Not to be confused with Dual-energy X-ray absorptiometry.
It can help diagnose a number of bone conditions, including cancer of the bone or metastasis, location of bone inflammation and fractures (that may not be visible in traditional X-ray images), and bone infection (osteomyelitis).
In the 1950s and 1960s calcium-45 was investigated, but as a beta emitter proved difficult to image.
Other bone radiopharmaceuticals include Tc with HDP, HMDP and DPD.
Mineralisation occurs at osteoblasts, representing sites of bone growth, where MDP (and other diphosphates) "bind to the hydroxyapatite crystals in proportion to local blood flow and osteoblastic activity and are therefore markers of bone turnover and bone perfusion".
The more active the bone turnover, the more radioactive material will be seen.
In a typical bone scan technique, the patient is injected (usually into a vein in the arm or hand, occasionally the foot) with up to 740 MBq of technetium-99m-MDP and then scanned with a gamma camera, which captures planar anterior and posterior or single photon emission computed tomography (SPECT) images.
In order to view small lesions SPECT imaging technique may be preferred over planar scintigraphy.
In a single phase protocol (skeletal imaging alone), which will primarily highlight osteoblasts, images are usually acquired 2–5 hours after the injection (after four hours 50–60% of the activity will be fixed to bones).
A two or three phase protocol utilises additional scans at different points after the injection to obtain additional diagnostic information.
A dynamic (i.e. multiple acquired frames) study immediately after the injection captures perfusion information.
A second phase "blood pool" image following the perfusion (if carried out in a three phase technique) can help to diagnose inflammatory conditions or problems of blood supply.
PET bone imaging
Main article: PET for bone imaging
Although bone scintigraphy generally refers to gamma camera imaging of Tc radiopharmaceuticals, imaging with positron emission tomography (PET) scanners is also possible, using fluorine-18 sodium fluoride ([F]NaF).
For quantitative measurements, Tc-MDP has some advantages over [F]NaF.
MDP renal clearance is not affected by urine flow rate and simplified data analysis can be employed which assumes steady state conditions.
It has negligible tracer uptake in red blood cells, therefore correction for plasma to whole blood ratios is not required unlike [F]NaF.
However, disadvantages include higher rates of protein binding (from 25% immediately after injection to 70% after 12 hours leading to the measurement of freely available MDP over time), and less diffusibility due to higher molecular weight than [F]NaF, leading to lower capillary permeability.
Patient experience is improved as imaging can be started much more quickly following radiopharmaceutical injection (30-45 minutes, compared to 2-3 hours for MDP/HDP).
[F]NaF PET is hampered by high demand for scanners, and limited tracer availability.
Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Bone scintigraphy.