JOURNAL CLUB: Evaluation of Diffusion Kurtosis Imaging of Stroke Lesion With Hemodynamic and Metabolic MRI in a Rodent Model of Acute Stroke

Lu, Dongshuang; Jiang, Yinghua; Ji, Yang; Zhou, Iris Yuwen; Mandeville, Emiri T.; Lo, Eng H.; Wang, Xiaoying; Sun, Phillip Zhe

doi:10.2214/ajr.17.19134

Cited by 25 publications

(24 citation statements)

References 50 publications

(52 reference statements)

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“…This finding confirmed that the MK-and MD-mismatched region represents tissues with less damage that should concern the doctor and attempted to be rescued. Weber et al 32 and Lu et al 33 also confirmed that the mismatched regions can return to normal levels.…”

Section: Discussionmentioning

confidence: 87%

Diffusion kurtosis imaging and pathological comparison of early hypoxic–ischemic brain damage in newborn piglets

Xiao

Tian

et al. 2020

Sci Rep

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To investigate the application value of magnetic resonance diffusion kurtosis imaging (DKI) in hypoxic–ischemic brain damage (HIBD) in newborn piglets and to compare imaging and pathological results. Of 36 piglets investigated, 18 were in the experimental group and 18 in the control group. The HIBD model was established in newborn piglets by ligating the bilateral common carotid arteries and placing them into hypoxic chamber. All piglets underwent conventional MRI and DKI scans at 3, 6, 9, 12, 16, and 24 h postoperatively. Mean kurtosis (MK) and mean diffusivity (MD) maps were constructed. Then, the lesions were examined using light and electron microscopy and compared with DKI images. The MD value of the lesion area gradually decreased and the MK value gradually increased in the experimental group with time. The lesion areas gradually expanded with time; MK lesions were smaller than MD lesions. Light microscopy revealed neuronal swelling in the MK- and MD-matched and mismatched regions. Electron microscopy demonstrated obvious mitochondrial swelling and autophagosomes in the MK- and MD-matched region but normal mitochondrial morphology or mild swelling in the mismatched region. DKI can accurately evaluate early ischemic–hypoxic brain injury in newborn piglets.

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Section: Discussionmentioning

confidence: 87%

Diffusion kurtosis imaging and pathological comparison of early hypoxic–ischemic brain damage in newborn piglets

Xiao

Tian

et al. 2020

Sci Rep

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“…The ischemic diffusion lesion was automatically segmented from the ADC map using a K-means clustering algorithm of two clusters, with the label for the ischemic lesion automatically identified as the cluster of a reduced ADC. 44 The ipsilateral ischemic lesion was mirrored to the contralateral brain along the midline. 22 The pH-specific MRAPT analysis (ΔMRAPTR) is calculated as the difference between R 1 -scaled MTR asym and an estimated baseline image that is not pH-dependent.…”

Section: Discussionmentioning

confidence: 99%

“…In addition, APT‐weighted images were processed using MTR asym

()(, \frac{I (- 3.5 ppm) - I (+ 3.5 ppm)}{I_{0}})

, T 1 ‐normalized MTR asym

()(, R_{1} \cdot \frac{I ()(, - 3.5 ppm) - I ()(, + 3.5 ppm)}{I_{0}})

, and AREX

()(, R_{1} c o s^{2} θ \cdot ()(, \frac{I_{0}}{I ()(, + 3.5 ppm)} - \frac{I_{0}}{I ()(, - 3.5 ppm)}))

. The ischemic diffusion lesion was automatically segmented from the ADC map using a K‐means clustering algorithm of two clusters, with the label for the ischemic lesion automatically identified as the cluster of a reduced ADC 44 . The ipsilateral ischemic lesion was mirrored to the contralateral brain along the midline 22 …”

Section: Methodsmentioning

confidence: 99%

Investigating the origin of pH‐sensitive magnetization transfer ratio asymmetry MRI contrast during the acute stroke: Correction of T₁ change reveals the dominant amide proton transfer MRI signal

Jiang

Sun

2020

Magnetic Resonance in Med

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Purpose Amide proton transfer (APT) MRI is promising to serve as a surrogate metabolic imaging biomarker of acute stroke. Although the magnetization transfer ratio asymmetry (MTRasym) has been used commonly, the origin of pH‐weighted MRI effect remains an area of investigation, including contributions from APT, semisolid MT contrast asymmetry, and nuclear Overhauser enhancement effects. Our study aimed to determine the origin of pH‐weighted MTRasym contrast following acute stroke. Methods Multiparametric MRI, including T1, T2, diffusion and Z‐spectrum, were performed in rats after middle cerebral artery occlusion. We analyzed the conventional Z‐spectrum )(IΔωI0 and the apparent exchange spectrum )(Rex)(normalΔnormalω, being the difference between the relaxation‐scaled inverse Z‐spectrum and the intrinsic spinlock relaxation rate )(R10.166667em·0.166667emcos2normalθ0.166667em·0.166667emnormalI0normalI)(normalΔnormalω-R1ρ)(normalΔnormalω. The ischemia‐induced change was calculated as the spectral difference between the diffusion lesion and the contralateral normal area. Results The conventional Z‐spectrum signal change at −3.5 ppm dominates that at +3.5 ppm (−1.16 ± 0.39% vs. 0.76 ± 0.26%, P < .01) following acute stroke. In comparison, the magnitude of ΔRex change at 3.5 ppm becomes significantly larger than that at −3.5 ppm (−2.80 ± 0.40% vs. −0.94 ± 0.80%, P < .001), with their SNR being 7.0 and 1.2, respectively. We extended the magnetization transfer and relaxation normalized APT concept to the apparent exchange–dependent relaxation image, documenting an enhanced pH contrast between the ischemic lesion and the intact tissue, over that of MTRasym. Conclusion Our study shows that after the relaxation‐effect correction, the APT effect is the dominant contributing factor to pH‐weighted MTRasym following acute stroke.

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“…The mean MTR (MMTR) and MTR asym was calculated as

1 - \frac{I_{italicref} + I_{italiclabel}}{2 I_{0}}

and

\frac{I_{ref} - I_{label}}{I_{0}}

, respectively, where I ref and I label are the reference (−3.5 ppm) and label (+3.5 ppm) scans while I 0 is the control image without RF saturation. The ischemic diffusion lesion was automatically segmented from the ADC map using the K‐means clustering algorithm . We calculated the contrast‐to‐noise ratio (CNR) as the ratio of the difference and standard deviation from the ischemic lesion and the contralateral normal tissue.…”

Section: Methodsmentioning

confidence: 99%

Demonstration of magnetization transfer and relaxation normalized pH‐specific pulse‐amide proton transfer imaging in an animal model of acute stroke

Sun

2020

Magnetic Resonance in Med

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Purpose: pH-weighted amide proton transfer (APT) MRI is promising to serve as a new surrogate metabolic imaging biomarker for refined ischemic tissue demarcation.APT MRI with pulse-RF irradiation (pulse-APT) is an alternative to the routine continuous wave (CW-) APT MRI that overcomes the RF duty cycle limit. Our study aimed to generalize the recently developed pH-specific magnetization transfer and relaxationnormalized APT (MRAPT) analysis to pulse-APT MRI in acute stroke imaging. Methods: Multiparametric MRI, including CW-and pulse-APT MRI scans, were performed following middle cerebral artery occlusion in rats. We calculated pH-sensitive MTR asym and pH-specific MRAPT contrast between the ipsilateral diffusion lesion and contralateral normal area. Results: An inversion pulse of 10 to 15 ms maximizes the pH-sensitive MRI contrast for pulse-APT MRI. The contrast-to-noise ratio of pH-specific MRAPT effect between the contralateral normal area and ischemic lesion from both methods are comparable (3.25 ± 0.65 vs. 3.59 ± 0.40, P > .05). pH determined from both methods were in good agreement, with their difference within 0.1. Conclusions: Pulse-APT MRI provides highly pH-specific mapping for acute stroke imaging. K E Y W O R D Sacidosis, acute stroke, amide proton transfer (APT), chemical exchange saturation transfer (CEST), pulse-CEST MRI | 1527 SUN mismatch into perfusion/pH lesion mismatch (benign oligemia) and pH/diffusion lesion mismatch (metabolic penumbra), refining the routine mismatch paradigm. 13,14 Indeed, recent clinical trials have shown that response to endovascular reperfusion is not time dependent in patients with salvageable tissue, underscoring the importance of accurate penumbra mapping. [15][16][17] Although CEST MRI has often been implemented with continuous wave (CW) RF irradiation, the irradiation scheme of an RF pulse train is of reduced RF duty cycle and specific absorption rate (SAR), making it amenable to all scanners. 18 For slow exchangeable protons, it has been shown that pulse-CEST MRI with inversion pulses of intermediate durations provides similar contrast to that of CW-CEST MRI. [19][20][21] The routine magnetization transfer (MT) ratio asymmetry (MTR asym ) analysis, despite its pH sensitivity, is susceptible to the slightly asymmetric magnetization transfer (MT) effects. MTR asym is heterogeneous across the intact white and gray matter despite their little pH difference. 22 It has been shown that in rats, the T 1w -normalized CEST effects for the intact brain WM and GM are 2.08 ± 0.20 vs. 2.00 ± 0.23%/s (APT), −1.79 ± 0.88 vs. −0.89 ± 0.97%/s (MT contrast asymmetry) and 4.42 ± 0.58 vs. 3.38 ± 0.42%/s (nuclear overhauser enhancement, NOE), respectively. 23 Indeed, the noticeable NOE and MT contrast between brain WM and GM despite their little pH difference suggest that NOE and MT effects are not pH specific. The recently developed MT and relaxation-normalized APT (MRAPT) analysis minimizes the intrinsic non-pH related heterogeneity in pH-weighted MTR asym image toward pH-specific im...

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JOURNAL CLUB: Evaluation of Diffusion Kurtosis Imaging of Stroke Lesion With Hemodynamic and Metabolic MRI in a Rodent Model of Acute Stroke

Abstract: The present study confirms that DKI provides an expedient approach for refining the heterogeneous DWI lesion that is associated with graded metabolic derangement, which is promising for improving the infarction core definition and ultimately helping to guide stroke treatment.

Cited by 25 publications

References 50 publications

Diffusion kurtosis imaging and pathological comparison of early hypoxic–ischemic brain damage in newborn piglets

Diffusion kurtosis imaging and pathological comparison of early hypoxic–ischemic brain damage in newborn piglets

Investigating the origin of pH‐sensitive magnetization transfer ratio asymmetry MRI contrast during the acute stroke: Correction of T₁ change reveals the dominant amide proton transfer MRI signal

Demonstration of magnetization transfer and relaxation normalized pH‐specific pulse‐amide proton transfer imaging in an animal model of acute stroke

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JOURNAL CLUB: Evaluation of Diffusion Kurtosis Imaging of Stroke Lesion With Hemodynamic and Metabolic MRI in a Rodent Model of Acute Stroke

Abstract: The present study confirms that DKI provides an expedient approach for refining the heterogeneous DWI lesion that is associated with graded metabolic derangement, which is promising for improving the infarction core definition and ultimately helping to guide stroke treatment.

Cited by 25 publications

References 50 publications

Diffusion kurtosis imaging and pathological comparison of early hypoxic–ischemic brain damage in newborn piglets

Diffusion kurtosis imaging and pathological comparison of early hypoxic–ischemic brain damage in newborn piglets

Investigating the origin of pH‐sensitive magnetization transfer ratio asymmetry MRI contrast during the acute stroke: Correction of T1 change reveals the dominant amide proton transfer MRI signal

Demonstration of magnetization transfer and relaxation normalized pH‐specific pulse‐amide proton transfer imaging in an animal model of acute stroke

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Investigating the origin of pH‐sensitive magnetization transfer ratio asymmetry MRI contrast during the acute stroke: Correction of T₁ change reveals the dominant amide proton transfer MRI signal