Influence of labeling parameters and respiratory motion on velocity‐selective arterial spin labeling for renal perfusion imaging

Abstract

Purpose Arterial transit time uncertainties and challenges during planning are potential issues for renal perfusion measurement using spatially selective arterial spin labeling techniques. To mitigate these potential issues, a spatially non‐selective technique, such as velocity‐selective arterial spin labeling (VSASL), could be an alternative. This article explores the influence of VSASL sequence parameters and respiratory induced motion on VS‐label generation. Methods VSASL data were acquired in human subjects ( n = 15), with both single and dual labeling, during paced‐breathing, while essential sequence parameters were systematically varied; (1) cutoff velocity, (2) labeling gradient orientation and (3) post‐labeling delay (PLD). Pseudo‐continuous ASL was acquired as a spatially selective reference. In an additional free‐breathing single VSASL experiment ( n = 9) we investigated respiratory motion influence on VS‐labeling. Absolute renal blood flow (RBF), perfusion weighted signal (PWS), and temporal signal‐to‐noise ratio (tSNR) were determined. Results (1) With decreasing cutoff velocity, tSNR and PWS increased. However, undesired tissue labeling occurred at low cutoff velocities (≤ 5.4 cm/s). (2) Labeling gradient orientation had little effect on tSNR and PWS. (3) For single VSASL high signal appeared in the kidney pedicle at PLD < 800 ms, and tSNR and PWS decreased with increasing PLD. For dual VSASL, maximum tSNR occurred at PLD = 1200 ms. Average cortical RBF measured with dual VSASL (264 ± 34 mL/min/100 g) at a cutoff velocity of 5.4 cm/s, and feet‐head labeling was slightly lower than with pseudo‐continuous ASL (283 ± 55 mL/min/100 g). Conclusion With well‐chosen sequence parameters, tissue labeling induced by respiratory motion can be minimized, allowing to obtain good quality RBF maps using planning‐free labeling with dual VSASL.

Multi‐organ comparison of flow‐based arterial spin labeling techniques: Spatially non‐selective labeling for cerebral and renal perfusion imaging

“…First of all, during the paced-breathing condition subjects were asked to shortly hold their breath during the image acquisition, but not necessarily during labeling. However, effects are expected to be small because a cut-off velocity (5 cm/s) was chosen to prevent subtraction artefacts because of respiratory motion, and our results indeed did not show the typical high intensity subtraction artefacts as described by Bones et al 5 In addition, VSASL-and AccASL-labeling have been shown to depend on the cardiac cycle. 36 Effects are expected to average out when using a sufficient number of averages, but will still lower tSNR-values.…”

“…Image acquisition was planned in coronal–oblique orientation, parallel to the muscles anterior to the kidney, to minimize through‐slice motion. Optimal scan parameters for renal imaging were not known for all flow‐based ASL techniques, so they were chosen partly based on previous research 5,23,24 and partly on preliminary experiments (Table 1). The durations of the VSS‐ and ASS‐labeling modules were set to 50 ms, and gradient orientation to the slice direction, that is, anterior–posterior (AP) direction, to minimize effects of respiratory motion on labeling 5 .…”

“…The durations of the VSS-and ASS-labeling modules were set to 50 ms, and gradient orientation to the slice direction, that is, anterior-posterior (AP) direction, to minimize effects of respiratory motion on labeling. 5 FAIR was implemented as described in Harteveld et al, 24 including Q2TIPS, 25 which was placed anterior to the imaging acquisition with a 10-mm gap ( Table 1).…”

“…Flow-based ASL techniques create label also within the ROI, making them less sensitive to transit delays. [2][3][4][5] Reduced sensitivity to transit delays is especially valuable in cases where blood flow is slow, for example, in elderly 6 patients with MoyaMoya disease 2,3,7 or in patients with renal artery stenosis. 8,9 Moreover, flow-based ASL techniques do not require planning of a spatial labeling volume, making it easier and more time efficient to apply in practice.…”

“…Recently, a number of flow‐based ASL techniques have been introduced where blood is labeled based on its flow velocity or acceleration instead of spatial location. Flow‐based ASL techniques create label also within the ROI, making them less sensitive to transit delays 2‐5 . Reduced sensitivity to transit delays is especially valuable in cases where blood flow is slow, for example, in elderly 6 patients with MoyaMoya disease 2,3,7 or in patients with renal artery stenosis 8,9 …”