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. 2022 Nov 7:9:1008447.
doi: 10.3389/fvets.2022.1008447. eCollection 2022.

Temporal and sequence-related variability in diffusion-weighted imaging of presumed cerebrovascular accidents in the dog brain

Elizabeth Boudreau  1 , Sharon C Kerwin  1 , Emily B DuPont  1 , Jonathan M Levine  1 , John F Griffin 4th  2
Affiliations

Temporal and sequence-related variability in diffusion-weighted imaging of presumed cerebrovascular accidents in the dog brain

Elizabeth Boudreau et al. Front Vet Sci. .

Abstract

Diffusion-weighted MRI (DWI) is often used to guide clinical interpretation of intraparenchymal brain lesions when there is suspicion for a cerebrovascular accident (CVA). Despite widespread evidence that imaging and patient parameters can influence diffusion-weighted measurements, such as apparent diffusion coefficient (ADC), there is little published data on such measurements for naturally occurring CVA in clinical cases in dogs. We describe a series of 22 presumed and confirmed spontaneous canine CVA with known time of clinical onset imaged on a single 3T magnet between 2011 and 2021. Median ADC values of < 1.0x10-3 mm2/s were seen in normal control tissues as well as within CVAs. Absolute and relative ADC values in CVAs were well-correlated (R2 = 0.82). Absolute ADC values < 1.0x10-3 mm2/s prevailed within ischemic CVAs, though there were exceptions, including some lesions of < 5 days age. Some lesions showed reduced absolute but not relative ADC values when compared to matched normal contralateral tissue. CVAs with large hemorrhagic components did not show restricted diffusion. Variation in the DWI sequence used impacted the ADC values obtained. Failure to identify a region of ADC < 1.0x10-3 mm2/s should not exclude CVA from the differential list when clinical suspicion is high.

Keywords: ADC; MRI; canine; diffusion; ischemia; stroke.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
Schematic of record search and case selection process.
Figure 2
Figure 2
Examples of ROI (blue outline) and contralateral normal control (red outline) region selection for a single slice from representative example ischemic CVA. A region was selected for every slice on the T2-FLAIR transverse images and copied to the corresponding slice for the DWI and ADC series. The histogram at the right shows the ADC values within the ROI, as well as the median ADC value within the contralateral control region (dotted line).
Figure 3
Figure 3
Correlation between absolute and relative median ADC values for ischemic (black circles) and hemorrhagic (gray circles) CVAs. The dashed line is best-fit linear regression (equation in text). R2 = 0.82, indicating good correlation.
Figure 4
Figure 4
ADC value histograms for eight ischemic CVAs, arranged by duration of clinical signs (more recent events below older events). Black outline bars indicate non-EPI DWI, and light gray bars indicate EPI DWI. The dotted lines show median ADC values for the control regions for each histogram, with black dotted lines corresponding to non-EPI DWI, and gray dotted lines corresponding to EPI DWI. Median absolute and relative ADC values for the T2-FLAIR ROIs, median absolute ADC values for the contralateral control regions, and anatomical locations of the lesions/control selections are listed in Table 1. For most cases, the ROIs had median absolute ADC values −3 mm2/s and median relative ADC values < 1. The CVAs with the shortest duration had the lowest ADC values.
Figure 5
Figure 5
Examples of ROI (blue outline) and contralateral normal control (red outline) region selection for a representative example hemorrhagic CVA. The regions were selected on the T2-FLAIR transverse images and copied to the DWI and ADC series. The region of T2* hypointensity was defined on the corresponding T2* transverse image (lavender outline). Pixels that were within both the T2-FLAIR hyperintense region and the T2* hypointense region (green outline) were excluded from the resulting probability histogram (right). The histogram shows the ADC values of non-excluded pixels within the ROI, as well as the median ADC value within the contralateral control region (dotted line).
Figure 6
Figure 6
ADC value histograms for the T2-FLAIR hyperintense region adjacent to eight hemorrhagic CVAs, arranged by duration of clinical signs (more recent events below older events). Black outline bars indicate non-EPI DWI, and gray bars indicate EPI DWI. The dotted lines show median ADC values for the control regions for each histogram, with black dotted lines corresponding to non-EPI DWI, and gray dotted lines corresponding to EPI DWI. Median absolute and relative ADC values for the T2-FLAIR ROIs, median absolute ADC values for the contralateral control regions, and anatomical locations of the lesions/control selections are listed in Table 1. There was no evidence of restricted diffusion adjacent to the T2* hypointense region in any dog.
Figure 7
Figure 7
Probability histograms of pixel values within the T2* hypointense ROIs for b0 (A) and b1 (B) DWI series (see text for variable definitions). Non-EPI series used b1 = 800s/mm2 and are shown in black outline. The pixel values within ROIs defined by the T2* hypointense region were more likely to be zero or close to zero on non-EPI ADC series for both b0 and b1.
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