Download Bone Densitometry

RAD216 ADVANCED
IMAGING MODALITIES
BONE DENSITOMETRY
INTRODUCTION
Over the last 50+ years, medical
imaging has been at the forefront in
the development of ways to better
diagnose bone mineral loss. This
bone loss is called osteopenia or
osteoporosis.
HISTORY
Until the 1960s radiologists could
only make a diagnosis of bone
mineral loss by analyzing
radiographic images. Visible loss of
bony trabecula usually meant a bone
loss of between 30% and 50%. A
more sensitive quantitative method
was needed to determine bone
mineral loss.
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HISTORY
Bone densitometry had its origins in
nuclear medicine in the 1960s. It
was called single photon
absorptiometry (SPA). It used
iodine-125 which emitted 35 keV
gamma rays.
HISTORY
The use of an x-ray tube instead of a
gamma ray source introduced singleenergy x-ray absorptiometry (SXA).
The x-ray beam was heavily filtered
in order to produce a near
homogeneous beam (hence the term
“single energy”).
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HISTORY
The 1970s saw the introduction of
dual photon absorptiometry (DPA).
This technique used a radioactive
source that could emit gamma
radiation in two energies.
Gadolinium-153 emits gamma rays
with energies of 44 and 100 keV.
HISTORY
In the 1980s dual-energy x-ray
absorptiometry (DXA) becomes the
radiographic extension of DPA.
Modern systems use a “fan beam”
configuration. Dual energies are
achieved by the use of beam filtering
or variation of generator output.
HISTORY
Around the same time, CT finds
application in bone densitometry,
called quantitative computed
tomography (QCT). However, the
use of CT for this purpose is costly,
requiring more radiation and no more
accurate than DXA.
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HISTORY
The use of ultrasound to perform
bone density measurements has been
around since the 1960s, but has yet
to achieve the degree of precision
provided by DXA. This method is
called quantitative ultrasound (QUS).
BONE DENSITOMETRY
Various methods to measure bone
mineral content in order to accurately
diagnose osteoporosis.
OSTEOPOROSIS
A condition involving loss of bone
mineral density to the extent defined
by the World Health Organization
(WHO).
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OSTEOPOROSIS
The WHO defines osteoporosis on the
basis of statistical comparison with
historical data. The computation of
scores is compared to a standard.
OSTEOPOROSIS
The bone densitometry procedure
produces 4 important values:
Bone mineral content
Bone mineral density
T score
Z score
BONE MINERAL CONTENT
(BMC)
The amount of mineralization present
in a given volume of bone and
measured in grams (g).
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BONE MINERAL DENSITY
A derived unit indicating the
concentration of mineralization
present per square centimeter
(g/cm2).
T-SCORE
A calculation based on comparison
with an average person of young age
and peak bone mineralization. The
score is a normalized value that
ranges from -3 to +3 standard
deviations.
Z-SCORE
A calculation based on a comparison
with an average person of the same
age and sex.
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T-SCORE & OSTEOPOROSIS
Of the four values, the t-score is the
most significant. According to the
WHO, a patient whose t-score falls
below -2.5 is considered to have
osteoporosis.
T-SCORE & OSTEOPENIA
As defined by the WHO, a patient
with a score in the range of -1.0 and
-2.5 is said to have osteopenia, an
intermediate level of bone mineral
density loss.
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BONE PHYSIOLOGY
Bone is a living tissue in constant
state of breakdown and repair. Bone
cells called osteoblasts and
osteoclasts are involved in the repair
and breakdown process, respectively.
Certain conditions cause the rate of
breakdown to exceed the rate of
repair, resulting in net bone loss due
to resorption.
RISK FACTORS (AND
INDICATIONS)
Post menopausal women are potentially at risk if
they have one or more of the following risk
factors:
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Family history
History of fractures
Smoking
Alcohol consumption
Low body weight
Sedentary lifestyle
Low calcium & vitamin D intake
Taking certain medications (corticosteroids,
thyroid replacement, Dilantin, etc.)
CONTRAINDICATIONS
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Pregnancy
Deformities of anatomy to be scanned
Previous fracture at site to be scanned
Excessive body part thickness
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PATIENT PREPARATION
Patients only need to wear loosefitting clothing (gown preferred) with
no metallic objects such as zippers to
obscure anatomy.
PATIENT PREPARATION
 NO CALCIUM SUPPLEMENTS FOR 24
HOURS BEFORE EXAM
 IF CONTRAST STUDY PERFORMED,
MUST WAIT 10-14 DAYS BEFORE DXA
PERFORMED
 WAIT 10-14 DAYS POST CT OR
NUCLEAR MEDICINE STUDY
SELECTION OF ANATOMY
Patient history usually determines
what anatomy is examined. For most
DXA procedures, the lumbar spine or
proximal femur (hip) is examined
(called central axis imaging).
Peripheral imaging of the elbow,
wrist, finger, lower leg and calcaneus
can also be examined by DXA using
dedicated peripheral units.
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SELECTION OF ANATOMY
Only anatomy that is not fractured or
deformed should be evaluated in
order to obtain the most accurate
results.
LUMBAR SPINE
Patient lies on back with legs
supported. A scout (pilot) image is
obtained and the vertebrae selected
(usually L1 or L2 through L4).
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HIP
The patient lies with the midsagittal
plane aligned with the midline of the
table. Legs are extended and feet
inverted 15 to 20 degrees. A pilot
image is obtained of the hip and
proximal femur. The femur should be
parallel to the long axis of the image.
QUANTITATIVE
ULTRASOUND
Usually performed on peripheral
structures (toe, calcaneus, finger).
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POSTPROCEDURE
INSTRUCTIONS
Patients do not require any special
instructions, but should check back
with their referring physician to
obtain results.
TECHNOLOGY UPDATE
Hologic®, a manufacturer of DXA
equipment, introduced the Discovery
QDR™ series of scanners.
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Discovery QDR features
 High-definition Instant Vertebral
Assessment (IVA) to visually evaluate
lumbar deformities
 CADfx uses software to quantify
vertebral deformities
 Hip Structure Analysis (HSA) to
evaluate structural geometry
 Measurement of possible coronary
artery disease (FDA approved)
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