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The objective of this study is to determine lung air distribution and focal heterogeneity after surfactant treatment of RDS, using computerized image analysis of chest radiographs (CXRs). This is a retrospective observational non-paired study where CXRs were assessed within 6\u00a0h after surfactant instillation in the surfactant-treated group [STG] (\n                    <jats:italic>n<\/jats:italic>\n                    \u2009=\u2009 52; median 24\n                    <jats:sup>+4<\/jats:sup>\n                    ; range 22\n                    <jats:sup>+0<\/jats:sup>\n                    \u201327\n                    <jats:sup>+5<\/jats:sup>\n                    \u00a0weeks gestation) and at the same postnatal age in the pre-surfactant group [PSG] (\n                    <jats:italic>n<\/jats:italic>\n                    \u2009=\u20098; 25\n                    <jats:sup>+3<\/jats:sup>\n                    ; 23\n                    <jats:sup>+6<\/jats:sup>\n                    \u201326\n                    <jats:sup>+4<\/jats:sup>\n                    ). Digital image analysis was performed by ImageJ of lung intercostal segments 2\u20137 bilaterally: mean pixel intensity (MPI) determines focal lung density and correlates negatively with lung aeration; focal heterogeneity in pixel intensity (FHPI) defines focal differences in aeration and correlates positively with overexpansion\/atelectasis. MPI was higher in the left lung in STG than in PSG (\n                    <jats:italic>p<\/jats:italic>\n                    \u2009=\u20090.008). MPI was higher in the apical compared to the basal regions bilaterally, in both STG (right,\n                    <jats:italic>p<\/jats:italic>\n                    \u2009=\u20090.024; left,\n                    <jats:italic>p<\/jats:italic>\n                    \u2009=\u20090.015) and PSG (right,\n                    <jats:italic>p<\/jats:italic>\n                    \u2009=\u20090.047; left,\n                    <jats:italic>p<\/jats:italic>\n                    \u2009&lt;\u20090.001). FHPI was higher on the right compared to the left 7th intercostal segment in STG (\n                    <jats:italic>p<\/jats:italic>\n                    \u2009=\u20090.006). FHPI of the right 7th segment was higher in STG than in PSG (\n                    <jats:italic>p<\/jats:italic>\n                    \u2009&lt;\u20090.001).\n                  <\/jats:p>\n                  <jats:p>\n                    <jats:italic>Conclusions<\/jats:italic>\n                    :\u00a0In this retrospective observational study of CXRs in extremely preterm infants, the right lungs were more aerated than the left lungs after surfactant, whereas the basal regions were more aerated than the apical regions regardless of surfactant treatment. We hypothesize that increased focal heterogeneity in these more aerated regions after surfactant may reflect overexpansion\/atelectasis, which may be secondary to an inhomogeneous surfactant distribution, an observation that needs to be further validated in future studies.\n                    <jats:table-wrap>\n                      <jats:table>\n                        <jats:tbody>\n                          <jats:tr>\n                            <jats:td colspan=\"2\">\n                              <jats:bold>What is Known:<\/jats:bold>\n                              \u2022\n                              <jats:italic>Surfactant treatment has a major impact on survival in extremely preterm infants (EPIs) with respiratory distress syndrome (RDS), but less is known about the achieved early air distribution and its possible implications for future lung outcomes.<\/jats:italic>\n                              <jats:bold>What is New:<\/jats:bold>\n                              \u2022\n                              <jats:italic>Computerized image analysis of plain chest radiographs (CXRs) provides more detailed information on the air distribution than clinical radiological grading whereby the optimal time point and administration techniques for surfactant instillation can be evaluated in EPIs with RDS.<\/jats:italic>\n                            <\/jats:td>\n                          <\/jats:tr>\n                        <\/jats:tbody>\n                      <\/jats:table>\n                    <\/jats:table-wrap>\n                  <\/jats:p>","DOI":"10.1007\/s00431-025-06466-1","type":"journal-article","created":{"date-parts":[[2025,10,14]],"date-time":"2025-10-14T16:05:21Z","timestamp":1760457921000},"update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":3,"title":["Computerized chest radiograph analysis of air distribution after surfactant treatment of respiratory distress syndrome in extremely preterm infants"],"prefix":"10.1007","volume":"184","author":[{"given":"Julia","family":"Fall","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Richard","family":"Sindelar","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Malin","family":"Helenius","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Eva","family":"Penno","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Leif D.","family":"Nelin","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Laszlo","family":"Markasz","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"297","published-online":{"date-parts":[[2025,10,14]]},"reference":[{"key":"6466_CR1","doi-asserted-by":"publisher","unstructured":"Seger N, Soll R (2009) Animal derived surfactant extract for treatment of respiratory distress syndrome. 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Consent to participate is not applicable, as the ethical review board considered it nonethical to approach parents of deceased infants in this retrospective study.","order":2,"name":"Ethics","group":{"name":"EthicsHeading","label":"Ethics approval and consent to participate"}},{"value":"Parental consent is not applicable according to the ethical review board, due to the retrospective design of the study.","order":3,"name":"Ethics","group":{"name":"EthicsHeading","label":"Consent for publication"}},{"value":"The authors declare no competing interests.","order":4,"name":"Ethics","group":{"name":"EthicsHeading","label":"Competing interests"}}],"article-number":"690"}}