Protocols for two-day (top) and one-day (bottom) examinations.
In the remaining cases, the radiopharmaceutical must be administered twice. If the stress examination shows normal perfusion and muscle contractility, no additional resting examination is required, which significantly reduces the patient’s exposition to radiation. In low-risk patients, a stress SPECT-CT examination with attenuation correction is performed first to exclude coronary artery disease. At the Silesian Center for Heart Diseases, the only radiopharmaceutical used for myocardial perfusion imaging is 99mTc-MIBI, and the most frequently employed acquisition protocol is the two-day protocol.įigure 1 presents the 2-day and the one-day protocol using radiopharmaceuticals labeled with 99mTc. Notwithstanding, most current perfusion investigations are performed with the use of non-redistributable compounds labeled with 99mTc. Some laboratories use mixed protocols using both 201Tl and 99mTc. Firstly, it is obtained with the use of a cyclotron secondly, its long half-life requires the use of appropriately smaller activities, which in turn translates into worse image quality. However, the use of 201Tl is not widespread for two main reasons. A one-time administration of 201Tl at peak stress enables the performance of a one-day examination that will visualize radiotracer uptake during stress as well as rest because the radiotracer is redistributed after a while. The latter, hardly used in Poland, differs from the compounds labeled with technetium in that it undergoes redistribution in the myocardium. Other radiotracers include tetrofosmin or thallium ( 201Tl). The most frequently used radioactive tracer is methoxy-isobutyl-isonitrile (MIBI) labeled with technetium 99m ( 99mTc-MIBI). The imaging of cardiac perfusion involves the use of radiopharmaceuticals their uptake by muscle cells is directly proportional to blood flow. This type of examination involves both transmission and emission as it consists in both a tomographic examination (exposition to X-ray radiation) and a second, main tomographic examination, superimposed over the first one, for imaging left ventricular perfusion (emission scintigraphy). CT enables reconstruction with attenuation correction, facilitating the elimination of false perfusion deficits resulting from the attenuation of emission by extracardiac tissues. The gamma camera, turning around the patient’s chest and imaging the isotope’s activity in many angular projections, enables the reconstruction of the 3D geometry of isotope activity within the heart.Ī SPECT-CT device is additionally equipped with a tomograph integrated with the gamma camera.
In this manner, the radiotracer’s activity in the examined organ is visualized as a projection on a plane. The registered light impulses are multiplied by photomultipliers and converted into electric current of various intensity. The main element of the gamma camera is the scintillator crystal, which, under the influence of gamma radiation, emits photons visible as flashes of light (i.e., scintillations hence the phrase “single-photon” in the name of the examination). After the image is reconstructed, radiotracer activity is evaluated in sections along the short and long axis: the sagittal and frontal section. Isotopic tomographic examination enables the determination of radiotracer accumulation in many sections. The name tomography stems from Greek tomos, meaning “section” or “cut”. The source emitting the radiation is the patient, who is administered a radioactive tracer. Single-photon emission computed tomography (SPECT) is an imaging method that enables, among other things, the evaluation of myocardial perfusion.
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