Inhance (Inflow Inversion Recovery) Non-contrast Renal MRA: Comparison with 3D Gadolinium Enhanced MRA in Clinical Patients

Purpose: Contrast-enhanced MR Angiography (CE-MRA) is a widely accepted technique for evaluation of the renal arteries; however, recent concerns regarding the development of nephrogenic systemic fibrosis (NSF) after gadolinium contrast agent administration in patients with reduced renal function have emphasized the need for robust non-contrast MRA methods. One such technique is steady state free precession with in-flow inversion recovery (Inhance). We performed both Inhance MRA and 3D CE MRA in 24 patients referred for renal or abdominal MRA and evaluated Inhance images for accuracy in detection of renal artery stenosis as well as image quality and artifacts. Methods: Inhance is a respiratory-triggered 3D steady state free precession sequence in which high arterial signal intensity is achieved via inflow effect during the inversion time of a slab inversion pulse (IR). The IR pulse suppresses static tissue and inflowing venous blood and is applied to the imaging volume and a variable volume inferior to the imaging slab. An axial volume was acquired with the following parameters: TR/TE 4.0/2.0 msec, TI 200 msec, flip angle 70, receiver bandwidth 125kHz, FOV 30-42 cm, section thickness 2 mm, 56 views, imaging matrix 256x256, with parallel imaging acceleration factor 2, spectral spatial saturation pulse, and respiratory triggering. 3D CE MRA was performed in a coronal oblique plane with the following parameters: TR/TE 3.4/1.6ms, flip angle 30, receiver bandwidth 83 kHz, FOV 26-30cm, section thickness 1.6mm, 42 views, matrix 256x224. 0.1 mM/kg gadolinium contrast was injected at 3 ml/s, with the scan delay determined by a test bolus. 24 patients referred for renal or abdominal MRA had both Inhance and 3D CE MRA performed. Inhance images were evaluated independently by two readers who assessed each renal artery for the presence or absence of significant (>50%) stenosis. Two separate readers in consensus graded the CE MRA images in a similar fashion, and also qualitatively assessed visualization of proximal and distal main renal arteries, intrarenal arteries, and accessory arteries in the Inhance and CE MRA sequences using a 5 point scale (1 = uninterpretable, 5 = perfect image). Results: Inhance images were judged interpretable in all cases by one reader and in 23/24 cases by the second reader. CE MRA revealed significant (>50%) stenosis in 11/54 renal arteries. Sensitivity and specificity for detection of significant (>50%) renal artery stenosis for the two readers versus CE MRA are listed in Table 1. Reader 1 detected 52/54 renal arteries; reader 2 did not evaluate 9 accessory renal arteries, which reduced his sensitivity relative to reader 1. Two accessory arteries were not detected by reader 1: these were not included in the Inhance FOV, and one of these had a severe stenosis. Examples of Inhance and conventional CE MRA images in a patient with significant renal artery stenosis are shown in Fig. 1. Fig. 2 shows ratings of image quality for proximal and distal main renal arteries, intrarenal branches, and accessory arteries.