Diffusion- and T2-Weighted MR Imaging of Lipiodol Induced Cerebral Infarcts in Cat: Early Findings in the Findings in the First 3 Hours

PURPOSE: This study was designed to evaluate early parenchymal changes of acute cerebral ischemia / infarct by using T2-weighted, diffusion-weighted, and calculated apparent diffusion coefficient (ADC) MR imaging. MATERIALS AND METHODS: The brain MR images were successfully obtained 30, 60, 90, 120, 150 and 180 minutes after intraarterial administration of Lipiodol (0.4 - 0.6 ml) into the common carotid artery in 10 of 11 cats (91%). T2-and diffusion-weighted images and ADC were analyzed and compared with histopathologic findings. RESULTS: High signal intensity on T2-weighted and diffusion-weighted images was found in one cerebral hemisphere 30 minutes after Lipiodol injection, which tended to increase with time until 3 hours. Subcortical white matter showed higher signal intensity than cortical gray matter since 30 minutes after embolization. ADC images showed decreased signal intensity in the embolized hemisphere, which tended to decrease until 3 hours. Microscopic findings of the area corresponding to the abnormal signal intensity on MR images revealed varying degrees of edema in the gray and white matters involved. CONCLUSION: It is suggested that Lipiodol can be used as a good embolic agent causing early ischemic changes in experimental models. In addition to T2-weighted images, diffusion-weighted and ADC images can provide the further informations in the evaluation of the early parenchymal changes of cerebral infarct.

A Study Using Diffusion-Weighted MR Image in the Experimental Models with Diffusion Difference

PURPOSE: To see the stability and error in the diffusion-weighted magnetic resonance (MR) imaging technique in the experimental models and to observe the signal intensities in the early cerebral lesions of the animal models. MATERIALS AND METHODS: Diffusion coefficients of acetone and distilled water were measured by diffusion-weighted MR image and were compared with actual values. Differentiation of diffusion from perfusion were done at the resin flow phantom. The signal intensities caused by early parenchymal changes were measured in normal, hypovolemic, and embolic, and dead animal models by using diffusion-weighted image and compared with pathoIogic finding and vital staining. RESULTS: Diffusion coefficients of acetone and distilled water were 4.48 x 10-3 and 2.72 x 10-3 which were very close to the actual values. Diffusion-weighted MR image obtained at flow phantom was not affected by flow (perfusion) at the 100-400 of b-factor range. Animal study done at that b-factor range revealed a significant signal difference between the left and right sides only at the embolic model induced by polyvinyl alchol particles (p<0.05). These changes were not detected in microscopic finding but could be identified in vital staining. CONCLUSION: Diffusion-weighted MR image can be used to detect early parenchymal change when the appropriate b-factor range was applied.

P MR spectroscopy study of the brain at 4.7 T in new borns

In vivo 31P NMR spectra were obtained in eight infant brain at 4.7T. Each phosphorus metabolite and its ratio were analyzed to evaluate the brain damage and maturity, and compared with the reported data obtained at the lower field strength. Measurement of T1 relaxation time at 4.7T was done in an infant and a cat brain in vivo. PCr/Pi and PCr/β-ATP ratio were used as a marker of brain damage. PME/PDE revealed higher values than those of the reported data obtained at the lower field strength and the difference was partly attributed to the long T1 relaxation time of PME rather than the brain immaturity. Although the resolution of the spectrum was improved at 4.7T, a long repetition time is recommended to minimize T1difference of phosphorus metabolites of brain at 4.7T.

An Experimental Study on Appearance of Flow in Multisection MR Imaging of Laminar Flow

In order to observe the pattern of a flow image on multisection MR imaging technique, a flow phantom experiment was preformed using a superconducting high filed 2.0 Tesla MRI scanner. The pattren of the first section images was homogeneous round at all flow velocities until the turbulence forming level. The patterns of the second section images,however,changed into a homogeneous round shape, a ring shape, a target shape, and a small round shape as the velocity increased. When scanned at velocities higher than the trubulence forming level, the images become distored and irregular, and eventually disappeared after the cut-off velocity. The homogeneous round image senn at the lower velocity levels in throught to be due to the overwhelming effects of fully managetized spins influxed into the imaging section during the prior repetition time(TR). Later in the higer velocity levels the effects of the partially saturated spins and fully magnetized spins influxed during the section transit time(TR/slice number) are added, and result in ring, target, and small round patterns in the second section image.