Cerebral blood volume (CBV) (often relative CBV: see below) is one of the parameters generated by perfusion techniques (CT perfusion and MR perfusion). CBV is defined as the volume of blood in a given amount of brain tissue, most commonly milliliters of blood per 100 g of brain tissue ¹.

CBV can be calculated by assessing the area under the concentration-time curve, which in turn can be generated from signal intensity-time curves generated using dynamic susceptibility contrast (DSC) MR perfusion or other techniques. 

CBV vs rCBV

Absolute cerebral blood volume can only be calculated with the above method if two pharmacokinetic conditions are met: 

1. no recirculation of contrast
2. no capillary permeability

The first can be corrected for by assessing only the first pass of contrast. The second is more problematic as permeability can vary dramatically. Due to this difficulty in most instances what is actually being calculated is CBV relative to an internal control (e.g. contralateral normal white matter or an arterial input function) ². As such it is usually referred to as relative cerebral blood volume (rCBV) and has no units (since it is just a ratio). 

Quantitative CBV (qCBV) can be estimated using specific techniques, and varies significantly between white and grey matter (roughly twice as high in grey vs white matter) ³: 

• grey matter: ~2.5 +/- 0.4 mL/100 g *
• white matter: 1.7 +/- 0.4 mL/100 g *

* these are rounded figures as differences exist between techniques and publications