BONE SCINTIGRAPHY: WHAT IT IS FOR AND NORMAL VALUES - MEDICINE - 2025

The bone scintigram is a special imaging study that allows determining the presence of abnormalities in the skeleton. It uses nuclear medicine techniques and small amounts of radioactive contrast to "stain" the bones, which are then photographed using equipment very similar to those used to obtain X-rays.

This contrast - or more correctly, this tracer isotope - travels through the blood and is deposited in the bones. There it gives its radioactive capacity to bone tissue in the form of gamma rays, which are then detected by special sensors located in scintigraphy equipment. These devices produce an image similar to an X-ray.

If there are alterations in the bones, whatever their cause, the uptake of the tracer isotope is modified. This change can be an increase in uptake (known as hyperuptake) or decrease (known as hypouptake). The results of these images are analyzed by a radiologist or other experienced specialist.

What is it for?

The bone scintigraphy has multiple applications in the medical world. Most of these are direct injuries to the bone or other systemic diseases that can affect the skeleton. The most important reasons for the indication of this study are infectious, oncological and traumatic processes.

This study has a very high sensitivity when there are alterations in bone metabolism. It can even detect early bone lesions when no significant clinical manifestations or apparent lesions have even appeared on classical radiographs.

One of the most frequent uses of the bone scintigraphy is the global visualization of the human skeleton. It is one of the few studies that allow this possibility, helping health professionals to evaluate all of the bones without the need to review several plates as occurs with traditional X-rays, CT scans or MRIs.

Infectious processes

Osteomyelitis (infection of the bone) is the main indication of the bone scintigraphy. Since the appearance of phosphates and polyphosphates, nuclear imaging has become essential in the diagnosis and control of bone infections, providing very valuable information to treating physicians.

The most requested test is the three-phase scintigraphy. Depending on the time elapsed since the administration of the isotope, the perivascular space can be evaluated in a first phase, the bone fluid space in the second phase, and in the third and last phase the bone is evaluated as such.

Cancer

Scintigraphy is the standard procedure for the detection of bone metastases generated by any primary tumor. It is much more sensitive when there are osteolytic lesions with a high osteoblastic response; this means that in lymphomas or several solid tumors, with poor osteoblastic response, it can give imprecise information.

However, when used in conjunction with MRI, it is the ideal study to evaluate metastases.

It is also part of the usual protocol in primary bone tumors, although it is not the initial study as it does not allow the evaluation of the surrounding soft tissues or the necessary anatomical measurements.

Trauma

Numerous are the indications that the bone scintigraphy has in the trauma world. One of the advantages is its use in early and hidden lesions that, despite having clinical manifestations, cannot be detected with classical radiological studies. It is also combined with MRI for better results.

Sports injuries can be detected through this study. For a long time it was the quintessential imaging exam when stress fractures or medial tibial stress syndrome were suspected, but has recently been superseded by the same MRI and its specialized variants.

Other clinical uses

In other medical conditions, a bone scan may be indicated. Among the most important we have the following:

Rheumatology

Arthritis, plantar fasciitis, polymyositis, and Paget's disease.

Metabolic diseases

Hyperparathyroidism, osteomalacia, and acromegaly.

Pediatrics

Osteochondritis of the hip, bone infarcts due to sickle cell disease, osteoid osteoma.

Normal values

As it is not a laboratory test, there is no range of values ​​or levels considered normal. Evaluation of the results is based on the two conditions mentioned above: hyper-uptake or under-uptake of reactive tracer isotopes.

Hyper-uptake

Most of the diseases that affect the bone produce hyper-uptake of the radioactive isotope used. This is due to the normal periosteal and osteoblastic inflammatory response that is generated in the bone tissue in the event of an attack, which is a factor that favors uptake.

The vast majority of oncological diseases that cause bone lesions or metastases - with the exception of lymphoma and some solid tumors - generate hyperuptake of the tracer. The same occurs with infectious processes, in which the image is conclusive for the diagnosis of osteomyelitis.

Hypocaptation

Traumatological injuries that generate a solution of continuity in the bone, especially if there is vascular damage, can cause local under-uptake with perivascular or perivascular hyper-uptake. It is evident that, in the absence of adequate blood supply, the isotope does not reach the site of injury.

Some benign tumors such as cysts or osteomas, as they are not vascularized, are hypocaptant lesions. This phenomenon also occurs when chronic injuries are not treated correctly and the bone tissue becomes devitalized.

As there is no osteoblastic reaction or production of new bone, there is no uptake or subsequent generation of gamma rays.

Precautions

In order to carry out this study, certain caution must be exercised in some cases, even with absolute contraindications.

Allergies and drug interactions

Although extremely rare, allergic reactions to radiopharmaceuticals can occur. They are usually mild and do not generate complications, but they should not be ignored.

Isotope interactions have also been described with certain medications, some commonly used such as corticosteroids, nifedipine, and iron.

Local reactions

Administration of a tracer isotope can cause pain, phlebitis, and reddening of the skin. This reaction is highly dependent on the infusion rate and the size of the vessel into which the catheter was inserted. The discomfort disappears quickly and does not limit the performance of the study.

Tissue injury

There is always some risk of injury and cell death when a radioactive isotope is administered, despite its low radiation level. It happened more frequently with phosphates, but today tracers are much safer.

Pregnancy and breastfeeding

The vast majority of authors recommend that the study be delayed until the end of pregnancy and lactation.

If the clinical condition of the woman makes it necessary to carry out the study, she must be aware of the possible complications regarding her health and that of the fetus. The chances of miscarriage, stillbirth, and birth defects are high.

References

1. Radiological Society of North America (2018). Skeletal Scintigraphy (Bone Scan). Recovered from: radiologyinfo.org
2. Van den Wyngaert, T et al. (2016). The EANM practice guidelines for bone scintigraphy. European Journal of Nuclear Medicine and Molecular Imaging, 43: 1723-1738.
3. Wenham, Claire; Grainger, Andrew and Conaghan, Philip (2015). Imaging of osteoarthritis. Rheumatology, Sixth Edition, Volume 2, 1483-1491.
4. Wikipedia (last edition 2018). Bone scintigraphy. Recovered from: en.wikipedia.org
5. Van der Wall, Hans et al. (2012). Bone Scintigraphy in Trauma and Sport Injuries. Radionuclide and Hybrid Bone Imaging, 481-521.
6. Pineda, Carlos; Espinosa, Rolando and Pena, Angelica (2009). Radiographic Imaging in Osteomyelitis: The Role of Plain Radiography, Computed Tomography, Ultrasonography, Magnetic Resonance Imaging, and Scintigraphy. Seminars in Plastic Surgery, 23 (2): 80-89.
7. Hanh, S et al. (2011). Comparison of FDG-PET / CT and bone scintigraphy for detection of bone metastases in breast cancer. Acta radiológica, 52 (9): 100-1014.