**2.1.2 Positron emitting agents**

PET, which is short for positron emission computed tomography, is the most advanced equipment in the field of nuclear medicine even in the area of image science. Lots of kinds of positron emitting radionuclide have been used in practice, such as 18F, 11C (carbon-11), 15O (oxygen-15), 13N (nitrogen-13), etc. The most widely used radionuclide is fluorine-18 (18F) and carbon-11 (11C). The 18F radiolabelled and 11C labelled skeletal radiopharmaceuticals are used in PET imaging, which reflect the bone metabolism. The following table (table 2) summarizes their nuclear physics characteristics.

Skeleton System 291

In pediatric cases the physiology and metabolism is different from adults' and the uptake of radiopharmaceuticals vary greatly, for example the bone uptake in children is up to 80% compared with that of adults at up to 40%. The pediatric dose of radiopharmaceuticals is calculated based on the standard weight method (the pediatric dose=(patient weight in kg×standard adult dose)÷70kg) or body surface area methods. With 99mTc labelled radiopharmaceuticals, we suggest a 24 to 36 hr breast feeding delay, and 67Ga based

After the radiopharmaceuticals prepared, an emission computed tomography is needed. Tomography is the process of producing a section or slice in a picture of an object. The emission computed tomography (ECT) can produce a picture of the distribution of radiopharmaceuticals administered to the patient. At present the widespread used ECT are

By far the most popular SPECT consists of a rotating Anger camera, which equipped with a large field of view detector, mounted on a 360-degree rotation gantry. Multipledetector SPECT has increased the diagnostic sensitivity and lessened the acquisition time. In skeletal

PET is one of the exciting tomographic techniques, and provides functional information of blood flow and metabolism. As a positron meets a free electron in the tissue, annihilation occurs and the two 511keV annihilation photons are detected by coupled opposing detectors in coincidence. PET is more sensitivity than SPECT, and differs from SPECT by "electronic

According to the different imaging objects, the nuclear physician chose the proper protocols. Generally speaking, the imaging type are divided into whole body scan, local static bone scan, local bone tomography, dynamic bone scan (i.e. three phase imaging: blood flow phase, blood-pool phase, and delay scan). The whole body bone scan is the most widely

The appearance of the normal skeletal scintigram should be clear, symmetric and uniform and the uptake of joints, junctions, and scapulas increased. In some older patients the image may have a globally poor quality. The normal image can change dramatically among infancy, childhood, adolescence and mature adulthood. In adults, growth center activity normally becomes equal to activity in adjacent bone, on the contrary more radioactivities in growth center than adjacent bone in childhood. Tracer uptake is greatest in the axial skeleton (spine and pelvis), and relatively less intense uptake in the extremities and skull. The kidneys are routinely visualized in normal subjects and should have less intensity than the adjacent lumbar spine because the urinary system is the excretion pathway of the radiopharmaceuticals. If the kidneys show equal or greater intensity, a renal abnormality or

imaging protocols we often chose a low energy and high resolution collimator.

In pregnant women, the nuclear medicine examinations are forbidden.

**2.2 Technique of skeletal radionuclide imaging** 

**2.2.1 Technique of skeleton SPECT imaging** 

**2.2.2 Technique of skeleton PET imaging** 

**2.3 Appearance of normal skeleton scintigram** 

used scintigraphy, which reflects the whole skeleton situation.

**2.1.4 Precautions** 

products for a 72 hr delay.

SPECT and PET.

collimation".


Table 2. The nuclear physics characteristics of positron radionuclide 18F, 11C

18F-2-fluoro-2-deoxy-d-glucose (18F-FDG), 18F sodium fluoride (18F-NaF) and 11C-choline PET imaging is also called bone metabolic imaging. Here we will mention 18F-FDG and 18F-NaF imaging. 18F-FDG (2-fluoro-2-deoxy-d-glucose) is a glucose analogue with a fluorine atom replacing a hydroxyl group in the C-2 position of d-glucose. 18F exchanges with the hydroxyl (OH) ion in the hydroxyapatite. Although the mechanisms are not completely understood, the principal of bone imaging is fairly basic. Radiopharmaceuticals used in bone imaging can localize in soft tissues, demonstrating not only calcification but also inflammation, trauma, and tumor.
