Ultrasound in urology

Ultrasound is one of the most accessible diagnostic methods in medicine. In urology, ultrasound is used to detect structural and functional changes in the genitourinary organs. Using the Doppler effect - echodopplerography - hemodynamic changes in organs and tissues are assessed. Minimally invasive surgical interventions are performed under ultrasound control. In addition, the method is also used in open interventions to determine and record the boundaries of the pathological focus (intraoperative echography). The developed ultrasound sensors of a special shape make it possible to pass them through the natural openings of the body, along special instruments during laparo-, nephro- and cystoscopy into the abdominal cavity and along the urinary tract (invasive or interventional ultrasound methods).

The advantages of ultrasound include its availability, high information content in most urological diseases (including urgent conditions), and harmlessness to patients and medical personnel. In this regard, ultrasound is considered a screening method, a starting point in the algorithm of diagnostic search for instrumental examination of patients.

Doctors have at their disposal ultrasound devices (scanners) with various technical characteristics, capable of reproducing two- and three-dimensional images of internal organs in real time.

Most modern ultrasound diagnostic devices operate at frequencies of 2.5-15 MHz (depending on the type of sensor). Ultrasound sensors are linear and convex in shape; they are used for transcutaneous, transvaginal and transrectal examinations. Radial scanning transducers are usually used for interventional ultrasound methods. These sensors have the shape of a cylinder of varying diameter and length. They are divided into rigid and flexible and are used to insert into organs or cavities of the body both independently and with special instruments (endoluminal, transurethral, intrarenal ultrasound).

The higher the frequency of ultrasound used for diagnostic examination, the higher the resolution and lower the penetrating ability. In this regard, for examination of deep-seated organs it is advisable to use sensors with a frequency of 2.0-5.0 MHz, and for scanning of superficial layers and superficial organs 7.0 MHz and more.

During ultrasound examination, body tissues on gray scale echograms have different echodensity (echogenicity). Tissues with high acoustic density (hyperechoic) appear lighter on the monitor screen. The densest ones - stones - are visualized as clearly contoured structures, behind which an acoustic shadow is defined. Its formation is due to the complete reflection of ultrasound waves from the stone surface. Tissues with low acoustic density (hypoechoic) appear darker on the screen, and liquid formations are as dark as possible - echo-negative (anechoic). It is known that sound energy penetrates into a liquid medium almost without loss and is amplified when passing through it. Thus, the wall of a liquid formation located closer to the sensor has less echogenicity, and the distal wall of a liquid formation (relative to the sensor) has increased acoustic density. Tissues outside the liquid formation are characterized by increased acoustic density. The described property is called the effect of acoustic amplification and is considered a differential diagnostic feature that allows detecting liquid structures. Doctors have ultrasound scanners in their arsenal, equipped with devices that can measure tissue density depending on acoustic resistance (ultrasound densitometry).

Visualization of vessels and assessment of blood flow parameters are performed using ultrasound Dopplerography (USDG). The method is based on a physical phenomenon discovered in 1842 by the Austrian scientist I. Doppler and named after him. The Doppler effect is that the frequency of an ultrasound signal when it is reflected from a moving object changes proportionally to the speed of its movement along the axis of signal propagation. When an object moves towards the sensor generating ultrasound pulses, the frequency of the reflected signal increases and, conversely, when the signal is reflected from a moving object, it decreases. Thus, if an ultrasound beam encounters a moving object, the reflected signals differ in frequency composition from the oscillations generated by the sensor. The difference in frequency between the reflected and transmitted signals can be used to determine the speed of movement of the object under study in the direction parallel to the ultrasound beam. The image of the vessels is superimposed as a color spectrum.

Currently, three-dimensional ultrasound has become widely used in practice, allowing one to obtain a three-dimensional picture of the organ being examined, its vessels and other structures, which, of course, increases the diagnostic capabilities of ultrasonography.

Three-dimensional ultrasound has given rise to a new diagnostic method of ultrasound tomography, also called multi-slice view. The method is based on collecting volumetric information obtained during three-dimensional ultrasound and then decomposing it into slices with a given step in three planes: axial, sagittal and coronary. The software performs post-processing of the information and presents images in gray scale gradations with a quality comparable to that of magnetic resonance imaging (MRI). The main difference between ultrasound tomography and computer tomography is the absence of X-rays and the absolute safety of the study, which is of particular importance when it is carried out on pregnant women.