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7 Measurements and Volume Calculations: Basic Considerations, Graphs…
107
abc
Fig. 7.3 (a–c)Ventricular size measurements in pediatric neurosonography (a) Standard diameter
measurements of lateral (1, 2) and third (3) ventricle diameter at level of the foramen of Monro in
coronal section; sometimes area (4) and circumference used (....)—more sensitive towards subtle
changes. (b) Standard depth measurements of third (1) and fourth (2) ventricle in sagittal midline
section. (c) Measurement of parenchymal width, particularly important in hydrocephalus:
Parasagittal schematic section showing measurement of ventricular distance (↔1) and occipital
parenchymal width (↔2)
7.3 Artifacts andOther Aspects that May
Impact Measurements
Some artifacts may cause confusion andimpair proper measurements (see Chap. 2
& respective images).
• Bowing artifact.
• Mirroring.
• Refraction artifact.
• Side loop artifact.
Need to be recognised and addressed/corrected before taking measurements. If
measurement points cannot clearly be dened—measurements should be avoided,
or understood and declared as only orienting size information (Fig.7.4a).
7.3.1 Miscellaneous Other Considerations
Some basic physical phenomena have to be considered when taking measurements—may have serious impact on results particularly when measuring tiny distances or cross sections.
Examples for possible errors:
• Errors may occur from tilting transducers as mentioned above with hip US
according to the Graf method (see Fig. 16.7) or, e.g. when measuring crosssectional area of vessels as used for ow volume estimates (Fig.7.5).
108
M. Riccabona
a
c
b
c
d
d
e
Fig. 7.4 Illustration of potential measurement errors by not using appropriate sections. (a) Liver
length—the upper and lower borders are not seen, therefore no reliable measurement is possible.
Also note another artifact: some mirroring in the lower left corner by the echogenic diaphragm/
lung surface. (b, c, and d) different renal length (nearly 1cm!) depending on acquired section
shown in two images (c too short, d correct) and the correlating schematic drawing based on a renal
3DUS based volumetry (b) illustrating the source of error. (e) Bladder measurements need to be
taken orthogonally to respective other section to avoid errors—by tilted orientation not only bladder shape appears different, but also bladder volume/capacity calculations become biased
• Measurements and size may be affected by lling status, hydration, or function—e.g. the pyloric muscle can be contracted in pylorospasm mimicking thickening in hypertrophic pyloric stenosis, a renal collecting system may be collapsed
in poor hydration or with an empty bladder, and structures may be compressed
by transducer pressure (e.g., not visible jugular vein, appendix & bowel loops …).
a b
ce
7 Measurements and Volume Calculations: Basic Considerations, Graphs…
109
Note A measurement within itself without considering all other aspects (age, ll-
ing, clinical symptoms …) does not constitute or “rule out” a diagnosis, e.g. lymph
nodes may be pathologic even if they do not reach the usually given cut of values,
whereas even large and spherical lymph nodes do not necessarily indicate
malignancy.
• Measurements may vary depending on resolution and transducer and device
setting (curved versus linear for hip US, harmonic versus fundamental imaging with or without compounding for particularly small distances as, for
example, vessel wall/intima media thickness assessment, focus position,
depth …). This may additionally differ with equipment and manufacturer. For
example—with 7MHz spatial resolution is around 0.22 mm (measurement
accuracy even lower), with 14MHz the spatial resolution is 0.11mm; thus, all
measurements less than 0.2 or 0.1mm, respectively, are not real physical measurements. According to a phantom study by Wunsch (done on GE Logic
series) the best resolution was achieved with Speckle Reduction Imaging/
d
c
d
Fig. 7.5 Illustration of potential measurement errors by tilting transducers or inadequate sections.
(a) Schematic drawing illustrating source of error. (b–d) Respective images from an abdominal
aorta, where the error becomes most obvious in the axial sections (c, d) as indicated in the longitudinal image (b); furthermore the inuence of magnication and different device settings (with/
without harmonic imaging and compounding becomes obvious. (e) Same section as in gure b) but
acquired during diastole—note the signicant difference in diameter, with about 25% variation!
110
ab
M. Riccabona
*
Fig. 7.6 Impact of magnication on accurateness of measurements, particularly but not only
important for tiny structures. (a) Length measurement of a duplex kidney with pus in the upper
moiety collecting system (*). (b) Enlarged view of same image showing the large error in placing
the cursor, with upper pole border (indicated by arrow) being shorter than indicated in the
measurement
noise lters and fundamental imaging, followed by crossbeam/(directional)
compounding techniques. Harmonic imaging may be more inaccurate for
measurements of very small structures.
Note Zooming may signicantly impact accuracy of measurement point denition,
particularly important for measurement of small structures (Fig.7.6). Devices may
show numbers that are below physical resolution of transducer at respective driving
frequency.
• When assessing uids not contained in a nicely and geometrically shaped compartment that is only partially accessible by US such as pleural effusions or peritoneal uid, consider that uid is redistributed depending on patient position—thus
an accurate estimation of pleural and peritoneal uid is difcult, cumbersome
and may even be misleading or wrong. Small amounts of pelvic uid can be
missed if the bladder is empty and the US access is hindered by gaseous bowel.
Tip To reduce errors, consider using a constant, same and standardized patient
position (and bladder lling) for follow-up (e.g., sitting upright for pleural effusion).
Part III
US Investigations of the Various Organs
Neurosonography inNeonates,
Infants andChildren
MichaelRiccabona
8.1 Requisites
8.1.1 Equipment andTransducer Needs
Any system operating high-resolution sector, vector, micro-curved and linear transducers, plus CDS capabilities.
Transfontanellar Access
• Basic US scan performed using sector (vector) or micro-curved transducers, frequency of 10–5MHz in neonates, 5–2MHz in older infants—until the fontanel
is closed.
• Linear transducers with trapezoid/virtual convex mode operating at midfrequency range (4–12MHz) increasingly used as basic Tdx, not only for detailed
surface analysis (Fig.8.1).
8
Note If micro-curved array used, curvature should not be too narrow to avoid com-
pression of intracranial structures, particularly the brain surface and superior sagittal sinus.
• High-resolution linear transducers for detailed study of brain surface using
high frequencies (10–17MHz)+high-resolution imaging modes.
M. Riccabona (*)
Department of Radiology, Division of Pediatric Radiology, Medical University Graz
and University Hospital Graz, Graz, Austria
e-mail: michael.riccabona@medunigraz.at
© Springer Nature Switzerland AG 2020
M. Riccabona (ed.), Pediatric Ultrasound,
https://doi.org/10.1007/978-3-030-47910-7_8
113
114
Fig. 8.1 Trapezoid view using high-resolution linear transducer for transfontanellar brain
US.Normal neonatal brain US in a coronal section through foramen of Monro (a) and sagittal section in midline (b)
M. Riccabona
Transtemporal Access
• Transtemporal, transmastoid or other accesses such as occipital fontanel should
be used in neonates for detailed assessment of certain brain areas.
• In older children only transtemporal access with sector (vector) transducers (frequency 5–1MHz) applicable.
8.1.2 Indications forBrain US
(Typical standard) Indications in Neonates and Young Infants
• Asphyxia and birth trauma, prematurity (screening, i.e. third and seventh day).
• Macro- or hydrocephalus and (fetally) suspected cerebral malformations.
• Suspicion of brain haemorrhage.
• Clinical neurologic symptoms.
• Disease potentially associated with cerebral manifestations (e.g. septicaemia
with brain abscess, tuberous sclerosis and other syndromic disease), meningeal
empyema, meningoencephalitis, etc.
• Some centres perform screening neonatal brain US.
• US may play a role in suspected inicted/non-accidental (NAI).
Indications in Older Children
• Hydrocephalus, also after shunting—using transtemporal access.
• Suspected cerebral perfusion alteration, such as with cardiac malformations,
after hypoxia or drowning, sickle cell disease, monitoring during surgery or
ECMO, etc.
8 Neurosonography inNeonates, Infants andChildren
115
• Cerebral perfusion can be monitored at bedside in ICU for optimising ventilation
(“individual optimal PCO2”).
• Assessment of (post-)haemorrhagic or tumourous midline shift, large vascular
malformations or brain death.
8.1.3 How toInvestigate
Positioning Child in stable position—supine or lateral decubitus.
Note Avoid pressure of transducer on fontanel.
Transfontanellar Access
• Assessment of entire visible brain in serial coronal and (para-)sagittal sections
(Fig.8.2). A sweep documented by a video-clip often helpful for retrospective
reassessment and comparison during follow-up.
Fig. 8.2 Transfontanellar US—typical sections+ respective images that should be documented.
Standard sections in scheme with corresponding respective images of normal US appearance. (a)
sagittal midline, (b) parasagittal, (c) anterior coronal, (d) median coronal and (e) occipital coronal
116
M. Riccabona
• Documentation of anterior, middle and posterior fossa as well as midline structures and lateral ventricles. Important features that need to be documented: corpus callosum, ventricles including foramina of Monro with measurements if
enlarged, temporal and occipital horn of lateral ventricles, basal ganglia, peripheral parenchyma and interhemispheric ssure.
• In case of trauma or palpable bumps—assess calvarium using high-resolution
linear transducers.
• For special queries—add transmastoid, transtemporal or transoccipital access
(e.g. visualisation of aqueduct, posterior horn, posterior fossa structures and cerebellum particularly in preterms, medulla oblongata), basal vessels.
• CDS: basal (and some more peripheral) vessels, compare ow between left and
right hemisphere.
Note Use same routine for every investigation in order not to miss anything—sys-
tematic consistent approach.
Transtemporal, Transcranial, Mastoid Access, etc.
• Every less ossied part of the calvarium can be used, also osseous defects such
as after surgery. Particularly the mastoid view frequently used to assess posterior
fossa structures or to posterior horns (Fig.8.3).
• Axial and transverse sections acquired by rotating transducer.
• Coronal and oblique sections obtainable as needed.
Note Has become a standard in neonatal brain US—not just in exceptional
queries.
Fig. 8.3 Mastoid view of
posterior fossa; cerebellum
with both hemispheres and
brain stemm/crura cerebri
nicely displayed
a
b
c
8 Neurosonography inNeonates, Infants andChildren
117
Morphometry and Documentation
• Standardised image orientation:
– Left side of US image = frontal (sagittal/axial view) and right patient side
(coronal view).
– Always use proper labelling or pictograms.
• Standardised measurement of ventricular diameter and size, particularly if
enlarged (Fig.8.4). See also chapter measurements and respective gures.
• Width of extra-axial CSF space: interhemispheric ssure, subfontanellar space, frontotemporal space (e.g. arachnoid cyst) and sylvian ssure—see also hydrocephalus.
• Width of brain parenchyma (anterior, occipital, temporopolar) (Fig.8.4c–d).
• Size of the cerebellum (Fig.8.5, Table8.1).
• Minimum documentation includes the following:
– Three to four coronal views (anterior, foramen of Monro, posterior horn, peri-
ventricular posterior parenchyma).
– Three to ve sagittal views (midline, left and right parasagittal through lateral
ventricles, periventricular parenchyma on both sides particularly in
preterm babies).
d e
Fig. 8.4 Measurements on brain US. (a) Coronal section, hydrocephalus: ventricle measurements—
diameters, circumference and area. (b) Coronal section, linear transducer, near led view: extra-axial
CSF size and interhemispheric ssure distance measurements (↔). (c) US image in parasagittal section:
hydrocephalus with severely narrowed frontal and occipital parenchyma (+1, +2). (d) Coronal section:
parenchyma (↔) to ventricle ratio can be calculated, useful for follow-up incorporating physiological
growth with stable relations in spite of increasing values. (e) Normal values for ventricular size (mm,
circumference of lateral ventricle at level of foramen of Monro) related to head circumference (cm)