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Questions and Answers
What is the most common reason for a Superscan in bone imaging?
What is the main reason for minimal renal or bladder activity in bone imaging with 99mTc-MDP?
In the context of bone imaging, what do decreased activity in multiple contiguous vertebral bodies on a PET scan indicate?
What is the radiographic feature seen in the proximal tibia of a teenager with Osteogenic Sarcoma?
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Which type of skeletal involvement is typically seen in a Superscan during bone imaging?
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Why would there be minimal bladder or renal activity identified in a bone scan?
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What is the primary cause of increased activity seen on a bone scan?
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How can one differentiate between radiation therapy defects and metastases on a PET scan?
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In bone imaging, what does 'mottled sclerosis and periosteal reaction' suggest?
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Why is it important to differentiate between radiation therapy defects and metastases in PET scans?
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What is the reason for minimal renal or bladder activity identified in bone imaging with 99mTc-MDP?
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What is the predominant skeletal involvement seen in a Superscan during bone imaging?
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Why does a patient with radiation therapy to the spine exhibit decreased activity in multiple contiguous vertebral bodies on a PET scan?
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In bone imaging, what does mottled sclerosis and periosteal reaction suggest?
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What is the common outcome of a bone scan when a Superscan is observed?
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How can one differentiate a radiation therapy defect from metastases on a PET scan?
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'Osteogenic Sarcoma' involves which feature based on the provided text?
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'Posterior fluorine-18 sodium fluoride positron emission tomography (PET) scan image' indicates involvement primarily in which region?
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'Sagittal and coronal PET/computed tomography scans of the spine' assist in identifying defects due to what cause?
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In Superscan during bone imaging, there is involvement of the entire axial and proximal appendicular skeleton. Diffuse osteoblastic metastases are typically seen from carcinoma of the ______.
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Radiation therapy to the spine can result in decreased activity in multiple contiguous vertebral bodies on a PET scan, which may be mistaken for metastases. These defects are actually due to the radiation therapy, not the presence of ______.
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Osteogenic Sarcoma often presents with mottled sclerosis and periosteal reaction in the proximal ______ of a teenager.
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A bone scan can show increased activity in areas affected by Osteogenic Sarcoma, indicating the presence of ______.
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In bone imaging with 99mTc-MDP, minimal renal or bladder activity is identified because the metastases have accumulated most of the ______.
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Study Notes
Bone Scanning
- Bone scanning is widely used for evaluating various benign and malignant diseases affecting the skeletal system.
- It provides an earlier diagnosis and detects more lesions than planar radiographic procedures.
- The presence of a lesion on a bone scan is non-specific, but its monostotic or polyostotic status and anatomic distribution can provide important clues for differential diagnosis.
Anatomy and Physiology
- Bone is composed of an inorganic mineral phase of crystals bound to protein, largely collagen.
- Normal bone is in a constant state of remodeling, which may be accelerated by pathologic conditions such as fractures, infections, bone tumors, or metastases.
- The skeleton is composed of two parts: axial (skull, spine, and shoulder girdle) and appendicular (upper extremities, pelvis, and lower extremities).
Radiopharmaceuticals
- Bone-seeking radiopharmaceuticals are analogs of particular components of the mineral portion of bone, such as hydroxyapatite, calcium, hydroxyl groups, or phosphates.
- The most widely used radiopharmaceuticals are technetium-labeled diphosphonates (99mTc-MDP), which distribute in the skeleton based on differences in regional perfusion and bone turnover.
- Fluorine-18 sodium fluoride (18F-NaF) is a positron emission tomography (PET) imaging agent that has higher first-pass extraction efficiency and a more favorable bone-to-background tissue ratio than 99mTc-MDP.
Technique
- Planar scans are performed 2-4 hours after injection of the radiopharmaceutical, while single-photon emission computed tomography (SPECT) and PET/CT scans are performed 1-2 hours after injection.
- A three-phase study is performed in patients suspected of having osteomyelitis or cellulitis, which includes a radionuclide angiogram, initial blood pool image, and routine images.
- SPECT imaging is useful for detecting skeletal lesions in patients with specific regional complaints and may establish or better localize an abnormality suspected on routine planar images.
Normal Scan
- A normal scan varies in appearance between children and adults.
- In children, areas of growth in the region of the epiphyses show intense radionuclide accumulation.
- In adults, the quality of the bone scan can be related to age, and older patients may have a higher proportion of poor-quality scans.
Clinical Applications
- Bone scanning is useful for detecting and following skeletal metastases, differentiating between osteomyelitis and cellulitis, determining bone viability, and evaluating fractures difficult to assess on radiographs.
- Whole-body bone scanning is able to survey the entire skeleton on a single study and can demonstrate metastatic lesions much earlier than radiography.
- 18F-NaF PET imaging has higher sensitivity and specificity than 99mTc-MDP planar bone imaging for detecting skeletal metastases.### Tumors and Bone Metastases
- Multiple myeloma is characterized by lytic lesions with decreased vascularity and low osteoblastic activity, making bone-seeking radiopharmaceuticals have a low sensitivity (50% false-negative rate)
- 18F-fluorodeoxyglucose (FDG) has higher sensitivity for lytic lesions and early detection of marrow metastases
- 80% of patients with known neoplasms and significant bone pain have metastases documented by bone scan
- 30% to 50% of patients with metastases do not have bone pain, so it is recommended to scan patients with asymptomatic tumors that have a propensity to metastasize to bone (e.g., breast, lung, and prostate)
Interpreting Bone Scans
- A single lesion is often secondary to benign disease, especially in a rib
- Multifocal areas of increased activity in noncontiguous ribs are likely metastatic disease
- In the spine, multiple foci of linear activity in the vertebral bodies suggest osteoporotic fractures, while lesions extending into the posterior elements or involving the vertebral pedicle are likely metastatic
- Distribution of lesions in multifocal metastatic disease: thorax and ribs (37%), spine (26%), pelvis (16%), limbs (15%), and skull (6%)
Bone Metastases and Treatment Response
- Follow-up bone scans to assess response in patients undergoing treatment for advanced breast and prostate cancer should be interpreted with caution
- 18F-FDG measures tumor metabolism, which decreases with treatment success, while bone-seeking tracers may provide an indirect indication of tumor improvement through repair of adjacent bone
- The "flare phenomenon" is a favorable response to chemotherapy, characterized by increased uptake at involved sites, which can give a false impression of new lesions
Other Causes of Cold Lesions on Bone Scan
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Localized overlying attenuation artifact caused by pacemaker, barium, etc.
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Instrumentation artifact
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Radiation therapy
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Infarction
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Early aseptic necrosis
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Osseous metastases from neuroblastoma, renal cell carcinoma, thyroid carcinoma, anaplastic tumors, etc.
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Generalized diseases such as primary or secondary hyperparathyroidism### Bone Scan Technique
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10 to 20 mCi (370 to 740 MBq) of technetium diphosphonate radiopharmaceutical is injected intravenously for routine planar scans.
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Patient is imaged 2 to 4 hours later, with site of injection recorded.
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Injection site should be distant from suspected osseous pathology to avoid false positives.
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Even slight extravasation of isotope at injection site can cause a focus of increased soft-tissue activity.
Normal Bone Scan
- In children, areas of growth in the region of epiphyses show intense radionuclide accumulation.
- In adults, quality of bone scan can be related to age, with older patients typically having poorer-quality scans.
- Skull, sternum, sternoclavicular joints, acromioclavicular joints, shoulders, iliac crests, and hips are usually well-visualized.
- Increased activity in knees is common in older patients due to arthritic changes.
Clinical Applications
- Detection and follow-up of skeletal metastases
- Differentiation between osteomyelitis and cellulitis
- Determination of bone viability: infarction or avascular necrosis
- Evaluation of fractures difficult to assess on radiographs
- Evaluation of bone pain in patients with normal or equivocal radiographs
- Evaluation of the significance of an incidental skeletal finding on radiographs
- Metastatic disease: 80% of patients with known neoplasms and significant bone pain have metastases documented by bone scan.
Metastatic Disease
- Single lesions are often secondary to benign disease, especially in ribs.
- Multiple foci of increased activity in non-contiguous ribs suggest metastatic disease.
- Lesions extending into posterior elements or involving vertebral pedicle are likely metastatic.
- Regional distribution of lesions for common bone-seeking primary tumors: thorax and ribs (37%), spine (26%), pelvis (16%), limbs (15%), and skull (6%).
- Follow-up bone scans to assess response in patients undergoing treatment for advanced breast and prostate cancer should be interpreted with caution.
Superscan
- Diffuse involvement of the skeleton by metastases can cause a superscan, characterized by decreased renal activity with diffusely increased activity throughout the axial skeleton.
- A superscan can also be caused by metabolic conditions, such as primary or secondary hyperparathyroidism.
- Increased activity primarily in the peripheral skeleton may be seen in hematologic disorders.
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Description
Explore the interpretation of fluorine-18 sodium fluoride positron emission tomography (PET) and PET/computed tomography (CT) scans in clinical scenarios. Understand how imaging findings can aid in the diagnosis and management of patients with metastatic disease.
