• Increase the acquisition rates of spectroscopic

techniques.

• Study the source of optical signatures (biochemis-

try and tissue microstructure) in spectroscopic methods

References

] American Heart Association. 1997. 1997 Heart and Stroke, Statistical Update.

2 Fuster, V., et al. 1992. The pathogenesis of coronary artery disease and the acute coronary syndromes. N Eng J Med 326:242-250.

3 Loop, F.D., etal. 1983. Coronary artery surgery in women compared to men: analysis of risk and longterm results. J Am ColI Cardiol 2: 383-390.

4 Kahn, J.K., etal. 1992. Comparison of procedural results and risks of coronary angioplasty in men and women. Am J Card 69:1241-1242.

5 Brezinski, M.E., etal. 1996. Optical coherence tomogra- phy for optical biopsy: properties and demonstration of vascular pathology. Circulation 93:1206-1213.

6 Brezinski, M.E., et al. 1997. Assessing atherosclerotic plaque morphology: comparison of optical coherence to- mography and high frequency intravascular ultrasound. Heart 77:397-404.

VIII Opportunities for Optical Technologies in Neurology/ Neurosurgery Stereotactic and Functional Neurosurgery

More than one million people in the USA suffer from

essential tremor, and 500,000 from Parkinson's disease.

Precise localization within the globus pallidus, thala-

mus, and related areas of the brain is essential to en-

hance the safety and efficacy of both ablative and

stimulation techniques for the treatment of movement

disorders. Accuracy and safety for the placement of

electrodes could be improved using information in addi-

tion to electrophysiological monitoring. Optical probes

and other techniques could be used to detect blood ves-

sels and tissue regions to be avoided (e.g., the optic

tract or the internal capsule). I Elastic-scattering spec-

troscopy could be used to differentiate gray matter from white matter in tissue localization. 2

For stereotactic brain biopsy to diagnose a suspected brain tumor, an optical probe--possibly combined with

other parameters such as tissue oxygen content and/or

tissue density--can provide real-time diagnostic infor-

mation? The risk of hemorrhage from the biopsy needle

traversing the brain would be reduced, as would the

likelihood of a "missed" diagnosis (both of which occur

in approximately 5% of stereotactic brain biopsies for

tumor). 4 Such a probe would also reduce operative ex-

pense by eliminating the time spent waiting for the

pathologist's frozen section results.

Similarly, an "optical biopsy" probe used during ster-

eotactic brain biopsy procedures for conditions other

than tumor could yield real-time information regarding

the diagnosis of encephalitis, cerebral vasculitis, Alz-

heimer's disease, and multiple sclerosis.

Open Neurosurgery

The number of patients harboring brain tumors who

can benefit from open surgical excision is certainly over

50,000, and may approach 100,000. This includes both

primary and metastatic tumors, the latter being approxi-

mately five times as common as the former. Metastatic tumors are a growing problem for women in particular (a

consequence of the increase in smoking among women).

Lung is the number one site for the primary tumor, with breast and gastrointestinal cancer also very common pri-

mary sites for tumors with brain metastases. A small

hand-held probe that can be used to survey the brain tu-

mor resection bed for residual tumor (i.e., tumor not vis-

ible to the eye) would increase the "gross total" tumor removal rate for both primary and metastatic brain tumor

surgery. Probes for brain tumor diagnosis based on elas-

tic-scattering spectroscopy or fluorescence spectroscopy

could be developed, similar to those that have been used

for detection of cancer in the GI tract and bladder.

The combination of optical technology for tumor di-

agnosis with the same technology for guiding tumor

treatment (e.g., removal or ablation by a robotically con-

trolled laser) is certainly feasible. Such a system could

be automated but under the direct control of the physi-

cian/surgeon.

During craniotomy to clip an intracranial aneurysm, precise clip placement is essential. Small blood vessels

may be inadvertently occluded by the clip--vessels

which may be too small to be detected by intraoperative

angiography, but which may cause significant neurologi-

cal impairment postoperatively. There is need for a min-

iature probe which could identify vessels outside the

surgeon's field of view through the operating micro-

scope, and which could determine the patency of those

vessels. This would not only obviate intraoperative an-

giography (which harbors some risk and is time-consum-

ing in the operating room) but would lessen the chance

of undetected small-blood-vessel occlusion.

S 1 8 9

For neuroprotection during neurosurgical procedures,

optical probes or multimodality probes using optical

and other technologies (e.g., electrophysiological and

blood flow monitoring) could enhance the safety of neu- rosurgical procedures. These probes might be similar to those noted under "Long-term tissue monitoring."

Endoscopy

In the USA, over 350,000 intervertebral disc opera- tions are performed each year. Endoscopic, laparoscop-

ic, and percutaneous techniques are rapidly becoming the standard of care to reduce the length of surgery, the

length of hospital stay, and the post-operative discom- fort. 5 However, as the visualization becomes further re-

moved from "direct vision" (e.g., the use of I-ram-di- ameter flexible fiberoptic endoscopes), it becomes in- creasingly difficult for the surgeon to identify tissue

with confidence. Having a miniature (approximately 1-mm diameter) probe, which could be applied to the

tissue in question for real-time identification, would greatly enhance the safety and rapidity of endoscopic disc operations.

A related application is laparoscopic anterior lumbar fusion using the interbody fusion cages recently ap- proved by the FDA. A probe placed through the laparo- scope to identify tissue along the anterior aspect of the spinal column could aid in protecting small but impor- tant nerves and blood vessels.

In intracranial neuroendoscopy, one example is that an optical probe could assist in optimizing the place-

ment of third ventriculostomies and identify blood ves- sels, e.g., the basilar artery.

Interventional Vascular Access

A miniature optical probe could be used to monitor clot lysis using, e.g., t-PA, in acute stroke. Such a

probe might be combined with a miniature laser-Dop- pler blood flow probe and/or a miniature ultrasound probe. 6 More precise real-time information on restoring blood flow would be obtained, and repeated arterio-

grams avoided.

As with cardiovascular disease, another intravascular application would be a probe to monitor plaque removal during endarterectomy, Optical reflectance/scattering or fluorescence could be used to detect when plaque has

been removed to the point of the desired depth within the blood vessel wall--minimizing the risks of inad- equate endarterectomy or vessel wall injury.

A third application could be using the vascular tree

for a minimally invasive approach to lesions such as

strokes, vascular aneurysms and arteriovenous malfor-

mations, and tumors. An optical probe could monitor blood flow changes and/or the reaction of tissues to neuroprotective and chemotherapeutic agents.

Long-Term Tissue Monitoring

Transcranial monitoring of brain oxygen saturation-- using near infrared spectroscopy--is already available for clinical use. The parameters monitored and the ver- satility of the instrumentation could be expanded to im-

prove management in situations with abnormal cerebral metabolism (stroke, head injury, and post-craniotomy).

The technology currently exists to monitor such pa-

rameters as brain pH, PO 2, and PCO 2 continuously (i.e., using a 0.5-ram diameter optical absorbance or optical fluorescence probe). 7 Hundreds of thousands of people

suffer from stroke or severe head injury each year; such

continuous direct monitoring of brain function could make the treatment of stroke and head injury more effi- cacious.

Key Barriers to Implementing Optical Technolo- gies in Neurology/Neurosurgery

The primary barrier to implementing optical tech-

nologies in this area is the barrier encountered by many

new technologies--resistance to change on the part of those with a vested interest in maintaining the tradi- tional diagnostic and therapeutic methods. The two specific areas are (1) neurosurgeons who resist operative

techniques that reduce their ability to "see with their

own eyes" and "operate with their own hands," and (2) pathologists who resist the use of technology to perform tissue diagnoses.

In both cases the technological advances could im-

prove on safety, efficacy, or both. Computer-aided and robotic neurosurgical techniques could reduce or elimi-

nate the "human error" in surgery, and allow a precision which is beyond the physiologic tremor and visual acu-

ity limitations of man. For the pathologist, there are the automated laboratory techniques that have now become accepted standards: e.g., automated CBC (complete blood count) and UA (urinalysis).

In our present cost-driven health care delivery sys- tem, implementing optical technologies should not

present a major problem if the cost-benefit data are pre- sented widely and the changes instituted diplomatically.

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References

i Burns, J.M., S. Wilkinson, J. Kieltyka, et al. 1997. Analy- sis of pallid0tomy lesion positions using three-dimen- sional reconstruction of pallidal lesions, the basla gan- glia, and the optic tract. Neurosurgery 41:1303-1318.

2 Liu, H., M. Johns, and C.A. Giller. 1998. Investigation of optical reflectance from human brain in vivo for guiding brain surgery. Digest of the OSA Meeting on Biomedical Optical Spectroscopy and Diagnostics March.

3 Andrews, R., R. Mah, A. Galvagni, et al. In press. Robotic multimodality stereotactic tissue identification: work in progress. Stereotact Funct Neurosurg.

4 Bernstein, M., and A.G. Parrent. 1994. Complications of CT-guided stereotactic biopsy of intra-axial brain le- sions. J Neurosurg 81:165-168.

5 Foley, K.T., and M.M. Smith. 1997. Microendoscopic discectomy. Techniques in Neurosurgery 3:301-307.

6 Gilsbach, J., M. Mohadjer, and F. Mundinger. 1987. A new safety device to prevent bleeding complications during stereotactic biopsy: the "sterotactic" Doppler sonogra- phy. Acta Neurochir (Wien) 89:77-79.

7 Zauner, A., E.M.R. Doppenberg, J.J. Woodward, et al. 1997. Continuous monitoring of cerebral substrate deliv- ery and clearance: initial experience with 24 patients with severe acute brain injuries. Neurosurgery 41:1082- 1093.

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