Duel-Energy X-ray Absorptiometry (DEXA) and Adaptix

What does DEXA stand for?

Duel-energy x-ray absorptiometry

DEXA is a 2-dimentional technology which is used to measure ..

• Bone mass

• Lean mass (muscle)

• Fatty mass (adipose tissue)

What is DEXA?

• Originally developed for use in human patients

• Precise method in determining body fat distribution

• Not available at standard veterinary practices

How does it work?

• Uses two low-dose energy x-rays

• Although radiation exposure is minimal, some health and safety aspects still apply

• X-ray source positioned underneath the machine table supporting the patient and the director is encased in an arm above

DEXA uses two low-dose energy rays to distinguish the type and amount of tissue begin scanned. These two energies are used for ..

• Separating mineral (bone) and soft-tissue components

• One energy is absorbed mainly by soft tissue and the other by bone

• There is a high energy photon and a low energy photon

Radiation exposure is much lower than standard radiography - depending on the area of the body being examined - at just 10% of normal everyday background radiation. Lead PPE (apron, thyroid guard) is not warranted, however ..

Dosimeters must be worn by the operator to monitor individual radiation exposure levels

DEXA machine

• Large, heavy machines and require a lot of floor space in practice

• Expensive to purchase

• Often why these machines aren’t used in general practice

During the scan

• The arm presses over the body as a beam of x-rays are passed through the area being scanned

• X-ray source and detector move together over the patient

• X-ray photons of the 2 different energy levels are absorbed differently by bone, adipose and lean tissue

• X-ray detector in arm measures the amount of x-rays passed through the body to produce a two-dimensional image and the scan results

The scan takes approximately ..

5-10 minutes to complete

The accuracy and precision of the scan has been determined with ..

Cadaver analysis of dogs and cats

DEXA - Patient preparation and support

• Withhold food the evening before the scan - due to the administration of a sedative or GA

• Sedation or GA is required to ensure the patient remains absolutely still during scan - movement blur may occur

• Metal items must be removed - collars, harnesses, dog coats etc ..

• Be await of metal implants as they are dense objects which will contribute towards density/mass - hip replacements, internal fixators etc ..

• Check patient history → DEXA scan must not be performed within 10-14 days of a contrast study

DEXA relies on the assumption that lean mass is uniformly hydrate at 0.73ml water/g. This must be taken into consideration when performing the scan on certain patients, for example ..

• Dehydration, renal disease, oncology patients etc ..

• This is because the results may not be entirely accurate

• Clients should be advised to remove the patients water in the morning of the scan rather than withholding water overnight

Patient positioning for DEXA

• Dorsal, ventral and lateral positioning possible - as patient will be sedated or GA

• Whichever position is used, sequential scans must be performed in the same position to prevent variable and to standardised practice

• Scan limit borders marked on table top mattress - the patients must be positioned within the borders

Patient positioning depends on the area being scanned and the type of scanner. What else will influence the patient position?

The thickness of the tissue/area

How else may we use DEXA in veterinary patients?

• Systemic disease - neoplasia cachexia

• Orthopaedic disease

• Meat/livestock industry

Pros of DEXA

• Non-invasive and a quick procedure

• Instant results

• No primary complication

• Precise method in determining body fat distribution

• Can be used to monitor progress/deterioration

Cons of DEXA

• Room/space required

• Initial start up cost

• Staff training required

• Uses ionising radiation

• Sedation/DA required

• Unable to predict who will experience a fracture (but can be used to prevent and determine if treatment is required)

• Same machine required for repeat scans due to variation in results (if using different machines)

Adaptix uses ..

• Uses Digital Tomosynthesis to create a 3D x-ray

• Originally designed for human breast mammography

What is Adaptic and how does it work?

• X-ray head creates low-dose x-rays that perform a ‘sweeping’ motion over the patient to make x-ray slices then create a 3D image from the slices

• Is a mobile system and can be ‘table-top’ so easily stored and can be used outside of the veterinary practice

• Can shown soft tissue and bone, like a 2D radiograph

Adaptix machine

• Patient to be positioned on the x-ray plate

• Recumbency type isn’t a concern unless multiple x-rays are being taken, then the same recumbency must be used

• X-ray head, internal beam moves - no outward movement

• X-ray plate

During the Adaptix scan

• The scan itself take about 30 seconds to complete

• Changing the x-ray imaging slices from 2D to 3D is instantaneous within the computer programme

• A 3D digital x-ray is produced that can be manipulated and ‘zoomed’ between the slices

Patient preparation for Adaptix

• May need to be sedated/anaesthetised - very much depends on the image being taken

• Otherwise, preparation is that of a normal x-ray

Clinical use of Adaptix - Orthopaedics

• Excellent definition of bones and joints

• Can be used in theatre during fracture repair

Clinical uses of Adaptix - Dentistry

• Excellent definition of jaw and teeth

• Patients can be put in 1 lateral recumbency and whole jaw x-rayed

Clinical use of Adaptix - Exotics

• Excellent definition of finer bones

• Very good for small mammals and reptiles

• Is easier to get ‘through’ Chelonia shell

Pros of Adaptix

• Non-invasive and a quick procedure

• Instant results

• No primary complications

• Mobile machine

Cons of Adaptix

• Initial start up cost Staff training required

• Uses ionising radiation

• Sedation/GA sometimes required

• is yet to be tested with contrast media

• Not in many practices .. yet

• Still patented so can only buy from one company