**2.3 Appearance of normal skeleton scintigram**

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 used scintigraphy, which reflects the whole skeleton situation.

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

Skeleton System 293

①Asymmetric focal areas of increased or decreased activity: basically, this type of abnormality can happen in almost every scintigram. Focal increased activity can be associated with more blood flow (caused by hyperaemia, such as trauma, inflammation, etc)

②"Super scan" is another scintigraphic pattern, with good bone-to-soft tissue background ratio, bone uptake showing brightly, absent or faint visualization of kidney and bladder, an increased uptake in the axial versus appendicular skeleton (appendicular skeleton, distal extremities, facial bones, subtle asymmetries of the rib, skull vault, and proximal long bones, and no soft-tissue uptake apparent at normal intensities). In some patients with breast cancer or prostate cancer the entire axial skeleton becomes diffusely and rather uniformly

Fig. 2. A patient diagnosed as prostate cancer, the whole body bone scan with 99mTc-MDP showed "super scan": absent visualization of kidney, increased uptake in the axial versus

③Cold areas, which means diminished activity or none distribution of activity, is indicative of osteonecrosis, osteoporosis, osteomalacia, multiple myeloma, radiation or steroid therapy, end-stage cancer patients with diminished metabolism, renal cell carcinoma,

④"Donut" sign is the typical scintigram of osteonecrosis of the femoral head. The cold area within the femoral head is highly specific and is the earliest scintigraphic evidence of avascular necrosis. Over a period of weeks to months, increased uptake represents revascularization and repair surrounds, and eventually replaces the region of photopenia. The central region of photopenia with surrounding zone of increased uptake is termed as

appendicular skeleton and no soft-tissue uptake apparent at normal intensities.

thyroid cancer, anaplastic tumors, neuroblastoma.

"donut" sign (Figure 3).

and active of osteogenesis (such as bone metastases of prostate cancer).

involved with metastatic disease (Figure 2).

concomitant drug therapy should be suspected. Here shows a normal skeleton scintigram (Figure 1).

Fig. 1. Normal skeletal scintigram shows the symmetric and uniform activity absorption in anterior and posterior image.

A number of normal variants must be recognized for correct interpretation. Here we list some possible conditions as below.

①Bilaterally increased radionuclide concentration may be normal.

②The anterior aspect of the mandible may appear as a "hot spot" on lateral views of the skull.

③The laryngotracheal cartilages are usually seen in adults probably related to some degree of calcification.

④The thyroid gland can be visualized because of avid accumulation of unbound pertechnetate.

⑤Some mild diffuse asymmetry in paired joints is commonly seen in adults especially in shoulders and correlates with handedness.

⑥Some asymmetry is frequently seen in the sacroiliac joints, and this should be interpreted with caution in patients with scoliosis.
