Nora-Josefin Breutigam¹, Federico von Samson-Himmelstjerna¹, and Matthias Günther^1
1MR Physics, Fraunhofer MEVIS, Bremen, Germany

A dynamic feedback algorithm to find the optimal free-lunch (FL) bolus-length in a multi-TI Hadamard-encoding scheme is presented. An estimated FL bolus-length is often not ideal for the examined subject. In arterial spin labeling (ASL) this frequently results in unwanted arterial transit-delay (ATD) artefacts. The proposed method allows approaching the optimal FL bolus-length individually by analyzing intermediate decoded perfusion-weighted images during a running MRI scan. The aim is to reduce the FL bolus-length as much as necessary, but to keep it as long as possible to yield maximal signal.

Thomas W. Okell^1
1FMRIB Centre, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom

A new golden angle radial arterial spin labeling acquisition method is proposed in which labeled blood water is continuously imaged as it passes through the large arteries and into the tissue.  Both angiographic and perfusion images can then be reconstructed from the same raw data set at any retrospectively chosen time points and temporal resolution.  This makes efficient use of the post-labeling delay dead time to provide a more complete assessment of blood flow into the brain, which may be of use in a variety of cerebrovascular diseases.

Xingxing Zhang¹, Carson Ingo¹, and Matthias J.P. van Osch^1,2
1C. J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, Netherlands, ²Leiden Institute for Brain and Cognition, Leiden, Netherlands

ASL-prepared IVIM is proposed to study the arterial IVIM signal as a function of post-labeling-delay. The D*-value as calculated from ASL-IVIM decreases as a function of PLD, reaching a plateau for PLDs>2000ms. Signal from conventional IVIM shows an intermediate D*-value corresponding to the ASL-IVIM-signal for a PLD of ~1750ms indicating the IVIM signal does not only originate from the microvasculature, but also includes vascular signal. The alternative explanation of extravasation of labeled spins into the extravascular compartment seems unlikely, since the observed D* at these PLDs are still a factor 3~4 higher than the diffusion coefficient of the slow compartment.

Daniel Arteaga¹, Megan Strother¹, Taylor Davis¹, Carlos Faraco¹, Lori Jordan², Allison Scott¹, and Manus Donahue^1
1Radiology, Vanderbilt University, Nashville, TN, United States, ²Neurology, Vanderbilt University, Nashville, TN, United States

Non-invasive, hemodynamic markers are needed to better characterize stroke risk in patients with symptomatic intracranial (IC) stenosis. We developed and applied a planning-free vessel-encoded pseudo-continuous arterial spin labeling sequence in IC stenosis patients during room air and hypercapnia to examine the extent of geometrical changes in cerebral blood flow territories. IC stenosis patients demonstrated increased shifting relative to healthy controls; among IC stenosis patients, shifting was higher in those who experienced non-cardioembolic stroke within two-years. Shifting of cerebral blood flow territories may provide a novel marker of hemodynamic impairment and stroke risk.

Samantha Holdsworth¹, Audrey Fan¹, Marc Lebel², Zungho Zun³, Ajit Shankaranarayanan⁴, and Greg Zaharchuk^1
1Department of Radiology, Stanford University, Stanford, CA, United States, ²GE Healthcare, Calgary, Canada, ³George Washington University, Washington, DC, United States, ⁴GE Healthcare, Menlo Park, CA, United States

One promising approach to multi-delay ASL is to perform the labeling using a Hadamard-encoded method, which promises to improve the SNR efficiency compared with sequential multi-delay ASL.  In this study, we compared single-delay ASL, sequential multi-delay ASL, and Hadamard-encoded multi-delay ASL in normal subjects and in patients with cerebrovascular disease.  Consistent with theory, Hadamard-encoding had better SNR than sequential multi-delay ASL for measuring CBF and arterial transit delay.

Evita Wiegers¹, Kirsten Becker¹, Hanne Rooijackers², Cees Tack², Arend Heerschap¹, Bastiaan de Galan², and Marinette van der Graaf^1,3
1Radiology and Nuclear Medicine, Radboud umc, Nijmegen, Netherlands, ²Internal Medicine, Radboud umc, Nijmegen, Netherlands, ³Pediatrics, Radboud umc, Nijmegen, Netherlands

Hypoglycemia-induced changes in global and regional cerebral blood flow (CBF) were investigated in patients with type 1 diabetes (T1DM) and impaired (IAH) or normal awareness of hypoglycemia (NAH) and in healthy subjects. CBF-weighted images were acquired using pseudo-continuous arterial spin labeling MRI. Global CBF increased in response to hypoglycemia in T1DM IAH subjects, but not in T1DM NAH or in healthy controls. Hypoglycemia induced regional relative increases in CBF in the thalamus of both T1DM NAH and healthy controls, and in the frontal lobes of T1DM NAH, while no such increases were found in the T1DM IAH group.

Wenbo Li^1,2, Peiying Liu¹, Hanzhang Lu¹, John J. Strouse³, Peter C.M. van Zijl^1,2, and Qin Qin^1,2
1Radiology, Johns Hopkins University School of Medicine, Baltimore, MD, United States, ²F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States,³Division of Pediatric Hematology, Johns Hopkins University School of Medicine, Baltimore, MD, United States

The knowledge of arterial blood T1 is important to quantify cerebral blood flow with ASL or the inversion time for VASO experiments.  We used a fast blood T1 protocol to measure the arterial T1 values in the internal carotid artery in vivo. Ex-vivo experiments were conducted to validate our method. Excellent correlation and agreement was found between in vivo and ex vivo results. The group-averaged arterial blood T1 value over 9 healthy volunteers was 1864+/-92ms (Hct=0.41+/-0.04), which is 200 ms longer than the widely adopted number obtained from bovine blood experiments. The arterial T1 value per subject was found to have significant correlation with the individual Hct values.

Joshua S. Greer^1,2, Yue Zhang², Christopher Maroules², Orhan K. Oz², Ivan Pedrosa^2,3, and Ananth J. Madhuranthakam^2,3
1Bioengineering, University of Texas at Dallas, Richardson, TX, United States, ²Radiology, UT Southwestern Medical Center, Dallas, TX, United States, ³Advanced Imaging Research Center, UT Southwestern Medical Center, Dallas, TX, United States

Flow Alternating Inversion Recovery (FAIR) has been studied extensively for pulmonary perfusion imaging at 1.5T, but suffers from low SNR, and is often corrupted by bright signal in the major vasculature and image misregistration artifacts due to respiratory motion. The purpose of this study was to evaluate FAIR at 3T for increased SNR and compare against SPECT perfusion, to combine FAIR with inflow saturation to reduce signal in the major pulmonary vessels, and to combine FAIR with background suppression strategies to minimize artifacts due to image misregistration.

Luis Hernandez-Garcia¹, Jon-Fredrik Nielssen², and Douglas Noll^1
1FMRI Laboratory, University of Michigan, Ann Arbor, MI, United States, ²Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States

We introduce a class of adiabatic RF pulses that can invert the magnetization of spins moving at specific velocity bands, regardless of their position within the coil.  Velocity selective adiabatic pulses (VSAI) are more robust to B1 inhomogeneity than their non-adiabatic counterparts. We discuss the theory and design considerations and demonstrate their utility in an ASL experiment on a human brain at 3T.

Zhensen Chen¹, Xihai Zhao¹, Wouter Teeuwisse², Bida Zhang³, Peter Koken⁴, Jouke Smink⁵, and Matthias J.P. van Osch^2
1Certer for Biomedical Imaging Research, School of Medicine, Tsinghua University, Beijing, China, People's Republic of, ²C. J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, Netherlands, ³Philips Research China, Beijing, China, People's Republic of, ⁴Innovative Technologies, Research Laboratories, Philips Technologie GmbH, Hamburg, Germany, ⁵Philips Healthcare, MR Clinical Science, Best, Netherlands

The pCASL perfusion sequence was modified to incorporate a labeling efficiency measurement during the post-labeling delay. Our in vivo data showed that the incorporated labeling efficiency measurement had no influence on SNR of the perfusion measurements, with almost no additional time penalty. The additional labeling efficiency measurement was demonstrated its ability to identify severe underestimation of CBF caused by sub-optimal labeling, proofing its clinical potential. Moreover, the measured labeling efficiency is artery-specific, which is important because arteries may have different labeling efficiency due to differences in flow velocity and/or off-resonance effects.