| Objecticve: To assess image quality and to select the optimal keV levels for osteoblastic metastases on the vertebral body of lung cancer and to investigate the factor of detection rate and diagnostic value.Materials and Methods: Patients with lung cancer proved by pathology who had undergone spectral CT(Discovery CT750 HD, GE) for chest or abdomen from 2011 August to 2014 August were analyzed retrospectively.And the patients have examined chest or abdomen CT after their spectral CT examination until at least 6months.There were many high-density lesion-s on vertebral body and at least one of them was confirmed to be osteoblastic metastases by follow-up CT examinations,ECT,PET/CT by two radiologists.Exclud the patients who suffered fr-om other malignancies, spinal fractures and surgeries, spinal tuberculosis. A total of 25 patients were included in the study.Reconstructed 140 kVp and 40~140keV monochromatic images(interval 10keV). Addition of two radiologists(observer 1 and 2) were required to find high-density lesions of vertebral bodies in 140 kVp images independently. Analysing the undetected lesions of the two radiologists for objective evaluation. Measure the CT number and standard deviation(SD) of the lesions and backgr-ound of 140 kVp and monochromatic images and then calculated the signal-to-noise rati-o(SNR) and contrast to noise ratio(CNR);Then the two observers were required to read 60 keV,70keV images and to read 140 kVp images again(each of two sequence at a interval of 4 weeks)to detect the highdensity lesions and sore them.T-he standard was as follow:0,be sure non-metasta-se;1, not sure metastase;2, tend to metastase;3,be sure metastase,and lesions which were undetected were recorded 0. Using paired sample t test to compare SNR and CNR among 40-140 keV and 140 kVp images. Using McNemar test to compare the detection rate of two raters and different image sequences.Using receiver operating characteristic curve(ROC curve)to analyse the diagnostic value of defere nt observers and different images.Using Wilcoxon signed rank test to compare th e difference of the sores of the matastases.Make all α=0.05.Results:1.The SNR of 50,60 and 70 keV images were higher than that of 140 kVp and that of 60 keV were the highest,70 keV images were higher than 50keV(all p<0.05).The CNR of 50,60,70 and 80 keV images were higher than that of 140 k Vp images and 70 keV images had the highest CNR,60 keV and 70 keV had higher CNR than 50 keV and 80keV(all p<0.05).2. In the same sequence,there were no significant difference of the detection rate between the two observers(p>0.05).Both the observers showed that the detection rate of 60 keV and 70 keV images were higher than 140kVp(p<0.05),and the-re were no significant difference between 60 keV and 70 keV images(p>0.05).3.The area under the ROC curve of observer1 were 0.737,0.776,0.828 and that of observer2 were 0.724,0.781,0.805 in 140 kVp,60keV,70 keV images respectively.70 keV image had the highest diagnostic value.Compared to observer2,observe r1 had the lower sensitivity and higjer specificity At the same critical value.4.For observer1,it showed that the score of metastases of 70 keV images we re higer than that of 140 kVp images(p<0.05),there were no significant diference between 60 keV and 140 kVp,and also between 60 keV and 70 keVimages.For obsev er2, 60 keV,70keV image scores are higher than 140 kVp, and the 70 keV image s cores were the highest(p<0.05).There were no significant diference between the t wo observers of 140 kVp image scores.In 60 keV and 70 keV images the score of observer2 were higher than observer1.Conclusion:1.60 keV, 70 keV images can improve the image quality, increase the contrast of lesiongs, so as to improve the detection rate and the diagnostic efficiency of osteoblastic metastases of lung cancer, 70 keV was the optimal energy level;2.Detection rate and diagnostic efficiency has no obvious effect between obser vers with different experience. The the image quality had greater influence. More e xperienced observer has lower misdiagnosis rate and the less experienced observ er hase lower missed diagnosis rate relatively.3.Image quality had moer impact on diagnostic confidence and the workless observer depends more on image quality. |
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