The Clinical Translational Research Center
(CTRC) of Cincinnati Children’s Hospital Medical Center operates three Hologic
QDR-4500A densitometers by Hologic Inc., Bedford, MA. The main DXA facility
is in Location E, floor 2, room E2.328. . An additional DXA facility
is at our satellite in the Cincinnati Center for Clinical Research (CCCR)
at 619 Oak St., Room 2669.
Our hours of operation are:
- 7:30 am-5:30 pm
Monday-Friday and one evening per week until 7 pm by request
- 7:30 am-1:30 pm
Saturday (available on a limited basis, by request; for research only)..
Appointments may be made by calling
513-636-6204.
All core staff are Ohio Department of
Health-licensed general X-ray machine operators. In addition, two of our
staff also are certified bone densitometry technologists (CBDT) from the
International Society for Clinical Densitometry.
Institutional Review Board (IRB), radiation
safety and CTRC Scientific Advisory Committee approval are needed for all
research protocols requesting DXA services. Physicians may complete a
diagnostic testing order form and fax to 803-1111 to order DXA scans for
clinical patients. There is a weight limit of 350 pounds on the
densitometers.
DXA has become increasingly popular for
measurement of total body bone, lean and fat mass and for measurement of
regional bone mass and density. It is highly accurate, precise and sensitive in
both pediatric and adult populations. Scans available include: whole body, AP
lumbar spine, lateral spine, proximal femur or hip, distal femur and forearm.
We have the latest software (Apex) from
Hologic Inc., for scan analysis and an FDA-approved pediatric reference
database. The software includes a new “auto low density” mode for analyses of
spine, hip and whole body scans. This new analysis mode uses lowered thresholds
at which the algorithms determine bone and soft tissue to account for smaller
body sizes. The analysis program automatically determines which threshold to
use based on the body size it detects. This allows for a more accurate and
reliable assessment of pediatric bone density and body composition.
Additionally, we have high-power whole-body
software to be used in people >250 pounds. This allows for more
accurate analysis of lean and fat tissue in larger body sizes but also
increases the radiation exposure by a factor of three for total body scans.
The FDA-approved pediatric reference
database gives updated Z-scores for lumbar spine and whole body bone
mineral density (BMD) for ages 3-20 years and for hip BMD ages 5-20 years.
Reference data on BMC-for-height are not yet available. In the last 10 years,
there have been several technological changes in DXA scan acquisition and
analysis that affect the appropriateness of the original Hologic reference
database. The new reference database was developed from scans acquired on
modern fan beam systems and analyzed with the new software.
Our precision data were calculated from
scanning 20 adults and 16 children < 12 years of age. BMD for all scans and
body composition measurements from the total body scan in adults have %CV’s of
1 percent or less. %CV’s for pediatric scans are slightly higher as follows:
Lumbar spine BMD = 0.85
Total hip BMD = 3.21
Total body BMD = 1.30
Total body lean mass = 0.98
Total body fat mass = 3.39
Total body percent fat = 2.48
Scan results are available either as a hard
copy report or as a database export in MS Access.
Radiation exposure from DXA scans is
minimal. The National Council of Radiation Protection and Measurements (NCRP)
has recommended the annual effective dose limit for infrequent exposure of the
general public that would include children is 5,000 µSv and that an annual
effective dose of 10 µSv be considered a negligible individual dose. The
average annual background radiation exposure in the United States is 3,000
µSv/yr or about 8 µSv/day. The following table lists the effective doses for
DXA scans:
Age (years) | Effective dose (µSv) |
Lumbar spine | Hip scan,
male | Hip scan,
female | Whole body scan, male | Whole body scan, female | Forearm scan |
1 | 4.7 | 15.2 | 6.4 | 3.4 | 3.5 | 0.14 |
5 | 3.3 | 13.2 | 6.1 | 2.9 | 3.0 | 0.10 |
10 | 2.7 | 8.3 | 5.6 | 2.5 | 2.7 | 0.066 |
15 | 2.2 | 6.3 | 4.7 | 2.0 | 2.2 | 0.03 |
Adult | 2.2 | 5.1 | 4.6 | 1.8 | 2.1 | 0.03 |
Thomas, S., Kalkwarf, H., Buckley, D., & Heubi, J. (2005). Effective dose of dual-energy X-ray absorptiometry scans in children as a function of age. Journal of Clinical Densitometry, 8(4), 415-422.
Peripheral Quantitative Computed Tomography (pQCT) Imaging.
The Clinical
Translational Research Center at Cincinnati Children’s Hospital Medical
Center operates a Stratec XCT 2000 pQCT (Orthometrix, White Plains, NY). It is
operated by the same technologists and during the same hours as the DXA
equipment. IRB / radiation safety approval and CTRC Advisory Committee approval
are needed for all research protocols. The pQCT is available for research scans
only. It is not available yet for clinical purposes as there is no pediatric
reference database (normal range) available for interpretation.
The pQCT densitometer measures volumetric
bone mineral density (BMD) (mg / cm3) and cross-sectional bone dimensions at
peripheral skeletal sites: the radius and tibia. The pQCT allows for selective
measurement of cortical and trabecular density, bone area, cortical area,
cortical thickness, periosteal and endosteal circumference, muscle
cross-sectional area and biomechanical strain strength indices. Bone density
measurements by DXA (a two-dimensional technique) are affected by skeletal
size, and changes in density may be obscured by changes in skeletal size.
Measurement of volumetric BMD is advantageous because it is independent of
skeletal size.
A pQCT scan takes about 10 minutes and is
therefore generally not feasible in children under 6 years of age.
Radiation exposure expressed as effective dose per scan site is approximately
0.3µSv.
