Liver blood pool scintigraphy (liver blood pool scintigraphy) is a nuclear medicine diagnostic procedure for imaging liver perfusion (blood flow). The liver is the central metabolic organ of the human organism. It has important synthesis and metabolization functions in carbohydrate, protein and lipid metabolism (sugar, protein and fat metabolism) and thus plays a crucial role in the detoxification of endogenous and xenogenous substances. The synthesized products can be released into the bloodstream on the one hand and secreted (excreted) into the small intestine with the bile on the other. The blood supply is provided by two different circuits: the liver’s own arteries (A. hepatica propria) and the portal vein (V. portae hepatis). After the blood passes through the liver parenchyma (tissue), it enters the hepatic veins (Vv. hepaticae) and, via these, eventually the superior vena cava (V. cava). In liver blood pool scintigraphy, radioactively labeled erythrocytes (red blood cells) can be used to measure liver perfusion as well as estimate the relationship between arterial and portal venous blood flow. In particular, increased vascularized (vessel-rich) tumors can be visualized.
Indications (areas of application)
Liver blood pool scintigraphy is indicated when hepatic hemangiomas (blood sponges) are suspected: hemangiomas are very common benign (benign) liver tumors characterized by a neoplasm of dilated vessels. They are usually asymptomatic (do not cause symptoms), but in very rare cases they can spontaneously rupture (rupture) and cause peritoneal hemorrhage (bleeding into the abdominal cavity), especially if they are markedly large. Compared to liver perfusion scintigraphy, blood pool scintigraphy is more suitable for hemangioma diagnosis because radioactively labeled erythrocytes are used, which remain intravascular (in the vessels) much longer. In cases of suspected portal hypertension, portal vein thrombosis, graft rejection, or follow-up of a transjugular intrahepatic portosystemic shunt (TIPS; interventional method of creating a shunt to bypass the hepatic flow area), liver perfusion scintigraphy (e.g., using 99mTc-DTPA as a radiopharmaceutical, also called a tracer) is indicated instead of liver blood pool scintigraphy.
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
The labeling of erythrocytes can be done in two different ways:
- In vivo (in the body): intravenous injection (administration through the vein) of tin pyrophosphate, after 20-30 min post-injection of 99mTc-pertechnetate. The erythrocytes are radiolabeled in the bloodstream and enter the liver with the blood flow.
- In vitro (outside the body): intravenous injection of tin pyrophosphate, after about 15 min removal of 10 ml of blood, incubation of the blood in vitro on a shaker with 99mTc-pertechnetate, after about 10 min reinjection of the now labeled blood volume.
After 15 min, early images are obtained with high-resolution multihead systems (SPECT = single photon emission computed tomography). After 2 h, late images are taken. Due to cavernous transformation (cavernous transformation with dilated vessels), hemangioma usually shows decreased blood flow. In the course of time, however, the contrast to the surrounding liver tissue becomes more and more obvious due to the increased filling. Especially in large hemangiomas, late imaging should not be omitted because of this delayed “fill in.”
Potential 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 a radiation-induced late malignancy (leukemia or carcinoma) is increased, so that a risk-benefit assessment should be performed.
