Study Of Application Of Diffusion Weighted Imaging In The Diagnosis Of Spinal Metastases

Objective:To investigate the display capabilities on diffusion-weighted imaging of spinal metastases,and to quantify the SAR, SNR and ADC in different b values, at the same time, tooptimize the scan sequence.Materials and Methods:45cases with spinal metastases in patients confirmed pathologically or clinicallymetastatic spinal tumor underwent MR routine scan and multi-b-value diffusion-weightedimaging, to study its performance in each sequence, to compare DWI sequence andconventional sequence of DWI lesions display capabilities, and different b valuesinfluencing factors and calculate the SAR value of the vertebra and adjacent normalvertebral DWI images, ADC values and SNR.Results:（1） General MRI and DWI appearance:45patients with spinal metastases in patientswith a total of92vertebral involvement. Most of the vertebra in T1WI showed low signal;compared with the normal vertebral vertebra on T2WI showed slightly higher signal andother low signal and mixed signal; most of STIR and DWI expressed as high signal, fewof them show a low signal.（2） The lesions detection rate on DWI sequence （b=500s/mm²）and general MRIsequences: The detection capability on TIWI, STIR and DWIsequence are higher than which on T2WI sequence，The differences between them aresignificant （p<0.001）, The capability to show the lesions on TIWI, STIR and DWIsequence were similar （p>0.01）.（3） The comparison of ADC value: on DWI，the ADCvalue of lesions and normal vertebral were: b=200s/mm²，1.29士0.17x10^-3s/mm²、0.56士0.07x10^-3s/mm²; b=300s/mm²，1.340士0.19x10^-3s/mm²、0.54士0.08x10^-3s/mm²；b=400s/mm²，1.32±0.16x10^-3s/mm²，0.51±0.11x10^-3s/mm²； b=500s/mm²， 1.35±0.14x10^-3s/mm²，0.48±0.09x10^-3s/mm²。At the same imaging conditions，theADCvalue of lesions was significantly higher than normal vertebral body （p <0.01）. Take b=500s/mm²,95%confidence interval of the ADC values of adjacent normal vertebral limit0.59x10^-3 s/mm²as a critical value, the diagnosis of metastases sensitivity92.5%,specificity80.5%.（4） The comparison of SAR value: on DWI, the SAR value of lesionsand normal vertebral were:: b=200s/mm²，31.35±1.37%、13.28±1.24%；b=300s/mm²，33.57±1.46%、15.31±1.03%; b=400s/mm²，38.19±1.33%、18.49±1.21%；b=500s/mm²，47.83±1.28%、21.24±1.16%。 At the same imaging conditions，the SAR value of lesionswas significantly higher than normal vertebral body （p <0.01）. Take b=500s/mm²whenthe upper limit of the adjacent normal vertebral body SAR value of the95%confidenceinterval25.35%as the threshold, the sensitivity of the diagnosis of metastases of91.25%and a specificity of72.28%.（5）The comparison of SNR value: b=200s/mm²，26.62±3.81、 b=300s/mm²，20.25±3.24、 b=400s/mm²，14.38±3.15、 b=500s/mm²10.92±3.43。The differences between them are statistical significance （p<0.001）。（6）The comparison of the three types of metastatic spinal tumor ADC value （take b=500s/mm²）: comparison between the three groups （b=500s/mm²） osteolytic type, mixedand osteoblastic type transfer tumor ADC values were1.83±0.21x10^-3s/mm²、1.61±0.18x10^-3s/mm²、0.94±0.15x10^-3s/mm²，Guests between three types have significantdifferences （p <0.01）.（7） Comparison of the three types of spinal metastases SAR value(take b=500s/mm²: Osteolytic type, mixed, osteoblastic metastases SAR value each57.54±3.76%,48.82±3.42%,32.15±3.38%,there were significantly different betweenthe three types （p <0.01）.（8） Correlation between ADC value and SAR values: DWIsequence, the same organization in the same conditions, the SAR value and ADC valuesbetween positive correlation, and the correlation was significant （p <0.01）.（9） ADC map:The ADC map reflects the diffusing capacity of the different spinal metastases，whichdiffusing capacity higher than normal tissue and showed high signal.（10） DWI imagequality has some correlation with the b value, the smaller the b value, the sharper theimage. Conclusion:DWI have a high diagnostic accuracy on spinal metastases, SAR values and ADCvalues can be used as a reliable basis for spinal metastases and normal vertebraeidentification，Take into account the SNR，two b values should be used in order to obtainaccurate data and clear images.