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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5797_Библиотеки_им_академика_М_И_Перельмана.pdf
1 Overview ofSkin Ultrasound
ab
Depth
c d
21
Fig. 1.29 Adjustment of depth. (a)Depth buttons on operator panel (red circle). (b)Depth is too shallow. (c)Depth is
too deep. (d)Depth is proper (lesion is indicated by arrows)
ab
Fig. 1.30 Focus. (a) Focus button on the operator panel (red circle). (b)Focus marker on the right side of the screen
(arrow)
output power, the weaker the ultrasound penetration, and the clearer the image display.
(6) Dynamic range: It is referred to the loga-
rithm of the amplitude ratio of the maximum
processed signal to the minimum processed
signal, which is used to adjust the contrast
resolution of the image. The wider the
dynamic range, the lower the contrast resolution; conversely, the higher the contrast resolution. In general, the dynamic range of the
skin ultrasound is narrower than that of the
abdominal ultrasound (Fig.1.31).
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51dB 60dB 90dB
H.-X. Xu et al.
Fig. 1.31 Dynamic range. Left: The narrower the
dynamic range (51dB), the higher the contrast resolution.
Right: The wider the dynamic range (90dB), the lower the
contrast resolution. Middle: the contrast resolution is optimal when the dynamic range is proper (60dB)
Adjustment of Color Doppler Flow Imaging
(1) Preparation to establish a satisfactory blood
ow display environment: (1) Selecting a
transducer with appropriate frequency.
Understanding the characteristics of PRF,
and taking into account penetration, resolution, and real-time performance according to
specic needs, (2) Optimizing the gray-scale
image. Appropriately reducing the gain of
the two-dimensional image. (3) Displaying
the longitudinal axis of the vessel, and
adjusting the Doppler angle to the
minimum.
(2) Color box: Firstly, it is necessary to adjust
the size of the color box on color Doppler
ultrasound. If the color box is too large, the
frame rate will reduce, resulting in image
lagging. If the color box is too small, the
blood ow of the target lesion cannot be displayed completely. Therefore, the appropriate color box should be slightly larger than
the lesion, including some surrounding tissues (Fig.1.32).
(3) Color gain: Proper gain settings are essential
to accurate and reproducible Doppler measurements. When the color gain is too high,
color ow signals overow with artifacts in
the perilesional area occurs; while the color
gain is too low, intralesional blood ow sig-
Fig. 1.32 Color box. The dotted box pointed by the
arrow is the color box
nals cannot be completely displayed
(Fig.1.33). The proper color gain setting is
rstly increasing the color gain until the
extravascular noise appears, then reducing
the color gain until the disappearance of
extravascular noise. Also, the gray-scale gain
should be appropriately reduced.
(4) Scale (pulse repetition frequency): In order to
optimize the display of blood ow, it is necessary to adjust PRF, also known as scale.
Frequency (Hz), average velocity value
(cm/s), or velocity level (high, medium, and
low) can be used to represent the magnitude of
PRF in color Doppler. The general principle
of regulating PRF is to make the blood ow
signal as rich as possible in the color box,
without aliasing artifact (that is, the blood
ow signal in the same direction shows the
red and blue at the same time, which is generally caused by too low scale) as optimal.
Adjustment of Pulse Wave Doppler Imaging
1. Sample volume: It should be kept as central as
possible, and adjusted to 1/2 ~ 1/3 of the
diameter of the target vessel in width.
2. Doppler gain: The Doppler gain is adjusted by
rotating the Doppler Gain button. When
Doppler ow visualization is clear and the
background is clean, the Doppler gain is
believed to be proper.
3. Angle correct: Angle correct refers to the
adjustment of Doppler angle, which is used
1 Overview ofSkin Ultrasound
23
a
b
c
Fig. 1.33 Adjustment of color gain. (a)Color gain is too high (arrows). (b)Color gain is too low (arrows). (c)Color
gain is proper (arrows)
to calibrate the angle between acoustic beam
and blood ow direction of the target vessel,
and display the actual blood ow velocity
The adjustment of power Doppler ow imaging is similar to that of color Doppler ow imaging, so it will not be repeated here.
through the correction of cosine value of
this angle. The acoustic beam shall be kept
parallel with the direction of blood ow, and
the angle between the two shall be as mini-
1.4.4 Inuencing Factors forSkin
Ultrasound Imaging
mal as possible, with the maximum angle
less than 60°.
4. Velocity scale: The velocity scale was selected
according to the velocity of blood ow in the
vessels. Lower velocity scales are generally
selected for skin diseases.
5. Wall lter: By adjusting the lter button to
change the wall lter value, the low-frequency
and high-intensity noise caused by vessel wall
or tissue motion is eliminated. The wall lter
values can be set to low, medium, and high.
Low-pass lter is used for low-velocity blood
ow, and high-pass lter is used for highvelocity blood ow.
1.4.4.1 Pressure
Surface pressure has a great impact on highfrequency skin ultrasound imaging, and pressure
may lead to deformation or blood ow imaging
distortion of the lesion, even lead to the lesion or
its blood ow invisible. Direct contact of the
transducer with the skin should be avoided during skin ultrasound examinations, and it is recommended to ll with gel (>1mm in thickness)
to isolate the skin from the transducer, thereby
eliminating the surface pressure caused by the
transducer. In addition, the gel pad can also be
used to isolate the skin from the transducer to
24
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H.-X. Xu et al.
improve the image quality, but the pressure of the
gel pad itself on the skin still cannot be ignored.
1.4.4.2 Hairs
Small and ne hairs have no signicant effect on
ultrasound imaging. The thick hair may produce
acoustic shadowing, while air is present among
the hairs, both of which can reduce the quality of
the ultrasound image (Fig.1.34). In this regard,
the image quality can be improved by hair
removal or lling with more gel.
1.4.4.3 Wrinkles
There are various wrinkles formed naturally in
the skin, thus the skin surface cannot be closely
tted with the transducer, affecting the quality of
ultrasound imaging. At this time, the image quality can be ensured by straightening the skin, lling it with more gel, adding a gel pad, or other
methods to t the skin at the wrinkles to the transducer (Fig.1.35).
1.4.4.4 Temperature
Temperature mainly affects the blood ow signal
of color Doppler ow imaging. If the temperature
is too low, the blood ow signal may be reduced.
If the temperature is too high, it may cause an
abnormal increase in blood ow. Examination at
room temperature around 20°C is recommended,
and heated gel is not recommended.
Fig. 1.34 Effect of hairs on skin ultrasound imaging.
(a)Sparse hairs and a small amount of air are observed on
the skin surface, and the image quality is not signicantly
affected (male, leg; transducer frequency: 30 MHz).
Fig. 1.35 Effect of wrinkles on skin ultrasound imaging.
(a)Skin wrinkles contain air, forming acoustic shadowing
and resulting in unclear display of skin structure and layers (male, palm; transducer frequency: 34MHz). (b)The
(b)Dense hairs and air form acoustic shadowing, signicantly reducing the image quality (male, head; transducer
frequency: 30MHz). Arrows point to the hair, circle is air
among hairs
skin at this site is straightened, and then the skin structure
and layers can be clearly displayed. Arrows point to skin
wrinkles
1 Overview ofSkin Ultrasound
25
1.4.4.5 Precautions
Due to the supercial location of the skin and
related diseases, ultrasound images are required
to have sufcient resolution to show tiny structures. At the same time, the depth involvement of
skin diseases is closely related to disease progression, and ultrasound with sufcient penetration ability is needed to display the information
of depth involvement of the lesion. Therefore,
skin ultrasound imaging needs to take into
account both resolution and depth. In addition,
various pathophysiological conditions such as
obesity, keratinization, scar, and edema can lead
to acoustic wave attenuation, impacting the quality of ultrasound imaging.
Finally, the skin ultrasound imaging is sensitive to pressure. When the transducer is placed
on the skin surface, the deformation and distortion of lesion morphology and ultrasound image
may result from the weight of the transducer
itself or the pressure applied during the
examination.
Therefore, according to previous literatures
and our clinical practice, attention should be paid
to the following factors when performing skin
ultrasound imaging.
1. For dermal and epidermal ultrasound imag-
ing, the frequency of the transducer shall be
at least 20MHz. When the frequency meets
this condition, it is feasible to distinguish
epidermis, dermis, and subcutaneous tissue
and clearly display various layers of skin. If
the frequency of the transducer increases to
50MHz, the internal structure of the epidermis can be further visualized, but the structures below the papillary dermis may not be
visualized due to decreased penetration. As
the frequency increases further (e.g.,
≥100 MHz), the penetration of ultrasound
will decrease signicantly and cannot show
the whole lesion, which is not clinically
practical.
2. The skin varies greatly among individuals, the
lesion is complex, and the size may span multiple scales from nm, μm, mm to cm, so the
frequency of the transducer needs to be fre-
quently switched to meet the imaging requirements of lesions with different sizes. In
clinical practice, it is necessary to take into
account the imaging resolution and depth at
the same time according to specic circumstances, so as to obtain the optimal images.
3. In case of poor contact due to the presence of
hairs and wrinkles on the surface of the lesion,
more gel or gel pad should be used. The transducer should not be pressed to avoid deformation of the lesion.
4. It is necessary to pay attention to the disinfection and isolation of ultrasound transducers,
so as to avoid cross infection. The transducer
must be disconnected from the ultrasound
device and cleaned with running water or soap
solution after each patient examination. For
lesions with open wounds, it is recommended
to use a protective sleeve to isolate the transducer prior to examination to protect the
transducer from blood, tissue debris, secretions, or other body uids.
Key Points
• Before the ultrasound examination, a detailed
history of the patient and careful observation
for the appearance of the lesion are required.
• Multiple factors should be avoided in skin
ultrasound examinations.
• Skin ultrasound imaging needs to take into
account both resolution and depth.
• Protecting throughout the examination to
avoid cross infection.
1.5 Cleaning ofUltrasound
Device andPersonnel
Protection
1.5.1 Cleaning ofUltrasound Device
1. Ultrasound devices should be avoided to contact the patient during the whole examination.
2. It is recommended to cover the operator panel
with transparent plastic lm to prevent dust
and water, and to wipe the lm with a medical
disinfectant wipe after a daily examination.
26
H.-X. Xu et al.
3. Wiping the screen of the ultrasound device
daily with a non-woven cloth to remove stains.
4. After daily check, the device is disinfected by
ultraviolet irradiation, and the screen is protected by drape during irradiation.
5. The above maintenance and cleaning shall be
carried out under power-off status. Other precautions can refer to the instructions for use or
consult the engineer.
1.5.2 Cleaning ofTransducer
1. At the end of the daily work, the transducer
and cable are wiped with medical sterile
towels.
2. If the surface of the lesion is without rupture
and ulceration, the transducer does not require
special protection and cleaning, and the examination can be continued after wiping the
residual gel on the transducer.
3. When there is an open wound on the skin surface or there is blood or exudates, the transducer should be isolated to avoid cross
infection as following.
1) Prior to examination, the transducer should be
disconnected from the ultrasound device. It is
recommended to use running water to clean
the transducer, and routinely apply gel on the
surface of the transducer (either sterile or conventional), and then use a special disposable
protective sleeve to wrap the transducer (if
not, wrap it with rubber gloves).
2) During the examination, the transducer is
contacted with the wound surface by using the
sterile gel, and attention should be paid to
keep the transducer from the surrounding skin
of the lesion and other objects.
3) After the examination, the gel on the wound
surface should be wiped with sterile gauze. It
is recommended to change the dressing and
bandaging of the lesion according to the surgical routine disinfection. Discard the medical
waste generated in the above process according to the relevant requirements.
4) Finally, the transducer is disconnected from
the device. The transducer is washed again
with running clean water, and is cleaned with
soap solution or disinfectant wipe.
5) After using the transducer to check lesions
with open wounds of patients with infectious
diseases such as condyloma acuminatum,
syphilis, or acquired immune deciency syndrome (AIDS), 2% glutaraldehyde should be
used for disinfection 30 min, then washed
with clean water or sterilized with UV-C
ultraviolet lamp. However, it should be noted
that the chemical reagents may corrode the
transducer material. The instructions or the
engineer should be consulted before use.
1.5.3 Personnel Protection
1. For lesions without open wounds, blood, or
exudates, the operator and the assistant do not
need special protection.
2. For lesions with open wounds, blood, or exudates, the operator and the assistant need to
wear gloves and masks during the examination and to clean the transducer after the
examination. Hand disinfection is required
before and after each examination (Fig.1.36).
Hat
Goggle
Mask
Gloves
White
coat
Protective
clothing
Shoe cover
Fig. 1.36 Protection of examiner. The left gure shows
level 1 protection, and the right shows level 2 protection
1 Overview ofSkin Ultrasound
27
3. When the patient suffers from Class B or
above infectious diseases, no matter whether
the lesion is ulcerated or not, the operator and
the assistant need to wear protective clothing,
shoe covers, protective goggles for full protection (Fig.1.36).
4. Before and after the examination, the window
should be opened daily for ventilation for
30 min. If the lesion is odorous, ventilation
should be performed for at least 10min after
the examination.
5. Room environment disinfection is performed
regularly in a week.
Key Points
• It is necessary to clean the device and protect
the operator during the ultrasound
examination.
• Cleaning of ultrasound devices and protection
of operator should be carried out according to
relevant regulations and quality control
standards.
1.6.1 Extended Field ofView
Extended eld of view (EFOV) imaging, also
known as broad-view imaging, can obtain image
information beyond the display range of normal
ultrasound images. EFOV is suitable for large
lesions. The basic principle is to obtain a series of
two-dimensional ultrasound images through the
unidirectional, constant speed, and stable movement of transducers on the basis of conventional
ultrasound. When the transducer moves, the
image moves from one frame to the next, which
has a great overlap area. At this time, it is necessary to use the calculation of computer vector
change to accurately estimate the movement of
the transducer from one frame to another frame,
register the frame by frame, and nally reconstruct and stitch this series of two-dimensional
images into an image with continuous extended
eld of view. For larger skin lesions, complete
visualization of the whole lesion on one image
can be achieved using EFOV imaging (Fig.1.37).
1.6 New Ultrasound Technology
inSkin Ultrasound
In recent years, a number of new ultrasound
technologies have been gradually used in clinical practice. These technologies can provide
more information for the diagnosis of skin diseases and further broaden the application of
ultrasound in the diagnosis and treatment of
skin diseases. These new technologies are
mainly as follows.
Fig. 1.37 Extended feld of view imaging of supercial
basal cell carcinoma. Male, lesion located in left temporal
of the face. (a) The examination is performed using a
high-frequency ultrasound transducer with a frequency of
22MHz, and the broad-view of the lesion (arrows) and the
1.6.2 Ultrasound Elastography
Because different tissues have different stiffness,
it is possible to differentiate the benign from
malignant lesions by stiffness information. At
present, the elastography used in clinical practice
mainly includes strain elastography (SE) and
shear wave elastography (SWE). SE is based on
manual pressure to deform the tissue which can
only provide qualitative data. SWE is based on
the measurement of the transverse shear wave
ba
adjacent normal skin are displayed by extended feld of
view imaging. (b) The lesion (arrows) is only partially
displayed without extended feld of view imaging. The
boundary and adjacent tissue of the lesion is invisible
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H.-X. Xu et al.
ba
c
Fig. 1.38 Ultrasound elastography. (a) Gray-scale ultra-
sound shows an oval, well-dened, hypoechoic structure
(arrows) in the dermis and subcutaneous tissue. The lesion
is heterogeneous (Frequency: 15MHz). (b)Color Doppler
ultrasound shows no blood ow signal in the lesion
(arrows) (Frequency: 15 MHz). (c) Two-dimensional
shear wave elastography is conducted to assess the stiffness of the lesion qualitatively. The lesion and the sur-
propagation speed induced by acoustic pulse
from the ultrasound transducer within the tissue.
Shear wave speed can be quantied as the
Young’s modulus in kilopascals (kPa). SWE
includes point SWE and two-dimensional
SWE.Among them, point SWE reects the quantitative information of stiffness in the region of
interest (ROI), and two-dimensional SWE not
only can provide quantitative information, but
also intuitively reect the tissue stiffness in the
ROI through color coding.
Elastography is widely used in the liver, thyroid, breast, and other organs. It is also suitable for
skin lesions to differentiate benign from malignant
lesions by measuring the stiffness of lesions. This
technique provides stiffness information in addi-
d
rounding tissues show homogeneous blue, indicating no
signicant difference in the stiffness between the lesion
and surrounding tissues (arrows). (d)Shear wave elastography is conducted to assess the stiffness of the ROI quantitatively (arrows), with a maximum elastic modulus of
35.5kPa, a mean elastic modulus of 14.1kPa, and a minimum elastic modulus of 6.8kPa
tion to anatomical information and a new modality
for the diagnosis of skin diseases (Fig.1.38).
1.6.3 Contrast-Enhanced Ultrasound
Contrast-enhanced ultrasound is a pure blood pool
imaging technology, adopting low mechanical
index contrast-specic imaging technique and second-generation ultrasound contrast agent. The
microcirculation perfusion of a target lesion is
dynamically visualized in real time by injecting
microbubble contrast agent into peripheral vein,
which can reect the blood supply and perfusion in
the lesion. Contrast-enhanced ultrasound improves
1 Overview ofSkin Ultrasound
29
the diagnostic accuracy of skin diseases by obtaining morphological and functional information of
the lesion through qualitative and quantitative analysis (i.e., enhancement pattern, enhancement intensity, and time intensity curve) (Fig.1.39).
Parametric imaging technology is a postprocessing mode based on the original data of
contrast image. The basic principle is that each
ROI on the contrast image has its corresponding
time intensity curve (TIC) to reect the amount
and speed of contrast agent entering into the
lesion. The technology can automatically identify and display the average arrival time and area
under the curve corresponding to the intensity
threshold on the TIC in each ROI, constituting
the image of parametric imaging. Other quantitative parameters of TIC are also obtained such
a b
as peak intensity (i.e., the maximum intensity of
the TIC), time to peak (i.e., the time from the
rst microbubble entering the lesion to the
microbubble reaching the peak intensity),
ascending slope, etc. Compared with the original contrast image analysis, the parametric
imaging can more intuitively display the subtle
differences in the contrast agent perfusion of the
internal and peripheral of the lesion, overcoming the shortcomings of conventional qualitative
diagnosis. Studies have showed that malignant
tumors can achieve higher peak intensity on TIC
than benign tumors, which is conducive to the
differential diagnosis of benign and malignant
diseases. TIC showing a rapid increase often
indicates malignant perfusion characteristics
(Fig.1.40).
Fig. 1.39 Contrast-enhanced ultrasound. (a) Gray-scale
ultrasound shows an oval, well dened, slightly
hypoechogenic lesion (arrows and dotted line) in the
dermis and subcutaneous tissue, with slight posterior
Fig. 1.40 Time intensity curve (TIC). TIC analysis of the lesion (arrows and dotted line) shows peak intensity is −65.4
(dB); time to peak, 7.230seconds; ascending slope, 0.863, and area under the TIC is 236.377
acoustic shadowing (Frequency: 15MHz). (b) Contrastenhanced ultrasound shows that the lesion (arrows and
dotted line) is homogeneously hyperenhanced compared
with the surrounding soft tissue (Frequency: 9MHz)
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H.-X. Xu et al.
The contrast agent SonoVue (Bracco, Italy),
which is now widely used in clinical practice, is a
representative of the second-generation ultrasound contrast agent (Fig.1.41). It has high safety
and good tolerance, and the probability of lifethreatening allergic reaction is extremely low,
about 0.001%, which can be injected repeatedly
(Fig.1.42). SonoVue is mainly composed of sulfur hexauoride (SF6) gas and white lyophilized
powder. This contrast agent stays only in the
blood pool without entering into the extracellular
space and is a pure-blood pool contrast agent.
Novel ultrasound contrast agents such as
Sonazoid can be phagocytosed by Kupffer cells
in the liver and spleen and have a special postvascular phase beyond the vascular phase, which
can provide more diagnostic information.
In addition, two new ultrasound molecular
imaging contrast agents, BR55 and Multiselection,
have emerged in recent years. Those agents can
specically bind to disease-related molecular
markers expressed by endothelial cells and
achieve molecular imaging with high sensitivity
and long duration.
1.6.4 Three-Dimensional Ultrasound
Three-dimensional ultrasound is an imaging
mode based on two-dimensional ultrasound.
Through mechanically or electronically driven
transducers, a series of two-dimensional images
with equal distance or angle are obtained to form
a three-dimensional database. After processing
and reconstruction by computer, the threedimensional image of ROI is obtained. It can
visually and vividly display more information of
Fig. 1.41 Sample of contrast agent. (a) Contrast agent before use. (b)Contrast agent after dispersion with normal
saline
Fig. 1.42 Injection of contrast agent. (a) Injection of contrast agent. (b)Flush the tube with normal saline