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Thesis Format

Integrated Article

Degree

Master of Science

Program

Medical Biophysics

Supervisor

Christopher McIntyre

Abstract

Introduction: Sodium hemostasis is altered in patients with chronic kidney disease (CKD) due to long term loading, and sodium (23Na) can be deposited in the skin, muscle and skeleton. We measured 23Na content in these tissues of CKD patients, using 23Na magnetic resonance (MR) imaging.

Methods: This is a pilot cross-sectional study of CKD stage 4-5D patients and healthy controls. Subjects underwent a 23Na MR study of their right lower leg using a multinuclear-capable 3.0-T MRI. An axial proton T1-weighted fast-low-angle-shot sequence was acquired to delineate the anatomy; followed by a 23Na MR image obtained with a custom-made 23Na coil and sodium-optimized pulse sequences. Concentration maps were generated using saline solutions at different 23Na concentrations as calibration vials. Four regions of interest (ROIs) were drawn: 1) pre-tibial skin, 2) posterior leg skin, 3) tibia, and 4) soleus muscle. Baseline characteristics and blood samples were also collected.

Results: 10 controls, 12 CKD and 23 dialysis (10 peritoneal dialysis (PD) and 13 hemodialysis (HD)) subjects participated in the study. 23Na concentration in all four tissues was significantly higher in dialysis patients compared to controls (p-value23Na of HD, PD and CKD groups. Tissue sodium levels correlated strongly with markers of mineral bone disease and inflammation. Associated factors appear to be tissue specific.

Conclusion: Dialysis patients were found to have significantly higher 23Na level in their tissues compared to healthy controls. The effect and clinical utility of tissue 23Na remains to be studied.

Summary for Lay Audience

Introduction: When the kidney malfunctions, individuals cannot excrete sodium. This results in the deposition of sodium in the skin, muscle and bones, especially in patients who require dialysis because of minimal kidney function. We used magnetic resonance technology to study the amount of sodium in these tissues of patients with kidney disease.

Methods: We studied 10 healthy individuals, 12 patients with kidney disease not on dialysis and 23 dialysis patients (13 on hemodialysis and 10 on peritoneal dialysis - the two most common types of dialysis). Each subject was brought in for a study visit, where we collected their medical history and blood samples, and obtained a cross-sectional image of their R leg. The image was taken with a modified magnetic resonance scanner which detects sodium content. We had vials with known sodium concentration included in the image, to calibrate the level of sodium in the different regions. Four regions of interest were drawn over the image: over the soleus muscle, the bone, and two areas of the skin (the skin over the shin and from the back of the calf) - to highlight the different tissues.

Results: Sodium levels in all four areas (three tissues) were higher in dialysis patients compared to healthy individuals. We did not find a difference between patients on peritoneal dialysis, hemodialysis, or not on dialysis yet. Higher sodium levels in the muscle and bone were associated with increased inflammation, as well as other markers of kidney disease. The sodium levels in the different tissues were associated with different factors.

Conclusions: Dialysis patients have higher sodium levels in their skin, muscle and bone, compared to healthy individuals. The mechanism of sodium storage and its effect on individuals needs to be studied further.

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Elena Thesis Changes.docx (83 kB)
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