Synopsis

Keywords: High-Field MRI, Prostate

We made a three-channel endorectal coil for prostate imaging on the 5T magnetic resonance system and compared the imaging performance of the coils with the same structure on the 5T system and the 3T system. Prostate images at resolution of 0.78 mm × 0.78 mm × 2.5 mm were performed. In vivo prostate study shows that the endorectal coil works on the 5T system shows better image quality compared with the endorectal coil and surface coil array on the 3T system.

INTRODUCTION

The endorectal coil (ERC) has been shown to be effective in increasing signal-to-noise (SNR) in the prostate area for magnetic resonance imaging (MRI)^1,2. Increasing the strength of the magnetic field also works since the signal intensity is proportional to the static magnetic field. In previous work, we have made a three-channel ERC for a 3T magnetic resonance (MR) system³. In this study, we made an ERC essentially with the same structure as the former for prostate on the 5T system. A body coil was employed as the transmitter. We aimed to compare the performance of the ERC on 5T and 3T systems. In vivo studies were performed on a beagle with prostate cancer. As a comparison, the same imaging experiments were performed on the 3T system by a 12-channel surface coil array.

METHOD

The coil was formed by three loops wound side by side on a PVC structure (figure 1). The structural part is a cylinder with a diameter of 25 mm and a length of 5 cm, a part of which was cut off and formed a D-shaped section. The loops were decoupled by overlapping, as shown in figure 2. The coupling coefficients and reflection coefficients of the endorectal coils were tuned below -10 dB (figure 2). Of the in vivo studies, condoms were put on the endorectal coils and inserted into the rectum of the beagle. A fast- spin-echo (FSE) sequence with TR = 3154 ms, TE = 132.66 ms, FOV = 200 × 200 mm², matrix = 256 × 256, slice thickness = 2.5 mm, and NEX =1 was performed on 3T MRI scanner. (uMR 790, Shanghai United Imaging Healthcare, Shanghai, China). And the parameters were: TR = 3450 ms, TE = 118.4 ms, FOV = 200 × 200 mm2, matrix = 256 × 256, slice thickness = 2.5 mm, and NEX =1, when performed on 5T system (uMR Jupiter, Shanghai United Imaging Healthcare, Shanghai, China). As a comparison, a 12-channel surface coil array (Body Array Coil, Shanghai United Imaging Healthcare, Shanghai, China) was covered on the abdomen of the beagle for imaging.

RESULTS AND DISCUSSION

Of the in vivo study, anatomical images were acquired with endorectal coil and surface coil (figure 4). The bladder, prostate and tumor can be identified on all imaging. The image obtained by the ERC on 5T system is clearer and shows richer details than that obtained with surface coil as well as ERC on the 3T system. The coupling coefficients and reflection coefficients of coils are generally considered to be important factors affecting the image quality. The S-parameters of the ERC works on the 3T system (-15 dB) were much better than the ERC works on 5T system (-10 dB). Although the latter shows advantages in this study, we believe there is still room for improvement.

CONCLUSION

In this work, we made a three-channel endorectal coil and compared the imaging performance of the coil of this configuration on 5T and 3T systems. A surface coil array was employed as a comparison. Of the in vivo in a beagle, the coil works on the 5T system shows better image quality compared with the endorectal coil and surface coil array on the 3T system.

Acknowledgements

This work was supported in part by the National Key Scientific Instrument Development Project (Grant No. 81927807); National Key Research and Development Program of China, 2021YFE0204400; the Strategic Priority Research Program of Chinese Academy of Sciences, XDB25000000; National Natural Science Foundation of China, U22A20344; Youth Innovation Promotion Association of CAS No. Y2021098; Key Laboratory Project of Guangdong Province, 2020B1212060051; Shenzhen city grant, RCYX20200714114735123.