Arterial Spin Labeling

Tuesday 13 May 2014

Katherine L. Wright¹, Dan Ma¹, Yun Jiang¹, Vikas Gulani^1,2, Mark A. Griswold^1,2, and Luis Hernandez-Garcia^3
1Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, United States, ²Radiology, Case Western Reserve University, Cleveland, Ohio, United States, ³UM fMRI Lab, University of Michigan, Ann Arbor, Michigan, United States

The purpose of this study is to explore the use of the MR Fingerprinting framework for ASL-based parameter quantification. MRF has recently been introduced as an accurate and efficient approach for simultaneous quantification of multiple physical or physiological parameters. Here we show how MRF can be extended to quantitation of ASL perfusion-related parameters, including cerebral blood flow (CBF) and transit time. The goal of this work is to develop a theoretical framework that could overcome limitations in traditional ASL by providing a new approach to acquisition of ASL data and estimation of perfusion parameters.

Ruth Oliver¹, Enrico De Vita¹, Xavier Golay¹, and David Thomas^1
1Institute of Neurology, University College London, London, United Kingdom

Partial volume effects due to low spatial resolution are known to introduce errors in quantification of perfusion estimates using ASL. This is particularly problematic in patients where atrophy is and cortical thinning occurs. The most common correction methods are based on segmentations of anatomical data which are transformed to perfusion space. This can introduce a significant error into the correction method. A comparison is made of partial volume corrected grey matter flow values using segmentations derived from anatomical data and GRASE data, for single time point ASL.

Sophie Schmid¹, Esben T. Petersen², Wouter M. Teeuwisse¹, and Matthias J.P. van Osch^1
1C.J. Gorter Center for High Field MRI, Radiology, Leiden University Medical Center, Leiden, Netherlands, ²Radiology, University Medical Center Utrecht, Utrecht, Netherlands

For AccASL it is unknown where in the vascular tree label is created. The aim of this study was to get more insight into the origin of the label mechanism in AccASL by combining this method with a VS module. Summing the signal of AccASL and VS-ASL acquired separately was compared with AccASL and VS-ASL acquired immediately after each other. The difference in this signal suggests that the label from AccASL originates from both macro- and micro-vascular level.

Qin Qin^1,2 and Peter C.M. van Zijl^1,2
1Radiology, Johns Hopkins University, Baltimore, Maryland, United States, ²Kirby Center, Kennedy Krieger Institute, Baltimore, Maryland, United States

A novel velocity-selective inversion pulse preparation is developed based on the k-space formalism, which is robust to B0/B1 inhomogeneity and eddy currents by embedding a pair of adiabatic pulses for refocusing in each k-segment. This new pulse, dubbed Double-Refocused Inversion with Velocity Encoding (DRIVE), is applied to velocity-selective Arterial Spin Labeling (VSASL) for cerebral blood flow (CBF) measurement at 3T. We performed VSASL using the DRIVE pulse train and a standard Pseudo-Continuous ASL (PCASL) with 3D whole-brain acquisition for comparison. The results show excellent agreement between the two methods in both CBF quantification and SNR level.

Jia Guo¹ and Eric C. Wong^2
1Department of Bioengineering, University of California San Diego, La Jolla, California, United States, ²Departments of Radiology and Psychiatry, University of California San Diego, La Jolla, California, United States

It is challenging to measure WM CBF using ASL due to the low WM CBF and the heterogeneous and long transit delays. VSASL is inherently insensitive to transit delays, but for typical parameters it has a lower SNR than conventional ASL methods such as PCASL. However, compared with PCASL in which a long PLD was required in WM measurements, VSASL with two Velocity Selective Saturation (VSS) modules provided a comparable SNR (P=0.52) and CBF values (P=0.61) in WM, and even had a higher SNR in GM (P<0.01). VSASL may be more favorable than other tagging methods in applications where long transit delays are expected.

Youngkyoo Jung¹, Megan E Johnston¹, Christopher T Whitlow¹, Joseph A Maldjian¹, and P Pearse Morris^1
1Wake Forest School of Medicine, Winston-Salem, NC, United States

Access to valid vascular territory atlases is important to advance our knowledge regarding the pathophysiology of cerebrovascular diseases and the effects of interventions and treatments. To date, however, only crude cerebral vascular territory atlases exist based on digitization of colorized figures. Moreover, anatomical variations of the cerebral arteries and knowledge of this variation is essential to avoid misdiagnosis and to plan tailored treatment. Probabilistic vascular territory atlases are well suited to take this vascular variation into account and we demonstrate experiment-based vascular territory atlases of major arteries using arterial spin labeling based vascular territory mapping.

Jan Petr¹, Georg Schramm¹, Frank Hofheinz¹, Jens Maus¹, and Jörg van den Hoff^1
1PET center, Institute of Radiopharmaceutical Cancer Research, Helmholtz-Zentrum Dresden Rossendorf, Dresden, Germany

The magnetization transfer (MT) effects were studied in pseudo-continuous ASL (pCASL). The MT exchange rate was obtained from two pCASL sequences with and without labeling acquired at multiple delays. A mean white-matter MT exchange rate was obtained and the exchange rate in blood was derived from it. Effect on CBF quantification was then calculated using the standard pCASL quantification model for different distances from the labeling plane and different blood velocities in the arteries. CBF underestimation of up to 6% was shown in the slices closest to the labeling plane if the MT effects were ignored.

Murat Aksoy¹, Julian Maclaren¹, Melvyn Ooi¹, Jakob Ehrl¹, Didem Aksoy¹, Zungho Zun¹, and Roland Bammer^1
1Radiology, Stanford University, Stanford, CA, United States

Prospective motion correction using optical tracking is gaining popularity, due to its advantages over MR-based navigator methods, which include fast response time and applicability to any imaging sequence. In this study, we demonstrate the application of prospective optical motion correction on 3D pseudo-continuous arterial spin labeling.

Kevin Murphy¹, Anja Hayen², Mari Herigstad², and Kyle T.S. Pattinson^2
1CUBRIC, School of Psychology, Cardiff University, Cardiff, Wales, United Kingdom, ²Nuffield Dept Clinical Neurosciences & FMRIB Centre, University of Oxford, United Kingdom

It has previously been demonstrated that the optimal approach to removing physiological noise from ASL data is to separate tags and controls first. The purpose of this study is to extend this finding to determine the optimal approach for multiple inversion time ASL data. In this study we find that both the naive approach of not separating the data and the approach of separating tags from controls introduce far more noise than they remove. Separating both TIs and tags/controls alleviates this problem allowing for good repeatability of signal across TIs and improved fits of the kinetic curve model.

Manoj Shrestha¹, Toralf Mildner¹, Torsten Schlumm¹, Kathrin Lorenz¹, Scott Haile Robertson², and Harald E. Möller^1
1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, ²Center for In Vivo Microscopy, Duke University Medical Center, Durham, NC, United States

Trajectories of cylindrically-encoded 3D center-out EPI readout were used to track an ASL bolus of well-defined length. This was achieved by time-resolved acquisition of single segments of k-space for a period of about 3 s after bolus termination. The steady state created in the imaging volume by the repeated slab selective excitation was maintained also during the ASL bolus. All segments of k-space belonging to the same time after ASL bolus termination were combined and reconstructed. The time-resolved difference images between the labeling and control conditions clearly show the passage of the ASL bolus inside the large brain-feeding arteries.