Quantitative Perfusion Measurements: A Comparison of MRI Using Arterial Spin Labeling (ASL) with Radioactive and Fluorescence Microspheres


Quantitative Perfusion Measurements: A Comparison of MRI Using Arterial Spin Labeling (ASL) with Radioactive and Fluorescence Microspheres

Bos, A.; Bergmann, R.; van den Hoff, J.

Aim: Arterial Spin Labeling (ASL) is a Magnetic Resonance Imaging (MRI) technique for perfusion evaluation, which is based on spin inversion in the arterial blood and observation of relaxation effects. However, quantitative accuracy of ASL measurements in small animals is not well investigated. The purpose of this work was to assess accuracy of quantitative ASL perfusion measurements in rat brain by comparison with microspheres derived regional perfusion information using dedicated micro Positron Emission Tomography (PET) and ex vivo Optical imaging (OI).
Methods: Catheters were implanted through the right carotid artery in the left ventricle of the heart for administration of labeled microspheres (diameter 20 µm) and in the left femoral artery for blood sampling. Microspheres were double-labeled with either Cu-64 or Ga-68 for PET and X-sight 670 LSS for OI. ASL measurements were performed in a 7T small animal system using a Flow-sensitive Alternating Inversion Recovery (FAIR) sequence with an adiabatic hyperbolic secant inversion pulse (length-bandwidth product: 80) and Echo Planar Imaging (EPI) acquisition. Global and selective T1 images, correspondingly cut brain sections, and PET data were used for perfusion values calculation. All the crucial physiological parameters were monitored. Perfusion of the whole brain (PET, OI) and two dedicated slices (PET, OI, MRI) were estimated independently with specified methods. The consistency of OI compared to PET for whole brain was used as criterion for inclusion of the respective animal into further data evaluation.
Results: A mean perfusion of the whole brain was 88.8 mL/100g/min. In slices measured with ASL (cerebellum with pons and hemispheres in caudate putamen region) perfusion was calculated with each technique separately. Results from MRI and PET were considered for Cu-64, Ga-68 and for whole data set. The estimated correlation factor for MRI vs. PET is 0.91 and Renkin-Crone model fitting yields a plausible Permeability Surface product (PS) for water (182 mL/g/min). The same data was fitted also with linear regression forced to zero-point (y=0.76x). The left-right disparity in Cortex, Thalamus and Cerebellum was observed because of catheter implantation, namely for 73% of animals perfusion in the left part of the brain was higher.
Conclusions: The quantitative perfusion measurements in the rat brain using ASL are possible but require thorough data analysis. Overall regional contrast provided by ASL is concordant with regional distribution of microspheres in the rat brain. However, deviations from linear correlation are visible and are the subject of further investigations. In order to be useful for routine application in small animal imaging, ASL data acquisition and data evaluation needs to be further optimized. A final calibration via a quantitative comparison with radio- and fluorescent-labeled microspheres seems mandatory.

Keywords: Perfusion; ASL; PET; OI; microspheres

  • Poster
    World Molecular Imaging Congress 2011, 02.-10.09.2011, San Diego, USA
  • Contribution to proceedings
    World Molecular Imaging Congress 2011, 02.-10.09.2011, San Diego, USA
    Proceedings of the World Molecular Imaging Congress 2011, S721

Permalink: https://www.hzdr.de/publications/Publ-16515
Publ.-Id: 16515