High resolution continuous arterial spin labeling of human cerebral perfusion using a separate neck tagging RF coil

Abstract

For standard clinical applications, ASL images are typically acquired with 4–8 mm thick slices and 3–4 mm in-plane resolution. However, in this paper we demonstrate that high-resolution continuous arterial spin labeling (CASL) perfusion images can be acquired in a clinically relevant scan time using current MRI technology. CASL was implemented with a separate neck coil for labeling the arterial blood on a 4.7T MRI using standard axial 2D GE-EPI. Typical-resolution to high-resolution (voxels of 95, 60, 45, 27, or 7 mm 3 ) images were compared for qualitative and quantitative cerebral blood flow analysis (CBF) in nine healthy volunteers (ages: 24–32 years). The highest resolution (1.5x1.5x3 = 7 mm 3 ) CASL implementation yielded perfusion images with improved cortex depiction and increased cortical CBF measurements (53 ± 8 ml/100g/min), consistent with reduced partial volume averaging. The 7 mm 3 voxel images were acquired with 6 cm brain coverage in a clinically relevant scan of 6 minutes. Improved spatial resolution facilitates CBF measurement with reduced partial volume averaging and may be valuable for the detection of perfusion deficits in small lesions and perfusion measurement in small brain regions.

Sub-Millimetre Resolution Laminar Fmri Using Arterial Spin Labelling in Humans at 7 T

“…However, the B1 + inhomogeneities remain a major hurdle [33]. While We were able to mitigate this to some extent using dielectric pads [50,51], Future studies will be able to take advantage of advances in parallel transmission (pTx) technology [102] or the use of dedicated labelling-only RF-coils [103][104][105][106] to potentially further optimise highresolution ASL fMRI at ultra-high fields.…”

Clinical utility of arterial spin labeling imaging in disorders of the nervous system

“…CBF is then quantified and reported in physiological units of ml/100 g/min. 6,26,28 RF pulses can be applied in one of several methods: pulsed ASL (PASL), continuous ASL (CASL), and pseudocontinuous ASL (pCASL). In PASL, one short RF pulse is applied to a thick (15-20 cm) "slab" area of the neck for a duration of 10-20 msec to convert the arterial water spins; this approach is technically easier to implement but carries the disadvantages of a lower signal-to-noise ratio (SNR), lower delivery of labeled magnetization, and greater amount of T1 decay.…”

“…Given the potential advantages of ASL over other perfusion-based techniques, research is ongoing with efforts to increase image quality and ease of use. Mora Álvarez et al 28 obtained high-resolution images using a CASL technique by combining a separate neck coil to another coil used during RF excitation during a 6-minute scan time on 4.7-T MRI. The higher resolution was demonstrated in comparison to standard 2D and qualitative perfusion images in the same subjects; the method also showed superior perfusion visibility in small deep-brain structures.…”

“…This could have clinical relevance in detecting perfusion deficits in smaller areas of the brain, which are more likely to go undetected in lower-resolution techniques. 28,31,46 Another problem in ASL results from difficulties in predicting the optimum PLD; while multiphase PLD may respond to varying arterial flow rates, it is prone to lower SNR, making single-phase PLD the preferred method in clinical practice. However, this method can lead to inaccuracies in predicting peak flow rates, making image capture at the most appropriate time to maximize image quality difficult and necessitating imaging at multiple PLD patterns.…”

Laminar fMRI at ultra-high fields

“…Lastly, while high-resolution ASL at ultra-high field is possible using the standard commercial head-coil (NOVA Medical, USA), B1 + field inhomogeneity is a major hurdle. While we were able to mitigate this to some extent using dielectric pads, advances in parallel transmission (pTx) technology and use of dedicated labelling-only RF-coils [259][260][261][262] can potentially further optimise high-resolution ASL fMRI at ultra-high field. 140 5 General Discussion…”