MRI measurements of water diffusion: impact of region of interest selection on ischemic quantification.
OBJECTIVE
To investigate the effect of ADC heterogeneity on region of interest (ROI) measurement of isotropic and anisotropic water diffusion in acute (< 12 h) cerebral infarctions.


METHODS
Full diffusion tensor images were retrospectively analyzed in 32 patients with acute cerebral infarction. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values were measured in ischemic lesions and in the corresponding contralateral, normal appearing brain by using four ROIs for each patient. The 2 x 2 pixel square ROIs were placed in the center, the lateral rim and the medial rim of the infarction. In addition, the whole volume of the infarction was measured using a free hand method. Each ROI value obtained from the ischemic lesion was normalized using contralateral normal ROI values.


RESULTS
The localization of the ROIs in relation to the ischemic lesion significantly affected ADC measurement (P < 0.01, using Friedman test), but not FA measurement (P = 0.25). Significant differences were found between ADC values of the center of the infarction versus whole volume (P < 0.01), and medial rim versus whole volume of infarction (P < 0.001) with variation of relative ADC values up to 11%. The differences of absolute ADC for these groups were 22 and 23%, respectively. The lowest ADC was found in the center, followed by medial rim, lateral rim and whole volume of infarction.


CONCLUSIONS
ADC quantification may provide variable results depending on ROI method. The ADC and FA values, obtained from the center of infarction tend to be lower compared to the periphery. The researchers who try to compare studies or work on ischemic quantification should be aware of these differences and effects.
Department of Radiology, School of Medicine, Adnan Menderes University, Aydin 09100, Turkey. yozsunar@adu.edu.tr
Yelda
Y
Ozsunar
Kutsi
K
Koseoglu
Thierry A G M
TA
Huisman
Walter
W
Koroshetz
A Gregory
AG
Sorensen
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D001834:Body Water / Q000737:chemistry; D001921:Brain / Q000473:pathology; D001923:Brain Chemistry; D002545:Brain Ischemia / Q000175:diagnosis* / Q000473:pathology; D002544:Cerebral Infarction / Q000175:diagnosis* / Q000473:pathology; D002648:Child; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods* / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008297:Male; D016555:Matched-Pair Analysis; D008875:Middle Aged; D012189:Retrospective Studies; D018709:Statistics, Nonparametric; D020521:Stroke / Q000175:diagnosis / Q000473:pathology