The life and times of the
ImPACT Group – CT evaluations
through four decades
RAD Magazine, 38, 440, 15-16
by Sue Edyvean*, Maria Lewis* and
Alan Britten
Medical Physics and Clinical Engineering
Department, St George’s Healthcare NHS Trust,
London
*until September 2011
Invention of the CT scanner
Forty years ago an unlikely alliance was forged
between leading UK music business EMI, the UK
Department of Health and a specialist neurological hospital, to put into clinical use a new
imaging system that EMI engineer Godfrey
Hounsfield had developed. The prototype CT
head scanner was duly installed in Atkinson
Morley’s Hospital, South London, and on October
1, 1971 the first patient was scanned under the
direction of neuro-radiologist Dr James Ambrose
(figure 1). The following year saw three papers
on this scanner in the British Journal of
Radiology; by Godfrey Hounsfield, Dr James
Ambrose, and local physicist Dr John Perry, covering the invention, clinical application and radiation dose aspects of the new technology
respectively.1-3
This innovative combination of digital computers and
radiation detection was the start of a revolution in medical
imaging, leading to our current multi-slice scanners and the
key diagnostic role of CT worldwide today. Godfrey
Hounsfield later received a Nobel prize, and a Knighthood
for his work.4,5
The evaluation group emerges
Soon, commercial versions of this scanner were being rapidly
installed into hospitals across the world. In 1977, the
Department of Health, together with Dr Perry, decided that
these scanners required comparison for consistency in image
quality and radiation dose (figure 2), and research physicist
John Atkinson, was appointed to assist Dr Perry.
As body scanners, and other manufacturers emerged into
the arena, it became clear that more work was required and
Sue Edyvean was given a two-year appointment in 1983.
John Williams and Dr Bill Howarth, scientists at the
Department of Health and Social Security (DHSS), were
closely involved in the work, aiming to test the existing
scanners and finish the project. However, as scanners continued to develop, the two-year evaluation task became
three, four and eventually 28 years, with the evaluation project growing into the ImPACT group with up to seven staff
and gaining recognition as the leading centre worldwide for
CT scanner evaluation (figure 3).
There were times when scanner development seemed to
have halted and the demise of CT was forecast. However,
new methods emerged such as helical scanning, multi-slice
systems, dose saving and dynamic techniques, each requiring new ways of testing and evaluation in order to establish
a fair comparison.
The evaluation group took on the ImPACT name and
identity after Maria Lewis and Julia Carden joined the team
in 1988. Other staff joined and made their contribution
including Gavin Howard, Andy Keene and Ralph Smith.
Leigh Donnison provided a clinical radiographer’s view. The
team worked with Dr Alan Britten, the centre supervisor
following Dr Perry’s retirement in 1989.
A new era began in 1998 when Nick Keat became a key
member of the team, followed by Anne Hill, David Platten,
Bernhard Warr and Jim Weston. Margaret Burns was the
friendly Scots voice on the end of the phone to many inquirers. Latterly the reduced team of Sue and Maria was joined
by Jonathan Turner.
The work of ImPACT
The core work of the group was to devise ways of testing
and comparing the performance of CT scanners, to publish
the results and make the information accessible to users,
as well as to educate and inform professionals on the key
issues within CT.
In response to scanner advances, ImPACT developed test
phantoms, radiation dose measurement and digital image
analysis techniques to facilitate performance testing. Test
objects were produced by the engineers at St George’s,
including a head phantom with a bone equivalent exterior,
and more recently phantoms to test automatic exposure controls. Early analysis was on the University of London mainframe computer, with programs and image data on punched
cards, then on an Atari home computer, and finally to desktop workstations analysing the thousands of images from
an evaluation of a modern multi-slice system.
Analysis included calculation of a “Q value”, enabling
scanners to be directly compared and ranked according to
the efficiency of the dose to the level of image quality.
Contentious discussions sometimes arose, with delegations of
manufacturers’ engineers, physicists and heads of divisions
making their way from Germany, Japan, Holland, Israel,
USA or elsewhere to debate the results in South London.
The conclusion was always that ImPACT’s independent
objective methodology could not be faulted.
Evaluations over two days were carried out at clinical
sites or at the manufacturer’s factory (figure 4). A full set
of phantoms loaded onto two trolleys was required (figure
5), and careful planning and support from manufacturers
and clinical sites was necessary for the organisation and
logistics. Evaluations at manufacturers’ sites were not only
great opportunities to get access to new systems and to
speak to the engineers producing the systems, but also gave
opportunities to enjoy the different cultural aspects of other
countries (figure 6).
Following each evaluation, results were published and
distributed to the NHS, and available further afield. Many
readers may recall the famous “Blue Cover Reports”, produced by a number of related evaluation centres working
on a wide range of technologies. CT Blue Cover reports
became the essential references on CT imaging performance,
highly valued by users during system purchasing, acceptance testing and commissioning. One was even discovered
being used in a remote part of Asia, by an IAEA inspector
after his long boat ride up a river. Detailed hands-on physics
testing and Blue Cover reports stopped in 2006, though evaluation reports continued in different forms (figure 7). Paper
publications were supported by web access to information,
and the ImPACT website (www.impactscan.org) became the
leading source for CT information worldwide, with over two
million page downloads per year at its peak, and is still
accessible today.
A key feature of ImPACT was that it was clearly independent from commercial influence. This was important in
the support of the DoH bulk purchase programme of 200
scanners over five years from 2000 to 2005. ImPACT provided updated reports of specification comparisons and measured data, to every hospital in each purchase phase. This
ensured that there was timely data for each decision, and
hospitals could concentrate on the clinical aspects of the
scanner and how it matched their requirements, with the
assurance that the technical aspects had been covered
by ImPACT, resulting in an estimated saving of over
£1.6 million.
Dose calculator
CT radiation dose has been an important topic for many
years, with ImPACT contributing measurements and comparisons, and education to help users to understand and
optimise systems. The “ImPACT dose calculator” arose out of
many questions to the group concerning the use of the
NRPB CT dose data for new scanners, and was developed
with data collected by many physicists throughout the UK
and
further
afield.
Nick
Keat
designed
an
excellent front-end spreadsheet calculator which is now used
worldwide and frequently referenced by studies
(http://www.impactscan.org/ctdosimetry.htm).
Courses and education
CT has become increasingly complex, and the ImPACT
course ‘CT technology, dose and performance’ proved to be a
popular format for education, with lectures, a workshop and
a quiz to keep everyone interested (figure 8). The two-day
course, popular with physicists and radiographers, was held
11 times and oscillated between London and York. Delegates
came from a wide range of places, one course hosting attendees from the UK, the Republic of Ireland, France,
Germany, Denmark, Norway, Sweden, Germany, Greece and
the USA.
ImPACT staff have been fortunate over many years in
giving invited lectures, including lectures to the BIR, RCR,
IPEM, UKRC, other radiology professional bodies, manufacturers’ courses in the UK, and internationally with invitations from the USA, Australia, Japan, Holland, Denmark,
Portugal, Belgium, and Ireland.
The group has also worked with national and international standards bodies, contributing to guidance and standards from the IAEA and ICRU, the European Commission,
various Government bodies and medical physics societies
around the world.
Imaging evaluation centres
ImPACT was one of the national imaging evaluation centres supported by the DoH, including over the years
KCARE, FAXIL, GCAT, UEEP, MAGNET and PACSnet.
The evaluation programme was initially funded by the
Scientific and Technical branch of the DHSS. Over time,
responsibility passed through various departments and agencies of the DoH (Supplies Technology Division, the Medical
Devices Directorate, the Medical Devices Agency, the
Medicines and Healthcare products Regulatory Agency),
then to NHS PaSA (Purchasing and Supply Agency) in 2006,
and finally to NICE in March 2010. ImPACT at St Georges
was closed towards the end of 2011, with NICE including
diagnostic radiology within their emerging technology assessment programme. This heralds a different approach, more
focussed on cost effectiveness and clinical outcomes
(www.nice.org.uk).
The ImPACT team would like to thank everyone they
have been privileged to work with over many years, and
who have contributed to increasing the knowledge and
awareness of issues within CT, for the good of the NHS and
the wider CT community. We would especially like to thank
colleagues within the NHS, clinical sites, those within the
DoH and their various agencies who have administered the
project, manufacturers for their invaluable support, and the
many people who have contributed to the work of CT scanner evaluations, without whom the work would not have
been possible.
References
1, Hounsfield G N. Computerised transverse axial scanning (tomography):
Part 1. Description of system. The British Journal of Radiology 1973;46:10161022.
2, James Ambrose. Computerised transverse axial scanning (tomography):
Part 2. Clinical application. The British Journal of Radiology 1973;46:10231047.
3, Perry B J, Bridges C. Computerised transverse axial scanning (tomography): Part 3. Radiation dose considerations. The British Journal of
Radiology 1973;46:1048-1051.
4, Beckmann E C. President’s conference paper, CT scanning the early days.
The British Journal of Radiology 2006;79:5-8.
5, Sir Godfrey Newbold Hounsfield KT CBE, P N T Wells FRS Biogr Mems
Fell R Soc 2005;51:221-235. http://rsbm.royalsocietypublishing.org/
content/51/221.full.pdf (accessed 22 Nov 2011).
6, Jones D G, Shrimpton P C. NRPB-SR250: Normalised organ doses
for x-ray computed tomography calculated using Monte Carlo techniques.
Health Protection Agency web site. http://www.hpa.org.uk/web/
HPAweb&HPAwebStandard/HPAweb_C/1195733753330. Published 1993.
Accessed Dec 2011.
FIGURE 1
First clinical head CT scan (courtesy St George’s
Hospital).
FIGURE 2
From the notebooks of Dr John Perry; dose profiles
from the prototype EMI CT scanner.
FIGURE 3
The ImPACT group of 2002: Sue Edyvean, Nick Keat,
Margaret Burns, David Platten, Maria Lewis and
Julia Carden.
FIGURE 6
Tea after testing Toshiba scanners enjoyed by Nick
Keat, David Platten and Maria Lewis.
FIGURE 7
FIGURE 4
A selection of ImPACT reports from 1978-2010.
Testing a Philips system are Maria Lewis and Sue
Edyvean.
FIGURE 8
Quiz questions on an ImPACT course, led by Jim
Weston.
FIGURE 5
Equipment required for two days scanner testing
transported by David Platten and Nick Keat.