title: Influence of blood/tissue differences in contrast agent relaxivity on tracer-based MR perfusion measurements.
abstract: OBJECTIVE
  Perfusion assessment by monitoring the transport of a tracer bolus depends critically on conversion of signal intensity into tracer concentration. Two main assumptions are generally applied for this conversion; (1) contrast agent relaxivity is identical in blood and tissue, (2) change in signal intensity depends only on the primary relaxation effect. The purpose of the study was to assess the validity and influence of these assumptions.
  
  
  METHODS
  Blood and cerebral tissue relaxivities r1, r2, and r2* for gadodiamide were measured in four pigs at 1.5 T. Gadolinium concentration was determined by inductively coupled plasma atomic emission spectroscopy. Influence of the relaxivities, secondary relaxation effects and choice of singular value decomposition (SVD) regularization threshold was studied by simulations.
  
  
  RESULTS
  In vivo relaxivities relative to blood concentration [in s(-1) mM(-1) for blood, gray matter (GM), white matter (WM)] were for r1 (2.614 ± 1.061, 0.010 ± 0.001, 0.004 ± 0.002), r2 (5.088 ± 0.952, 0.091 ± 0.008, 0.059 ± 0.014), and r2* (13.292 ± 3.928, 1.696 ± 0.157, 0.910 ± 0.139). Although substantial, by a nonparametric test for paired samples, the differences were not statistically significant. The GM to WM blood volume ratio was estimated to 2.6 ± 0.9 by r1, 1.6 ± 0.3 by r2, and 1.9 ± 0.2 by r2*. Secondary relaxation was found to reduce the tissue blood flow, as did the SVD regularization threshold.
  
  
  CONCLUSIONS
  Contrast agent relaxivity is not identical in blood and tissue leading to substantial errors. Further errors are introduced by secondary relaxation effects and the SVD regularization.
authors: Section of Radiology, Department of Radiology, Oncology and Radiation Sciences, Uppsala University, Uppsala, Sweden, arvid.morell@gmail.com.
authors: Arvid
authors: A
authors: Morell
authors: Fredrik
authors: F
authors: Lennmyr
authors: Ove
authors: O
authors: Jonsson
authors: Thomas
authors: T
authors: Tovedal
authors: Jean
authors: J
authors: Pettersson
authors: Jonas
authors: J
authors: Bergquist
authors: Vitas
authors: V
authors: Zemgulis
authors: Gunnar Myrdal
authors: GM
authors: Einarsson
authors: Stefan
authors: S
authors: Thelin
authors: Håkan
authors: H
authors: Ahlström
authors: Atle
authors: A
authors: Bjørnerud
mesh_terms: D000818:Animals; D001783:Blood Flow Velocity / Q000502:physiology*; D001921:Brain / Q000033:anatomy & histology / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D003198:Computer Simulation; D003287:Contrast Media / Q000493:pharmacokinetics; D019786:Gadolinium DTPA / Q000493:pharmacokinetics*; D066128:Gray Matter / Q000033:anatomy & histology / Q000502:physiology; D018810:Magnetic Resonance Angiography / Q000379:methods*; D008955:Models, Cardiovascular; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013552:Swine; D066127:White Matter / Q000033:anatomy & histology / Q000502:physiology
chemical_list: D003287:Contrast Media; C064925:gadodiamide; D019786:Gadolinium DTPA