What is a bone density test and how it is carried out: types and interpreting the results
For the treatment of bone pathologies, the importance of early diagnosis of the disease. In connection with this question: how is bone density test, interested in more and more people learned about existence of this method of research. Bone densitometry allows with sufficient accuracy to detect early signs of osteoporosis at an early stage, and preventive research with the use of this technology would eliminate the development of disease in humans related to increased risk, especially the elderly.
the essence of the diagnostic method
Densitometry is a nondestructive method for determining the mineral density of bone tissue; mainly based on measuring the level of calcium in the bone structure, which largely determines the strength of the bone. The most important areas of research are spine and neck of the femur, pathology which often lead to the loss of motor abilities. Critical densitometry of the spine for the elderly, since the level of bone calcium begins to decrease after 35 years and can drop to critical values by the age of 52-55 years.
The Main objectives of the study: the identification of the two main bone pathologies – osteoporosis and osteomalacia. Osteoporosis characterized by a decrease in tissue density by reducing the amount of bone substance per unit volume – a quantitative change in bone mass. Osteomalacia is caused by deficiency of mineral ingredient in the normal amount – qualitative change of bone structure. If osteoporosis most often develops on the background of age-related degeneration of tissue, osteomalacia can occur in pregnancy and postnatal period as a result of loss of calcium (for example, with the breast milk).
Numerous studies have shown that the problem of osteoporosis is laid in childhood, and at the base of this bone disease are genetic, hormonal, nutritional, mechanical causes; chronic diseases and metabolic syndromes. If the children are not an optimal bone mass, the risk of osteoporosis and fractures in later is large enough. Control the development of the child's bone structure is one of the areas of densitometry.
The Risk of osteoporosis is different in different parts of the human skeleton, therefore, in determining the localization zone densitometry, it is important to determine the optimal impact position. In the General case, the bone tissue contains two major layers: compact (cortical) matter, to the greatest extent form the strength of bones, but with small rate of metabolism, and spongy (trabecular) a substance that is actively involved in metabolism.
Different types of pathology different strike these layers. Postmenopausal, steroid hypogonadal and osteoporosis basically destroy trabecular substance. Lesion of the cortical substance occurs with senile osteoporosis, hyperthyroid, and diabetic giperparatireozom types of the disease. If the pathology affects the growing skeleton (aged under 18), it is often installed system bone lesion impaired in both layers.
Currently there are many ways to determine bone density.
Practical use is made of the following technologies:
- Dual-energy x-ray densitometry (absorptiometry) is based on passing two x-rays. The main purpose is the study of the spine and hips. The principle is based on the fact that increased tissue density reduces the permeability of such rays. Analysis and comparison are results of the passage of the two rays (bone and soft tissues). The accuracy of the method is estimated at around 2% change in bone mass for the year.
- Peripheral bone densitometry technique similar to the previous one, but designed to study the bones of the extremities, but may not be used for studies of the spine and hips. Used small portable x-ray sources. The accuracy of the method is not sufficiently high, so it is used often for diagnosis and for monitoring treatment process and screening.
- two-photon absorptiometry involves the use as sources of radioactive isotopes. Radioactive radiation allows to determine the bone density of matter in hip and vertebral divisions.
- Quantitative computed tomography-based three-dimensional picture of the bone structure using x-rays. Method is rarely used because of high radiation concentration.
- the Ultrasonic technique is based on the definitionthe propagation velocity of ultrasonic waves and its dispersion in bone tissue. Method has a wide distribution. It has a lower informative ability in comparison with x-ray method, but it is absolutely safe and available.
Densitometry is assigned a doctor and should be held to the people within high risk of occurrence of bone abnormalities, with a frequency of 2 times per year. risk Group consists of the following people: women after the age of 42-45 years and men older than 55 years; women at menopause, if it came prematurely; women after adnexectomy; after bone fractures; patients with pathology of parathyroid glands; people over the age of 35 who have close relatives with osteoporosis, persons taking medications with the effect of decalcification (corticosteroids, anticoagulants, oral hormonal contraceptives, tranquilizers, diuretics, anticonvulsants and psychotropic drugs); in case of alcohol abuse and Smoking; people with a fixed way of life and improper diet; after a system of starvation; people experiencing significant long-term physical overload; patients with endocrine and rheumatic diseases, diseases of the spine.
A Particularly important research if you have any signs of osteoporosis. X-ray densitometry methods are contraindicated in pregnant women and nursing mothers. Should not get the procedure after administration of contrast composition during a previous CT or MRI, if less than 6-7 days. Using radioisotope diagnostics is necessary to maintain the appropriate interval. Ultrasonic waves are considered absolutely safe.
The methods x-ray densitometry carried out using three types of devices: axial x-ray densitometers; portable densitometers peripheral and peripheral ultrasonometry. Axial stationary instruments used to implement the dual-energy absoptiometry and can perform 4 programs of study; portable – to study the forearm, upper limbs (especially the calcaneus).
This technology allows to conduct the following studies:
- densitometry of the lumbar spine;
- study of the proximal femur: analysis is the state of the division and its parts – the neck (especially ward's triangle), the greater trochanter, shaft, intertrochanteric area;
- assessment of the entire skeleton and its parts – the spine, pelvis, legs;
- examination and ultradistal distal sections of the forearm
- study the calcaneus.
As a result of x-rays is determined by the surface mineral density – the amount of minerals on the area that is traversed by the beam. The study is carried out using machines fan and point type.
Ultrasound definition bone density
Ultrasound densitometry is based on the use of portable densimeter. The technique allowed for examination of pregnant and lactating women. The sensor unit records the speed of passing waves, depending on bone density. In addition, it identifies broadband signal attenuation as a result of its uptake by bone tissue.
The results go into a computer, which analyzes them. Studies are often conducted in peripheral areas of the skeleton. Undergo ultrasound densitometry of the heel and tibia, phalanges, patella.
The basis of the densitometric diagnostic methods based on the norm of bone density, which differ in different zones of the skeleton.
Analysis of the data (decryption) is performed according to established standard indicators, gender, age and individual peculiarities of the person.
The Main indicators of the research are:
- Navy. Indicator mineral composition of bone, is measured in grams.
- BMD. Indicator mineral tissue density; determined in g/cm2.
The Analysis of indicators is based on two main criteria:
- T-criterion. The ratio of the resulting density bone density normal (the value for a completely healthy person of similar age and gender).
- Z-criterion. The obtained ratio of bone density to the average of a group of people of the same age and gender.
The Norm of the T-criterion is set in the range of -0,9 to +2, indicating a normal condition of the bone tissue. When the first signs of bone pathology (osteopenia) a value of T-test drops to (-1) to(-2,5). In the case when the criterion is lowered below -2,5 we can talk about the development of osteoporosis.
Technique and training
Preparations for densitometry requires no special procedures. To exclude improper influences are recommended only a few limitations:
- the discontinuation of medications with calcium supplements 24 hours beforeresearch;
- you must inform the physician about the following circumstances: procedures the introduction of barium or other contrast; pregnancy; testing using x-ray, CT scan or radioactive isotopes; presence of pacemaker or metal implant;
- compliance with immobility during the procedure.
The Pose, which is held the impact of the beam or wave is selected depending on which area of the skeleton is studied. Over the studied plot slowly moves the sensor, the signal from which is projecting the computer monitor. The procedure lasts from 15 to 35 minutes, and for peripheral surveys in minutes. The result of the study is recorded in the doctor-radiologist for decryption.
When densitometry the patient remains in a dressed condition, if the clothes are quite nice and has metal elements. Repeated bone density test is recommended to be held once in two years to determine the dynamics of change in bone density.