Assessment of diffusion-weighted MRI and 18F-fluoro-deoxyglucose PET/CT in monitoring early response to neoadjuvant chemotherapy in adenocarcinoma of the esophagogastric junction.

BACKGROUND & AIMS: To prospectively assess whether changes in apparent diffusion coefficient (ADC) values or standardized uptake value (SUV) changes in 18F-fluorodeoxyglucose (FDG) PET correlate with treatment response under neoadjuvant chemotherapy in patients with locally advanced adenocarcinoma of the esophagogastric junction (AEG). METHODS: Fifteen patients (median age, 64 years) with histologically proven AEG type I and II received 1.5 Tesla MRI including "diffusion-weighted imaging" and FDG PET/CT before and 14 days after neoadjuvant EOX chemotherapy. The FDG uptake of the tumor was quantified by calculating the SUV in static PET scans. ADC values within the tumor tissue were quantitatively assessed using a region-of-interest analysis excluding necrotic areas. Early metabolic response was defined as a decrease in the SUV(mean) >/= 35% in FDG PET two weeks following the start of neoadjuvant chemotherapy, which had been reported to be predictive of histopathological response and survival. Concordance between ADC and SUV changes, differences at first examination and overall survival were assessed. RESULTS: The ADC within the AEG tumors was significantly lower than in normal esophagus and increased following neoadjuvant chemotherapy by 16.0 +/- 1.1% (p=0.007). Tumor glucose SUV decreased by 29.1 +/- 23.2% (p=0.002). Initial ADC and SUV were comparable in both groups (p=0.65, p=0.82). ADC increase and metabolic PET-response were concordant in 73.3% of all patients. The median overall survival was 757 days for PET-responders and 623 days for PET-non-responders (p=0.138). CONCLUSION: The ADC increase in AEG tumors following chemotherapy is concordant in the majority of cases to PET-response, but not correlated to prognosis in this study.

Fibrosis and pancreatic lesions: counterintuitive behavior of the diffusion imaging-derived structural diffusion coefficient d.

INTRODUCTION: Stroma reaction leading to fibrosis is the most characteristic histopathological feature of both pancreatic carcinoma and chronic pancreatitis with increased fibrosis compared with healthy pancreatic tissue and further increased fibrosis during radiochemotherapy. Recent studies using intravoxel incoherent motion-derived parameters did not show differences for structural diffusion constant D between these 2 diseases. The aim of this study was to verify the hypothesis that D correlates with the histopathological grade of fibrosis in pancreatic lesions. MATERIALS AND METHODS: We included 15 patients with histopathologically proven pancreatic carcinoma and 9 patients with histopathologically proven focal chronic pancreatitis. Diffusion-weighted magnetic resonance imaging was performed using 10 b values between 25 and 800 s/mm² before surgery. We calculated the apparent diffusion coefficient and the intravoxel incoherent motion-derived parameters D and f within tumors and focal chronic pancreatitis. The resected tissue was evaluated with regard to the grade of fibrosis. RESULTS: Fourteen patients were found to have moderate fibrosis and 10 patients had severe fibrosis. The difference between the D values for the moderate and severe fibrosis was significant with mean (SD) D value of 1.02 × 10⁻³ (0.48 × 10⁻³ mm/s) and mean (SD) D of 1.22 × 10⁻³ (0.76 × 10⁻³) mm²/s. There were no significant differences for the f and ADC values. CONCLUSIONS: Contrary to our hypothesis, D rises from moderate to severe fibrosis. It seems that cellular complexes surrounded by fibrosis provide more structural limitations than does fibrosis alone. Our data suggest that D is not intuitively related to the degree of fibrosis. Compared with healthy tissue, D is reduced in moderate fibrosis but increases when severe fibrosis is present.

Toward a non-invasive screening tool for differentiation of pancreatic lesions based on intra-voxel incoherent motion derived parameters.

Early recognition of and differential diagnosis between pancreatic cancer and chronic pancreatitis is an important step in successful therapy. Parameters of the IVIM (intra-voxel incoherent motion) theory can be used to differentiate between those lesions. The objective of this work is to evaluate the effects of rigid image registration on IVIM derived parameters for differentiation of pancreatic lesions such as pancreatic cancer and solid mass forming pancreatitis. The effects of linear image registration methods on reproducibility and accuracy of IVIM derived parameters were quantified on MR images of ten volunteers. For this purpose, they were evaluated statistically by comparison of registered and unregistered parameter data. Further, the perfusion fraction f was used to differentiate pancreatic lesions on eleven previously diagnosed patient data sets. Its diagnostic power with and without rigid registration was evaluated using receiver operating curves (ROC) analysis. The pancreas was segmented manually on MR data sets of healthy volunteers as well as the patients showing solid pancreatic lesions. Diffusion weighted imaging was performed in 10 blocks of breath-hold phases. Linear registration of the weighted image stack leads to a 3.7% decrease in variability of the IVIM derived parameter f due to an improved anatomical overlap of 5%. Consequently, after registration the area under the curve in the ROC-analysis for the differentiation approach increased by 2.7%. In conclusion, rigid registration improves the differentiation process based on f-values.

Enhancing pancreatic adenocarcinoma delineation in diffusion derived intravoxel incoherent motion f-maps through automatic vessel and duct segmentation.

Diffusion-based intravoxel incoherent motion imaging has recently gained interest as a method to detect and characterize pancreatic lesions, especially as it could provide a radiation- and contrast agent-free alternative to existing diagnostic methods. However, tumor delineation on intravoxel incoherent motion-derived parameter maps is impeded by poor lesion-to-pancreatic duct contrast in the f-maps and poor lesion-to-vessel contrast in the D-maps. The distribution of the diffusion and perfusion parameters within vessels, ducts, and tumors were extracted from a group of 42 patients with pancreatic adenocarcinoma. Clearly separable combinations of f and D were observed, and receiver operating characteristic analysis was used to determine the optimal cutoff values for an automated segmentation of vessels and ducts to improve lesion detection and delineation on the individual intravoxel incoherent motion-derived maps. Receiver operating characteristic analysis identified f = 0.28 as the cutoff for vessels (Area under the curve (AUC) = 0.901) versus tumor/duct and D = 1.85 µm(2) /ms for separating duct from tumor tissue (AUC = 0.988). These values were incorporated in an automatic segmentation algorithm and then applied to 42 patients. This yielded clearly improved tumor delineation compared to individual intravoxel incoherent motion-derived maps. Furthermore, previous findings that indicated that the f value in pancreatic cancer is strongly reduced compared to healthy pancreatic tissue were reconfirmed.

Intravoxel incoherent motion MRI for the differentiation between mass forming chronic pancreatitis and pancreatic carcinoma.

PURPOSE: To determine which of the quantitative parameters obtained from intravoxel incoherent motion diffusion weighted imaging (DWI) is the most significant for the differentiation between pancreatic carcinoma and mass-forming chronic pancreatitis. MATERIALS AND METHODS: Twenty-nine patients with pancreatic masses were included, 9 proved to have a mass-forming pancreatitis and 20 had a pancreatic carcinoma. The patients were studied using intravoxel incoherent motion DWI with 11 b-values and the apparent diffusion coefficient (ADC), the true diffusion constant (D) and the perfusion fraction (f) were calculated. The diagnostic strength of the parameters was evaluated using receiver operating characteristic analysis. RESULTS: The ADC in chronic pancreatitis was higher than in pancreatic carcinoma with significant differences at b = 50, 75, 100, 150, 200, 300 s/mm (ADC50 = 3.17 ± 0.67 vs. 2.55 ± 1.09, ADC75 = 2.46 ± 0.4 vs. 1.93 ± 0.52, ADC100 = 2.28 ± 0.48 vs. 1.73 ± 0.45, ADC150 = 1.97 ± 0.26 vs. 1.63 ± 0.40, ADC200 = 1.98 ± 0.24 vs. 1.53 ± 0.28, and ADC300 = 1.76 ± 0.19 vs. 1.46 ± 0.31 × 10(-3) mm2/s). No significant differences were found at b = 25, 400, 600, and 800 s/mm (ADC25 = 4.69 ± 0.65 vs. 4.04 ± 1.35, ADC400 = 1.57 ± 0.21 vs. 1.37 ± 0.30, ADC600 = 1.38 ± 0.18 vs. 1.24 ± 0.25, and ADC800 = 1.27 ± 0.10 vs. 1.18 ± 0.19 × 10(-3) mm2/s) nor using ADCtot (1.42 ± 0.23 vs. 1.28 ± 0.12 × 10(-3) mm2/s). The perfusion fraction f was significantly higher in pancreatitis compared with pancreatic carcinoma (16.3% ± 5.30% vs. 8.2% ± 4.00%, P = 0.0001). There was no significant difference between groups for D (1.07 ± 0.224 × 10(-3) mm2/s for chronic pancreatitis and 1.09 ± 0.3 × 10(-3) mm2/s for pancreatic carcinoma, P = 0.66). For f, the highest area under the curve (0.894) and combined sensitivity (80%) and specificity (89.9%) were found. CONCLUSIONS: There were significant differences in ADC50-300 between chronic pancreatitis and pancreatic carcinoma. Because D is not significantly different between groups, differences in ADC can be attributed mainly to differences in perfusion. The perfusion fraction f proved to be the superior DWI-derived parameter for differentiation of mass-forming pancreatitis and pancreatic carcinoma.