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INTERVENTIONAL AND OTHER TECHNIQUES 255
Methods of ultrasound guidance
There are various ways of performing ultrasoundguided
procedures: organ/lesion localization
(‘blind biopsy’), biopsy guide or freehand technique.
The choice of method depends upon the
procedure in question, equipment and the experience
and skill of the operator.
Blind biopsy
With this method a position on the skin surface is
marked overlying the organ or lesion to be biopsied,
using ultrasound to localize. This remains acceptable
for diffuse disease, when only a representative
sample of liver tissue is required. Nevertheless, it is
good practice even in these situations to visualize
the needle during the procedure, and this method
of biopsy is now used less frequently.
Biopsy guidance
Most manufacturers provide a biopsy guide which
fits snugly on to the transducer head and provides
a rigid pathway for the needle (Fig. 11.1). These
are now the commonest and preferred method of
biopsy. Previously adjustable angle biopsy guides
were available; however these offered no specific
advantages and were prone to user error. The fixed
biopsy guides contain a groove for a series of plastic
inserts ranging from 14G to 22G size, depending
on the size of the biopsy needle. It is often preferred
to use one size greater than the needle, that
is a 16G insert for an 18G needle, as the needle
tends to move more freely. These guides are sterilized
and fitted on to the transducer, which can
either be covered by a sterile sheath or thoroughly
cleaned with chlorhexidine solution. The use of a
sheath is highly recommended, as it maintains the
sterility of the procedure, reducing the risk of
infection, with no adverse effect on the image.
The needle pathway is displayed on the ultrasound
monitor electronically as a line or narrow
sector, through which the needle passes. The operator
then scans in order to align the electronic
pathway along the chosen route, the needle is
inserted and the biopsy taken. These attachments
should be tested regularly to ensure the needle follows
the correct path (Fig. 11.2).
Freehand
A freehand approach, in which the operator scans
with one hand and introduces the needle near to
the transducer with the other, may be used for
larger or more superficial lesions. This technique is
commonly used for breast biopsy and biopsy in the
head and neck. The needle is inserted from one
end of the probe at right angles to the ultrasound
beam; generally speaking the angle utilized is shallow
in comparison with the fixed guide systems for
deeper structures.
d
C
a
b
A
B
Figure 11.1 (A) Necessary component parts to perform an ultrasound-guided biopsy procedure. A series of plastic
inserts (A) range in size from 14 to 22G. The appropriate insert is inserted into a fixed biopsy guide (B). The procedure
is performed with sterile jelly (C) and a sterile probe cover (D) if required. (B) The assembled biopsy guide.