Diffusion Weighted Magnetic Resonance Imaging of the Human Kidney: 'Best Regression' for the Determination of Diffusion Constants

摘要

The use of diffusion weighted magnetic resonance imaging (DWI) has been more and more extended to abdominal organs. In comparison to the human brain the tissue of the kidney shows considerably different microscopic structure, which must be considered in the calculating of the apparent diffusion constant (ADC). In most studies ADC is determined using a mono-exponential model. Due to the high vascularization in the kidney a bi-exponential approach is reasonable to allow for a differentiation between pure diffusion fraction and a fraction influenced by perfusion effects. In our work we analyzed whether the mono- or bi-exponential approach is more accurate from statistical point of view for in-vivo DWI of the kidney. For this purpose we acquired DWI in five healthy subjects. Further we simulated a DWI signal varying the value of the perfusion fraction to investigate the relation between the results of mono- and bi-exponential analysis. Besides we simulated a DWI signal at different signal to noise ratios to analyze the influence of noise on the ADC resulting from the mono- and bi-exponential approach. The statistical analysis of F-test, Akaike's information criterion (AIC) and Schwarz criterion (FC) of the in-vivo data shows that the bi-exponential approach represents the "best regression" to determine ADC. In five in-vivo investigations 87% (F-test), 95 % (AIC) and 92% (SC) of the pixels possessed bi-exponential characteristics. The simulation of the DWI signal asserts increasing mono-exponential calculated ADC values with rising perfusion fraction within the tissue. Further our simulation shows that the variations of the mono-exponential results with increasing noise are less than that of bi-exponential approach.