Cerebral blood flow quantification in the rat: a direct comparison of arterial spin labeling MRI with radioactive microsphere PET

Background
Arterial spin labeling magnetic resonance imaging (ASL-MRI) has been recognised as a valuable method for non-invasive assessment of cerebral blood flow but validation studies regarding quantification accuracy by comparison against an accepted gold standard are scarce, especially in small animals. We have conducted the present study with the aim of comparing ASL flow-sensitive alternating inversion recovery (FAIR)-derived unidirectional water uptake (K₁) and ⁶⁸Ga=⁶⁴Cu microsphere (MS)-derived blood flow (f ) in the rat brain.
Methods
In 15 animals, K₁ and f were determined successively in dedicated small animal positron emission tomography and MR scanners. The Renkin-Crone model modified by a scaling factor was used for the quantification of f and K₁.
Results
Below about 1 mL/min/mL, we obtain an approximately linear relationship between f and K₁. At higher flow values, the limited permeability of water at the blood brain barrier becomes apparent. Within the accessed dynamic flow range (0.2 to 1.9 mL/min/mL), the data are adequately described by the Renkin-Crone model yielding a permeability surface area product of .1.53 ± 0.46/ mL/min/mL.
Conclusion
The ASL-FAIR technique is suitable for absolute blood flow quantification in the rat brain when using a one-compartment model including a suitable extraction correction for data evaluation.

Trial registration
24-9168.21-4/2004-1 (registered in Freistadt Sachsen, Landesdirektion Dresden)