Diagnostic ultrasound ( PDFDrive )

1592 PART V Pediatric Sonography
include the need for intensive training, diiculty in inding speciic
vessels by sound, and lack of unit availability in radiology departments.
Duplex Doppler sonography with color imaging using
low MHz transducers via the temporal bone has increased the
utility of TCD sonography. Advantages of TCDI include rapid
vessel identiication, a shorter learning curve, and availability of
units in radiology departments. his imaging technique allows
more conident vessel identiication, resulting in easier, more
reliable, and reproducible information. 8-11 However, with training
and experience, both techniques have been shown to be reliable
and reproducible. 12,13
SONOGRAPHIC TECHNIQUE
he anterior fontanelle typically remains open through the irst
year of life. Once closed, three cranial windows (in addition to
burr holes and surgical defects) can be used routinely to insonate
the intracranial circulation: the transtemporal window, orbital
window, and the suboccipital window. he submandibular
window can also be used to complete the examination of the
cervical segment of the internal carotid artery (ICA). 14
he transtemporal approach is through the thin suprazygomatic
portion of the temporal bone using a low MHz (2- to 2.5-MHz)
transducer. he transtemporal acoustic window is usually found
on the temporal bone just cephalad to the zygomatic arch and
anterior to the ear. he intracranial anatomic landmark in this
plane by gray-scale imaging is the heart-shaped cerebral
peduncles (Fig. 47.1A). Just anterior to the peduncles is the
star-shaped, echogenic interpeduncular or suprasellar cistern.
Anteriorly and laterally from this basilar cistern lies the echogenic
issure for the middle cerebral artery (MCA). Color Doppler
sonographic imaging (Fig. 47.1B, Video 47.1) and spectral analysis
(Figs. 47.1C and 47.2A, Video 47.2) of this vessel show low
toward the transducer. Insonating the vessel deeper toward the
midline directs the operator into the bifurcation of the A1 segment
of the anterior cerebral artery (ACA) and the MCA (Video
47.3). Spectral analysis at this bifurcation landmark will show
bidirectional low, that is, low toward the transducer in the
MCA and low in the ACA away from the transducer (Fig. 47.2B).
As the Doppler gate is moved more medial anteriorly, low is
seen entirely in the ACA away from the transducer (Fig. 47.2C).
he MCA should be studied from its most peripheral location
to the point of bifurcation, and the ACA studied as medially as
possible. he distal internal carotid artery (DICA) is just inferior
to the bifurcation. he low of the DICA may be dampened with
a harsher sound from the increased angle of insonation, with
low typically directed toward the transducer (Fig. 47.2D). he
posterior cerebral artery (PCA) can be visualized as it circles
around the cerebral peduncles. Flow in this vessel may be away
or toward the transducer depending on curser placement (Fig.
47.2E). At times, the MCA, the ACA, and the PCA on the opposite
side may also be visualized. Ideally, each side should be studied
through the ipsilateral window whenever possible.
he vertebral and basilar arteries can be studied through the
suboccipital window via the foramen magnum with a low MHz
transducer. he patient lies on one side or prone, and the head
is bowed slightly so the chin touches the chest, causing a gap
between the cranium and the atlas to enlarge. he transducer is
placed midline in the nape of the neck and angled through the
foramen magnum toward the orbits. he normal landmark is
the rounded hypoechoic medulla just anterior to the echogenic
clivus (Fig. 47.3A). he vertebral arteries appear in a V-shaped
manner as they rise to the medullopontine junction to form the
basilar artery between the hypoechoic medulla-pons junction
and the echogenic clivus (Fig. 47.3B). From this posterior view,
low in the vertebral and basilar arteries should be directed away
from the transducer (Fig. 47.3C).
he transorbital window allows for evaluation of the ophthalmic
artery (OA), the retinal artery, and the carotid siphon.
his evaluation is performed with the eyes closed using a higher
MHz (5- to 7.5-MHz) transducer on its lowest power setting
(Fig. 47.4). Unlike the temporal approach in which the bone
attenuates a majority of sound thus requiring a low MHz transducer,
the luid-illed globe only minimally attenuates the sound
waves. Although no bioefects from the ultrasound evaluation
of the eye are known, ocular damage can potentially occur as
ultrasound energy can create cavitation and heat. he U.S. Food
and Drug Administration (FDA) guidelines suggest limiting
spatial peak temporal average to 17 mW/cm 2 for orbital imaging
and limit the mechanical index to 0.28. 15,16 he time of insonation
must also be as minimal as possible to decrease risk of damage
to sot tissues. 17 he FDA has approved certain imaging transducers
on various manufacturer equipment for the evaluation of
the orbit. It is important for operators to determine which
transducer is approved for orbital imaging for their system.
A liberal amount of gel is needed on the eyelid with only light
pressure utilized on the globe. he orientation marker should
be pointed medially toward the nose. Flow in the OA should
be toward the transducer. he OA enters the optic foramen
and lies lateral and slightly inferior to the optic nerve. It then
usually crosses superior to the optic nerve and proceeds anteriorly
on the medial side of the orbit. he color pulse repetition
frequency should be decreased to visualize the OA. he mean
velocity of the OA is 21 + 5 cm/sec with high pulsatility. 18 he
central retinal artery branch of the OA is the easiest branch to
interrogate with color low Doppler imaging, just posterior to
the retina. Because visualization of this central retinal artery
entails directing sound waves through the lens, the lowest power
setting must be used to minimize the risk of lens injury and
subluxation. However, a large OA branch proceeds along the
nasal or medial wall of the orbit. Because interrogating this
vessel does not involve directing the sound beam through the
lens, a higher power setting may be used for this branch. In the
carotid siphon, low direction varies depending on the segment:
toward the probe in the infraclinoid segment, bidirectional in the
genu, and away from the probe in the supraclinoid segment. he
mean velocity of the carotid siphon is 47 + 14 cm/sec with a low
resistance signal. 18
he submandibular window, located at the angle of the jaw,
allows for examination of the extracranial ICA, including
morphology, low direction, and velocities. Once the vessels have
been identiied, diferent information can be obtained through
evaluation of the spectral waveform. Flow direction is one of
the irst parameters obtained with evaluations (by convention,