Technetium (99mTc) sestamibi

"MIBI scan" redirects here. For the MIBG scan, see Iobenguane.

Technetium (^99mTc) sestamibi

Systematic (IUPAC) name
Hexakis(2-methoxy-2-methylpropylisonitrile) technetium (99mTc)
Clinical data
Licence data	US FDA:link
Pregnancy cat.	C(US)
Legal status	℞-only (US)
Routes	Intravenous
Pharmacokinetic data
Bioavailability	NA
Protein binding	1%
Metabolism	Nil
Half-life	Variable
Excretion	Fecal (33%) and renal (27%)
Identifiers
CAS number	109581-73-9
ATC code	V09GA01
PubChem	CID 5384
Chemical data
Formula	C36H66N6O6Tc
Mol. mass	777.852 g/mol
Y(what is this?)  (99mTc) sestamibi (verify)

Technetium (^99mTc) 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.

Cardiac imaging

Main article: Myocardial perfusion imaging

Technetium (^99mTc) sestamibi is a lipophilic 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 rays 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^[when?] 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.^{[citation needed]} 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 dipyridamole, a brand name of which is Persantine, a MIBI scan is often referred to as a Persantine MIBI scan.

Parathyroid imaging

Main article: Sestamibi parathyroid scan

In primary hyperparathyroidism, one or more of the four parathyroid glands either develops a benign tumor called an adenoma 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

Main article: Scintimammography

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.^{[citation needed]}

Radioguided surgery of the parathyroids

Following administration, ^99mTc MIBI collects in overactive parathyroid glands. During surgery, the surgeon can use a probe sensitive to gamma rays to locate the overactive parathyroid before removing it.^[1]

References

1. ^ Untch, B. R.; Barfield, M. E.; Bason, J.; Olson Jr, J. A. (2007). "Minimally Invasive Radio-guided Surgery for Primary Hyperparathyroidism". Annals of Surgical Oncology 14 (12): 3401–3402. doi:10.1245/s10434-007-9519-0. PMID 17899291.  edit

External links

• Cardiolite.com
• Dilon Breast-Specific Gama Imaging
• Miraluma
• Myoview.com
• Parathyroid.com
• Pharmalucence Inc.
• POLATOM.PL