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Development of an automatic focusing system for a precise laser ablation system in neurosurgery
International Congress Series 1256 (2003) 514 – 521
Development of an automatic focusing system for a precise laser ablation system in neurosurgery E. Aoki a,*, E. Kobayashi a, H. Inada b, S. Omori c,d, T. Maruyama d, H. Iseki d, Y. Muragaki d, K. Takakura d, I. Sakuma a a
Graduate School of Frontier Sciences, Room 722, Engineering Building #14, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656, Japan b Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656, Japan c Terumo Corporation, Japan d Field of Advanced Techno Surgery, Institute of Biomedical Engineering and Science, Graduate School of Medicine, Tokyo Women’s Medical University, Graduate School of Information Science and Technology, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656, Japan Received 15 March 2003; received in revised form 18 March 2003; accepted 19 March 2003
Abstract In treatment of diseases such as encephaloma using neurosurgery, it is very important to remove the tumor accurately at the boundary between the tumor and normal tissue. This is to prevent the recurrence of cancer. To achieve this precise removal of the tumor, we have proposed a new treatment method using 5 Aminolevulinic Acid (5-ALA) and a microlaser with a wavelength of 2.8 Am. In this method, the tumor is labeled by 5-ALA induced fluoresced and is cauterized by the microlaser. Since the ablation by microlaser depends on the displacement from the focal point, it is necessary to keep the distance between the laser probe and the target the focal length. In this research, we have developed the automatic focusing mechanism using two guide lasers and a CCD camera. We have performed focusing accuracy evaluation experiment and irradiation experiment using in porcine pig. Experimental results showed that the focusing accuracy was within 0.5 mm and possibility of clinical application was demonstrated. D 2003 Published by Elsevier Science B.V. Keywords: Automatic focusing; Laser ablation; Neurosurgery
* Corresponding author. Tel.: +81-35841-7480; fax: +81-35841-6446. E-mail address: [email protected] (E. Aoki). 0531-5131/03 D 2003 Published by Elsevier Science B.V. doi:10.1016/S0531-5131(03)00293-0
E. Aoki et al. / International Congress Series 1256 (2003) 514–521
515
1. Purpose We can remove most part of the tumor with an accuracy of few millimeters using a combination of conventional surgical instruments such as electric cautery and computeraided navigation system. Nevertheless, the residual tumor may induce recurrence, it is necessary to remove the tumor as much as possible while keeping the normal tissue intact. It is difficult to know the exact boundary between tumor and normal tissue. Excessive ablation of the normal tissue of brain will damage its function. For treatment of residual tumor, or tumor that cannot be treated by surgical intervention, pharmacotherapy or radiotherapy is applied. This therapy is effective, however, there are problems such as side effects. Therefore, more precise surgical treatment as compared to conventional surgical instruments is needed. To solve those problems, we have proposed a novel approach to the therapy using 5 Aminolevulinic Acid (5-ALA) and a microlaser ablation system. In this therapy, the boundary between the tumor and the normal tissue is recognized by the fluoresced tumor with the 5-ALA [1] and the tumor is accurately cauterized by the microlaser. The wavelength of the microlaser is 2.8 Am, which is most absorbable to the water. Therefore, this laser is effective only on the surface of the brain tissue, which enables precise ablation in boundary between tumor and normal tissue [2]. On the other hand, the ablation by this laser depends on the displacement from focal point (Fig. 1). Therefore, the robotic automatic focusing system is necessary for the microlaser ablation system. By the combination of the robotic positioning system with the precise laser abrasion, more accurate and precise operation is realized. In this research, we have developed an automatic focusing system for the microlaser ablation system to achieve an accurate operation in neurosurgery [3].
2. Method We set following requirements for the automatic focusing system: (1) Positioning accuracy in automatic focusing is less than 0.5 mm.
Fig. 1. The brain tissue cauterized by microlaser.
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E. Aoki et al. / International Congress Series 1256 (2003) 514–521
(2) Working range in focusing direction is 5 mm. (3) The system is small in size and lightweight. In order to meet the above requirements, we used the following method. As shown in Fig. 2, when the target is located at the focal point of the laser, the two guide lasers intersect at one point on the surface of the target. Assuming that the target surface is perpendicular to the plane determined by the two laser beams, the relationship between the distance of the target plane from the focal point, h, and distance of two light spots on the target surface, dz, is described as follows: dz ¼ hd=D
ð1Þ
in which dz denotes distance between the focal point and the target surface, h denotes focal length, d denotes distance between two spots, and D denotes distance between two guide lasers. We can determine the distance between the focal point and the surface of target by monitoring the distance between two spots of the guide lasers. The advantages of this method are noncontact, accessibility to intraoperative view, small in size and lightweight. For guide laser, we used a red laser with a wavelength of 640 nm and a green laser with wavelength of 532 nm, respectively. We used a pulse motor for the automatic focusing. The size of system was 270 mm, and the weight was 475 g.
Fig. 2. Method of calculating displacement.
E. Aoki et al. / International Congress Series 1256 (2003) 514–521
517
Fig. 3. Figure of automatic focusing system in general.
Fig. 3 indicates the automatic focusing mechanism using two guide laser and a CCD camera. The process of the automatic focusing is as follows: (1) Take the view of the operating field, which includes the two spots of each laser by the CCD camera. (2) Extract the spots and erase the rest field by image data processing.
Fig. 4. Method of evaluating the accuracy.
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Fig. 5. Positioning error on the horizontal plane.
(3) Measure the length between two spots and calculate the moving distance for automatic focusing. (4) Input motion command to the motor.
3. Results We performed experiments to evaluate the basic function of the automatic focusing system and in vitro experiments. 3.1. Positioning accuracy evaluation As a initial point, we set focal point of the device on the horizontal target plane. The device was moved vertically, and 5 and 5 mm from the focal point, with interval of 0.1 mm near focal point. Between 0.5 and 0.5 mm around the focal point, we moved the device on every 0.01 mm. After we performed automatic focusing on each point, we
Fig. 6. Positioning accuracy evaluation of the oblique plane.
E. Aoki et al. / International Congress Series 1256 (2003) 514–521
519
Fig. 7. The result of descending slope.
evaluated positioning error from focal point (Fig. 4). To measure the error, we used an electric displacement sensor with laser (LB-62, Keyence, Tokyo, Japan). As Fig. 5 shows the average of the error was 0.18 mm and the maximum error was 0.55 mm. This result demonstrated that the device does satisfy the requirement of positioning accuracy of less than 0.5 mm, with not considering the area between 0.5 and 0.5 mm around the focal point. 3.2. Positioning accuracy of the system on the oblique plane We also evaluated the tracking error of the automatic focusing system when the system scanned the plane on the oblique plane with 45j (Fig. 6). Scanning velocity of the device was constant 2 (mm/s) and we varied the distance between target plane and the microlaser module around the focal point ranging from 5 to + 5 mm. Actual distance between the device and a target plane was measured by the same method as in Section 3.1. In this experiment, comparing ascending slope with descending slope, the tracking accuracy for descending slope was better than that for ascending slope. On descending slope, the average of positioning error was 0.09 mm (Fig. 7).
Fig. 8. The result of ascending slope.
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Fig. 9. In vitro experiment.
That for ascending slope was 0.56 mm (Fig. 8). The system moved at a constant speed on the horizontal plane. Therefore, in tracking on a slope, the focal point changed after the time lag of graphic data processing and positioning. This was main factor of positioning error. 3.3. In vitro experiment on porcine brain We performed an in vitro experiment. We performed ablation test on a porcine brain test sample. As Fig. 9 indicates, ablating was done 10 mm in length and five lines at interval of 1 mm, This experiment was repeated six times. Without automatic focusing system, the trace of ablation was wide and unclear. On the other hand, with the automatic focusing system, the trace was constant in depth and width (Fig. 10). This result showed that this
Fig. 10. Comparison of the result in experiment whether using automatic focusing or not (right: no focusing) (left: using focusing).
E. Aoki et al. / International Congress Series 1256 (2003) 514–521
521
system could follow the surface of brain tissue and maintain effectively the distance between the target and the device at the focal length. The system focused the laser ablation device accurately even under the existence of light scattering on the brain surface.
4. Conclusion In this research, we have developed a new automatic focusing system for 2.8 Am microlaser ablation device using two guide lasers and a CCD camera, which has advantages of noncontact accessibility to intraoperative view, small in size and lightweight. We achieved the positioning accuracy of 0.18 mm in average on the horizontal plane and less than 0.56 mm on the oblique plane of 45j. The results of in vitro experiments have demonstrated feasibility of this automatic focusing system for clinical application. We are now developing a real-time tumor detection system based on fluorescence labeling using 5-ALA. In the future, by integrating this system with the automatic focusing system, real-time tumor detection and laser ablation will be achieved simultaneously, which will have ability of accurate and precise operation in neurosurgery.
References [1] T. Maruyama, Y. Muragaki, H. Iseki, et al., Intraoperative detection of malignant gliomas using 5-Aminolevulinic acid induced protoporphyrin fluorescence, open MRI and real-time navigation system, Computer Assisted Radiology and Surgery 15 (2001) 270 – 275. [2] S. Omori, H. Iseki, Y. Muragaki, et al., Laser etching on brain tumors by E = 2.8 Am microlaser, Japan Society of Computer Aided Surgery 11 (2002) 17 – 18. [3] E. Aoki, T. Kato, E. Kobayashi, S. Omori, H. Iseki, I. Sakuma, Development of an automatic focusing system for a compact neurosurgical laser instrument, Japan Society of Computer Aided Surgery 11 (2002) 15 – 16.
Development of an automatic focusing system for a precise laser ablation system in neurosurgery E. Aoki a,*, E. Kobayashi a, H. Inada b, S. Omori c,d, T. Maruyama d, H. Iseki d, Y. Muragaki d, K. Takakura d, I. Sakuma a a
Graduate School of Frontier Sciences, Room 722, Engineering Building #14, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656, Japan b Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656, Japan c Terumo Corporation, Japan d Field of Advanced Techno Surgery, Institute of Biomedical Engineering and Science, Graduate School of Medicine, Tokyo Women’s Medical University, Graduate School of Information Science and Technology, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656, Japan Received 15 March 2003; received in revised form 18 March 2003; accepted 19 March 2003
Abstract In treatment of diseases such as encephaloma using neurosurgery, it is very important to remove the tumor accurately at the boundary between the tumor and normal tissue. This is to prevent the recurrence of cancer. To achieve this precise removal of the tumor, we have proposed a new treatment method using 5 Aminolevulinic Acid (5-ALA) and a microlaser with a wavelength of 2.8 Am. In this method, the tumor is labeled by 5-ALA induced fluoresced and is cauterized by the microlaser. Since the ablation by microlaser depends on the displacement from the focal point, it is necessary to keep the distance between the laser probe and the target the focal length. In this research, we have developed the automatic focusing mechanism using two guide lasers and a CCD camera. We have performed focusing accuracy evaluation experiment and irradiation experiment using in porcine pig. Experimental results showed that the focusing accuracy was within 0.5 mm and possibility of clinical application was demonstrated. D 2003 Published by Elsevier Science B.V. Keywords: Automatic focusing; Laser ablation; Neurosurgery
* Corresponding author. Tel.: +81-35841-7480; fax: +81-35841-6446. E-mail address: [email protected] (E. Aoki). 0531-5131/03 D 2003 Published by Elsevier Science B.V. doi:10.1016/S0531-5131(03)00293-0
E. Aoki et al. / International Congress Series 1256 (2003) 514–521
515
1. Purpose We can remove most part of the tumor with an accuracy of few millimeters using a combination of conventional surgical instruments such as electric cautery and computeraided navigation system. Nevertheless, the residual tumor may induce recurrence, it is necessary to remove the tumor as much as possible while keeping the normal tissue intact. It is difficult to know the exact boundary between tumor and normal tissue. Excessive ablation of the normal tissue of brain will damage its function. For treatment of residual tumor, or tumor that cannot be treated by surgical intervention, pharmacotherapy or radiotherapy is applied. This therapy is effective, however, there are problems such as side effects. Therefore, more precise surgical treatment as compared to conventional surgical instruments is needed. To solve those problems, we have proposed a novel approach to the therapy using 5 Aminolevulinic Acid (5-ALA) and a microlaser ablation system. In this therapy, the boundary between the tumor and the normal tissue is recognized by the fluoresced tumor with the 5-ALA [1] and the tumor is accurately cauterized by the microlaser. The wavelength of the microlaser is 2.8 Am, which is most absorbable to the water. Therefore, this laser is effective only on the surface of the brain tissue, which enables precise ablation in boundary between tumor and normal tissue [2]. On the other hand, the ablation by this laser depends on the displacement from focal point (Fig. 1). Therefore, the robotic automatic focusing system is necessary for the microlaser ablation system. By the combination of the robotic positioning system with the precise laser abrasion, more accurate and precise operation is realized. In this research, we have developed an automatic focusing system for the microlaser ablation system to achieve an accurate operation in neurosurgery [3].
2. Method We set following requirements for the automatic focusing system: (1) Positioning accuracy in automatic focusing is less than 0.5 mm.
Fig. 1. The brain tissue cauterized by microlaser.
516
E. Aoki et al. / International Congress Series 1256 (2003) 514–521
(2) Working range in focusing direction is 5 mm. (3) The system is small in size and lightweight. In order to meet the above requirements, we used the following method. As shown in Fig. 2, when the target is located at the focal point of the laser, the two guide lasers intersect at one point on the surface of the target. Assuming that the target surface is perpendicular to the plane determined by the two laser beams, the relationship between the distance of the target plane from the focal point, h, and distance of two light spots on the target surface, dz, is described as follows: dz ¼ hd=D
ð1Þ
in which dz denotes distance between the focal point and the target surface, h denotes focal length, d denotes distance between two spots, and D denotes distance between two guide lasers. We can determine the distance between the focal point and the surface of target by monitoring the distance between two spots of the guide lasers. The advantages of this method are noncontact, accessibility to intraoperative view, small in size and lightweight. For guide laser, we used a red laser with a wavelength of 640 nm and a green laser with wavelength of 532 nm, respectively. We used a pulse motor for the automatic focusing. The size of system was 270 mm, and the weight was 475 g.
Fig. 2. Method of calculating displacement.
E. Aoki et al. / International Congress Series 1256 (2003) 514–521
517
Fig. 3. Figure of automatic focusing system in general.
Fig. 3 indicates the automatic focusing mechanism using two guide laser and a CCD camera. The process of the automatic focusing is as follows: (1) Take the view of the operating field, which includes the two spots of each laser by the CCD camera. (2) Extract the spots and erase the rest field by image data processing.
Fig. 4. Method of evaluating the accuracy.
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E. Aoki et al. / International Congress Series 1256 (2003) 514–521
Fig. 5. Positioning error on the horizontal plane.
(3) Measure the length between two spots and calculate the moving distance for automatic focusing. (4) Input motion command to the motor.
3. Results We performed experiments to evaluate the basic function of the automatic focusing system and in vitro experiments. 3.1. Positioning accuracy evaluation As a initial point, we set focal point of the device on the horizontal target plane. The device was moved vertically, and 5 and 5 mm from the focal point, with interval of 0.1 mm near focal point. Between 0.5 and 0.5 mm around the focal point, we moved the device on every 0.01 mm. After we performed automatic focusing on each point, we
Fig. 6. Positioning accuracy evaluation of the oblique plane.
E. Aoki et al. / International Congress Series 1256 (2003) 514–521
519
Fig. 7. The result of descending slope.
evaluated positioning error from focal point (Fig. 4). To measure the error, we used an electric displacement sensor with laser (LB-62, Keyence, Tokyo, Japan). As Fig. 5 shows the average of the error was 0.18 mm and the maximum error was 0.55 mm. This result demonstrated that the device does satisfy the requirement of positioning accuracy of less than 0.5 mm, with not considering the area between 0.5 and 0.5 mm around the focal point. 3.2. Positioning accuracy of the system on the oblique plane We also evaluated the tracking error of the automatic focusing system when the system scanned the plane on the oblique plane with 45j (Fig. 6). Scanning velocity of the device was constant 2 (mm/s) and we varied the distance between target plane and the microlaser module around the focal point ranging from 5 to + 5 mm. Actual distance between the device and a target plane was measured by the same method as in Section 3.1. In this experiment, comparing ascending slope with descending slope, the tracking accuracy for descending slope was better than that for ascending slope. On descending slope, the average of positioning error was 0.09 mm (Fig. 7).
Fig. 8. The result of ascending slope.
520
E. Aoki et al. / International Congress Series 1256 (2003) 514–521
Fig. 9. In vitro experiment.
That for ascending slope was 0.56 mm (Fig. 8). The system moved at a constant speed on the horizontal plane. Therefore, in tracking on a slope, the focal point changed after the time lag of graphic data processing and positioning. This was main factor of positioning error. 3.3. In vitro experiment on porcine brain We performed an in vitro experiment. We performed ablation test on a porcine brain test sample. As Fig. 9 indicates, ablating was done 10 mm in length and five lines at interval of 1 mm, This experiment was repeated six times. Without automatic focusing system, the trace of ablation was wide and unclear. On the other hand, with the automatic focusing system, the trace was constant in depth and width (Fig. 10). This result showed that this
Fig. 10. Comparison of the result in experiment whether using automatic focusing or not (right: no focusing) (left: using focusing).
E. Aoki et al. / International Congress Series 1256 (2003) 514–521
521
system could follow the surface of brain tissue and maintain effectively the distance between the target and the device at the focal length. The system focused the laser ablation device accurately even under the existence of light scattering on the brain surface.
4. Conclusion In this research, we have developed a new automatic focusing system for 2.8 Am microlaser ablation device using two guide lasers and a CCD camera, which has advantages of noncontact accessibility to intraoperative view, small in size and lightweight. We achieved the positioning accuracy of 0.18 mm in average on the horizontal plane and less than 0.56 mm on the oblique plane of 45j. The results of in vitro experiments have demonstrated feasibility of this automatic focusing system for clinical application. We are now developing a real-time tumor detection system based on fluorescence labeling using 5-ALA. In the future, by integrating this system with the automatic focusing system, real-time tumor detection and laser ablation will be achieved simultaneously, which will have ability of accurate and precise operation in neurosurgery.
References [1] T. Maruyama, Y. Muragaki, H. Iseki, et al., Intraoperative detection of malignant gliomas using 5-Aminolevulinic acid induced protoporphyrin fluorescence, open MRI and real-time navigation system, Computer Assisted Radiology and Surgery 15 (2001) 270 – 275. [2] S. Omori, H. Iseki, Y. Muragaki, et al., Laser etching on brain tumors by E = 2.8 Am microlaser, Japan Society of Computer Aided Surgery 11 (2002) 17 – 18. [3] E. Aoki, T. Kato, E. Kobayashi, S. Omori, H. Iseki, I. Sakuma, Development of an automatic focusing system for a compact neurosurgical laser instrument, Japan Society of Computer Aided Surgery 11 (2002) 15 – 16.