我們建立了一個一階電子式SQUID梯度計系統在屏蔽環境下去測量小動物的心臟磁場.此一階電子式梯度計系統是由二個高溫rf SQUID所組成.在屏蔽的環境下使用梯度計時仍有低頻的雜訊.所以我們用了回饋系統去消除此一外在雜訊.此動態補償方法是利用一個參考SQUID磁量計去測量在屏蔽屋內磁場然後給予一個反相磁場去消除屋內的雜訊磁場.而回饋線圈式纏繞在屏蔽屋內垂直方向.我們也利用一個低通濾波器其截止頻率在44Hz,一個高通濾波器其截止頻率在0.1Hz還有一個60Hz的帶拒濾波器.
做實驗時候,我們將小動物放在一個電腦控制的X-Y方向移動病床上,藉由電腦控制可以在二點之間快速且準確的移動.而在屏蔽屋的雜訊在1Hz以上約為1pT.所以在此一環境下我們可以呈現兔子的心臟磁場.我們也做了健康兔子以及高血酯兔子的二維空間心臟磁場圖.

ABSTRACT
We set up 1st-order electronic high-Tc SQUID gradiometer system to measure the magnetocardiography (MCG) of small animals in moderate magnetically shielded environment. The 1st-order gradiometer system consists of two high-Tc rf SQUID.
Because the low frequency noise is not reduced sufficiently by the magnetically shielded room or 1st-order gradiometer, therefore we use a feedback system to reduce the external noise level leaking into the shielded room. This is an active compensation technique for improving the performance of SQUID gradiometer in a μ-metal magnetically shielded room. Active compensation system is established by canceling the magnetic field inside the magnetically shielded room detected by the reference SQUID magnetometer. The reference sensor is used to feed a current through coils surrounding the room. The noise field inside the room is then eliminated. We used the active compensation for magnetic field in the vertical direction in the magnetically shielded room. We also used the low-pass filter with the cut off frequency at 44 Hz to filter out the high frequency noise, the high-pass filter with the cut off frequency at 0.1 Hz is used to suppress the low frequency fluctuation and the 60 Hz notch filter to reduce the power line interference.
In the experimental process, we mount the small animal on the X-Y translation bed which is controlled by a computer. In this way, we can move the test object between scanning points fast and locate the object accurately. The noise measured by the 1st-order gradiometer MCG system in the moderate magnetically shielded room was about 1 pT above 1 Hz. Therefore, we can perform MCG measurements of rabbits in the moderate shielded environment. A two dimensional MCG mapping of healthy and hypercholesterolemic rabbits were obtained. The results are discussed.

[1] R. M. Baule, R. McFee, Am. Heart J. 55, 95 (1963)
[2] D. Cohen, E. A. Edelsack, and J. E. Zimmeerman, Appl. Phys. Lett. 16, 278 (1970)
[3] J. Clarks, in SQUID Sensors：Fundamentals, Fabrication and Applications, NATO ASI series, edited by H. Weinstock (Kluwer Academic, Dordrecht),p.1 (1996)
[4] J. Vrba, in SQUID Sensors ：Fundamentals, Fabrication and Applications, NATO ASI series, edited by H. Weinstock (Kluwer Academic, Dordrecht), p.117 (1996)
[5] Dongfeng He and Y. Zhang, Physica C 282, 2481 (1997)
[6] Y. Zhang, G. panaitov, S. G. Wang, N. Wolters, R. Otto, J.schubert, W. Zander, H. –J. Krause, H. Soltner, H. Bousack, and A. I. Braginski, Applied Physics Letters, 76, 907 (2000)
[7] H. C. Yang, S. Y. Wang, J. T. Jeng, and J. H. Chen, IEEE Transactions On Applied Superconductivity. 13, 360 (2003)
[8] C. Guyton and J. E. Hall, “Human Physiology and Mechanisms of Disease”, 6th ed. W B Saunders, December 1 (1996)
[9] K. G. Beauchamp and C. K. Yuen, “Digital Methods For Signal Analysis”, George Allen & Unwin, November 7 (1979)
[10] H. J. M ter Brake, H. J. Wieringa and H. Rogalla, Meas. Sci. Technol. 2, 596 (1991)
[11] H. J. M ter Brake, R. Huonker and H. Rogalla, Meas. Sci. Technol. 4, 1370 (1993)
[12] D. Platzek, H. Nowak, F. Giessler, J. Rother, and M. Eiselt, Rev. of Sci. 70, 2465 (1999)
[13] A. Kandori, H. Kanzaki, K. Miyatake, S. Hashimoto, S. Itoh, N. Tanaka, T. Miyashita, and K. Tsukada, Med. Biol. Eng. Comput. 39, 21 (2001)