Bone isotope scans are a sensitive method for detecting bone abnormalities. They involve injecting radioactive tracers that are drawn to bone tissue, allowing areas of abnormal bone metabolism to be visualized. Common clinical uses include detecting bone cancer metastases, stress fractures, and infections like osteomyelitis. The scan may reveal single or multiple problematic areas and provides diagnostic information beyond plain X-rays.

1. BONE ISOTOPE SCAN الدكتور قصي المقبل أستاذ مشارك - قسم الأشعة والطب النووي كلية الطب - جامعة العلوم والتكنولوجيا الأردنية

2. Introduction Bone scan is one of the most commonly performed procedures in nuclear medicine. Bone scan often provides an earlier diagnosis and demonstrates more lesions than are found by radiographic procedures.

3. Sensitivity and Specificity Bone scan is very sensitive study but it is not specific. Although findings on bone scan are non-specific, its monostotic or polyostotic status and anatomical distribution can provide important clues to the differential diagnosis.

4. Radiopharmaceuticals They are bone seeking agents. They are labeled with Tc99m. They are phosphate analogs. Most commonly used one is HDP (Hydroxy Methylene Diphosphonates). They are given intravenously.

5. Mechanism of Localization Phosphate groups bind to the hydroxyapatite [Ca3(Po4)2] structure of bone tissue by a mechanism called chemisorption. The hydroxyapatite structure of the bone is exposed during bone remodeling. So, more radiopharmaceutical will deposit in that region giving “hot” area. 50-60% of injected dose localized on bone, remain dose is cleared by kidneys.

6. Whole body bone scan This is the bony phase of bone scan. Inject radiopharmaceutical and image in 2-4 hours. When we say bone scan, we usually mean whole body bone scan.

11. Three Phase Bone Scan It is done to see if there is soft tissue hyperemia. First phase is the perfusion phase or vascular phase. Second phase is the blood pooling phase or soft tissue phase. Third phase is the bony phase.

12. First Phase 30-60 dynamic images are usually obtained over 1 minute immediately after injection. This is radionuclide angiography and gives an idea about the local vasculature. During the first minute after injection, injected dose is still intravascular.

13. Perfusion

14. Second Phase Static image is obtained in 5 minutes after dose injection. Within 5 minutes post injection, radiopharmaceutical moves from intravascular space to extravascular space (soft tissue). It gives idea about soft tissue edema.

15. Blood Pool

16. Hyperemia If there is focal increased activity in the first and second phases, hyperemia or acute inflammatory process is present .

17. Third Phase It is the bony phase image obtained in 2-4 hours post injection. It is the same as whole body bone scan.

18. Clinical Applications Malignancy 1- Primary bone cancer 2- Secondary metastatic bone disease Osteomyelitis Stress fractures

19. Primary Bone Malignancy (Sarcomas) MRI provides more exact information regarding tumor extent, particularly in soft tissue. So, bone scan is not a diagnosis image in primary bone tumors.

20. Bone sarcomas-cont.. Bone scan is a staging and restaging image in bone sarcomas. It is performed to see if there is bone metastatic disease (bone to bone). 40 – 50% of patients with either Ewing’s sarcoma or osteosarcoma develop osseous metastases within 2 years of presentation.

23. Metastatic Bone Disease Bone scan is an extremely important tool in decision making during management of cancer patients. Any cancer potentially could cause bone metastatic disease. However, prostate, breast and lung cancers have propensity to metastasize to bone.

24. Metastatic Bone Disease and Bone Pain About 80% of patients with known cancer and bone pain have metastases documented by bone scan. 30 – 50% of patients with metastatic bone disease do not have bone pain.

25. Metastatic Bone Disease and Image Findings The hallmark of metastatic bone disease is multiple foci of increased osteoblastic activity in bony skeleton. However, single lesion could be also metastatic.

31. Stress Fractures It is often difficult to visualized on a plain radiograph. Fractures may be identified by bone scan as early as 24 hours after occurrence. 3-phase bone scan is usually done. There is hyperemia and osteoblastic process (three phases are positive).

32. Stress Fracture Blood Pool Anterior Posterior Anterior Posterior Left Lat Right Lat Left Lat Right Lat 2 hour delay

33. Stress Fracture

34. Acute Osteomyelitis Early plain radiography signs of osteomyelitis are non-specific. 3-phase bone scan is usually the procedure of choice to differentiate between osteomyelitis and cellulitis.

35. Acute Osteomyelitis-cont.. If first and 2nd phases are positive (hyperemia) with normal third phase, diagnosis would be cellulitis. In acute osteomyelitis all 3-phases are positive (hyperemia and osteoblastic process in the bone).

36. Perfusion

37. Blood Pool

38. Whole Body Bone Scan