Research On Evaluating Pulmonary Embolism By Histogram Of Ventilation/Perfusion Scans

Background: Nuclide ventilation/perfusion lung scans(V/Q) is one of the main methods for diagnosis of pulmonary embolism (PE). The diagnosis results of qualitative analysis can be divided into four categories: high-, intermediate-, low-probability of PE and normal scans. Both the positive predictive value of high-probability of PE and the negative predictive value of normal can reach more than 90%, which has been approved in clinical practices. It has been reported that 30% of intermediate and low probability are PE, so the qualitative analysis may lead to high rate of misdiagnosing and missed diagnosis.Objective: By calculating V/Q ratio in each pixel and the distribution histogram of V/Q ratio frequency, the aim of this study is to improve the diagnosis efficiency of PE, and to discuss the effect of the quantitative analysis method on diagnosing small airway lesion.Methods: We used 99Tcm-MAA (Albumin Aggregated and Stannous Chloride) and 99Tcm-DTPA (Pentetate Acid and Stannous Chloride) to carry on ventilation/perfusion lung scans for 25 normal comparison groups (including 10 non-smoking volunteers and 15 smoking volunteers), and 112 suspected PE patients. We referred to the revised standard of PIOPED to carry on qualitative analysis, and applied distribution histogram of V/Q ratio frequency to carry on quantitative analysis. Taking the final clinical diagnosis as the basis, we analyzed the characteristics of distribution histogram of V/Q ratio frequency in normal groups, PE groups and COPD groups, and evaluated the diagnosis efficiency of quantitative analysis among the groups of normal on qualitative analysis, intermediate and low probability of PE, and high probability of PE. In addition, we analyzed the characteristics of distribution histogram of V/Qratio frequency in groups of non-smoking, smoking and COPD. Results:1,Characteristics of distribution histogram of V/Q ratio frequency in normal group, PE group and COPD groupIn normal control group, most of V/Q ratio frequency (above 60%) distribute in 0.8～1.2 interval, formed the middle bar"rear obviously", and the bars of the two edges are relatively lower. The distribution of histogram in <0.8 interval is higher than that in >1.2 interval. Compared with the normal group, the height of bar in 0.8～1.2interval is lower, and the height of bar in >1.2 interval is rising obviously in PE group, while it is nearly the same as the normal group in <0.8 interval. In COPD group, the height of bar is lowered greatly in 0.8～1.2interval; while the high bar is formed in <0.8 interval, which is relatively lower in the normal group; but the height of bar is nearly the same as the normal group in >1.2 interval. There are significant differences among these groups (p<0.05).2,Characteristics of distribution histogram of V/Q ratio frequency in qualitatively analyzing different probability groupsIn the normal group, the shapes of the distribution histogram of V/Q ratio frequency are quite similar with the normal control group, and there is no significant difference in each V/Q ratio intervals between these groups.In the high probability of PE, the shapes of the distribution histogram of V/Q ratio frequency are similar with the PE group, and there is no significant difference in each V/Q ratio interval between these groups, but there are significant differences between these two groups and the normal comparison group.In the intermediate and low probability of PE group, the shape of the distribution histogram of V/Q ratio frequency is similar with the shapes of the normal group and the high probability. When the"cut-off value"is 16.63% in the V/Q ratio >1.2 interval, as well as perfusion defects >75%, there are another 3 persons diagnosed as PE; the sensitivity, specificity, positive predictive value and negative predictive value to predict a value in the intermediate and low probability of PE group are 20%, 100%, 100% and 76%.3. Characteristics of distribution histogram of V/Q ratio frequency in groups of non-smoking, smoking and COPD.In every interval of the smoking group, the height of distribution histogram of V/Q ratio frequency is similar with the non-smoking group and the COPD group; Comparing two groups of the three respectively, there are significant differences (p<0.05) in <0.8 and 0.8~1.2 intervals, but there are not significant differences (p>0.05) in >1.2 interval.Conclusions:1. The method of distribution histogram of V/Q ratio frequency is helpful for distinguishing normal, PE and COPD.2. The methods of distribution histogram of V/Q ratio frequency and qualitative analysis have similar efficacy of diagnosis for the high probability of PE and for qualitatively analyzing normal or near normal V/Q scan.3. Combining the method of distribution histogram of V/Q ratio frequency with the qualitative analysis, may be helpful for distinguishing PE patients from the intermediate and low probability of PE groups, so the ration of the indefinite diagnosis group can be decreased, then the efficacy of diagnosis of the V/Q scan can be increased.4. The method of distribution histogram of V/Q ratio frequency can early prompt small airway lesion in smoking group...