Hologic DISCOVERY A, Technical Manual

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1-1
Section 1
INTRODUCTION
1.1 System Overview
The Hologic Discovery
®
X-ray Bone Densitometer (Discovery-C and -W is shown in Figure 1-1
on Page 1-2; Discovery-A and -SL is shown in Figure 1-2 on Page 1-2) 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.
This manual uses "Discovery" to refer to all models in the Discovery series of 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 grams/
cm
2
of the same compound.
In most cases, no additional shielding is necessary for patient, operator, or room. The Discovery
system can be placed in any convenient non-shielded examination room. Contact your state
regulatory agency for details about additional shielding requirements, if any.
The Discovery system 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 Discovery, 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.