The corticomedullary gradient is largely responsible for developing the gradients that are needed to concentrate urine (more solutes and less water). The ability of the kidneys to produce concentrated urine is a major determinant of the ability to survive the warm weather. When temperatures are high, we lose water through sweat, and so the kidneys retain water to maintain fluidity in the blood. The maintenance of a sodium (salt) gradient is required for urine concentration because increased medullary sodium concentration increases the reabsorption of water into the kidney, to be redistributed in the blood. The purpose of this study is to know if the corticomedullary gradient is altered in patients across a wide spectrum of kidney disease using sodium Magnetic Resonance Imaging (MRI), a machine that takes pictures and measures the salt content in the kidneys. 23Na kidney MRI, will provide functional MR of the kidney as a non-invasive tool to describe medullary function to improve management of chronic and kidney disease.

This study is a pilot exploratory study (preliminary project to assess the use of a kidney sodium coil across a wide spectrum of kidney disease). Approximately 200 patients from the London Health Sciences Regional Renal Program will be recruited. This study involves two visits at Robarts Research Institute or St. Joseph's Hospital, London, Ontario depending on scanner availability, lasting approximately 2 hours.

At the first study visit participants will undergo a sodium MRI scan of your kidneys. Prior to the scan, participants will have their sitting blood pressure and heart rate measured three times consecutively using a standard automatic blood pressure monitor. In addition to this, participants will be asked to provide a spot urine sample and have blood work done. If participants have been treated for nephrolithiasis, they will be responsible for completing a 24-hour urine volume test sometime the week before the MRI scan.

Inclusion Criteria:

• Age ≥ 18 years
• For healthy controls: lack of kidney disease, heart failure, liver cirrhosis and peripheral edema
• For CKD stage 1-5: Estimated GFR < 90 mL/min/1.73m²
• For patients on maintenance hemodialysis or peritoneal dialysis: more than 3 months duration of therapy

Exclusion Criteria:

• Pregnant, breastfeeding or intending pregnancy

• Contraindication to MRI

  • Inability to tolerate MRI due to patient size and/or known history of claustrophobia.
  • Mechanically implanted, electrically, or magnetically activated device or any metal in their body which cannot be removed, including but not limited to pacemakers, neurostimulators, biostimulators, implanted insulin pumps, aneurysm clips, bioprosthesis, artificial limb, metallic fragment or foreign body, tattoos, shunt, surgical staples (including clips or metallic sutures and/or ear implants.)

CKD stage 1-5 Transplanted patients Maintenance dialysis (hemo and PD) ADPKD patient Patients treated for nephrolithiasis Healthy controls, including kidney donors