SERIAL DETERMINATIONS OF CEREBRAL WATER-CONTENT BY MAGNETIC-RESONANCE-IMAGING AFTER AN INFUSION OF HYPERTONIC SALINE

Objective: To determine regional cerebral water content in vivo by mag netic resonance imaging (MRI) after the administration of 7.5% saline in brain-lesioned rabbits. Design: Randomized, controlled, interventio n trial. Setting: University animal laboratory. Subjects: Eighteen mal e New Zealand white rabbits, randomly assigned to one of three groups. Interventions: The animals were anesthetized (1% halothane), intubate d, and mechanically ventilated to maintain end-tidal CO2 tension betwe en 30 and 35 mm Hg (4 and 4.7 kPa). Arterial and central venous cathet ers were inserted and arterial blood samples were serially obtained du ring the experiment. Serum osmolality was measured. A cryogenic cerebr al lesion was produced by pouring liquid nitrogen for 1 min into a fun nel placed on the intact skull over the right hemisphere. One group of animals received 20 mL of 7.5% saline intravenously 150 mins after th e cerebral lesion was generated (7.5% saline group, n = 7). A second g roup of animals received the same volume of 0.9% saline intravenously (0.9% sa line group, n = 7). In a third group of animals (control grou p, n = 4) no lesion was created and no fluid administered. Measurement s and Main Results: Five spin-echo TS-weighted MRIs of the brain were acquired at 90 mins (Baseline 1), 120 mins (Baseline 2), 150 mins (Inf usion), 180 mins (Infusion + 30 mins), and 210 mins (Infusion + 60 min s) after the generation of the cerebral lesion. In the control group, two scans separated by a time interval of 120 mins were performed. The percent changes in signal intensity between the first and the four fo llowing scans of a coronal slice of the central region were determined . Analysis of variance and the Mann Whitney U test were used for stati stical analysis. Data are presented as mean +/- SD; p < .05 was consid ered significant. Serum osmolality increased significantly from 308 +/ - 13 mosm/L to 349 +/- 19 mosml/L after the infusion of 20 mt of 7.5% saline, but did not change after the administration of 0.9% saline. Si gnal intensity in the area between the caudal edge of the core of the lesion and the basal ganglia was 9 +/- 8% higher on the injured side t han in the corresponding area on the contralateral side (p < .05). Com pared with Baseline 1, signal intensity at Infusion + 60 mins decrease d by 26.3 +/- 13.7% in the 7.5% saline group, whereas it decreased by 10.4 +/- 8.6% in the 0.9% saline group (p < .05 between groups). Signa l intensity decreased only slightly and nonsignificantly by 0.6 t 4.4% between the two scans in the control group. Conclusions: The administ ration of a 7.5% saline solution causes a prompt and substantial decre ase in cerebral water con tent as assessed by spin echo T2-weighted MR I. Magnetic resonance imaging offers the opportunity for repeated, non invasive in vivo determinations of cerebral water content.