RadiopharmaceuticalRadiopharmaceutical

Tc-99m diphosphonate Tc-99m diphosphonate 140 KeV; T1/2 6 hrs140 KeV; T1/2 6 hrs Excreted by glomerular filtration in kidneysExcreted by glomerular filtration in kidneys

– 40% by 4 hrs; 80% by 24 hrs (in normals)40% by 4 hrs; 80% by 24 hrs (in normals) Normal renal function clears soft tissue activity, Normal renal function clears soft tissue activity,

which improves image quality b/c of improved which improves image quality b/c of improved target/backgroundtarget/background

3-4 hrs after injection is a good compromise 3-4 hrs after injection is a good compromise between remaining radioactivity and background between remaining radioactivity and background reductionreduction

The Bone ScanThe Bone Scan

Is a map of osteoblastic activity in Is a map of osteoblastic activity in response to a variety of conditionsresponse to a variety of conditions

Complements anatomic studiesComplements anatomic studies Blood flow is required to deliver the Blood flow is required to deliver the

radiopharmaceutical to the radiopharmaceutical to the extracellular space around osteoblastsextracellular space around osteoblasts

Osteoclastic function not measured by Osteoclastic function not measured by bone scanbone scan

Three-Phase Bone ScanThree-Phase Bone Scan

Early arterial flow seconds after injectionEarly arterial flow seconds after injection Increased blood pool a few minutes Increased blood pool a few minutes

before bone labeling beginsbefore bone labeling begins Intense delayed labeling >3 hrs after Intense delayed labeling >3 hrs after

injectioninjection Requires several days before Requires several days before

developmentdevelopment Radiographic changes may not be seen Radiographic changes may not be seen

for 10-14 daysfor 10-14 days

Three-Phase DDxThree-Phase DDx

OsteomyelitisOsteomyelitis RSD (aka Complex Regional Pain RSD (aka Complex Regional Pain

Syndrome)Syndrome) Trauma/FractureTrauma/Fracture Cellulitis (2-phase +)Cellulitis (2-phase +)