title: Rapid 3-D mapping of hyperpolarized 3He spin-lattice relaxation times using variable flip angle gradient echo imaging with application to alveolar oxygen partial pressure measurement in rat lungs.
abstract: OBJECTIVE
  The purpose of this work was to develop a rapid 3-D, variable flip angle (VFA) method for measurement of hyperpolarized (3)He T(1) which accounts for the effects of radiofrequency (RF) pulses without the need for additional flip angle information.
  
  
  METHODS
  The 3-D, VFA method was validated in vitro over a range of oxygen partial pressures ranging from 0.04 to 0.52 atm. The approach was also tested in vivo in five healthy rats as a function of increasing number of wash-out breaths. The T(1) accuracy of the VFA method in the presence of flip angle mis-setting and RF field non-uniformity was compared with the CFA method using simulations and experiments.
  
  
  RESULTS
  T(1) measurements were found to provide p(A)O(2) estimates, both in vitro and in vivo consistent with those predicted based on gas dilution and/or ventilation para- meters. For the RF pulse mis-setting (4%) and RF field non-uniformity (3%) used here, the VFA method provided a T(1) accuracy of better than 5% compared to 12% for the CFA method.
  
  
  CONCLUSIONS
  With sufficient RF field homogeneity (3%) and proper calibration (4%), the VFA approach can provide rapid and reliable 3-D T(1) mapping of hyperpolarized (3)He without the need for additional flip angle information.
authors: Imaging Research Laboratories, Robarts Research Institute, P.O. Box 5015, 100 Perth Drive, London, ON, N6A 5K8, Canada. ouriadov@imaging.robarts.ca
authors: Alexei V
authors: AV
authors: Ouriadov
authors: Wilfred W
authors: WW
authors: Lam
authors: Giles E
authors: GE
authors: Santyr
mesh_terms: D000818:Animals; D002138:Calibration; D017352:Echo-Planar Imaging / Q000379:methods*; D006371:Helium / Q000737:chemistry; D007089:Image Enhancement / Q000379:methods*; D021621:Imaging, Three-Dimensional; D007554:Isotopes / Q000737:chemistry; D008297:Male; D010100:Oxygen / Q000378:metabolism*; D010313:Partial Pressure; D019047:Phantoms, Imaging; D011650:Pulmonary Alveoli / Q000378:metabolism / Q000473:pathology; D051381:Rats; D017208:Rats, Wistar; D015203:Reproducibility of Results; D013113:Spin Labels; D013997:Time Factors
chemical_list: D007554:Isotopes; D013113:Spin Labels; D006371:Helium; D010100:Oxygen