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Bone scintigraphy is a diagnostic imaging technique, used to evaluate the anatomy of the skeleton and especially any vascular and metabolic alterations of the bones. For this purpose, radioactive drugs containing diphosphonates labeled with technetium-99m are used, capable of depositing themselves in the bone, mirroring them. the blood supply (district blood perfusion) and the metabolic behavior (given by the degree of activity of the osteoblasts, cells specialized in the synthesis of bone tissue).
The amount of radiation emitted by the skeleton is therefore proportional to the concentration of the radioactive drug and allows, with the aid of a suitable receiver device and a computer, to obtain detailed images and to evaluate any vascular and metabolic alterations. The greater the blood flow and metabolism of a particular bone region, the greater the concentration of the tracer (see figure).
Bone scan is a highly sensitive but non-specific examination; it is not in fact able to reveal the nature of the pathology found. For this reason it is generally used in conjunction with radiological examinations or other imaging methods such as magnetic resonance.
Among the main indications of bone scintigraphy, the identification and follow-up of primary skeletal tumors and bone metastases, ie remote localizations of a malignant tumor, stands out. breast, lung, kidney and bladder. Due to its ability to highlight anomalies already at an early stage - when symptoms or evident structural alterations of the bone still have to manifest themselves - the scintigraphy is carried out immediately after the diagnosis of the most statistically correlated neoplasms to secondary bony localizations. In the presence of metastases, it will therefore be possible to notice areas of tracer hypercaptation (darker); however, remembering the scarce specificity of the technique, especially in single localizations, the accumulation could be consequent to other conditions, such as a recent fracture or an arthrosic process. In addition to being very useful for the diagnosis and staging of the tumor, bone scintigraphy allows to evaluate the effects of the therapeutic intervention undertaken (chemotherapy or radiotherapy).
Further indications for bone scintigraphy are represented by the recognition of inflammatory osteo-articular pathologies, such as rheumatoid arthritis, which involve sites that cannot be explored radiologically (eg joints), microfractures (such as those from stress), necrosis of the femoral head , osteomyelitis (diabetic foot), pain in orthopedic prostheses, pain assessment in patients with normal radiography, algoneurodystrophies and assessment of the viability of bone implants.
Is the examination painful? What are the risks? Are there any contraindications?
Bone scintigraphy is a simple and painless technique, even if the radiopharmaceutical must be administered intravenously. The doses of isotope administered are very low and do not involve significant risks for the patient, even if the use of the scintigraphic technique remains contraindicated in pregnancy. As a precaution, moreover, in women of childbearing age the scintigraphy is generally carried out within ten days following the beginning of the last menstruation, in order to exclude the risk of an ongoing pregnancy. During breastfeeding, some radioactive substances can pass into breast milk; therefore, at the discretion of the doctor specialized in nuclear medicine, the scintigraphy can be postponed or performed unless breastfeeding is suspended more or less prolonged.
Scintigraphy can also be performed on children (the amount of drug used is proportional to body weight) and repeated over time to assess the course of a disease.
The tracers used are not contrast media and as such do not cause any disturbance or allergic phenomena.
How is a bone scan performed?
The examination begins with a preliminary visit aimed at investigating the clinical history, the use of particular drugs and any documentation on the pathology in progress. Metal objects such as necklaces, brooches, earrings, watches, bunches of keys, etc. must be removed to do not interfere with the diagnostic procedure. The investigation proceeds with the administration of the radiopharmaceutical intravenously. At this point, depending on the technique used, some initial images may or may not be detected, as occurs in triphasic scintigraphy; in this case the patient is kept lying on the couch for about twenty minutes. At the end of this first phase it is necessary, in both cases, to wait three / four hours to give the radiopharmaceutical time to fix itself in the bones. During this period, the amount of unbound tracer is filtered by the kidney and expelled with the urine: therefore, in order to facilitate the elimination of non-absorbed radioactivity, therefore superfluous, in the time interval between injection of the radiopharmaceutical and execution of the bone scan, the patient should drink at least half a liter of water (preferably a liter). For the same reason it is important to empty the bladder frequently, even before the scan itself, since a full bladder tends to cover the pelvic bones and does not allow for an accurate examination of this area.
During the waiting period the patient - due to the low radioactivity eliminated - must remain in the ward, without coming into contact with family members or carers. For the same reason, it must emit its own urine in special toilets connected to a tank that discharges the sewage into the sewer only after the radioactivity has disappeared. During urination, the patient should also be careful not to stain clothing or skin with urine.
The actual examination is then performed two / three hours after the injection; the patient is again invited to lie down on the table in the supine position, trying to remain as still as possible.The heads of the chamber range (the device that records the radiation emitted by the patient) are then made to slide along the body for a time ranging from 15 to 30 minutes. To reduce the radioactive exposure of healthcare personnel, the patient will not be in this phase, in direct contact with the service operators, who in any case will be at a minimum distance and able both to observe the patient and to talk to him. In all, therefore, the examination takes about four hours, a time that can vary according to the clinical needs of the patient being treated.
No special preparations are required before a bone scan; fasting is not normally necessary, but good hydration can improve image quality.
At the end of the bone scan, the patient can immediately resume his usual activities, without particular precautions; the doctor can still invite him to drink more fluids than usual to facilitate the elimination of the radiopharmaceutical; after using the toilet it is advisable to run plenty of water and wash your hands thoroughly. In the first 48 hours after the bone scan, always as a precaution (the absorbed radiations are not so dangerous, but it is still right to save unnecessary irradiation), the patient should avoid close contact with small children and pregnant women.
