| Objective: Solitary pulmonary nodules (SPN) are common findings on chest radiograph resulted from different lung diseases. If no specific signs to help diagnosis , SPN should be regarded as indeterminate. So, how to diagnose a SPN qualitatively and quantitatively is a challenge and is very important with regard to taking different measures accordingly. In this study, we evaluated enhancement features of SPNs after administrating iodine contrast material with four-slice spiral dynamic CT, on the basis of difference in the degree of vascularity and metabolism of SPNs in order to determine the clinical efficacy of enhanced dynamic CT in differentiating malignant from benign nodules. Perfusion of SPNs were also calculated by applying a nuclear medicine processing technique to the rapidly increasing period of time-density curve(TDC) to help clinical diagnosis.Methods: 37 patients with SPNs were included in this study and performed enhanced dynamic CT. The SPNs were less than 3cm in diameter and no calcification and cavity. All patients were instructed in and practiced the breath-holding to reproduce precisely the same degree of inspiration. The location and maximum cross-section through the center of SPNs, which werealso the scanning slice in dynamic CT, were determined before administration. Iodinated, nonionic contrast material was administered intravenously via antecubital vein at 5 ml/sec for a total 75 ml by using auto-injector. Dynamic scanning was triggered at tenth second. Both the first and second series scanning time were 20 seconds and the interval was 10 seconds. After that were seven single-scan, intervals of the first there scans were 10 seconds, the others were 15 seconds .A total of 144 images were obtained. Reconstruction images parameters were transmitted to CT workstation and analyzed with dynamic software. TDCs were calculated by drawing the region of interest (ROI) over the SPNs&aorta (or subclavian artery if the aorta was not included in the section) at least 70% of the diameter, averting necrosis and cavity. ROI should included the most enhanced area on the SPNs. Precontrast values and maximum enhancement values, defined as peak height of TDC minus baseline precontrast attenuation, were determined and the ratios of the maximum enhancement values of SPNs to that of aorta were calculated as well. Perfusion values of the SPNs were calculated based on the equation described by Miles:P=TACSpN/PHAorta, where P= perfusion in milliliter of blood flow per minute per milliliter of tissue, TACSpn= maximum gradient of the SPN time-attenuation curve in Hounsfield units per minute, and PHAorta=maximurn enhancement of aorta in Hounsfield units. Enhancement pattern was evaluated on the image that was the most enhanced and wasclassified as follows: homogeneous, heterogeneous, central, peripheral and non-enhancement. All values were expressed on a mean+standard deviation. The significant different level was 0.05. All the statistical analysis were performed with SAS 6.12 software package. The threshold value was defined and sensitivity, specificity, accuracy, the positive and negative predictive value were calculated respectively .Results: l.The TDC appeared differently for the malignant, benign, and inflammatory SPNs. Malignant TDC described as type 1 curve, showed rapid increase to the peak height at fiftieth second and maintained a plateau. Inflammatory curve, described as type 2 curve, showed moderate increase to peak height later than type 1 and decreased slightly after seventy-fifth second. The TDC of benign nodules show little or a little increase after injection of contrast material. 2.Post-contrast values of malignant, inflammatory nodules were significantly higher than pre-contrast value(t= 14.3729, 10.1891, p<0.01 respectively), but it was not the case of benign nodules (t=2.02, P>0.05). 3.Maximum enhancement of the malignant and the inflammatory nodules were significantly higher than that of benign modules (P<0.01). 4.Both malignant and inflammatory nodules had higher SPN-to-aorta maximum enhancement ratios than that of benign nodules(p<0.01), but the difference between the former two groups was not significant. 5.Perfusion values of malignant and inflammatory SPNs are significantly higher than that of benign SPNs(pO.Ol). 6.The correlation between aorticmaximum enhancement values and the malignant nodule maximum enhancement, ratios of SPN-to-aorta were significant. The regressive equations and r values were: y=-92.5889+0.4136x, r=0.8083; y=-l 4.8284+0.087 lx, r=0.6713 respectively. A less strong relationship was found between the aorta maximum enhancement and perfusion values of malignant nodules, y=-3.3768+0.0142x, r=0.5283. 7.Of 20 malignant nodules, 8 showed complete homogeneous enhanced pattern, 9 heterogeneous, 3 peripheral. Of 12 benign nodules, 5 showed no or little enhancement, 4 peripheral(2 of which showed ring-like fashion ), one was central and two were heterogeneous. The difference between malignant and benign modules in enhancement pattern was significant, x 2=9.653, p<0.01. 8. The maximum enhancement value of 20Hu was considered as threshold (higher than 20Hu were considered malignant ) and sensitivity would be 95%, specificity 70%, and accuracy 84%. The positive predictive value was 80% and negative predictive value 92%. If the ratio of SPN-to-aorta of 6% was threshold, the sensitivity was 100%, specificity 71%, accuracy 86%, and the positive and negative predictive values were 80%, 100% respectively.Conclusions: Maximum enhancement of SPNs reflected the degree of vascularity and metabolism. The threshold of 20Hu was clinically significant in differentiating malignant nodules from benign ones. The ratio of maximum enhancement of SPN-to-aorta was also applicable in differential diagnoses...
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