Leukocyte scintigraphy as an inflammatory diagnostic method

This includes, in particular, the suspicion of an infection without knowing how exactly it is spreading. Leukocyte scintigraphy is also one of the diagnostic methods for acute and chronic osteomyelitis. Detailed information about the procedure and explanations of the procedure follow.

Summary of the process of a scintigraphy

In summary, doctors use leukocyte scintigraphy to locate sites of inflammation in the body. The diagnostic procedure is part of nuclear medicine and is based on a patient’s blood sample. Here, a radioactive marking of the granulocytes contained in the blood takes place. This is followed by reinjection of the marked blood, which then spreads throughout the body. As a result, the leukocytes migrate to the site of the inflammation. They emit a small amount of radioactive radiation. A gamma camera creates an image based on the measured rays, which ultimately enables the desired localization of the inflammation.

Granulocytes and their role in inflammation

Within the framework of the immune system, leukocytes assume important functions in the defense against pathogens. Medicine differentiates between granulocytes, lymphocytes and monocytes in the white blood cells . The majority of the leukocytes are accounted for by the granulocytes, which account for between 50 and 65 percent. As part of their immune activity, the granulocytes take over the phagocytosis of pathogens, for example. The leukocytes release inflammatory mediators that attract more granulocytes. As a result, leukocytes concentrate at sites of inflammation.

Application scenarios of the imaging process of nuclear medicine

Leukocyte scintigraphy uses the increased concentration of granulocytes in inflammation. A radioactive material marks the white blood cells, which the doctor then locates with a gamma camera. The presented diagnostic method is used in different situations. Basically, physicians use the method when they suspect an inflammation, but do not know its location or its spread.

These include, for example:

• Acute or chronic osteomyelitis (inflammation of the bone marrow),
• osteitis (bone inflammation),
• infections in vascular prostheses,
• suspected infection in a joint prosthesis,
• fever of unknown origin,
• Early diagnosis of pneumonia.

Detailed information on the process of leukocyte scintigraphy

Leukocyte scintigraphy is based on a weakly radioactive drug. It is a monoclonal antibody directed against the granulocytes. The procedure is divided into several steps. First, the doctor takes a blood sample from the patient. This is followed by isolation of the leukocytes from the venous blood.

In order to isolate enough white blood cells, the method presented requires between 20 and 40 milliliters of blood in adults. If the patient’s blood contains relatively few leukocytes, the amount to be removed increases. If the method is used in children, less venous blood is sufficient. The minimum is ten milliliters.

 

Labeling of the leukocytes in the blood sample

The leukocytes are then marked in vitro by a so-called tracer (radioactive substance). The leukocyte preparation consists of 80:20 granulocytes and lymphocytes. Due to the radiation-sensitive properties of the lymphocytes, their activity is lost after the addition of the tracer. As a result, only the marked granulocytes remain.

The cells are isolated and labeled at room temperature in a laminar flow chamber. Sterile removal material and protective gloves during the entire process are a basic requirement. It is also extremely important to ensure that the samples are labeled exactly. This is especially true for laboratories that work with multiple patient samples at the same time.

Re-injection of the marked granulocytes

In the next step, the doctor reinjects the leukocytes marked by the radioactive material. The process usually takes place within one to two hours of blood collection. A waiting period then follows. Meanwhile, the granulocytes reach the site of inflammation. The waiting time to be observed depends on the drug used. Since the radioactive radiation has a very low intensity, there is no need for special radiation protection measures. This means that contact with other people during the waiting time is not a problem.

Recordings with the gamma camera

Finally, the physicians use gamma cameras, which capture images of the radioactive leukocytes. They create scintigraphic images in which the doctor can identify the localization of the foci of inflammation. Gamma cameras are considered to be the most commonly used devices in nuclear medicine. They are based on the gamma radiation emitted by the patient.

It occurs because the radiopharmaceuticals break down in the body. A detector absorbs the rays, which the device transforms into a light emission. So-called photo multipliers convert the light into electrical signals. A monitor displays the measured pulses, creating the image used for diagnosis.

Different tracers to choose from

There are several tracers that are used in scintigraphy of leukocytes. The selection of the radiopharmaceutical depends on the indication. In the case of chronic inflammation, there are remedies that have a long half-life. In this regard, In-111 toxin is considered the preferred choice. On the other hand, in the case of acute herds, tracers with a short half-life are the better alternative because rapid migration of the granulocytes suggests itself. Physicians prefer TC-99m-HMPAO.

Depending on the tracer used, the attending physician uses the gamma camera to take pictures at different times. These usually take place within the first three to four hours. In addition, if necessary, the doctor will carry out a late admission after 24 hours. Meanwhile, he produces full-body pictures and individual shots. The examination does not require a fasting state.

In the course of the scintigraphy of the leukocytes, various complications threaten. The application of the labeled leukocytes into the arm vein may lead to local injuries to the vessels and nerves. In addition, although the radiation exposure is low, there is a theoretical residual risk of a late malignancy caused by the radiation in the form of a carcinoma or leukemia .

Absolute and relative contraindications

Contra-indications describe situations that completely exclude the diagnostic procedure or require special measures. In this regard, medicine differentiates between absolute and relative contraindications. An absolute contraindication – and thus a complete ban on scintigraphy – is during pregnancy .

Relative contraindications actually reject the corresponding measure, but nevertheless accept it because it does more good than harm. In the case of the diagnostic procedure presented, there are relative contraindications during the breastfeeding phase and in the context of a repeat examination.

If a mother breastfeeds her child, the scintigraphy requires a 48-hour interruption in the supply of breast milk. This serves to protect the child in order to rule out any danger. After a scintigraphy of the leukocytes, a break of at least three months is recommended before a repeated examination of the same type takes place. The reason is the exposure to radioactive radiation.

further:

https://www.aerzteblatt.de/pdf/89/28/a2462.pdf

http://www.nuklearmedizin-berlin.de/leukozyten.html

http://www.nuklearmedizin.de/leistungen/leitlinien/html/t_leuko_szin.php?navId=5

http://www.uniklinikum-saarland.de/einrichtungen/kliniken_institute/radiologie/nuklearmedizin/patienteninformationen/untersuchungen/leukozytenszintigraphie/