Bone Scan Protocol and Imaging Techniques

Bone Scan Protocol

  • Radiopharmaceutical(s):

    • Adult Dose: 99mTc-MDP 500-1110 MBq
    • Can be increased to 11-13 MBq/kg for markedly obese patients (refer to BMI chart)
    • Pediatric Dose: 9-11 MBq/kg
    • Typical dose: 170-210 MBq
    • Minimum dose: 20-40 MBq
    • Maximum dose: not exceeding the maximum for a healthy adult.

  • Indications:

    • Bone tumors (primary/metastatic)
    • Osteomyelitis
    • Bone infarct
    • Reflex sympathetic dystrophy
    • Stress fractures/stress reaction
    • Therapeutic response to treatment
    • Arthritides
    • Avascular necrosis
    • Unexplained bone pain
    • Bone graft viability
    • Metabolic bone disease

Three Phase Bone Scan

  1. Blood Flow Phase (Vascular Phase):
    • Dynamic acquisition (3 sec/frame for 60 sec total)
  2. Blood Pool Phase (Tissue Phase):
    • Planar static image acquired immediately after blood flow for typically 2 min duration.
    • Multiple blood pool images may be acquired.
    • Blood pool images must be completed within 10 min post-injection of tracer.
  3. Delayed Bone Scan Phase (Skeletal Phase):
    • Planar or tomographic images acquired 2-4 hours post-injection.
    • Delayed images, if necessary, can be obtained up to 24 hours post-injection.
  4. Fourth Phase:
    • Less frequently performed, specific protocols used for patients with poor renal clearance.

Single Site Bone Scans vs Whole Body Bone Scans

  • Single Site Bone Scans:

    • Always 3-phase, flow and blood pool performed for all indications.
    • Injection technique varies depending on region of interest (ROI).
    • Static images (128x128 or 256x256 matrix required).
    • Required counts:
    • 500K-1M for thorax and abdomen
    • 250K-400K for skull/large joints
    • 150K-250K for extremities

  • Whole Body Scans:

    • Flow and blood pool may not be required for all indications.
    • Positioning crucial; standard anatomical position preferred with arms at sides and palms inward.
    • Aggregated counts: 1.5 million total.

Injection Site for Radiopharmaceutical

  • Injection site should be distant from any suspected skeletal pathology.
  • Common injection technique involves straight injection.
  • For upper extremity osseous pathology:
    • Butterfly injection with saline flush
    • Angiocatheter with saline flush

Patient Positioning

  • Single Site: Centered in FOV, patient in Ant/Post position except for hands/feet.
  • Whole Body: Patients flat on imaging bed, arms down, feet secured.
    • Avoid torso/hip rotation to prevent artifacts in imaging.

Fracture Healing and Imaging

  • Bone scans can detect fractures as early as 24 hours post-trauma in children and may take longer in adults.

  • Fractures types include:

    • Fragility Fracture: Result from weakness
    • Occult Fracture: Hidden fracture
    • Pathological Fracture: Occurs in abnormal bone
    • Stress Fracture: Resulting from repeated stress

  • Healing Phases:

    • Acute Phase: Increased tracer activity around fracture site.
    • Subacute Phase: More localized activity.
    • Healing Phase: Decrease in tracer uptake, may take months to years to normalize.

Factors Affecting Fracture Healing

  • Patient age, weight-bearing, fixation, nerve damage, blood supply, infection, steroid use, and extent of fracture can all impact healing.

Additional Notes on Non-Accidental Pediatric Fractures

  • Children with unexplained multiple fractures or fractures that seem disproportionate to the event should raise suspicion for abuse.
  • Common locations for concern: ribs, diaphysis of long bones.

Image Quality Critique

  • Assess patient positioning, tracer uptake, image display intensity, artifacts present, and required annotation.
  • Evaluate the overall quality of the image to determine if it meets diagnostic standards.