Rationale and Objectives
The aim of this study was to investigate the potential of magnetic resonance imaging (MRI) T1 mapping and T1 relaxation time in the rotating frame (T1rho) for assessment of renal fibrosis in a rat model of unilateral ureteral obstruction (UUO).
Materials and Methods
UUO was created in 36 rats. Six rats were scanned at each of the six time points (on days 0, 1, 3, 5, 10, and 15 after UUO). The contralateral kidneys were examined as controls. Hematoxylin-eosin, Masson’s trichrome, and alpha-smooth muscle actin (α-SMA) antibody staining assays were performed. MRI data obtained with a 3.0T scanner were analyzed with α-SMA expression and Masson’s staining.
Results
The T1 relaxation times and T1rho values increased, and the mean apparent diffusion coefficient (ADC) values decreased with time after UUO. Simple regression analysis indicated that the mean ADCs, T1 relaxation times, and T1rho values had strong correlations with the α-SMA expression levels (R 2 = 0.34, R 2 = 0.66, R 2 = 0.71, respectively; P < .001) and positive Masson’s staining (R 2 = 0.38, R 2 = 0.67, R 2 = 0.65, respectively; P < .001).
Conclusions
The T1 mapping and T1rho parameters had better correlations with α-SMA expression and Masson’s staining than ADC values.
Introduction
Chronic kidney disease has become a global public health problem. Renal fibrosis is the common outcome and major pathologic basis for the progression of chronic kidney disease to end-stage renal failure . Therefore, assessment of renal fibrosis is important in determining the diagnosis, assessing the prognosis, and guiding treatment. Ideally, pathologic changes of the kidneys should be observed by renal biopsy. However, this is an invasive procedure, so it cannot be used repeatedly to monitor disease changes . In addition, serologic markers lack sufficient specificity and sensitivity to be useful in clinical practice .
Magnetic resonance imaging (MRI) may provide information regarding the structure and function of the kidneys . Diffusion-weighted imaging (DWI) reflects the random Brownian motion of water molecules in tissues, quantified by the apparent diffusion coefficient (ADC), which indirectly reflects the microstructure. Recently, some studies have shown that renal ADC values strongly correlate with histologic measures of fibrosis . However, the use of ADC to evaluate renal fibrosis is still controversial .
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Materials and Methods
Animal Protocol
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MRI
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MRI Data Analysis
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Histopathologic Examination
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Statistical Analysis
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Results
Histopathologic Examination
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ADC Values, T1 Relaxation Times, and T1rho Values on the Kidney with UUO
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TABLE 1
Mean Apparent Diffusion Coefficient (ADC) Values, T1 Relaxation Times, and T1rho Values of the Renal Parenchyma Before and After Unilateral Ureteral Obstruction (UUO) (mean ± SD) for the UUO Kidney
Time (d) n (35) ADC (×10 −3 mm 2 /s) T1 Relaxation Time (ms) T1rho Value (ms) 0 6 1.83 ± 0.15 1183 ± 72 142 ± 9.6 1 6 1.49 ± 0.08 1290 ± 93 149 ± 10.2 3 6 1.50 ± 0.06 1543 ± 112 175 ± 16.2 5 6 1.46 ± 0.09 1552 ± 152 187 ± 19.9 10 6 1.42 ± 0.06 1698 ± 97 212 ± 22.8 15 5 1.36 ± 0.06 1852 ± 137 228 ± 26.9P value <.001 <.001 <0.001
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Relationships Between ADC, T1 Mapping, and T1rho with α-SMA Expression and Masson’s Trichrome Staining
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Contralateral Side (Control) Kidneys
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TABLE 2
Mean Apparent Diffusion Coefficient (ADC) Values, T1 Relaxation Times, and T1rho Values of the Renal Parenchyma (mean ± SD) for Contralateral (Control) Kidneys
Time (d) n (35) ADC (×10 −3 mm 2 /s) T1 Relaxation Time m(ms) T1rho Value (ms) 0 6 1.85 ± 0.14 1184 ± 78 142 ± 8.4 1 6 1.85 ± 0.15 1214 ± 61 139 ± 7.4 3 6 1.91 ± 0.21 1149 ± 58 143 ± 9.4 5 6 1.87 ± 0.15 1171 ± 43 146 ± 8.2 10 6 1.87 ± 0.15 1161 ± 39 144 ± 8.2 15 5 1.90 ± 0.07 1158 ± 57 146 ± 8.9P value .984 .458 .708
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Discussion
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Conclusions
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