Diffusion-weighted imaging (DWI) of the spleen in patients with liver cirrhosis and portal hypertension.

OBJECTIVE: The purpose of this study was to assess the influence of liver cirrhosis and portal hypertension on diffusion coefficients of the spleen. MATERIAL AND METHODS: We retrospectively evaluated 50 patients with liver cirrhosis and 50 patients without any history of liver disease who underwent magnetic resonance imaging of the upper abdomen, including echo planar diffusion-weighted imaging using b values of 50, 300 and 600mm(2)/s. Spleen apparent diffusion coefficient (ADC), liver ADC, muscle ADC and normalized spleen ADC (defined as the ratio of spleen ADC to muscle ADC) were compared between cirrhotic patients and patients in the control group and correlated with Child-Pugh stages. Reproducibility was assessed by measuring interclass correlation coefficient (n=11). Additionally, in eight patients, ADC measurements were performed 1 day before and 3 days after transjugular intrahepatic portosystemic shunt (TIPSS) implantation. RESULTS: Compared with control subjects, patients with cirrhosis and portal hypertension had significantly higher spleen ADCs (P=.0001). There was a statistically significant correlation between Child-Pugh grade and spleen ADC (Pearson correlation coefficient, observer 1 r=0.6, P=.0001; observer 2 r=0.5, P=.0001). After TIPSS implantation, we observed a reduction in spleen ADC values. Spleen ADC measurements showed a high reproducibility (interclass correlation coefficient 0.75, P=.001). CONCLUSION: Our data suggest that different stages of liver cirrhosis and portal hypertension correlate with ADC values of the spleen. Furthermore, ADC values of the spleen decrease after TIPSS implantation. Further studies are required to understand the potential clinical values of these observations.

Impact of blood flow on diffusion coefficients of the human kidney: a time-resolved ECG-triggered diffusion-tensor imaging (DTI) study at 3T.

PURPOSE: To evaluate the impact of renal blood flow on apparent diffusion coefficients (ADC) and fractional anisotropy (FA) using time-resolved electrocardiogram (ECG)-triggered diffusion-tensor imaging (DTI) of the human kidneys. MATERIALS AND METHODS: DTI was performed in eight healthy volunteers (mean age 29.1 ± 3.2) using a single slice coronal echoplanar imaging (EPI) sequence (3 b-values: 0, 50, and 300 s/mm(2)) at the timepoint of minimum (20 msec after R wave) and maximum renal blood flow (200 msec after R wave) at 3T. Following 2D motion correction, region of interest (ROI)-based analysis of cortical and medullary ADC- and FA-values was performed. RESULTS: ADC-values of the renal cortex at maximum blood flow (2.6 ± 0.19 × 10(-3) mm(2)/s) were significantly higher than at minimum blood flow (2.2 ± 0.11 × 10(-3) mm(2)/s) (P < 0.001), while medullary ADC-values did not differ significantly (maximum blood flow: 2.2 ± 0.18 × 10(-3) mm(2)/s; minimum blood flow: 2.15 ± 0.14 × 10(-3) mm(2)/s). FA-values of the renal medulla were significantly greater at maximal blood (0.53 ± 0.05) than at minimal blood flow (0.47 ± 0.05) (P < 0.01). In contrast, cortical FA-values were comparable at different timepoints of the cardiac cycle. CONCLUSION: ADC-values in the renal cortex as well as FA-values in the renal medulla are influenced by renal blood flow. This impact has to be considered when interpreting renal ADC- and FA-values.

Comparison of different mathematical models of diffusion-weighted prostate MR imaging.

PURPOSE: To evaluate which mathematical model (monoexponential, biexponential, statistical, kurtosis) fits best to the diffusion-weighted signal in prostate magnetic resonance imaging (MRI). MATERIALS AND METHODS: 24 prostate 3-T MRI examinations of young volunteers (YV, n=8), patients with biopsy proven prostate cancer (PC, n=8) and an aged matched control group (AC, n=8) were included. Diffusion-weighted imaging was performed using 11 b-values ranging from 0 to 800 s/mm(2). RESULTS: Monoexponential apparent diffusion coefficient (ADC) values were significantly (P<.001) lower in the peripheral (PZ) zone (1.18±0.16 mm(2)/s) and the central (CZ) zone (0.73±0.13 mm(2)/s) of YV compared to AC (PZ 1.92±0.17 mm(2)/s; CZ 1.35±0.21 mm(2)/s). In PC ADC(mono) values (0.61±0.06 mm(2)/s) were significantly (P<.001) lower than in the peripheral of central zone of AC. Using the statistical analysis (Akaike information criteria) in YV most pixels were best described by the biexponential model (82%), the statistical model, respectively kurtosis (93%) each compared to the monoexponential model. In PC the majority of pixels was best described by the monoexponential model (57%) compared to the biexponential model. CONCLUSION: Although a more complex model might provide a better fitting when multiple b-values are used, the monoexponential analyses for ADC calculation in prostate MRI is sufficient to discriminate prostate cancer from normal tissue using b-values ranging from 0 to 800 s/mm(2).

Temporally resolved electrocardiogram-triggered diffusion-weighted imaging of the human kidney: correlation between intravoxel incoherent motion parameters and renal blood flow at different time points of the cardiac cycle.

PURPOSE: To evaluate the influence of pulsatile blood flow on apparent diffusion coefficients (ADC) and the fraction of pseudodiffusion (F(P)) in the human kidney. MATERIALS AND METHODS: The kidneys of 6 healthy volunteers were examined by a 3-T magnetic resonance scanner. Electrocardiogram (ECG)-gated and respiratory-triggered diffusion-weighted imaging (DWI) and phase-contrast flow measurements were performed. Flow imaging of renal arteries was carried out to quantify the dependence of renal blood flow on the cardiac cycle. ECG-triggered DWI was acquired in the coronal plane with 16 b values in the range of 0 s/mm(2) and 750 s/mm(2) at the time of minimum (MIN) (20 milliseconds after R wave) and maximum renal blood flow (MAX) (197 ± 24 milliseconds after R wave). The diffusion coefficients were calculated using the monoexponential approach as well as the biexponential intravoxel incoherent motion model and correlated to phase-contrast flow measurements. RESULTS: Flow imaging showed pulsatile renal blood flow depending on the cardiac cycle. The mean flow velocity at MIN was 45 cm/s as compared with 61 cm/s at MAX. F(p) at MIN (0.29) was significantly lower than at MAX (0.40) (P = 0.001). Similarly, ADC(mono), derived from the monoexponential model, also showed a significant difference (P < 0.001) between MIN (ADC(mono) = 2.14 ± 0.08 × 10(-3) mm(2)/s) and MAX (ADC(mono) = 2.37 ± 0.04 × 10(-3) mm(2)/s). The correlation between renal blood flow and F(p) (r = 0.85) as well as ADC(mono) (r = 0.67) was statistically significant. CONCLUSION: Temporally resolved ECG-gated DWI enables for the determination of the diffusion coefficients at different time points of the cardiac cycle. ADC(mono) and FP vary significantly among acquisitions at minimum (diastole) and maximum (systole) renal blood flow. Temporally resolved ECG-gated DWI might therefore serve as a novel technique for the assessment of pulsatility in the human kidney.

Diffusion-attenuated MRI signal of renal allografts: comparison of two different statistical models.

OBJECTIVE: Contrast-enhanced MRI is considered problematic in renal allograft recipients because of the development of nephrogenic systemic fibrosis. Therefore, we assessed the clinical value of a monoexponential model and a distribution function model of diffusion-weighted imaging (DWI) in renal allografts. MATERIALS AND METHODS: A total of 23 patients were divided into three groups, as follows: group A, stable renal allograft function for at least 6 months; group B, transplantation within the past 30 days, with good renal allograft function; and group C, an acute deterioration or decrease in renal allograft function. T2-weighted axial, T1-weighted coronal, and a paracoronal DWI sequences with 16 b values (b = 0-750 s/mm(2)) were performed on a 1.5-T scanner. Region of interest-based analysis of the apparent diffusion coefficient (ADC) of the renal cortex was used. RESULTS: Monoexponential analysis showed mean (± SD) ADC values of 1932 ± 98, 2095 ± 246, and 1636 ± 200 10-(6) mm(2)/s for patient groups A, B, and C, respectively. The distribution function revealed a mean ADC of 2487 ± 185, 2850 ± 325, and 2142 ± 31410-(6) mm(2)/s for groups A, B, and C, respectively. The difference between groups A and B combined and group C (p < 0.005) was statistically significant for both models. R(2) yielded the best regression of mathematic fitting for the distribution function model (p < 0.0001). DISCUSSION: Unenhanced evaluation of renal allografts with DWI correlated well with renal function for both the monoexponential analysis and the distribution function model. There was no statistically significant difference in ADC values and renal allograft function between both types of analysis, but the distribution function showed the best regression.