Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5795_Библиотеки_им_академика_М_И_Перельмана.pdf
24
ab
Fig. 2.7 Refraction artefact causing
two upper kidney poles (left
longitudinal ank scan)—may be
confusing, may cause wrong
distance measurements
M. Riccabona
Fig. 2.8 Anisotropy effect:
schematic drawing illustrating
phenomenon
Fig. 2.9 Inuence of anisotropy effect on image appearance: Different appearance of a tendon
(arrow) when scanned orthogonally (a, echogenic—reections from internal structure return to
transducer) or obliquely with a tilted transducer position (b, hypoechoic—all echoes reected out
of receive eld); phenomenon may also be reduced by cross beam imaging/image compounding
Anisotropy
Property of directional structure
Echogenicity depends on insonation angle
2.5.2.11 Anisotropy
Occurs in tissues composed of very structured strong reectors (e.g. brillar pattern)—echoes vary with insonation angle (Fig. 2.8), typically with muscles and
tendons (Fig.2.9).
• Can usually be eliminated by changing transducer position/angulation.
• Of utmost importance in musculo-skeletal US—if unrecognised may lead to
incorrect interpretation (i.e. tear, etc.).
2 US Methods, Artefacts, Biologic Eects, Practice
25
2.6 Biologic Effects
2.6.1 General Remarks
Biologic effects of diagnostic US based on physical phenomena caused by interaction of emitted US with tissue depending on frequency, wave length and output energy.
Different devices may cause variable tissue impact with same application—
because of different output gain settings/other device-specic presets.
2.6.2 Thermal Effects
2.6.2.1 Tissue Heating
Caused by energy absorption—amount of temperature rise depends on output
energy and intensity of sound eld. Increases with higher frequency by deposition
of higher amounts of energy in smaller volume (less penetration).
Additionally, temperature-handling ability of tissue is important, e.g. vascular-
ised and well-perfused tissue can better tolerate temperature changes than little or
non-perfused tissue.
Human tissue with highest thermal absorption is bone; therefore experiences
highest temperature rise with secondary biologic effects particularly on neighbouring tissue.
Note Some heat generated by transducer itself is also transmitted to skin/tissue.
2.6.2.2 Biological Effects, Tissue Heating
Even on routine diagnostic scans using modern diagnostic US devices, measurable
increase in temperature may occur; particularly important for foetal examinations
and (trans)cranial US.However, temperature that causes degeneration of proteins
(i.e. >41.5°C) or potentially cell death (>45°C) does usually not occur in diagnostic applications.
This effect must be considered when examining patients with high fever to avoid
potential dangerous heat production; e.g. relatively short insonation of individual
areas advisable. Commonly used parameter=thermal index (TI). Three different
types of TI dened depending on tissue examined: TIS—small part, TIB—bone,
TIC—cranial (see below):
• General rule of thumb: TI never >3, TIC <1.7, in neonatal brain (and other sensitive or poorly perfused structures) TIC <1 (or better <0.7) advisable.
26
M. Riccabona
2.6.3 Mechanical Effects andResonance
Resonance of molecules proportional to applied frequency depends on output
energy, separate from mechanical impact on tissue by sound pressure.
In order to maintain safety, diagnostic US devices initially did not allow energies
>100mW/cm2. According to experimental observations, intensity measure changed,
at present sound pressure levels considered more important:
• Relative upper limit of negative peak pressure is dened by 1mPa; no relevant mechanical and resonance-induced tissue damage should occur below
this level.
• (Sound)Pressure waves have positive and negative partition; the latter is called
suction force. This negative pressure causes a sort of vacuum—has highest
potential for tissue damage by implosion or “cavitation”.
Danger/risk of mechanic effects estimated by mechanical index (MI): in general
MI should be kept below 1.7; in more risky areas <1; in very sensitive areas <0.7:
(e.g. neonatal brain) and for low-MI contrast-enhanced US (ce-US) MI around
0.1–0.3 (see below).
2.6.3.1 Cavitation
Acoustic Cavitation
Sound-induced occurrence of hollow areas as well as gas bubbles in insonated
material may undulate and change size. These small cavities and their activity cause
wide spectrum of physical, chemical and biological effects.
Negative Peak Pressure
Crucial parameter for estimation of cavitation effect: negative peak pressure within
insonation eld. Additionally need cavitation seed—usually microscopic gas bubbles that explosively increase in size during negative sound pressure.
Cavitation effects are independent from thermal effects; e.g. US impulse with
Note
high pressure and low frame rate can cause cavitation without any signicant thermal changes.
In human tissue, inert cavitation is no major problem—practically no cavita-
tion seeds exist, except for tissue containing air or gas such as lung or intestines.
However, if US contrast media (based on stabilised microbubbles) used, cavitation effects may become relevant, as for US of target adjacent to aerated
structures:
• When respecting given limits/application guidelines, no clinical relevant damage
by diagnostic US (even using US contrast media) is currently reported.
2 US Methods, Artefacts, Biologic Eects, Practice
27
2.6.4 Potential Risks ofDiagnostic US
Signicant effects can be produced by US on all kinds of tissues. This potential is
used therapeutically (e.g. lithotripsy, sonophoresis and treatment of tendinous
calcications).
Diagnostic US uses much lower energy levels than therapeutic US, though—
using maximum output gain and long sound exposure on single site—biological
effects can be demonstrated in animal experiments (cavitation, mechanical and thermal effects added, duration of exposure essential).
With prudent use, no signicant impact in human medical diagnostic use in
terms of carcinogenesis, teratogenesis or higher mutation rates found.
2.6.4.1 Specific Risks
Higher risks for sound-induced effects: long duration of pulsed duplex-Doppler and
amplitude-coded CDS (aCDS) investigations with stationary US beam and higher
sound energy, particularly in vicinity to bone (for these applications higher sound
energy with focused focal pulse is usually used); i.e. transcranial US, echocardiography—especially in border areas with vicinity to aerated lung
• M-Mode: slightly higher-output energies used for depicting clear M-Mode signal.
• Harmonic Imaging: slightly higher energy necessary to create a harmonic signal
strong enough to reach back to the transducer at higher frequency (than emitted
fundamental frequency) with reasonable penetration.
Note Try to avoid focused pulsed duplex-Doppler and M-Mode for foetal echocar-
diography (risk-benet ratio to be considered, particularly related to heating).
2.6.4.2 Guidelines andRecommendations
In order to maintain biologic sound-induced risks as low as possible, some aspects
need to be considered:
• Diagnostic US—medical imaging; there should be clear indications on rm
medical grounds for every investigation (with some exceptions for scientic and
educational needs).
• Always try to minimise output gain by using maximum receive gain.
• Keep exposure times of specic area as short as possible; make use of frozen
images for analysis instead of looking at same structure for long times under
real-time US conditions (unless you need dynamic-functional observation).
• Always rst optimise image, particularly for Doppler investigations: only activate your colour box or PW-duplex gate after area of interest has been dened,
measurement point/gate has been adjusted, angle correction has been dened, etc.
• Try to avoid cavitation seeds or bones in vicinity of duplex-Doppler beam.
• Further recommendations can be found in literature and with various US societies (e.g. EFSUMB; AIUM; OEGUM/DEGUM).
28
M. Riccabona
2.6.5 Various Methods andIndices that Allow Estimation
ofBiological Risks
2.6.5.1 Mechanical Index (MI)
Introduced to describe peak pressure in tissue (in mPa) depends on output gain. The
used frequency and focus pre-describe potential risk of sound pressure-induced tissue damage as well as cavitation risk.
Mostly used in B-Mode sonography and should be kept below 1; short increases
(if diagnostically necessary) up to 1.5mPa acceptable in individual situations.
Note MI should be lower for vulnerable regions, particularly for foetal exams, for
examination of the neonatal brain (transfontanellar), for eye US and for ce-US to
avoid damage of specically sensitive structures or to minimise danger in the presence of cavitation seeds (see also above).
2.6.5.2 Thermal Index (TI)
Describes risk of tissue heating with consecutive tissue damage:
1. TIS (soft tissue thermal index)—used for soft tissue.
2. TIB (bone thermal index)—used for bone.
3. TIC (cranial thermal index)—used for transcranial applications.
Mainly depends on tissue, output gain, focal zone and frequency used.
TI—most important in Doppler sonography as well as for foetal US.TI should
be kept below 1—brief increase accepted if diagnostically necessary in individual
examinations (e.g. Doppler sonography usually works with higher TI values).
2.6.5.3 Display ofActual Indices
Indices must be displayed by equipment throughout investigation and constantly
updated depending on individually altered settings (gain, focus zone, frequency,
etc.), should also be documented on saved images.
2.7 How toPerform Paediatric US
2.7.1 Requisites
2.7.1.1 Indications
Every investigation must rely on thorough indication. Referring physician has to
provide detailed question; US investigation must potentially offer diagnostically
relevant result with therapeutic or prognostic consequence.
Only exceptions:
• Screening (e.g. urinary tract, hip) should have signicant preventive effects:
– Increasingly under discussion, with widespread foetal US and new knowl-
edge on impact of screening approaches in last decade.
2 US Methods, Artefacts, Biologic Eects, Practice
29
– Besides hip US general screening rarely proposed in childhood; selected
screening established in dened patient groups (e.g. familiar/syndromal/
genetic increased cancer risk …).
• For scientic or educational purpose.
2.7.1.2 Environmental Requisites
• Proper and comfortable positioning facilities.
• Quiet room with sufcient light dimming.
• Proper and ergonomic positioning of investigator.
• Ergonomic styling of surrounding working area—includes separate reading
facility with monitors and separate sitting area for consultation with patients and
parents.
Note Have sufcient chairs available, as usually more people than just the
patient.
• Proper room temperature with additional heating available for neonates and
infants.
• Even with children, privacy must be respected; therefore proper changing rooms and
towels mandatory, furthermore cleaning facilities, and adjacent restroom desirable.
2.7.1.3 Specific Needs inChildren
• Usually accompanying persons are present during investigation and for consultation afterwards—rooms must be adequately sized and equipped.
• Accompanying parents and brothers or sisters can help pacify infant during
investigation, additionally monitors for displaying either US image or movies
and toys are helpful. Other pacifying measures: books, music.
• Warm US gel, but prevent bacterial and fungal growth in gel bottle.
• Initial introductory comment understandable to child and accompanying persons
is helpful—enables them to understand investigation, what is going to happen
and to reduce fears. Explain equipment as well as procedure.
• Effort of establishing good relation prior to starting investigation—often essential to enable peaceful and diagnostically valuable investigation.
Empathetic action is important! Try to avoid strong and abrupt transducer
Note
pressure as well as fast movements. Sometimes also helpful to keep skin contact
with hand/nger that holds transducer.
2.7.1.4 Specific Needs inInfants andNewborns
• Higher room temperature, additional heating and swaddling facilities are
mandatory.
• Helpful to have some warm tea/formula and paciers ready at hand:
– Paciers can furthermore be enhanced by specic tastes such as fruit extracts.
Glucose drops particularly effective in rst months of life.
30
M. Riccabona
2.7.2 Positioning
• Abdominal US: usually lying supine, sometimes prone or lateral decubitus position is helpful. Some abdominal areas can also be investigated with baby lying in
arms of mother—e.g. urinary tract screening in anxious and excited infants, provided acceptable position for the investigator is granted, too.
• Urinary tract US: same as abdominal US standard; additional prone positioning
for examining kidneys from dorsal approach is advisable. Additional approach:
perineal US (see respective chapter).
• US of neonatal brain/transtemporal US: any position where head can be kept still
and stable with sufcient acoustic access for US probe; for posterior fossa investigation, transoccipital or transnuchal access in lateral decubitus position with
exed cervical spine is helpful (see respective chapter).
• US of neonatal spine and spinal canal: prone or lateral decubitus—try to avoid
hyperextended back to assure sufcient access to spinal canal (see respective
chapter).
• Echocardiography: usually supine position with slight lateral rotation; additional
pillows underneath back may be helpful. For suprasternal access, neck extension
with some support of shoulder and side turning of head is helpful—provided the
baby can tolerate positioning (see respective chapter).
• Hip US: standardised procedure with standardised positioning partially using
dedicated positioning devices; depends on technique applied (see respective
chapter).
• Small part and neck US: sometimes helpful to comfortably position targeted area
by help of supporting pillows and towels (see respective chapter).
Note In adults and bigger children, positioning manoeuvres or breath holding
and flexion or rotation is routinely used to optimise US window for proper
access to diagnostically relevant deeper regions. In children, particularly
infants and neonates, this is practically impossible, therefore “golden rule for
US in infants”: do not move child towards transducer trying to depict pathology, but try to move transducer to sonographic window that allows optimal
access to targeted areas.
If in older children positioning manoeuvres are attempted, try to use age- adequate
commands such as “show me your big belly” or “take a deep breath and hold it as if
you were diving”.
Nevertheless, positioning manoeuvres may become necessary and helpful also in
children for specic queries, e.g. differentiate if structure in papilla or in collecting
system, if mobile or xed to wall … (Fig.2.10).
• Remember also to have a comfortable examiner position for health reasons—
avoid degenerative disease/work related musculo-skeletal disorders.
2 US Methods, Artefacts, Biologic Eects, Practice
31
ab
Fig. 2.10 Lower pole calix of a kidney with some echogenicities (arrow): the scans in both prone
(a) and supine (b) position demonstrate that sludge is always staying in the dependent area and
thus is mobile within in collecting system, not adherent to/in papilla
2.7.3 Device Handling
2.7.3.1 General Remarks
Particularly in paediatric US, investigator must be accustomed with device and its
handling, as child motion and agitation as well as need for communication and
devoted emphasis would impair capabilities to struggle with equipment. Additionally,
experienced handling speeds up investigations allowing for better results and
focused concentration on child and image—without withdrawing attention towards
handling of device.
Therefore it is practical to import all data (such as patient name/numbers) and set
up machine (selecting transducers/presets) prior to positioning of child.
2.7.3.2 Choice ofDevice andTransducer
• Handling of different US equipment varies—large variability in requirements.
• A particularly helpful feature is cine loop—store video clips for retrospective review:
– Depending on device, varying number of images is constantly stored to hard
disc at any time during investigation. Allow for review of preceding parts of
investigation; video clip is constantly updated.
– Review of cine loop: single frames can be captured and stored; some machines
and picture archiving and communication systems (PACS) also allow storage
of clips.
– As children are often less cooperative, this feature is particularly helpful for
selecting optimal frames for measurements and documentation as well as
image analysis.
32
M. Riccabona
2.7.3.3 How toStart Investigation
Once machine is set up, select transducer and the respective preset, and position
patient:
• After positioning of transducer, adapt receive gain and TGC as well as focus,
frame, size and penetration. All these parameters need to be constantly updated
during investigation—as different body areas and positions request different
equipment settings.
Modern devices offer automated adaptation and optimisation algorithms (“magic
button”, etc.…), so they can speed up investigations, helpful for general overview.
Additional adaptation and variation of settings will still be necessary for certain queries, for detailed investigations or in certain body areas (such as behind urinary bladder). Particularly post-processing, sufciently fast frame rate and proper placement of
focal zone are essential—need to be changed and adapted constantly; this task cannot
always reliably be performed by automated image optimising programmes.
Once you have chosen an adequate preset, changes of preprocessing factors, etc.
become only necessary in rare cases:
• Presets usually selected by deciding on certain investigation category—optimised towards dedicated queries.
Note May become necessary to change presets during one examination, for exam-
ple, during abdominal US, you may need conventional abdominal, pelvic and intestinal or vascular presets.
2.7.4 Transducer Selection
2.7.4.1 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 sufcient penetration should be chosen (see also above—“types of
transducers”).
• Basic recommendations for transducer selections exist.
2.7.4.2 Neurosonography (See Chap. 8)
• Neonatal transfontanellar neurosonography: generally sector transducers from 5
to 15 MHz used; alternatively small curved linear arrays with the same frequency range.
2 US Methods, Artefacts, Biologic Eects, Practice
33
Note Transducers should not have small radius in order to avoid pressure on brain
surface.
• For evaluation of supercial structures (located close to brain surface such as
interhemispheric ssure and cortical areas) as well as skull and extra-axial
pathology: high-resolution linear transducers (5–18MHz) applied. Use sufcient US gel; sometimes stand-off pads helpful. With introduction of trapezoid
steering of linear transducers this in neonates becomes often the transducer of
choice, supplemented by sector transducer for more lateral/peripheral regions.
• Transtemporal US: sector transducers, frequencies vary with age from 10MHz
in preterms to 1MHz in adolescent patients.
• Spinal US: high-resolution linear transducers with broad frequency range
depending on age, ossication and patient; sometimes curved linear arrays as
well as sector/vector probes additionally used for specic queries in older
patients.
2.7.4.3 Small Part andMusculo-Skeletal US
(See Respective Chapters)
For most small part applications (neck, musculo-skeletal, etc.), high-resolution linear transducers (frequency range 3–18MHz) applied—depending on patient size
and targeted structure.
Sometimes at curved linear array and stand-off pads are helpful.
2.7.4.4 Chest US (See Chap. 12)
• For assessment of supercial structures (chest wall, pleura, breast, etc.), highresolution linear transducers are used.
• Deeper structures usually imaged by sector transducers with age and depth
adapted range of frequencies (1–10 MHz)—allow intercostal, transdiaphragmatic or jugular/suprasternal access.
• For transabdominal access (for basal structures) or diaphragmatic US, abdominal curved linear array probes are very helpful.
• Echocardiography: mainly performed with sector or vector transducers; in neonates linear transducers can be used. Transoesophageal transducers allow
visualisation of areas difcult to access transthoracically, usually used in older
patients. Frequencies vary depending on age, but additionally proper Doppler
ranges are important; frequencies used for Doppler investigations tend to be
lower than for anatomic imaging (10–1MHz).
2.7.4.5 Abdominal US (See Respective Chapters)
• Basically curved linear arrays are used, increasingly also linear transducers in
trapezoid mode, particularly in infancy. Sometimes sector transducers are helpful for areas with small US window. For assessment of supercial structures,
linear transducers are mandatory. Frequencies vary with patient age and size
(2–15MHz).