Renal plasma flow (RPF) measured with multiple-inversion-time arterial spin labeling (ASL) and tracer kinetic analysis: Validation against a dynamic contrast-enhancement method

Abstract

Purpose-To propose and validate a method for accurately quantifying renal plasma flow (RPF) with arterial spin labeling (ASL).Materials and methods-The proposed method employs a tracer-kinetic approach and derives perfusion from the slope of the ASL difference signal sampled at multiple inversion-times (TIs). To validate the method's accuracy, we performed a HIPAA-compliant and IRB-approved study with 15 subjects (9 male, 6 female; age range 24-73) to compare RPF estimates obtained from ASL to those from a more established dynamic contrast-enhanced (DCE) MRI method. We also investigated the impact of TI-sampling density on the accuracy of estimated RPF.Results-Good agreement was found between ASL-and DCE-measured RPF, with a mean difference of 9 ± 30 ml/min and a correlation coefficient R = 0.92 when ASL signals were acquired at 16 TIs and a mean difference of 9 ± 57 ml/min and R = 0.81 when ASL signals were acquired at 5 TIs. RPF estimated from ASL signals acquired at only 2 TIs (400 and 1200 ms) showed a low correlation with DCE-measured values (R = 0.30). Conclusion-The proposed ASL method is capable of measuring RPF with an accuracy that is comparable to DCE MRI. At least 5 TIs are recommended for the ASL acquisition to ensure reliability of RPF measurements.

Motion-corrected multiparametric renal arterial spin labelling at 3 T: reproducibility and effect of vasodilator challenge

“…Our ASL values for cortical renal perfusion are in agreement with those obtained at 3 T using breath-hold multi-TI sequences: 151 ± 37 to 215 ± 65 ml/min/100 g [20,21], but even in healthy volunteers at this field strength single-TI values range between 229 ± 41 to 327 ± 63 ml/min/100 g [10,11,26]. This variation can be attributed to different acquisition schemes, kinetic models and study populations.…”

“…Previous work has relied on acquiring data at multiple inversion times during separate breath-holds at 3 T [20,21], or using prospective respiratory gating at 1.5 T [22,23]. The disadvantage of prospective gating is that it prolongs acquisition time unnecessarily if separation of respiratory phases is not required.…”

“…The disadvantage of prospective gating is that it prolongs acquisition time unnecessarily if separation of respiratory phases is not required. Alternatively, sequential breath-hold acquisitions may be up to 24 s [20], leading to a technical failure rate of approximately 8% [24,25]. Whilst affine registration can adjust for bulk motion [26], our non-linear elastic model may be more suited to the non-rigid motion typical of abdominal imaging and enabled a time-efficient free-breathing acquisition for multi-TI ASL.…”

“…The longer T 1 of tissues at high field strength also allows for longer postlabelling delays and therefore higher signal in PWI [27]. Previous studies using multiple post-labelling delays have demonstrated good correlation between ASL-derived parameters and dynamic contrast-enhancement (DCE) [20], although more modest agreement was observed with 99m Tc-MAG3…”

Functional Magnetic Resonance Imaging of the Kidneys—With and Without Gadolinium-Based Contrast

“…Cutajar et al 24 showed that for a group of healthy subjects, ASL-measured renal blood flow was comparable to contrast-enhanced measures (263±41 vs 287±70 ml/min/100g), and had better day-to-day reproducibility than the latter. Conlin et al 25 performed the comparison between ASL and the contrast-enhanced method in both healthy subjects and patients with estimated GFR 46–93 ml/min. The averaged difference between RPF measured by the two methods was 9 ml/min.…”