Significant dehydration, ascites, anasarca, and renal and/or hepatic failure cause increased soft-tissue uptake, resulting in a low bone-to-background ratio and degraded scan images. Unlabeled 99mTc-pertechnetate and oxidation of 99mTc-labeled phosphate complex may also increase the background activity, with undesirable tracer accumulation in the thyroid and liver as well as disturbance of alimentary tract excretion (see Chap. 5). On the other hand, the systemic administration of adjuvant chemo-therapeutic agents, steroids, or iron is known to suppress bone uptake of tracer (Hladik et al. 1982). It is of interest that adjuvant chemotherapy may occasionally cause healing bone malignancies to flare up with increased tracer uptake so that they appear unresponsive to the treatment (Gillespie et al. 1975; see Chap. 17).
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