A Preliminary Study Of Dual-energy Virtual Non-contrast Of Dual Source CT In The Lesion Of Mediastinal Lymph Nodes

Objectives: To evaluate the image quality of dual-energy virtual non-contrast(VNC) of dual source computed tomography(CT), and to explore the value of VNC technology in the differential diagnosis of the lesion of mediastinal lymph nodes.Methods: Fifty cases with mediastinal lymph nodes were performed chest conventional non-contrast(CNC) and dual-energy enhanced scanning. VNC images of arterial and venous phase and iodine distribution images were obtained.(1) Mean CT values, signal to noise ratio(SNR), and image quality scores of muscle behind the thoracic vertebral body at the tracheal bifurcation level were comparatively analysed between CNC and VNC.(2) One hundred and sixty lesions were divided into three groups: malignant group(including twenty-six metastatic lymph nodes and thirty-two lymphomas), benign group(including twenty-three tuberculous lymph nodes and thirteen hyperplasia lymph nodes) and normal group(containing sixty-six lesions). The mean CT values of CNC,VNC of arterial and venous phase were measured and analyzed by variance analysis with P<0.05 for statistically significant difference.(3) The energy parameter indicators of iodine distribution images in three groups were separately measured: CT overlay value of arterial phase(CTOA), CT overlay value of venous phase(CTOV), iodine concentration of arterial phase(ICAP), iodine concentration of venous phase(ICVP), normalized iodine concentration of arterial phase(NICAP) and normalized iodine concentration of venous phase(NICAP), various energy parameter values were analyzed with P < 0.05 for statistically significant difference.Results:(1) The mean CT values of muscle behind the thoracic vertebral body at the tracheal bifurcation level in CNC and VNC of arterial and venous phase were:51.93±2.98 HU, 52.63±2.97 HU and 53.29±3.08 HU, the difference was not statisticallysignificant(P>0.05). The SNR: 3.62±0.39, 3.96±0.43 and 4.08±0.46, the difference was statistically significant(P < 0.05). The image quality scores: 4.58±0.61, 4.40±0.73 and4.50±0.68, the difference was not statistically significant(P > 0.05). Comparing to conventional three phase scan, CTDIvol, DLP and ED was higher than dual-energy two phase scan(P<0.05). Comparing to conventional three phase scan, ED of dual-energy two phase scan reduced approximately 1.74 mSv.(2) The mean CT values of lymph nodes in the three groups were measured(P<0.05). The energy parameters of the three groups in the iodine distribution images were different each other(P<0.05).(3) The mean CT value of lymphoma in CNC and VNC of arterial and venous phase was higher than of that metastatic lymph nodes in the malignant group(P<0.05). The hyperplasia lymph nodes was higher than the tuberculous lymph nodes in the benign group(P < 0.05).(4) The energy parameters of lymphoma were higher than the metastatic lymph nodes(P<0.05).CTOA, ICAP, ICVP of reactive hyperplasia lymph nodes were higher than tuberculous lymph nodes(P<0.05). Furthermore, CTOV and NICAP of reactive hyperplasia lymph nodes were slightly higher than tuberculous lymph nodes. However, the NICVP of reactive hyperplasia lymph nodes was slightly lower than tuberculous lymph nodes(P>0.05).Conclusion: The images quality of dual-energy VNC of dual source CT has nothing difference with that of CNC. Dual-energy VNC of dual source CT can satisfy the need of clinical diagnosis as well as CNC. It can also reduce radiation doses for CT examination.Dual-energy VNC technology of dual source CT can contribute to the differential diagnosis of malignant group(lymphoma and metastatic lymph nodes), benign group(tuberculous lymph nodes and reactive hyperplasia lymph nodes) and normal group. It has an important clinical value in the diagnosis of mediastinal lymph nodes.