Computed Tomography Equipment Techniques PDF

Middle Technical University (MTU) College of Health and Medical Techniques -Baghdad Radiological Techniques Department Computed Tomography EquipmentsTechniques Second stage/ 2nd coarse Title: Positron Emission Tomography/ PET-CT Single-photon emission computed tomography (SPECT) Name of the instruct...

Middle Technical University (MTU) College of Health and Medical Techniques -Baghdad Radiological Techniques Department Computed Tomography EquipmentsTechniques Second stage/ 2nd coarse Title: Positron Emission Tomography/ PET-CT Single-photon emission computed tomography (SPECT) Name of the instructor: Lec. Dr. Lamyaa Fadhil Abdul Hussein Target population: Students of second class 99 Positron Emission Tomography/ PET-CT Positron emission tomography, also called PET imaging or a PET scan, is a type of nuclear medicine imaging, of dual-modality imaging that utilizes the advantages of both positron emission tomography (PET) and computed tomography (CT). Nuclear medicine uses small amounts of radioactive material called radiotracers, to diagnose, evaluate, and treat various diseases. Radiotracers are molecules linked to, or "labeled" with, a small amount of radioactive material. They accumulate in tumors or regions of inflammation. They can also bind to specific proteins in the body. The most common radiotracer is 2-[F-18]fluoro-2-deoxy-D-glucose (FDG), a molecule similar to glucose. Fluorine-18 is an unstable radioisotope and has a half-life of approximately 110 minutes. Cancer cells are more metabolically active and may absorb glucose at a higher rate. It accumulates in the area under examination. A special camera detects gamma ray emissions from the radiotracer. The camera and a computer produce pictures and supply molecular information.CT imaging uses special x-ray equipment to produce multiple images of the inside of the body. A radiologist views and interprets these images on a computer monitor. CT imaging provides excellent anatomic information. Figure1: the principle of PET-CT 100 The common uses of PET-CT detect cancer and/or make a diagnosis. determine whether a cancer has spread in the body. staging of cancer which potentially can be treated radically establish baseline staging before commencing treatment determine if a cancer has returned after treatment. evaluate prognosis. assess tissue metabolism and viability. map normal human brain and heart function. assessing response to therapy evaluation of suspected disease recurrence, relapse and/or residual disease The procedure of PET-CT Ordinary x-ray exams pass x-rays through the body to create an image. The radioactive materials (F-18 fluorodeoxyglucose) injected the bloodstream intravenously, or may swallow it or inhale it as a gas. The material accumulates in the area under examination (tumor cells, that have a high metabolic rate), where it gives off gamma rays. Special cameras detect this energy and, with the help of a computer, create pictures that detail how the organs and tissues look and function. Unlike other imaging techniques, nuclear medicine focuses on processes within the body. These include rates of metabolism or levels of various other chemical activities. of the radiotracer and where there is a high level of chemical or metabolic activity. Less activity. 101 The radioactive materials detection The positron-emitting isotope administered to the patient undergoes + decay in the body, with a proton being converted to a neutron, a positron (the antiparticle of the + particle), and a neutrino. The positron travels a short distance and annihilates with an electron. The annihilation reaction results in the formation of two high energy photons which travel in diametrically opposite directions. Each photon has an energy of 511 keV. Two detectors at opposite ends facing each other detect these two photons traveling in opposite directions, and the radioactivity is localized somewhere along a line between the two detectors. This is referred to as the line of response, fig.(2). Figure 2. Beta decay causing the positron electron annihilation at 180 degree. PET-scanner These scanners are made up of the various many small detectors which are usually placed in adjacent rings around the patient. The clinical PET system was having a ring 102 diameter of 70 100 cm with the extent of 10 25 cm and made up to 25,000 detectors. The single PET detector is made up of the very high-density scintillator crystal which are capable of converting the photons striking on the detector into light. The crystals used in the construction of PET scanner detectors are called scintillators. Photons interact in the crystal, resulting in the emission of light, which is collected by an array of photomultiplier tubes (PMT), where the light will be converted into an amplified electric signal (Figure 3). Figure 3: the principle of PET-CT Single photon emission computed tomography (SPECT) is a three-dimensional nuclear medicine imaging technique combining the information gained from scintigraphy with that of computed tomography. This allows the distribution of the radionuclide to be displayed in a three-dimensional manner offering better detail, contrast and spatial information than planar nuclear imaging alone. It is used to help diagnose seizures, strokes, stress fractures, infections, and tumors in the spine. shows how blood flows into and within tissues and organs. 103 Design SPECT machines combine an array of gamma cameras (ranging from one to four cameras) which rotate around the patient on a gantry. SPECT may be also combined with a separate CT machine in a form of hybrid imaging; single photon emission computed tomography-computerized tomography (SPECT-CT) mainly for the purposes of attenuation correction and anatomical localization. Principle Gamma cameras rotate around the patient providing spatial information on the distribution of the radionuclide within tissues. The use of multiple gamma cameras increases detector efficiency and spatial resolution. The projection data obtained from the cameras are then reconstructed into three-dimensional images usually in axial slices. When SPECT-CT is used, attenuation correction and higher resolution anatomical localization can be achieved SPECT vs PET Single photon emission computed tomography (SPECT) and positron emission tomography (PET) are nuclear medicine imaging techniques which provide metabolic and functional information unlike CT and MRI. They have been combined with CT and MRI to provide detailed anatomical and metabolic information. Positron emission tomography (PET): uses positron emitting radioisotope (tracer) o F-18 fluorodeoxyglucose (FDG) gives better contrast and spatial resolution (cf. SPECT) has a ring of multiple detectors 104 Single-photon emission computed tomography (SPECT): uses gamma emitting radioisotope (tracer): o technetium-99m o iodine-123 o iodine-131 gives poorer contrast and spatial resolution (cf. PET) usually one large crystal based detector 105