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High temporal resolution parametric MRI monitoring of the initial ischemia/reperfusion phase in experimental acute kidney injury.

Pohlmann A, Hentschel J, Fechner M, Hoff U, Bubalo G, Arakelyan K, Cantow K, Seeliger E, Flemming B, Waiczies H, Waiczies S, Schunck WH, Dragun D, Niendorf T - PLoS ONE (2013)

Bottom Line: There is an unmet need to better understand the mechanisms operative during the initial phase of ischemic AKI.Our study demonstrated for the first time that continuous and high temporal resolution parametric MRI is feasible for in-vivo monitoring and characterization of I/R induced AKI in rats.This technique may help in the identification of the timeline of key events responsible for development of renal damage in hypoperfusion-induced AKI.

View Article: PubMed Central - PubMed

Affiliation: Berlin Ultrahigh Field Facility, Max Delbrück Center for Molecular Medicine, Berlin, Germany. andreas.pohlmann@mdc-berlin.de

ABSTRACT
Ischemia/reperfusion (I/R) injury, a consequence of kidney hypoperfusion or temporary interruption of blood flow is a common cause of acute kidney injury (AKI). There is an unmet need to better understand the mechanisms operative during the initial phase of ischemic AKI. Non-invasive in vivo parametric magnetic resonance imaging (MRI) may elucidate spatio-temporal pathophysiological changes in the kidney by monitoring the MR relaxation parameters T2* and T2, which are known to be sensitive to blood oxygenation. The aim of our study was to establish the technical feasibility of fast continuous T2*/T2 mapping throughout renal I/R. MRI was combined with a remotely controlled I/R model and a segmentation model based semi-automated quantitative analysis. This technique enabled the detailed assessment of in vivo changes in all kidney regions during ischemia and early reperfusion. Significant changes in T2* and T2 were observed shortly after induction of renal ischemia and during the initial reperfusion phase. Our study demonstrated for the first time that continuous and high temporal resolution parametric MRI is feasible for in-vivo monitoring and characterization of I/R induced AKI in rats. This technique may help in the identification of the timeline of key events responsible for development of renal damage in hypoperfusion-induced AKI.

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Standardized segmentation model of the rat kidney that is used to place regions-of-interest (ROI) in the cortex (C1,C2,C3), the outer medulla (O1,O2,O3) and the inner medulla (I1,I2,I3).A) Segmentation model overlaid onto a photograph of a freshly excised coronal view of a rat kidney. During analysis the rectangular reference frame is manually positioned around the kidney in the coronal view. The ROIs are placed automatically at pre-defined relative positions within this reference frame (number ranges signify percentages of the reference frame dimensions). B) Example of a color-coded T2* parameter map, showing a rat kidney in-vivo together with an overlay of the segmentation model.
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pone-0057411-g001: Standardized segmentation model of the rat kidney that is used to place regions-of-interest (ROI) in the cortex (C1,C2,C3), the outer medulla (O1,O2,O3) and the inner medulla (I1,I2,I3).A) Segmentation model overlaid onto a photograph of a freshly excised coronal view of a rat kidney. During analysis the rectangular reference frame is manually positioned around the kidney in the coronal view. The ROIs are placed automatically at pre-defined relative positions within this reference frame (number ranges signify percentages of the reference frame dimensions). B) Example of a color-coded T2* parameter map, showing a rat kidney in-vivo together with an overlay of the segmentation model.

Mentions: Mean T2* (R2*) and T2 (R2) values for several regions-of-interest (ROI) within the renal cortex, outer medulla and inner medulla were calculated from the parameter maps. To reduce operator-induced variability in the ROI placement a standardized segmentation model of the rat kidney was developed. For this purpose special care was taken with regard to the location of the ROIs in the kidney. The aim was to determine ROIs strictly according to morphological kidney features, i.e., the distinct renal layers: cortex, outer medulla, and inner medulla (Figure 1). To this end, the dimensions of the rat kidney layers were measured in a series of freshly harvested kidneys as well as in a series of formalin-fixed kidneys (altogether 16 kidneys). To account for the inter-individual variability of the absolute length (cranial to caudal extremities) and width (lateral to medial border) of the kidneys, a rectangular frame that tightly encloses the kidney in the coronal view was used as a reference. The segmentation model consists of nine ROIs at defined relative positions (percentages of both diameters) within this rectangular reference frame (Figure 1). The size and positions of nine ROIs were defined for three ROIs in the renal cortex (COR), for three ROIs in the outer medulla (OM), and for three ROIs in the inner medulla (IM). All ROIs were placed in safe distance from the borders between these kidney layers to avoid any ‘contamination’ from the neighboring layers (partial segment effects) and to allow for inter-individual variations in morphology without the need to change the ROI position. The implementation of this model in a semi-automated analysis program developed in ImageJ (NIH, Bethesda, MD, USA, http://imagej.nih.gov/ij) limited user interaction to the placement of the rectangular reference frame around the kidney. The automatically placed ROIs were overlaid onto the parameter maps and their position was visually validated. ROIs that included artifacts were excluded from further analysis.


High temporal resolution parametric MRI monitoring of the initial ischemia/reperfusion phase in experimental acute kidney injury.

Pohlmann A, Hentschel J, Fechner M, Hoff U, Bubalo G, Arakelyan K, Cantow K, Seeliger E, Flemming B, Waiczies H, Waiczies S, Schunck WH, Dragun D, Niendorf T - PLoS ONE (2013)

Standardized segmentation model of the rat kidney that is used to place regions-of-interest (ROI) in the cortex (C1,C2,C3), the outer medulla (O1,O2,O3) and the inner medulla (I1,I2,I3).A) Segmentation model overlaid onto a photograph of a freshly excised coronal view of a rat kidney. During analysis the rectangular reference frame is manually positioned around the kidney in the coronal view. The ROIs are placed automatically at pre-defined relative positions within this reference frame (number ranges signify percentages of the reference frame dimensions). B) Example of a color-coded T2* parameter map, showing a rat kidney in-vivo together with an overlay of the segmentation model.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3585384&req=5

pone-0057411-g001: Standardized segmentation model of the rat kidney that is used to place regions-of-interest (ROI) in the cortex (C1,C2,C3), the outer medulla (O1,O2,O3) and the inner medulla (I1,I2,I3).A) Segmentation model overlaid onto a photograph of a freshly excised coronal view of a rat kidney. During analysis the rectangular reference frame is manually positioned around the kidney in the coronal view. The ROIs are placed automatically at pre-defined relative positions within this reference frame (number ranges signify percentages of the reference frame dimensions). B) Example of a color-coded T2* parameter map, showing a rat kidney in-vivo together with an overlay of the segmentation model.
Mentions: Mean T2* (R2*) and T2 (R2) values for several regions-of-interest (ROI) within the renal cortex, outer medulla and inner medulla were calculated from the parameter maps. To reduce operator-induced variability in the ROI placement a standardized segmentation model of the rat kidney was developed. For this purpose special care was taken with regard to the location of the ROIs in the kidney. The aim was to determine ROIs strictly according to morphological kidney features, i.e., the distinct renal layers: cortex, outer medulla, and inner medulla (Figure 1). To this end, the dimensions of the rat kidney layers were measured in a series of freshly harvested kidneys as well as in a series of formalin-fixed kidneys (altogether 16 kidneys). To account for the inter-individual variability of the absolute length (cranial to caudal extremities) and width (lateral to medial border) of the kidneys, a rectangular frame that tightly encloses the kidney in the coronal view was used as a reference. The segmentation model consists of nine ROIs at defined relative positions (percentages of both diameters) within this rectangular reference frame (Figure 1). The size and positions of nine ROIs were defined for three ROIs in the renal cortex (COR), for three ROIs in the outer medulla (OM), and for three ROIs in the inner medulla (IM). All ROIs were placed in safe distance from the borders between these kidney layers to avoid any ‘contamination’ from the neighboring layers (partial segment effects) and to allow for inter-individual variations in morphology without the need to change the ROI position. The implementation of this model in a semi-automated analysis program developed in ImageJ (NIH, Bethesda, MD, USA, http://imagej.nih.gov/ij) limited user interaction to the placement of the rectangular reference frame around the kidney. The automatically placed ROIs were overlaid onto the parameter maps and their position was visually validated. ROIs that included artifacts were excluded from further analysis.

Bottom Line: There is an unmet need to better understand the mechanisms operative during the initial phase of ischemic AKI.Our study demonstrated for the first time that continuous and high temporal resolution parametric MRI is feasible for in-vivo monitoring and characterization of I/R induced AKI in rats.This technique may help in the identification of the timeline of key events responsible for development of renal damage in hypoperfusion-induced AKI.

View Article: PubMed Central - PubMed

Affiliation: Berlin Ultrahigh Field Facility, Max Delbrück Center for Molecular Medicine, Berlin, Germany. andreas.pohlmann@mdc-berlin.de

ABSTRACT
Ischemia/reperfusion (I/R) injury, a consequence of kidney hypoperfusion or temporary interruption of blood flow is a common cause of acute kidney injury (AKI). There is an unmet need to better understand the mechanisms operative during the initial phase of ischemic AKI. Non-invasive in vivo parametric magnetic resonance imaging (MRI) may elucidate spatio-temporal pathophysiological changes in the kidney by monitoring the MR relaxation parameters T2* and T2, which are known to be sensitive to blood oxygenation. The aim of our study was to establish the technical feasibility of fast continuous T2*/T2 mapping throughout renal I/R. MRI was combined with a remotely controlled I/R model and a segmentation model based semi-automated quantitative analysis. This technique enabled the detailed assessment of in vivo changes in all kidney regions during ischemia and early reperfusion. Significant changes in T2* and T2 were observed shortly after induction of renal ischemia and during the initial reperfusion phase. Our study demonstrated for the first time that continuous and high temporal resolution parametric MRI is feasible for in-vivo monitoring and characterization of I/R induced AKI in rats. This technique may help in the identification of the timeline of key events responsible for development of renal damage in hypoperfusion-induced AKI.

Show MeSH
Related in: MedlinePlus