What's this ?
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. To this end, radioactive drugs containing technostium-99m-labeled diphosphonates are used, capable of depositing at the bone level reflecting their blood supply (district blood perfusion) and metabolic behavior (given by the degree of activity of osteoblasts, cells specialized in tissue synthesis). bone).
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 special receiver and a computer, to obtain detailed images and to assess any vascular and metabolic alterations. The greater the blood flow and the metabolism of a particular bone region, the greater the concentration of the tracer (see figure).
Bone scintigraphy 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 association with radiological examinations or other imaging methods such as magnetic resonance imaging.
Among the main indications of bone scintigraphy, the identification and follow-up of primitive skeletal tumors and bone metastases, ie localizations of a malignant tumor, stands out. Among those that most frequently give bone metastases we mention prostate, breast, lung, kidney and bladder cancer. Because of its ability to detect anomalies already at an early stage - when symptoms or obvious structural changes in the bone still have to occur - scintigraphy is performed immediately after the diagnosis of neoplasms that are more statistically related to secondary bone localizations. In the presence of metastases, it will therefore be possible to note areas of hypercaptation of the tracer (darker); however, remembering the poor 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 neoplasia, bone scintigraphy allows to evaluate the effects of the therapeutic intervention undertaken (chemotherapy or radiotherapy).
Additional indications for bone scintigraphy are represented by the recognition of osteo-articular inflammatory pathologies, such as rheumatoid arthritis, which involve sites that are not well explored radiologically (eg the joints), micro-fractures (such as stress), necrosis of the femoral head, osteomyelitis (diabetic foot), pain relief in orthopedic prostheses, pain assessment in patients with normal radiography, algoneurodystrophies and assessment of the vitality of bone implants.
Is the exam painful? What are the risks involved? Are there any contraindications?
Bone scintigraphy is a simple and painless technique, although the radiopharmaceutical must be administered intravenously. The doses of isotopes 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. For precautionary purposes, moreover, in women of fertile age the scintigrafia is generally carried out within the ten days following the beginning of the last menstruation, so as to exclude the risk of a pregnancy in course. During lactation some radioactive substances may pass into breast milk; therefore, at the discretion of the physician specialized in nuclear medicine, scintigraphy can be postponed or performed unless suspension of breastfeeding is 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 agents and as such do not cause any disturbance or allergic phenomena.
How is bone scintigraphy performed?
The examination begins with a preliminary visit to investigate 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. they must be removed so as not to 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. After this first phase, in both cases it is necessary to wait three to four hours to allow the radiopharmaceutical to settle in the bones. During this period, the proportion of unbound tracer is filtered by the kidney and expelled with the urine: therefore, in order to facilitate the elimination of the non-absorbed, therefore superfluous, radioactivity in the time interval between the radiopharmaceutical injection and the execution of bone scintigraphy, the patient should drink at least half a liter of water (better a liter). For the same reason it is important to empty the bladder frequently, even before the same scintigraphy, since a full bladder tends to cover the bones of the pelvis and does not allow accurate examination of this area.
During the waiting period the patient - due to the albeit low radioactivity eliminated - must remain in the ward, without coming into contact with relatives or carers. For the same reason, he must emit his urine in special toilets connected to a tank that introduces sewage into the sewer only after the disappearance of radioactivity. During urination the patient must also be careful not to stain clothing or skin with urine.
The actual exam is then performed two / three hours after the injection; the patient is again invited to lie down on the couch in a supine position, trying to remain as still as possible. The heads of the gammacamera (the device that records the radiation emitted by the patient) are then made to flow along the body for a variable time ranging from 15 to 30 minutes. To reduce the radioactive exposure of health personnel, the patient will not, at this stage, be 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, which can vary depending on the patient's clinical needs.
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 bone scintigraphy, the examiner can immediately resume his usual activities, without special precautions; the doctor can, however, invite him to drink more fluids than usual to facilitate the elimination of the radiopharmaceutical; after using the toilet it is good to let the water flow thoroughly and wash your hands thoroughly. In the first 48 hours after bone scintigraphy, again as a precautionary measure (the absorbed radiation is not so dangerous, but it is still safe to save unnecessary radiation), the patient should avoid close contact with small children and pregnant women.
