A DEXA scan uses dual energy x-ray absorption to measure bone mineral density and assess osteoporosis risk. It involves passing two low-dose x-ray beams through the body to create a 2D image and calculate the density in specific areas like the spine or hip. DEXA is the most effective technique for measuring bone mineral density and uses T-scores and Z-scores to evaluate results against young adults and age-matched peers respectively.

1. DEXA SCAN and Its
Application
Sarbari Saha
Asst Professor
Radiology

2. What is DEXA scan?
• DUAL ENERGY X-RAY ABSORPTION (DEXA) is a most effective technique used to
measure Bone Mineral Density (BMD).
• It measures the density or thickness of bones and amount of calcium in specific area of
bone.
• Average bone mineral density =BMC/W.
Where, BMC = bone mineral content=g/cm.
W = width at the scanned line.
• The more the mineral is bone measured , the less greater is the bone density or bone
mass.

3. Various ways to measure BMD
• DUAL ENERGY X-RAY ABSORPTION (DEXA).
• PERIPHERAL DUAL ENERGY X-RAY ABSORPTION (P-DEXA).
• DUAL PHOTON DEXA.
• QUANTATIVE COMPUTER TOMOGRAPHY(QCT)
• QUANTATIVE ULTRASOUND.

4. Who should under go
 Menopausal women, all women above 65 age
or older and males over 70 age.
Long term steroids , hormonal theraphy, Vit D,
Calcium, Low estrogen level.
Lumphangiomatosis and low body weight.
Kyphosis.
Previous history of fracture.
Nutritional deficiency- rickets, lupus, Turner
syndrome, rheumatoid arthritis.

5. Working Principal
• Photons are produced from low energy source.
• 2 X-ray beams with different energy peaks pass through the body.
• One peak absorbs by the soft tissue and other by the bone.
• Creates a 2D image.
• Soft tissue is subtracted from the total area, giving the bone mineral
density.
• These measurements are then measured with the normal ranges
matched for chronological age with the help of T-score and Z- Score.

7. Contraindication
• Bilateral hip replacement.
• Metal implants in the area.
• Pregnancy.
• Weight about (120-130)kg.
• Recent contrast studies.

9. Report Format

10. T-score
T- Score shows the amount of bone that is compared with a young
adult of the same gender with peak bone mass. The T-score is
mainly to determine the risk of developing fracture.
As per WHO diagnostic classification of osteoporosis
1 A score above -1 is Normal
2 A score between -1 to -2.5 is Osteopenia (low bone mass).
3 A score between -2.5 is defined as Osteoporosis.
4 A score below -2.5 is sever Osteoporosis with history of fragile fracture.

12. Z-score
Z- Score shows the amount of bone ,compared with other people
in same age group of the same size, height and gender. Z score
mainly to determine risk of having a fracture.
A low Z-score below –2.0 is a warning sign of low bone mass than expected
people of same age of 30-year-old man/woman.
Z score = T-score – Reference T- Score.

13. Procedure for Spine

15. Procedure for Hip

17. Benefits
Quick and non invasive procedure.
No anaesthesia required.
Accurately measures the fracture
risk.
Less radiation exposure almost
0.001mSv.

18. Prevention
• To prevent low bone density it is adviced to intake sufficient
calcium and vitamin.
• Regular excersise.

19. DEXA Machine