炎性和转移性淋巴结弥散加权成像b值选择的初探

目的对新西兰大白兔炎性和转移性腘窝淋巴结模型弥散加权成像图像质量定性和定量评价,选择合适的成像参数即b值。方法分别建立炎性和转移性淋巴结新西兰大白兔动物模型12只,分别选择b值=300、600、900对两组进行弥散加权成像,计算信噪比,进行非参Kruskal-WallisH检验。所有淋巴结经病理证实。结果肿瘤组当b=300、600、900三组的平均秩次分别为54.00、29.67、25.83,χ2值(即H值)为25.574,p=0.000,可认为三组信噪比(SNR)有差异。炎症组当b=300、600、900三组的平均秩次分别为54.13、37.04、18.33,χ2值(即H值)为35.574,p<0.05SNR有差异。结论选择合适的扩散梯度系数能够得到较佳的信号对比度,同时也能较准确地区分炎性和转移淋巴结。

MR perfusion and diffusion imaging for the diagnosis of benign and malignant bone tumors

Objective： MR-PWI and MR-DWI were supplementary functional methods to differentiate benign from malignant bone tumors. The aim of this study was to assess the diagnostic potential of MR-PWI conjunction with MR-DWI in differentiating benign from malignant bone tumors. Methods： MR-PWI and MR-DWI were performed on 39 patients by using a 1.5 T MR imager. Perfusion imaging was started with GRE-EPI sequence as soon as the bolus administration commenced. With b value as 300 s/mm^2, diffusion imaging was performed with SE-EPI sequence. Type of TIC, peak enhancement, steepest slope, signal difference between 2 baselines and ADC were compared between benign and malignant bone tumors. The data were analyzed with soft-ware （SPSS, version 13.0）. Subjective overall performance of two techniques was evaluated with Receiver Operating Characteristic （ROC） analysis. Results： 1. MR-PWI： （1） The Patterns of TIC of most benign bone tumors （17/21） were type Ⅰ and Ⅱ, and all malignant bone tumors were type Ⅲ and Ⅳ. （2） There were significant differences in peak enhancement （17.52 ± 2.37 vs. 52.42 ± 5.74） %, steepest slope （4.69 ± 2.84 vs. 9.63 ± 4.05）%/s and signal difference between 2 baselines （6.87 ±3.34 vs. 31.75 ± 11.09） % between benign and malignant groups. And their diagnosis accuracy was 82.1%, 79.5% and 87.2%, respectively. （3）. 4 highly vascularized benign bone tumors were mistaken in diagnosis as malignant ones according to their perfusion characteristics. 2. MR-DWI： There was significant difference between ADC of benign and malignant groups [（1.86 ± 0.38） vs. （1.44± 0.26）] ×10^-3 mm^2/s when b value was 300 s/mm^2. The diagnosis accuracy was 79.5% when ADC value less than 1.63 × 10^-3 mm^2/s was considered as malignant ones. 3. The diagnosis accuracy of M R-PWI and MR-DWI were 89.7% and 79.5%, respectively. Conclusion： MR-PWI is the better valuable technique than MR-DWI in differentiation benign from malignant bone tumors. To suspicious highly vascularized bone tumors, MR-PWI combining with MR-DWI lead to higher diagnosis accuracy.

Diffusion-weighted imaging of biliopancreatic disorders:Correlation with conventional magnetic resonance imaging

Diffusion-weighted magnetic resonance imaging(DWI)is a well established method for the evaluation of intracranial diseases,such as acute stroke.DWI for extracranial application is more difficult due to physiological motion artifacts and the heterogeneous composition of the organs.However,thanks to the newer technical development of DWI,DWI has become increasingly used over the past few years in extracranial organs including the abdomen and pelvis.Most previous studies of DWI have been limited to the evaluation of diffuse parenchymal abnormalities and focal lesions in abdominal organs,whereas there are few studies about DWI for the evaluation of the biliopancreatic tract.Although further studies are needed to determine its performance in evaluating bile duct,gallbladder and pancreas diseases,DWI has potential in the assessment of the functional information on the biliopancreatic tract concerning the status of tissue cellularity,because increased cellularity is associated with impeded diffusion,as indicated by a reduction in the apparent diffusion coefficient.The detection of malignant lesions and their differentiation from benign tumor-like lesions in the biliopancreatic tract could be improved using DWI in conjunction with findings obtained with conventional magnetic resonance cholagiopancreatography.Additionally,DWI can be useful for the assessment of the biliopancreatic tract in patients with renal impairment because contrast-enhanced computed tomography or magnetic resonance scans should be avoided in these patients.

Modified Wiener method in diffusion weighted image denoising

To denoise the diffusion weighted images （DWls） featured as multi-boundary, which was very important for the calculation of accurate DTIs （diffusion tensor magnetic resonance imaging）, a modified Wiener filter was proposed. Through analyzing the widely accepted adaptive Wiener filter in image denoising fields, which suffered from annoying noise around the edges of DWIs and in turn greatly affected the denoising effect of DWIs, a local-shift method capable of overcoming the defect of the adaptive Wiener filter was proposed to help better denoising DWIs and the modified Wiener filter was constructed accordingly. To verify the denoising effect of the proposed method, the modified Wiener filter and adaptive Wiener filter were performed on the noisy DWI data, respectively, and the results of different methods were analyzed in detail and put into comparison. The experimental data show that, with the modified Wiener method, more satisfactory results such as lower non-positive tensor percentage and lower mean square errors of the fractional anisotropy map and trace map are obtained than those with the adaptive Wiener method, which in turn helps to produce more accurate DTIs.