Diffusion-weighted imaging of the healthy pancreas: apparent diffusion coefficient values of the normal head, body, and tail calculated from different sets of b-values.

PURPOSE: To evaluate differences in apparent diffusion coefficient (ADC) values between head, body, and tail regions and the impact of sets of b-values used in diffusion weighted imaging (DWI) of the normal pancreas. MATERIALS AND METHODS: In 51 healthy volunteers echo-planar DWI of the pancreas was prospectively performed with b-values of 50, 400, and 800 s/mm(2) . All four possible combinations of b-values were used to calculate ADC values in a total of 587 regions in the pancreas head, body, and tail regions. Dependency of ADC values on the anatomical regions and on the applied sets of b-values was calculated using multivariate analysis of variance (ANOVA). RESULTS: Mean ADC values differed significantly between the anatomical regions with the lowest values measured in the pancreatic tail (head 1.13 ± 0.20, body 1.05 ± 0.20, and tail 0.94 ± 0.18 × 10(-3) mm(2) /s; P < 0.05). ANOVA showed no dependency of ADC values on the sets of b-values used. CONCLUSION: ADC values differed significantly between the pancreatic head, body, and tail region, with decreasing ADC values toward the tail. Cautious interpretation of DWI results with adjusted, normalized values adapted to the anatomical region seems advisable. The knowledge of such differences may enhance the method's capability to differentiate between different pancreatic pathologies.

Quantification of [18F]-FDG uptake in atherosclerotic plaque: impact of renal function.

OBJECTIVE: Impaired renal function causes both increased and prolonged tracer availability in the blood-pool which might result in increased tracer accumulation in atherosclerotic lesions. Therefore, the aim of this study was to investigate a possible correlation between the intensity of tracer uptake in atherosclerotic lesions and renal function. METHODS: Data from 50 [18F]-FDG scans were visually evaluated for tracer uptake in vessel wall alterations. Lesions were analyzed semiquantitatively by determining the blood-pool standardized uptake values (SUV(blood-pool)s), maximum SUVs (SUV(max)s), and the target-to-background ratio (TBR). These parameters were tested for correlation with estimated glomerular filtration rate (eGFR), and cardiovascular risk factors. RESULTS: Both SUV(blood-pool)s (r(s) = -0.32, p = 0.03) and SUV(max)s for [18F]-FDG (r(s) = -0.50, p < 0.0001) showed a significant negative correlation with eGFR. TBRs for [18F]-FDG demonstrated a significant positive correlation with eGFRs (r(s) = 0.21, p = 0.02). CONCLUSION: This study found that both intravascular tracer availability (SUV(blood-pool)) and intralesional tracer uptake (SUV(max)) are influenced by renal function. Calculation of TBR to account for that effect may result in overcorrection in case of [(18)F]-FDG. Renal insufficiency or subclinical changes in renal function have to be considered as a confounding factor in PET of atherosclerotic lesions.