Phase aberration is one of the major causes of deterioration in the quality of medical acoustic imaging. To suppress the effect of aberration, we employ a focused transmit beam with a low center frequency for the calculation of an aberration correction value set. The aberration correction value set is applied to an imaging process utilizing high-frequency transmission. To evaluate the focus quality under severe aberration conditions, we introduce an evaluation criterion for beam patterns using the second moment of the acoustic field. The result implies that in severe aberration conditions without aberration correction, a low-frequency transmission acquires a better beam pattern, and the aberration correction value set for a high-frequency transmission should be calculated using a low-frequency transmission. (C) 2010 The Japan Society of Applied Physics