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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5790_Библиотеки_им_академика_М_И_Перельмана.pdf
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NOTE: May become necessary to change presets during one examination, for
example during abdominal US, you may need conventional abdominal, pelvic and
intestinal or vascular presets.
1 Theory and Basics
1.6.4 Transducer Selection
1.6.4.1 General Remarks
Transducer needs vary – depending on targeted area and patient age.
Proper transducer selection is essential to achieve good results with diagnostic quality:
• Particularly important in paediatrics with vast range of size and ages as well as
targeted areas that demand a variety of transducers.
• Transducer with highest possible frequency that offers best resolution but still has
sufficient penetration should be chosen (see also above – “types of transducers”).
• Basic recommendations for transducer selections exist.
1.6.4.2 Neurosonography
• Neonatal transfontanellar neurosonography: generally sector transducers from 5 to
15 MHz used, alternatively small curved linear arrays with same frequency range.
NOTE: transducers should not have small radius in order to avoid pressure on
brain surface.
• For evaluation of superficial structures (located close to brain surface such as
interhemispheric fissure and cortical areas) as well as skull and extra-axial
pathology: high-resolution linear transducers (7–18 MHz) applied. Use suffi-
cient US gel; sometimes stand-off pads helpful.
• Transtemporal US: sector transducers, frequencies vary with age from 10 MHz
in preterms to 1 MHz in adolescent patients.
• Spinal US: high-resolution linear transducers with broad frequency range depend-
ing on age, ossification and patient; sometimes curved linear arrays as well as
sector/vector probes additionally used for specific queries in older patients.
1.6.4.3 Small Part US
For most small part applications (neck, musculoskeletal, etc.), high-resolution linear transducers (frequency range 3–18 MHz) applied – depending on patient size
and targeted structure.
Sometimes flat curved linear array and stand-off pads are helpful.
1.6.4.4 Chest US
• For assessment of superficial structures (chest wall, pleura, breast, etc.), high-
resolution linear transducers are used.
• Deeper structures usually imaged by sector transducers with age and depth
adapted range of frequencies (1–10 MHz) – allow intercostal, transdiaphrag-
matic or jugular/suprasternal access.
• For transabdominal access (for basal structures) or diaphragmatic US, abdomi-
nal curved linear array probes are very helpful.
1.6 How to Perform Paediatric US
23
• Echocardiography: mainly performed with sector or vector transducers; in neo-
nates linear transducers can be used. Transoesophageal transducers allow visu-
alisation of areas difficult to access transthoracically, usually used in older
patients. Frequencies vary depending on age, but additionally proper Doppler
ranges are important; frequencies tend to be lower than for anatomic imaging
(10–1 MHz).
1.6.4.5 Abdominal US
• Basically curved linear arrays are used. Sometimes sector transducers are help-
ful for areas with small US window. For assessment of superficial structures,
linear transducers are mandatory. Frequencies vary with patient age and size
(2–15 MHz).
• For assessment of intestinal structures, perineal US, detailed analysis of liver
surface or renal parenchyma, as well as for appendicitis, mesenteric nodes or
pylorus, linear transducers are advisable (frequency range 3–15 MHz, depending
on age/targeted area); high-resolution curved linear arrays may offer larger field
of view at only slightly reduced resolution – helpful supplement.
1.6.5 Course of Investigation and Measurements
1.6.5.1 General Remarks
Entire targeted area is evaluated in serial longitudinal and axial sections, complemented by oblique sections if necessary; always includes surrounding structures
and other relevant areas that might cause similar complaints:
• Always assess and document size, contour, shape, position, echostructure and
internal anatomy as well as motility/correlation to adjacent structures.
• Documentation is usually standardised for various queries and body areas; even
normal findings are documented in longitudinal and axial section. Pathology
needs to be documented in two planes and measured.
• Various documentation standards/recommendations are available (e.g. DEGUM/
OEGUM – see: www.oegum.at/content/view/506/210/).
Standardised images and sections help to improve comparability and reduce
interobserver variation – usually predefined by documentation recommendations
(more details listed in organ-specific chapters). 3-dimensional US (3DUS) offers
possibility to store entire volume of targeted organ thus improving documentation.
1.6.5.2 Transducer Handling
Transducers should be moved slowly, carefully, without pressure, no sudden movements and with continuous smooth contact with skin. Specific techniques such as
graded compression or positioning manoeuvres helpful, sometimes mandatory
(e.g. appendix US), for some applications irreplaceable (for DDx), but try to inform
or alert child prior to these measures in order to gain cooperation and avoid sudden
unexpected frightening experience. Remember to effectively, but gently clean the
transducers after each investigation.
24
1 Theory and Basics
Fig. 1.10 Schematic drawing of some organs where US measurements are commonly applied.
Organ shape and relevant measurement axes are given. The equation for calculating the volume
and age-adapted normal value charts can be found in the respective organ chapters and textbooks.
1 sternal line (STL), 2 right middle clavicular line (MCL), 3 axillar line (AL), 4 spleen length,
5 spleen depth/width, l length, w width, d depth
1.6.5.3 Measurements
Basically every organ should be measured, particularly important in paediatric US
as sizes vary with age, depending on patient weight/size (Fig. 1.10).
NOTE: Measurements are for orientation and not always reliable, may vary significantly even within one investigator during same examination.
Measurements are always performed in longitudinal and axial sections and documented
– either as 2-D distance or planimetric definition of (manually) defined plane.
All measurements are performed in standardised, representative and reproducible sections that grant optimal depiction of maximal length and diameters.
Organ sizes are assessed according to age-matched normal value graphs:
• Partial (e.g. liver, spleen and pancreas) distance measurements at standardised
sections are sufficient.
• For other organs, volume calculations are preferred due to inaccuracies or inad-
equate meaning of 2D distance measurements (e.g. kidney, bladder) – volumes
1.7 Documentation and Interpretation
25
are estimated using equations based on geometrical pre-assumptions (ellipsoid
equation = L × H × D × correction factor, usually 0.523). These mathematic esti-
mations sometimes are inaccurate, as organs may exhibit irregular shape. For
these cases, planimetric approaches or 3DUS-based volumetry may improve
results; at least correction factor should be adapted.
NOTE: Always compare measurements/volumes with age/size matched normal.
1.7 Documentation and Interpretation
1.7.1 Image Documentation
Every imaging investigation needs to be documented in sufficient diagnostic quality
and detail; minimal documentation requirements are usually standardised by
individual hospitals/medical societies in form of guidelines or recommendations
(see above).
Documentation is essential not only for medicolegal issues and reimbursement
but also for retrospective reassessment and comparison during follow-up.
Documentation can be performed by various methods: printout from frozen
monitor images using various printing media (video printers, hardcopies, etc.),
storage to hard disc and export into some storage memory; many hospitals store
captured digital images to their PACS. Increasingly not only single images but
also short video clips or 3D volumes are stored for improved documentation.
Images/clips can be retrieved from PACS for reading, printout or digital
distribution.
Media for Documentation
• Polaroid pictures: rather expensive, suboptimal quality, danger of fading, not
used frequently any longer.
• Video paper or colour printers: particularly black and white less expensive, very
practical, still widely used.
NOTE: Durability restricted – prone to fading and damage.
• Multi-format camera: excellent quality, excellent durability, inexpensive in
maintenance and for individual copies but requires significant initial investment.
Was the major documentation in the past but increasingly outdated by digital
documentation.
• Laser imager: good image quality and durability, comparable to multi-format
camera – but even more expensive, and due to large size, difficult to transport;
still commonly used in places without PACS.
• Photo camera: acceptable image quality – but cumbersome handling and devel-
opment; only rarely used, mainly for teaching or publication purposes.
• Video tape: best documentation of entire investigation, particularly useful/valu-
able for echocardiography where it is still commonly used. Setbacks: unpracti-
cal handling of all the tapes with significant space requirements for archiving,
26
1 Theory and Basics
difficult to retrieve single specific investigation; adequate video players must
be available for review. Increasingly being replaced by digital cine-loop clip
storage.
• Digital documentation – increasingly used method. All modern systems store
digital images and short clips to hard drive, can be exported either to workstation
and PACS or transferred to other storage media such as optical discs and external
hard drive.
1.7.2 Report
Documentation not only includes representative images but also the final written
report.
Reports vary with institution and country – usually referring physician gets final
report but no or only some selected representative images, unless images can be
retrieved from PACS or another digital environment.
NOTE: Archiving demands vary with country, include both images and report.
When setting up an US service, adequate precautions to comply with local documentation, archiving and regulatory demands are mandatory.
1.7.2.1 How to Issue a Report
US is an ongoing real-time investigation that (except for video tape documentation
or 3DUS) cannot be entirely documented. Description of investigation is essential;
should be included – not only all areas assessed but also listing all areas and aspects
which could not be properly visualised (e.g. due to overlapping gas) as far as relevant for investigation or actual query, to allow referring physician to perceive
restrictions of investigation.
After descriptive part (usually includes description of organs, measurements/
sizes, with relation to age, weight/size) responsible reader should state a conclusive
diagnosis rating importance of individual findings with respect to clinical symptoms
and query.
1.7.2.2 Diagnosis
Diagnosis – interpretation of findings retrieved from US investigation, should
comprehensively and conspicuously draw conclusion from findings detailed in
description stating diagnosis and listing important DDx. One should always
include limitations of investigation and – if applicable – list supplementing imaging steps.
NOTE: Purpose of structured report – to enable referring physicians to reassess
interpretation of findings. Additional findings received in the meantime or changed/
deteriorated patient symptoms may indicate re-evaluation. By dividing report into
descriptive part and diagnostic assumption, referring physicians are enabled to draw
different conclusions in the light of recent changes. Not as important in patients
with normal or unequivocal clear cut findings/screening conditions – here short
report versions can be used.
1.8 Doppler Sonography
27
1.7.2.3 Predefined Reports
Predefined report forms are increasingly in use trying to standardise reports and to
integrate them into electronic systems; however, often tend to become very extensive or may not provide sufficient flexibility to properly communicate all aspects of
individual investigations, particularly in rare findings.
1.7.2.4 Nomenclature
Use of proper terms and consistent nomenclature is extremely important; standardised image orientation is recommended.
Topographic definitions on US image:
• In general (abdominal and small part US): cranial/proximal, left; caudal/distal,
right; right image side usually left image (supine position).
• Neurosonography: frontal – left in sagittal views; for coronal sections right
image side – left patient side.
• Echocardiography: see Chap. 5.
• Hip US: see Chap. 11.
• Use of pictograms and markers as well as image inscriptions is helpful.
NOTE: One has to define whether axial descriptions refer to body or organ axis.
• A number of typical sonomorphologic descriptions used referring to definition
and contour, echotexture (inhomogeneous or not, etc.), its relative mobility
(good, poor, missing, etc.) and echogenicity (echoic or echogenic, hyperechoic,
anechoic, etc.). Use them consistently.
1.8 Doppler Sonography
1.8.1 The Doppler Phenomenon
Physical principal see Fig. 1.5/text above.
Application
• Doppler effect is used to assess flow direction and velocity – mostly of blood.
• Based on known sound velocity in tissue, sound beam direction and frequency and
direction of imaged motion (e.g. course of vessel on screen – thus defining angle
α between sound beam and motion direction); flow velocity can be calculated.
How Doppler Information Is Displayed
• Received signals exhibit frequency shift – used for calculation. Result displayed
acoustically (flow noise) or graphically; the latter achieved by complex signal
analysis (based on fast Fourier analysis) creating flow graph on monitor – flow
velocity and direction on y-axis, with time encoded on x-axis (see Fig. 1.5).
• Averaged flow velocity information can be superimposed on conventional gray
scale US image by colour displays called colour Doppler sonography (CDS,
Fig. 1.11).
28
Fig. 1.11 CDS – general display. Colours superimposed on gray scale image display flow direc-
tion and mean flow direction; the colour bar in the right of the image indicates the respective scale
(red towards transducer, blue away from transducer, 0.29 cm/s – depictable mean peak velocity –
without aliasing)
1 Theory and Basics
1.8.2 Different Techniques and Applications
of Doppler Sonography
1.8.2.1 Continuous Wave Doppler (CW)
Principle:
• Simultaneous emission and receiving of US beam with two different crys-
tals allows assessment of all movements that occur throughout entire beam
range.
• Reflected signals undergo spectral analysis to decode different flow velocities
and directions.
• Information then displayed by modulating graph intensity depending on distribu-
tion of individual flow velocity (Fig. 1.12).
Application:
• CV Doppler used for quantitative assessment and analysis of high flow velocities
– particularly in echocardiography or in severe stenosis.
• Also used for acoustic depiction and assessment of flow in angiology or phlebol-
ogy as well as for vessel puncture (“Doppler stick”, Fig. 1.12).
Restrictions:
• All information throughout entire beam is displayed – no identification of spe-
cific flow information of individual area.
1.8.2.2 Pulsed Wave Doppler (PW)
Principle:
Offers the benefit to individually target and analyse flow in a single vessel.
• PW Doppler uses a crystal that alternatingly is used to send and then to receive.
After transmitting a short well-defined US signal – longer receive period is acti-
vated to register reflected echoes.
• Time interval between sending and receiving can be defined – signal can be
exactly located at a specific definable depth.
• Volume of sampled area can be defined by variation of receive time (sample volume).
1.8 Doppler Sonography
Fig. 1.12 CW-Doppler scheme. CW Doppler is a single constant US beam without defining any
pulse repetition. Usually applied by a small stick-like apparatus that is easily portable; can also be
integrated in normal US devices. All flow velocities within range of beam are depicted and displayed no matter whether they come from different location. No aliasing – excellent for analysing
very high flow velocities. Method used in echocardiography and for orienting information, e.g.
patency of vessel, signs of significant flow alteration (e.g. screening for leg vein thrombosis) or
finding a vessel for puncture
29
• Thus, one can choose individually adaptable partitions at variable sizes through-
out imaged field; all other areas within are neglected.
• Flow velocity measurements can be performed after applying angle correction
(Fig. 1.13, Table 1.2).
Intrinsic Restrictions:
• By using predefined send/receive time and sample volume, a maximum value is
defined above which flow velocities cannot be measured (Nyquist border). This
correlates with the pulse repetition frequency (PRF).
• All velocities higher than the Nyquist border cause “aliasing”.
• Aliasing – velocities higher than Nyquist border cannot be displayed and may
occur on bottom of Doppler trace, creating partially confusing images and inter-
fering particularly with automated measurements. Aliasing takes place as soon
as PRF is at least twice the maximum Doppler frequency (Nyquist frequency)
caused by the frequency shift from reflection at moving particle.
• PRF depends on depth and minimally on sample volume size – the deeper a ves-
sel the lower PRF must be set. Consequently, the maximum velocity measurable
in deep vessels is relatively low.
1.8.2.3 Duplex-Doppler Sonography
Principle:
• Combination of B-Mode US with Doppler sonography. Simultaneous performance
and display of B-Mode image and PW-/CW-/colour-Doppler-sonography information:
– If three modes performed simultaneously – “triplex-Doppler sonography”,
improving exact location of sample volume, often at sacrifice of (temporal)
resolution.
30
1 Theory and Basics
a b
Fig. 1.13 PW Doppler/angle correction and graphic display. (a) PW Doppler: vessel seen by
B-Mode or CDS; the Doppler angle is corrected by manually moving line into vessel/flow long
axis. Doppler gate is placed at vessel; gate size should be adapted to vessel diameter. (b) Respective
graphic flow display after Fourier analysis. Relatively turbulent arterial flow – has a more homogenous white appearance with little dark areas under the Doppler trace. Laminar flow usually has a
clear “Doppler window” and only exhibits a narrow line of maximum velocities. Y-axis encodes
flow velocity, x-axis encodes time
Table 1.2 Angle
dependency of Doppler US
measurements
Degree cos Error (%)
20° 0.94 6
60° 0.5 50
80° 0.17 83
Cosine-induced error for Doppler measurements depending on
insonation angle: lower angles have less error than higher angles;
reliable measurements can only be achieved up to 50°–60°
• Immensely important for correct assessment: proper angle correction is essential
for quantification of blood flow velocity if angle >10°. Doppler flow measure-
ments significantly depend on angle between US beam and motion direction –
this tool is essential for flow quantification and measurements (see Table 1.2).
Restrictions:
• Due to development of the cosine of angle α, measurements at Doppler angles
>50 to maximum 60° become inaccurate and unreliable – should not be used for
diagnosis.
• When angle reaches 90°, cosine of angle α becomes 0, therefore no Doppler
information can be retrieved.
1.8.2.4 Colour-Coded Doppler Sonography or Colour Doppler
Sonography (CDS)
Principle:
• CDS – simultaneous PW Doppler at many individual points of image (defined by
“colour box”).
1.8 Doppler Sonography
31
• Depending on equipment, variably averaged mean value of flow velocities and
direction encoded by colours superimposed on conventional black and white
gray scale B-mode image.
• Depending on colour preset, the main colour usually displays flow direction
(e.g. red – towards transducer, blue – away from transducer); flow velocity varia-
tions within same direction are then encoded by different colour intensities or
shades (see Fig. 1.11).
Application and Restrictions:
• Helpful for quick assessment of flow information.
• Helps to quickly find vessels and differentiate them from other cystic or tubular
structures.
• Helps to optimise quantitative PW duplex-Doppler investigation of specific
areas.
• Intrinsically does not allow detailed assessment of flow dynamics except for a
general impression of laminar versus pulsating flow, flow direction and average
flow velocity – no angle correction possible.
• Size of individual samples can be modified impacting frame rate. Additionally
other parameters for image optimisation such as filtering and velocity scales to
be applied.
NOTE: Slow frame rates caused by high resolution and low flow velocity imag-
ing may create motion-induced artefacts, particularly in uncooperative children.
1.8.2.5 Amplitude-Coded Colour Doppler Sonography (aCDS)
Synonyms:
Angio-mode, Power Doppler (PD), Colour Doppler energy (CDE).
Principle:
• Does not use flow velocity but integrated velocity spectrum for calculation and
colour display.
• Higher sensitivity, reduced angle dependency.
• Uses amplitude of reflected Doppler signals that is significantly dependent on
number of reflecting particles (much more than on frequency shift) – displays
flow volume rather than flow velocity.
• Furthermore – due to homogeneous low background noise – higher output and
receive gains can be used, again increasing potential to depict very low flow
velocities at poor Doppler angles down to 0.2 mm/s in experimental settings.
• Doppler information displayed by colour overlay on gray scale image as in con-
ventional CDS (Fig. 1.14).
Restrictions:
• High sound pressure in tissue.
• No information on flow velocity and flow direction.
• Higher risk of motion artefacts (“flash” artefacts).
Application:
• Used for vessel depiction at poor insonation angle or with low flow velocities.
• Ideal for assessment of peripheral parenchymal vascularisation – particularly
helpful in assessing the kidney.