scanner manufacturers because the dose was calculated as if distributed throughout the whole body, whereas most of the radiation is absorbed in the skin and tissues immediately underneath. Other professors from the radiology department at UCSF disagree with the claims of the signing four professors. The UCSF professors requested that additional data be made public detailing the specific data regarding sensitive areas, such as the skin and certain organs, as well as data on the special (high-risk) population. In October 2010, the FDA and TSA responded to these concerns. The letter cites reports which show that the specific dose to the skin is some 89,000 times lower than the annual limit to the skin established by the NCRP. Regarding the UCSF concerns over the high-risk population to sensitive organs, the letter states that such an individual "would have to receive more than 1,000 screenings to begin to approach the annual limit". John Sedat, the principal author of the UCSF letter, responded in November 2010 that the White House's claim that full-body scanners pose no health risks to air travelers is in error, adding that the White House statement has "many misconceptions, and we will write a careful answer pointing out their errors." In a December 2, 2010 letter to the House of Representatives, Dr. Steven Smith, inventor of the body scanner in 1991, stated that the concerns of Brenner and UCSF regarding the skin dose of backscatter scanners is incorrect and the result of a confusion between dose and imaging penetration. Smith demonstrated this difference with two experiments using plastic (with a similar rate of absorption as body tissue), copper (the image subject), and an x-ray scanner. The dose-penetration experiment shows that plastic samples absorb 5% and 50% of the beam intensity respectively, whereas the imaging penetration experiment shows that plastic samples reduce the image darkness by 23% and 50% respectively. Dr. Smith states that those who calculate high skin dosage have incorrectly used the shallow imaging penetration value of a few millimeters (c. ), whereas the actual dosage is calculated by the deeper dose penetration. The TSA has also made public various independent safety assessments of the Secure 1000 Backscatter X-ray Scanner. Radiation safety authorities including the National Council on Radiation Protection and Measurements, The Health Physics Society and the American College of Radiology, have stated that there is no specific evidence that full-body scans are unsafe. The Secure