Leukocyte Scintigraphy

Leukocyte scintigraphy is a diagnostic procedure used in nuclear medicine to visualize accumulations of radioactively labeled leukocytes (white blood cells), for example, in inflammatory sites. Leukocytes, along with erythrocytes (red blood cells) and thrombocytes (blood platelets), make up the cellular component of blood. Leukocytes are part of the immune system and therefore serve the body’s defense function. They can be further divided into granulocytes, monocytes and lymphocytes. The main group is formed by granulocytes (called neutrophils; these are the most common leukocytes with a share of 50-65%), which are carriers of the non-specific defense. They are attracted to the site of demand by chemotaxis (influencing granulocyte locomotion by secreted chemical substances) and perform their tasks such as phagocytosis of pathogens (elimination of pathogens by absorption into the cell). Granulocytes secrete inflammatory mediators in the course of their activity and are thus significantly involved in the inflammatory response. The mediators attract further granulocytes, whose exit from the capillaries into the tissue is additionally facilitated by increased perfusion (blood flow) and increased vascular permeability (permeability). Consequently, granulocytes are enriched in a focus of inflammation compared to the rest of the body – a fact that is utilized in leukocyte scintigraphy. By radioactively labeling the patient’s leukocytes (specifically granulocytes), once they have migrated to the site of inflammation, they can be detected using, for example, a gamma camera.

Indications (areas of application)

The indication for leukocyte scintigraphy is suspected inflammation or inflammation whose exact location or extent must be determined:

  • Suspicion of (V. a.) joint prosthesis infection.
  • V. a. Vascular prosthesis infection, question about the extent of infection.
  • V. a. acute/chronic osteomyelitis (bone marrow inflammation).
  • Clarification of fever of unknown genesis (cause).

Less common indications, but possible in individual cases, include, for example, early diagnosis of pneumonia (pneumonia) in opportunistic pathogens (pathogens that cause symptoms only under favorable conditions such as immunosuppression of the patient), suspected postoperative abdominal abscess (encapsulated collection of pus in a non-preformed body cavity resulting from inflammatory tissue meltdown) or highly florid (highly symptomatic) stages of inflammatory bowel disease.

Contraindications

Relative contraindications

  • Lactation phase (breastfeeding phase) – breastfeeding must be interrupted for 48 hours to prevent risk to the child.
  • Repeat examination – no repeat scintigraphy should be performed within three months due to radiation exposure.

Absolute contraindications

  • Gravidity (pregnancy)

The procedure

  1. Blood is drawn from the patient. Leukocytes are selected from this by special processing procedures.
  2. Radioactive labeling is performed on a mixed leukocyte preparation, which consists of about 80% granulocytes and about 20% lymphocytes. However, the lymphocytes are radiosensitive and lose all activity after labeling, resulting in pure granulocyte labeling.
  3. The choice of radioactive tracer depends on the indication. In acute processes, tracers with short half-lives (99mTc, HWZ (half-life) 6h) are suitable, as rapid granulocyte migration can be expected. In chronic inflammation, tracers with long half-lives can be used (111In, HWZ 2.8d).
  4. Subsequently, the labeled leukocytes are applied intravenously to the patient.
  5. A waiting period must be observed for the radiolabeled leukocytes to reach the site of inflammation. In addition, for successful scintigraphy, a favorable target-background relation must be established, i.e., the specific radioactivity accumulation in the inflammatory focus must be clearly distinguishable from the nonspecific background radiation. The time interval between injection and the scintigraphic image depends on the radiopharmaceutical used.In the meantime, due to the only low radiation intensity, no separate radiation protection measures need to be taken, so the patient can attend other appointments during the waiting time.
  6. For the acquisition of radioactivity or preparation of the scintigraphy, gamma cameras are used as a planar technique (representation in one plane with superimpositions) or slice imaging systems (single photon emission computed tomography, SPECT) for superimposition-free representation of particularly relevant body sections.

Possible complications

  • Intravenous application of radiopharmaceutical may result in local vascular and nerve lesions (injuries).
  • Radiation exposure from the radionuclide used is rather low. Nevertheless, the theoretical risk of radiation-induced late malignancy (leukemia or carcinoma) is increased, so that a risk-benefit assessment should be performed.