To investigate clinical feasibility of free-breathing gadoxetic acid-enhanced liver MRI using incoherent undersampling in patients with transient dyspnea.In this IRB-approved prospective ongoing study, 17 patients (M:F =10:7, mean age 56.2 ± 13.1 years, range 25-73) have been enrolled and informed consent was obtained from all patients. Gadoxetic acid-enhanced liver MRI using golden-angle radial sparse parallel (GRASP) sequence was performed at 3T (1). A total of 10cc of saline was injected intravenously to check intravenous line patency at a rate of 1.5mL, then, a standard dose of gadoxetic acid (0.025mmol/kg) was intravenously injected at a rate of 1.5mL/sec, followed by 20mL of saline chaser. Precontrast T1-weighted image (T1WI), T1WI of saline injection phase (for 1-1.5 minutes, each) and post-contrast T1WI were obtained (for 3min 30sec). On post-contrast scan, consecutive 1204 spokes were continuously acquired. Imaging parameters were as follows: TR/TE = 3.4/1.5, flip angle =12º; FOV 450x450 mm2, imaging matrix = 256x256; slice thickness was 3-4mm with interpolation. Later, hepatobiliary phase was obtained 20 minutes after contrast media injection. For T1WI, Patients’ vital sign and respiratory motion were carefully monitored, and their breathing capacity was checked before contrast media injection. Postcontrast images were reconstructed by grouping 89 consecutive spokes and the time resolution was 13 seconds with or without respiratory gating (window, 0.5). The recorded respiratory pattern during post-contrast phase was compared with that of saline injection phase to identify patients with transient dyspnea. The images were analyzed by two radiologists in consensus regarding a) motion artifact; b) aliasing artifact; c) overall image quality of the arterial, portal venous and transitional phases on five-point scale, in all patients. Regarding with motion and aliasing artifacts, higher score indicates a significant artifact, and higher score of image quality indicates a better exam.

In 17 patients, the mean breathing capacity was 35.6 ± 17.1 seconds (range, 0, 60) and mean breathing cycle (inspiration to next inspiration) was 4.16 ± 1.56 seconds (range, 2.38, 8.61). On precontrast phase, two patients showed an irregular breathing pattern and the others showed a regular breathing pattern. During saline injection period, none of the patients showed transient irregular motion (Fig 1). However, transient motion was observed in 88.2% (15/17) of the patients on postcontrast phase (Fig 2). In fifteen patients with transient irregular breathing motion, the transient motion was observed right after contrast media injection, and the mean duration of the transient motion after gadoxetic acid injection was 33.8 ± 5.3 (range, 26.6, 43.7). Motion artifact substantially decreased after gating on arterial, portal and transitional phases (P=0.001) whereas aliasing artifact tended to increase after gating (Table 1). Overall image quality of gated GRASP reconstruction showed significantly better on late arterial and portal venous phases (Table 1, Fig 3). However, there was no significant difference of image quality on early arterial and transitional phases (P=0.22, 0.50, respectively). Our study results showed that the onset of transient dyspnea and its duration in patients who underwent gadoxetic acid-enhanced liver MRI. Given that common fixed delay of 15 seconds at gadoxetic acid-enhanced liver MRI (2), there might be high possibility of unwanted motion contamination on late arterial phase. Thus, a strategy might be needed to acquire an arterial phase with acceptable image quality timely and consistently.

Our study showed that incoherent undersampling using GRASP technique may play a role for obtaining arterial phase at gadoxetic acid-enhanced liver MRI consistently in all patients. Furthermore, late arterial phase and following portal venous phase image quality could be improved on gated GRASP reconstruction images.