Imaging techniques are being used during narcosis in
a process called ‘ultrasound-guided regional
anaesthesia’, during which a greater part of the
patient’s body is anaesthetised prior to an
operation. This involves a doctor injecting the
anaesthetic directly around the key nerves in
question.
Locating and tracing: A cross-section of the anatomy
of the groin, and identification of the so-called
anatomical landmarks. The ultrasound image: The
assistant tags the key anatomical landmarks within
the body. Same section as in the figure.
Illustration: Helene E. Mørk.
Ultrasound-guided regional anaesthesia is a
preferred approach in many cases because it can
spare the patient unnecessary narcosis, and ensures
that the anaesthetic is applied correctly and the
subsequent operation carried out with the least
possible pain and discomfort to the patient. If this
also results in shorter hospital stays, then society
as a whole also benefits.
However, the technique requires a high degree of
accuracy. For this reason, researchers at SINTEF are
currently developing software that can assist
doctors in interpreting ultrasound images in real
time with the help of 3D images – in this case
involving regional anaesthesia of the main nerve
running through the thigh. The aim here is to
achieve precision within a few millimetres of the
target.
SINTEF researcher Frank Lindseth emphasises that
this tool is intended to act as an assistant and a
guide during the ultrasound-guided insertion of the
needle. It is not a robot.
In order to understand ultrasound images, they must
be closely examined and interpreted, and this is a
very demanding task requiring detailed knowledge and
experience. And it doesn’t suit everyone. Many
doctors attempt to learn the procedure, but never
get as far as performing an injection because they
encounter major problems in interpreting the
ultrasound images. Moreover, interpretations vary
even among experts, in spite of their many years of
experience.
Thus the work that Lindseth and his team have
carried out has included generating a reference
model describing how images of the human body should
be interpreted based on the somewhat cryptic
ultrasound images. This has been carried out in
close collaboration with doctors at St. Olav’s
University Hospital in Trondheim.
Kai F. Johansen is a Senior Consultant at the
Orthopaedic Unit at St. Olav’s and has been a key
figure in the development of the SINTEF software. He
will soon be testing the assistant at the hospital.
His work has involved locating and tracing the
body’s so-called ‘anatomical landmarks’ – that is to
say key structures within the body as displayed on
the ultrasound images during anaesthesia.
“The challenge doctors face when interpreting
ultrasound images is finding what they’re looking
for”, says Lindseth. “Their task is to navigate on
the basis of known anatomical landmarks within the
body – in this case to locate the right nerve so
that they can accurately position the needle. This
applies both to anaesthesia and pain relief
procedures. Our findings show that even among the
experts there is a great deal of variation when it
comes to interpreting the ultrasound images and
accurately locating structures within the body”, he
says.
“The assistant will be very useful for training
doctors in the interpretation of ultrasound images”,
he says. “Anatomical landmarks such as blood vessels
and membranes are key aids in identifying
ultrasound-guided nerve blocks. If you can spot
these on the ultrasound images, it becomes easier to
localise the nerve that has to be anaesthetised”,
explains Johansen.
“One particular challenge has been the variation in
the interpretations made by experts”, he says. “This
makes it more difficult to establish a reference
model to which the assistant can attempt to find
matches. This also says something about the level of
difficulty involved in developing a robust, entirely
automatic and real time system”, adds Lindseth.
By using the reference model as a template, the team
has developed a software programme that will be
installed in ultrasound machines to act as a guide
and assistant during the use of ultrasound on
patients. A sensor in the ultrasound probe
communicates its position using the programme, which
then displays 3D images of key anatomical landmarks,
and subsequently interprets what it is being
revealed by the ultrasound signals. Furthermore, it
will be possible to follow the progress of the
needle to precisely the location where the injection
is required.
The entire process is complicated by the fact that
humans refuse to be standardised. We are all
different, and some of us are more different than
others. “There can be enormous anatomical
differences from patient to patient”, says Lindseth.
“So it isn’t difficult to imagine that this is a
challenging project”, he says.
“Sooner or later, the need for this type of
assistant will begin to increase”, explains Lindseth.
“Knowledge and experience linked to the
interpretation of ultrasound images will be in
ever-greater demand once ultrasound is applied in an
increasing number of new procedures. Our task is to
develop this into a user-friendly tool”, he says.
There are many different regional anaesthesia
procedures, and all of them require an ultrasound
assistant. If SINTEF’s system is well received, the
development of assistants for the remaining
procedures will also become a hot topic.
Early next year, the programme will be the subject
of clinical tests carried out by experts in the
Netherlands, Ireland and Germany.
For more information
SINTEF
MDN |