Lung ventilation scintigraphy - what is the ideal radioaerosol?

Objectives: To assess if ^99mTc MDP and ^99mTc MIBI when used as radioaerosols are good substitutes for ^99mTc DTPA in lung ventilation scintigraphy of patients with suspected pulmonary thromboembolism during sporadic supply or shortage of ^99mTc DTPA. METHODS This was a prospective study that included participants referred to our institution for ventilation - perfusion (VQ) scans between August 2015 and July 2017. One hundred and twenty-nine subjects were randomized to either receive ^99mTc -DTPA, MDP or MIBI radioaerosol as the ventilation agent. All the participants had normal chest x rays and debilitated participants were excluded from the study. The quality of images obtained from the different radioaerosols was visually assessed with the aid of a scoring system. The alveolar clearance was also assessed using a semi-quantitative method by tracing a region of interest (ROI) around the periphery of both lungs on early and late posterior images. The percentage of tracer lost during the time interval between the early and late images was then calculated. These were all done by a nuclear medicine physician blinded to the use of the different radioaerosols. Ethics approval was obtained from the University of Witwatersrand’s Human Research Ethics Committee and signed informed consent was obtained from all study participants. RESULTS MIBI had higher count rates than DTPA and MDP, with a statistically significant difference when compared with DTPA (p=0.021). Alveolar clearance of the three radioaerosols was compared using ANOVA with Bonferroni correction. MIBI clearly showed slower alveolar clearance when compared with the clearance of DTPA (p= <0.0001) and MDP (p= < 0.001). In terms of image quality, none of the 129 participants had non-interpretable images or images with poor peripheral penetration. MIBI generally had better quality images as compared to the other two radioaerosols, with a statistically significant difference when compared with DTPA (p= 0.001; logistic regression). Fewer participants had bronchial/tracheal and stomach activity in the MIBI group when compared to the MDP and DTPA groups. CONCLUSION To our knowledge, this is the largest and the first randomized prospective study in this regard. We have shown that ^99mTc MIBI and ^99mTc MDP are very good substitutes for ^99mTc DTPA for lung ventilation scintigraphy in patients being evaluated for suspected pulmonary thromboembolism. ^99mTc MIBI demonstrated the best image quality and slowest alveolar clearance. Although not statistically significant in our study, ^99mTc MDP also performed better than ^99mTc DTPA. We therefore recommend that these agents can replace ^99mTc DTPA whenever clinically and economically applicable..

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