We retrospectively analyzed the bpMRI scans of 31 patients (26 females and 5 males, aged 20–68 years, with a mean age of 41 years), including 5 patients with transplanted kidneys, between September 2020 and October 2024. All of the patients had clinical and laboratory data indicative of nephritis.

Image acquisition MRI examinations were performed on a 3T MRI (Achieva, Philips Medical Systems), with a 16-channel and a torso-phased array coil. All initial and follow-up protocols included axial, sagittal, and/or coronal Turbo Spin Echo (TSE) and Fast Spin Echo (FSE) Spectral Pre-saturation Inversion Recovery (SPIR) T2W images, axial in-phase and opposed-phase images,  axial three-dimensional (3D) gradient recall echo (GRE) fat-saturated T1W images, and axial DWI using  b-values of 0, 500, and 1,000 s/mm²,  no interslice gap, and ADC maps generated in post-processing. All sequences, as previously mentioned, used an identical slice thickness of 3-5 mm. 

All images were reviewed by two radiologists (E.A. and M.S.) with 3 and 15 years of experience, respectively, in interpreting abdominal DWI/ADC data.

Qualitative analysis: the morphology, number, size, and signal intensity (SI) of the focal nephritic areas were assessed. The SI of the lesions on the ADC map was categorized into three groups as follows: 1) homogeneous moderately hypointense; 2) homogeneous markedly hypointense; 3) heterogeneous, moderately and markedly hypointense.

Quantitative analysis: the signal intensity (SI) on the ADC map was measured by manually placing circular regions of interest (ROIs) within the lesion, and the mean ADC was calculated. In patients with single or multiple lesions, SI was measured on the largest hypointense lesion,  in heterogeneous lesions, at the most hypointense portion on the ADC map.

The mean ADC of the lesion was compared with the mean ADC of the grayscale (Table 1 and Fig. 1), calculated as follows:

                                       Grayscale ADC_mean value = (ADC_max + ADC_min) / 2

where ADCmax and ADCmin refer to the SIs obtained from water/fluid (e.g., cerebrospinal fluid) and bone, respectively.

The percentage difference (PD) between the ADC mean value of each lesion and the mean ADC value of the grayscale map was calculated using the following formula:

Percentage difference = (grayscale ADC_mean value − ADC mean value of the lesion) / grayscale ADC_mean value × 100

Descriptive statistics were used to summarize the data as means and ranges. Quantitative ADC data were expressed as percentages and as mean ± standard deviation (SD).