DETECTABILITY OF EARLY BRAIN MENINGITIS WITH MAGNETIC-RESONANCE-IMAGING

RATIONALE AND OBJECTIVES. The ability of high-field (1.5 T) magnetic r esonance imaging (MRI) to detect early brain meningitis was evaluated in a canine model, Contrast dose, timing postinjection, and imaging te chnique (specifically the use of magnetization transfer) were assessed . METHODS. Imaging of five canines was performed at 1.5 T 24 hours aft er injection of Cowans staphylococcus into the cisterna magna, Two con trol animals also were imaged using the same protocol, with one animal receiving a cisternal injection of nutrient broth only and the other no injection, Contrast doses of 0.1, 0.3, and 0.8 mmol/kg gadoteridol (Gd HP-DO3A or Pro-Hance) were compared, Scans were performed at 2, 12 , and 22 minutes after an initial injection of 0.1 mmol/kg, At each ti me point, paired T1-weighted scans with and without magnetization tran sfer (MT) were acquired, Thirty minutes after the initial injection of contrast, a supplemental dose of 0.2 mmol/kg was given (for a cumulat ive dose of 0.3 mmol/kg), Scans were then repeated at 2, 12, and 22 mi nutes after this dose was administered, A second supplemental contrast injection of 0.5 mmol/kg (for a cumulative dose of 0.8 mmol/kg) was g iven at 70 minutes, and immediate postinjection scans with and without MT were acquired, RESULTS. In the animals receiving a cisternal injec tion of bacteria, the degree of meningeal enhancement,vas greatest at 0.8 mmol/kg, intermediate at 0.3 mmol/kg, and least at 0.1 mmol/kg, Th ese conclusions mere constant whether imaging was performed with or wi thout MT. Scans in control studies did not demonstrate abnormal mening eal enhancement, High-contrast dose, MT, and acquisition of immediate postcontrast scans all resulted in statistically significant improveme nt, On masked film review, abnormal meningeal enhancement was noted in only 2 of 5 experimental dogs at a dose of 0.1 mmol/kg (regardless of the use of MT) compared with all animals at a dose of 0.3 mmol/kg, In 18 of 37 dogs (paired scans with and without MT), when abnormal enhan cement was noted, the use of MT improved the visualization of abnormal meningeal enhancement, CONCLUSIONS. In early brain meningitis, high-c ontrast dose (0.3 mmol/kg), MT, and scanning immediately after injecti on improve detection of abnormal meningeal enhancement, thus facilitat ing the diagnosis of meningitis, Of these factors, contrast dose is th e most important.