A bone scan, formally known as skeletal scintigraphy, is a specialized nuclear medicine procedure used to evaluate the metabolic activity of the skeleton. This test provides images reflecting how bones function at a cellular level, unlike a standard X-ray which only shows structure. Bone scans are used to identify subtle fractures, detect the spread of certain cancers, or diagnose bone infections like osteomyelitis. This highly sensitive method pinpoints areas of increased bone turnover that may indicate disease or injury.
The Scintigraphy System: Components and Appearance
The machine capturing the images is typically a gamma camera system, which can appear large in the examination room. This device is not a closed tube like an MRI or CT scanner. Instead, it consists of a narrow, motorized patient table positioned between one or two large, flat detectors housed within a gantry, often resembling a rectangular C-frame structure.
The flat panels are the gamma camera heads, designed to detect radiation emitted from the patient’s body. These detectors do not generate or send radiation toward the patient. The camera’s internal components include a sodium iodide crystal and photomultiplier tubes that translate energy signals into an image. The machine’s size often requires a larger room environment to accommodate its movement and operation.
The core of the system is the gantry, which supports the cameras and allows them to move around the patient. This structural frame is often encased in smooth plastic and metal. The patient table slides horizontally through the space between the camera heads, which are typically positioned parallel above and below the patient to capture a comprehensive view of the entire skeletal system.
Preparing for the Scan: The Radiotracer
The imaging machine requires introducing a radioactive substance, called a radiotracer, into the patient’s system. The most common agent used is Technetium-99m (Tc-99m) complexed with methylene diphosphonate (MDP). This compound is administered intravenously, typically through an injection into a vein in the arm or hand.
The radiotracer needs time to travel through the bloodstream and accumulate in the bones, a process known as uptake. This accumulation happens preferentially in areas where bone metabolism is high, such as sites of injury, fracture, or disease. Patients must wait between two and four hours after the injection before the actual scanning begins.
During this waiting period, patients are encouraged to drink several glasses of water and frequently empty their bladder. This practice flushes unabsorbed radiotracer out of the soft tissues. Clearing the background activity results in clearer images, allowing the camera to better detect the activity concentrated in the skeletal structures.
Patient Experience: Movement and Imaging
Once uptake is complete, the patient lies still on the narrow, padded table of the gamma camera system. The technician positions the patient, often asking them to remove all metal objects, and emphasizes the need for absolute stillness. The actual scan duration ranges from 30 to 60 minutes, depending on the examination scope.
For a standard whole-body bone scan, the table moves very slowly, passing the patient through the stationary camera heads. This process captures a continuous two-dimensional image of the skeleton from head to toe, providing both an anterior (front) and posterior (back) view. The camera heads remain close to the body but do not make physical contact.
In some cases, a more detailed view requires Single-Photon Emission Computed Tomography (SPECT) imaging. For a SPECT scan, the camera heads rotate slowly in an arc or full circle around a specific area, such as the spine or pelvis. This rotation gathers data from multiple angles, which a computer uses to reconstruct a three-dimensional, cross-sectional image of the bone activity.