| 2.1.Objective(??)To evaluate the diagnostic significance of nonenhanced(NE)single source dual energy computed tomography(ss DECT)in differentiating adrenal cysts(ACs)and hypodense adrenal adenomas(HAAs).2.2. Materials and Methods(?????)A retrospective study was carried out involving 58 patients(mean age 52.14 ± 10.5 years,range 27-74 years)who underwent adrenal protocol NE ss DECT on GE Discovery 750 HD scanner(Gemstone Spectral Imaging(GSI),GE healthcare,Milwaukee,WI)between August 2011 and July 2015 and were diagnosed with hypodense adrenal nodule,suspected by CT imaging and confirmed by histopathology to be either AC or AA.The study included 18 ACs(8 males,10 females)and 40 HAAs(15 males,25 females).Virtual monochromatic spectral(VMS)and material decomposition(MD)images were generated with ss DECT.Spectral CT attenuation values against 40 to 140 ke V and effective atomic number(eff-z)from the VMS images,fat and water densities from the fat and water based MD images,respectively for ACs and HAAs were measured twice(i.e.;ROI 1 and ROI 2)on image showing maximum diameter of the lesion,with a gap of 10 days' time interval in between.Each ROI was 2/3 of the size of the lesion and it was homogenous excluding any hemorrhage or necrosis.Slope(k)of the spectral HU curve was computed for spectral HU values against virtual monochromatic photon energies(ke V).The consistency of measurements between ROI 1 and ROI 2 for non-parametric data of CT value at 60 ke V for ACs was calculated using Spearman Correlation Coefficient(rs)while intraclass correlation coefficient(ICC)was used for the normally distributed data of CT value at 40,50,70 to 140 ke V,k,eff-z,fat(water)and water(fat)density for ACs and HAAs and CT value at 60 ke V for HAAs.The difference of CT values at 40,50,70 to 140 ke V,k,eff-z,fat(water)and water(fat)density between ACs and HAAs were statistically compared using t test while CT value at 60 ke V by mann whitney test.Receiver operating characteristic(ROC)curves were generated to compare the diagnostic efficacy of these parameters in discrepancy of ACs and HAAs.The spectral HU curves were classified into ascending(k > 0.1),straight(-0.1 ? k ? 0.1)and descending(k <-0.1)curve types depending on the measured k of the spectral HU curve and were subsequently analyzed using the fisher exact test.2.3. Results(??)All the measurements between ROI 1 and ROI 2 were statistically well correlated(ICC >.75,rs =.934).CT value(mean ± SD)at 40,50,70 ke V(29.68 ± 11.85 HU,21.72 ± 7.67 HU,13.97 ± 5.02 HU),eff-z(7.72 ±.12),water(fat)density(1203.83 ± 122.17 mg/cm3)and CT value at 60 ke V(median,interquartile range)(17.80,5.86 HU)for ACs were greater than those of HAAs(-.843 ± 9.61 HU,3.93 ± 6.37 HU,9.09 ± 4.64 HU),(7.37±,.13),(865.39 ± 1116.23 mg/cm3),(6.55,6.18HU)(p value<.05).However CT value for HAAs at 120 to 140 ke V(12.77 ± 5.46 HU,12.99 ± 5.55 HU,13.17 ± 5.63 HU),k(.14 ±.11)and fat(water)density(147.53 ± 119.15 mg/cm3)were higher than that of ACs(9.27 ± 4.89 HU,8.94 ± 4.96 HU,8.68 ± 5.01 HU),(-.21 ±.13),(-187.06 ± 111.09 mg/cm3)(p <.05).While CT value at 80 to 110 ke V were not statistically different between ACs and HAAs(p ?.05).The ROC curves displayed area under curve(AUC)for k(.981),fat(water)density(.975),water(fat)density(.978),eff-z(.976)and CT number at 40 ke V(.972)were the highest ones for differentiating ACs from HAAs using threshold value of-.008,-3.05 mg/cm3,1009.4 mg/cm3,7.50 and 19.70 HU respectively.Eff-z,fat(water)density,water(fat)density,k and CT value at lower ke V's had the leading sensitivities and specificities both in discriminating ACs from HAAs.Moreover CT values at 40 and 50 ke V had the uppermost specificity(97.5 %)from all other remaining parameters and also from CT value at 70 ke V(87.5 %),with 70 ke V being close to the average energy produced by the conventional 120 k Vp NECT.There were 66.7 % descending,33.3 % straight and no ascending type spectral HU curve for ACs comparative to 2.5 %,32.5 % and 65 % for HAAs,respectively and the difference between ACs and HAAs was statistically significant(p <.05)2.4. Conclusion(??)The spectral HU curve,fat(water),water(fat)density,eff-z,CT value at lower ke V's(40 to 70 ke V)and higher ke V's(120 to 140 ke V)using NE ss DECT are proficient diagnostic parameters for discriminating ACs and HAAs which may substitute followup imaging.Besides using CT attenuation threshold value at 40 or 50 ke V with ss DECT has improved both sensitivity and specificity for the purpose contrary to conventional 120 k Vp NECT. |
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