What code would you recommend for an MRI perfusion study of the brain?

At the present time, there are no additional codes for this service. Imaging of the brain (including perfusion studies) is best defined by the existing codes for typical brain MRI. They are:

70551 Magnetic resonance (e.g., proton) imaging, brain (including brain stem); without contrast material
70552 Magnetic resonance (e.g., proton) imaging, brain (including brain stem);with contrast material(s)
70553 Magnetic resonance (e.g., proton) imaging, brain (including brain stem);without contrast material, followed by contrast material(s) and further sequences