The Technology Of Whole Body Diffusion Weighted Imaging (WB-DWI) And Its Application In Diagnosis Of Tumor

Part IObjective:In the free-breathing state, short TI inversion recovery echo-planar imaging diffusion weighted sequence (STIR-EPI-DWI) and body coil were used to obtain the whole body diffusion-weighted imaging (WB-DWI). Then, the WB-DWI images were reconstructed using the maximum intensity projection (MIP) and images similar to PET images can be achieved. Through technical improvement and optimization of scan parameter, to explore the value of this method in the clinical diagnosis of tumor and the feasibility of search for tumor metastasis in patients with new non-invasive method.Materials and methods:1) The optimized center frequency was selected as a CF of whole body scan.2) Choose the sequence of STIR-EPI-DWI with b=400 s/mm2, 600 s/mm2 and 800 s/mm2.3)The signal-to-noise ratio (SNR) and contrast noise ratio (CNR) of images of three sequences and their detection rate of lesions were compared. The SNR and CNR of original images of STIR-EPI-DWI were compared with T2W image of the same slice. Meanwhile, lipid-suppressed coronal images of six cases of tumor patients obtained using STIR sequence were compared with the STIR-EPI-DWI reconstructed images by the naked eyes.Results:The suitable CF is crucial to the image quality. When b=600 s/mm2, SNR of images obtained using STIR-EPI-DWI sequence was 60.94±14.69 and CNR was 56.03±11.82.When b=400 s/mm2, SNR was 58.76±17.45 and CNR was 48.90±13.54, When b=800 s/mm2,SNR was 56.40±17.27 and CNR was 51.32±15.11. The results reveal b=600 s/mm2 is the best choice, reconstructed 3D MIP images can fully demonstrate lesions in patients. Application of STIR sequence to obtain whole-body coronal plane with fat suppression requires multi-segment collection and image mosaicking. Although it can be used in clinical diagnosis, it is difficult to perform in practice due to its time-consuming.Conclusion:unification CF should be calculated manually, the average of CFs of the first and third segment. The selection of b value is very important, the higher b values, the bigger differences in diffusion, but the higher b values, the lower the SNR of image, and this impacts image clarity. Reducing the b value to 400 s/mm2 can make up insufficient SNR, but also lower the diffusion limited features. This may overestimate the diffusion-limited lesions. Therefore, the rational choice of b values in different parts of and optimization of imaging parameters appear particularly important to the lesions reveal. Our experience is that b value=600 s/mm2 is appropriate. Through the improvement of the pre-scanning technology, stable and high-resolution WB-DWI images can be successfully obtained. Using STIR fat suppression techniques will reduce signal contamination of fat and muscle tissue. WB-DWI technique has important clinical value not only in detecting primary malignant tumor and distant metastasis, but also in tumor diagnosis and monitoring effects of chemotherapy.PartⅡObjective:To investigate the diffusion characteristics of the normal adult tissues and organs, establish standard values of apparent diffusion coefficient (ADC) of different organs, and explore its relationship with gender and age.Materials and Methods:20 cases of healthy volunteers,41-50 years old, both 10 cases of men and women, short TI inversion recovery echo-planar imaging sequence (STIR-EPI) whole-body diffusion-weighted imaging (WB-DWI) was used and b values were 0 and 600s/mm2. ADC values were measured in brain gray and white matter, caudate nucleus head, lentiform nucleus, thalamus, pons, bilateral submandibular gland, bilateral parotid gland, left ventricular wall, greater curvature side of stomach, liver (left and right lobe), spleen, head of pancreas, bilateral kidneys, T8 thoracic vertebrae, T5-9 disc, L2 lumbar vertebrae, L2-3 intervertebral disc, prostate peripheral zone in the central lobe and, bilateral breast, uterus and uterine cavity. The difference of ADC values between sexual groups were analyzed statistically.Results:The average ADC values in various organs of the middle-aged healthy people is in the small volatile, following the laws of nature, there was no significant difference of ADC values among bilateral cerebral gray matter and white matter, caudate nucleus and bilateral kidney, breast and liver lobe. And there was no significant difference of ADC values between the men and women.Conclusion:In our study, the ADC values of all major organs of the normal middle-aged people were measured, and the standards of the ADC values of the various organs were established. The results show that the ADC value of the normal tissues had no significant difference in gender and between the left and right side. This provids basis of reference in whole body DWI and the semi-quantitative analysis.PartⅢObjective:The number of advanced tumor is increasing obviously,in order to know the actual changes of the size and number of the metastatic tumors pre-and post-treatment,CT and/or MRI scaning were usually applied in the past,only a small number of patients could payed for PET(positron emition tomography).But there exists many problems,including redundantly exposure to radiation,too long check and heavy financial burden.Therefore we evaluate the application of whole body diffusion weighted imaging in diagnosis of tumor and metastatic tumor. To evaluate the accuracy of detecting tumor and metastasis using whole body diffusion weighted imaging (WBDWI)Methods:sixty-eight patients (49 male,19 female, age ranging from 29 to 84 years with mean age of 61 years) with variety tumors were investigated by CT and/or MRI scan, seventeen patients were compared with positron emission tomography (PET).All tumors were classified according to diameter into four groups of<1 cm,≥1-<2 cm,≥2-<3 cm and≥3cm. At the same time, detection condition of lesions from different parts was analysed.Results:The detection rate of four groups were 30%,78%,96% and 100% respectively. The skeletal system had the highest sensitivity and accuracy among parts of body. There exists some difficulty in diagnosing lesion of which diameter is small than 1 cm in lung and small 2cm in the neck and cavitas pelvis. Conclusion:whole body diffusion weighted imaging is safe, convenient, effective and economic for screening wide-ranging tumor focus. After improvement of parameter, WBDWI could be as a new effective whole body examination technique.