The fallacy of the lacune hypothesis.

bath value of 161 mW/cm spatial peak temporal average yields an estimated in situ intensity of 95 mW/cm for the standard Transpect. For this study, the power was increased to yield an estimated in situ intensity of 800 mW/cm. Throughout the article, the term "power" should be understood to mean "that power that would result in an estimated in situ intensity of 800 mW/cm" (or other level stated). The term "amplitude" for the loudness of the recorded waveform would be technically acceptable, but might be confused with peak velocity by clinical users of transcranial Doppler. Waveform "intensity" is a reasonable alternate term for the loudness in decibels, which was the critical measurement made. In his letter, Dr. Eden has made a constructive contribution to the general problem of skull-related power loss with his new unit of estimated intracranial intensity, which takes some of this into account. This is based on waterbath measurements made through cadaver skull by Grolimund, using the result from the thinnest skull tested. Our experience suggests that 90% power loss is a more reasonable figure for adult practice. Obviously, more in vitro measurements through skulls should be made to establish this objectively. Unlike Dr. Eden, we have never seen waveform improved by reduction of power. In all cases, there is an average waveform intensity loss of about 3.5 dB, or a 50% reduction in emitted power. Since submission of that study, we have collected additional data on rates of failure at 1000 mW/cm estimated in situ intensity. For ages over 70 years, the rate of failure in white males is 7.5%, in white females 29%, in black males 33%, and in black females 73%; for ages 51-70 years the rate in white males is 1.6%, in white females 18-5%, in black males 10.4%, and in black females 52%. Too few younger subjects have been studied to make reporting of data from younger age groups meaningful.