Differentiation of serous and purulent fluids in vitro and in vivo by means of diffusion-weighted MR imaging.

Aim: The aim of this study was to test the feasibility for differentiation of serous fluid collections and abscess fluid with diffusion-weighted imagi ng and to compare three different diffusion sequences. Material and Methods : Thirteen puncture samples (6 serous, 7 purulent) and 19 patients with eit her serous fluid collections (n=12) or abscesses (n=7)were examined with di ffusion-weighted spin-echo (SE), stimulated-echo (STE), and fat-suppressed SE (SE-SPIR) sequences. For in vitro studies 4 different b-factors (0, 87, 355, 798 s/mm(2) in SE and SE-SPIR and 0, 51, 204, 460 s/mm(2) in STE) were chosen and the apparent diffusion coefficient (ADC) was calculated. For in vivo measurements identical sequences with two b-factors (0,598 s/mm(2) in SE and SE-SPIR and 0,360 s/mm(2) in STE) were applied and the normalized s ignal attenuation was calculated. A navigator-echo technique and peripheral pulse triggering was used for motion artifact reduction. Results: The in v itro study yielded an ADC of serous fluid, which was close to that of free water, whereas for purulent fluid a significantly lower ADC was calculated. During in vivo examinations, serous fluids showed a strong signal attenuat ion (down to 22-32% of basic value) compared to a minor signal attenuation in purulent fluids (down to 86-94% of basic value) (p<0.05). Conclusions: I n summary, with all three investigated diffusion schemes serous and purulen t fluids can be clearly differentiated.