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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_1110_Библиотеки_им_академика_М_И_Перельмана
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8 Benign Anorectal Diseases
Fig. I.9. Diagram of echographic equip-
ment with amplitude mode (A-mode)
display: transmitter (a), receiver (b),
oscilloscope (c), trigger signal (d), pulse
electrical signal (e), piezoelectric transducer (f), pulse mechanical signal (g),
medium 1 (h), medium 2 (i), medium 3 (l)
distance from the probe along a single observation direction (A-mode, or amplitude mode), or
the return signals may be displayed as luminous
dots on the screen (B-mode, or brightness mode),
the brightness of which is amplitude dependent.
Grey scale means that the brightness is assigned
to one of a fixed series of shades of grey, usually
256 in number. The illuminate dots are displayed
on the screen in the same sequence of time and
geometry according to which the ultrasonic signal
encounters a differing acoustic impedance along
its path while the ultrasonic beam moves in the
scanning plane. This system permits two-dimen-
sional imaging of a section (tomography) in the
scanning plane. If a sequence of scans is performed at a sufficiently high frequency, a continuous,real-time display is supplied of sections of the
organ even though the organ is in motion.
Information on the absorption of different tissues
and the depth of the organ to be studied allow a
choice of probes for various applications. The
highest frequencies give better resolution and better display of detail, but the tradeoff for this is a
short focal zone and limited penetration. With a
mechanically rotated single crystal, this is fixed by
the design of the transducer. Focusing describes
the optimum range of resolution for the transduc-
er to work at. For the B-K Medical 10-MHz transducer, the axial resolution is <0.05 mm and the
lateral resolution 0.5–1 mm, with a focal range of
5–45 mm [1–2].
Artefacts
Reverberation is an artefact due to a gross mismatch of acoustic impedance at an interface, usually an air/tissue interface, causing a very strong
reflection which is only partially absorbed by the
transducer and which is reflected back to the
interface where it is again reflected back to the
transducer. The beam therefore reverberates back
and forth from the interface and transducer, creating a series of reflections separated by a constant distance, which indicates the distance of the
reflection from the transducer (Fig. I.10).
Reverberation echoes are common in anal
endosonography when there is loss of acoustic
contact within the canal (Fig. I.11).
Interpretative Principles
The prime determinant of the strength of ultrasonic echoes is the impedance mismatch between
adjacent tissue components. The larger the mismatch, the stronger the echo.The echogenicity of
any structure may be characterized by the level of
echoes within it (hyper- or hypoechoic).The echo
pattern may be homogeneous or inhomogeneous. Water has the lowest reflectivity and
appears black.Fat varies in reflectivity but is usually moderately reflective. Collagen is more
reflective and whiter whereas muscle fibers are
Section I • Fundamental Principles of Ultrasound Imaging 9
Fig. I.10. Reverberation echoes develop
when there is a very strong reflection
returning to the transducer. Part will be
reflected from the transducer back into
the tissue. This, in turn, will be reflected
back to the transducer, and so on. This
creates a series of equally spaced reflections. The gap indicates the distance
between the transducer (T) and the initial
reflection
a b
Fig. I.11. The image has been taken with the probe free standing in air. The gas impedance mismatch at the cone/air interface
creates major reflection echo patterns with an equally spaced series of concentric rings (a).The probe has been inserted beyond
the anal canal into the rectal ampulla.Acoustic contact has been lost from 9–11 o’clock, producing a reverberation echo (b)
poorly reflective and blacker. Solid tumors are
usually poorly reflective and inhomogeneous.
While uniform regions of fiber or fat are echopoor, admixtures between them and watery tis-
References
1. Bartram CI, FrudingerA (1997) Basic principles of ultrasonography. In: Bartram CI, Frudinger A. Handbook of
anal endosonography. Wrightson Biomedical, Petersfield, UK
sues give stronger echoes. For a given impedance
mismatch, a region that contains a large number
of scatterers is more echogenic than one where
they are spread out.
2. Santoro GA, Di Falco G (2004) Basic principles of
ultrasonography. In: Santoro GA, Di Falco G. Atlas of
endoanal and endorectal ultrasonography. Springer
Italy, Milan
SECTION II
New Technical Developments
in Endoanal and Endorectal
Ultrasonography
New Technical Developments in Endoanal and
Endorectal Ultrasonography
In order to obtain meaningful ultrasonic images,
the operator must have an overall understanding
and therefore correct use of the controls available
on the ultrasound device. In fact,unsuitable regulation of the equipment produces poor images
and can lead to false positive or negative diagnosis.
Many types of ultrasound probes have been
developed to evaluate the rectal wall and anal
sphincter. Most of these have been made to examine the prostate gland and are not suitable for
evaluating the wall of the anorectum and the
immediately adjacent tissues. The types of
endorectal probes include mechanical sector
probes with a single transducer,which may have a
limited field of view of 120–210° or may incorporate radial probes with a full 360° field of view and
linear and curved array probes, which have a limited 120–210° field of view. Some of these probes
are biplanar and can be changed from the axial
plane to the longitudinal (sagittal, coronal) plane
with the press of a button.All of these probes have
a frequency range from 5 to 10 MHz. The focal
range of a 7.0-MHz transducer is 2–5 cm whereas
a 5.5-MHz transducer has a focal range of 1–4 cm.
The longer focal length provides an advantage in
examining perirectal structures. The 10.0-MHz
transducer is preferred in the anal canal as it gives
improved resolution of the sphincter mechanism
over the 7.0-MHz transducer.
We currently use an Hawk 2102 EXL B-K
Medical scanner (B-K MedicalA/S, Mileparken 34,
DK-2730 Herlev, Denmark) (Fig. II.1) with a 1850
radial array probe,which gives a 360° axial view of
the rectal wall (Fig. II.2) [1–3]. The radial probe
has a 24-cm metal shaft with a rotating transduc-
G.A. Santoro, B. Fortling
Fig. II.1. B-K Medical scanner: Hawk 2102 EXL
14 Benign Anorectal Diseases
Fig. II.2. B-K Medical rotating endoprobe type 1850
a
er at its tip. This 8539 transducer has a frequency
range from 5 to 10 MHz with a focal length of
2–5 cm and a 90° scanning plane and is rotated at
4–6 cycles per second to get a radial scan of the
rectum and surrounding structures (Fig. II.3)
[4–5]. The B-K unit must be assembled carefully
(Fig. II.4). The rectal tube (UA 0878) fits over the
central axle that holds the transducer and slot into
the handle with a screw collar to tighten the tube
onto a rubber compression ring. The rotating
transducer is pushed into the end of the axle and
is covered by a latex balloon that is held in place
b
Fig. II.3. B-K Medical transducer type 8539 (a, b)
by two metal rings, one of which screws onto the
metal shaft (Fig. II.5).A syringe filled with 50 ml
of tap water is manipulated to remove air bubbles
then attached to a spigot at the base of the probe.
Fig. II.4. B-K Medical anorectal probe type 1850 (dismantled), with rectal tube, 10 MHz transducer, plastic cone,and latex bal-
loon
Section II • New Technical Developments in Endoanal and Endorectal Ultrasonography 15
Fig. II.5. Transducer, metal rings, and latex balloon for
endorectal ultrasound
Fig. II.6. B-K Medical anorectal probe type 1850 assembled
with latex balloon
Water is gently injected into the balloon; the water
is then withdrawn again with the transducer tip in
the dependent position.In this way,all of the air is
removed from the water-filled balloon. This procedure may have to be repeated to remove all of
the air (Fig. II.6). Latex balloon filled with
degassed water allows acoustic coupling between
the transducer and the rectal wall (Fig. II.7). The
rectum can be of varying diameters and therefore
the volume of water in the balloon may have to be
adjusted intermittently.
Endoluminal ultrasound is usually performed
with the patient in the left lateral decubitus posi-
tion. Before the probe is inserted into the rectum,
a digital rectal examination may be performed to
identify the size, fixation, morphology, and location of the tumor, if it is low enough. If there is a
stenotic annular lesion, the finger can check to
determine whether it will allow easy passage of
the probe [6–7]. The entire shaft of the probe is
coated with a thin layer of warm gel using a paper
towel.The probe tip is gently inserted through the
anal canal and then angled posteriorly and
advanced cephalad to as high a level as possible,
with the bony sacrum used as a curved landmark.
The patient should be instructed before the exam-
ination that no pain should be experienced. If
Fig. II.7. Diagrammatic representation of
an endorectal ultrasonography
16 Benign Anorectal Diseases
Fig. II.8. B-K Medical transducer type
6005
pain should occur, the study should be halted
until the cause of the pain is elucidated.Under no
circumstances should force be used to advance
the probe. The examiner should never try to push
the tip through a narrow stenotic lesion.However,
in most instances, passage can be achieved
although the volume of the fluid in the balloon
will have to be substantially reduced in order to
withdraw the probe through the stenotic portion.
In some instances, a plastic cone filled with water
will facilitate the imaging of a stenotic lesion, or it
may be necessary to use a smaller probe, 7 mm in
diameter (7 MHz,type 6005, focal range: 0.5-3 cm)
(Fig. II.8). Once the tip is advanced to as high a
level as possible, usually 10–14 cm from the anal
verge, the balloon can be inflated with 50 ml of
water. The amount of water may have to be
increased to provide complete acoustic coupling
with the rectal wall. The examiner should never
distend the balloon with more than 80 ml of
degassed water, as it may rupture. If this occurs,
the probe must be removed from the rectum and
cleaned, a new balloon installed, and the whole
procedure started over.If air or stool gets between
the balloon and rectal wall, it will prevent visualization of the wall. To avoid this, we administer an
enema 2 h before the examination, but despite
this, problems can arise, and it may be necessary
to remove the probe and suction out the rectum
with reintroduction of the probe in order to optimize the image.
With the probe at the highest level possible
and with good visualization of the rectal wall,
images are obtained at 1-cm intervals as the
probe is withdrawn. The tip of the ultrasound
probe should be maintained in the center of the
rectal lumen to gain optimal imaging of the rec-
tal wall and perirectal structures. Some adjustments may have to be made in the gain of the
ultrasound unit to provide optimal imaging.
Occasionally, it is possible to perfectly depict all
five layers of the rectum circumferentially, but
usually, only a portion of the rectal wall at a time
will be optimally imaged, and minor adjustments
will have to be made in the location of the probe
relative to the rectal wall at various locations to
optimally image all five layers. The exact level of
the transducer tip can be read off the metal shaft
of the ultrasound probe. More closely spaced
images (0.5 cm) are obtained in the area of any
abnormality.The balloon may have to be deflated
and reinflated to maintain good acoustic contact
with the rectal wall as the probe is withdrawn
down the rectum. Once the entire rectum down
to the anal sphincter has been evaluated, the bal-
loon is fully deflated, and the probe is removed
from the rectum.
In most instances,the use of a large-bore proctoscope serves several purposes (A.4522,Sapimed,
Alessandria, Italy) (Fig. II.9).Firstly,it allows visual examination of rectal lesions with exact determination of their location, both with respect to
circumferential involvement of the rectal wall and
the distance from the anal verge. Secondly, it
allows suctioning of any residual stool or enema
fluid that might interfere with the acoustic pathways of the ultrasound waves, which may distort
the image. Most importantly, however, it allows
easy passage of the probe to insure complete
imaging of the rectum. This is of extreme importance in the preoperative staging of rectal cancer.
Once the 20-cm scored mark on the shaft of the
probe is at the proximal end of the proctoscope,
the proctoscope is then pulled back on the probe
Section II • New Technical Developments in Endoanal and Endorectal Ultrasonography 17
Fig. II.9. Rectosigmoidoscope for endorec-
tal ultrasonography (A.4522, Sapimed)
as far as possible,thus exposing the transducer for
2 cm beyond the end of the proctoscope. The balloon is then instilled with 30–60 cc of water, the
volume of fluid usually needed to gain optimal
imaging.
If the anus is being evaluated, the same probe
is used with a transducer that has a shorter focal
zone of 1–4 cm. A water-filled, hard-plastic cone
(WA 0543) made of sonolucent polymethyl pentene (TPX) plastic and 1.7 cm in outer diameter is
used in place of the latex balloon (Fig. II.10) [8].A
hole at the top allows air to escape as the assembly
is filled with degassed water. A gel-containing
condom is then placed over the probe, and a thin
layer of water-soluble lubricant is placed on the
exterior of the condom. Any air interface will
cause a major interference pattern. The probe is
now ready for insertion. The outer walls of this
cone are parallel so that the probe may be moved
within the anal canal without causing any
anatomical distortion (Fig. II.11). This is very
important when assessing the canal at different
levels. There does not appear to be any benefit
from asking the patient to “squeeze” their pelvic
floor to assess sphincter contraction.At the origin
of the canal, the“U”-shaped sling of the puborectalis is the main landmark and should be used for
final adjustment [9].
When the patient is in the left lateral position
and the spigot for introducing water into the
probe is pointing toward the ceiling, by conven-
tion, the anterior aspect of the anus will be superior (12 o’clock) on the screen,right lateral will be
left (9 o’clock) on the screen, left lateral will be
right (3 o’clock) on the screen, and posterior will
be inferior (6 o’clock) on the screen (just as in the
image on axial CT scan) (Fig. II.12).
Future Directions
When we display a normal two-dimensional (2-D)
ultrasound cross-sectional view, there are many
elements of the image that will not be correctly
recognized as components of a three-dimensional
(3-D) structure – or at least not perceived in their
true spatial relationships. With ultrasound imaging, we are usually looking at a 3-D structure that
contains a solid volume of echoes and that therefore does not readily translate onto a 2-D projection. In routine clinical scanning, the operator
forms a mental representation of the 3-D anatomic or pathological structure while viewing a large
series of 2-D slices interactively. In this case, the
operator is using manual sense information about
the physical location of the individual slices in
building up 3-D subjective impressions. Threedimensional and, indeed, four-dimensional (4-D)
ultrasound has been promoted by different ultrasound companies for several years. The acquisition of a 3-D data volume and the underlying
techniques are, however, different from application to application.Some areas of the human body
require extremely high-resolution 3-D volumes of
data for adequate and precise diagnostic evaluation (anal sphincter,rectal wall,fistula,urethral
sphincter complex, etc.); other areas require less
when it comes to sampling the 3-D data volume
(baby face, kidney, pancreas). For endoanal and
endorectal ultrasound in general, the problems
will be in assessing anatomy and in characterizing
tissue structure and type.
Three-dimensional reconstruction of 2-D
images is possible by connecting the ultrasound
apparatus to a computer equipped with special
software (BK 3Di) (Fig. II.13) [10].A normal dig-
18 Benign Anorectal Diseases
a b
Fig. II.10. Transducer and plastic cone for endoanal ultrasonography (a, b)
ital ultrasound image is displayed using a display
matrix of around 700¥700 pixel elements, with
each pixel assigned a value between 0 and 255
(256 levels of grey). The result seen on the ultrasound monitor is a 2-D image with no depth
information. Adding the third dimension to the
pixels means that the pixels are transformed to
voxels (voxel is a pixel, X- and Y-plane only, in
the ultrasound image with an added Z-plane),
each of which also will have an assigned value
between 0 and 255. The depth of the voxel is crit-
ical to the resolution of the 3-D image, and this
depth is directly related to the spacing between
two adjacent images. Ideally, the voxel should
form an exact cube, but because generally sampling with slightly lesser resolution in the Zplane (due to acquisition speed considerations)
compared with the 700¥700 matrix, the resolution in Z-plane is marginally lower. High-resolution data volumes may consist of typical voxel
sizes around 0.15¥0.15¥0.2 mm (or 0.25 mm).
This means that an acquisition based upon, for
Fig. II.11. Diagrammatic representation
of an endoanal ultrasonography
Section II • New Technical Developments in Endoanal and Endorectal Ultrasonography 19
a
Fig. II.12. Lesion localization with patient in left lateral posi-
tion when the spigot for introducing water into the balloon is
pointing toward the ceiling (a,b)
example, sampling of transaxial images over a
distance of 60 mm in the human body will result
in a data volume block consisting of between 240
and 300 transaxial images. This is far more than
any 4-D technique can handle using computer
power as we know it today. High-resolution 3-D
technique and consequently much slower acquisition speed does not function in 4-D mode. Four
to five transaxial images are, as mentioned, sampled per 1-mm distance (in the Z-plane).
Acquisition of a high number of parallel transaxial images can be performed using a special colorectal pullback mover (UA0552) with the B-K
Medical ultrasound probe type 1850 (Fig. II.14).
The colorectal pullback mover is a computercontrolled, motor-driven device that can be
operated at different levels of resolution. For the
endoanal application, the usual setting is
0.2–0.3 mm between adjacent transaxial images.
Scanning the anal canal with these settings over
a pullback distance of 35 mm will typically yield
175 parallel images (Fig. II.15). This approach
provides a neat way of uniformly scanning a
solid volume, the acquisition taking typically
60 s. However, it is subject to the important limitation of being rather bulky. An alternative
approach is to use a manual technique. In the
case of manual acquisition, the samples will not
be uniform, and they may be anisotropic in the
sense that a voxel gives different values. Extreme
cases will result in voxels either having no samples, that is, having data gaps, or having multiple
samples. Gaps cause visually distracting artefacts in the resulting displays. The new B-K
Medical 2050 anorectal transducer solves most
b
Fig. II.13. Hardware (BK 3Di) for acquisition, reconstruction,
and visualization of three-dimensional ultrasound images
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