title: Rapid dark-blood carotid vessel-wall imaging with random bipolar gradients in a radial SSFP acquisition.
abstract: OBJECTIVE
  To investigate and evaluate a new rapid dark-blood vessel-wall imaging method using random bipolar gradients with a radial steady-state free precession (SSFP) acquisition in carotid applications.
  
  
  METHODS
  The carotid artery bifurcations of four asymptomatic volunteers (28-37 years old, mean age = 31 years) were included in this study. Dark-blood contrast was achieved through the use of random bipolar gradients applied prior to the signal acquisition of each radial projection in a balanced SSFP acquisition. The resulting phase variation for moving spins established significant destructive interference in the low-frequency region of k-space. This phase variation resulted in a net nulling of the signal from flowing spins, while the bipolar gradients had a minimal effect on the static spins. The net effect was that the regular SSFP signal amplitude (SA) in stationary tissues was preserved while dark-blood contrast was achieved for moving spins. In this implementation, application of the random bipolar gradient pulses along all three spatial directions nulled the signal from both in-plane and through-plane flow in phantom and in vivo studies.
  
  
  RESULTS
  In vivo imaging trials confirmed that dark-blood contrast can be achieved with the radial random bipolar SSFP method, thereby substantially reversing the vessel-to-lumen contrast-to-noise ratio (CNR) of a conventional rectilinear SSFP "bright-blood" acquisition from bright blood to dark blood with only a modest increase in TR (approximately 4 msec) to accommodate the additional bipolar gradients.
  
  
  CONCLUSIONS
  Overall, this sequence offers a simple and effective dark-blood contrast mechanism for high-SNR SSFP acquisitions in vessel wall imaging within a short acquisition time.
authors.affiliation: Department of Radiology, University Hospitals of Cleveland and Case Western Reserve University, 11100 Euclid Avenue, Cleveland, OH 44195, USA.
authors.forename: Hung-Yu
authors.initials: HY
authors.lastname: Lin
authors.forename: Chris A
authors.initials: CA
authors.lastname: Flask
authors.forename: Brian M
authors.initials: BM
authors.lastname: Dale
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Duerk
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology; D002339:Carotid Arteries / Q000033:anatomy & histology*; D003198:Computer Simulation; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D018810:Magnetic Resonance Angiography / Q000379:methods*; D019047:Phantoms, Imaging