Currently, the commonly used imaging techniques on diagnosis of malignant tumor are CT, MRI and PET-CT. In recent years, because of its convenience in whole body examination, whole body MRI is growing popular, especially in the tumor diagnosis ^[1-2]. However, studies focused on comparison between diagnostic capability of WBDWI and PET-CT examination have been rare. In the present work, the diagnostic ability of whole-body diffusion-weighted imaging (WBDWI) in malignant lesions is compared with that obtained with ¹⁸F-FDG PET-CT.

Thirty-five patients with pathologically proved malignant tumors were enrolled. Prior consent was obtained. All patients underwent both WBDWI and PET-CT, and then were followed up for more than 6 months. WBDWI examination: All patients were scanned in a 1.5T MR scanner (GE Signa HDx). Scanning parameters used were as follows: 30 slices with 6 mm thickness without gap, FOV = 40 cm × 40 cm, matrix = 96 × 128, TR/TE = 5100/81.9 ms, b value = 600 s/mm², 4 averages. WBDWI was divided into 6~8 segments for scanning, scan time was 2 min 48 s for each segments. 3D-MIP and the black and white inversion technique were used for post processing. PET-CT examination: PET-CT was performed by GE Discovery ST-16 scanner, imaging agent was ¹⁸F-FDG, the patient’s blood glucose level was control in <8.1 mmol/L. CT was firstly scanned, acquisition conditions were as follows: 120 kV tube voltages, tube current of 150 mA, pitch 1.75:1. Then, PET 3D images were acquired. Body station collection included 5 beds with 3 min for each one and head station collection included 2 beds with 5 min for each one. By using CT data for attenuation correction, PET image were reconstructed and fused with CT image using PET-CT image workstation. Image analysis: Two experienced MR diagnostic physicians assessed the WBDWI image independently, and the other two professional PET-CT diagnostic physicians read the PET-CT image respectively. The results of from these two techniques were then compared with the gold standard results, which were determined based on the results of pathology and clinical follow-up. ADC and SUVmax of each lesion were measured. The receiver operating characteristic (ROC) curve, sensitivity, specificity and accuracy were compared between the two methods. Kappa analyses were used to compare the diagnostic consistency betweenthe two methods. Areas under the curve were compared by Hanley & McNeil test. Categorical variables were tested with the Chi-square test or McNamara test.

Images using WB DWI and PET/MR of the same patient with Follicular lymphoma (Grade III) were shown in Fig. 1. It can be seen that WBDWI had substantial consistency with PET-CT. However, it is shown in Fig. 2 that significant difference between two techniques was also seen in a patient with a mediastinal soft tissue sarcoma. PET-CT scanning in whole-body PET-MIP image shows the right axillary increased uptake change after operation, there was no more tumor, systemic CT image only left ilium bone island, but WBDWI detection of left pubis and sacrum, femur, right ischial ramus and sternal handle multiple bone metastasis. The area under the ROC curve of WBDWI, PET-CT, eADC, and SUVmax were 0.952, 0.970, 0.844, and 0.858, respectively (see Fig. 3). There was no significant statistically difference between measurements from WBDWI and PET-CT, eADC and SUVmax (Z = 2.153、1.195, P ＞ 0.05), but Az(WBDWI) were significantly larger than Az(ADC) (Z = 7.456, P ＜ 0.01), Az(PET-CT) were significantly larger than Az(SUV) (Z = 6.821, P ＜ 0.01). The sensitivity, specificity and accuracy were 86.6%, 95.3%, and 89.5% in WBDWI, and 94.4%, 94.3%, and 94.3% in PET-CT. Kappa value of the diagnostic consistency between WBDWI and PET-CT was 0.745.WBDWI was seen to have a high sensitivity, specificity and accuracy in detecting malignant lesions, and a substantial consistency with PET-CT. WBDWI was an effective method for screening bone metastasis, especially suitable for radiation-vonuerable population, and it is better than PET-CT in detecting low grade malignant tumor. WBDWI is low cost option without the injection of a contrast agent and it can obtain images with valuable diagnostic information. In summary, WBDWI can be used as a potential alternative to PET/CT in addition to conventional MR examination.