The discovery of x-rays in 1895 revolutionized medicine. It allowed doctors to diagnose and treat many medical problems more easily.22 The ability to image teeth also transformed dental care. However, as x-ray technology developed in the early 20th century, false beliefs about biologic differences between Black and White people affected how doctors used this technology.
Ideas about racial differences in bone and skin thickness appeared in the 19th century and remained widespread throughout the 20th.5 Theodor Waitz’s 1863 Introduction to Anthropology asserted, for instance, that “The skeleton of the Negro is heavier, the bones thicker.”23 Such claims reflected both beliefs about behaviors attributed to Black people (eg, violence)23.24 and the interests of White scientists and slave owners who justified slavery.16.19
The ideas persisted even as contexts changed. Nearly a century later, in 1959, An Atlas of Normal Radiographic Anatomy described the skull bones of Black people as “thicker and denser” than those of White people.25 Researchers continued to report race differences in bone density throughout the 20th century.26 However, when the US Public Health Service’s National Center for Radiological Health (NCRH) reviewed this question in 1968, it raised doubts about the claims (eg, “unsubstantiated,” “doubtful validity”), noted that reported differences might have environmental causes ( eg, nutrition, exercise), and emphasized that large variations exist within so-called races.27.28
The belief that Black people have denser bones, more muscle, or thicker skin led radiologists and technicians to use higher radiation exposure during x-ray procedures. A physician in 1896 asserted that “black being perfectly opaque,” black skin would “offer some resistance to cathode rays.”5 A 1905 review explained how “the skin of the negro offers more resistance to the X-rays than non-pigmented cuticle.” This resistance made it difficult “to get a good skiagraph of a negro’s spine”: “The large surface exposed (abdomen and back) contains so much pigment that a good deal of X-ray energy is lost.”4 The New York Evening World described a celebrated Black boxer with a skull that was “almost impregnable”: it took “the utmost skill of Joseph Klober, the celebrated electrician and Roentgen ray operator, to get a picture of the interior workings.”5.29
Formal teaching about race adjustment for x-rays appears to have begun later. Clifton Dummett, a prominent Black American dentist, described being taught in the 1940s to increase x-ray exposure times for the teeth and jaws of Black patients because their oral tissues were more resistant to x-rays.30
Reprinted with permission from the American Society of Radiologic Technologists.32
Reprinted from Jacobi and Paris.35
In the 1950s and 1960s, x-ray technologists were told to use higher radiation doses to penetrate Black bodies. Roentgen Signs in Clinical Diagnosis, published in 1956, described the radiographic examination of a Black person’s skull as a “technical problem” that required a modified technique. The author suggests increasing exposure by 10 kilovolts (an increase of 12.5 to 21%).31 A 1957 article in The X-Ray Technician classified “whites” as “normal.” For “Black or brown” patients, adjustment was recommended to get a better radiograph (eg, use a dose 4 kilovoltage peak higher than normal — an increase of 9.5 to 25%) (Figure 1).32 Race adjustments appeared in several other textbooks as well.33 The second (1960) edition of Jacobi and Hagen’s X-Ray Technology added the unexplained recommendation that Black patients be given an exposure 40 to 60% higher than that given to White patients. This guidance remained in the third (1964) edition (Figure 2).34.35
The General Electric Company (GE), then the largest manufacturer of diagnostic x-ray equipment, made its own race-based recommendations. In the 1961 and 1963 editions of its pamphlet “How to Prepare an X-ray Technic Chart,” it advised that Black patients needed increased radiation exposure.28 In 1968, GE spokesperson Robert Molitor explained that the recommendation had reflected “current medical thinking” among radiologists.27
Black people were not alone in receiving more radiation. The guidelines and textbooks also recommended higher doses for people who were “extremely obese” or “muscular”; in patients with sclerosis, osteomyelitis, or Paget’s disease; and in patients wearing a cast. Meanwhile, thin patients, children, elderly patients, and those with osteoporosis were given lower doses (Figure 2).35 It is not clear which adjustments were based on intuitions or anecdotal experiences and which, if any, were based on careful study.
Several estimates offer a sense of the prevalence of race-based dose adjustment. Surveys of x-ray technicians in the San Francisco Bay Area in 1968 found that 75 of 90 technicians “usually increased X-ray doses of Negroes.”36 They said they did so because “'[Black people’s] bones are harder and denser,’ ‘Their skin is darker,’ and ‘Their flesh is harder.’”27 A sample of chief x-ray technicians in New York also found that Black patients received increased radiation doses. As Goldman explained, “a ‘significant proportion’ of the State’s X-ray technicians apparently have routinely exposed Negroes to higher radiation dosages than whites.”1
We do not know what percentage of x-rays taken of Black Americans used increased exposures. We also do not know how many people were potentially harmed. The radiation received during a chest x-ray is comparable to 10 days’ worth of natural exposure.37 An increase of 40 to 60% in radiation from a single x-ray would have little effect on a person’s lifetime risk (and the increase used for Black people was less than that used for muscular or obese people). However, the cumulative effect could have been substantial for people who received multiple exposures. This question of the harm of low-risk radiation exposures was examined by the Advisory Committee on Human Radiation Experiments.38 Even though most of those Cold War experiments probably did little physiological harm, the research subjects experienced other harms (eg, being used for research without consent). The situation has parallels with race-adjusted x-rays: many people were exposed to an increased risk (even if small), presumably without their knowledge, because of unsubstantiated beliefs grounded in racist science.