First-Generation X-Ray System

Editor

We learned that our May 2011 Radiology article, “Characteristics of a First-Generation X-Ray System” (1), contains an error that requires correction: Crookes tube number 9 was actually connected with a polarity opposite to that indicated in the article. Please see the erratum on page 612 of this issue. This unconventional wiring, which was needed to generate observable x-rays, does not affect the article’s conclusions.

In the series of experiments using Crookes tube number 9 and the older coil of Ruhmkorff (C. Gerhardt, Bonn, Germany), no x-rays were generated after assembling the system, but after reversal of polarity, the system functioned. Rechecking our notes and photographs proved that to generate these x-rays, we had applied a polarity that was opposite to the one commonly used for this tube. Only with this polarity, and not with the standard wiring, did we detect x-rays, as was documented by using a pinhole with a computed radiography plate and electronic dosimeters. In figure 1b and appendix E5 (online) of the article, we mistakenly imply that both Crookes tubes (numbers 1 and 9) were connected in the common way.

Actually, the pattern of the greenish light in Crookes tube number 9 shown in figure 5 is rather different from the pattern that is typically observed for this tube. Normally, the greenish light (and the x-rays) are generated at the wide end of the tube (2), instead of halfway down the long axis. The latter pattern is consistent with the middle electrode being the cathode. At the time of writing, we did not consider the possibility that Crookes tube number 9 might have to be driven differently than the previously tested Crookes tube number 1. The different green light pattern was attributed to a poor vacuum, which is, after all, probably the cause of the tube’s odd behavior. The polarity of Crookes tube number 1 was in line with common use and correctly described in the article. Unfortunately, Hoffmans (3) did not provide information on the wiring he applied.

Results from the experiments using Crookes tubes numbers 1 and 9 were rather similar in terms of x-ray dose rate, half-value layer in Al, and imaging properties. Within the range of uncertainties inherent in the unknown gas pressure in the x-ray tubes and other small differences in experimental conditions, we believe our data to be representative for the system as used by Hoffmans and van Kleef in 1896.

We are indebted to A. Wright, H. Dijkstra, J. Behary, F. Jones, and Z. Hakim for kindly pointing out this error and for providing additional useful information.

Disclosures of Potential Conflicts of Interest: M.K. No potential conflicts of interest to disclose. T.J.D. No potential conflicts of interest to disclose. J.D. No potential conflicts of interest to disclose. H.J.M.H. No potential conflicts of interest to disclose. J.E.W. Financial activities related to the present article: none to disclose. Financial activities not related to the present article: individual and institution received payment for lectures from Bayer Schering Pharma, Boston Scientific, Siemens Medical Solutions, and GE Healthcare. Other relationships: none to disclose. J.M.A.v.E. No potential conflicts of interest to disclose. G.J.K. No potential conflicts of interest to disclose.