8, 1998 Design News
SPECIAL MEDICAL ISSUE
From the regional editors
Filmless x-ray system measures bone
High-resolution direct digital
x-ray capture and advanced image-processing software
combine to detect osteoporosis
Julie Anne Schofield, Senior Editor
Manhattan Beach, CA--One
out of every two women and one out of every five men
in the U.S. today will suffer from osteoporosis, a disease
characterized by low bone mass and increased risk of
hip, spine, wrist, and other fractures, according to
the National Osteoporosis Foundation. A progressive
disease, osteoporosis usually strikes older people and
results in over 1.5 million fractures per year in the
U.S., costing healthcare systems more than $14 billion
Treatments exist, and the disease is preventable if
detected early. In fact, there are more than 25 new
osteoporosis drugs in the pipeline. But the disease
A new device from CompuMed--the Digital OsteoView 2000TM--may
change that. The automated device captures images of
the hand using amorphous silicon filmless x-ray detection.
Proprietary software analyzes the images to determine
bone mineral density and thus detect osteoporosis.
The firm had already developed bone density software
that determined bone mineral density from standard hand
x-rays and ran a lab that analyzed such x-rays for doctors.
"The bone density measurements that we make from
the middle phalanges of the index, middle, and ring
fingers are more precise and more accurate that any
other bone mass measurements," says David Edelstein,
executive director of CompuMed's OsteoSystems Division.
He cites three clinical studies, one of which showed
the software had a 0.6% precision error and 0.983 correlation
to ash weight--found by measuring cadaver bone after
analyzing the bone x-rays.
"We use those bones because they're about half
cortical (dense) and half trabecular (spongy). These
represent the two types of bones in the body,"
says Edelstein. The software analyzes the bones in 1-mm
transverse slices and can determine the soft tissue
on either side of a slice. Using the assumption that
the phalange is almost a cylinder, the software can
project the mass of soft tissue around the top and bottom
of the bone as well the sides and subtract it from the
x-ray image, leaving only bone.
Analyzing x-rays in the lab is a 15-minute, 20-step
process. CompuMed decided to automate the process to
reduce lab costs--and to build a machine that could
take the hand images and automatically run the bone
The OsteoView uses an aluminum alloy reference wedge
placed next to the index finger and runs an enhanced
version of the bone density software. "We look
at the optical density of the wedge image on the film
or the digital image, and we compare it to the known
material density of that wedge," explains Edelstein.
"From that we can calculate the contribution of
various conditions such as x-ray spectrum drift, then
correct the measured bone mass."
Traditional x-ray machines are not tightly calibrated,
he says, and doing so can be expensive. The OsteoView
corrects for calibration drift in software using the
The other key component of the machine is the amorphous
silicon flat-panel detection technology CompuMed licensed
from Varian Associates. The technology was developed
by Varian and Xerox Corp. under a grant from the U.S.
Defense Advanced Research Projects Agency (DARPA).
"We've done bone density measurement with CCDs,
but amorphous silicon will let us get extremely high
resolution in a very light-efficient way," says
Edelstein. The detector is so sensitive that it reduces
the x-ray dose from 30 to less than 1 millirem.
The amorphous silicon detector works like an active-matrix
LCD, but in reverse. When x-rays pass through the hand,
they strike the phosphor layer, which emits light. The
light is picked up by the photodiode layer, which sends
out a charge through the thin-film transistor layer.
The charge goes to ASICs on a readout board, and is
reconstructed into a digital image. Each pixel is 127
microns square, and Edelstein says the resulting image
is just about as good as x-ray film.
The high resolution of the amorphous silicon detector
combined with the improved software can do fine detail
analysis of bones and joints that has not been possible
with the current generation of x-ray and ultrasound
densitometers. Such fine detail analysis is the key
to detecting arthritis as well as reliably and quickly
tracking changes that result from osteoporosis and arthritis
treatments, says Edelstein.
CompuMed plans to release the Digital OsteoView 2000
after concluding clinical trials and U.S. FDA 510(k)
marketing clearance later this year.†
Additional details?Contact David
Edelstein, Executive Director, OsteoSystems Division,
CompuMed, 1230 Rosecrans Ave., Manhattan Beach, CA 90266,
Tel: (800) 421-3395, FAX (310) 536-6128, website www.compumed.net