Dynamic susceptibility contrast (DSC) MR perfusion

Dynamic susceptibility contrast (DSC) MR perfusion is one of the most frequently used techniques for MRI perfusion, and relies on the susceptibility induced signal loss on T2* weighted sequences which results from a bolus of gadolinium-based contrast passing through a capillary bed.  The most commonly calculated parameters are rCBV, rCBF and MTT. 

Confusingly this technique is sometimes referred to, perhaps more accurately, as dynamic susceptibility contrast-enhanced MR perfusion, still abbreviated to DSC. This should not be confused with dynamic contrast-enhanced (DCE) MR perfusion which relies on T1 shortening due to gadolinium-based contrast. 

Physics and technique

DSC perfusion exploits the regional susceptibility-induced signal loss caused by paramagnetic contrast agents (such as commonly used gadolinium-based compounds) on T2 weighted images ^1,2. Although this technique can be performed with both T2 (e.g. spin echo) and T2* (e.g. gradient-echo echo-planar) sequences, the former requires higher doses of contrast, which is why T2* techniques are more commonly employed ². 

A bolus of gadolinium-containing contrast is injected intravenously and rapid repeated imaging of the tissue (most commonly brain) is performed during the first pass. This leads to a series of images with the signal in each voxel representing intrinsic tissue T2/T2* signal attenuated by susceptibility-induced signal loss proportional to the amount of contrast primarily in the microvasculature ^1,2. 

Then a region's signal is interrogated over the time-course of the perfusion sequence, and a signal intensity-time curve is generated, from which various parameters can be calculated (rCBV, rCBF, MTT etc..) 

These values can then be used to create colour maps of regional perfusion. 

Pitfalls

Because this technique relies upon detecting signal loss due to small amounts of contrast, if there is significant signal loss due to presence of calcification or blood products, or due to artifact from adjacent dense bone or aerated sinuses, obtained values will not be reliable. Similarly, values in a region immediately adjacent to large vessels will also be affected.