MRIs and other types of diagnostic imaging could someday replace invasive biopsies currently used to identify patients who are at risk of developing kidney disease.
The kidneys are two bean-shaped, fist-sized organs. They are located just below the ribcage, one on each side of the body. Each day, the kidneys filter 120 to 150 quarts of blood to produce about one to two quarts of urine. Health kidneys are important, in that they prevent the buildup of toxic waste and excess fluid inside the body. Kidneys stabilize levels of potassium, sodium and other electrolytes. The kidneys also help make hormones that regulate blood pressure, make red blood cells, and maintain strong bones.
About Kidney Disease
Kidney disease is a condition where the kidneys do a poor job of filtering toxins from the blood, and this allows these toxins to accumulate in the body and eventually cause illness. Early detection of kidney disease is essential, as untreated kidney disease can result in chronic kidney disease.
Renal fibrosis is an inevitable consequence of nearly every type of kidney disease. In renal fibrosis, excessive fibrous connective tissue develops in the kidneys. Renal fibrosis is an early sign of kidney failure. Kidney failure, also known as end-stage renal disease, is the last stage of chronic kidney disease. Kidney failure means the kidneys are not working well enough for the person to survive without dialysis or a kidney transplant. Early detection of kidney disease, then, is essential for survival.
Certain health conditions increase the risk for chronic kidney disease, a condition where the kidneys slowly lose their ability to filter toxins from the body. High blood pressure and diabetes are the two primary causes of kidney disease. Together, these two conditions are responsible for up to two-thirds of all chronic kidney disease cases. Doctors help prevent kidney disease in patients with diabetes and high blood pressure through screening.
In addition to other diagnostic tools, such as urine and blood tests, doctors perform renal biopsies to assess kidney health and function. Renal biopsy is an invasive procedure associated with minor and major complications.
Doctors currently use renal biopsy to detect signs of renal fibrosis. There are two main types of renal biopsy procedures. The most common type of renal biopsy procedure is the percutaneous biopsy, in which the doctor removes a small amount of kidney tissue through a thin biopsy needle inserted into the skin. In a surgical biopsy, also known as an open biopsy, the surgeon removes kidney tissue through an incision in the skin near the kidneys. In both procedures, the doctor sends the kidney tissue sample to a laboratory for analysis.
Using Imaging to Detect Kidney Disease
Researchers from Osaka University collaborated with several Japanese companies to test a number of imaging tools to study renal fibrosis in lab rats, in hopes of someday replacing invasive biopsies with non-invasive imaging tests. The non-invasive MRI imaging test is useful because it can detect a particular sign of renal fibrosis, known as abnormal perfusion, in the kidneys.
A special type of MRI, known as diffusion tensor MRI (DTI), is an ideal imaging tool for detecting renal fibrosis damage because it uses the movement of water molecules as contrast to create MRI images – and the main function kidneys is to move water.
Doctors currently use DTI to image brain structures because the spread of water, or diffusion or water, throughout the brain is similar to diffusion of water throughout the kidneys. Specifically, the diffusion of water in the brain and kidneys is anisotropic, which is to say the movement of water has different value when measured in one direction than when measured in another direction. Wood is a simple example of anisotropy – wood is stronger along the grain than it is across the grain.
Doctors have used DTI to study kidney problems in the past, with limited success. In a new study, researchers added an MRI technique, known as a spin-echo sequence, to the DTI. They also added a special kidney attachment that, along with the spin-echo sequence, allowed the researchers to observe renal fibrosis in diabetic rats. The anisotropy of the fluid flow inside the kidneys allowed the scientists to create maps of different regions of the kidneys and identify which regions had renal fibrosis. The researchers could also compare the fluid dynamics in various regions of the kidneys in live diabetic and healthy rats.
The results of the research mean that patients at high risk for kidney disease could someday skip the biopsy and have an MRI instead. That is great news for patients who want to avoid the discomfort and possible complications of a biopsy.