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SYSTEM OVERVIEW
The Hologic QDR
4500 X-ray Bone Densitometer (Figure 1-1) estimates the bone mineral
content (BMC) and bone mineral density (BMD) of selected areas of the body, or of the entire
skeleton. It does so using X-rays of two different energy levels. This dual-energy scheme allows
soft tissue within the selected area to be subtracted out, leaving only bone to be scanned and
estimated.
Note: This manual uses "QDR 4500" to refer to all models in the QDR 4500 series systems.
Information presented in this manual, that applies only to a particular model, or models,
will be noted as such.
The patient lies face up on the table and, with the aid of a cross-hair laser, the operator positions
the scanning arm over the region of interest. After entering patient data and selecting the type
and size of scan desired, the operator initiates the scan with a single keystroke.
The operator is not required to select technique factors, as tube current and voltage are pre-
selected and fixed. Since testing is performed by fan beam method rather than by flooding the
area as in conventional radiography, the scanning time is a function of the dimensions of the area
to be measured, the desired resolution and the desired precision.
BMC results are expressed in grams of calcium hydroxyapatite, and BMD is reported in
2
grams/cm
of the same compound.
Note: In most cases, no additional shielding is necessary for patient, operator or room, and the
QDR 4500 can be placed in any convenient non-shielded examination room. Contact your
state regulatory agency for details about additional shielding requirements, if any.
The QDR 4500 employs a patented Automatic Internal Reference System, which continuously
calibrates the machine to eliminate the effects of variations in temperature, tube flux, etc. No
daily calibration is required. The daily scanning of a quality control phantom is required to
provide assurance that the system is functioning correctly, and to aid in the detection of any long-
term drift.
The X-ray scans produced by the QDR 4500, and displayed on the monitor, are intended only to
locate anatomical sites for measurement, and to assure the operator that the machine is operating
properly. They are not intended as a substitute for conventional film-based diagnostic scans.
SECTION 1
INTRODUCTION
1-1
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