Abscess Diffusion features(DWI / ADC )

Diffusion imaging may help in the differential diagnosis of cerebral abscess versus necrotic neoplasm. 
This is a rapid acquisition with moderate spatial resolution that can yield information on the entire brain and multiple lesions, even in agitated patients. 
Optimizing echo-planar scan parameters (phase offset and delay) is important to obtain high-quality diffusion images. For this reason, the scan is often simulated prior to being run to allow optimization of these parameters. This may take 1 to 3 min. The values obtained are then passed to the scanner and the sequence performed. (This is unique to Marconi's system.) 
Acquire images at b-values  of both 0 and 1000 sec/mm2, each applied in three orthogonal directions. 
These data provide raw diffusion-weighted multishot echo-planar images and is used to process apparent diffusion coefficient (ADC) maps. 


DWI / ADC features for Abscess 

• high DWI signal is usually present centrally
• often this represents true restricted diffusion (low signal on ADC)
• peripheral or patchy restricted diffusion may also be seen; this finding is however not as constant as one may think, with up to half of rim enhancing lesions demonstrating some restriction not proving to be abscesses 2.  
• in many instances high DWI are associated with high ADC signal, consistent with T2 shine through of the central necrotic portion