| Virtually all currently
available conventional x-ray based cardiac catheterization
systems, such as those developed and marketed
by Philips
Medical, Siemens
Medical, GE
Medical and Toshiba
Medical, use the same fundamental imaging
technology, which has not changed dramatically
over the past 40 years. Incremental improvements
to individual component have optimized system
performance over decades to close to the theoretical
limits. However, current systems still exhibit
problems with limited image quality and radiation
exposure.
The key problems relate to imaging, radiation
hazards, and operational issues.
Imaging
| • |
Limited image quality
in larger patients or when imaging at steep
angles. The most difficult imaging task
in the cardiac catheterization lab is imaging
large patients or imaging patients at steep
viewing angles. With conventional systems,
a large-area detector close to the patient
causes more scattered radiation reaching the
detector than image radiation, severely degrading
image quality. Therefore, physicians often
use the high-radiation diagnostic (cine) mode
during interventions to obtain better quality
images. |
| |
|
| • |
Best image quality
is only possible for a short period of time.
Conventional cardiac catheterization systems
can only run in the diagnostic (cine) mode
for approximately 20 seconds before the x-ray tube reaches its maximum temperature and
shuts down automatically. It may take several
minutes before the x-ray source cools down
and imaging can resume. |
| |
|
| • |
Overlying anatomy
inhibits viewing and navigation. Conventional
cardiac catheterization systems produce a
shadowgram image that shows objects with no
depth information. Discerning 3-D anatomy
from these flat images is difficult. In addition,
image clutter and shadowing of the heart by
ribs or the spine often degrades image clarity. |
Radiation hazard
| • |
Excessive radiation
to patient and interventionalist. Conventional
systems expose patients to the equivalent
of 200 to 500 chest x-rays per minute in the
interventional (fluoro) mode. With up to 60
minutes of imaging time during a long interventional
procedure, patients can be exposed to the
equivalent of 12,000 to 30,000 chest x-rays
per procedure. Such prolonged exposure can
cause radiation skin burns on patients and
increase the risk of cancer to the interventionalists
and catheterization lab staff. Radiation exposure
risk is particularly acute in certain electrophysiology
procedures due to long exposures of single
areas of anatomy. The FDA is aware of the
risk of high radiation exposure to patients
during interventional procedures and continues
to consider this a major risk factor. The
FDA has recommended adoption of ALARA (As
Low As Reasonably Achievable) guidelines for
minimizing patient radiation. Additionally,
the American
College of Cardiology1 has
warned about the dangers of excessive radiation
exposure to physicians, which can result in
a 20% higher risk to the physician of developing
a fatal cancer than the general population.
Preventative measures for physicians include
use of heavy and cumbersome wrap-around lead
aprons and vests, thyroid shields, and goggles. |
Operational issues
| • |
Obstructed
access to patient. Conventional cardiac
catheterization systems require that the large-area
detector be positioned close to the patient,
restricting access to the patient by the clinical
staff. This design is not only claustrophobic
for the patient, but is also an obstruction
if cardiac pulmonary resuscitation (CPR) is
required. |
______________________________________________________________________________________
1 ACC, Radiation safety in the
Practice of Cardiology
|
