Skeletal_System

Mode of Uptake of Radiopharmaceuticals

  • Chemisorption:

    • Involves accumulation of labeled phosphate compounds such as [Tc-99m]MDP and [Tc-99m]HDP onto hydroxyapatite crystals in the bone

Factors Affecting Accumulation

  • Accumulation depends on:

    • Local blood flow

    • Osteoblastic activity

    • Extraction efficiency

  • Increased blood supply leads to a blood pool image showing heightened activity

Clinical Indications for Bone Imaging

  • Detection of primary lesions and staging of metastatic disease

  • Differentiation between osteomyelitis and cellulitis

  • Evaluation of infections, avascular necrosis, prosthesis pain, and Paget disease

  • Assessment of bone pain, trauma, fractures, osteoporosis, and other osteopathies

  • Evaluation of arthritis and joint diseases

  • Viability assessment of bone grafts and reflex sympathetic dystrophy evaluation

  • Evaluation of chemotherapy, radiation therapy, and antibiotic responses

Patient History Considerations

  • Inquire about:

    • History or family history of cancer, bone, or kidney disease

    • Previous chemotherapy or radiation therapy

    • Current bone pain, recent falls, fractures, or trauma

    • Presence of pumps, pacemakers, or prostheses

    • Previous scans or x-rays, or any upcoming diagnostic testing

Patient Preparations

  • Recommended actions before imaging:

    • Administer 4-6 glasses of liquid during uptake to reduce radiation exposure and clear RP

    • Encourage frequent voiding prior to imaging

    • Advise movement if possible

    • Remove all metal objects (jewelry, coins, belts) prior to the procedure

Contraindications

  • Situations requiring caution or non-administration of radiopharmaceuticals:

    • Pregnancy or breastfeeding

    • Recent nuclear medicine study

    • Radiopharmaceutical dependent situations

    • No oral contrast (barium) within 24-48 hours prior

Radiopharmaceuticals Used

  • [Tc-99m] hydroxymethylene diphosphonate (HDP)

  • [Tc-99m] methylene diphosphonate (MDP)

  • Half-life: 6 hours

  • Energy: 140 keV gamma

  • Mechanism of uptake: chemisorption (hydroxyapatite)

  • Dose administered: 20-30 mCi

  • Administration route: IV

  • Injection should occur in the opposite side of the area of interest

Bone Scanning Phases

Phase 1: Flow Imaging

  • Technique: 1 second/frame for 60 frames

  • Immediate imaging following bolus injection

  • Focus on Region of Interest (ROI)

Phase 2: Blood Pool Imaging

  • Image acquisition: 120 seconds/image or 200-500k counts/image

  • Timing: Image 5 minutes post-injection

Phase 3: Whole Body Imaging

  • Imaging occurs 3-4 hours after injection

  • High resolution

  • Anterior/posterior views possible

  • Optional SPECT 360° imaging upon request

Phase 4: Delayed Imaging

  • 24-hour delay imaging (uncommon)

  • Compare with initial images to assess radiopharmaceutical uptake in specific patient populations

Procedure Phases

Phase 1

  • Position patient, focus on ROI

  • Inject radiopharmaceutical, initiate imaging immediately

Phase 2

  • Acquire immediate blood pool images of ROI

  • Ensure all extremities are included

Phase 3

  • Patient may leave but must return in 2-4 hours for delayed imaging

  • Reinforce hydration and frequent voiding

Phase 4

  • 24-hour delayed images may be conducted for better uptake assessment

Interpretation of Results

Normal Results

  • Expected findings include:

    • Symmetric uptake with increased activity in joints

    • Kidneys showing faint activity and bladder bright

    • Delayed identification of fractures often takes 3-5 days

    • Bright epiphyseal plates in growing children

Abnormal Results

  • Indicators of abnormal uptake:

    • Asymmetry: areas of increased or decreased activity

    • Super Scan findings correlate with widespread metastatic disease

    • Non-tumor causes include increased uptake from Paget disease and hyperparathyroidism

    • Diminished activity often indicative of osteonecrosis or late-stage cancer

    • Osteomyelitis confirmed by increased uptake patterns across phases

Artifacts in Imaging

  • Common artifacts include:

    • Glove phenomenon and improper injections

    • Gastric or thyroid uptake related to free pertechnetate

    • Issues related to full bladders leading to imaging challenges

Review Questions

  1. What is the mode of uptake for [Tc-99m]MDP in the bone?

    • Options: Phagocytosis, Simple Diffusion, Chemisorption, Active Transport

  2. Chemisorption occurs on the ______ of the bone.

    • Options: Bone marrow, Phosphorus matrix, Hydroxyapatite crystals, Calcium crystals

  3. In what site should the RP be injected for a patient with right carpal tunnel syndrome?

    • Options: Left antecubital fossa, Right antecubital fossa, etc.

  4. What should a patient do post-injection to improve imaging results?

    • Options involving hydration and minimizing stillness

  5. Identify potential issues with obtained imaging results (wrong collimator, renal failure, etc.).

Conclusion

  • Always follow proper procedures and contraindications for safe and effective imaging of the skeletal system.