This prospective cohort study was approved by the local ethics committee and written informed consent had obtained from all individuals. This study was performed in accordance with the declaration of Helsinki;1964.
The inclusion criteria included patients with the stone disease and normal renal function. The exclusion criteria were chronic kidney disease, obstructive uropathy due to causes other than stone, hepatic or splenic disorder, and renovascular disorder. One of these patients was referred he had received a second session of Extra Corporeal Shock Wave Lithotripsy [ESWL]. The standard protocol of the management was done for all of them included clinical examination, analgesic administration to relief the pain and non-contrast CT to detect a potentially urinary stone. All patients were diagnosed with ureteric stones related to the affected site of pain.
Additionally, an appropriate management plan was designed for each one of them. MRI examinations for all patients were done after receiving the appropriate renal colic management, and no contraindication to MRI examination. The mean duration of the time between the arrival to the emergency department to apply MRI examination was 30 min range [20 to 45 min] and maximum up to 8 min range [5–8 min] from taking analgesia before its effect could be achieved, while the mean duration between the initial symptoms and MR imaging was 13 h [range, 10–24 h].
Another group of sixteen healthy volunteers was involved in control group, matched to the patients regarding age and sex (4 women, 12 men). The control group had no history of renal disease, previous stone formation, or related renal disorders. Additionally, the control group had no history of hypertension, vascular or systemic diseases, and no recent medication history. All the control group underwent the same protocol of MRI examination.
MR imaging was performed with a 1.5-T unit (Magnetom Avanto; Siemens, Germany) using a 12-channel body coil used for all sequences.
For morphologic evaluation, axial T2-weighted half-Fourier rapid acquisition was performed with the following parameters (time of repetition (TR), 10,000–14,000 ms; time to echo (TE), 80–90 ms; section thickness, 5 mm; intersection gap, 0 mm; matrix, 256 · 160; the number of excitations (NEX), 2; field of view (FOV), 36 cm).
For functional evaluation, axial and coronal multi-section echo-planar diffusion-weighted MR imaging (DWI) was performed with the following parameters: (thickness, 5 mm; intersection gap, 1 mm), the field of view, 36 cm; matrix, 192 × 192; bandwidth, 1446 Hz per pixel; and partial Fourier, 6/8. Diffusion gradient b values were applied (in seconds per square millimeter) as follows: b values were (0, 50, 100, 200, 500 and 800 s/mm2). These values were applied in three orthogonal planes to minimize the effects of diffusion anisotropy. Respiratory triggering was used to reduce physiological motion artifact.
Two experienced radiologists with 17 and 12 years in body MRI imaging [HS and HA, respectively] were involved independently in interpreting MRI sequences. Both radiologists were blinded to the results of CT. From a statistical point, we have excluded the presence of the stones as it was a constant finding in all patients. We evaluated the associations between other CT findings [hydronephrosis and perinephric strands] as absence or presence with the diffusion pattern.
Regarding DWI signals, both radiologists have evaluated both kidneys independently, using the signals of the spleen and the signal pattern of the kidneys in the control group as a reference for judgment. We compared the signal pattern of DWI at both kidneys with that of the control group. When there was a restricted bright signal of one kidney, we compared its signal with the contralateral side and the spleen. Kidneys were assigned as positive when there is a diffuse increased signal intensity of the renal parenchyma higher than that of the control group or contralateral side and near the splenic signal intensity parenchyma.
Regarding the interpretation of ADC measures, a circular region of interest (ROIs) was placed in the upper pole, mid-zone, and lower pole of the parenchyma at both kidneys to take the average ADC value of the affected kidneys as well as the control group. In the case of the control group, ADC values at both kidneys were averaged to give a single value. The measurement of ADC values was done with Syngo VB17 software.
A sample size estimation was calculated to be at least 16 patients and 16 control subjects from a power analysis based on previous diffusion-weighted MR imaging results in native kidneys (9), assuming similar standard deviations. For comparison between patients and control groups regarding the diffusion restriction pattern, nominal variables were used to assess if there is a significant association between diffusion changes at both groups using Chi-square or Fisher Exact tests. Additionally, the same tests were used to compare the association between CT signs other than stones and DWI pattern at both groups.
Cohen's Kappa test was run to determine whether there was an agreement between the two radiologists on whether there was a restricted or free diffusion of the kidneys at the patient's group compared with the control group and the contralateral kidneys of the same patients.
ADC values for both groups showed no violation of normal distribution as assessed by the Shapiro–Wilk test and no significant Skewness or kurtosis with comparable means and median at both groups. An independent sample t-test was performed to assess the significant difference among ADC values between the two groups. For all statistical tests, a p value of less than 0.05 was considered a statistically significant difference. Statistical analyses were performed with STATA/IC Version 15.and SPSS software (SPSS, version 23, SPSS, Chicago).