Skeletal Scintigraphy By Ahmed Ramadan Assistant Lecturer Clinical Oncology &Nuclear Medicine Department Mansoura University

Bone Scan Introduction – Definition – Advantages vs Disadvantages Anatomy Techniques – Radiopharmaceutical – Mechanism of uptake – Imaging Technique Interpretation of bone scan Clinical applications

Definition A bone scan is a test that detects areas of increased or decreased bone activity by injecting a certain radiopharmaceutical i.e. Tc-99m MDP. This may indicate bone injury or disease.

Advantages VS Disadvantages Needs radiopharmaceuticals & gamma camera not widely available Low specificity Cost is high. Whole-body evaluation in one test/ same rad exposure. Low radiation exposure Sensitive evaluation

Anatomy

Anatomy Axial skeleton [head and trunk] Skull Thorax (ribs & sternum), Spines (includes sacrum & coccyx) Appendicular skeleton Shoulder girdle: clavicle & scapula Upper Extremity Pelvic girdle Lower Extremity

Radiopharmaceuticals Bone-seeking agents are analogs of calcium, phosphates. The most widely used Radiopharmaceuticals is Tc-99m labeled diphosphonates Tc-99m Methylene diphosphonate (Tc-99m MDP) Tc-99m MDP

Tc-99m MDP Used within 4 hrs after preparation. Labelling yield: > 95%, avoid injecting air into the vial »»» oxidation of Tc »»» oxidized Tc »»» poor tagging of phosphates. High target/bcg ratio within 2-3 hrs. with 50-60% of the injected activity localizing in bone (max sk uptake at 5 hrs) Rapid renal clearance Renal Impairment: increased soft tissue activity, poor image quality, delayed excretion, higher radiation exposure due to retained high activity

Pathophysiology Tc-99m MDP uptake depends on osteoblastic and osteoclastic activity. Increased uptake Decreased uptake osteoblastic activity osteoclast activity pure lytic lesion

Pathophysiology Possible Mechanism of Increased Uptake: Increased blood flow Increased osteoid formation Increased mineralization of osteoid Interrupted sympathetic nerve supply

Technique Preparation: None Injection of Tc-99m 20-25 mCi IV, (250 uCi/Kg) for children, good hydration afterwards & frequent voiding Wait for about 2-3 hrs to start imaging, avoid contamination Empty bladder prior to scanning Change the cloth and remove things likely cause artifact.

Poor Image Quality Renal impairment Decreased cardiac output Dehydration Extravasation of the radiopharamceutical Aging. Underdosage of the radiopharmacetical. Obesity.

Imaging Acquisition Routine whole-body bone scan 3-phase bone scan imaging SPECT & SPECT/CT imaging

Routine Bone Scan Imaging Whole-body planar imaging in anterior and posterior projection Additional static images if required eg. Oblique or additional spot views(squat view)

3-phase bone scan imaging Phase 1; Vascular phase: 60 s dynamic immediately post injection Phase 2; Soft-tissue (blood-pool) phase: 5 min post injection. Phase 3; Delayed (bone) phase: 2-3 hr post injection. Indications: • Infection: DDx acute osteomyelitis vs cellulitis • Avascular necrosis • Tumors: primary tumor Vascular phase delayed 2-3hr Soft-tissue

Indications Neoplastic disease: Primary bone tumors & Bone metastasis – Staging for malignancies that have high incidence of bone metastasis eg. cancers of prostate, breast, lung, neuroblastoma. – Unexplained bone pain in a patient with known malignancy (neg X-ray) – Unexplained bone pain in a patient with no history of malignancy. Trauma: Fracture/ Stress injuries (eg, stress fracture, shin splints). Infection:(osteomyelitis) Avascular necrosis Arthritis:Degenerative changes Metabolic & Endocrine disorders: (eg, Paget’s Disease, Hyperparathyroidism) Bone marrow diseases: Sickle cell disease

Interpretation Lytic lesions must cause at least 30%- 50% demineralization to be visible by radiography. Bone scan is much more sensitive in detecting metastatic lesions in majority of cancers. Results Normal- symmetrical Abnormal • Increased uptake • Decreased uptake • Mixed

Normal Whole Body Bone Scan The scan on the right shows normal distribution of the tracer, mild normal soft tissue activity, excretion from the kidneys into the bladder, scoliosis and mild associated degenerative changes in the lumbar spine.

Normal Pediatric Bone Scan Normal pediatric bone scan showing increased tracer activity in the epiphysis (growth plates).

False negative bone scan Multiple myeloma Renal cell carcinoma Thyroid carcinoma Neuroblastoma Highly aggressive anaplastic tumors

False positive bone scan Contamination Physiologic activity eg. urine along urinary tract. In patients with known malignancy and no benign radiographic explanation for a bone scan lesion, additional workup is necessary. False positive bone scan is also high when a single lesion is seen e.g: • A single spinal lesion on bone scan has a 10%-20% chance of representing a metastatic focus. • A single rib lesion on bone scan has a 10% chance of representing a metastatic focus. Lesions in consecutive ribs are almost always traumatic in origin. Lesions in nonconsecutive ribs have a high chance of representing metastatic disease. • A single sternal lesion on bone scan in a patient with breast cancer, on the other hand, has an 80% chance of representing a metastatic focus. • In the case of prostate cancer, PSA level < 10 μg/L is a good predictor of a negative bone scan.

Bone Metastases Disseminated Bone Metastasis from breast cancer. Lesions in the vertebral bodies and the femur neck, which are at the risk for pathological fracture should be mentioned separately.

Metastatic Superscan Diffuse metastatic disease, from prostate prostate*, breast, lung cancer. In a super scan from bone metastasis, there is intense diffuse uptake in the skeleton (in the distribution of active marrow) and minimal activity in the kidneys, bladder, and the soft tissues.

Metabolic Superscan Diffusely increased bone activity (increased bone vs soft tissue activity) causes: Metabolic bone disease hyperparathyroidism. Hematological diseases Renal osteodystrophy.

Flare phenomenon The bone scan appears worsening, or even shows new lesions, during the first several months following chemotherapy, orchiectomy and radiation therapy, while the patient's clinical condition improves A repeat bone scan will show marked improvement after several months. The flare phenomenon occurs in up to 20% of patients; depending on tumor type, therapeutic regimen and the interval between therapy and the bone scan. This phenomenon may persist upto 6 months

Primary bone tumor affecting right upper tibia. Osteosarcoma Primary bone tumor affecting right upper tibia.

Degenerative Changes Joints: Arthritis – Knees & Ankles Spine: Spondylosis & Disc prolapse –Dorsal Spine –lumbar Spine

Delayed images from a bone scan showing fracture of the left 6th rib. Traumatic Fracture Whole body bone scan showing multiple occult bilateral rib fractures (arrowed). The linear alignment is typical of fractures. Delayed images from a bone scan showing fracture of the left 6th rib.

Stress Fracture fractures will not be evident on initial More than 80% of stress fractures will not be evident on initial radiographs, while the sensitivity of bone scan approaches 100% Delayed images from the bone scan of a runner showing stress fracture at the right distal tibial medial cortex.

(cold) area surrounded by an area of increased activity Avascular Necrosis Diagram shows how a subcapital fracture of the femoral neck cuts off othe blood supply to the femoral head, resulting in osteonecrosis Central Photopenic (cold) area surrounded by an area of increased activity

Hypertrophic Pulmonary Osteoarthropathy Hypertrophic Pulmonary Osteoarthropathy (HPOA), from lung cancer. Linear cortical uptake can also be seen with shin splints.

Paget’s Disease of The Bone Paget’s disease Involvement of L4 resembles the Mickey mouse sign.

Sickle Cell Disease Bone marrow expansion from anemia (increased bone vs soft tissue activity), splenic uptake from repeated infarctions and calcifications. Increased uptake can be seen in the kidneys from iron overload, from multiple transfusions.

Osteomyelitis Acute Osteomyelitis of the right calcaneus positive on all three phases.

Three Phase Bone Scan In Infection

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