TRIPLE PHASE BONE SCAN

Question 1

Bone-seeking Radiopharmaceuticals

Answer 1

• Available since early days of nuclear medicine.
• Example: Phosphonates studied by Subramanian et al. in 1971.
• Technetium 99m-methylene diphosphonate (Tc99m-MDP) developed in 1975.
• Predominant radiotracer for skeletal scintigraphy

Question 2

Uses of Bone-seeking Radiopharmaceuticals

Answer 2

• Studied for infection, tumor, and hardware complications.
• Tc99m-MDP injected intravenously by clinicians.
• Imaging typically done 2 to 4 hours post-injection.

Question 3

Triple-phase Bone Scan

Answer 3

• Additional imaging method for specific cases.
• Provides better identification of pathology.
• Involves imaging at earlier time points than standard scan.
• Enhances diagnostic accuracy in certain situations.

Question 4

Preparation for Bone Scintigraphy

Answer 4

• Patients should arrive well hydrated and wear clothes without metallic objects.
• Procedure duration: 3 to 6 hours.
• Patient should void before the study; if catheterized, the catheter should not be clamped.

Question 5

Radiotracer and Imaging Process

Answer 5

• Radiotracer: Usually methyl diphosphonate (MDP) or hydroxydiphosphonate (HDP) complexed with Technetium 99m.
• Administered dose: 20 to 30 mCi (740 to 1110 MBq) for adults.
• Imaging begins immediately after injection.
• Dynamic imaging (1 to 3 seconds per frame) shows relative perfusion (flow phase).

Question 6

Imaging Phases

Answer 6

• Flow Phase: Demonstrates perfusion characteristics immediately after injection.
• Blood Pool Phase: Shows blood pool accumulation in soft tissues and bones.
• Delayed Phase: Obtained 2 to 3 hours post-injection, evaluates tracer accumulation and clearance in bones and soft tissues.
• SPECT Imaging: 3D imaging for complex anatomical localization, often fused with CT for precise localization.

Question 7

Indications for Three-Phase Bone Scanning

Answer 7

• Scope: Narrower than traditional single delayed phase imaging.
• Includes:
  Evaluation for osteomyelitis:
  High sensitivity (approx. 95%) detecting changes early.
  Differentiation between osteomyelitis and cellulitis:
  Shows increased activity in all phases for osteomyelitis.
  Complex regional pain syndrome (CRPS):
  Demonstrates increased perfusion and characteristic patterns on delayed imaging.

Question 8

Additional Indications

Answer 8

• Evaluation of inflammatory arthritides: Improved diagnostic accuracy with perfusion and blood pool phases.
• Evaluation of orthopedic prosthetic infection versus loosening: Useful screening tool despite variable accuracy.
• Evaluation of myositis ossificans: Shows non-specific uptake early, with increased uptake on delayed phase.

Question 9

Normal and Critical Findings in Three-Phase Bone Scanning

Answer 9

Flow Phase:
-Normal: Prompt and symmetric blood flow.
-Abnormal (e.g., infection): Asymmetric blood flow to affected area.
Blood Pool Phase:
-Normal: Symmetric radiotracer activity.
-Abnormal (e.g., infection): Disproportionate activity in affected region.
Delayed Phase:
-Normal: Activity throughout osseous structures with cleared soft tissue activity (washout).
-Abnormal: “Superscan” indicates diffuse malignant metastatic disease.

Interpretation Tips:Knowledge of normal radiotracer distribution crucial

Positive Findings:
Intense, focal activity outside normal areas suggests pathology.

Question 10

Pathological Conditions Detected by Three-Phase Bone Scanning

Answer 10

Conditions Showing Positivity:
-Osteomyelitis, complex regional pain syndrome, acute fractures, orthopedic prosthesis abnormalities, inflammatory arthritides, immature myositis ossificans, aggressive tumors.
Flow and Blood Pool Phase Findings:
-Positive in soft tissue abnormalities (e.g., cellulitis, sarcoma).
-Similar appearance in osteomyelitis and cellulitis but different underlying causes of increased blood pool.
Delayed Phase Findings:
-Increased activity with minimal soft tissue involvement suggests bone-confined pathology (e.g., shin splints, osteoblastic metastasis).

Question 11

Interfering Factors in Three-Phase Bone Scanning

Answer 11

Medical Conditions affecting blood flow:
* Example: Advanced vascular atherosclerotic disease leading to decreased flow.
* Result: Abnormal activity in affected areas during flow and blood pool phases.
Renal Function:
* Poor renal function can lead to soft tissue activity in delayed phases.
* Limits visualization of bony structures; 24-hour delayed phase may be used.
Urine Contamination:
* Can lead to apparent decreased activity in osseous structures.
* May mimic pathology if overlying bones.
Free Technetium:
* Occurs due to poor labeling efficiency (>5%).
* Localizes to salivary glands, thyroid, and stomach, confounding bone imagi

Question 12

Complications and Considerations

Answer 12

Allergic Reactions:
* Rare but possible with radiopharmaceuticals.
* Generally mild; precautions include patient history review.
Extravasation Risk:
* Potential pain, redness, swelling at injection site.
* Increased risk of cellular damage from radiation exposure.

Question 13

Radiotracer Clearance and Radiation Dose

Answer 13

Radiotracer Clearance:
* Predominantly cleared by the kidneys.
* Instruct patient to void frequently post-injection to minimize bladder dose.
Radiation Dose:
* Average dose for skeletal scintigraphy: 4.2 mSv.
* Approximately half the dose of an average abdominal CT scan.

Question 14

Monitoring and Potential Side Effects

Answer 14

Side Effects:
* Methyl diphosphonate may cause low blood pressure in some patients.
* Monitor patient post-injection and during imaging for safety.

Question 15

Breastfeeding Considerations

Answer 15

Breastfeeding and Radiotracers:
* Technetium 99m tagged radiotracers excrete into breast milk.
* Instruct breastfeeding patients to use formula or stored milk for 24 hours post-study.
* Advise pumping and discarding breast milk during this time.

Question 16

Clinical Significance of Three-Phase Bone Scan

Answer 16

Differentiation:
Helps differentiate between cellulitis and osteomyelitis.
Complex Regional Pain Syndrome (CRPS):
Assists in diagnosis by demonstrating characteristic patterns.
Inflammatory Arthritides:
Improves diagnostic accuracy with perfusion and blood pool phases.
Orthopedic Prostheses:
Evaluates hardware loosening versus infection.
Heterotopic Ossification:
Assesses maturity of foci.