Pixel-by-Pixel Spatiotemporal Progression of Focal Ischemia Derived Using Quantitative Perfusion and Diffusion Imaging

• Published in: Journal of cerebral blood flow and metabolism 2003-12, Vol.23 (12), p.1479-1488
• Main Authors: Shen, Qiang, Meng, Xiangjun, Fisher, Marc, Sotak, Christopher H., Duong, Timothy Q.
• Format: Article
• Language: English
• Subjects: Acute Disease; Animals; Biological and medical sciences; Brain Ischemia - pathology; Cerebrovascular Circulation; Diffusion; Diffusion Magnetic Resonance Imaging - methods; Diffusion Magnetic Resonance Imaging - standards; Image Processing, Computer-Assisted - methods; Image Processing, Computer-Assisted - standards; Male; Medical sciences; Neurology; Perfusion; Rats; Rats, Sprague-Dawley; Reproducibility of Results; Stroke - pathology; Vascular diseases and vascular malformations of the nervous system
• ISSN: 0271-678X; 1559-7016
• DOI: 10.1097/01.WCB.0000100064.36077.03

Pixel-by-pixel spatiotemporal progression of focal ischemia (permanent occlusion) in rats was investigated using quantitative perfusion and diffusion magnetic resonance imaging every 30 minutes for 3 hours. The normal left-hemisphere apparent diffusion coefficient (ADC) was 0.76 ± 0.03 × 10−3 mm2/s and CBF was 0.7 ± 0.3 mL · g−1 · min−1 (mean ± SD, n = 5). The ADC and CBF viability thresholds yielding the lesion volumes (LV) at 3 hours that best approximated the 2,3,5-triphenyltetrazolium chloride (TTC) infarct volumes (200 ± 30 mm2) at 24 hours were 0.53 ± 0.02 × 10−3 mm2/s (30% ± 2% reduction) and 0.30 ± 0.09 mL · g−1 · min−1 (57% ±11% reduction), respectively. Temporal evolution of the ADC- and CBF-defined LV showed a significant “perfusion-diffusion mismatch” up to 2 hours (P < 0.05, n = 11), a potential therapeutic window. Based on the viability thresholds, three pixel clusters were identified on the CBF-ADC scatterplots: (1) a “normal” cluster with normal CBF and ADC, (2) an “ischemic core” cluster with markedly reduced CBF and ADC, and (3) a “mismatch” cluster with reduced CBF but slightly reduced ADC. These clusters were color-coded and mapped onto the image and CBF-ADC spaces. Lesions grew peripheral and medial to the initial ADC abnormality. In contrast to the CBF distribution, the ADC distribution in the ischemic hemisphere was bimodal; the relatively time-invariant bimodal-ADC minima were 0.57 ± 0.02 × 10−3 mm2/s (corresponding CBF 0.35 ± 0.04 mL · g−1 · min−1), surprisingly similar to the TTC-derived thresholds. Together, these results illustrate an analysis approach to systemically track the pixel-by-pixel spatiotemporal progression of acute ischemic brain injury.