Analysis of Chemical Shift Artifacts Using the TSE Pulse Sequence and Bandwidth at MR Imaging
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In order to experimentally analyze the artifacts of the chemical shift of water and oil, we made a phantom by mixing water and oil to change the turbo spin-echo (TSE) pulse sequence and various bandwidth (BW) and parameters. A phantom made of water and canola oil was prepared, and an eight-channel head coil of MRI 1.5 T and 3.0 T was used. The scan parameters were TR (5069 ms), TE (100 ms), water fat shift (0.999 and 1.891 pix) at 1.5 T and TR (3000 ms), TE (100 ms), and water fat shift (3.836 pix) at 3.0 T. In all sequences, a matrix (256×256), field of view (FOV) (240 mm), and slice thickness were scanned at 3 mm; the frequency direction was RL (right-left), and the BW was calculated using the Philips ACR Bandwidth Calculator. The images were analyzed by obtaining the plot profile and the Fourier transform image. The signal-to-noise ratio (SNR), peak signal-to-noise ratio (PSNR), mean square error (MSE), root mean square error (RMSE), and maximum absolute error (MAE) were calculated to evaluate the images according to the 1.5 T and 3.0 T BWs of MR. In order to compare the image of chemical shift artifact, the layer of the chemical shift artifact was larger than that of 1.5 T of BW 114.9 Hz compared to 217.5 Hz, and at 3.0 T, 113.2 Hz compared to 218.1 Hz, and chemical shift artifact. The spatial frequency changes due to the Fourier transform were 1.5 T and 3.0 T. The reference image (BW 55.7 kHz) and the test image (BW 29.4 kHz) had the SNR of 7.753 dB, PSNR of 22.869 dB, RMSE of 26.808, and MAE of 7.758 in the 1.5 T MRI. The reference image (BW 55.9 kHz) and the test image (BW 29 kHz) had the SNR of 17.79 dB, PSNR of 34.062 dB, RMSE of 33.401, and MAE of 5.971 in the 3.0 T MRI. The SNR and PSNR were measured at 1.5 T and 3.0 T when the BW parameter was changed. At the 1.5 T and 3.0 T MRI, there was a statistically significant difference (p-value<.05). The chemical shift artifacts occurred in the phantom of water and oil, and the artifact was less at 1.5 T than at 3.0 T, and the artifact decreased as the BW increased. In order to reduce the chemical shift artifact in MRI, it is considered appropriate to decrease the intensity of the field and to broaden the BW.
Abstract
In order to experimentally analyze the artifacts of the chemical shift of water and oil, we made a phantom by mixing water and oil to change the turbo spin-echo (TSE) pulse sequence and various bandwidth (BW) and parameters. A phantom made of water and canola oil was prepared, and an eight-channel head coil of MRI 1.5 T and 3.0 T was used. The scan parameters were TR (5069 ms), TE (100 ms), water fat shift (0.999 and 1.891 pix) at 1.5 T and TR (3000 ms), TE (100 ms), and water fat shift (3.836 pix) at 3.0 T. In all sequences, a matrix (256×256), field of view (FOV) (240 mm), and slice thickness were scanned at 3 mm; the frequency direction was RL (right-left), and the BW was calculated using the Philips ACR Bandwidth Calculator. The images were analyzed by obtaining the plot profile and the Fourier transform image. The signal-to-noise ratio (SNR), peak signal-to-noise ratio (PSNR), mean square error (MSE), root mean square error (RMSE), and maximum absolute error (MAE) were calculated to evaluate the images according to the 1.5 T and 3.0 T BWs of MR. In order to compare the image of chemical shift artifact, the layer of the chemical shift artifact was larger than that of 1.5 T of BW 114.9 Hz compared to 217.5 Hz, and at 3.0 T, 113.2 Hz compared to 218.1 Hz, and chemical shift artifact. The spatial frequency changes due to the Fourier transform were 1.5 T and 3.0 T. The reference image (BW 55.7 kHz) and the test image (BW 29.4 kHz) had the SNR of 7.753 dB, PSNR of 22.869 dB, RMSE of 26.808, and MAE of 7.758 in the 1.5 T MRI. The reference image (BW 55.9 kHz) and the test image (BW 29 kHz) had the SNR of 17.79 dB, PSNR of 34.062 dB, RMSE of 33.401, and MAE of 5.971 in the 3.0 T MRI. The SNR and PSNR were measured at 1.5 T and 3.0 T when the BW parameter was changed. At the 1.5 T and 3.0 T MRI, there was a statistically significant difference (p-value<.05). The chemical shift artifacts occurred in the phantom of water and oil, and the artifact was less at 1.5 T than at 3.0 T, and the artifact decreased as the BW increased. In order to reduce the chemical shift artifact in MRI, it is considered appropriate to decrease the intensity of the field and to broaden the BW.
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