The Value Of Single-source Dual-energy CT Virtual Monochromatic Series For Displaying Of Vertebral Osteolytic Metastases

Objecticve:To assess image quality and select the optimal ke V levels for the displaying of vertebral osteolytic metastases in different background.Materials and Methods:Patients with cancer proved by pathology who had undergone spectral CT(Discovery CT750 HD,GE)for chest or abdomen from2011 August to 2015 January were analyzed retrospectively.All the patients have examined chest or abdomen CT more than two times.There were some hypodense lesions on vertebral body and at least one of them was confirmed to be osteolytic metastases by follow-up CT examination,ECT,PET/CT.The patients were excluded,who suffered from other malignancies,fracture,tuberculosis metabolic bone disease and surgery.A total of 42 patients had vertebral osteolytic metastases,26 female and 16 males,age range from 35 to 93 years old,the average age 58 years old,including 14 cases of breast cancer,21 cases of lung cancer,2 cases of gastric cancer,1 case of lymphoma,1 case of renal cell carcinoma,1 case of gallbladder,1 case of liver cancer,1 case of malignant thymoma.A total of 113 lesions were included in the study,and80 lesions involving vertebral margin,70 lesions involving spinal canal,40 lesionswith MR scanning images.The patients had a thoraco-abdominal scan on a spectral CT using gemst one spectral imaging(GSI)scan mode with a single tube.Image scanning parameters were:(1)pitch of 1.375:1;(2)rotation time 0.8 s/r;(3)detector widthof 0.625 mm×64;(4)GSI scan mode with rapid kilovoltage switching between low energy(80 k Vp)and high energy(140 k Vp);(5)tube current of 550 m A;(6)slice thickness and interval of 5mm;(7)CT dose index of 18.28 m Gy.Images at 140 k Vp as well as eleven sets of virtual monochromatic images(VMS)with energy levels from 40 to 140 ke V(intervals of 10 ke V)were chosen for study.The CT value Hounsfield and the standard deviations of the lesions and adjacent normal fat,muscle and spinal canal(background)were measured on all images.Signal to noise ratio(SNR)and Contrast to noise ratio(CNR)were calculated.VMS images at 40,70 ke V and images at 140 k Vp were chosen for the subjective scoring.Two residents in radiology,who were blinded to the imaging information and the final diagnosis,scored the 80 lesions involving vertebral margin,and 70 lesions involving spinal canal on a three point scale respectively.For 40 lesions with MR scanning images,VMS images at 40 ke V and 70 ke V were scored compared with MR images.The statistical analyses were calculated using SPSS version 17 software.Paired sample t test was used to compare the difference of SNR and CNR among the monochromatic images and the images at 140 k Vp.The inter-observer agreement between the two residents was calculated by kappa.The intra-observer score was compared by Mc Nemar test.Values were considered to be significant if p < 0.05.Calculate sensitivity,specificity,Yueden,s index of VMS images at 40 ke V,70 ke V and 140 k Vp images.Results:1.The SNR of different background(fat,muscle,vertebral canal)in 140 k Vp image were 2.73±1.06,2.85±1.13,2.57±1.82,which were lower than VMS image from 40 to 140 ke V(intervals of 10 ke V).The peak SNR was at VMS image 70 ke V P<0.05.2.The CNR of different background(fat,muscle,vertebral canal)in 140 k Vp image were 6.24±3.35,0.80±0.59,1.20±0.70.When fat and vertebral canal were choosed as background,the peak CNR was at VMS image 70 ke V P<0.05.When muscle was choosed as background,the peak CNR was at VMS image 40 ke V P<0.05.3.To 80 lesions involving vertebral margin,the inter-observer agreement of the subjective score was moderate with k= 0.58 on images at 140 k Vp,high with k=0.67 on images at 40 ke V,moderate with k= 0.43 on images at 70 ke V.The subjective score of images at 40 ke V and 70 ke Vwas higher than that of imagesat 140 k Vp P <0.05.4.To 70 lesions involving spinal canal,the inter-observer agreement of the subjective score was high with k=0.63 on images at 140 k Vp,total with k=0.95 on images at 40 ke V,moderate with k= 0.53 on images at 70 ke V.The s ubjective score of images at 70 ke V was higher than that of images at 140 k Vp and 40 ke V,P <0.05.5.Sensitivity,specificity,Yueden,s index of images at 140 k Vp,VMS image 40 ke V70,ke V were 0.50,0.79,0.29;0.74,0.90,0.64;0.78,0.91,0.69.Conclusion:1.Single-source dual-energy CT virtual monochromatic series can significantly improve the image quality of vertebral osteolytic metastases.When fat and vertebral canal are choosed as the background,is the optimal VMS iimage is 70 ke V,but muscle as background,the optimal VMS image is 40 ke V.2.To lesions involving vertebral margin,the 40 ke V images have the higher observer’s reliability and subjective scoring compared with 140 k Vp and 70 ke V images.To lesions involving spinal canal,140 k Vp and 70 ke V images have good observer’s reliability,and 70 ke V images have higher subjective scoring.3.To lesions involving spinal canal,compare with MR images,VMS images at 70 ke V have better ability of displaying than 140 k Vp and other VMS images.