Low-dose Computed Tomography Pulmonary Angiography

Part I Investigation of the model test[PURPOSE] To approve the probability of reducing X-ray dose by the vitro model test, and to select reasonable low-dose (mA) and threshold value of the lowest dose. [MATERIALS AND METHODS] 1. 78 test cases of the chest plain CT examinations were randomly chosen. We not only recorded their heights and weights, but also calculated weight-height ratio and body mass index(BMI);Measure the CT value of air of both intra- and extra- the trachea on the level of 1cm above the carina of trachea on the CT image. Difference of density were calculated;We analyzed the relationship between the difference of air density of intracorporal-invitro and weight, weight-height ratio , BMI.. 2. We made a noise-measure model and a PE model by using phenol-formaldehyde colophony. The water-model, noise-measure model and PE model were scaned separately with the same tube voltage and reduced the tube current step by step and scan. We measure homogeneity by using water model;measure water model by using five point ROIs method, and scaled noise-measure model and water model by using maximal homogeneous ROIs method. We compared noise of five point ROIs method with noise of maximal homogeneous ROIs method;compared noise of standard reconstruction algorithm with tissue reconstruction algorithm;measure rate of display of simulative pulmonary artery in PE model by grouping.[RESULTS] 1.the difference of air density of intracorporal-invitro had positive correlation with BMI (r=0.415,p<0.001). The difference of air density which corresponding to the BMI both ranged form 20 to 55Hu. 2. There was no difference of statistics in homogeneity of image under each tube current. 3. The noise level in tissue reconstruction algorithm lower than standard reconstruction algorithm(pO.OOl). 4. When the tube current were 60mA, The noise increase a little;Whereas the tube current reduction to 30mA, the increase was obvious;when the tube current was under 30mA, there were disagreement between observation of simulative pulmonary artery and embolism. [CONCLUSION] Phenol-formaldehyde colophony could be used in investigation of low-dose CTPA;The group Investigation of model testified that we could choose two group of tube current sets: 60mA and 30mA;tissue algorithm imaging were propitious to decrease the reducing of Signal-to-Noise.Part II Clinical investigation[PURPOSE] To validate the result of low-dose CTPA in clinical PE cases. [MATERIALS AND METHODS] Suspicious patients were executed double-period PE examination by using conventional tube current (280mA) and low-dose (60mA or 30mA). 47 positive case were attained (display one embolism of pulmonary artery at least) which were divided two group according to low-dose condition (60mA or 30mA). Three radiologists independently read all information by using assessed the image sets in random and record results, perform statistic analyse. [RESULTS] The bulk of interobserver and intraobserver agreement (Kappa value) arrived at middling agreemeng (Kappa value=0.4). statistic difference appeared between uncertain result and positive result, but it did not related with tube current level;The group of 60mA and 30mA both had upper sensitivity, speciality, veracity and reliability;There were statistic difference in the grade of Quality of intervasal radiography in 30mA group, but 60mA group had no difference. [CONCLUSION] low-dose CTPA were viable, 60mA tube current level could be used conventional sets of CTPA examination, 30mA tube current level could be used countercheck sets.