Advanced Computed Tomography
Technology and Patient Dose:
A Literature Review
Thomas M. Bailey, RT(R)(CT), CRA and Beth L. Vealé, PhD, RT(R)(QM)
• Cumulative patient radiation dose is a hot
topic making headlines today. Responsible for almost two thirds of the medical
radiation dose given to patients, computed tomography (C T) has been the major
target of these news articles.
• Through this review of peer reviewed
publications, an examination of the relationship between the advancement of
technology in CT equipment and the
increasing patient dose are explored.
Discussion includes CT scan protocols,
demands of physicians, equipment capabilities, and possible solutions to address
• Although most of these issues are well
known in the imaging community, a few
of the results are somewhat surprising.
The information disclosed will help form a
path to a future with lower radiation
doses received by all patients.
Computed axial tomog-
raphy, or CAT scan as it was known in
the early days, was a new technology with
almost limitless potential. It would later
be shortened and commonly referred to
as computed tomography, or CT. To-
mography is from the Greek word “to-
mos” meaning “slice” or “section” and
“graphia” meaning “describing.” CT was
invented at the EMI laboratories in 1972
by British engineer Godfrey Hounsfield. 1
Hounsfield’s first C T scanner took several
hours to acquire the raw data for a single
scan or “slice” and took days to recon-
struct a single image from this raw data.
The first clinical equipment installed
between 1974 and 1976 were limited to
only examinations of the head. Whole
body imaging equipment with larger pa-
tient gantries became available in 1976.
CT examinations became widely avail-
able around 1980.2 Not much changed
over the next decade with the exception
of some computer enhancements. A
single piece of technology changed the
direction and potential of CT technol-
ogy advancement forever. CT scanners
manufactured between 1974 and 1987
would spin in one direction to make an
image then would have to spin in the op-
posite direction to make the next slice.
Between each slice, the patient table was
moved forward by an increment equal
to the thickness of a slice. 1 In 1987, an
innovation called the “power slip ring”
allowed scanners to rotate continuously.
This development led to a new type of
CT called “spiral” or “helical” scanning. 3
The current multislice helical CT systems
can collect up to 64 slices of data in about
350 ms and reconstruct a 512 × 512 ma-
trix image from millions of data points in
less than a second. An entire chest (about
300 one mm slices) can be scanned in five
to ten seconds using the most advanced
multislice CT system. 2