SCINTIGRAFIA OSOASA TIFAZICA

Triphasic Bone Scan

- See: Technetium 99m

- Discussion:    - initial dynamic images are aquired over the area of concern and then followed immediately afterwards by static images obtained over            longer periods of time;

- First Phase:    - demonstrates perfusion to a lesion;    - first phase, the nuclear angiogram or flow phase, consists of serial 2- to 5-sec images of the area of suspected osteomyelitis that are             obtained during injection of the radiopharmaceutical.    - classically, with cellulitis, diffuse increased uptake occurs in first two phases, but uptake is normal or diffusely increased in third phase;    - osteomyelitis causes focally increased uptake in all three phases;

- Second Phase:    - relative vascularity;    - second phase, the blood-pool image, is obtained within 5 min after injection;           - in areas of inflammation, capillaries dilate, causing increased blood flow and blood pooling.    - classically, with cellulitis, diffuse increased uptake occurs in first two phases, but uptake is nl or diffusely increased in third phase;    - osteomyelitis causes focally increased uptake in all three phases;    - first phase characterizes the blood flow to the area, while the 2nd visualizes the blood pool;           - these 2 early phases act to characterize degree of inflammation and hyperemia that may be present;           - diseases such as degenerative disease, healing fractures, non- infected prosthesis with loosening, well treated osteomyelitis, may have                    little abnormal activity on the early phases in spite of increase uptake on delayed images;           - it may be difficult to distinguish osteomyelitis from diabetic osteoarthropathy, which are often abnormal on all 3 phases;           - in contrast, a soft tissue infection classically appears only in early phases, with little abnormal focal bone activity seen on delayed images;

- Third Phase:    - demonstrates relative bone turnover associated w/ a lesion;    - 3rd phase, bone image, is obtained about 3 hr later, when urinary excretion has decreased the amount of the radionuclide in soft tissues.    - if present, diffuse incr uptake in third phase is probably due to regional hyperemia caused by cellulitis;    - osteomyelitis causes focally increased uptake in all three phases;

- Peds:    - In neonates, the sensitivity of the three-phase bone scan decreases;    - neonates with osteomyelitis have falsely normal or cold defects on three-phase bone scans 22-68% of the time;    - cold lesion on 3rd phase may be caused by subperiosteal abscess;    - in children, large portion of blood supply to the bone comes from periosteal vessels, and these are apparently disrupted by the            subperiosteal abscess;    - when clinical findings strongly suggest osteomyelitis, but findings on three-phase bone scan are normal, then consider gallium scan