Computed tomography (CT) Scan also called computerized axial tomography (CAT) scan or body section röntgenography is the process of the creating a cross-sectional tomography plane (slice) of any part of the body. The word "tomography" is derived from the Greek tomos (slice) and graphein (image). A patient is scanned by an x-ray tube rotating about the body part being examined. A detector assembly detects the radiation The image which is reconstructed by a computer using x-ray absorption measurement collected al multiple points about the periphery of the part being scanned.
Today, CT is a well-accepted imaging modality for many body applications, since CT imaging often provide a great deal of unique diagnostic information. CT is used for a wide variety of neurologic and somatic procedures. CT provides diagnostic information that cannot be achieved with any other method. The most common procedures involve the head (e.g., brain, skull, sinuses, facial bones, orbits, IACs and sella tursica),chest, abdomen and pelvic (e.g., liver, gallbladder, pancreas, spleen,kidney,adrenal glands, intestines, reproductive organs). Computed tomography is used to detect abnormalities such as blood clots, cysts, fractures, infections, and tumors in internal structures (e.g., bones, muscles, organs, soft tissue). It also can be used to detect abnormalities in the neck and spine (e.g., vertebrae, intervertebral discs, spinal cord) and in nerves, blood vessels upper and lower extremities.
The procedure also may be used to guide the placement of instruments within the body (e.g., to perform a biopsy) and drainage of fluid collections offer an alternative to surgery for some patients. Although the procedures are considered invasive, they offer shorter recovery periods, no exposure to anesthesia, and less risk of infection. CT is also used in radiaio oncology for radiation therapy treatment planning. CT Scan taken through the treatment field, with the patient in treatment position, have drastically improved the accuracy and quality of therapy provided.
The amount of radiation used in a CT scan is low, and the procedure is considered to be safe. However, CT scans should be used with caution in women who are pregnant, especially during the first trimester. Other diagnostic tests (e.g., ultrasound) may be used during pregnancy.
Comparison with conventional radiography
Reviewing conventional radiography helps explain the uniquensess of CT diagnostic information. When a conventional x-ray exposure is made, the transmitted radiation passes through the patien and is detected by x-ray film or an image-intensifer phosphor. First, for each exposure to radiation, one diagnostic image with a fixed density and contrast is produced. Second, all body structures are superimposed on one sheet of x-ray film. Thus, the highlighting of certain anatomy requires exact positioning of the patient. Often the use of contrast agents, and frequently more than one exposure.
Low tissue density that would normally be abscured by higher-density anatomy on a conventional radiograph can be clearly visualized with CT. for this reason CT is valuable in neurologic work in which the brain is surrounded by the skull. Like wise, in many body examinations. Low tissue density that would otherwise be hidden or blend with surrounding anatomy can be clearly visualized.
Although it seems obvious, it should also be noted that the CT image displays the entire cross section of the slice of anatomy that was scanned. Thus the size and location of any pathologic condition can be determined with extreme accuracy within a given CT slice. With conventional radiography, multiple exposures and contrast media are often required to estimate the size and location of the diseased area.
Contrast of Image : CT measures and can reveal significantly more minute differences in x-ray attenuation than can be recorded by conventional radiography. For example, conventional radiography requires a minimum difference in tissue of a 2% to 5% to radiographyically separate the structures. CT can resolve differences in tissue density as low as 0.5%. in Figure below the gray and the white matter in the brain can be distinguished easily.
Image manipulation : In conventional radiography, only a single radiography with a fixed contrast and density is obtained for each patient exposure to radiation. Once the film has been processed, the patient must be exposed to radiation again to produce another image. The CT image, on the other hand, is the result of complex mathematical calculation that the computer performs to reconstruct an image which is stored in the computer’s memory. The CT image is displayed on the monitor and can be altered in many ways.
HISTORICAL DEVELOPMENT
In the early 1900s, the Italian radiologist Alessandro Vallebona proposed a method to represent a single slice of the body on the radiographic film. This method was known as tomography. The idea is based on simple principles of projective geometry: moving synchronously and in opposite directions the X-ray tube and the film, which are connected together by a rod whose pivot point is the focus; the image created by the points on the focal plane appears sharper, while the images of the other points annihilate as noise. This is only marginally effective, as blurring occurs only in the "x" plane. There are also more complex devices which can move in more than one plane and perform more effective blurring.
The first successful clinical demonstration of CT was conducted in 1970 by Godfrey Newbold Hounsfield from the Central Research Laboratory of EMI, Ltd and Dr.James Ambrose, a physician at Atkinson Morley’s Hospital in London , England are generally given credit for development of CT. In 1971 the first full-scale unit for head scanning was installed at Atkinson Morley’s Hospital, Wimbledon, England. Its value for providing neurologic information enabled it to again rapid acceptance.
The first CT units in the United States were installed in 1973 at the Mayo Clinic and Massachusets General Hospital. In 1974, Dr. Robert Ledley at Georgetown University Medical Center developed the first scanner capable of visualizing any section of the body (whole body scanner) which greatly expanded the diagnostic capabilities of CT.
TECHNICAL ASPECTS
To obtain one axial image, a series of steps is performed by the computer. The tube rotates about the patient, radiating the area of interest. The detector measure the remnant radiation, translate it into an attenuation coefficient, and relay it to the computer. When the computer receives the data from detector, it creates a CT number based on the average intensity of the remnant radiation
CT numbers are also termed Hounsfield units (HU). CT numbers or Hounsfield units ( HU in honor of the inventor Godfrey Newbold Hounsfield) are defined as relative comparison of x-ray attenuation of each voxel of tissue with an equal volume of water. CT numbers or HU varies proportionately with tissue density ( high CT number indicate dense tissue, low CT number indicate less dense tissue).
In general, they are related to the attenuation coefficient of water (µw) as follow :
HU = (µ- µw) x 1000 x 1/ µw
Table 1. Sample CT numbers for various tissues.
Tissue CT number (HU)
Metal +2000 to +4000
Bone +1000
Liver +40 to +60
Aorta +35 to +50
White matter ~+20 to +30 HU
Grey matter ~+37 to +45 HU
Tumor +25 to +100
Blood ( Fluid) +25 to +50
Blood (clotted) +50 to +75
Blood (old) +10 to +15
Muscle +10 to +40
Kidney +30
Cerebrospinal fluid +15
Gall Bladder +5 to +30
Cyst -5 to +10
Water 0
Orbits -25
Fat -50 to -100
Air -1000
In accordance with this system, lesions whose attenuation values are close to that of water are consistent with, but not specific for, cysts. Lesions composed solely or predominantly of fat produce negative CT numbers; however, some types of liposarcoma contain great amounts of fat, and some forms of lipoma reveal abundant nonfatty tissue. haematomas characteristically demonstrate inhomogeneous areas with regions of both high attenuation (approximately 50 HU) and low attenuation (approximately 10 HU) in the subacute stage and homogeneous areas of low attenuation (120 HU) in the chronic stage. The measurement of attenuation values of bone lesions may be more difficult, especially in narrow bones in which the contribution of the cortex may prohibit accurate assessment.
The identification of gas in soft tissue or bone by CT is possible owing to its very low attenuation value. Gas within a vertebral body documented by CT, for example, is an important sign of ischaemic necrosis of bone. Intraosseous gas is also identified in some cases of osteomyelitis and in subchondral cysts (pneumatocysts), particularly in the ilium and vertebral body.
SCANNER COMPONENTS
The major components of a CT scanner are the computer and operator console, the gantry, and the table. Scanner will have slight variations in design and appearance according to manufactures.
The gantry houses the x-ray tube, data acquisition system (DAS; part of the detector assembly that converts analog signals to digital signals ttaht can be used by the CT computer), and detector for radiation production and detection. Every gantry has an opening, or aperture, to accommodate most patients. The Gantry can be tilted in either direction.
The table is an automated device linked to the computer and gantry. CT tables are made of either wood or low-density carbon composite, both of which will support the patients without causing image artifacts
The operator console is the point from which the operator controls the scanner. In this area operator (radiographer) can adjust the examination protocols, adjust the image by changing the width or center (level) of the window.
The Procedures of CT Scan Examination
Before undergoing a CT scan, patients must remove all metallic materials (e.g., jewelry, clothing with snaps, zippers) and may be required to change into a hospital gown that will not interfere with the x-ray images. Patients lie on a movable table, which is slipped into a doughnut-shaped computed tomography scanner.
To provide clear images, patients must remain as still as possible during CT scan. At certain points during a CT scan of the chest or abdomen, the radiographers may ask the patient not to breathe for a few seconds. CT scans can be performed on an outpatient basis, unless they are part of a patient's inpatient care. Although each facility may have specific protocols in place, generally, CT scans follow this process:
1. When the patient arrives for the CT scan, he/she will be asked to remove any clothing, jewelry, or other objects that may interfere with the scan.
2. If the patient will be having a procedure done with contrast, an intravenous (IV) line will be started in the hand or arm for injection of the contrast medication. For oral contrast, the patient will be given medication to swallow.
3. The patient will lie on a scan table that slides into the gantry
4. As the scanner begins to rotate around the patient, x-rays will pass through the body for short amounts of time.
5. A detector assembly detect the x-rays exiting the patient and feeds back the information, referred to as raw data to the host computer.
6. The computer will transform the information into an image to be interpreted by the radiologist.
CONTRAST AGENT
A contrast agent (e.g., iodine-based dye, barium solution) may be administered prior to CT scan to allow organs and structures to be seen more easily. Contrast agents can be administered through a vein (IV), by injection, or taken orally. Patients usually are instructed not to eat or drink for a few hours prior to contrast injection or IV because the dye may cause stomach upset. Patients may be required to drink an oral contrast solution 1–2 hours before CT scan of the abdomen or pelvis.
Contrast dye may cause a rash, itching, or a feeling of warmth throughout the body. Usually, these side effects are brief and resolve without treatment. Antihistamines may be administered to help relieve symptoms.
A severe anaphylactic reaction (e.g., hives, difficulty breathing) to the contrast dye may occur. This reaction, which is rare, is life threatening and requires immediate treatment. Patients with a prior allergic reaction to contrast dye or medication and patients who have asthma, emphysema, or heart disease are at increased risk for anaphylactic reaction. Epinephrine, corticosteroids, and antihistamines are used to treat this condition. Rarely, contrast dye may cause kidney failure. Patients with diabetes, impaired kidney function, and patients who are dehydrated are at higher risk for kidney failure.
Advances in computed tomography technology
Advances in computed tomography technology include the following:
• high-resolution computed tomography
This type of CT scan uses very thin slices (less than one-tenth of an inch), which are effective in providing greater detail in certain conditions such as lung disease.
• helical or spiral computed tomography
During this type of CT scan, both the patient and the x-ray beam move continuously, with the x-ray beam circling the patient. The images are obtained much more quickly than with standard CT scans. The resulting images have greater resolution and contrast, thus providing more detailed information.
• ultrafast computed tomography (also called electron beam computed tomography)
This type of CT scan produces images very rapidly, thus creating a type of "movie" of moving parts of the body, such as the chambers and valves of the heart. This scan may be used to obtain information about calcium build-up inside the coronary arteries of the heart.
• Multidetector computed tomography: Multidetector computed tomography(MDCT) is also known by a confusing array of other terms such as multidetector CT, multidetector-row computed tomography, multidetector-row CT, multisection CT, multislice computed tomography, and multislice CT MSCT).
In MDCT or MSCT, a two-dimensional array of detector elements replaces the linear array of detector elements used in typical conventional and helical CT scanners. The two-dimensional detector array permits CT scanners to acquire multiple slices or sections simultaneously and greatly increase the speed of CT image acquisition. Image reconstruction in MDCT or MSCT is more complicated than that in single section CT. Nonetheless, the development of MDCT has resulted in the development of high resolution CT applications such as CT angiography and CT colonoscopy. .
• Combined computed tomography and positron emission tomography (PET/CT)
The combination of computed tomography and positron emission tomography technologies into a single machine is referred to as PET/CT. PET/CT combines the ability of CT to provide detailed anatomy with the ability of PET to show cell function and metabolism to offer greater accuracy in the diagnosis and treatment of certain types of diseases, particularly cancer. PET/CT may also be used to evaluate epilepsy, Alzheimer's disease, and coronary artery disease.
Patient Radiation Doses
The various factor affecting patient dose are;patient thickness, generator and tube factors (kilovoltage, filtration, tube current, scan on time and focal-spot size), gantry factors (beam collimation, slice width and overlap, scan orientation, and detector efficiency), and image quality desired.
The main issue within radiology today is how to reduce the radiation dose during CT examinations without compromising the image quality. Generally, a high radiation dose results in high-quality images. A lower dose leads to increased image noise and results in unsharp images. Unfortunately, as the radiation dose increases, so does the associated risk of radiation induced cancer - even though this is extremely small. A radiation exposure of around 1200 mrem (similar to a 4-view mammogram) carried a radiation-induced cancer risk of about a million to one. However, there are several methods that can be used in order to lower the exposure to ionizing radiation during a CT scan.
1. New software technology can significantly reduce the radiation dose. The software works as a filter that reduces random noise and enhances structures. In this way, it is possible to get high-quality images and at the same time lower the dose by as much as 30 to 70 percent.
2. Individualize the examination and adjust the radiation dose to the body type and body organ examined. Different body types and organs require different amounts of radiation.
3. Prior to every CT examination, evaluate the appropriateness of the exam whether it is motivated or if another type of examination is more suitable.
COMPUTED TOMOGRAPHY (CT SCAN)
NUCLEAR MEDICINE
Nuclear medicine is a branch of medical imaging that involves the use of radioactive isotopes in the diagnosis and treatment of disease. This imaging may also be referred to as radionuclide imaging or nuclear scintigraphy. The procedures use pharmaceuticals that have been labeled with radionuclides (radiopharmaceuticals). The radionuclides used in nuclear medicine are produced in nuclear reactors or particle accelerator (cyclotrons). In diagnosis, radiopharmaceuticals are administered to patients and the radiation emitted is measured using a gamma camera. The radiation from the radiopharmaceutical makes it possible to radiograph the distribution of the medicinal product throughout the body. The radiation is usually very low, lower than the level of radiation from X-ray investigations.
History
Nuclear medicine began as a medical specialty area for diagnosis and treatment of disease in the late 1950s and early 1960s.However, long before that in the early 1800s scientists such as Jhon Dalton and Amedeo Avogadro were proposing theories on atomic and molecular structure that would serve as the basis for later research and eventually the discovery of radioactivity by A.H.Becquerel in 1896.
Its origins stem from many scientific discoveries, most notably the discovery of x-rays in 1895 and the discovery of "artificial radioactivity" in 1934. The first clinical use of "artificial radioactivity" was carried out in 1937 for the treatment of a patient with leukemia at the University of California at Berkeley.
A landmark event for nuclear medicine occurred in 1946 when a thyroid cancer patient's treatment with radioactive iodine led to complete disappearance of the patient's cancer. This has been considered by some as the true beginning of nuclear medicine. Wide-spread clinical use of nuclear medicine, started in the early 1950s as its use increased to measure the function of the thyroid and to diagnose thyroid disease and for the treatment of patients with hyperthyroidism.
In the mid-sixties and the years that followed, the growth of nuclear medicine as a specialty discipline was phenomenal. The use of nuclear medicine as a specialty discipline began to see exciting growth with significant advances in nuclear medicine technology. The 1970s brought the visualisation of most other organs of the body with nuclear medicine, including liver and spleen scanning, brain tumour localisation, and studies of the gastrointestinal tract.The 1980s saw the use of radio-pharmaceuticals for such critical diagnoses as heart disease and the development of digital computers to add additional power to the technique.
Today, very complex imaging and computer systems are used with these different radioactive components, not only to image and threat disease, but also to provide functional and quantitative analysis of many body system. Nuclear medicine has found a unique niche in the medical imaging field by virtue of its functional imaging capacity.
Physical Principles of Nuclear Medicine
The atomic number describes the number of protons in the nucleus. For a neutral atom this is also the number of electrons outside the nucleus. Subtracting the atomic number from the atomic mass number gives the number of neutrons in the nucleus.
Isotopes are atoms of the same element (i.e., they have the same number of protons, or the same atomic number) which have a different number of neutrons in the nucleus. Isotopes of an element have similar chemical properties. Radioactive isotopes are called radioisotopes. Most of the elements in the periodic table have several isotopes, found in varying proportions for any given element. The average atomic mass of an element takes into account the relative proportions of its isotopes found in nature.
A nuclear binding force holds the nucleus of the atom together. The nuclear mass defect, a slightly lower mass of the nucleus compared to the sum of the masses of its constituent matter, is due to the nuclear binding energy holding the nucleus together. The mass defect can be used to calculate the nuclear binding energy, with E = mc2. The average binding energy per nucleon is a measure of nuclear stability. The higher the average binding energy, the more stable the nucleus.
The Bohr model of the atom described the electrons as orbiting in discrete, precisely defined circular orbits. Electrons can only occupy certain allowed orbitals. For an electron to occupy an allowed orbit, a certain amount of energy must be available.Each orbit is assigned a quantum number, with the lowest quantum numbers being assigned to those orbitals closest to the nucleus. Only a specified maximum number of electrons can occupy an orbital. Under normal circumstances, electrons occupy the lowest energy level orbitals closest to the nucleus. By absorbing additional energy, electrons can be promoted to higher orbitals, and release that energy when they return back to lower energy levels.
Photons are used to describe the wave-particle duality of light. The energy of a photon depends upon its frequency. This helps to explain the photoelectric effect; only photons having a sufficiently high energy are capable of dislodging an electron from the illuminated surface. E = hv where E is the photon energy in J, v is the photon frequency in Hz, and h is Planck's constant, 6.626 x 10-34 J/Hz.Quantum theory offers a mathematical model to help explain the nature of the atom.Quantum theory describes a region surrounding the nucleus which has the highest probability of locating an electron. These orbital "clouds" have some unusual and interesting shapes.
Radioactive decay is the process in which an unstable atomic nucleus spontaneously loses energy by emitting ionizing particles and radiation. These emissions are collectively called ionizing radiations. Depending on how the nucleus loses this excess energy either a lower energy atom of the same form will result, or a completely different nucleus and atom can be formed. The most common types of radiation are called alpha, beta, and gamma radiation, but there are several other varieties of radioactive decay.Radioactive decay rates are normally stated in terms of their half-lives, and the half-life of a given nuclear species is related to its radiation risk. The different types of radioactivity lead to different decay paths which transmute the nuclei into other chemical elements. Examining the amounts of the decay products makes possible radioactive dating.
There are quite a few naturally occurring radionuclides. Any nuclide with an atomic number greater than 83 is radioactive. An atom's atomic number is simply the total number of protons found in the nucleus. There are also many naturally occurring radionuclides with lower atomic numbers.While some radionuclides occur naturally in the environment, there is another class of "man-made" or artificial radionuclides. Artificial radionuclides are generally produced in a cyclotron or some other particle accelerator, in which stable nucleus bombarded by specific particles (neutrons, protons, electrons or some combination of these). By doing so, the nucleus of starting material unstable, and this nucleus will then try to become stable by emitting radioactivity.
Nuclear Pharmacy (radiopharmaceuticals)
Nuclear Pharmacy involves the preparation of radioactive materials for use in nuclear medicine procedures. Radionuclides are combined with other chemical compounds or pharmaceuticals to form radiopharmaceuticals. Radiopharmaceuticals are administered to patients and the radiation emitted can localize to specific organs or cellular receptors. The external detectors (gamma cameras) capture and form images from the radiation emitted by the radiopharmaceuticals.
The concept of nuclear pharmacy was first described in 1960 by Captain William H. Briner while at the National Institutes of Health (NIH) in Bethesda, Maryland. Along with Mr. Briner, John E. Christian, who was a professor in the School of Pharmacy at Purdue University, had written articles and contributed in other ways to set the stage of nuclear pharmacy. William Briner started the NIH Radiopharmacy in 1958. He also brought about principles and procedures important to the assurance of quality radiopharmaceuticals. Christian developed the first formal lecture and laboratory courses in the United States for teaching the basic principles of radioisotope applications. John Christian and William Briner were both active on key national committees responsible for the development, regulation and utilization of radiopharmaceuticals.
In the mid 1970s a petition was formed requesting the formation of a Section on Nuclear Pharmacy in the Academy of General Practice, currently called the Academy of Pharmacy Practice and Management. On April 23, 1975, the petition was finally approved by the American Pharmacists Association (APhA) Board of Trustees. Nuclear pharmacy thus became a new area in pharmacy.
The most commonly used isotope in nuclear medicine is Technetium-99m that is readily and continuously available from a generator system. This generator system uses molybdenum-99 as the ‘parent.”Molybdenum-99 can be the product of either U-235 fission in a nuclear rector or neutron radiation of Mo-98 in reactor. Molybdenum-99 has a half life of 66.7 hours and decay (82%) to a daughter product known as metastable technetium (Tc 99m). The most commonly used radioisotope in nuclear medicine F-18, is not produced in any nuclear reactor, but rather in a circular acclererator called a cyclotron. The cyclotron is used to accelerate protons to bombard the stable heavy isotope of oxygen O-18. The O-18 constitutes about 0.20% of ordinary oxygen (mostly O-16), from which it is extracted. A typical nuclear medicine study involves administration of a radionuclide into the body by intravenous injection in liquid or aggregate form, ingestion while combined with food, inhalation as a gas or aerosol, or rarely, injection of a radionuclide that has undergone micro-encapsulation. Some studies require the labeling of a patient's own blood cells with a radionuclide (leukocyte scintigraphy and red blood cell scintigraphy). Most diagnostic radionuclides emit gamma rays, while the cell-damaging properties of beta particles are used in therapeutic applications. Refined radionuclides for use in nuclear medicine are derived from fission or fusion processes in nuclear reactors, which produce radioisotopes with longer half-lives, or cyclotrons, which produce radioisotopes with shorter half-lives, or take advantage of natural decay processes in dedicated generators, i.e. molybdenum/technetium or strontium/rubidium.
The most commonly used intravenous radionuclides are: Technetium-99m, Iodine-123 and 131, Gallium-67, Thallium-201, Fluorine-18 Fluorodeoxyglucose, and Indium-111 Labeled Leukocytes. The most commonly used gaseous/aerosol radionuclides are: Krypton-81m, Xenon-133, Technetium-99m Technegas, and Technetium-99m DTPA
The generator forms the radionuclide that is retained on an internal column until the generator is "milked". When "milking" the generator, sodium chloride is passed over the column, which removes the radioactive material. The eluate is then collected in a shielded evacuated vial. After performing quality assurance tests on the eluate, it can be used in the preparation of the final radiopharmaceutical products.
Clinical Nuclear Medicine
Nuclear medicine procedures are generally divided into three basic categories : in Vivo, in Vitro/radioimmunoassay (RIA) and radionuclide therapy procedures.
In Vivo Procedures
The term in vivo is defined as “ within the living body.” This category includes all diagnostic nuclear medicine imaging procedures. Since diagnostic imaging procedures are based on the distribution of radiopharmaceuticals”within the body,”they are classified as in vivoexaminations.
There are wide variety of in vivo/diagnostic imaging examination performed in nuclear medicine. These examination can be described based on the imaging method used : Static, whole body dynamic, Single Photon Emission Computed Tomography (SPECT), and Positrion Emission Tomography (PET).
In Vitro Procedures
In vitro is defined as “ withn a glass; observable n a test tube; in an artificial environment.” This category is use to describe those nuclear medicine examination that require an evaluation or analysis of radioactive samples taken from the human body. Results from these examination are usually a specific quantitative value rather than a diagnostic image.
Radioimmunoassay
Radioimmunoassay (RIA) procedures are performed on body samples such as whole blood, serum, spinal fluid, and urine. Spesific target structures or ligands, such as antibodies or metabolically active drugs, are labeled with a radioactive tracer to determine their levels. Examples radioimmunoassay include thyroid hormone values (T3-Triiodothyronine, T4-Thyroxine, or TSH-thyroid stimulating hormone), drug levels (digoxin, digitoxin, methyltrexate, theophylline, aminophylin, cyclosporine), and vitamins (Vitamin B12, folic acid). Level of these particular hormones, drugs, and vitamins are determined by counting these labeled samples in a specialized scintillation counter. These assay are very sensitive and specific and are used to determine minute levels (µG/dl) of a wide range of ligands.
Analysis
The end result of the nuclear medicine imaging process is a "dataset" comprising one or more images. In multi-image datasets the array of images may represent a time sequence (ie. cine or movie) often called a "dynamic" dataset, a cardiac gated time sequence, or a spatial sequence where the gamma-camera is moved relative to the patient. SPECT (single photon emission computed tomography) is the process by which images acquired from a rotating gamma-camera are reconstructed to produce an image of a "slice" through the patient at a particular position. A distribution of radionuclide in the patient.
Many of the procedures being performed in nuclear medicine department require some form of quantitative analysis, which provides physicians with numeric results based on function. Specialized software allows nuclear medicine computers to collect, process, and analysis functional information information obtained from nuclear medicine imaging system. Cardiac ejection fraction are one of the more common quantitative results provided from nuclear medicine procedures.
The nuclear medicine computer may require millions of lines of source code to provide quantitative analysis packages for each of the specific imaging techniques available in nuclear medicine. Time sequences can be further analysed using kinetic models such as multi-compartment models or a Patlak plot.
Radiation Safety
The radiation protection requirements in nuclear medicine are unique and different from general radiation safety measures used for diagnostic x-ray. Most of the radionuclides used in nuclear medicine are in either liquid or gaseous form. Because of the nature of radioactive decay, these liquids or gases continually emit radiation (unlike diagnostic x –ray which can turn on and off mechanically) and therefore require special precautions.
The radiation dose from a nuclear medicine investigation is expressed as an effective dose with units of sieverts (usually given in millisieverts, mSv). The effective dose resulting from an investigation is influenced by the amount of radioactivity administered in megabecquerels (MBq), the physical properties of the radiopharmaceutical used, its distribution in the body and its rate of clearance from the body.
Effective doses can range from 6 μSv (0.006 mSv) for a 3 MBq chromium-51 EDTA measurement of glomerular filtration rate to 37 mSv for a 150 MBq thallium-201 non-specific tumour imaging procedure. The common bone scan with 600 MBq of technetium-99m-MDP has an effective dose of 3 mSv (1).
Formerly, units of measurement were the curie (Ci), being 3.7E10 Bq, and also 1.0 grams of Radium (Ra-226); the rad (radiation absorbed dose), now replaced by the gray; and the rem (Röntgen equivalent man), now replaced with the sievert. The rad and rem are essentially equivalent for almost all nuclear medicine procedures, and only alpha radiation will produce a higher Rem or Sv value, due to its much higher Relative Biological Effectiveness (RBE). Alpha emitters are nowadays rarely used in nuclear medicine, but were used extensively before the advent of nuclear reactor and accelerator produced radioisotopes. The concepts involved in radiation exposure to humans is covered by the field of Health Physics.
In order to provide protection while handling radioactive material, most compounding is done behind leaded glass shielding and using leaded glass syringe shields and lead containers to hold the radioactive material. Lead is an excellent shielding material that serves to protect the nuclear worker from the radioactive emissions.
