title: Optimization of 4D vessel-selective arterial spin labeling angiography using balanced steady-state free precession and vessel-encoding.
abstract: Vessel-selective dynamic angiograms provide a wealth of useful information about the anatomical and functional status of arteries, including information about collateral flow and blood supply to lesions. Conventional x-ray techniques are invasive and carry some risks to the patient, so non-invasive alternatives are desirable. Previously, non-contrast dynamic MRI angiograms based on arterial spin labeling (ASL) have been demonstrated using both spoiled gradient echo (SPGR) and balanced steady-state free precession (bSSFP) readout modules, but no direct comparison has been made, and bSSFP optimization over a long readout period has not been fully explored. In this study bSSFP and SPGR are theoretically and experimentally compared for dynamic ASL angiography. Unlike SPGR, bSSFP was found to have a very low ASL signal attenuation rate, even when a relatively large flip angle and short repetition time were used, leading to a threefold improvement in the measured signal-to-noise ratio (SNR) efficiency compared with SPGR. For vessel-selective applications, SNR efficiency can be further improved over single-artery labeling methods by using a vessel-encoded pseudo-continuous ASL (VEPCASL) approach. The combination of a VEPCASL preparation with a time-resolved bSSFP readout allowed the generation of four-dimensional (4D; time-resolved three-dimensional, 3D) vessel-selective cerebral angiograms in healthy volunteers with 59 ms temporal resolution. Good quality 4D angiograms were obtained in all subjects, providing comparable structural information to 3D time-of-flight images, as well as dynamic information and vessel selectivity, which was shown to be high. A rapid 1.5 min dynamic two-dimensional version of the sequence yielded similar image features and would be suitable for a busy clinical protocol. Preliminary experiments with bSSFP that included the extracranial vessels showed signal loss in regions of poor magnetic field homogeneity. However, for intracranial vessel-selective angiography, the proposed bSSFP VEPCASL sequence is highly SNR efficient and could provide useful information in a range of cerebrovascular diseases. © 2016 The Authors. NMR in Biomedicine published by John Wiley & Sons Ltd.
authors.affiliation: FMRIB Centre, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK.
authors.forename: Thomas W
authors.identifier: 0000-0001-8258-0659
authors.initials: TW
authors.lastname: Okell
authors.affiliation: MR Application and Workflow Development, Siemens AG, Healthcare Sector, Erlangen, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Schmitt
authors.affiliation: MR R&D, Siemens Healthcare, Los Angeles, CA, USA.
authors.forename: Xiaoming
authors.initials: X
authors.lastname: Bi
authors.affiliation: FMRIB Centre, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK.|Institute of Biomedical Engineering, University of Oxford, Oxford, UK.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Chappell
authors.affiliation: FMRIB Centre, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK.|Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Rob H N
authors.initials: RH
authors.lastname: Tijssen
authors.affiliation: Neuroradiology, Oxford University Hospitals NHS Trust, Oxford, UK.
authors.forename: Fintan
authors.initials: F
authors.lastname: Sheerin
authors.affiliation: FMRIB Centre, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK.
authors.forename: Karla L
authors.initials: KL
authors.lastname: Miller
authors.affiliation: FMRIB Centre, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK.
authors.forename: Peter
authors.initials: P
authors.lastname: Jezzard
mesh_terms: D000328:Adult; D000465:Algorithms; D001783:Blood Flow Velocity / Q000502:physiology; D002533:Cerebral Angiography / Q000379:methods*; D002536:Cerebral Arteries / Q000033:anatomy & histology* / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods*; D018810:Magnetic Resonance Angiography / Q000379:methods*; D008297:Male; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D013113:Spin Labels
chemical_list: D013113:Spin Labels
keywords: balanced steady-state free precession (bSSFP); non-contrast-enhanced dynamic (time-resolved) magnetic resonance angiography; vessel-encoded pseudo-continuous arterial spin labeling (VEPCASL); vessel-selective angiography