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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, MTT and Tmax ⁵.

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.?

After image acquisition, a region's signal is interrogated over the time-course of the perfusion sequence, generating a signal intensity-time curve, from which various parameters can be calculated (e.g. rCBV, rCBF, MTT). These values can then be used to create color 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 the 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.

Post-processing software can also introduce difference in results, with data showing that the same DSC data analyzed with different software packages can lead to different perfusion values⁴.

The presence of a leaky blood-brain barrier (for example in brain tumors) often leads to contrast agent leakage into the extracellular space, in these cases a leakage correction can be implemented to maintain the accuracy of parameter estimations ⁵.

Artifacts

DSC perfusion suffers from different type of artifacts ⁵:

• geometric distortion

  • close to regions with changes in tissue properties

  • appears as deformation in phase encoding direction

  • can be corrected with a B₀ field map acquired in opposite phase

• intravoxel dephasing

  • caused by local magnetic field variations across tissue boundaries within a voxel

  • can be reduced with shorter TE (not shorter than 30ms at 3T)

• slice timing misalignment

  • due to sliced acquired sequentially

  • exacerbated by long TR

  • can be reduced with shorter TR (<1000ms) or multi-slice acquisition

• B₁ intensity variations

  • spatially varying signal intensities in the image

  • can be corrected with acquisition of a B₁+ field map and a T1 map

• subject motion