Three-dimensional balanced SSFP (bSSFP) can provide high blood signal of arteries and veins by intrinsic T2/T1 effect; however, it would usually be difficult to depict a certain artery selectively. Time-spatial labeling inversion pulse (time-SLIP) is a non-contrast-enhanced MR angiography (MRA) technique, which provides selectively good quality MRA images from the aorta to the renal artery branches,¹ and showed as a promising technique for assessing the renal arterial stenosis.^2,3 However, an insufficient respiratory gating may degrade the image quality, and the depiction of inferior vena cava (IVC) would interfere an interpretation of renal arteries.

The purpose of this study is to develop a non-gated single breath-hold (about 20 sec) renal MRA using inflow bSSFP with a simple technique of signal suppression of IVC, and to evaluate the diagnostic ability of the proposed method compared with renal MRA using respiratory gated time-SLIP.

Institutional review board approval and informed consent were obtained. All MR examinations were performed using at a 1.5-T clinical imager (EXCELART VantageTM XGV PPP powered by Atlas, Toshiba, Japan), equipped with using an Atlas SPEEDER body and an Atlas SPEEDER spine coil. Thirteen healthy volunteers (11 male, 2 female, mean age: 27.6+/-6 y.o.) participated in this study. TECHNIQUES Figure 1 shows a typical example of slice slab plan. The slice slab of head side was tilted backward not to include the abdominal aorta above renal arteries in order to obtain higher signal of inflowing arterial blood. On the other hand, the slice slab of foot side was placed to include IVC as much as possible for the suppression of blood signal within IVC. Flip angle of bSSFP was optimized to 100 degree (maximum due to SAR), which gave higher signal of blood over renal parenchyma. The number of segmentation was optimized to 4, which gave high blood signal of inflowing abdominal aortic artery and renal artery with reduced IVC blood signal. Breath-hold MRA with 3D bSSFP was used with parameters as follows: TR=4.3 msec, TE =2.2 msec, section thickness of 2 mm (with ZIP interpolation), field of view=35 x 30 cm, matrix=256 x 208, parallel imaging factor=2.5, segment=4, flip angle=100 deg, and a total scan time of about 20 sec. Respiratory-gated time-SLIP with 3D bSSFP was used with parameters as follows: TR=5 msec, TE =2.5 msec, section thickness of 2 mm (with ZIP interpolation), field of view=35 x 30 cm, matrix=256 x 256, parallel imaging factor=2.5, segment=2, flip angle=120 deg, and a total scan time of about 5 min. CNR values of renal artery obtained by non-gated bSSFP and respiratory-gated time-SLIP were calculated with the CNR=(SIA–SIP)/SD formula (SIA: signal intensity of renal artery; SIP: signal intensity of renal parenchyma; SD: standard deviation of renal artery). The visualization of bilateral renal arteries and renal hilar arteries of bSSFP using MIP image was compared with those of time-SLIP using the 4-point scale as follows; grade 4, bSSFP is clearly superior to time-SLIP; grade 3, bSSFP is slightly superior to time-SLIP; grade 2, bSSFP is equal to time-SLIP; and grade 1, bSSFP is inferior to time-SLIP.Figure 2 shows CNR of bilateral renal arteries with bSSFP and time-SLIP. CNR of bSSFP was 2.8 almost equal to that of time-SLIP-MRA in 2.9. Figure 3 shows the comparison of the visualization of renal arteries and hilar arteries using these two methods. bSSFP showed almost equal visualization to that of time-SLIP in left renal artery and bilateral hilar arteries. However, the visualization right renal artery with bSSFP was superior to that of time-SLIP, because of considerable signal suppression of IVC in bSSFP. Figure 3 shows a typical case of MRA images of bSSFP and time-SLIP.The reason of IVC signal suppression in bSSFP is thought to be less IVC signal due to the slab tilting, as well as a greater number of segmentations and large flip angle in bSSFP parameters might decrease the signal of inflowing blood within IVC, which would contribute the improved visualization of right renal artery. In two cases, the image quality of distal hilar arteries in bSSFP was inferior because of less inflow blood flow during short data acquisition time of four segmentations. In one case the visualization of renal artery was inferior because of the breath-hold failure, which indicates that further reduction of the breath-hold acquisition time is required in clinical study.The single 20-second breath-hold renal MRA with 3D bSSFP provides good quality renal MRA with high SNR and sufficient suppression of IVC blood signal. The technique is simple, easy to apply to the renal artery examination in clinical practice.