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Chapter 6 Radioisotopes and Nuclear Medicine
Published in B H Brown, R H Smallwood, D C Barber, P V Lawford, D R Hose, Medical Physics and Biomedical Engineering, 2017
Bone consists largely of a matrix of calcium phosphates. A variety of phosphate compounds have been developed which are rapidly incorporated into bone when introduced via the bloodstream. It has proved possible to label these compounds with 99mTc and thus visualize the bones in the body with a gamma camera. A compound widely used for bone imaging is 99mTc-methylene diphosphonate (99mTc-MDP), although others have been developed and new bone-seeking radiopharmaceuticals are still under investigation. MDP and other similar substances deposit in the normal bone, allowing the skeleton to be imaged. They also localize in bone tumours, around fractures and metabolic disorders such as Paget’s disease. They do not localize in dead or necrosed bone. The mechanism of increased uptake appears to depend on a mixture of increased vascular flow and osteoblastic activity, i.e. deposition of new bone, and both of these are increased around bone tumours and fractures. In the case of fractures increased bone deposition around the site of fracture is to be expected as the bone heals and rejoins. Bone tumours are usually associated with breakdown of the bone, oseteolytic activity, and this will eventually result in the reduction of the density of the bone to the point where it breaks. However, pathological osteolytic activity seems to be associated with osteoblastic activity, and the latter at the site of a tumour results in increased deposition. There is also increased blood flow to the tumour site. Deposition is irreversible over the duration of the investigation.
Medical Imaging
Published in John G. Webster, Halit Eren, Measurement, Instrumentation, and Sensors Handbook, 2017
James T. Dobbins III, Sean M. Hames, Bruce H. Hasegawa, Timothy R. DeGrado, James A. Zagzebski, Richard Frayne
Radionuclide images can be interpreted visually or quantitatively. For example, the radiopharmaceutical [99mTc]-methylene diphosphonate (MDP) is incorporated into the bone matrix by osteoblastic activity [43]. A radiologist will inspect a nuclear medicine image for sites demonstrating focal uptake of 99mTc-MDP to determine the extent and degree of trauma, inflammation, degeneration, metastatic disease, or other skeletal disease processes. Typically, 99mTc-MDP images are interpreted visually but are not analyzed to determine the quantity of radiotracer incorporated into the skeleton.
Nuclear Medicine in Oncology
Published in Computer Methods in Biomechanics and Biomedical Engineering: Imaging & Visualization, 2018
Carla Oliveira, Rui Parafita, Ana Canudo, Joana Correia Castanheira, Durval C. Costa
The bone scintigraphy uses radiopharmaceuticals with affinity to parts of the skeleton that have an increased osteoblastic activity, which allows detection of functional alterations of bone neoformation that precede the structural alterations. These radiopharmaceuticals are diphosphonates labelled with 99mTc – such as methylene diphosphonate (MDP) – whose mechanism for bone uptake is believed to be that of fixation by adsorption in the active mineralisation layer of the bone with the exchange of phosphorous groups for the calcium in the hydroxyapatite crystals.