The Values Of Reduced Field Of View High Resolution DWI For The Solid Pancreatic Focal Lesions

Part 1: Comparisons of image quality and ADCs between reduced field-of-view and single shot echo planar imaging DWI of the solid pancreatic focal lesionsObjective: To compare image quality and apparent diffusion coefficients(ADCs) of the solid pancreatic focal lesions in reduced field-of-view(r FOV DWI) and single shot echo planar imaging DWI(ss-EPI DWI).Methods: r FOV DWI and ss-EPI DWI of the solid pancreatic focal lesions were performed in 38 healthy volunteers and 139 patients with surgical pathology-proven pancreatic focal lesions using b-values of 0 and 600 s/mm2. For all the sequences, the investigator performed qualitative analysis of r FOV DWI and ss-EPI DWI images both at b0 and b600 in terms of(a) anatomic structure visualization,(b) lesion conspicuity,(c) artifacts,(d) image quality score, and then measured ADCs for the head of normal pancreas and the pancreatic focal lesions. We compared the image quality scores and ADCs of pancreas in the two DWIs.Results: For b0 and b600, image quality scores was significantly different between r FOV DWI and ss-EPI DWI(p < 0.001). The value of ADC derived from r FOV DWI lower than that of ss-EPI DWI。The diagnostic accuracy of r FOV and ss-EPI DWI for PDAC is acceptable, what‘ more, the diagnositic efficacy of r FOV DWI is much higher than ss-EPI DWI.Conclusion: Reduced field-of-view DWI provided high quality images of pancreas. The diagnositic efficacy of r FOV DWI is much higher than ss-EPI DWI.Part 2: The values of reduced field view IVIM DWI in diagnosing solid pancreatic focal lesionsObjective: To evaluate the diagnostic potential of reduced field view IVIM DWI derived quantitative parameters(ADCtotal、ADCslow、ADCfast及 f) for differentiation of solid pancreatic focal lesions, and then compare the diagnostic effects between r FOV IVIM DWI and ss-EPI IVIM DWI.Methods: 139 patients with pathologically confirmed pancreatic focal lesions [including 105 pancreatic ductal adenocarcinomas(PDAC), 16 neuroendocrine tumors(NET) and 7 chronic pancreatitis(CP)], 11 solid pseudopapillary tumor(SPT) and 38 healthy volunteers were included in this study. Except for the conventional MR examinations, all the subjects examined accepted ss-EPI/reduced field view multiple-b-value DWI which included 10 b-values(0, 25, 50, 75, 100, 150, 200, 400, 600 and 800 s/mm2, respectively). Multiple-b-value DWI derived quantitative parameters of lesions and normal pancreases were measured by one observer, then we used Mann-Whitney U tests to compare the diffusion parameters between normal pancreas and PDAC groups. For the comparison between normal pancreas and pancreatic lesions with different pathologic results, we used Kruskal-Wallis test. The diagnostic performances were calculated and compared by using the receiver operating characteristic(ROC) curves.Results: Mann-Whitney U tests showed parameters(f and ADCtotal derived from full field view DWI and f derived from reduced field view DWI) between PDAC and NP groups had statistically significant differences. Kruskal-Wallis test showed that f and ADCtotal differed significantly between normal pancreas and pancreatic lesions.Conclusion: f derived from full field view/reduced field view multiple-b-value DWI provided higher diagnostic performance in differentiating common solid pancreatic focal lesions.Part 3: Application of a novel inhomogeneity index based on ADC maps analysis for differentiating pancreatic cancer from Mass-Forming Focal PancreatitisObjective: Diffusion weighted imaging(DWI), with quantitative measurement of apparent diffusion coefficient(ADC) values, is routinely performed in clinical practice in detection and characterization of pancreatic diseases. Differentiating mass-forming focal pancreatitis(MFCP) and pancreatic ductal adenocarcinoma(PDAC) is of great clinical importance as their treatment falls into different categories usually. For now, there is still diagnostic challenge in differentiating FP and PDAC. In this work, we propose a novel method to address the need above with a new parameter(inhomogeneity index) based on the ADC map analysis with different region of interest(ROI) size.Methods: Sixty-four patients with pathology-proven PDAC, seven patients with pathology-proven MFCP and eighteen healthy volunteers were recruited and underwent DWI(b-values = 0, 600 s/mm2) on 3.0T whole body system(GE HDxt). ADC maps were calculated on a voxel-by-voxel basis from the obtained DWI images using mono-exponential model(ADC = [ln(SIb0 / SIb600)] / 600), and were reconstructed with FOV of 380*380 mm2 and matrix of 256*256. A homemade software was used to measure mean value and standard deviation of ADC(Average ADC and SDADC) within each of 12 concentric round ROIs(areas: 20, 42, 59, 82, 99, 121, 139, 161, 176, 196, 227, and 242 mm2 with pixel numbers: 9, 19, 27, 37, 45, 55, 63, 73, 80, 89, 103 and 110, respectively) drawn on the solid part of the mass of lesions and the head of normal pancreas on the single slice of the ADC map, which contained the largest available targeted tumor area or normal pancreas. The inhomogeneity index, defined as the ratio of SDADC over Average ADC in each ROI, was also calculated for the lesions and normal pancreas for each of the ROI with different sizes. Water phantom was used to calculate the ideal inhomogeneity index as a reference measurement.Results: The averaged inhomogeneity index curves of MFCP(7 cases), PDAC(64 cases), normal pancreas(18 cases) and water phantom(8 cases) are shown in the text. Significant differences were observed for the inhomogeneity index measured by 12 different-size ROIs among FP, PDAC and normal pancreas. Near linear increment of the inhomogeneity index was observed on healthy volunteers with expanding ROI, while non-linear increasing character was observed for patients with FP and PDAC. A turning point of 55 mm2 was also seen: with region size below 55 mm2, inhomogeneity index of PDAC increases slower than FP; while with size above 55 mm2, inhomogeneity index of PDAC increases faster. Inhomogeneity index of PDAC is uniformly bigger than that of FP in areas detected.Conclusion: It is well known that lesions of pancreas usually feature with inhomogeneity. ADC measurements have been utilized to investigate pancreatic diseases; however, few studies have detected the inhomogeneity properties derived from different ROI sizes in PDAC or FP. This is the first study revealing the variation tendency of inhomogeneity and the inhomogeneity index curve could be used, but not limited, in differentiating PDAC, FP and normal pancreas. This approach might be valuable for differentiation in other disease and could potentially be applied in computer aided diagnose. The pathological causes associated with ADC heterogeneity may be further studied to better understand its utility.