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Ultrasound of the skin and subcutaneous fat
Medical expert of the article
Ultrasound examination of the skin is one of the "classic" diagnostic methods, for many years successfully used in medical and research centers. The principle of ultrasound is the same as in optical coherence tomography, only an acoustic wave is used instead of a light wave. Ultrasound oscillations during propagation obey the laws of geometric optics. In a homogeneous medium they propagate rectilinearly and at a constant rate. On the boundary of different media with unequal acoustic density, a part of the rays is reflected, and a part is refracted, continuing rectilinear propagation. The higher the gradient of the acoustic density difference of the boundary media, the greater part of the ultrasonic vibration is reflected. At the border of the transition of ultrasound from the air to the skin, 99.99% of the oscillations are reflected, so before the ultrasound scan, a special gel must be applied to the skin, playing the role of a transient medium. The reflection of the sound wave depends on the angle of incidence (the greatest reflection is when the wave is incident perpendicular to the surface) and the frequency of ultrasonic vibrations (the higher the frequency, the greater the reflection).
Today, ultrasound technology is actively used to monitor skin edema and wound healing, to study the structure of the skin in diseases such as psoriasis, scleroderma, panniculitis. An important application of the ultrasound method is the detection of tumor formations (melanoma, basal cell carcinoma, squamous cell carcinoma).
Methods of examination of ultrasound of the skin and subcutaneous fat
Examination of the skin should be carried out by RF sensors (15-20 MHz). For skin studies, ultrasonic waves with a frequency of 7.5 to 100 MHz are used. The resolution increases with increasing frequency of the ultrasonic wave, at the same time there is a strong attenuation of the echo amplitude in the deeper layers of the skin, so the depth of measurements at a high frequency is small.
Echocardiogram of the skin is normal
The skin looks like a hyperechoic homogeneous layer.
The thickness of the skin varies depending on the location, it is larger in men than in women.
The subcutaneous fat layer, as a rule, looks hypoechoic with alternating hyperechoic thin fibers reflecting connective tissue interlayers
Pathology of the skin and subcutaneous fat
Edema. With edema, the subcutaneous fat is thickened, its echogenicity is increased.
When an edema occurs, the connective tissue tissues of the fibrous lobes look hypoechoic, while the fatty layers are hyperechoic. Edema is usually observed with cellulitis, venous insufficiency, lymphadem.
Foreign bodies. Foreign bodies look like structures of increased echogenicity, surrounded by a hypoechoic rim. A hypoechoic rim that arises around a foreign body is a consequence of an inflammatory reaction.
Wooden and plastic objects look like hyperechoic structures with the effect of a distal acoustic shade.
Metal and glass objects give reverberation effect on the type of "comet's tail".
Lipomas. Lipomas can look like formations in the thickness of subcutaneous fat. Their echogenicity can be from hyper-to hypoechoic. They can be confined and enclosed in a thin capsule or diffuse without a clear capsule.
Hematomas. Hematomas look like anechogenous or hypoechoic fluid containing structures. Are formed as a result of trauma. Depending on the prescription, the internal structure of the hematoma may change.
Nevus. On the surface of the skin there is a pigmented "head" of the nevus. However, the base of the nevus is located deep in the thickness of the subcutaneous fat. As a rule, nevuses have an oval shape, clear outlines, are delimited from surrounding tissues with the help of a thin capsule. Their ehogennost low. There is a distal effect of echo enhancement.
Fibroma and fibrolipoma. Fibromas look like hypoechoic oval forms of formation in the thickness of subcutaneous fat. As a rule, a capsule that limits the formation is revealed. Palpator fibroids have a cartilaginous density, are limitedly mobile. Sometimes, it is possible to visualize a single vessel on the periphery of the formation.
Ossification. Hyperechoic inclusions in the thickness of the skin and subcutaneous fat can be formed after trauma, due to the deposition of calcium salts in the rumen, with diffuse systemic skin diseases (scleroderma). Sometimes, they are formed independently, by the type of sesamoid bones. Often sesamoid bones are revealed anterior to the patella.
Angiomas. These are vascular formations, consisting of various structural elements (hemangiomas, fibrolipoangiomas, angiomyolipomas, lipangiomas, etc.). The main characteristic is the presence of vessels in the base of education.