Diagnostic ultrasound ( PDFDrive )

CHAPTER 56 Pediatric Interventional Sonography 1945
collections can be drained this way, the necessary skills for
accurate needle placement in small organs or near critical
structures will never be learned. A single practitioner using an
ultrasound transducer in one hand and the access needle or
other device in the other hand is far superior to the “where’s my
needle now?”–type verbal communication required when there
are two operators.
Freehand Versus Mechanical Guides
Most ultrasound equipment manufacturers supply well-designed
mechanical guides that attach to a transducer and allow a predictable
needle path to be visualized. hese guides are useful for
keeping the needle in the plane of the ultrasound beam and can
be used for lesions with a simple approach path or a wide access
window. Most devices require a disposable sterile kit when the
device is used, adding to the cost of the procedure. Special needle
guides are useful for the initial puncture for transrectal abscess
drainage, 3 although many practitioners use simple freehand
ultrasound guidance imaging of the rectal puncture needle using
an anterior view through the illed bladder.
Freehand guidance is more diicult to learn but allows much
more lexibility of approach. When the needle can be positioned
45 to 90 degrees to the beam, even ine, 30-gauge needles are
easily visible. Freehand guidance allows the operator to choose
the most advantageous transducer geometry and to steer the
needle or biopsy device around other structures on the way to
the lesion. Accurate placement of local anesthetic on the peritoneum,
pleura, and other sensitive structures is made easier by
freehand technique.
Color Doppler Ultrasound
Color Doppler has been advocated for visualization of the moving
needle during interventional procedures, but our experience has
been that the potential for better visualization of the needle tip
is outweighed by the degradation of the gray-scale image and
lash artifacts when color Doppler is active. Various needle
tracking devices are available to enhance the visualization of the
needle, but with the exception of the Yueh (Cook, Bloomington,
IN) and Skater (InterV, Stenlose, Denmark) type sheathed access
devices, which have very small holes in the catheter tip, these
devices all add complexity and expense and are generally unnecessary
if accurate ultrasound technique is learned.
FREEHAND TECHNIQUE
Freehand technique requires that the transducer be held in one
hand and the needle or biopsy device in the other. he interventional
physician needs to be able to use either hand as the
needle or operating hand. For example, a biopsy specimen of
the liver might be obtained by placing the transducer on the
anterior abdominal wall using the right hand and making the
needle approach from the patient’s right lateral position, parallel
to the table, using the let hand. A let-sided biopsy would best
be performed by using the let hand for the transducer and the
right hand for the needle approach from the let lank. With
some practice and some simple rules, it is not diicult to use
the nondominant hand as the needle hand.
Initial Needle Placement and Localization
he most important technique to learn in freehand sonography
is needle localization. hese rules work equally well for a needle
entry site near the transducer or one at a distance (Fig. 56.2).
he entry point is chosen ater careful consideration of the
anatomy and important structures such as ribs, large vessels,
diaphragm, and bowel. Indentation of the entry site using a inger
to compress the skin (Fig. 56.3) allows the exact entry site to be
assessed. Once the entry site is chosen, a last check can be made
by placing the transducer exactly over the marked entry point
for a “needle’s-eye view” to ensure that there will be no surprises
such as the internal mammary artery during mediastinal biopsy
or inferior epigastric artery during paracentesis or abdominal
abscess drainage, which may be overlooked unless speciically
localized. Once the entry path has been chosen and ater proper
application of local anesthetic, the needle or biopsy device is
2
1
A
B
FIG. 56.2 Common Approaches. (A) The most common entry sites are either (1) lateral (parallel to the transducer face) or (2) adjacent to the
transducer. (B) When the needle is parallel to the transducer face, a prominent reverberation artifact is seen, or a “comet-tail” artifact is seen
when the needle is not parallel. The needle can be more dificult to locate in position 2.