerography of the vessels of the prostate gland is carried out.

Ultrasonic dopplerography of the prostate is normal

The peripheral zone of the prostate gland normally has a lowered vascularity. In the transition zone, vascularization is increased due to a greater number of vessels in the stroma of the gland. With age, with the development of benign prostatic hyperplasia, the contrast between the vascularization of the peripheral and transitional zones is enhanced. Pulsed-wave, or spectral, Doppler ultrasound allows to estimate the spectrum of blood flow velocities in blood vessels during its change in time. When conducting pulse-wave dopplerography of the organ blood flow of a day of individual elements of the vascular pattern, as a rule, we must limit ourselves to analyzing the parameters of the total peripheral resistance. Data of linear velocities of blood flow in the vessels of the prostate are difficult to evaluate, since their calculation is unreliable due to the insignificant duration of visualization of the vessel, its small diameter (about 0.1 cm) and the complexity of the spatial arrangement within the prostate gland. These reasons do not allow to correct the angle of the Doppler scan, which inevitably leads to significant errors in the measurement results and low reproducibility of the data. Objective parameters of pulsed wave Doppler ultrasound can be distorted due to deformation of the prostate tissues, which inevitably arise as a result of uneven pressure on the iron of the ultrasonic sensor inserted into the rectum. The inability to use angle-dependent indicators significantly limits the use of impulse Doppler mapping.