Ultrasound Doppler ultrasonography of prostate vessels

Ultrasound Dopplerography of the prostate gland vessels is an effective means of non-invasive assessment of blood flow in the prostate. Color velocity and power Dopplerography are usually used to assess blood flow in the prostate gland.

The prostate gland receives its blood supply from branches of the right internal iliac artery, which run along the posterior surface of the bladder and divide into two terminal branches: the prostatic and internal vesical arteries. The prostatic artery bifurcates into the urethral and capsular arteries. Branches of the urethral artery encircle the bladder neck and are visualized within the preprosthetic sphincter using color Doppler mapping.

These vessels supply the transition zone. Along the lateral surfaces of the gland, the capsular arteries form a network from which perforating vessels branch off, supplying the peripheral zone. The capsular arteries are part of the posterolateral vascular-nerve plexus, which includes the capsular veins and erectile nerves. At the base of the gland, the vascular plexus can imitate a nodular formation of reduced echogenicity during transrectal ultrasound examination. These structures are easily differentiated using color Dopplerography.

Periurethral vascular plexuses are identified either as a ring around the urethral cord on transverse scanning or as vascular structures oriented along the urethra on sagittal scanning and approaching the base of the prostate on transverse scanning.

Methods of ultrasound Dopplerography of the vessels of the prostate gland

In clinical practice, power Doppler mapping is often used for ultrasound examination of the prostate gland. This produces a two-dimensional picture of the location and shape of the vessels, highlighted in one color against the background of a normal B-mode image.

The power Doppler method indicates the fact of blood flow in the gland, but does not provide quantitative information on the average blood flow velocity. In this sense, it is close to the X-ray contrast angiography method and allows observing vessels with low blood flow velocities and small diameters. Color shades give an idea of the intensity of signals reflected by moving blood elements. The advantages of the method are almost complete independence from the Doppler scanning angle, increased sensitivity (compared to other Doppler methods), high frame rate, and the absence of ambiguity in spectrum measurement.

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

During a transrectal Doppler examination of the prostate, the following is usually included:

• color Doppler mapping of the prostate gland and/or examination in power Doppler mode;
• recording and analysis of blood flow characteristics in spectral Doppler mode,

In the last 5-7 years, the following modifications of transrectal Doppler ultrasound examination have appeared and entered into clinical practice:

• three-dimensional Doppler angiography of the prostate gland (3D Doppler as a variant of three-dimensional ultrasound examination of the prostate gland);
• Dopplerography of prostate vessels with enhancement (ultrasound contrast agents, other options for improving visualization and vessels).

Color Doppler mapping of the prostate gland and/or examination in the power Doppler mode are performed following transrectal ultrasonography in the gray scale mode, as well as at the end of the examination - when the sensor is removed from the rectum. Transrectal ultrasound Dopplerography in color and power modifications allows you to see the vascular pattern of the prostate gland, assess the degree of its expression and symmetry in different parts of the organ, which is why it is sometimes called ultrasound angiography. A certain difficulty lies in the fact that the researcher must interpret the image on the monitor screen in real time, and this assessment can sometimes be very subjective.

Each time, the equipment is individually adjusted (filter, power, pulse repetition frequency, etc.). The gain of the color signal is set to maximum, but always below the level of occurrence of flashing color artifacts. In color Doppler mapping for visualization of arteries, as a rule, a color scale with maximum speeds of 0.05-0.06 m/s is used, and for better visualization of veins - with a maximum speed of 0.023 m/s. The presence, degree of expression and symmetry of blood flow are assessed, as well as the diameter, direction of course, nature of branching of arteries and veins in the following areas of the prostate:

1. in the 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 zones of the prostate (in the interlobar or circumflex 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 the posterolateral periprostatic vascular plexuses (right and left);
6. in the anterior and anterolateral periprostatic vascular plexuses (right and left);
7. in the hemorrhoidal vascular plexuses (when removing the sensor).

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

In color Doppler mapping, the frequency shift of successive ultrasound pulses is converted into colors of different shades according to a scale and depending on the direction and degree of the shift. We typically use a standard blue-red scale, with shades of red mapping blood flow toward the transducer and shades of blue mapping blood flow away from the transducer. More pronounced frequency shifts and, correspondingly, higher velocities are shown in lighter shades.

Power Doppler is a method based on recording changes in the amplitude (strength), rather than the frequency of the ultrasound signal reflected from a moving object. Power Doppler, although it does not allow determining the direction of blood flow, is more sensitive in visualizing small vessels, which is why many researchers of prostate gland vessel visualization prefer to use this modification of Dopplerographic examination. 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.

Spectral Doppler blood flow analysis is performed after color Doppler mapping. Blood flow is sequentially recorded in the arteries and veins of the above-mentioned areas of the prostate gland.

In spectral doppler, the frequency shift is presented as a curve reflecting the direction and degree of shift in time. A curve deviation above the isoline indicates the direction of blood flow toward the sensor, and below the isoline, away from the sensor. The degree of curve deviation is directly proportional to the degree of Doppler shift and, accordingly, the blood flow velocity.

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

• maximum linear speed (V _max or A, m/s);
• minimum linear velocity (V _min or V, m/s);
• pulsation index (Gosling index, PI) = A - B/V;
• resistance index (Purcelot index, RI) = A - B/A;
• systolic-diastolic ratio (Augurt index, S/D) = A/B.

When examining intraprostatic veins, only linear blood flow velocity (VB) is usually recorded, since the blood flow in them is almost always non-pulsatile.

Correct recording of blood flow velocities in small parenchymatous vessels may 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 absolute velocity indicators directly depend on the angle between the sensor and the examined vessel, and, thus, it is errors in determining the direction of the vessel that can lead to incorrect calculation of blood flow velocities. It should be noted that the calculated relative indicators (pulsation and resistance indices, systolic-diastolic ratio) are not angle dependent and correctly characterize the blood flow even in cases where it is impossible to accurately determine the direction of the vessel.

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

Prostate Doppler Ultrasound is Normal

The peripheral zone of the prostate gland normally has reduced vascularization. In the transition zone, vascularization is increased due to a larger 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 transition zones increases. Pulse-wave, or spectral, Dopplerography allows for an assessment of the spectrum of blood flow velocities in the vessels as it changes over time. When performing pulse-wave Dopplerography of organ blood flow of individual elements of the vascular pattern, as a rule, it is necessary to limit oneself to an analysis of the indicators of total peripheral resistance. The data on linear blood flow velocities in the vessels of the prostate gland are difficult to assess, since their calculation is unreliable due to the insignificant duration of vessel visualization, its small diameter (about 0.1 cm) and the complexity of its spatial location within the prostate gland. These reasons do not allow for the correction of the Doppler scanning angle, which inevitably leads to significant errors in the measurement results and low data reproducibility. Objective indicators of pulsed wave Dopplerography may be distorted due to deformation of the prostate tissue, which inevitably occurs as a result of uneven pressure on the gland of the ultrasound sensor inserted into the rectum. The impossibility of using angle-dependent indicators significantly limits the use of pulsed Doppler mapping.