Arterial Spin Labeling
Thursday 23 April 2009
Room 323ABC 10:30-12:30

Moderators:

 Maria A. Fernandez-Seara and Jiongjiong Wang
 
10:30 619. Velocity Selective Inversion Pulse Trains for Velocity Selective Arterial Spin Labeling
    Eric Wong1, Jia Guo1
1University of California, San Diego, La Jolla, CA, USA
    A primary drawback of existing implementations of velocity selective arterial spin labeling (VSASL) is that the tagging pulse train produces velocity selective saturation rather than inversion, resulting in reduced SNR. We present here the design of composite velocity selective inversion pulse trains for use in VSASL. Preliminary results demonstrate B1 and B0 insensitivity, and higher SNR than current VSASL methods.
     
10:42 620. Labeling Efficiency Is Critical in Pseudo-Continuous ASL
    Sina Aslan1, Feng Xu1, Peiying L. Wang1, Jinsoo Uh1, Uma Yezhuvath1, Matthias van Osch2, Hanzhang Lu1
1Advanced Imaging Research Center, UT Southwestern Medical Center, Dallas, TX, USA; 2Department of Radiology, Leiden University Medical Center, Leiden, Netherlands
    Pseudo-Continuous Arterial Spin Labeling (pCASL) is a new ASL technique that has the potential of combining advantages of continuous ASL and pulse ASL. One of the most critical parameters in flow quantification using pCASL is the labeling efficiency. Here, we empirically determined the optimal labeling location to be 84mm distal to the AC-PC line. We then experimentally estimated the labeling efficiency using phase-contrast MRI as a normalization factor and found it to be 87±10%. Finally, we demonstrated that labeling efficiency may change with physiologic state and should be estimated for each physiologic condition.
     
10:54 621. Multi-Phase Pseudo-Continuous Arterial Spin Labeling (MP PCASL): Robust PCASL Method for CBF Quantification
    Youngkyoo Jung1, Eric C. Wong1,2, Thomas T. Liu1
1Radiology, University of California, San Diego, San Diego, CA, USA; 2Psychiatry, University of California, San Diego, San Diego, CA, USA
    The pseudo-continuous arterial spin labeling method for CBF quantification offers higher SNR and therefore the potential for improved quantification compared to pulsed ASL. The tagging efficiency of PCASL can be significantly modulated by both gradient imperfections and the off-resonance fields at the tagged vessels. We propose a novel PCASL method with multiple phase offsets which is less sensitive to these factors. Our result shows that the CBF measures obtained with the proposed method were more consistent with the reference CBF values obtained with FAIR and both conventional PCASL and MP PCASL provide higher SNR than the FAIR ASL method.
     
11:06 622. Evaluation of New ASL 3D GRASE Sequences Using Parallel Imaging, Segmented and Interleaved K-Space at 3T with 12- And 32-Channel Coils
    David Feinberg1,2, Sudhir Ramanna2, Matthias Gunther3
1Helen Wills Neuroscience Institute, University of California, Berkeley, CA, USA; 2Advanced MRI Technologies, Sebastopol, CA, USA; 3Mediri, Heidelberg, Germany
    Three new 3D GRASE ASL sequences utilizing parallel imaging (PI) segmentation and interleaved readout schemes were evaluated without changes in blood labeling and background suppression pulses. Comparisons were made at different spatial resolution in 64, 128 and 256 matrix images in 12- and 32-Channel head coils at 3T. All sequences reduced susceptibility artifacts by shortening RF pulse spacing in the CPMG sequence, The segmented and PI sequences reduced through-plane blurring by shortening echo train lengths. Higher bandwidth possible in 128 matrix scans reduced image distortions. The 32-Channel head coil consistently improved SNR and dependent image quality
     
11:18 623. QUIPSS II with Window-Sliding Saturation Sequence (Q2WISSE)
    Ruitian Song1, Ralf B. Loeffler1, Claudia M. Hillenbrand1
1Radiological Science, St Jude Children's Research Hospital, Memphis, TN, USA
    In Q2TIPS [quantitative imaging of perfusion using a single subtraction II (QUIPSS II) with thin-slice TI1 periodic saturation], a train of periodic saturation pulses is used to minimize variable transit delay error in assessment of perfusion. A new scheme referred as Q2WISSE (QUIPSS II with window-sliding saturation sequence) was developed to reduce SAR while still maintaining the sharp slice profile by using window-sliding saturation pluses to replace the train of saturation pulses. The method was tested on seven volunteers for both brains and kidneys, and a good agreement was found between Q2WISSE and Q2TIPS methods.
     
11:30 624. ASL Perfusion Measurement Using a Rapid, Low Resolution Arterial Transit Time Prescan
    Weiying Dai1,2, Philip M. Robson1,2, Ajit Shankaranarayanan3, David C. Alsop1,2
1Radiology, Beth Israel Deaconess Medical Center, Boston, MA, USA; 2Radiology, Harvard Medical School, Boston, MA, USA; 3Applied Science Laboratory, GE Healthcare, Menlo Park, CA, USA
    The arterial spin labeling signal reflects a mixture of perfusion and arterial transit time (ATT) effects. Unfortunately, ATT can span a wide range in broad clinical populations and optimization of these scans is problematic. Perfusion and ATT can be measured with images acquired at multiple delays, but such methods decrease the sensitivity of the perfusion measurement. Here, we propose a rapid, low resolution scan at multiple labeling delays to acquire a map of ATT. This ATT map can be used to optimize an ATT insensitive perfusion acquisition or to quantify perfusion from an ATT sensitive high resolution scan.
     
11:42 625. White Matter Cerebrovascular Reactivity Measured with Pseudo-Continuous Arterial Spin Labeling at 3T
    Reinoud Pieter Harmen Bokkers1, M J P van Osch2, Willem P. Mali1, Jeroen Hendrikse1
1Department of Radiology, UMC Utrecht, Utrecht, Netherlands; 2Department of Radiology, LUMC, Leiden, Netherlands
    The aim of this study was to study the ability of arterial spin labeling to assess cerebrovascular reactivity in the white matter after intravenous administration of acetazolamide using a pseudo-continuous ASL technique with background suppression. Herein, we found a significant increase in CBF in the white matter after injection of acetazolamide that corresponds with the increase in CBF of the gray matter. Knowledge of white matter autoregulative status may provide important understanding in the aetiology and pathogenesis white matter disease.
     
11:54 626. Multicenter Reproducibility of Continuous, Pulsed and Pseudo-Continuous Arterial Spin Labeling; Can We Use General Reference Values of Cerebral Blood Flow?
    Sanna Gevers1, Matthias J.P. van Osch2, Jeroen Hendrikse3, Reinoud P.H. Bokkers3, Dennis A. Kies2, Wouter M. Teeuwisse2, C.B. Majoie1, Aart J. Nederveen1
1Radiology, Academic Medical Center, Amsterdam, Noord Holland, Netherlands; 2Radiology, Leiden University Medical Center, Leiden, Netherlands; 3Radiology, University Medical Center , Utrecht, Netherlands
    Arterial spin labeling (ASL) is a non-invasive imaging technique that can be used to measure cerebral perfusion in the diagnosis and evaluation of brain disease. However, the complicated set up of ASL experiments raises the question whether comparable perfusion images would be obtained when scanning the same subject at different imaging sites and whether multicenter reproducibility of ASL allows the use of general reference values of cerebral blood flow. To answer these questions we assessed intra- and multicenter reproducibility of continuous, pseudo-continuous and pulsed ASL in a group of 6 healthy volunteers scanned twice at multiple sites.
     
12:06 627. Absolute Cerebral Blood Volume (CBV) Quantification Without Contrast Agents Using Inflow Vascular-Space-Occupancy (IVASO) with Dynamic Subtraction
    Manus Joseph Donahue1, Bradley J. MacIntosh1, Ediri Sideso2, Molly Bright1,3, James Kennedy2, Ashok Handa4, Peter Jezzard1
1Clinical Neurology, The University of Oxford, Oxford, UK; 2Nuffield Department of Clinical Medicine, The University of Oxford, Oxford, UK; 3Advanced MRI Section, LFMI, NINDS , The National Institutes of Health, Bethesda, MD, USA; 4Nuffield Department of Surgery, The University of Oxford, Oxford, UK
    A non-invasive approach for quantifying arteriolar cerebral blood volume (aCBV) using inflow vascular-space-occupancy with dynamic subtraction (iVASO-DS) is presented. iVASO-DS employs a “null” acquisition (arteriolar blood magnetization nulled) interleaved with a “control” acquisition (arteriolar blood magnetization positive), which are subtracted to yield an aCBV map. aCBV is found to be 2.8±0.9% in healthy volunteers (n=8), however was significantly (P<0.01) elevated bilaterally in patients with steno-occlusive artery disease (ipsilateral: 4.1±1.0%; contralateral: 3.8±1.1%). iVASO-DS should represent a useful, non-invasive complement to hemodynamic imaging protocols for understanding both healthy brain function and hemodynamic impairment in patients with abnormal CBV.
     
12:18 628. QUantitative Imaging of EXtraction of Oxygen and TIssue Consumption (QUIXOTIC) Using Velocity Selective Spin Labeling
    Divya S. Bolar1,2, Bruce R. Rosen1, A Gregory Sorensen1, Elfar Adalsteinsson1,2
1A.A. Martinos Center for Biomedical Imaging, HST/MGH/HMS/MIT, Charlestown, MA, USA; 2Electrical Engineering & Computer Science, MIT, Cambridge, MA, USA
    While oxygen extraction fraction (OEF) and cerebral metabolic rate of oxygen (CMRO2) are fundamental parameters in neuropathology and functional neuroactivation, a robust MRI-based OEF/CMRO2 mapping technique has not been established. OEF/CMRO2 mapping requires isolating signal from post-capillary venular blood to measure venular oxygen saturation (Yv). We propose and demonstrate a novel method to isolate this signal using velocity selective spin-labeling. We subsequently estimate T2 of PCV blood, convert T2 to Yv with a calibration curve, compute OEF from Yv, and baseline CMRO2 from OEF and CBF. This approach is dubbed QUantitative Imaging of eXtraction of Oxygen and TIssue Consumption (QUIXOTIC).