Bone-Seeking Radionuclides: AnIn VivoStudy of Factors Affecting Skeletal Uptake

Abstract

The factors governing the skeletal uptake of bone-seeking radionuclides in vivo have not been clearly defined. In this study, the effects of alteration in blood flow (thermal-induced) and alteration in osteogenesis (ricket-induced) on the skeletal uptake of these agents in rats were investigated. In vivo quantitative data were corroborated by the use of autoradiographic and well-counting techniques. Results indicate that the short-term uptake of commonly used bonescanning agents is closely correlated with blood flow and is largely independent of the rate of osteogenesis. S K E LE TAL IMAGING with radionuclides has gained wide clinical acceptance for the detection of metastatic bone disease (8, 13,42,49). Other skeletal disorders, namely primary bone tumors, arthritis, osteomyelitis, aseptic necrosis and metabolic bone disease, have also been studied and detected by means of bone-scanning procedures (4, 24, 39, 41, 43). Early clinical applications (6, 16, 17,21), using ca1cium-47 (t1h = 4.5 days, l' = 1.4MeV) and strontium-So (tl/2 = 65 days, l' = 512 keV), were severely limited due to the high radiation absorbed dose to the patient, which restricted the amount of radioactivity administered and resulted in poor count statistics and low-information images (8,49). The high gamma energies of these radionuclides were additional disadvantages for imaging with conventional equipment (9, 28).The introduction of the short-lived gamma emitters strontium-S'Zm (35) (tl/2 = 2.8 hr., l' = 390 keV) andfluorine-18 (9) (tl h = 1.8 hr., 'Y = 511 ke V) provided a distinct improvement, largely due to the greater amount of radioactivity which could be administered. The lower gamma energy of 87mSr was more efficiently collimated and detected with conventional scanning equipment. A major disadvantage of this agent was the expense of the 87mSr generators. Equally important was the biological property of strontium, namely slow renal and intestinal excretion, which resulted in high blood and soft-tissue levels during the effective halflife of the radionuclide (39, 43, 49). On the other hand, the extremely rapid blood clearance of 18F due to skeletal uptake and renal excretion provided improved target to nontarget ratios (8, 24,49). The short physical half-life of 18F and the necessity for shipping it from the cyclotron or reactor production site on the day of use contributed to its expensiveness and lack of availability for universal clinical application. Additionally, the high-energy photons resulting from positron annihilation were not easily collimated for imaging (28). The applicability of bone scanning in routine clinical practice was greatly expanded with the development of bone-seeking 99mTc_Sn-compounds of polyphosphate (45) and diphosplionate (12) that are easily prepared from commercially available kits. Technetium-Osrn (tl h = 6 hr., l' = 140 keV) is a nearly ideal agent for scanning procedures in nuclear medicine (28), i.e., a gamma emitter with energy suitable for imaging and readily available as an inexpensive generator. Th...

Atypical form of active melorheostosis and its treatment with bisphosphonate

“…Bone scintigraphy reveals greatly increased radionuclide uptake [4,8,9,10]. In our patient, bone scintigraphic activity increased markedly in some of the bones affected.…”

Therapeutic effects of one-year alendronate treatment in three cases of osteoporosis with parietal thinning of skull

“…The degree of radiotracer uptake is thought to depend on blood flow and rate of bone formation (6,7). This result suggests that there are no changes in blood flow and rate of bone formation in thin parietal bones of our three cases.…”

Blood flow and bone uptake of99mTc‐labeled methylene diphosphonate

“…Genant and associates (7) suggested that the rapid uptake of bone-seeking agents is largely dependent upon the rate of mineralization or matrix formation. Garcia and co-workers (6) theorized that the positive bone images of osteolytic lesions are caused entirely by the incorporation of skeletal agents as part of a compensatory boneseeking response.…”