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A temporal calibration method for freehand 3D ultrasound system: a preliminary result
International Congress Series 1256 (2003) 1365
A temporal calibration method for freehand 3D ultrasound system: a preliminary result Masahiko Nakamoto a,*,Yoshinobu Sato a, Kazuhisa Nakadaa, Yoshikazu Nakajima a, Kozo Konishi b, Makoto Hashizume b, Sinichi Tamura a a
Division of Interdisciplinary Image Analysis, Graduate School of Medicine, Osaka University, Suita Osaka 565-0871, Japan b Department of Disaster and Emergency Medicine, Graduate School of Medicine, Kyushu University, Japan Received 16 March 2003; received in revised form 16 March 2003; accepted 21 March 2003
In freehand 3D ultrasound (3D-US) system, the latency between acquisition of a US image and tracking a US probe causes misregistration of the reconstructed 3D-US volume with the real world. In previous works, several temporal calibration methods have been developed. However, there are several problems. Jacobs et al. [1] pointed out the need for managing latency, but calibration methods were not formulated. Prager et al.’s method [2] was considered to be inaccurate and unreliable, since a latency was estimated by a single measurement. In addition, quantitative evaluations were not performed in both of the above studies, thus, accuracy and effectiveness of the calibration were not clarified. The objectives of this paper are the development of a more accurate temporal calibration method and quantitative evaluation for the proposed temporal calibration. In our method, the latency is estimated by least squares, which makes the estimation more accurate and reliable. We demonstrate the effectiveness of the proposed method by experiments. Temporal calibration is the process of obtaining the constant latency between acquisition of a US image and measurement position and orientation of a US probe. The calibration is performed as the following steps: (1) Holding a US probe stationary at the location of a sampling point being imaged, 3D position of the point, p, is calculated from a 2D position on the US image and the tracker readings of the US probe. (2) Sweeping the US probe, US images imaging the sampling point and tracker readings corresponding to them are recorded. Adding the latency to tracker readings time-stamp, position and orientation of a US image is calculated by linearly interpolated tracker readings. Therefore, the 3D position of the sampling point in sweeping condition, qi, is calculated for each i-th US image. (3) Minimizing the squared sum of the difference between p and qi using the least squares, the latency can be obtained. We compared the proposed method with the conventional method, which was that image acquisition and tracking were performed sequentially without the latency correction. As a result, the average of errors were 1.9 and 2.9 mm by the proposed and conventional methods, respectively. We developed a method for a temporal calibration and performed experiments to evaluate the calibration quantitatively, which have not been performed in the previous studies. Experimental results showed that the proposed method was effective. This work was partly supported by JSPS Research for the Future Program, JSPS-RFTF99I00903, and JSPS Grant-in-Aid for Scientific Research (B)(2) 12558033. References [1] M.C. Jacobs, et al., Managing latency in complex augmented reality systems, Proceedings of 1997 Symposium on Interactive 3D Graphics, 1997, pp. 49 – 54. [2] R.W. Prager, et al., Stradx: real-time acquisition and visualisation of freehand 3D ultrasound, Medical Image Analysis 3 (2) (1999) 129 – 140. * Corresponding author. Tel.: +81-6-6879-3564; fax: +81-6-6879-3569. E-mail address: [email protected] (M. Nakamoto). 0531-5131/03 D 2003 Published by Elsevier Science B.V. doi:10.1016/S0531-5131(03)00327-3
A temporal calibration method for freehand 3D ultrasound system: a preliminary result Masahiko Nakamoto a,*,Yoshinobu Sato a, Kazuhisa Nakadaa, Yoshikazu Nakajima a, Kozo Konishi b, Makoto Hashizume b, Sinichi Tamura a a
Division of Interdisciplinary Image Analysis, Graduate School of Medicine, Osaka University, Suita Osaka 565-0871, Japan b Department of Disaster and Emergency Medicine, Graduate School of Medicine, Kyushu University, Japan Received 16 March 2003; received in revised form 16 March 2003; accepted 21 March 2003
In freehand 3D ultrasound (3D-US) system, the latency between acquisition of a US image and tracking a US probe causes misregistration of the reconstructed 3D-US volume with the real world. In previous works, several temporal calibration methods have been developed. However, there are several problems. Jacobs et al. [1] pointed out the need for managing latency, but calibration methods were not formulated. Prager et al.’s method [2] was considered to be inaccurate and unreliable, since a latency was estimated by a single measurement. In addition, quantitative evaluations were not performed in both of the above studies, thus, accuracy and effectiveness of the calibration were not clarified. The objectives of this paper are the development of a more accurate temporal calibration method and quantitative evaluation for the proposed temporal calibration. In our method, the latency is estimated by least squares, which makes the estimation more accurate and reliable. We demonstrate the effectiveness of the proposed method by experiments. Temporal calibration is the process of obtaining the constant latency between acquisition of a US image and measurement position and orientation of a US probe. The calibration is performed as the following steps: (1) Holding a US probe stationary at the location of a sampling point being imaged, 3D position of the point, p, is calculated from a 2D position on the US image and the tracker readings of the US probe. (2) Sweeping the US probe, US images imaging the sampling point and tracker readings corresponding to them are recorded. Adding the latency to tracker readings time-stamp, position and orientation of a US image is calculated by linearly interpolated tracker readings. Therefore, the 3D position of the sampling point in sweeping condition, qi, is calculated for each i-th US image. (3) Minimizing the squared sum of the difference between p and qi using the least squares, the latency can be obtained. We compared the proposed method with the conventional method, which was that image acquisition and tracking were performed sequentially without the latency correction. As a result, the average of errors were 1.9 and 2.9 mm by the proposed and conventional methods, respectively. We developed a method for a temporal calibration and performed experiments to evaluate the calibration quantitatively, which have not been performed in the previous studies. Experimental results showed that the proposed method was effective. This work was partly supported by JSPS Research for the Future Program, JSPS-RFTF99I00903, and JSPS Grant-in-Aid for Scientific Research (B)(2) 12558033. References [1] M.C. Jacobs, et al., Managing latency in complex augmented reality systems, Proceedings of 1997 Symposium on Interactive 3D Graphics, 1997, pp. 49 – 54. [2] R.W. Prager, et al., Stradx: real-time acquisition and visualisation of freehand 3D ultrasound, Medical Image Analysis 3 (2) (1999) 129 – 140. * Corresponding author. Tel.: +81-6-6879-3564; fax: +81-6-6879-3569. E-mail address: [email protected] (M. Nakamoto). 0531-5131/03 D 2003 Published by Elsevier Science B.V. doi:10.1016/S0531-5131(03)00327-3