Functional-morphologic MR imaging with ultrasmall superparamagnetic particles of iron oxide in acute and chronic soft-tissue infection: study in rats.
OBJECTIVE
To investigate the use of magnetic resonance (MR) imaging enhanced with ultrasmall superparamagnetic particles of iron oxide (USPIO) to identify acute, early chronic, and late chronic abscess formation in an experimental model of soft-tissue abscess.


METHODS
Experimental soft-tissue infection in 15 rats was imaged with an MR imaging unit on days 1 and 2 (acute), days 5 and 6 (early chronic), and days 8 and 9 (late chronic) after inoculation of the infectious agent. All animals were imaged without contrast enhancement and immediately and 24 hours after USPIO administration. MR and histopathologic findings were compared. The changes in relative signal intensity (SI) and in the extent and pattern of contrast enhancement (macrophage distribution) between the animal groups were analyzed. Statistical testing was performed with Kruskal-Wallis analysis of variance and the chi2 test.


RESULTS
At 24 hours after USPIO administration, the relative SI of the abscess wall and the relative macrophage extent were 0.50 (0.33-0.73) and 1.03 (0.90-1.08), respectively, for acute infection; 0.11 (0.10-0.18) and 0.94 (0.93-1.01) for early chronic infection; and 0.53 (0.44-0.58) and 0.80 (0.77-0.83) for late chronic infection. The changes in enhancement pattern (P <.001), relative SI (P <.001), and relative macrophage extent (P <.05) with time were significant.


CONCLUSIONS
The macrophage distribution pattern increases the specificity of MR findings in chronic infection and allows differentiation between areas with active inflammation and areas of reparative granulation tissue.
Kaim
Achim H
AH
Department of Diagnostic Radiology, University Hospital Basel, Switzerland. akaim@uhbs.ch
Jundt
Gernot
G
Wischer
Thorsten
T
O'Reilly
Terence
T
Frohlich
Johannes
J
von Schulthess
Gustav K
GK
Allegrini
Peter R
PR
D000208:Acute Disease; D000818:Animals; D002908:Chronic Disease; D005260:Female; D005290:Ferric Compounds; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008280:Magnetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D018461:Soft Tissue Infections / Q000473:pathology*
D005290:Ferric Compounds; C000499:ferric oxide