Sestamibi
Encyclopedia
Technetium sestamibi (trade name Cardiolite) is a pharmaceutical agent used in nuclear medicine
imaging. The drug is a coordination complex of the radioisotope technetium-99m
with the ligand
methoxyisobutylisonitrile (MIBI). The generic drug
became available late September 2008. A scan of a patient using MIBI is commonly known as a "MIBI scan."
Cardiolite is mainly used to image the myocardium (heart muscle). It is also used in the work-up of primary hyperparathyroidism
to identify parathyroid adenomas, for radioguided surgery of the parathyroid and in the work-up of possible breast cancer
.
cation which, when injected intravenously into a patient, distributes in the myocardium proportionally to the myocardial blood flow. Single photon emission computed tomography (SPECT) imaging of the heart is performed using a gamma camera
to detect the gamma ray
s emitted by the technetium-99m as it decays
. Two sets of images are acquired. For one set, 99mTc MIBI is injected while the patient is at rest and then the myocardium is imaged. In the second set, the patient is stressed either by exercising on a treadmill or pharmacologically. The drug is injected at peak stress and then imaging is performed. The resulting two sets of images are compared with each other to distinguish ischemic from infarcted areas of the myocardium. This imaging technique is limited to being correct only 76% of the time. The problem lies in choosing which images to compare to what. Resting images as discussed by Gorlin in the late 1950s are useful only for detecting tissue damage, while stress images provide evidence of coronary artery (ischemia) disease. Consequently, comparing these two images has led to many errors in disease detection and to results which fail to match results seen when the arteries of the heart are looked at using coronary angiography. Recent studies taking 10 years to complete have demonstrated (infra) that comparing stress-stress images can accurately detect ischemia while rest-rest images can accurately differentiate between dead (infarcted) heart (myocardium) tissue and stunned or hibernating myocardium.
Sestamibi was previously thought to not redistribute because earlier studies looked at individuals with no ischemia. This was an error unsupported by Maublant, Crane, Li, Fleming and Ono. The washout or redistribution rate (FHRWW) for such individuals without heart disease was approximately 15–20%, with half of this (10%) the result of technetium-99m decay over 55 minutes. It is now known that sestamibi redistributes more under conditions of ischemia with the most critical disease only detectable by "wash-in" where the Black Hole effect of cardiology is detected by a delay in uptake by the tracer (both sestamibi and myoview) during the first few minutes. Failure to image the heart at 5 minutes after stress leads to these individuals being missed and approximately 100,000 deaths each year in the United States alone. Specifically, the count activity increases at 60 minutes compared with 5-minute images when critical narrowing of coronary arteries is present.
, a brand name of which is Persantine, a MIBI scan is often referred to as a Persantine MIBI scan.
or undergoes hypertrophy as a result of homeostatic dysregulation. The parathyroid gland takes up 99mTc MIBI following an intravenous injection, and the patient's neck is imaged with a gamma camera to show the location of all glands. A second image is obtained after a washout time (approximately 2 hours), and mitochondria in the oxyphil cells of the abnormal glands retaining the 99mTc are seen with the gamma camera. This imaging method will detect 75 to 90 percent of abnormal parathyroid glands in primary hyperparathyroidism. An otolaryngologist or an endocrine surgeon can then perform a directed parathyroidectomy (less invasive than traditional surgery) to remove the abnormal gland.
, the surgeon can use a probe sensitive to gamma rays to locate the overactive parathyroid before removing it.
Nuclear medicine
In nuclear medicine procedures, elemental radionuclides are combined with other elements to form chemical compounds, or else combined with existing pharmaceutical compounds, to form radiopharmaceuticals. These radiopharmaceuticals, once administered to the patient, can localize to specific organs...
imaging. The drug is a coordination complex of the radioisotope technetium-99m
Technetium-99m
Technetium-99m is a metastable nuclear isomer of technetium-99, symbolized as 99mTc. The "m" indicates that this is a metastable nuclear isomer, i.e., that its half-life of 6 hours is considerably longer than most nuclear isomers that undergo gamma decay...
with the ligand
Ligand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...
methoxyisobutylisonitrile (MIBI). The generic drug
Generic drug
A generic drug is a drug defined as "a drug product that is comparable to brand/reference listed drug product in dosage form, strength, route of administration, quality and performance characteristics, and intended use." It has also been defined as a term referring to any drug marketed under its...
became available late September 2008. A scan of a patient using MIBI is commonly known as a "MIBI scan."
Cardiolite is mainly used to image the myocardium (heart muscle). It is also used in the work-up of primary hyperparathyroidism
Hyperparathyroidism
Hyperparathyroidism is overactivity of the parathyroid glands resulting in excess production of parathyroid hormone . The parathyroid hormone regulates calcium and phosphate levels and helps to maintain these levels...
to identify parathyroid adenomas, for radioguided surgery of the parathyroid and in the work-up of possible breast cancer
Breast cancer
Breast cancer is cancer originating from breast tissue, most commonly from the inner lining of milk ducts or the lobules that supply the ducts with milk. Cancers originating from ducts are known as ductal carcinomas; those originating from lobules are known as lobular carcinomas...
.
Cardiac imaging
Technetium (99mTc) sestamibi is a lipophilicLipophilic
Lipophilicity, , refers to the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene. These non-polar solvents are themselves lipophilic — the axiom that like dissolves like generally holds true...
cation which, when injected intravenously into a patient, distributes in the myocardium proportionally to the myocardial blood flow. Single photon emission computed tomography (SPECT) imaging of the heart is performed using a gamma camera
Gamma camera
A gamma camera, also called a scintillation camera or Anger camera, is a device used to image gamma radiation emitting radioisotopes, a technique known as scintigraphy...
to detect the gamma ray
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
s emitted by the technetium-99m as it decays
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...
. Two sets of images are acquired. For one set, 99mTc MIBI is injected while the patient is at rest and then the myocardium is imaged. In the second set, the patient is stressed either by exercising on a treadmill or pharmacologically. The drug is injected at peak stress and then imaging is performed. The resulting two sets of images are compared with each other to distinguish ischemic from infarcted areas of the myocardium. This imaging technique is limited to being correct only 76% of the time. The problem lies in choosing which images to compare to what. Resting images as discussed by Gorlin in the late 1950s are useful only for detecting tissue damage, while stress images provide evidence of coronary artery (ischemia) disease. Consequently, comparing these two images has led to many errors in disease detection and to results which fail to match results seen when the arteries of the heart are looked at using coronary angiography. Recent studies taking 10 years to complete have demonstrated (infra) that comparing stress-stress images can accurately detect ischemia while rest-rest images can accurately differentiate between dead (infarcted) heart (myocardium) tissue and stunned or hibernating myocardium.
Sestamibi was previously thought to not redistribute because earlier studies looked at individuals with no ischemia. This was an error unsupported by Maublant, Crane, Li, Fleming and Ono. The washout or redistribution rate (FHRWW) for such individuals without heart disease was approximately 15–20%, with half of this (10%) the result of technetium-99m decay over 55 minutes. It is now known that sestamibi redistributes more under conditions of ischemia with the most critical disease only detectable by "wash-in" where the Black Hole effect of cardiology is detected by a delay in uptake by the tracer (both sestamibi and myoview) during the first few minutes. Failure to image the heart at 5 minutes after stress leads to these individuals being missed and approximately 100,000 deaths each year in the United States alone. Specifically, the count activity increases at 60 minutes compared with 5-minute images when critical narrowing of coronary arteries is present.
With dipyridamole (Persantine MIBI scan)
When combined with the drug dipyridamoleDipyridamole
Dipyridamole is a drug that inhibits thrombus formation when given chronically and causes vasodilation when given at high doses over a short time.-Mechanism and effects:...
, a brand name of which is Persantine, a MIBI scan is often referred to as a Persantine MIBI scan.
Parathyroid imaging
In primary hyperparathyroidism, one or more of the four parathyroid glands either develops a benign tumor called an adenomaAdenoma
An adenoma is a benign tumor of glandular origin. Adenomas can grow from many organs including the colon, adrenal glands, pituitary gland, thyroid, prostate, etc. Although these growths are benign, over time they may progress to become malignant, at which point they are called adenocarcinomas...
or undergoes hypertrophy as a result of homeostatic dysregulation. The parathyroid gland takes up 99mTc MIBI following an intravenous injection, and the patient's neck is imaged with a gamma camera to show the location of all glands. A second image is obtained after a washout time (approximately 2 hours), and mitochondria in the oxyphil cells of the abnormal glands retaining the 99mTc are seen with the gamma camera. This imaging method will detect 75 to 90 percent of abnormal parathyroid glands in primary hyperparathyroidism. An otolaryngologist or an endocrine surgeon can then perform a directed parathyroidectomy (less invasive than traditional surgery) to remove the abnormal gland.
Breast imaging
The drug is also used in the evaluation of breast nodules. Malignant breast tissues concentrate 99mTc MIBI to a much greater extent and more frequently than benign disease. As such, limited characterization of breast anomalies is possible. Scintimammography has a high specificity for breast cancer, and has a sensitivity of 66% based on positive biopsy compared to mammography and ultrasound with a 29% positive biopsy.Radioguided surgery of the parathyroids
Following administration, 99mTc MIBI collects in overactive parathyroid glands. During surgerySurgery
Surgery is an ancient medical specialty that uses operative manual and instrumental techniques on a patient to investigate and/or treat a pathological condition such as disease or injury, or to help improve bodily function or appearance.An act of performing surgery may be called a surgical...
, the surgeon can use a probe sensitive to gamma rays to locate the overactive parathyroid before removing it.