Rationale and Objectives
Nephrosclerosis occurs with aging and is characterized by increased kidney subcapsular surface irregularities at autopsy. Assessments of cortical roughness in vivo could provide an important measure of nephrosclerosis. The purpose of this study was to develop and validate an image-processing algorithm for quantifying renal cortical surface roughness in vivo and determine its association with age.
Materials and methods
Renal cortical surface roughness was measured on contrast-enhanced abdominal computed tomography (CT) images of potential living kidney donors. A roughness index was calculated based on geometric curvature of each kidney from three-dimensional images and compared to visual observation scores. Cortical roughness was compared between the oldest and youngest donors, and its interaction with cortical volume and age assessed.
Results
The developed quantitative roughness index identified significant differences in kidneys with visual surface roughness scores of 0 (minimal), 1 (mild), and 2 (moderate; P < .001) in a random sample of 200 potential kidney donors. Cortical roughness was significantly higher in the 94 oldest (64–75 years) versus 91 youngest (18–25 years) potential kidney donors ( P < .001). Lower cortical volume was associated with older age but not with roughness (r = −0.03, P = .75). The association of oldest age group with roughness (odds ratio [OR] = 1.8 per standard deviation [SD] of roughness index) remained significant after adjustment for total cortex volume (OR = 2.0 per SD of roughness index).
Conclusions
A new algorithm to measure renal cortical surface roughness from CT scans detected rougher surface in older compared to younger kidneys, independent of cortical volume loss. This novel index may allow quantitative evaluation of nephrosclerosis in vivo using contrast-enhanced CT.
Nephrosclerosis (glomerulosclerosis, tubular atrophy, interstitial fibrosis, and arteriosclerosis) occurs with normal aging, hypertension, and chronic kidney disease (CKD) . Detection of nephrosclerosis in vivo requires a renal biopsy. Autopsy studies have characterized nephrosclerosis by a rough irregular cortical surface . The detection of these morphologic surface changes in the kidney may help clinicians identify nephrosclerosis. However, the ability to assess cortical surface roughness in vivo has not been previously demonstrated.
Volume computed tomography (CT) imaging with contrast agent enhancement provides submillimeter spatial resolution and good image contrast for kidney anatomy. Kidney volume decreases with older age, whereas kidney function and other CKD risk factors can be associated with either increased or decreased volume . The decline in cortical volume that occurs with older age has been attributed to underlying atrophy and sclerosis of nephrons (nephrosclerosis). However, it is not known whether changes in cortical surface morphology are detectable with CT imaging or whether such changes, if observed, relate to clinical characteristics.
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Methods
Study Population
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Image Acquisition
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Kidney Segmentation
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Renal Cortical Surface Roughness Algorithm
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Statistical Analysis
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Results
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Table 1
Demographic Characteristics for Each Data Set Analyzed
Set Age, Years (Mean ± Standard Deviation) Female White 1 44 ± 12 53% 100% 2 44 ± 13 61% 97% 3 48 ± 11 57% 100% 4 Old group: 67 ± 3
Young group: 22 ± 2 Old group: 57%
Young group: 40% Old group: 100%
Young group: 93%
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Discussion
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Conclusions
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