Further investigations when abdominal wall defects are diagnosed in utero.

Dr Bore (Aug 20, p 458) has raised some point concerning the interpretation of the nuclear magnetic resonance (NMR) spectra of the rhabdomyosarcoma which we had no space to discuss in our letter (June 25, p 435) He is right in saying that the pulse angle induced by a surface coli varies at different positions in the sample: this is well known and is discussed on pages 100-02 in the first reference in our letter. We found from experiments using various pulse durations that a 25 /ms pulse gave maximum signal from phosphorus nuclei close to the 4 cm coil. In a conventional NMR instrument this is termed a 90 ° pulse. For a surface coil this would be accurate only near the plane of the coil, so one could argue that we should have given only the pulse duration and not the flip angle, but it is surely better to give this important parameter in some way than, as in Taylor and colleagues' paper to leave it out. On one occasion a 50 ms pulse was used and the spectrum obtained from deeper tissue showed a large increase in phosphocreatine, leading us to believe that muscle was being detected. We considered the possibility that the change in the phosphocreatine peak at the second NMR examination, was due to a diminution of the signal from the interosseous muscles (or other tissues) but thought it unlikely.