Indium WBC Scan, Normal Distribution, Indium-111 vs Technetium WBC, NM Tagged Whole Body Scan

Content:

• What is Indium WBC Scan?
• Normal Distribution
• Indium-111 vs Technetium WBC
• NM Tagged Whole Body Scan

What is Indium WBC Scan?

An Indium WBC scan (Indium-111 labeled white blood cell scan) is a nuclear medicine imaging technique used primarily to detect and localize infection or inflammation in the body. The procedure involves drawing a sample of the patient’s blood, isolating the white blood cells (usually neutrophils), labeling them with the radioactive isotope Indium-111, and then re-injecting them into the bloodstream. These tagged cells migrate to areas of active infection, allowing for precise localization through gamma camera imaging.

This scan is especially useful in diagnosing conditions such as osteomyelitis, prosthetic joint infections, vascular graft infections, or fever of unknown origin. Compared to other imaging modalities, Indium WBC scans are highly specific for infection because they track the movement of the patient’s own immune cells rather than relying on indirect markers of inflammation.

Normal Distribution

In a normal Indium WBC scan distribution, the radiolabeled white blood cells accumulate primarily in the spleen, liver, bone marrow, and lungs shortly after injection. Over time, activity in the lungs clears, and the primary sites of uptake become the spleen and liver, with bone marrow uptake appearing as a more diffuse pattern along the axial skeleton and proximal long bones.

There should be no focal areas of abnormal uptake outside these expected regions. Abnormal findings are identified by focal accumulations of activity in regions such as bones, soft tissues, or organs where infection is suspected. For accurate interpretation, comparison with sulfur colloid bone marrow imaging may be used to differentiate infection from normal marrow uptake.

Indium-111 vs Technetium WBC

Indium-111 and Technetium-99m are the two most common isotopes used to label white blood cells for infection imaging. Indium-111 has a longer half-life (approximately 67 hours) and emits gamma rays at higher energies, making it ideal for delayed whole-body imaging and detecting chronic or deep-seated infections. However, its spatial resolution is lower compared to technetium due to the higher energy photons.

Technetium-99m labeled WBC scans offer better image quality and are typically used for imaging within 4–24 hours after injection. They are especially useful for abdominal or soft tissue infections. Indium is often preferred for orthopedic infections, prosthetic joint evaluations, or when longer imaging intervals are needed. In some cases, both isotopes may be used together to provide complementary information.

NM Tagged Whole Body Scan

A Nuclear Medicine (NM) tagged whole body scan with Indium-111 WBC is performed to evaluate for occult infection throughout the body. After injection of the labeled white cells, images are typically obtained at several time points, such as 4 hours and 24 hours post-injection. Whole-body imaging allows for the detection of unexpected infection sites in addition to the primary suspected area.

The procedure involves positioning the patient under a gamma camera, which captures the distribution of the radiolabeled cells throughout the body. Areas with abnormal focal accumulation suggest active infection or inflammation. This scan is particularly valuable when other imaging studies, such as CT or MRI, are inconclusive, or when multiple sites of infection are suspected. Its high specificity makes it a crucial tool in diagnosing complex infectious diseases.