Patients
The retrospective study included 216 patients with chronic kidney disease (CKD) who examined abdominal MRI for different reasons and had the information of eGFR within four weeks from imaging date between January 2015 and January 2016.
The eGFR was calculated using CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration equation) [6].
The data including demographic information,
clinical,
and laboratory findings were obtained from the medical records of the patients.
Patients were classified into four grouped stages of CKD according to eGFR values adapted from the K/DOQI CKD classification: grouped stage 1,
eGFR,
≥90 mL/min/1.73m2; grouped stage 2,
eGFR,
60–89 mL/min/1.73m2; grouped stage 3,
eGFR,
30–59 mL/min/1.73m2; and grouped stage 4,
eGFR,
≤29 mL/min/1.73m2 [7].
DWI Technique
Axial respiratory-triggered single-shot echo-planar DWI was performed using 3-T scanners,
with a 32-channel phased-array body coil.
DWI were performed with tri-directional diffusion gradient b-values of 0,
50,
500 and 750 s/mm2.
The axial DWI of both kidneys was performed with the following parameters: repetition time (TR),
1891 ms; echo time (TE),
54 ms; flip angle,
90 degrees; slice thickness,
5 mm; intersection gap,
1 mm; excitations (NEX),
2; field of view (FOV),
350 mm; and matrix size,
140 x 116.
A spectral attenuated inversion-recovery technique for fat suppression was applied.
The ADC value was acquired from automatically generated ADC maps.
ROI placement and image interpretation
The total of six region of interests (ROIs) were placed each in the upper pole,
interpolar region and lower pole of bilateral kidneys for measurement of ADC values.
Each of the circular ROIs was placed without any preference for cortex or medulla and the size was about 1 cm2 (Figure 1) [5].
The relationship between ADC values and grouped stages CKD according to eGFR was evaluated.
Statistical Methods
Descriptive statistics are reported as mean,
standard deviation,
median,
minimum,
maximum and frequency.
Kruskal–Wallis test was used to evaluate the difference between ADC values and the CKD grouped stage.
Box-and-Whisker plots were drawn to highlight the difference between variables.
Mann–Whitney U test was used as post-hoc comparison test.
ROC curve analysis,
sensitivity,
specificity,
PPV,
NPV and accuracy values were used to determine cut-off values.
Pearson’s correlation coefficient test was used to determine the association between ADC values and eGFR.
A p-value <0.05 was considered statistically significant.