Hello again sammy2004
Having spent some more time on your question, I am confident I can
give you some more valuable information in addition to my previous
"In the affluent nations, the increasing use of CT scans is
remarkable. The average annual rate per 1,000 population rose from 6.1
to 44, in the periods 1970-1979 vs. 1985-1990 (UNSCEAR 1993, p.283,
Table 8). For 1985-1990, the annual rate in the USA was about 14.5 CT
exams per 1,000 population; in Australia, 30 per 1,000; West Germany,
35 per 1,000; Belgium, 50 per 1,000; and Japan, 97 per 1,000 (UNSCEAR,
p.280-281, Table 7)."
UNSCEAR (refered to above) is the united Nations Scientific Committee
on the Effects of Atomic Radiation. http://www.unscear.org/
unfortunately, their web page that has the reports does not seem to be
working properly, and I was unable to access their reports. (I have
notified them of the problem and hopefully their reports will be
"Of the 93 million CT scans performed every year in the world, up to
65 million CT scans are performed in the United States alone, says Dr.
"The most frequent types of CT examinations are CT scans of the head,
the abdomen and the thorax, respectively 39%, 27% and 19% of all CT
examinations. The largest contribution to the average effective dose
per capita stems from CT abdomen scans (24% of the total from medical
Hounsfield, Sir Godfrey Newbold
"1919?, British electrical engineer. A radar expert for the Royal Air
Force during World War II, in the 1950s Hounsfield began developing
computer and X-ray technology for EMI, Ltd., an international
electronics and entertainment corporation. He built the prototype for
the first CAT scan machine, which produced detailed images of
cross-sections of the human body, in 1972. For this innovation he
shared the 1979 Nobel Prize in Physiology or Medicine with Allan
Cormack, who had independently derived and published the mathematical
basis of CAT scanning in 1963?64. Hounsfield was knighted in 1981"
A picture of the first CAT scanner can be found at the website below
along with a picture of an early brain scan using the machine:
"Original "Siretom" dedicated head CT scanner, circa 1974"
"Screening spiral CT scans are available outside of clinical trials,
though they cost $300 to $1,000 and health plans generally do not
cover the charges. About half of the hospitals in the United States
own spiral CT machines, each costing upwards of $1 million."
"Medical Technology as a Driver of Healthcare Costs: Diagnostic Imaging"
"80% of hospitals have CT scanners and 50% have MRI scanners."
"A typical Community Hospital may carry out over 80 Ultrasound and 50
C.T. scans alone per day."
"In the past five years the department has seen an increase of 18 per
cent in plain X-rays, 50 per cent in CT scans, 44 per cent in
ultrasound scans and over 40 per cent in interventional work."
"Over 10 percent of the CT scans each year are done on children, who
are much more sensitive than adults to radiation."
"CT examinations and procedures are performed annually in 7800 CT
facilities in the United States. The annuall number of CT
examinations in the United States increased almost 10-fold in less
than 2 decades."
"In 2003 the cost of an average CT scanner was 1.3 million dollars"
"The first CT instrument was placed in a British hospital in 1972, and
in 1973 the Mayo Clinic began operating the first machine in the U.S."
Thank you for your question, and if you need any clarification of my
answer, do not hesitate to ask before rating my answer.
Very best regards
Search strategy included:
"cat OR ct scans" annually
UNSCEAR "ct OR cat scans"
Clarification of Answer by
21 Jun 2004 07:11 PDT
Hello again sammy2004
To take the last point in your request for clarification first. In
the USA the FDA is responsible for monitoring CT scan standards. The
specific piece of Federal law can be seen here:
"PERFORMANCE STANDARDS FOR IONIZING RADIATION EMITTING PRODUCTS"
"How does FDA regulate CT Systems?"
As in the USA, other countries have their own governmental departments
for monitoring the safety of CAT scans. For example, a survey from
In the UK, 'imPACT' provides information that should be of interest to you:
"Welcome to the web site of the ImPACT group. We are the UK's CT
scanner evaluation centre, funded by the Medicines and Healthcare
products Regulatory Agency (MHRA). We provide a wide range of CT
(Computed Tomography) scanner related services to the UK's National
Health Service. On our site, we try to give you an idea of our work,
as well as providing resources for people involved in CT scanning."
By the way, the patent number for the first CT scanner:
"Hounsfield, G.N., 1972, "A Method of and apparatus for examination of
a body by radiation such as x-ray or gamma radiation", British Patent
In Europe (as a whole), monitoring of the safety of CAT scans is the
responsibility of individual member countries under:
"EU Directive on health protection of individuals against the dangers
of ionising radiation in relation to medical exposure." see:
In terms of what testing was done before the technology was released
to the world, there is not that much information available (online
anyway). I suspect that the harmful effects of radiation were
(partially!) understood and that 'safe' limits were established based
on that information, and that was how safety was established.
The most relevant documents for you would be:
(Not available online, but....)
"AMBROSE, J., ``Computerized transverse axial scanning (tomography):
Part 2. Clinical application'', British Journal of Radiology 1973;
"Houndsfield obtained his first patent in August of 1972 well after
the first clinical trials at the Atkinson Morley Hospital in October
1971 (Ambrose 1973 )."
I hope that helps a little more.
Very best regards.