A study on change in the center frequency depending on the fat content and on change in the fat saturation image with the use of a self-manufactured phantom depending on the center frequency adjustment method in an MRI breast scan

Abstract

This study examined the changes in the center frequency according to the fat content the using a self-manufactured phantom. In addition, the change in the fat saturation image according to when the center frequency was applied automatically or adjusted manually was analyzed to determine the importance of a manual adjustment of the center frequency. Distilled water and animal fat were solidified in a 10-ml syringe to manufacture nine phantoms for each condition (18 in total). A MR scanner at 1.5 Tesla was used to obtain a T1-weighted three dimensional fast low-angle shot (T1 3D FLASH) dynamic fat saturation image according to the spectral attenuated inversion recovery(SPAIR) method. The images obtained were classified into the following before analyzing the center frequencies for each image: Test A (image where fat was not saturated), Test B (image where fat was saturated in an automatic adjustment of the center frequency), and Test C (image where fat was saturated in a manual adjustment of the center frequency). The signal intensity (SI) values of water, fat and background were measured to calculate the signal to noise ratio (SNR) before examining the difference in the SNRs of water and fat (SNR difference = water SNR — fat SNR). The mean center frequency in Tests A, B and C was 63.631179 MHz when the fat content was 70% or lower. The mean center frequency for Tests A and B was 63.631002 MHz when the fat content was 80% or higher, which was 226 Hz lower than that for Test C (63.631228 MHz). The water SIs of Tests A, B and C with increasing fat content showed a pattern of change similar to that of the fat SIs of Tests A and C. On the other hand, the fat SI of Test B was similar to that of Test A when the fat content was 80%, which showed a large difference in change. The water SNRs of Tests A, B and C, and the fat SNR and SNR differences of Tests A and C showed similar changes according to the fat content. The difference between the fat SNR and the SNR of Test B was similar to that of Test A when the fat content was 80%.