Table 1 Spectral DWI parameters with corresponding hypothesized physiologic interpretation in the kidney cortex.
From: Detecting early kidney allograft fibrosis with multi-b-value spectral diffusion MRI
Compartment | Spectral parameters | Physiologic interpretation |
|---|---|---|
Vascular: Vasculature in the kidney cortex is composed of blood vessels including arteries, veins, and capillaries. | \({f_{vasc}}\) | Fraction of a voxel that is within blood vessels. |
\({D_{vasc}}\) | Diffusion coefficient, or speed, of the blood travelling within the vessels (\({D^*}\) in conventional IVIM). | |
\(f{D_{vasc}}\) | Proxy for the total blood flow in the vasculature; \(f{D_{vasc}}={f_{vasc}} \times {D_{vasc}}\) . (\(f{D^*}\) in conventional IVIM). | |
Tubular: Kidney tubules in the nephrons filter the glomerular filtrate and return nutrients to blood through reabsorption. The remaining fluid and waste become urine. In the cortex there are glomeruli and convoluted tubules. | \({f_{tubule}}\) | Fraction of a voxel that is within these tubules (no parameters in conventional IVIM). |
\({D_{tubule}}\) | Diffusion coefficient of the tubular filtrate (no parameters in conventional IVIM). | |
\(f{D_{tubule}}\) | Proxy for the total tubular flow in the renal tubules; \(f{D_{tubule}}={f_{tubule}} \times {D_{tubule}}\) (no parameters in conventional IVIM) | |
Tissue Parenchyma: The kidney contains solid tissue, vascular endothelial cells, and tubular epithelial cells. Diffusion in the tissue parenchyma includes passive diffusion across cell membranes, and within the extracellular matrix (ECM) of the kidney parenchyma. Fibrosis in the kidney is a pathological feature that occurs when there is an excessive ECM accumulation leading to scarring and renal dysfunction. | \({f_{tissue}}\) | Fraction of a voxel that is composed of these solid cells in the kidney parenchyma with and without ECM accumulation. (\(1 - f\) in IVIM). |
\({D_{tissue}}\) | Diffusion coefficient of molecules within the parenchyma and composed of tissue both with and without ECM accumulation. | |
\(f{D_{tissue}}\) | Proxy for the total restricted diffusive flow within solid tissue structure, cells, and in ECM scarring. \(f{D_{tissue}}={f_{tissue}} \times {D_{tissue}}\) (the (\(1 - f)D\) in IVIM). |
