Coronary Imaging Considered

28 February 2007 (Last Updated February 28th, 2007 18:30)

The development of coronary imaging technology has prompted intense debate between cardiologists and radiologists. Jim Banks meets an expert from each field to try to settle the argument.

Recent years have seen the capability of computed tomography angiography
(CTA) and magnetic resonance imaging (MRI) improve significantly, leading to
much greater use of these techniques in cardiac studies. Of the two, CTA has
shown the fastest rise in popularity. In 2006, the CT field became well-known
as cardiologists adopted the method of CTA, to the point where many observers
feel it will soon replace conventional angiography in diagnostic applications.
Nevertheless, the debate about the merits of MRI and CTA continues.

"Cardiac MRI is a hazardless technology and gives a large amount of data on
damage, though it is less clear on coronary arteries than 64-slice CT," says
Blase Carabello, an imaging expert from the American College of Cardiology.
"More sophisticated cardiac MRI and multi-slice scanning technology give you
immediate images and an enormous amount of data, but it is likely that
hospitals may not buy both technologies."

It seems that the balance is tilting towards cardiac CTA on the basis that
emerging systems are set to provide ever more detail on the condition of
coronary arteries. Many feel this is worth the hazards associated with the
scanning technique – namely the use of dye and the dose of radiation
administered to the patient.

CT is already used in many areas of medicine as a key source of images that
determine diagnosis and treatment, from neurology to nephrology. Improvements
in the technology suggest that evolving scanning techniques and image quality
suit it to use in cardiology. However, studies have yet to conclude whether
superior image quality ensures better diagnoses or therapeutic outcomes. Such
studies are ongoing, but the sheer pace of technology development limits their
relevance.

"The trials are worth doing, but they will be out of date when they are
published,’ believes Geoffrey D Rubin, chair of the American College of
Radiology (ACR) Committee on Cardiovascular Imaging. "The first multi-site
trial of CT angiography was recently published using 16-row CT. By the time of
its publication the technology had moved on to 64-row."

Carabello agrees: "There is no question that technology continues to evolve
faster than our ability to know when and where to utilise it. No one technology
is better than another. It depends on who uses the technology and how."

ACCELERATING EVOLUTION

CTA passed a landmark in 1998 with the introduction of the first
multi-detector row scanners, which used four rows of scanners on each rotation.
The technology moved incrementally but rapidly from four-row to 64-row
scanning, as systems vendors focused largely on adding more banks of detectors
to improve image quality and scanning speed.

"The balance is tilting towards cardiac CTA on the basis that emerging systems are set to provide ever more detail. Many feel this is worth the associated hazards."

Similarly, all vendors have subsequently focused their efforts on increasing
the rotation speed of the scanner, though now developers seem to be going off
on different tangents in pursuit of different methods to achieve the same
goals.

Some strive to produce thinner sections to increase the level of image
detail, while others continue to add more detectors, with 256-row systems the
next milestone. One vendor has even tested a combination of two scanners in one
machine to improve temporal resolution by cutting the scan time in half.

It seems certain that these different approaches will yield a broader range
of CT technologies in the next few years, which some feel will benefit the
market as a whole and improve its applications in coronary imaging.

"We will see a differentiation of CT technology from different vendors,
which will lead to more choice," says Rubin. "Some are looking to add
capability as before and taking the technology to 256 rows could, for instance,
enable us to image the whole heart in one rotation. As you can see, the heart
is influencing vendors’ approaches."

In fact, applications in cardiology are now the defining factor in the
development of CT imaging. "CT has been used successfully for 15 years for the
rest of the vascular system outside the field of coronary artery imaging," he
adds. ‘But in 2004, it became clear that all of the technology
improvements in CT are now directed specifically towards cardiac scanning.
Given that CT is a key element in the diagnosis of many diseases and
abnormalities, this focus on the heart is striking."

Improving temporal resolution, for instance, specifically benefits cardiac
imaging, as it addresses the problem of the constant motion of the coronary
arteries. Freezing this motion is vital for the production of more useful
images, so faster scanning is a must for coronary CT angiography.

WHO SHOULD CONTROL CT?

While CT imaging is used in the diagnosis of many diseases, it is only in
its application to coronary imaging that a debate has arisen regarding who
should control the use of the technology.

Cardiologists are accustomed to having an important role in the imaging
processes on which they rely. They will, for instance, be involved in the
process of catheter angiography, so they naturally expect to have a similar
role in cardiac CTA. This, however, throws into question the role of
radiologists, whose skills in the use of the technology and the interpretation
of data suggest that they, too, have a role to play in imaging the heart and
its surrounding structures.

"The issue of control is surfacing, and it is complex," notes Rubin.
"Cardiologists have evolved to become more involved in imaging than other
specialists. They have been imaging coronary arteries exclusively for 20 years.
They still want to do it and they want to use the latest tools."

The appetite of cardiologists has been further enhanced by a quantum leap in
the capabilities of cardiac imaging technologies. Rubin describes catheter
angiography as searching in a dark room with a flashlight: you only see where
you look In comparison, coronary CT is like finding the switch to turning on
all the lights and seeing everything at once.

One problem is that cardiologists require training in the interpretation of
cross-sectional images and the much greater volume of data that CT imaging
provides. Radiologists, however, already have these skills.

"There is no question that technology continues to evolve faster than our ability to know when and where to utilise it."

"Radiologists have been trained from day one to interpret cross-sectional
images – particularly CT images – so there is a process that is
ingrained in them," argues Rubin. "They must examine the full data set,
including the surrounding organs, to detect early stage or unusual
manifestation of a disease. Cardiologists will focus exclusively on the
heart."

"Imaging is not just about image capture, but about interpretation.
Radiologists are focused on that – it is part of their job description,"
he adds.

Furthermore, US legislation places responsibility for the scanning process
squarely on the shoulders of radiologists, so compliance issues lend weight to
their claim to the control of coronary CTA. In terms of patient care and the
quality of the final outcome, however, the feeling on both sides is that
whoever is responsible for the imaging process should be the best trained
person.

CLOSER COOPERATION REQUIRED

Overall, there is a growing feeling that radiologists and cardiologists
should work together more closely. "The quality of the image depends on the
quality of the artist," says ACC’s Carabello. "It is not just about the
technology. It requires people with background knowledge of how to make it
work. There are good and bad cardiologists, just as there are good and bad
radiologists."

"The question of who should have control is an old one," he continues. "It
arose with echocardiography, which is now used by many practitioners, including
anaesthesiologists. At the end of the day, it comes down to who is best trained
to use the technology, whether they are a cardiologist or a radiologist."

As CT technology differentiates, treatment centres will no doubt adopt
different strategies for cardiac imaging. In some it will be the preserve of
cardiologists, in others radiologists, and in others still a collaborative
approach between the two disciplines. The latter is increasingly seen as
desirable.

"It’s about capability, not about specialism," says Carabello."The
best solution would be a collaboration between radiologists and cardiologists,"
concurs Rubin.

Whether this can be successfully achieved remains to be seen, as the debate
over CT technology continues.