Detectibility of renal artery under high resolution MR angiography using steady state free precession sequence in Phantom study

Purpose: A balanced steady state free precession (b-SSFP) sequence is very effective in clinical examination for renal MR angiography (MRA) without a contrast medium. Generally, in image evaluation, the increase in spatial resolution causes decrease in SNR. Therefore, we investigated the performance of b-SSFP in the relation between SNR and matrix. Materials and Methods: A phantom consisting of 31 bottles of Gd-DTPA (Schering AG, Germany), from 0 to 50 mmol/L (mM), was used. The protocol of b-TFE was as follows: repetition time (TR) msec/echo time (TE) msec, 8.8/4.4; flip angle, 80 degrees. The combination of matrix and scan percentages were three types, 256 × 256 (100%), 256 × 512 (200%), and 256 × 1024 (400%). The contrast dynamic range (CDR) was measured from signal intensity of each Gd phantom. Ferucarbotran (Schering AG, Germany) solution of 0.33 mM was injected by 0.2 ml/sec to the inside of simulation vessel of 2 mm in diameter. The profile curve was drawn along the simulation vessel on maximum intensity projection (MIP) images. All images were acquired on 1.0 T MR system (Gyroscan Intera 1.0 T, Philips Medical Systems). Results and Discussions: The signal intensity increased as CDR became narrow. The increase was based on a noise, and was not change of tissue itself. Increasing the matrix did not influence the CDR and sensitivity. In the curve normalized on an inflow point, 1024 matrix of large CDR was higher than 256 matrix of small CDR. We thought that the increase in the noise causes deterioration of the quality of MIP images. Therefore, we consider that it is effective to decrease the noise by optimization of CDR. Conclusion: It is thought that b-SSFP covers the fault in the SNR of the high resolution MRA, and can utilize efficiently the high resolution capability, when the condition of CDR is optimized.