{"title":"Optimal Design of Selective Excitation Pulses in Magnetic Resonance Imaging using Genetic Algorithms","authors":"Mohammed A. Alolfe, Abou-Bakr M. Youssef, Yasser M. Kadah","volume":5,"journal":"International Journal of Biomedical and Biological Engineering","pagesStart":320,"pagesEnd":333,"ISSN":"1307-6892","URL":"https:\/\/publications.waset.org\/pdf\/12122","abstract":"
The proper design of RF pulses in magnetic resonance imaging (MRI) has a direct impact on the quality of acquired images, and is needed for many applications. Several techniques have been proposed to obtain the RF pulse envelope given the desired slice profile. Unfortunately, these techniques do not take into account the limitations of practical implementation such as limited amplitude resolution. Moreover, implementing constraints for special RF pulses on most techniques is not possible. In this work, we propose to develop an approach for designing optimal RF pulses under theoretically any constraints. The new technique will pose the RF pulse design problem as a combinatorial optimization problem and uses efficient techniques from this area such as genetic algorithms (GA) to solve this problem. In particular, an objective function will be proposed as the norm of the difference between the desired profile and the one obtained from solving the Bloch equations for the current RF pulse design values. The proposed approach will be verified using analytical solution based RF simulations and compared to previous methods such as Shinnar-Le Roux (SLR) method, and analysis, selected, and tested the options and parameters that control the Genetic Algorithm (GA) can significantly affect its performance to get the best improved results and compared to previous works in this field. The results show a significant improvement over conventional design techniques, select the best options and parameters for GA to get most improvement over the previous works, and suggest the practicality of using of the new technique for most important applications as slice selection for large flip angles, in the area of unconventional spatial encoding, and another clinical use.<\/p>\r\n","references":"[1] E.T. Jaynes, \"Matrix treatment of nuclear induction,\" Phys. Rev., vol.\r\n98, no. 4, pp. 1099-1105, May 1955.\r\n[2] A. N. Garroway, P. K. Grannell, and P. Mansfield, \"Image formation in\r\nNMR by a selective irradiative process,\" J. Phys. C, vol. 7, pp. L457-\r\nL462, 1974.\r\n[3] D. I. Hoult, \"The solution of the Bloch equations in the presence of a\r\nvarying B field-an approach to selective pulse analysis,\" J. Magn.\r\nReson., vol. 35, pp. 69-86, 1979.\r\n[4] Eliot T. Lebsack, Steven M. Wright, \"Iterative RF Pulse Refinement for\r\nMagnetic Resonance Imaging,\" IEEE Transactions on Biomedical\r\nEngineering, vol. 49, no.1, pp. 41-48,January 2002.\r\n[5] J. B. Weaver, Y. Xu, D. M. Healy, and J. R. Driscoll, \"Wavelet-encoded\r\nMR imaging,\" Magn. Reson. Med., vol. 24, pp. 275-287, 1992.\r\n[6] P. Mansfield, A. A. Maudsley, P. G. Morris, and I. L. Pykett, \"Selective\r\npulses in NMR imaging: A reply to criticism,\" J. Magn. Reson., vol. 33,\r\npp. 261-274, 1979.\r\n[7] P. R. Locher, \"Computer simulation of selective excitation in n.m.r.\r\nimaging,\" Phil. Trans. R. Soc. Lond., vol. B.289, pp. 537-542, 1980.\r\n[8] A. Caprihan, \"Effect of amplitude modulation on selective excitation in\r\nNMR imaging,\" IEEE Trans. Med. Imag., vol. MI-4, pp. 169-175, 1983.\r\n[9] M. S. Silver, R. I. Joseph, and D. I. Hoult, \"Highly selective \u00a4\u00c7\/2 and \u00a4\u00c7\r\npulse generation,\" J. Magn. Reson., vol. 59, pp. 347-351, 1984.\r\n[10] S. Conolly, D. Nishimura, and A. Macovski, \"Optimal control solutions\r\nto the magnetic resonance selective excitation problem,\" IEEE Trans.\r\nMed. Imag., vol. MI-2, pp. 106-115, 1986.\r\n[11] J. B. Murdoch, A. H. Lent, and M. K. Kritzer, \"Computer-optimized\r\nnarrowband pulses for multislice imaging,\" J. Magn. Reson., vol. 74, pp.\r\n226-263, 1987.\r\n[12] J. T. Ngo and P. G. Morris, \"General solution to the NMR excitation\r\nproblem for no interacting spins,\" Magn. Reson. Med., vol. 5, pp. 217-\r\n237, 1987.\r\n[13] J. Pauly, P. Le Roux, D. Nishimura, and A. Macovski, \"Parameter\r\nrelations for the Shinnar-Le Roux selective excitation pulse design\r\nalgorithm,\" IEEE Trans. Med. Imag., vol. 10, no. 1, pp. 53-65, March\r\n1991.\r\n[14] C.S. Burrus, et al, Computer-based Exercises for Signal Processing,\r\nPrentice Hall, New Jersey, 1994.\r\n[15] Y.M. Kadah and X. Hu, \"Pseudo-Fourier imaging: A technique for\r\nspatial encoding in MRI,\" IEEE Trans. Med. Imag., vol. 16, no. 6,\r\npp.893-902, Dec. 1997.\r\n[16] Randy L. Haupt, Sue Ellen Haupt, \"Practical Genetic Algorithm,\" John\r\nWiley & Sons, 2004.\r\n[17] Marek Obitko, \"Introduction to Genetic Algorithm,\" Gzech Technical\r\nUniversity.","publisher":"World Academy of Science, Engineering and Technology","index":"Open Science Index 5, 2007"}