Tripled Readout Slices in Multi Time-Point pCASL Using Multiband Look-Locker EPI

Abstract

Multi time-point pseudo-continuous arterial spin labelling (pCASL) with a Look-Locker EPI readout can sample the signal curve of blood kinetics at multiple time points after the labelling pulse. However, due to signal relaxation of labelled blood, the number of readout slices is limited. The aim of this study is to employ a multiband excitation technique to triple the number of readout slices in multi time-point pCASL. The multiband technique, along with 2-fold in-plane parallel imaging, was incorporated into the Look-Locker EPI for the multi time-point sampling of blood kinetic behaviour following the pCASL labelling scheme. The performance evaluation of the multiband and the single-band techniques were performed on four healthy subjects using a 32-channel head RF coil at 3T. Quantitative perfusion maps were analysed using a combination of labelling with and without flow suppression gradients. The perfusion maps provided by the multiband accelerated multi time-point pCASL were in good agreement with the conventional single-band technique. Multiband acceleration caused SNR loss but offered quantitative perfusion maps in 6.23 min with 18 slices compared with 6 slices within the same time period for the single-band method. As conclusion, the multiband technique can successfully triple the number of readout slices while achieving comparable perfusion data in the same measurement time as the conventional single-band readout.

High temporal resolution arterial spin labeling MRI with whole‐brain coverage by combining time‐encoding with Look‐Locker and simultaneous multi‐slice imaging

“…By employing an LL readout, 4 images were acquired for each Hadamard line at an interval of 150 ms, providing the second source of temporal information within this sequence (Figure ). One of the major advantages of this readout, in combination with the te‐pCASL labeling scheme, is that it provides an interpolation of the temporal encoding by te‐pCASL by acquiring 4 differently timed images for each Hadamard labeling block . To maintain a constant signal over the 4 LL readouts, a flip‐angle sweep of 30°, 35°, 45°, and 90° was applied.…”

“…To obtain whole‐brain coverage within the short LL interval of 150 ms, an SMS acquisition was applied; a parallel imaging method that excites multiple slices simultaneously with multi‐banded radiofrequency (RF) pulses, which allows for a narrower readout time window while keeping whole‐brain coverage . In this study, 4 slices were excited simultaneously, which led to a total coverage of 16 slices.…”

“…A Hadamard, also known as time‐encoded (te), labeling scheme was combined with a Look‐Locker (LL) readout to achieve a high temporal resolution of 75 ms during passage of the label through the vasculature (i.e., the angiography phase) and 150 ms during the perfusion phase. Because of this very dense sampling of the dynamic ASL signal, coverage of an LL readout would normally be limited to 5 to 7 slices . Since the recent introduction of simultaneous multi‐slice (SMS; i.e., multiband) acquisition, new opportunities were provided to maintain whole‐brain coverage in the short LL readouts by exciting multiple slices simultaneously.…”

A framework for motion correction of background suppressed arterial spin labeling perfusion images acquired with simultaneous multi‐slice EPI

“…Whereas for FMRI and DTI, the prime advantage of SMS‐EPI is the acceleration of the acquisition by shortening TR, for arterial spin labeling (ASL) this is much less beneficial because the preparation module for labeling and post‐labeling delay (PLD) is the main time‐consuming part of the sequence and not the readout. For measurement of tracer kinetics using multi time‐point ASL, however, SMS allows the number of slices to be increased within a limited acquisition window to achieve whole‐brain coverage . Another advantage of SMS for 2D‐multislice‐ASL is smaller variation of the level of background suppression (BGS) and PLD over the acquired slices.…”

Assessment of hypertensive cerebrovascular alterations with multiband Look–Locker arterial spin labeling

“…With this technique, however, it is difficult to achieve the short time interval between two consecutive TI measurements that is necessary for the accurate analysis of ASL temporal dynamics when a whole brain volume with a sufficient resolution is required. Recently, the simultaneous multislice imaging technique with multiband (MB) excitation was combined with LL pseudocontinuous ASL (pCASL) for whole‐brain quantitative perfusion measurement . Despite the improved temporal resolution, deploying this technique to quantify multiple parameters on ASL dynamics, especially observation of arterial blood signal, was limited due to the long labeling duration of pCASL.…”