Biomed Imaging Interv J 2007; 3(1):e7
© 2007 Biomedical Imaging and
Image-guided surgery and therapy
TZ Aziz, MBBS,
FRCS(SN), MD, D.Med.Sci
Oxford Functional Neurosurgery, Nuffield Department of
Surgery, University of Oxford, United Kingdom
I am pleased to see the publication of this very novel
issue. It brings together in one volume the role modern imaging has to play in
surgery and radiotherapy. Certainly in functional neurosurgery imaging has
transformed the way it is performed.
In its first blossoming in the 1950s, patients were fixed in
a stereotactic frame, contrast was injected into the ventricles and x-rays were
taken of the patient's head in the frame from AP and lateral projections. One
then had to make corrections for the degree of magnification and divergence of
the x-ray beam. Following this, the anterior and posterior commissure were
identified on the ventriculogram and the mid-commissural point and its
co-ordinates calculated. Having done so, the surgeon referred to an atlas based
upon cadaveric studies to calculate the position in the frame with the highest
probability of hitting the target. In those days, the motor thalamus or
pallidum was identified for Parkinson's disease and tremor . Morbidity after
contrast ventriculography was not unusual .
Although surgery was effective in abolishing tremor, there
were many side effects as the lesions were imprecise by nature. Alleviation of
pain with deep brain surgery had even more side effects as the targets, the
peri-acqueductal gray area and sensory thalamus, lay in pathways that were also
involved in emotion .
Deep brain stimulation though studied in the 1950s was never
used long term because of technical limitations. Also, with plain x-rays and
ventriculography it was never precise where the electrodes were placed .
Ventriculography was also poorly tolerated because it was associated with
headaches and nausea.
The introduction of computed tomography (CT) scanning came
about at a time when functional neurosurgery had all but stopped. However, for
the first time surgeons were able to visualise tumours and the frame emerged
again as a useful tool for biopsying tumours, which was in fact the first form
of image-guided neurosurgery . It was also used for stereotactic
craniotomies. However, CT scans could not visualise deep brain structures apart
from the AC and PC. Therefore in performing functional neurosurgery, CT
scanning eliminated the need for contrast ventriculography which made such surgery
far more tolerable . It also meant that the accuracy of localisation was no
better than CT scanning either.
With better understanding of the physiology of movement
disorders and pain, new and old targets became far more relevant for disease
alleviation. Accurate placement of lesions and electrodes became paramount.
Modern magnetic resonance imaging (MRI) scans were able to visualise target
areas clearly in the brain so probabilistic atlases were no longer vital and
distortions of the MRI space could be corrected by various methodologies. This
made localisation more accurate and to a large degree made prolonged sessions
of micro-electrode recordings unnecessary .
The article by Widman eloquently describes the development
of image-guided surgery from a point target frame based method to the
volumetric techniques that are in common use today. This development of
radiological images used interactively in 3D space has transformed modern
neurosurgery and made procedures safer and quicker . The use of such
technology to guide tools like the operating microscope and actual surgical
tools has largely supplanted stereotactic frame based surgery.
The use of new technologies has also allowed us to gain
better insights into how we can modify brain function in pathological states.
Today we can implant deep brain electrodes to alleviate movement disorders,
pain, epilepsy and psychiatric disorders. The electrodes can be externalised to
record deep brain activity and relate it to alteration of physiological function
. Careful physiological studies can reveal surprising new indications for
the therapy  as the paper by Pereira et al has shown. In a study of
the physiological changes that accompany pain alleviation, it emerged that
dorsally-placed electrodes raise blood pressure while ventrally-placed ones
decrease blood pressure. Given the vast numbers of patients with poorly
controlled blood pressure despite best medical therapy, we may be looking at
the emergence of a new indication.
Patients with chronically implanted deep brain electrodes
are not yet generally amenable to functional MRI (fMRI) scanning due to safety
issues  though there are some studies . To date, the only accepted
methodologies were single photon emission tomography (SPECT) and positron
emission tomography (PET)  scans with limitations of time and resolution.
However, since the 1990s magnetoencephalogram (MEG) scanning has been
extensively used to map out cortical activity by measuring changes in the
magnetic fields . Recently, paradigms have been developed to study the
activity in deep brain structures and also to render this information in 3D
space with better spatial and temporal resolution than PET, SPECT or fMRI. More
importantly, this can be done in patients with the stimulator on and off, and
can eliminate artefacts of stimulation. The work by Kringelbach et al
has demonstrated this for neuropathic pain and in this issue Wray and
Kringelbach report their study in a case of cluster headache which responded to
deep brain stimulation in the postero-infero-medial hypothalamus.
These are landmark developments. Image guidance has made
major brain tumour surgery safer. The use of diffusion tensor imaging to map
out connectivity of brain pathways and the use of MEG scanning to study brain
activation i.e., on and off stimulation, and correlating them all with field
potential recordings from the deep brain electrodes and changes in
physiological functions i.e., movement disorders, pain psychiatric disorders,
etc., will unravel mysteries of brain function in a way never possible before.
Oxford Functional Neurosurgery is supported by the MRC,
Charles Wolfson Charitable Trust and Norman Collisson Foundation.
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|Received 20 October 2006; accepted 25 October 2006
Correspondence: : Department of Neurosurgery, Level 3, West Wing, John Radcliffe Hospital, Headley Way, Headington, Oxford,OX3 9DU, United Kingdom. Tel.: 01865 234605; E-mail: firstname.lastname@example.org (Tipu Aziz).
Please cite as: TZ Aziz,
Image-guided surgery and therapy, Biomed Imaging Interv J 2007; 3(1):e7
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