Arterial Spin Labeling

Monday 22 April 2013

Xingxing Zhang¹, Eidrees Ghariq¹, Sophie Schmid¹, Wouter M. Teeuwisse¹, Andrew G. Webb¹, and Matthias J.P. van Osch^1
1C.J.Gorter center for high field MRI, Radiology, Leiden university medical center, Leiden, Zuid-Holland, Netherlands

Vessel selective dynamic ASL (VS-DASL) was proposed to do a fast cerebral flow territory mapping. The results were in good agreement with traditional vessel selective ASL. The percentage of correctly classified voxels in the flow territory map proved that VS-DASL has potential to map the flow territories in a short scan time (~30-60s), enabling the use in patients with acute stroke.

Nolan S. Hartkamp¹, Michael Helle², Michael A. Chappell^3,4, Thomas W. Okell⁴, Reinoud P H Bokkers¹, Jeroen Hendrikse¹, and Matthias J.P. van Osch^5
1Department of Radiology, University Medical Center Utrecht, Utrecht, Netherlands, ²Philips Research Laboratories, Hamburg, Germany, ³Institute of Biomedical Engineering, Department of Engineering Science, University of Oxford, Oxford, United Kingdom, ⁴FMRIB Centre, University of Oxford, Oxford, United Kingdom, ⁵C.J. Gorter Center, Department of Radiology, Leiden University Medical Center, Leiden, Netherlands

We show that the territorial perfusion maps produced by VE p-CASL agree reasonably well with the perfusion maps acquired with super-selective p-CASL. Special consideration should be taken when using k-means clustering since it tends to fail in regions with high mixed perfusion, such as the deep gray matter. VE p-CASL with k-means clustering appears suitable as a general purpose T-ASL strategy, but the Bayesian framework is preferable since it can determine mixed perfusion. This is however only reliable where the VE p-CASL images contain sufficient vessel selectivity. To accurately determine the perfusion territories of a vessel, super-selective p-CASL is still recommended.

Eric Wong¹ and Jia Guo^2
1Radiology/Psychiatry, UC San Diego, La Jolla, CA, United States, ²Bioengineering, University of California San Diego, La Jolla, CA, United States

In recent years, several methods have been introduced for mapping of arterial perfusion territories using arterial spin labeling. In this work, we adapt these remote sensing principles for mapping of vascular territories on the venous side, using spatial encoding of tissue water, and phase contrast based acquisition of signal from draining veins. Possible applications include venous thrombosis, multiple sclerosis, and mapping of oxygenation extraction.

Wouter M. Teeuwisse¹, Sophie Schmid¹, Andrew G. Webb¹, and Matthias J.P. van Osch^1
1Radiology, C.J.Gorter Center for High Field MRI, Leiden University Medical Center, Leiden, ZH, Netherlands

Time encoded pseudo continuous arterial spin labeling (te-pCASL, a.k.a. Hadamard encoded pCASL) combined with a Look-Locker (LL) read out was applied to sample the tracer kinetics curve with high temporal resolution (50 ms). To improve LL performance a flip angle sweep and a temporal shift of LL images in subsequent acquisitions were implemented. Perfusion signal curves in arteries and tissue were fitted and variants of perfusion modeling were evaluated. Measurement of tissue perfusion in the visual cortex demonstrated decreased arterial cerebral blood volume (aCBV) and arterial transit time (ATT) upon visual stimulation while cerebral blood flow (CBF) increased.

Sophie Schmid¹, Wouter M. Teeuwisse¹, Eidrees Ghariq¹, Andrew Webb¹, Hanzhang Lu², and Matthias J.P. van Osch^1
1C.J.Gorter Center for High Field Magnetic Resonance, Radiology, Leiden University Medical Center, Leiden, Zuid-Holland, Netherlands, ²UT Southwestern Medical Center, Dallas, Texas, United States

The aim of this study is to employ a method to measure the transverse relaxation time as a function of the inflow time and to distinguish spin compartments based on their T2 in a highly time-efficient and voxelwise manner. By the use of Time encoded (also known as Hadamar encoded) pseudo Continuous Arterial Spin Labeling (te-pCASL) in combination with T2-Relaxation-Under-Spin-Tagging (TRUST) it is feasible to be more specific due to the short bolus duration and reduce the measurement time, while still keeping an equal SNR compared to separate multi-timepoint pCASL scans.

Lirong Yan¹, Robert Smith¹, Collin Liu², Emily Kilroy¹, Yufen Chen³, and Danny J.J. Wang^1
1Neurology, UCLA, Los Angeles, CA, United States, ²Neurology, USC, Los Angeles, CA, United States, ³Radiology, Northwestern University, Chicago, IL, United States

Vascular compliance (VC) is an important risk factor for cardiovascular disorders and stroke. In this study, we propose a novel MRI technique for assessing intracranial VC by synchronizing dynamic arterial spin labeling (ASL) scans with systolic and diastolic cardiac phases respectively. VC is estimated as the ratio between changes in arterial blood volume (BV) and changes in blood pressure (BP) between systolic and diastolic phases (i.e., VC=¦¤BV/¦¤BP). Our results showed that intracranial VC mainly occurs in big arteries, gradually decreases in small arteries and arterioles, and finally disappears in capillaries and tissue. Initial data also showeda decreased VC with aging.

Steffen N. Krieger^1,2, Laurentius Huber¹, Gary F. Egan², and Robert Turner^1
1Neurophysics, Max-Plank Institute for Human Cognitive and Brain Sciences, Leipzig, Saxonia, Germany, ²Monash Biomedical Imaging, Monash University, Melbourne, Victoria, Australia

Beside the classical blood oxygenation level dependent (BOLD) contrast methods, cerebral blood volume (CBV) and cerebral blood flow (CBF) based functional MRI (fMRI) measurements have recently become frequently used tools in neuroscience. However, the quantitative relationships between each of these parameters is not yet fully understood. We present an fMRI technique that simultaneously measures CBV, CBF and BOLD signals. This method benefits from the high static magnetic field strength of 7T as well as the implementation of slab-selective VASO and a multiple EPI-readout in order to correct for BOLD contamination effects in the CBV- and CBF weighted MRI signals.

Xiang He¹, Serter Gumus¹, Ayaz Aghayev¹, and Kyongtae Ty Bae^1
1Department of Radiology, University of Pittsburgh, Pittsburgh, PA, United States

High pulsatile blood flow/velocity in the descending aorta renders the labeling bolus of a standard pulse ASL (PASL) experiment to be limited within a single cardiac RR interval. In this study, we took advantage of such temporally uneven blood flow to generate multiple labeling boluses across consecutive RR intervals. We demonstrated that the proposed multi-bolus PASL scheme improved the sensitivity of renal PASL perfusion signal by ~30 to 50%.

Ke Zhang¹, Hans Herzog¹, Christian Filss¹, Thomas Fischer², Walter Sturm³, Burkhard Brocke², and Nadim Jon Shah^1,4
1Institute of Neuroscience and Medicine 4, Medical Imaging Physics, Forschungszentrum Jülich GmbH, Jülich, Germany, ²Neurobiology of Personality and Neurogenetics, Department of Psychology, Dresden Universi Laboratory, Dresden, Germany, ³Clinical Neurology, University Hospital Aachen, Aachen, Germany,⁴Department of Neurology, JARA, RWTH Aachen University, Aachen, Germany

A number of studies have compared ASL-MRI and ¹⁵O-water PET for the evaluation of ASL reliability and reproducibility. But none of these studies had the possibility to perform both techniques simultaneously to minimize the physiological variations. In this work, a simultaneous ASL-MRI and ¹⁵O-water PET approach has been implemented on a hybrid MR-PET for a truly quantitative comparison between the two methods in absolutely the same physiological and functional status.

Alexander Graeme Gardener¹ and Peter Jezzard^1
1FMRIB Centre, Nuffield Department of Clinical Neurosciences, Oxford, United Kingdom

The measurement of White Matter perfusion (WM-CBF) using Arterial Spin Labeling techniques has proven difficult due to the low Contrast-to-Noise ratio and long labeled blood transit times found in this tissue. An Optimal Sampling Strategy approach was used to weight TI acquisition times to later blood arrival. This was combined with an ultra-high field 7T scanner to improve CNR and benefit from longer T1 relaxation time in labeled blood. It is shown that reasonable WM-CBF quantification can be achieved consistently in healthy human subjects. Fitted CBF and bolus arrival times were comparable to literature values.