BMD Learning

Bone Densitometry
Prepared by:
Behzad Ommani
Bachelor of Radiology
Master of Medical Engineering
Instructor Radiology Group
IN THE NAME OF GOD

Osteoporosis
Osteoporosis is the most common metabolic bone
disorder.
It has been defined by the National Institutes of Health
as an age-related disorder characterized by decreased
bone mass and increased susceptibility to fractures in
the absence of other recognizable causes of Bone Loss.

Primary osteoporosis
• Type 1: involutional osteoporosis affects mainly trabecular
bone, occurs in women during the 15-20 years after the
menopause, and is related to a lack of estrogen.
• This is thought to account for wrist and vertebral crush
fractures, which occur through areas of principally trabecular
bone.
Osteoporosis Type

• Type 2. senile involutional osteoporosis. The fractures of old
age seen at the hip, proximal humerus, pelvis and
asymptomatic vertebral wedge fractures.
Osteoporosis Type
• This affects both trabecular and
cortical bone and represents
progressive loss of bone mass from
the peak around the age of 18-35
years.

Secondary osteoporosis is due to an underlying medical
condition, such as renal disease, malabsorption, or hormonal
imbalance, or to medical treatment such as steroids or certain
anticonvulsants.
Osteoporosis Type

Osteoporosis Risk.F
Risk Factors for Primary and
secondary osteoporosis,
including :
Access

Osteoporosis Test Types :
 Plain Film
 SPA
 DPA
 DEXA
 QCT
 US & PDEXA
 MRI
Osteoporosis Measurement

 The history of BMD measurement dates back to the 1940s.
 At that time, bone density was measured on plain radiographs
(X-rays).
 However, because loss of bone density is not apparent on a
plain X-ray until approximately 40% of the bone is lost,
different methods of BMD measurement have been
developed.

 Singh Index
• The Singh index describes the trabecular patterns in the bone
at the top of the thigh bone (femur). X-rays are graded 1
through 6 according to the disappearance of the normal
trabecular pattern. Studies have shown a link between a Singh
index of less than 3 and fractures of the hip, wrist, and spine.

 Radiographic Absorptiometry
• Radiographic absorptiometry
was developed during the late
1980s as an easy way to
determine BMD with plain X-ray.
An X-ray of the hand is taken,
incorporating an aluminum
reference wedge. The X-ray is
then analyzed, and the density
of the bone is compared to the
density of the reference wedge.

Osteoporosis Test Types :
 Plain film
 SPA
 DPA
 DEXA
 QCT
 US & PDEXA
 MRI

 Single-Photon Absorptiometry
• In the early 1960s, a new method of measuring BMD, called
single-photon absorptiometry (SPA), was developed.
• In this method, a single-energy photon beam is passed
through bone and soft tissue to a detector. The amount of
mineral in the path is then quantified.

• The distal radius (wrist) is usually used as the site of
measurement because the amount of soft tissue in this area is
small.
• SPA measurements are accurate, and the test usually takes
about 10 minutes.
• The radioactive source gradually decays, however, and must
be replaced after some time.

 Dual-Photon Absorptiometry
• Dual-photon absorptiometry (DPA) uses a photon beam that
has two distinct energy peaks. One energy peak is absorbed
more by the soft tissue. The other energy peak is absorbed
more by bone. The soft-tissue component is subtracted to
determine the BMD.

• DPA allowed for the first time BMD measurements of the
spine and proximal femur.
• However, although DPA is accurate for predicting fracture risk,
the precision is poor because of decay of the isotope.
• In addition, the machine has limited usefulness in monitoring
BMD changes over time.

 Dual-Energy X-ray Absorptiometry
• Dual-energy X-ray absorptiometry (DXA) works in a similar
fashion to DPA, but uses an X-ray source instead of a
radioactive isotope.
• This measurement technique is superior to DPA because the
radiation source does not decay and the energy stays constant
over time.
• DXA has become the “Gold Standard" for BMD measurement
today.
• Scan times for DXA are much shorter than for DPA,
and the radiation dose is very low. (The skin dose for an
anteroposterior spine scan is in the range of 3 mrem)

• DXA scans are extremely precise. Precision in the range of 1%
to 2% has been reported.
• DXA can be used as an accurate and precise method to
monitor changes in bone density in patients undergoing
treatments.

 Quantitative Computed Tomography
• Measurement of BMD by quantitative computed tomography
(QCT) can be performed with most standard CT scanners.
• QCT is unique in that it provides for true three-dimensional
imaging and reports BMD as true volume density
measurements.

• The advantage of QCT is the ability to isolate an area of
interest from surrounding tissues.
• QCT can, therefore, localize an area in a vertebral body of only
trabecular bone, leaving out the elements most affected by
degenerative change and sclerosis.
• The radiation dose with QCT is about ten times that of DXA,
and QCT tests may be more expensive than DXA.

Peripheral Bone Density
• Lower cost portable devices that can determine BMD at
peripheral sites such as the Radius, Phalanges, or Calcaneus
are increasingly being used for osteoporosis screening.
• The advantage of using a portable device is the ability to bring
BMD assessment to a population who otherwise would not be
able to have the test.
• These machines are considerably less expensive than those
that measure BMD in the hip and spine.

• One of the problems with peripheral testing is that only one site is
tested; thus, low bone density in the hip or spine may be missed.
This may be a problem because of differences in bone density
between different skeletal sites.
• Although peripheral machines are considered accurate, doubts have
been raised about their precision. Peripheral machines may not be
good enough to monitor patients undergoing treatment for
osteoporosis.
• In postmenopausal women, differences in BMD between different
skeletal sites is more common. BMD may be normal at one site and
low at another site.
• In the early postmenopausal years, bone density in the spine
decreases first because the bone turnover in this highly trabecular
bone is greater than at other skeletal sites.
• Bone density becomes similar across the skeleton at approximately
70 years of age.

• In early postmenopausal women therefore, up to the age of
65 years the most accurate site to measure BMD is probably
the spine.
• In women older than 65 years, BMD is similar across the
skeleton; therefore, it may not make much difference which
site is measured.

• Caution must be used when interpreting spine scans
in elderly patients because degenerative changes
may falsely elevate BMD values. BMD measurements
are, however, mostly site specific, and the most
accurate predictor of fracture risk at any site is a
BMD measurement of the spine.
• At present, peripheral BMD testing machines are
good screening devices because of their portability,
availability, and lower cost.

• Magnetic resonance imaging of the spine is performed to
evaluate vertebral fractures for evidence of underlying
disease, such as cancer, and to assess the newness of the
fracture. New fractures demonstrate a better response to
treatment by Vertebroplasty and Kyphoplasty in certain
clinical situations.

DEXA Technology Type
 Pencil Beam
 Fan Beam
 Narrow Fan Beam (Digital Flash Beam)

DEXA Procedure
 Performing the exam include:
• Preparing the Patient
• Creating/Retrieving a Patient Biography
• Selecting the Scan Type and Mode
• Positioning the Patient and the C-arm
• Performing the Examination
• Exiting the Examination
• Performing the Analysis
• Exiting the Analysis
• Generating and Printing Reports

 Positioning the Patient and C-arm
• The goal for positioning the patient
on the table is to ensure that the
spine is as straight as possible for
the scan.
• Adjust the Knee Positioner by
rotating it until the femurs are as
vertical as possible. This will help
reduce the lordotic curve of the
lumbar spine.
• Also note that the area to be
scanned starts at about Middle T12
to Middle L5.
AP Lumbar Spine Exam

41
 Correct Spine ROI
• The spine is in the center of
the image including all L1-L4
vertebrae.
• (1) All of L4 (1) is shown.
• (2) The top of L5 (2) is shown.
• (3) Approximately lower half
of T12 (with ribs) is shown.

 Spine ROI
• Use High definition for patients
with heavy weight.
• Cover from L1-L4
• The Lines have to be parallel to
intervertebral space.
• Avoid Metals
• Delete osteophyte

 Positioning the Patient and C-arm
• The goal for positioning the patient
on the table is to ensure that the
hip is as straight as possible for the
scan.
• Positioning the patient for a hip
scan involves using the Foot
Positioner. This positioner helps to
align the patient’s hip and holds
the foot firmly in place.
• Laser adjust 3 inches below the
greater trochanter and 1 inch
medial to the shaft of the femur.
AP Hip Exam

46
 Correct Hip ROI
• The Femur image shows the
greater trochanter (1),
femoral neck (2), and ischium
(3).
• A minimum of three
centimeters of tissue should
be shown above the greater
trochanter and below the
ischium.
AP Hip Exam

 Hip ROI
• Use femoral neck, or total
proximal femur whichever is
lowest.
• BMD may be measured at
either hip.
• Internal rotation of femur so
that no or little lesser
trochanter is visualized.
AP Hip Exam

The Neck ROI should positioned as
follows:
• The Neck ROI includes no part
of the greater trochanter
• The Neck ROI includes soft
tissue on either side of the neck
• The Neck ROI is perpendicular
to the femoral neck
• The Neck ROI contains little or
no ischium
AP Hip Exam

Forearm Exam
• Hip and/or spine cannot be
measured or interpreted.
• Hyperparathyroidism
• Very obese patients (over the
weight limit for DXA table)
• Metallic devices in exam
region
• Children

51
• Use 33% radius (one- third radius)
use the non dominant forearm for
diagnosis.
• Measure the forearm to the ulna
styloid (A).
Forearm Exam

52
Left Forearm Scan:
start at the mid-forearm.
Right Forearm scan:
start at the first row of
carpal bones.
Forearm Exam

Forearm Exam
 Correct Forearm ROI
• The Reference line is located
at the distal tip of the ulna
styloid process.
• The UD ROI does not contain
the radial endplate [UD =
ultradistal)
• The vertical lines in the center
of the UD and 33% ROIs are
located between the radius
and ulna

• Osteoarthritis
• Previous barium, contrast/ radionuclide studies
• Stones
• Bony disorders:
(Bony lesions w increased density e.g. compression
fracture, osteoblastic lesions increased BMD)
Artifact (Internal)

Result
The results of the test are
usually reported as a "T score"
and "Z score.“
But we use T or Z score?

T score
- The T score compares your
bone density with that of
healthy young adult. (30
years)
- A score of 0 means your
BMD is equal to the standard
for a healthy young adult.

Z score
The Z score compares your bone
density with that of other
people of same age, gender, wt
and ethnicity.
A low Z-score (below —2.0) is a
warning sign that you have less
bone mass or that you are losing
bone more rapidly than
expected for someone of your
age.

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