Dual-Energy X-ray Densitometry (DEXA) And Visceral Fat Measurement

INTRO

How to measure Visceral Fat with Dual-Energy X-ray Densitometry (DEXA)?
Imaging visceral fat soft tissue with the DEXA method.

What is Dual Energy X-ray Absorptiometry?

Dual Energy X-ray Absorptiometry, DEXA for short, is a digital X-ray method. With minimal radiation dose. It can distinguish and measure the volume of bone density, muscle mass, and fat. The DEXA Scan is considered the most accurate way. To measure both bone density and body fat percentage.

DEXA Scan examination

The examination takes only a few minutes and requires no preparation. The examination results are summarized in a report. That is easy for you to understand and made available within 24 hours.

DEXA Measurement Usage

DEXA Scan is suitable for:

Measurement of bone density and thus prevention of osteoporosis
Measuring the percentage of fat and muscle mass in the body
Reliable data as a basis for individual nutrition and training plans
Continuous measurement of success in sport and diet.
A better understanding of your own body.

Dual-energy X-ray densitometry diagnosis

Dual-energy X-ray densitometry or dual-energy H-ray absorptiometry. It is one of the most common densitometric methods. Used in the diagnosis of changes in bone tissue. The method is based on the application of dual-energy absorptiometry of H rays. Which are of different strengths. And very small doses, which are passed through the examined bone.

Densitometry application

In the past, bone densitometry was determined using single-photon densitometry. With the help of monoenergetic iodine-125 gamma rays (27.5 keV). However, this method of measurement could only be applied in regions of the body. Where there is not much soft tissue. While in those parts of the body, layer of soft tissue is thicker around the bones. Gamma rays of americium-241 (60 keV) were applied.

Several years later. The application of two-photon densitometry. With the help of gadolinium-153 (44 and 100 keV) began.

Two-photon dual-energy X-ray absorptiometry (DEXA)

In the mid-80s of the 20th century. X-ray densitometry or dual-energy X-ray absorptiometry (DEXA) was developed. Which, although it applies the principles of two-photon absorptiometry. Uses X-rays or H- rays of two different energies. The advantage of this method compared to the previous ones is shorter imaging.

And better image resolution. The lower radiation dose. Better precision in the interpretation of the results. And the significantly shorter duration of imaging. For example, compared to SPA and DPA methods. This method today has become not only a leading. But also a modern method of densitometry for measuring bone density.

Body skeleton and soft tissue imaging with the DEXA method

During life, or in certain pathological processes in the bone system. Along with a disturbance in the amount and structure of collagen. Osteoporosis also occurs. Which is characterized by a decrease in the number of minerals in the bone tissue. That is a lower density of minerals in the bone. This is one of the causes of increased brittleness. I.e. bone fragility in patients with osteoporosis.

Bone mass and osteoporosis

Genetic changes consequently affect the structure and amount of collagen. And bone tissue cannot, for now, be directly influenced. It can be done to some extent by implementing certain prevention. Measures or using drugs, improving the number of minerals in the bones. And thereby reducing their fragility.

That is why it is important to assess the bone in osteoporosis. And similar diseases try to influence them to a certain extent risk factor. Responsible for the occurrence of bone fractures. In people with reduced bone mass.

DEXA bone density and visceral fat measurement

Today, dual-energy X-ray densitometry (DEXA). In which an X-ray tube is used as a source of radiation. Is the leading method used to measure bone density and visceral fat.

The dual-energy X-ray densitometry method is based on the difference. In the absorption of gamma X-rays. In bone and visceral soft tissue. For direct measurements of bone mass density (BMD). And bone mineral content (BMC). Which coincides with bone mass. Based on the obtained values. The bone mass can be assessed with great certainty. And osteoporosis can be diagnosed.

The most important hem region to measure bone mass are the lumbar spine. The neck of the femur. And the bones of the forearm. As these are the locations w the highest risk of fracture. If the bone mass is low.

Characteristics of the skeleton in densitometry

The standard measurement regions, using the DEXA method. Are the neck. And the total value in the area of the proximal part of the femur. And the lumbar spine (visceral fat).

Bones are made up of cortical and trabecular bones. Vertebrae and epiphyseal parts of large joints are built mainly from the trabecular bone. While long bones are built mainly from cortical bone. Metabolism is the most intense in trabecular bone.

So in most diseases and conditions. BMD changes are more pronounced in the trabecular than in he the cortical bone. An exception is hyperparathyroidism. In which demineralization predominantly affects the cortical bone. E.g. the neck of the femur or the distal third of the thumb.

Contrary to the above. In Cushing’s disease, the trabecular bone of the axial skeleton is affected. In hypogonadism the trabecular bone of the spine. And in acromegaly, a high level of growth hormone can lead to an increase in the density of the cortical bone. Of the appendicular skeleton.

Dual-energy X-ray densitometry standard measurement regions

The standard measurement regions, using dual-energy X-ray densitometry. Are the neck and the total value in the area of the proximal part of the femur. The lumbar spine (T-value for L1-L4). And the forearm (distal 1/3).

BMD measurement in the forearm area is performed in patients: with hyperparathyroidism. In patients with a body weight that exceeds the permissible weight limit. Specified by the manufacturer of the device for dual-energy X-ray densitometry. In the case of the impossibility of measuring and interpreting BMD in standard areas. For example after operations in the hip or spine area. In severe deformations and degenerative changes of the spine.

Method of performing densitometry

The densitometric method is based on dual-energy X-ray densitometry. Or, literally translated from English, dual-energy X-ray absorptiometry (DEXA). Is based on two different strengths of H-rays. Very small doses, heare passed through the examined bone.

Behind the examined bone are sensors. That m the intensity of the H-rays. That ray has passed through the bone. The results are then processed in an electronic computer. Based on the difference between the transmitted and absorbed energy of the H-rays. The mineral density in the bone is estimated. Which is expressed in absolute values, or g/cm².

The self-examination takes 10-15 minutes. And does not require any preparation. Except for the removal of metal parts from clothing. It is performed in a sitting position. While holding the forearms on the bed of the device or lying on it.

Areas of DEXA measurement

Bone mineral density (BMD) is measured by the DEXA method. In the area of the lumbar spine. The neck of the femur (hip), and the lower third of the thumb:

About 80% of the measurements are performed in the area of the lumbar spine. In the anteroposterior (AP) projection. About 10-15% of measurements are performed on the hip joint. In the AP projection.
The other 5-10% are specialized measurements. Such as measurements of the whole body.

Forearm, and lumbar spine in lateral projection.
The measurement of the lumbar spine of women. Is most significant 10-15 years after menopause. Where the area of the proximal part of the femur is more clinically significant.

Imaging the whole body is also increasingly used. Modern equipment for densitometry has made it possible. To shorten the time required for the examination.

DEXA radiation doses and advantages of densitometry method

The dose of H-radiation applied in DEXA densitometry is very low. The method is simple. Painless and fast. The advantages of this method are the low dose of radiation. High precision and relatively low price. The dose of radiation received during densitometry is so small. That even people working with the device are not particularly protected from H-radiation.

Because the dose is 1-3 mRem. Which is equivalent to the radiation dose received during a 3-9 hour airplane flight. Or on the Earth’s surface from cosmic radiation for 3-9 days. For the sake of comparison, with other methods. The examinee’s organism receives higher doses of radiation: with the SPA method, 5-10 mRem. And KCT 100-1,000 mRem. Also for the sake of comparison.

During X-ray imaging of the lungs. The average radiation dose is 300 mRem. And when imaging all teeth (orthopan) or CT of the abdomen. It is 1,000-6,000 Rem. The average dose of radiation on the Earth’s surface. That people receive annually is about 400 mRem.

Other methods are less precise or significantly more expensive. And some are associated with the use of high doses of radiation.

Interpretation of DEXA results

Interpretation of the results in the area of the neck of the femur

The basis for bone density measurements using a dual-energy radiation source. Is the difference in photon absorption in bone and soft visceral tissue. The mathematical equation. Which describes the absorption of two types of energy in a system. Consisting of two components. Soft visceral fat tissue and bone. Gives the values of the mass of bone and soft visceral fat tissue in g/cm2.

Radiation attenuation is proportional to bone mass, and bone density. And is calculated by dividing the total bone mass by the bone surface in the measured area.

Surface bone density

This method does not give the true bone density. But the so-called surface bone density is expressed in g/cm². Which partly depends on the volume of the bone. The expression of results in densitometric measurements consists of comparing the measurement values. Obtained in patients with reference values. Which are in the range for the population. Or in units of standard deviation from the mean value. Or deviation from the maximum value.

The values methods were obtained by densitometric measurement of bone mineral density (BMD). Are expressed in one of the following three ways:

In absolute values, in g/cm².
As a T score (T value). Or the deviation of the maximum measured BMD value from the peak bone mass. Of young people expressed in standard deviations (sd).
As a Z score (Z value). Or deviation of the measured mean value of BMD from the average bone mass. Of people of the same age expressed in standard deviations (sd).

Densitometric bone mineral density measurement

In 1994, the World Health Organization adopted a quantitative definition of osteoporosis in women. Based on the densitometric measurement of bone mineral density. And the assessment of the T value. Or as a bone mineral density BMD value of at least 2. 5 SD. Less than the average value for young healthy women (T-value ≤ – 2.5).

Given that DEXA densitometry is a fast, non-invasive method. With minimal radiation. A relatively precise. And reproducible asses. The adoption of this practical definition enabled the mass application of densitometry. In the diagnosis of osteoporosis and monitoring the results of treatment. It was determined that a decrease in BMD value. For each standard deviation was associated with a 1.5- to 2.5-fold increase. In the risk of fracture.

Based on DEXA densitometry. The measurement result obtained depends on the T value. Which according to the scale below indicates different bone mass:

Bone mass scale T value
Increased bone mass T > + 1
Normal bone mass T between – 1 and + 1
Osteopenia T between – 1.0 and – 2.5
Osteoporosis T < – 2.5 (or Z < – 1.0)

Measurement of total body bone mass and body composition

More modern devices for DEXA densitometry are equipped with a program. For measuring the composition of the body (body composition). Which measures the minerals in the bones, the fat, and lean tissue content. And displays the distribution of fat tissue in the body.

This program is used to monitor patients suffering. From Crohn’s disease, celiac disease, anorexia nervosa, cystic fibrosis, obesity, and metabolic syndrome.

Application of dual-energy X-ray densitometry in pediatrics

The application of dual-energy X-ray densitometry in pediatrics requires. A special type of interpretation of DEXA densitometry results. Because in children and adolescents, they are associated with significant change. In the size and shape of bones. During growth, especially in puberty.

As the application of dual-energy X-ray densitometry in pediatrics is still insufficiently studied. There are numerous limitations and disadvantages to its mass application. According to data from some studies. Dual-energy X-ray densitometry in children. For diagnostic purposes.

Should not be performed by doctors outside specialized pediatric centers. Or if the scan is performed outside these centers. The results should not be interpreted. And treatment should not be undertaken. Without consultation with experts in the field. Because most pharmaceutical preparations for the treatment of adults with low bone mass. Can only be given to children in a strictly monitored clinical trial.

Dual-energy X-ray densitometry use in Pediatrics

Primary osteoporosis (eg juvenile idiopathic osteoporosis, osteogenesis imperfecta), Secondary osteoporosis (eg Cushing’s syndrome, hyperthyroidism, hypopituitarism, hypogonadism, and various eating disorders). In children treated with glucocorticoids, antiepileptics, or chemotherapy.

CONTENT:

• What is Dual Energy X-ray Absorptiometry?
• DEXA Scan examination
• DEXA Measurement Usage
• Dual-energy X-ray densitometry diagnosis
• Densitometry application
• Two-photon dual-energy X-ray absorptiometry (DEXA)
• Body skeleton and soft tissue imaging with the DEXA method
• Bone mass and osteoporosis
• DEXA bone density and visceral fat measurement
• Characteristics of the skeleton in densitometry
• Dual-energy X-ray densitometry standard measurement regions
• Method of performing densitometry
• Areas of DEXA measurement
• DEXA radiation doses and advantages of densitometry method
• Interpretation of DEXA results
• Surface bone density
• Densitometric bone mineral density measurement
• Measurement of total body bone mass and body composition
• Application of dual-energy X-ray densitometry in pediatrics
• Dual-energy X-ray densitometry use in Pediatrics