Functional Sodium MRI in the Measurement of Corticomedullary Sodium Content and Its Role in Differentiating Between...

Sodium MRI (²³Na-MRI) measuring tissue sodium content may directly assess the corticomedullary gradient (CMG) in the kidney. However, it is understudied in transplanted kidneys.

To investigate associations between CMG in renal graft and urine concentrating ability, estimated glomerular filtration rate (eGFR), and biopsy-determined fibrosis scores, and to determine if CMG could differentiate between renal grafts with superior and inferior graft function.

Prospective.

57 participants (39 males) with renal transplantation.

3D T2-weighted turbo spin echo sequence and ²³Na-MR imaging at 3 T.

Urine specific gravity and eGFR were assessed as measures of kidney function. Thirty-eight participants underwent biopsy within 2 days of MRI, and the Banff fibrosis score was assessed. The average medulla to cortex ratio (MCR) was determined from ²³Na-MRI analysis. Transplanted kidneys were divided into those with superior graft function (SGF, eGFR ≥ 45 mL/min/1.73 m²) and inferior graft function (IGF, eGFR < 45 mL/min/1.73 m²) groups.

Correlation analysis (Pearson or Spearman coefficient, r), intraclass correlation coefficient, and area under the receiver-operating characteristic curve (AUC).

MCR was 1.27 ± 0.11 and mean urine specific gravity was 1.013 ± 0.005. MCR was significantly correlated with mean urine specific gravity (r = 0.32) and with eGFR (r = 0.795). MCR distinguished IGF (n = 42) from SGF (n = 15) with an AUC of 0.851 (95% CI: 0.732, 0.931) with a cutoff of ≥ 1.295. MCR was significantly correlated with the Banff fibrosis score of tubulitis in areas of interstitial fibrosis and tubular atrophy (t-IFTA) (r = 0.347).

²³Na-MRI has the potential to show the CMG in transplanted kidneys, with MCR being correlated with urine concentrating ability. In addition, the transplanted kidney CMG was related to eGFR and the Banff fibrosis score t-IFTA.

Level 2.

Stage 2.