IMAGING OF THE APPARENT DIFFUSION-COEFFICIENT FOR THE EVALUATION OF CEREBRAL METABOLIC RECOVERY AFTER CARDIAC-ARREST

The apparent diffusion coefficient (ADC) of water is a sensitive indic ator of water and ion homeostasis of brain. Resuscitation of the brain after cardiac arrest, the most frequent reason for global cerebral is chemia under clinical conditions, depends critically on the reversal o f disturbances of water and ion homeostasis. We, therefore, investigat ed whether ADC imaging can be used to monitor the development and reve rsal of ischemic brain injury during and after cardiac arrest. Ten adu lt mongrel normothermic cats were anesthetized with alfentanil and mid azolam, immobilized with pancuronium, and mechanically ventilated with O-2/N2O. Arterial, left ventricular, central venous, and intracranial pressures were monitored throughout the experiment. Magnetic resonanc e imaging was performed in a 4.7T MR scanner with a shielded gradient system. Diffusion-weighted images (DWI) were obtained by pulsed gradie nt spin echoes (diffusion weighting factor b: 0, 500, 1000, 1500 s/mm( 2)). Quantitative ADC images were calculated from DWIs by fitting sign al intensities against b-factors. Fifteen minute cardiac arrest was in duced in the magnet by electrical fibrillation. Resuscitation was also carried out in the magnet, using a pneumatic vest for remotely contro lled closed chest cardiac massage. Seven of 10 animals were resuscitat ed successfully and subsequently monitored for 3 h. During cardiac arr est, ADC declined from 678 +/- 79 x 10(-6) to 430 +/- 128 x 10(-6) mm( 2)/s (63% of baseline). In the successfully resuscitated animals ADC r eturned to 648 +/- 108 x 10(-6) mm(2)/s within 30 min and remained at this level throughout the 3 h of recirculation. Regional evaluations o f ADC revealed a transient overshoot in brainstem and basal ganglia to 114% of control at 15 min before returning to baseline values after 4 0 min. Failure of cardiac resuscitation prevented ADC normalization an d led to its further decline to below 50% of control. Postcardiac arre st normalization of ADC maps correlated with homogeneous return of ATP , glucose, and lactate to near normal, whereas failure of ADC normaliz ation was associated with depletion of ATP and glucose and severe lact ate accumulation. In conclusion, our data indicate, that normalization of ADC is a reliable indicator of cerebral recovery after resuscitati on from cardiac arrest.