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Invariant triplet phases can be determined experimentally by multi-beam interference experiments. In favourable conditions phases can also be determined from crystals of small macromolecules. The phase error is quite small, provided crystals of good quality are available. Single phases can be derived from triplet phases by means of maximum entropy based statistical methods. The number of experimental triplet phases necessary to solve a small protein crystal structure can be reduced by the application of an automatic refinement procedure. About 2.5 reflection phases per residue are necessary to solve the structure of a small protein if a high-resolution intensity data set is available.

Two children with double aortic arch and aortoesophageal fistula (AEF) are reported to warn of this lethal complication of double aortic arch and to stress important points in the diagnosis and management. A review of the records of 30 children with double aortic arch disclosed two patients who had AEF. The first patient had respiratory distress and repair of a vascular ring (double aortic arch) at 5 weeks of age. At 9 weeks of age, because of difficulty with tracheal extubation, aortopexy was performed. Ten days later, profuse upper gastrointestinal bleeding required control by a Sengstaken-Blakemore (SB) tube. Thoracotomy and repair of AEF was accomplished successfully under cardiopulmonary bypass. The second patient had hepatomegaly andPseudomonas sepsis. Endotracheal and nasogastric intubation was necessary, and subsequently the double aortic arch was demonstrated by magnetic resonance imaging (MRI). On the 48th day of hospitalization, life-threatening upper gastrointestinal hemorrhage required insertion of an SB tube. Cardiopulmonary bypass allowed successful repair of the AEF. Both children are alive, after 3 and 2 years (respectively). These patients demonstrate that AEF must be diagnosed clinically (no imaging technique is effective); its history and physical presentation are typical. The SB tube is effective for controlling the hemorrhage until cardiopulmonary bypass can be performed to allow repair.