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Real-time image tracking of a flexible bronchoscope
International Congress Series 1268 (2004) 753 – 757
www.ics-elsevier.com
Real-time image tracking of a flexible bronchoscope A. Schneider a,*, H. Hautmann b, H. Barfuss c, T. Pinkau b, F. Peltz b, H. Feussner a,d, A. Wichert a a
Workgroup MITI, Klinikum r. d. Isar, Technical University Munich, Troger Str. 26, 81675 Munich, Germany b Pneumology, 1st Medical Department, Klinikum r. d. Isar, Technical University Munich, 81675 Munich, Germany c Siemens Medical Solutions SPI, Erlangen, Germany d Surgical Department, Klinikum r. d. Isar, Technical University Munich, 81675 Munich, Germany
Abstract. Electromagnetical tracking devices have become so small, that tracking of flexible instruments is possible. Because of the low diagnostic yield of flexible bronchoscopy, we assembled and evaluated a system for navigation of the bronchoscopes tip. In order to evaluate the exactness of the electromagnetical tracking system in a preoperative CT-Scan, 16 patients underwent diagnostic flexible bronchoscopy with fluoroscopic guidance. Deviation was measured and computed. D 2004 Published by Elsevier B.V. Keywords: 3-D imaging; Diagnostic imaging; Bronchoscopy; Stereotaxy; Image-guided; Virtual bronchoscopy; Navigation; Tracking
1. Introduction Image-directed bronchoscopy plays a major role in evaluating peripheral localized pulmonary lesions since they cannot directly be visualized. Histopathological, cytological or microbiological assessment is essential in order to initiate adequate therapy. Different studies showed that the diagnostic yield of successful flexible bronchoscopy is between 18% and 62% [1]. Normally, it is performed under X-ray imaging (a.k.a. fluoroscopy) that provides no depth perception, does not depict the anatomy of the bronchial tree and is even hardly able to discern the target. One way to improve the diagnostic accuracy was the utilization of CT-guided bronchoscopic interventions [2]. However, the limited availability, costs and the additional radiation exposure are the drawbacks of this application [3]. * Corresponding author. Tel.: +49-89-4140-7385; fax: +49-89-4140-7393. E-mail address: [email protected] (A. Schneider). 0531-5131/ D 2004 Published by Elsevier B.V. doi:10.1016/j.ics.2004.03.278
754
A. Schneider et al. / International Congress Series 1268 (2004) 753–757
Navigation is a widely accepted additional aid to guide instruments in fields like neurosurgery, orthopaedic surgery and ear – nose and throat surgery here, rigid instruments, which make optical tracking possible, are used. Electromagnetical tracking systems have now reached a level of miniaturization and sophistication in recent years where the positions and orientations of small sensors within the body can be determined with accuracies having clinical relevance [4]. Electromagnetical guiding of transbronchial catheters or biopsy forceps is a novel method to increase the diagnostic yield [5]. This method can indicate the position of an instrument in real-time as well in three dimensions in a preprocedure CT- or MR dataset. We validated the electromagnetic tracking system generated position in a clinical setting with fluoroscopy. 2. Methods In order to evaluate the exactness of an electromagnetical tracking device in a preoperative CT-Scan, 16 patients underwent diagnostic flexible bronchoscopy with fluoroscopic guidance. Selection criteria were findings, which necessitated the use of fluoroscopy to guide biopsy forceps or transbronchial needle aspiration (TBNA). Preoperative spiral CT-Scans were acquired within 7 days before intervention. Standard protocols were used, in order to get usual diagnostic quality (120 kVp, 120 mAs, pitch 1.3, collimation 0.75 mm and a reconstruction of 5 mm). For navigation and reading the data from the electromagnetical tracker, an enhanced syngoR (Siemens Medical Solutions, Erlangen, Germany) workstation was used. We integrated two special navigation tab cards, one for the registration procedure, the other for real-time visualization of the instrument tip in the preoperative CT data. The electromagnetical tracker was a pre-production model AuroraR (Northern Digital, Waterloo, Ontario, Canada). This tracker is able to determine with the minimized sensor five degrees of freedom in a volume of 500 500 500 mm. Size of the Sensor coil integrated in a steralizeable catheter is 8.0 0.8 mm. The field generator (transmitter) dimensions are 220 220 170 mm. Inside the transmitter a pulsed DC electromagnetic field with a special symmetric setup of nine coils is generated. Data processing and delivering to the workstation is done by the system control unit (SCU) outside the intervention field. The connection to the workstation was done by a serial connection with 38400 baud. To exclude tracking errors because of other magnetic and electromagnetic parts in the room, prior to the study an accuracy measurement with a special measurement plate was done. This measurement plate allowed us to measure points all two centimetres in all three planes. With that measurement we were able to exclude distorsions of the magnetical field. In the intervention room we placed the field generator left beside the patient in high of the thorax as shown in Fig. 1 below. Patient data was transferred by standardized DICOM transfer from the CT console to the navigation workstation. A rigid registration procedure was done to match CT data with the patient in the tracking field. This was done by an identification of N equivalent pairs of corresponding points pi and piV in the tomographic images and the tracker space. Mathematically three
A. Schneider et al. / International Congress Series 1268 (2004) 753–757
755
Fig. 1. System setup in the intervention room.
pairs of points are enough for registration, for increased precision a minimum of four pairs of corresponding points were required. We used the proximal rim of the manubrium sterni and the distal end of the xiphoid as external landmarks. In preliminary experiments, exactness for navigation in the bronchoscopic tree was increased by an additional using of internal landmarks. Here we used the main carina and the right upper lobe carina, these are simply visible and reachable with the bronchoscope and in the CT-slices. Accuracy before the intervention was controlled by re-hitting the endobronchial marker points. If the error distance of one marker point exceeded 5 mm re-registration of that point was performed. After that procedure, navigation of the instrument tip (bronchoscope tip) in the preoperative was performed. The syngo workstation provided on a special tab card a crosshair in a sagital, coronal and transversal view, which showed the head of the navigation sensor. Additional a free multiplanar reconstruction (free MPR) image was integrated, which was equal to the view of the bronchoscope (Fig. 2). Testing for exactness was done by introducing and advancing the sensor into to the bronchial orifice, it lead most likely to the lesion as determined from a review of the preliminary diagnostic CT scan. When the sensor missed the lesion, it was repositioned until the tip of the sensor reached or penetrated the lesion on the computer display of the navigation system. In SPN’s, the position of the sensor was controlled by fluoroscopy in a posterior –anterior view. Then the distance from the margin of the nodule to the tip of the sensor was measured. In a second step the sensor was inserted into the upper lobe ipsilateral of the lesion and under control of the computer screen subsequently forwarded until it came to a stop at the most lateral position. An additional spot of interest was the most apical position of the upper lobe. These positions were each considered the visceral pleura, representing the inner lining of the thoracic wall. By means of fluoroscopy it was then verified whether the sensor tip was actually adjacent to the inner lining of the thoracic wall. On the computer display the distance between the crosshair, representing the sensor tip, and the visceral
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A. Schneider et al. / International Congress Series 1268 (2004) 753–757
Fig. 2. Navigation tabcard in the syngo workstation: on the main window the free MPR, right hand side sagital coronal and transversal view.
Fig. 3. Error distances between sensor tip and reference position.
A. Schneider et al. / International Congress Series 1268 (2004) 753–757
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pleura was measured. Subsequently, the sensor tip was again positioned on landmark 3 (main carina) to determine whether the error distance has been altered during the course of the procedure. 3. Results No complications occurred during bronchoscopy. All lesion were clearly identified on the computer screen, also the sensor tip, shown as yellow crosshair, was clearly visible. In two cases the volume which allows navigation did not cover the whole hemithorax. In this case the field transmitter was repositioned and a new registration procedure was performed. Rigid registration was done in 4.4 F 1.9 min (mean F S.D.). In the five patients with SPN’s the sensor tip penetrated the nodule in three cases. In the remaining cases the tip came close to the periphery. The resulting error distances are displayed in Fig. 3. The average diameter of the nodules was 22 F 6 mm (mean F S.D.) with a maximum distance to the pleura of 23 mm. In two cases of penetration the position of the sensor tip in relation to the nodule was verified by fluoroscopy. In three cases the nodule could not be clearly identified by fluoroscopy. When the sensor tip was forwarded to the lateral and apical thoracic wall, fluoroscopy could verify the pleural position of the sensor tip in all cases. 4. Conclusion With the help of the navigation system all infiltrations were clearly localized by the sensor. It was still possible to direct the sensor in the center of that specific infiltrate, even when it was not possible to identify the infiltrate by fluoroscopy. Electromagnetic flexible navigation is a possible method to increase the diagnostic yield in bronchoscopy. Use of the electromagnetical tracking unit is simple and after a measurement to exclude distorsions of the electromagnetic field a method with a sufficient exactness. New instruments, i.e. biopsy forceps with an integrated navigation sensor, are necessary to have the whole benefit of navigation. Another transmitter shape, for example a mat which could be positioned under the patient, could ease the setup for navigation, additional intervention table movement would be possible with such a transmitter map. References [1] K.G. Torrington, J.D. Kern, The utility of fiberoptic bronchoscopy in the evaluation of the solitary pulmonary nodule, Chest 104 (4) (1993) 1021 – 1024. [2] C.S. White, et al., Transbronchial needle aspiration: guidance with CT fluoroscopy, Chest 118 (6) (2000) 1630 – 1638. [3] U. Wagner, et al., Computer-tomographically guided fiberbronchoscopic transbronchial biopsy of small pulmonary lesions: a feasibility study, Respiration 63 (3) (1996) 181 – 186. [4] D.D. Frantz, et al., Accuracy assessment protocols for electromagnetic tracking systems, Physics in Medicine and Biology 48 (14) (2003) 2241 – 2251. [5] S.B. Solomon, et al., Three-dimensional CT-guided bronchoscopy with a real-time electromagnetic position sensor: a comparison of two image registration methods, Chest 118 (6) (2000) 1783 – 1787.
www.ics-elsevier.com
Real-time image tracking of a flexible bronchoscope A. Schneider a,*, H. Hautmann b, H. Barfuss c, T. Pinkau b, F. Peltz b, H. Feussner a,d, A. Wichert a a
Workgroup MITI, Klinikum r. d. Isar, Technical University Munich, Troger Str. 26, 81675 Munich, Germany b Pneumology, 1st Medical Department, Klinikum r. d. Isar, Technical University Munich, 81675 Munich, Germany c Siemens Medical Solutions SPI, Erlangen, Germany d Surgical Department, Klinikum r. d. Isar, Technical University Munich, 81675 Munich, Germany
Abstract. Electromagnetical tracking devices have become so small, that tracking of flexible instruments is possible. Because of the low diagnostic yield of flexible bronchoscopy, we assembled and evaluated a system for navigation of the bronchoscopes tip. In order to evaluate the exactness of the electromagnetical tracking system in a preoperative CT-Scan, 16 patients underwent diagnostic flexible bronchoscopy with fluoroscopic guidance. Deviation was measured and computed. D 2004 Published by Elsevier B.V. Keywords: 3-D imaging; Diagnostic imaging; Bronchoscopy; Stereotaxy; Image-guided; Virtual bronchoscopy; Navigation; Tracking
1. Introduction Image-directed bronchoscopy plays a major role in evaluating peripheral localized pulmonary lesions since they cannot directly be visualized. Histopathological, cytological or microbiological assessment is essential in order to initiate adequate therapy. Different studies showed that the diagnostic yield of successful flexible bronchoscopy is between 18% and 62% [1]. Normally, it is performed under X-ray imaging (a.k.a. fluoroscopy) that provides no depth perception, does not depict the anatomy of the bronchial tree and is even hardly able to discern the target. One way to improve the diagnostic accuracy was the utilization of CT-guided bronchoscopic interventions [2]. However, the limited availability, costs and the additional radiation exposure are the drawbacks of this application [3]. * Corresponding author. Tel.: +49-89-4140-7385; fax: +49-89-4140-7393. E-mail address: [email protected] (A. Schneider). 0531-5131/ D 2004 Published by Elsevier B.V. doi:10.1016/j.ics.2004.03.278
754
A. Schneider et al. / International Congress Series 1268 (2004) 753–757
Navigation is a widely accepted additional aid to guide instruments in fields like neurosurgery, orthopaedic surgery and ear – nose and throat surgery here, rigid instruments, which make optical tracking possible, are used. Electromagnetical tracking systems have now reached a level of miniaturization and sophistication in recent years where the positions and orientations of small sensors within the body can be determined with accuracies having clinical relevance [4]. Electromagnetical guiding of transbronchial catheters or biopsy forceps is a novel method to increase the diagnostic yield [5]. This method can indicate the position of an instrument in real-time as well in three dimensions in a preprocedure CT- or MR dataset. We validated the electromagnetic tracking system generated position in a clinical setting with fluoroscopy. 2. Methods In order to evaluate the exactness of an electromagnetical tracking device in a preoperative CT-Scan, 16 patients underwent diagnostic flexible bronchoscopy with fluoroscopic guidance. Selection criteria were findings, which necessitated the use of fluoroscopy to guide biopsy forceps or transbronchial needle aspiration (TBNA). Preoperative spiral CT-Scans were acquired within 7 days before intervention. Standard protocols were used, in order to get usual diagnostic quality (120 kVp, 120 mAs, pitch 1.3, collimation 0.75 mm and a reconstruction of 5 mm). For navigation and reading the data from the electromagnetical tracker, an enhanced syngoR (Siemens Medical Solutions, Erlangen, Germany) workstation was used. We integrated two special navigation tab cards, one for the registration procedure, the other for real-time visualization of the instrument tip in the preoperative CT data. The electromagnetical tracker was a pre-production model AuroraR (Northern Digital, Waterloo, Ontario, Canada). This tracker is able to determine with the minimized sensor five degrees of freedom in a volume of 500 500 500 mm. Size of the Sensor coil integrated in a steralizeable catheter is 8.0 0.8 mm. The field generator (transmitter) dimensions are 220 220 170 mm. Inside the transmitter a pulsed DC electromagnetic field with a special symmetric setup of nine coils is generated. Data processing and delivering to the workstation is done by the system control unit (SCU) outside the intervention field. The connection to the workstation was done by a serial connection with 38400 baud. To exclude tracking errors because of other magnetic and electromagnetic parts in the room, prior to the study an accuracy measurement with a special measurement plate was done. This measurement plate allowed us to measure points all two centimetres in all three planes. With that measurement we were able to exclude distorsions of the magnetical field. In the intervention room we placed the field generator left beside the patient in high of the thorax as shown in Fig. 1 below. Patient data was transferred by standardized DICOM transfer from the CT console to the navigation workstation. A rigid registration procedure was done to match CT data with the patient in the tracking field. This was done by an identification of N equivalent pairs of corresponding points pi and piV in the tomographic images and the tracker space. Mathematically three
A. Schneider et al. / International Congress Series 1268 (2004) 753–757
755
Fig. 1. System setup in the intervention room.
pairs of points are enough for registration, for increased precision a minimum of four pairs of corresponding points were required. We used the proximal rim of the manubrium sterni and the distal end of the xiphoid as external landmarks. In preliminary experiments, exactness for navigation in the bronchoscopic tree was increased by an additional using of internal landmarks. Here we used the main carina and the right upper lobe carina, these are simply visible and reachable with the bronchoscope and in the CT-slices. Accuracy before the intervention was controlled by re-hitting the endobronchial marker points. If the error distance of one marker point exceeded 5 mm re-registration of that point was performed. After that procedure, navigation of the instrument tip (bronchoscope tip) in the preoperative was performed. The syngo workstation provided on a special tab card a crosshair in a sagital, coronal and transversal view, which showed the head of the navigation sensor. Additional a free multiplanar reconstruction (free MPR) image was integrated, which was equal to the view of the bronchoscope (Fig. 2). Testing for exactness was done by introducing and advancing the sensor into to the bronchial orifice, it lead most likely to the lesion as determined from a review of the preliminary diagnostic CT scan. When the sensor missed the lesion, it was repositioned until the tip of the sensor reached or penetrated the lesion on the computer display of the navigation system. In SPN’s, the position of the sensor was controlled by fluoroscopy in a posterior –anterior view. Then the distance from the margin of the nodule to the tip of the sensor was measured. In a second step the sensor was inserted into the upper lobe ipsilateral of the lesion and under control of the computer screen subsequently forwarded until it came to a stop at the most lateral position. An additional spot of interest was the most apical position of the upper lobe. These positions were each considered the visceral pleura, representing the inner lining of the thoracic wall. By means of fluoroscopy it was then verified whether the sensor tip was actually adjacent to the inner lining of the thoracic wall. On the computer display the distance between the crosshair, representing the sensor tip, and the visceral
756
A. Schneider et al. / International Congress Series 1268 (2004) 753–757
Fig. 2. Navigation tabcard in the syngo workstation: on the main window the free MPR, right hand side sagital coronal and transversal view.
Fig. 3. Error distances between sensor tip and reference position.
A. Schneider et al. / International Congress Series 1268 (2004) 753–757
757
pleura was measured. Subsequently, the sensor tip was again positioned on landmark 3 (main carina) to determine whether the error distance has been altered during the course of the procedure. 3. Results No complications occurred during bronchoscopy. All lesion were clearly identified on the computer screen, also the sensor tip, shown as yellow crosshair, was clearly visible. In two cases the volume which allows navigation did not cover the whole hemithorax. In this case the field transmitter was repositioned and a new registration procedure was performed. Rigid registration was done in 4.4 F 1.9 min (mean F S.D.). In the five patients with SPN’s the sensor tip penetrated the nodule in three cases. In the remaining cases the tip came close to the periphery. The resulting error distances are displayed in Fig. 3. The average diameter of the nodules was 22 F 6 mm (mean F S.D.) with a maximum distance to the pleura of 23 mm. In two cases of penetration the position of the sensor tip in relation to the nodule was verified by fluoroscopy. In three cases the nodule could not be clearly identified by fluoroscopy. When the sensor tip was forwarded to the lateral and apical thoracic wall, fluoroscopy could verify the pleural position of the sensor tip in all cases. 4. Conclusion With the help of the navigation system all infiltrations were clearly localized by the sensor. It was still possible to direct the sensor in the center of that specific infiltrate, even when it was not possible to identify the infiltrate by fluoroscopy. Electromagnetic flexible navigation is a possible method to increase the diagnostic yield in bronchoscopy. Use of the electromagnetical tracking unit is simple and after a measurement to exclude distorsions of the electromagnetic field a method with a sufficient exactness. New instruments, i.e. biopsy forceps with an integrated navigation sensor, are necessary to have the whole benefit of navigation. Another transmitter shape, for example a mat which could be positioned under the patient, could ease the setup for navigation, additional intervention table movement would be possible with such a transmitter map. References [1] K.G. Torrington, J.D. Kern, The utility of fiberoptic bronchoscopy in the evaluation of the solitary pulmonary nodule, Chest 104 (4) (1993) 1021 – 1024. [2] C.S. White, et al., Transbronchial needle aspiration: guidance with CT fluoroscopy, Chest 118 (6) (2000) 1630 – 1638. [3] U. Wagner, et al., Computer-tomographically guided fiberbronchoscopic transbronchial biopsy of small pulmonary lesions: a feasibility study, Respiration 63 (3) (1996) 181 – 186. [4] D.D. Frantz, et al., Accuracy assessment protocols for electromagnetic tracking systems, Physics in Medicine and Biology 48 (14) (2003) 2241 – 2251. [5] S.B. Solomon, et al., Three-dimensional CT-guided bronchoscopy with a real-time electromagnetic position sensor: a comparison of two image registration methods, Chest 118 (6) (2000) 1783 – 1787.