June 13, 2001
Dear Doctor,
I wanted to address a topic that has recently come to light.
Several new spiral scanners have been introduced to the marketplace.
Unfortunately, they come without any data on sensitivity, specificity or
ability to detect and quantitate calcium. I have performed a small study
between EBCT and the Siemens Scanner, and attached a copy of the manuscript to
this mailing. I think it highlights some of the issues that you will face. I
have also made a synopsis of the literature for your assistance. I wanted to
make sure that you are aware of some of the false claims with spiral CT. There
are somewhere between 800 and 1000 peer reviewed published scientific papers
supporting the use of EBCT for cardiac imaging. The reason that EBCT is the gold
standard is due to temporal resolution. EBCT acquires frames at 50 milliseconds
or 100 millisecond frame rates. GE and Siemens use a mechanical x-ray tube
that takes at least 330 milliseconds to take each picture of the heart. Fast
"shutter speeds" equal less blurring. And, a faster picture means
less radiation exposure.
A recent publication estimated that EBCT is up to 38 fold
less radiation than the new multi-slice CT with Siemens. GE is even
higher. This is clinically important. An EBCT calcium scan or angiogram gives
about 0.7 to 1.0 rads per study. That is about one set of dental x-rays or one
abdominal x-ray. A scan with Siemens is at least 10 rads, a dose that exceeds
that of cardiac catheterization by 2-fold.
A bigger issue is angiography. While we have been developing
non-invasive angiography for the last 7 years, these new scanners are making
claims without any possibility of accurately detecting stenoses. The best
investigators in the world are unable to detect stenoses with a greater than
60% accuracy with these machines (Siemens and GE). The need for speed
precludes the ability of these scanners to do this work.
Unfortunately, the failure of these spiral CTs are ruining
the reputation of Electron Beam Angiography. While not perfect, we have
demonstrated sensitivities and specificities of >90%. The Siemens Volume
Zoom Plus 4 (most recent version) has been studied, and can visualize all
three major coronary arteries in only 30% of patients, with a sensitivity of
58% (Achenbach, et al. Circulation, 2001 in press). Another study demonstrates
a specificity of 54%, and that is excluding any patient with a heart rate
>70 bpm (Becker et al, JACC 2001, in press). Similarly, we just presented
data at the ACC that we can assess 93% of patients with the Imatron scanner
(Lu et al, JACC 2001). The issues are that these scanners are different, with
a much higher temporal resolution for Imatron than Siemens, GE or other spiral
scanners can achieve. We have been performing the study since 1994 and have
amassed an experience of over 2000 cases.
I completely agree that EB angiography is not a replacement
for angiography. However, use after bypass surgery to assess graft patency
(including LIMA and RIMA) has sensitivities of over 98%. Assessing angioplasty
or stent patency is similarly high. Some cardiologists use the technology to
follow-up borderline exercise testing results, follow progression of known
angiographic stenoses, and ruling out disease in atypical chest pain or heart
failure populations. Please do not confuse Electron Beam Angiography with the
product that is being performed by the Siemens, GE or Toshiba scanners. A
quick Medline search will assure you that these machines are completely
UNVALIDATED.
Sincerely
Matthew Budoff, MD, FACC
Assistant Professor of Medicine
Harbor-UCLA Medical
Center
