Abstract
This study aimed to investigate whether intravoxel incoherent motion (IVIM) parameters can identify ischemic changes in the rat cerebral cortex using a preclinical ultra-high-field 11.7 Tesla magnetic resonance imaging (11.7TMRI) scanner. In nine female Wistar rats (eight weeks old), diffusion-weighted imaging (DWI) for IVIM analysis was successfully performed before (Pre) and after unilateral (UCCAO) and bilateral (BCCAO) common carotid artery occlusion. From the acquired DWI signals averaged in six regions of interest (ROI) placed on the cortex, volume fraction of perfusion compartment (F), pseudo diffusion coefficient (D*), F × D* and apparent diffusion coefficient (ADC) were determined as IVIM parameters in the following three DWI signal models: the bi-exponential, kurtosis, and tri-exponential model. For a subgroup analysis, four rats that survived two weeks after BCCAO were assigned to the long survival (LS) group, whereas the non-LS group consisted of the remaining five animals. Each IVIM parameter change among three phases (Pre, UCCAO and BCCAO) was statistically examined in each ROI. Then, the change in each rat group was also examined for subgroup analysis. All three models were able to identify cerebral ischemic change and damage as IVIM parameter change among three phases. Furthermore, the kurtosis model could identify the parameter changes in more regions than the other two models. In the subgroup analysis with the kurtosis model, ADC in non-LS group significantly decreased between UCCAO and BCCAO but not in LS group. IVIM parameters at 11.7TMRI may help us to detect the subtle ischemic change; in particular, with the kurtosis model.
Highlights
Preclinical ultra-high-field magnetic resonance imaging (MRI) with static magnetic fields of more than 7 Tesla (T) has identified even subtle microstructural morphological and functional changes in biological tissues using diffusion-weighted imaging (DWI)[1,2,3,4]
Using ultra-high-field 11.7 T magnetic resonance imaging (11.7TMRI), we investigated in this study which DWI model of intravoxel incoherent motion (IVIM) parameters sufficiently identifies different ischemic states, how the cerebral hemodynamics changes in the common carotid artery occlusion (CCAO) model, and how the rat cortex is damaged in this animal model
The results of this study demonstrated that the features of the IVIM parameters change with depending on the DWI signal model used for the parameter calculation; in particular, the parameter determined with the Kur model identified the largest number of regions showing the significant change in the rat cortex among three CCAO phases in the three examined models
Summary
Preclinical ultra-high-field magnetic resonance imaging (MRI) with static magnetic fields of more than 7 Tesla (T) has identified even subtle microstructural morphological and functional changes in biological tissues using diffusion-weighted imaging (DWI)[1,2,3,4]. For IVIM analysis, various DWI signal models have been proposed to assess water diffusion features in different views such as diffusivities based on free (Gaussian) and restricted water molecules or fast and slow diffusivities in multiple compartments of the tissue[7,10]; it remains unknown which DWI model of IVIM parameter estimation can appropriately identify subtle changes in ischemic states, especially at early stages without the presence of infarcts seen in chronic ischemia. Using ultra-high-field 11.7 T magnetic resonance imaging (11.7TMRI), we investigated in this study which DWI model of IVIM parameters sufficiently identifies different ischemic states, how the cerebral hemodynamics changes in the CCAO model, and how the rat cortex is damaged in this animal model
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