Periodic Exhaust Examination (IMAGE) Physikalisch-Technische Bundesanstalt (PTB) Caption During the periodic exhaust examination, the proportion of soot particles is also determined. Credit Joint Research Centre Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.