The tool that the scientists are about to test is known as a bronchoscope, a pencil-thin flexible tube that is fed down the airways and into the bronchi. Photo: Thor Nielsen/SINTEF
The innumerable divisions of the bronchi often turn the hunt for tumours in the lungs into a game of chance. But soon, lung specialists will be able to navigate accurately inside the airways by “GPS”.
May 2013: in a bronchoscopy suite at St. Olav’s Hospital in
Trondheim, a team of physicians and engineers is in deep discussion with
a researcher. The next patient is currently at the focus of their
efforts to develop a life-saving technology. He has a tumour in his left
lung, and the main challenge is to find out whether it is benign or
malignant, precise and quick, at low cost for the patient.
3D navigation
While the patient is prepared with local anaesthetic for the bronchoscopy, the physicians discuss a set of CAT scans that were taken earlier. These are now going to be linked with a completely new diagnostic tool that enables the medical team to locate the tumour with much higher precision than before. The new technique has potential to increase the possibility of a more accurate and rapid diagnosis, and thereby offer the patient appropriate treatment as early as possible.
“Lungs are extremely complex organs. We can compare the bronchi to a
tree that divides into branches innumerable times. First the trachea
itself divides in two in the uppermost part of the chest, then the two
main bronchi continue dividing dichotomously – no fewer than 23 times on
each side,” explains Håkon Olav Leira, a physician who has recently
taken his doctorate degree on image-guided bronchoscopy.
This complexity makes it almost impossible to find an easy way
through the airways to the site where the medics wish to take their
samples. Today, the success rate is between 5 and 30 per cent in cases
where the doctors cannot see the tumour, bronchoscopically invisible
tumours. Nevertheless, they need to enter the bronchi and take a biopsy.
But now, a navigation system developed by SINTEF researchers and
engineers and pulmonologists at St. Olav’s Hospital provides the latter
with three-dimensional images of the route into the patient’s lungs and
airways, in which the examination will take place. If everything goes
according to plan, they will soon be able to localize the tumour within a
few millimetres range, with the help of the research scientist Erlend
Fagertun Hofstad, the engineer who is co-piloting the navigation at the
computer screen.
Camera, map and compass
The tool that the scientists are about to test is known as a
bronchoscope, a pencil-thin flexible tube that is fed down the airways
and into the bronchi. It is equipped with a camera and a little forceps
that enables it to take tissue samples. However, what makes this
bronchoscope special is that it is also fitted with a position sensor at
the tool-tip, which means that the physicians can always identify the
location of the bronchoscope tip in the tissue and bronchi. At the same
time, the screen shows them a three-dimensional pre-recorded image of
the total “lungscape”, so that they always know exactly where they are.
“The challenge lies in getting the system to realize that the
pictures that the bronchoscope is taking inside the patient, and the CAT
images that were taken earlier, refer to one and the same thing. The
two sets of images have to fit together like a hand in glove to give us
the accuracy that we require. And this has to be done fast. Since the
patient is under local anaesthetic but still awake, we have only a
certain amount of time to carry out this task,” says Erlend Hofstad.
One of the things that makes this a difficult task is the fact that
the lungs are constantly moving through the respiratory cycle; the
movements caused by the patient breathing in and out, and those of the
bronchoscope itself, mean that the tissue is changing shape and location
during the examination. This means that the equipment not only has to
take pictures under way but also has to relate these to the CAT images
that have already been made. Map and terrain have to match continuously.
Fumbling in the dark
In the examination room the temperature is rising. The patient
coughs, and the images on the monitor show that he has started to bleed
far down in his windpipe.
“Patients who are taking anticoagulants can be difficult to examine,
because they bleed more easily than other patients,” explains Håkon Olav
Leira, adding that this demonstrates another of the challenges that the
medical team often faces; the bronchoscope images are blurred because
blood is obscuring the camera lenses.
“In such situations, it is a huge advantage that we can manoeuvre according to what the position sensor and the 3D map that we have developed in collaboration with the SINTEF researcher tell us. Otherwise, we would just be fumbling in the dark.”
Then the bleeding stops by itself. Once again, everything is under
control, and the bronchoscoper soon finds the route through the
patient’s bronchi, aided by a steady hand and the images on the screen.
It will soon be time to take samples of the 3 cm invisible tumour hidden
in the patient’s left lung.
Algorithm
The equipment that is showing the way into the patient’s inner organs
also includes a set of advanced mathematical models that have been
developed by engineers at SINTEF’s Department of Medical Technology. In
practice, the GPS system operates in such a way that the CAT scan is
first adapted to the patient, via a registration procedure in which the
computer is told that the CAT images of the internal organs must match
those of the actual physical patient. The position sensor then registers
the movements and position of the sensor that sits at the tip of the
bronchoscope.
The system can then show where the bronchoscope is located on the CAT
images. The sensor is less than 1 mm in diameter, and a weak magnetic
field that envelopes the patient registers the location of the sensor in
three dimensions in real time. Both its direction and position inside
the patient are displayed on a screen, so that the doctor always knows
where the equipment is.
The scientists are able to localize the tumour within a few millimetres range. Photo: Thor Nielsen/SINTEF
Successful test
A good hour later, the team has finalized bronchoscopy with different samplings. At her fourth attempt, the bioengineer has managed to get the samples she needs. The team leader is pleased with the efforts of the medics and the scientists:
“That was a good job, well done,” he says to the group at the
controls of the equipment, before he thanks the patient for his
contribution. Bronchoscopy is a painless, but not exactly pleasant
procedure. Willing patients are essential if the scientists are to be
able to implement their ideas, and after his efforts, the patient needs
some rest.
Fact box:
The new navigated bronchoscopy proceduree has been developed at
SINTEF’s Department of Medical Technology, in collaboration with St.
Olav’s Hospital, Departments of Pulmonary Medicine and Medical
Technology. The research team has been collaborating closely with the
St. Olav’s Hospital doctors for several years and the partnership has
resulted in a number of medical innovations in the field of image-guided
diagnostics and therapy. Their solutions offer doctors
three-dimensional images of the body’s internal organs while they are
operating or performing examinations. For the most part, the techniques
utilise ultrasound in combination with CAT images, but magnetic
resonance (MR) spectroscopy is another important source of imagery for
the three-dimensional “maps”.
Source: SINTEF