Scintigraphy performed with Tc-99m labeled RBCs
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View The Radswiki's current disclosuresAt the time the article was last revised Mostafa Elfeky had no financial relationships to ineligible companies to disclose.
View Mostafa Elfeky's current disclosures- Technetium-99m labeled red blood cell
Tc-99m labeled RBCs - with radiolabelling technique in vivo or in vitro of red cells 3 - is one of the technetium radiopharmaceuticals used in the non-invasive assessment of gastrointestinal (GI) bleeding 2, characterized by high sensitivity (93%) and specificity (95%) 4. It is capable, in fact, of targeting intestinal hemorrhages of a few milliliters immediately after the injection of the radioactive tracer or in the following 12-24 hours (diluition principle) 5,6.
There are three ways to label erythrocytes, namely in vivo, modified in vivo, and in vitro methods. In vivo method injects stannous pyrophosphate into the patient's blood, followed by Tc99m-pertechnetate injection. However, this method has low labeling efficiency. In the modified in vivo method, the blood is withdrawn after injecting the stannous pyrophosphate. The blood is then withdrawn from the patient mixed with Tc-99m-pertechnetate and injected back into the same patient. In the in vitro method, the blood is first withdrawn from the patient and mixed with stannous pyrophosphate and Tc-99m-pertechnetate using a cold kit. After mixing, the blood is then injected back into the patient. This method has the highest labeling efficiency 7.
Stannous pyrophosphate is important because it acts as a reducing agent in order to prevent pertechnetate ions from diffusing into the extravascular spaces, affecting the labeling efficacy of the RBCs 8.
Characteristics
photon energy: 140 KeV
physical half-life: 6 hours
biological half-life:
normal distribution: heart, vessels, spleen
-
miscellaneous facts:
threshold for detection is 0.05-0.1 mL/min
angiography threshold is 0.5-1 mL/min
the criteria for positive scan are qualitative type: hot spot appears and conforms to intestinal anatomy, abnormal activity increases over time, activity moves antegrade or retrograde through bowel
Uses, doses and timings
timing: immediate/angioscintigraphic phase (1 sec frames x 60 sec); 1 min frames x 60-90 min; delayed imaging if necessary (6-8-24 hrs).
References
- 1. Emslie JT, Zarnegar K, Siegel ME, Beart RW. Technetium-99m-labeled red blood cell scans in the investigation of gastrointestinal bleeding. (1996) Diseases of the colon and rectum. 39 (7): 750-4. Pubmed
- 2. Grady E, Grady. Gastrointestinal Bleeding Scintigraphy in the Early 21st Century. (2016) Journal of nuclear medicine : official publication, Society of Nuclear Medicine. doi:10.2967/jnumed.115.157289 - Pubmed
- 3. Srivastava S, Srivastava CL, Srivastava. Radionuclide-labeled red blood cells: current status and future prospects. (1984) Seminars in nuclear medicine. doi:10.1016/s0001-2998(84)80022-7 - Pubmed
- 4. Bunker S, Bunker LR, Bunker TD, Bunker RM, Bunker RJ, Bunker BJ, Bunker BM, Bunker MR, Bunker RL, Bunker LA, Bunker. Scintigraphy of gastrointestinal hemorrhage: superiority of 99mTc red blood cells over 99mTc sulfur colloid. (1984) AJR. American journal of roentgenology. doi:10.2214/ajr.143.3.543 - Pubmed
- 5. Winzelberg G, Winzelberg MK, Winzelberg SH, Winzelberg WA, Winzelberg GA, Winzelberg. Evaluation of gastrointestinal bleeding by red blood cells labeled in vivo with technetium-99m. (1979) Journal of nuclear medicine : official publication, Society of Nuclear Medicine. doi: - Pubmed
- 6. Zuckerman D, Zuckerman BT, Zuckerman BE, Zuckerman. Massive hemorrhage in the lower gastrointestinal tract in adults: diagnostic imaging and intervention. (1993) AJR. American journal of roentgenology. doi:10.2214/ajr.161.4.8372742 - Pubmed
- 7. Grady E. Gastrointestinal Bleeding Scintigraphy in the Early 21st Century. J Nucl Med. 2015;57(2):252-9. doi:10.2967/jnumed.115.157289 - Pubmed
- 8. Front D, Israel O, Groshar D, Weininger J. Technetium-99m-Labeled Red Blood Cell Imaging. Semin Nucl Med. 1984;14(3):226-50. doi:10.1016/s0001-2998(84)80017-3
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