Articles

Articles are a collaborative effort to provide a single canonical page on all topics relevant to the practice of radiology. As such, articles are written and edited by countless contributing members over a period of time. A global group of dedicated editors oversee accuracy, consulting with expert advisers, and constantly reviewing additions.

Create new article

679 results found

Tissue to background ratio

The tissue to background ratio is a measure of the specificity of radiopharmaceutical uptake within the target organ in a nuclear medicine study. It is also referred to as tumor to background ratio in the literature. The presence of radiopharmaceutical in the background (tissues external to the...

Nuclide

A nuclide is a nuclear-centric term describing an atomic species by its nuclear composition and nuclear energy state. A nuclide has a specific number of protons and neutrons and will additionally have a specific energy state of its nucleus. Radionuclides are unstable nuclides that undergo radi...

Metastable state

A metastable state of an isomer is defined as an excited state that exists for greater than 10-6 seconds. In chemical notation, metastable species are identified by the letter 'm'. Typically, excited nuclei will instantaneously decay to a more stable energy state (within 10-15 seconds), emittin...

Isomer

In nuclear physics, isomers are atomic species that are identical in nuclear composition, sharing the same mass and atomic numbers, but differ in their relative energy states, and will therefore differ in their manner of radioactive decay. Examples of isomers include: metastable technetium-99,...

Nuclear shell model

The nuclear shell model is a theoretical construct in nuclear physics which describes that the nucleus of an atom can exist in discrete energy states. This model is partially analogous to the electron orbitals of the atomic shell model. The ground state is the lowest energy state for a specific...

Isotone

Isotones are atomic species that share the same number of neutrons and differ in the number of protons. Examples of isotones include carbon-12, nitrogen-13 and oxygen-14. These atoms all have six neutrons and six, seven and eight protons respectively. A mnemonic that can be used to differentia...

Isobar

Isobars are atomic species that have the same mass number (A), but a different atomic number (Z). Isobars should not be confused with isotopes, which share the same atomic number, and therefore belong to the same chemical element, but have varying mass numbers. Examples of isobars include 14,6...

Electronvolt (unit)

An electronvolt (eV) is defined as the energy required to accelerate a single electron at rest through an electron potential difference of one volt in a vacuum 3. This is different from the electrical potential difference applied to the X-ray tube in terms of kiloVolts (kV) 3. However, the kV ap...

Ripple

Ripple, or voltage ripple, refers to the fluctuation in voltage output of some X-ray generators. It is given a percentage value, and calculated as 100 x (Vmax - Vmin )/Vmax (%). Single-phase and two-phase generators have 100% ripple. Three-phase generators have ripple values between 5 and 15%. ...

Radiation weighting factor

The radiation weighting factor (WR) is a dimensionless constant that accounts for the relative biological effectiveness (RBE) of various types of ionizing radiation. The radiation weighting factor is used to calculate the equivalent dose (HT) by the following equation: Absorbed dose (DT) x rad...

Photopeak

The photopeak refers to the region of the pulse height spectrum caused by the complete photoelectric absorption of gamma rays by the scintillator crystal of a gamma camera. The energy value of the photopeak(s) should correspond to the characteristic energies of the gamma rays emitted by the rad...

Pulse height analyzer

A pulse height analyzer is an instrument used to analyze the frequency distribution of the spectrum of photon energies that are captured by a gamma camera. Energy windows are selected to only allow certain photon energies that fall within a preset range to contribute to the output pulse.

Photomultiplier tube (Gamma camera)

The photomultiplier tube array of a Gamma camera detects the visible light produced by the scintillator, and converts it to a measurable electronic signal 1. A series of photomultiplier tubes are mounted behind the scintillation crystal 1. Each photomultiplier tube is composed of a tightly se...

Scintillator (gamma camera)

The scintillator is the component of a gamma camera which receives the gamma rays emitted from a radionuclide in a nuclear medicine scan and converts it to visible light photons. It is located just behind the collimator device. The scintillator consists of a large, single photoluminescent cryst...

Collimator (Gamma camera)

The collimator of a Gamma camera used in nuclear medicine differs in structure and function to the beam collimators used in general radiography. They typically consist of a lead disc drilled with tens of thousands of closely packed holes, separated from each other by septa. Each hole only acce...

Photoluminescence

Photoluminescence is a property of a material to absorb, store and convert photons to light. Photoluminescent materials have important applications in radiology. Types Fluorescence is the instantaneous emission of light following photon absorption. It typically occurs within 10-8 seconds. Exa...

Transformer

A transformer is a passive electrical device used to transfer electrical energy from one circuit to another, via the phenomenon of electromagnetic induction. It is fundamental in the modulation of voltage and current in the x-ray generator. Components primary coil a set of insulated wires at...

Tube shielding

Tube shielding refers to the use of a material within the X-ray tube housing to limit leakage of scattered radiation, to protect both patients and staff from unnecessary exposure. Lead (Pb) is an ideal material for this purpose due to its high atomic density (Z = 82). Due to these properties, i...

Focusing cup

A focusing cup is a negatively charged, shallow depression on the surface of the cathode of an x-ray tube, which concentrates the electron beam towards the focal spot of the anode. It is typically composed of nickel. The negative charge of the focusing cup helps to accelerate the electrons towa...

Continuous X-ray spectrum

The continuous X-ray spectrum refers the range of photon energies produced in an X-ray tube due to the properties of Bremsstrahlung radiation. The energy of X-ray photons can take a value from zero to the maximum kinetic energy of the incident electrons. Both the continuous X-ray spectrum and ...

Mass attenuation coefficient

The mass attenuation coefficient (also known as the mass absorption coefficient) is a constant describing the fraction of photons removed from a monochromatic x-ray beam by a homogeneous absorber per unit mass. It is equivalent to the linear attenuation coefficient divided by the density of the...

Pixel shift (reregistration)

Pixel shift or reregistration is a post-processing technique used to improve misregistration artifact in digital subtraction angiography, where two images to be subtracted are spatially realigned with respect to one another, by shifting pixels vertically, horizontally or obliquely. Pixel shift...

Sequential CT image acquisition

Sequential CT scanning, also referred to as "scan-move-scan" or "step and shoot", was the conventional method of image acquisition in computed tomography before the advent of helical CT. In sequential scanning, the patient is moved forward along the longitudinal axis of the CT scanner, pausing...

Mean glandular dose

The mean glandular dose (MGD) is an estimate of the average absorbed dose to the glandular tissues of a breast during mammography. It is measured in Gray (Gy). The most commonly accepted method of calculating the mean glandular dose is described by Dance et al (2000): ...

Cardiac strain imaging

Strain imaging is a cardiac imaging technique that detects ventricular deformation patterns and functional abnormalities before they become obvious as regional wall motion abnormalities on conventional cine imaging or echo. It has become more popular lately due to several technological improveme...

Missile effect - MRI safety

Missile effect (or projectile effect) denotes the attraction exerted by the static magnetic field of the MRI scanner on ferromagnetic objects accidentally introduced into the MRI-scanner room (i.e. oxygen bottles, scissors, chairs, etc). This effect involves the risk of impact with the patient (...

Cardiac tissue characterization

Cardiac tissue characterization is a term for an approach in cardiac imaging used for the evaluation of the myocardial tissue in respect to its inherent properties as opposed to cardiac function e.g. in cine or strain imaging. In cardiac magnetic resonance imaging tissue characterization typica...

Late gadolinium enhancement

Late gadolinium enhancement is a technique used in cardiac MRI for cardiac tissue characterization, in particular, the assessment of myocardial scar formation and regional myocardial fibrosis 1-5. Terminology Late gadolinium enhancement is also known under the terms ‘late enhancement’ or ‘dela...

T2* mapping - myocardium

T2* mapping is a magnetic resonance imaging technique used to calculate the T2* time of tissue and display them voxel-vice on a parametric map. It is used for myocardial tissue characterization 1-4 and has been investigated for other tissues 5,6. Methodology T2* mapping is usually based on gra...

Emerging medical imaging technologies

This article is a summary of emerging medical imaging technologies currently in development (2023) or in the early phase of clinical adoption. The methods are listed by modality. Radiography dark-field radiography x-ray phase-contrast imaging CT dark-field CT deep-learning reconstruction ...

Photon-counting computed tomography

Photon-counting computed tomography (PCCT) is an emerging technology (c.2021) in CT, which could represent the next major technological milestone in the field. Briefly, PCCT uses energy-resolving detectors, thereby enabling scanning at multiple energies. Physics Current clinical CT systems rel...

Color-write priority

Color-write priority is an adjustable setting of color Doppler duplex ultrasound and determines whether a particular pixel on the image displays color or grayscale B-mode information at the moment. Color-write priority is rarely changed directly during routine ultrasound imaging, even though it...

T2 mapping - myocardium

T2 mapping is a magnetic resonance imaging technique used to calculate the T2 times of a certain tissue and display them voxel-vice on a parametric map. It has been used for tissue characterization of the myocardium 1-5 and has been investigated for cartilage 6,7 and other tissues 4. The T2 tim...

Extracellular volume - myocardium

Extracellular volume (ECV) refers to the space or volume of a tissue, which is not occupied by cells. Apart from the usual extracellular space, which surrounds the cells of a specific tissue it also includes the intracapillary plasma volume 1,2. It measures the space, which is occupied by the ex...

T1 mapping - myocardium

T1 mapping is a magnetic resonance imaging technique used to calculate the T1 time of a certain tissue and display them voxel-vice on a parametric map. It has been used for myocardial tissue characterization 1-6 and has been investigated for other tissues 5. T1 is the spin-lattice or longitudin...

Reynolds number

The Reynolds number (Re) is the primary parameter used to define the transition of fluid motion between laminar and turbulent flow patterns 1. The Reynolds number represents the ratio of inertia forces to viscous forces, and as such has no units (i.e. is a dimensionless quantity) 1. Calculatio...

Central volume principle

The central volume principle is used generating perfusion maps. It relates three perfusion parameters to each other as follows: CBF = CBV/MTT This means that provided you can measure two of these parameters you can calculate the third.

End-diastolic velocity (Doppler ultrasound)

End-diastolic velocity (EDV) is an index measured in spectral Doppler ultrasound. On a Doppler waveform, the EDV corresponds to the point marked at the end of the cardiac cycle (just prior to the systolic peak) 1. In some equipment, the timing of cardiac cycle events may be automatically marked ...

Peak systolic velocity (Doppler ultrasound)

Peak systolic velocity (PSV) is an index measured in spectral Doppler ultrasound. On a Doppler waveform, the peak systolic velocity corresponds to each tall “peak” in the spectrum window 1. Explanation When traveling with their greatest velocity in a vessel (i.e. during systole), red blood cel...

CT dose

CT dose is measured and reported via a variety of methods, put simply, it can be divided into three primary categories: exposure, absorbed dose, and effective dose. It is important to note that to accurately determine a patients dose from a CT scan one must know the patient size and the radiat...

Schuller's view

Schuller's view is a oblique radiographic projection used to demonstrate the petrous temporal bone, internal auditory canal and bony labyrinth. It has an increasingly limited role in contemporary clinical practice because of the universal use of CT and MRI for imaging the temporal bone. Patien...

Starry sky artifact (MRI)

Starry-sky artifact in parallel imaging MRI (e.g. SENSE) is relatively common, and typically encountered as non-uniform distribution of image noise, typically affecting the center part of the image (being more distant from the surface coils) more than the superficial tissues. Note that many othe...

Elevational resolution (ultrasound)

Elevational (azimuthal) resolution represents the extent to which an ultrasound system is able to resolve objects within an axis perpendicular to the plane formed by the axial and lateral dimensions. As one component of overall spatial resolution, the elevational axis represents the height or “t...

Calcium mass score

The calcium mass score was introduced to determine the absolute mass of coronary artery calcium with the help of a cardiac calibration phantom and the use of correction factors 1,4. The method itself comprises the integration of signal above a given threshold 3. Even though higher sensitivity a...

Electron capture

Electron capture is the radioactive decay process by which an atom's inner orbital electron is absorbed within the nucleus followed by conversion of a proton to a neutron and emission of a neutrino (ve) 1. Accompanying this decay method is the emission of Bremsstrahlung, characteristic x-ray emi...

Temporal resolution (ultrasound)

Temporal resolution in ultrasound represents the extent to which an ultrasound system is able to distinguish changes between successive image frames over time (i.e. movement). Temporal resolution is chiefly determined by the image frame rate of the system (measured in Hertz), which may vary dep...

Gamma decay

Gamma decay refers to the release of a gamma (γ) ray photon, a form of high energy electromagnetic radiation, due to radioactive decay of a nucleus. Typically, the energy spectra is in the ~100 keV to ~10 MeV range 1. Gamma decay Gamma decay is a mode of radioactive decay. It differs from alph...

Gustav Bucky

Gustav Bucky (1880-1963) was a German-born, American radiologist who pioneered the development of anti-scatter grids in projectional radiography with his invention, the Bucky diaphragm. Early life Gustav Peter Bucky was born in the city of Leipzig, Germany on 3 September 1880 2,3,5. He had a k...

Cinematic rendering

Cinematic rendering is a novel 3D rendering algorithm that produces a more photorealistic representation of 3D images with enhanced depth and shape perception than achieved with standard volume rendering (VR) 1. It was developed by Siemens Healthineers 2. It is not currently approved for clinica...

Axial plane for imaging of the brain

A consistent axial plane for imaging of the brain needs to be chosen to allow for reproducible image acquisition and comparison. Unlike the sagittal plane, which is intrinsically defined by our inherent left-right plane of symmetry, axial and coronal planes need to be agreed upon and over the ye...

3D fast spin echo (MRI sequence)

3D fast spin-echo sequences are relatively recent MRI pulse sequences that are able to rapidly image relatively large volumes of tissue with high resolution whilst retaining many of the advantages of fast spin-echo sequences. They are able to create the same weightings as traditional 2D sequen...

Transient arterial phase respiratory motion-related artifact

Transient arterial phase respiratory motion-related artifact refers to common self-limited dyspnea observed immediately after the administration of gadoxetate disodium during liver MRI studies. The pathophysiology behind this phenomenon is poorly understood and its incidence varies among differe...

Contrast-enhanced voiding urosonography

Contrast-enhanced voiding urosonography (occasionally abbreviated as ce-VUS) is a relatively novel contrast-enhanced ultrasonographic technique utilizing microbubbles to detect vesicoureteral reflux. Indications Suspected or confirmed vesicoureteral reflux is currently the primary indication ...

Rotating envelope x-ray tube

Rotating envelope x-ray tubes (RET), are a relatively novel type of high-performance x-ray tube developed in the early 2000s. Their two main features are the direct contact of the anode plate with the cooling oil, and rotation of the entire envelope around the axis of the anode. In rotating en...

Imaging technology

Imaging technology is home to the technical aspects of diagnostic and therapeutic procedures within radiology. Rather than focus on the practical aspect of imaging as seen in imaging in practice, imaging technology pertains to the technical aspect of the equipment and technology used. See also...

Virtual reality

Advancements of technology have enabled various simulated reality devices, including virtual reality (VR) and augmented reality (AR). Both technologies provide stereoscopic and three-dimensional (3D) immersion of a simulated object. VR simulates a virtual environment while AR overlays simulated ...

Impact factor

Impact factor is a bibliometric index. It expresses the "impact" of a publication on the reference scientific community. Specifically, it measures the average number of citations of a scientific article by other researchers. Development of the impact factor The impact factor was invented by an...

FABS position

The FABS position relates to MRI elbow examinations for improved visualization of the distal biceps brachii tendon insertion and is a mnemonic for elbow flexed, shoulder abducted and forearm supinated.

CT liver volumetry (protocol)

CT liver volumetry is an essential imaging study in preoperative assessment for living donor liver transplantation. NB: This article is intended to outline some general principles of protocol design. The specifics will vary depending on CT hardware and software, radiologists' and referrers' pre...

Incidence

The incidence is an epidemiological term for the number of new cases of a condition (e.g. brain tumors or diabetes), in a given population, during a specified time interval. The formulas for incidence can express it as a rate or a proportion, e.g. x new cases / y population count / z time period...

Nuclear medicine

Nuclear medicine in vivo is the practice of utilizing small amounts of radioactive substances (unsealed radioactive sources) to diagnose, monitor and treat disease. The utilization of radiopharmaceuticals (radionuclide + pharmaceutical) offers a unique perspective on both disease and cancer trea...

Hydrolyzed reduced technetium-99m

Hydrolyzed reduced technetium-99m (HR-Tc-99m) is a secondary product of the radiolabeling process. It is the chemical species of reduced technetium-99m; oxidation states: +5 and +4. It represents one of the possible impurities present in the technetium agents. It does not bind to the carrier mol...

Computer vision syndrome

Computer vision syndrome is a condition that affects primarily workers who use computers (including tablets and other devices with computer screens) many hours a day with symptoms that can include blurred vision, eye strain, and headache. Epidemiology Computer vision syndrome is a growing phen...

Radiation effects on embryonic and fetal development

Radiation effects on embryonic and fetal development are generally considered low risk compared to the normal risks of pregnancy. Most diagnostic x-ray and nuclear medicine examinations are <50 mSv and have not been demonstrated to produce any significant impact on fetal growth and development. ...

Excitation

Excitation in radiobiology and medical physics refers to excitation of an outer orbital (valence) electron to a higher energy level. By absorbing some energy, but insufficient to cause ionization, the valence electron overcomes the weak attractive force of the nucleus, causing it to move further...

Ionization

Ionization is the principal means by which ionizing radiations dissipate their energy in matter. In this process the orbital electrons absorb energy from the incident photon, resulting in ejection of that electron, leaving the atom positively charged (positively ionized). In tissue this proces...

Linear energy transfer

Linear energy transfer (LET) is the average (radiation) energy deposited per unit path length along the track of an ionizing particle. Its units are keV/μm. Linear energy transfer describes the energy deposition density of a particular type of radiation, which largely determines the biological ...

Radicals

Radicals (formerly called free radicals) are uncharged atoms or molecules in which an electron orbit has a single unpaired electron. Terminology Historically the International Union of Pure and Applied Chemistry (IUPAC) also used the term radical for any joined up group of atoms forming a side...

Extended reality

Extended reality, sometimes referred to as XR, is a term for technologies, such as those that include augmented reality, virtual reality and mixed reality, that allow visualization of three dimensional virtual imaging. Although such technologies have their roots in art and computer gaming, they ...

Intima-media thickness

Intima-media thickness (IMT) is an indirect sonographic assessment of the degree of atheromatous vascular disease of end organs. The thickness of the media and the intima of the vessels changes following many conditions and it can be easily and reliably assessed with ultrasound on B mode in the ...

Samarium-153

Samarium-153 (Sm-153) is a radioisotope used in metabolic radiotherapy for the treatment of pain from bone metastases. It is produced in nuclear reactors, by neutron irradiation of samarium-152 (Sm-152 Sm2O3). Samarium-153 decays by emitting both beta minus particles and gamma photons with a ch...

Fluoroscopy vs fluorography

Fluoroscopy and fluorography are very similar imaging techniques and, in many instances, can be performed on the same equipment. Fluoroscopy vs fluorography Fluoroscopy low current (0.5-5 mA), continuous or near-continuous x-ray exposures relatively low signal to noise ratio (SNR) prioritis...

Photocathode

A photocathode is a negatively charged electrode in a light detection device such as the input screen in an image intensifier (II) that is coated with a photosensitive compound. When this is struck by light photons, the absorbed energy causes electron emission due to the photoelectric (PE) effec...

Output phosphor

The output phosphor is a component of the image intensifier in fluoroscopic systems that converts the energy from the electrons into light photons. In an II, the large number of light photons produced are subsequently captured by various imaging devices to produce a visible image. Composition ...

Fluorography

Fluorography is the use of relatively intense (50-1000mA), pulsed x-ray exposures (pulses are of short duration and applied at 1-12 pulses/second) to form an x-ray image. The resultant images have a relatively high signal to noise ratio (SNR), i.e the images are of better quality than those ac...

Fluoroscopy

Fluoroscopy is an imaging modality that allows real-time x-ray viewing of a patient with high temporal resolution. It is based on an x-ray image intensifier coupled to a still/video camera. In recent years flat panel detectors (which are similar to the digital radiography used in projection radi...

Myocardial mapping

Myocardial mapping or parametric mapping of the heart is one of various magnetic resonance imaging techniques, which has evolved and been increasingly used in the last decade for non-invasive tissue characterization of the myocardium 1-5. Unlike normal T1-, T2- or T2*- images, parametric mapping...

Ultrasound elastography

Ultrasound elastography, also called as sono-elastography, is a modern evolutionary method of sonographic imaging. Techniques include shear wave elastography (also known as transient elastography) and strain elastography (also known as static or compression elastography). These techniques utiliz...

Ammonia (N-13)

13NH3 is a PET tracer used for studies of myocardial perfusion imaging. It is produced in a cyclotron by proton irradiation of the enriched water of the oxygen-16. Ammonia (N-13) is administered intravenously, at a dose of 10-20 mCi (370-740 Mbq) in adults; its physical half-life is 10 minutes. ...

Quantum noise

Quantum noise, also called quantum mottle, is the main and the most significant source of noise in plain radiography. It is a random process due to fluctuations in the number of photons reaching the detector from point to point. This means that exposing the detector in the absence of an object w...

Lymphoscintigraphy

Lymphoscintigraphy is a nuclear medicine technique to visualize regional lymphatic drainage, especially for mapping sentinel lymph nodes, from a site of radiopharmaceutical injection. Radiopharmaceutical Colloidal agents are used as these particles enter lymphatic channels and migrate to lymph...

Cone beam effect

Cone beam effect artifacts are seen in multidetector row CT (cone beam CT) acquisitions 1. Modern CT scanners use more detector arrays to increase the number of sections acquired per rotation. This causes the x-ray beams to become cone-shaped as opposed to fan-shaped 2. As a result instead of co...

Transient interruption of contrast

Transient interruption of contrast (TIC) is a common flow artifact seen in CT pulmonary angiography (CTPA) studies. The contrast opacificiation of the pulmonary arteries is suboptimal due to an increase in the flow of unopacified blood from the inferior vena cava (IVC) to the right side of the h...

Choline C-11

Carbon-11-choline (choline C-11 or 11C-choline) is the most studied isotope carbon-11 PET radiopharmaceutical. The molecule is used for oncologic Imaging 1-4. Choline is one of the components of phosphatidylcholine, a fundamental element of cell membrane phospholipids 5. Cancer cells tend to ha...

Color flash artifact

The color flash artifact is a commonly encountered artifact on color Doppler ultrasound, representing spurious flow signal arising due to tissue/transducer motion. Physics The flash artifact is caused by movement of reflective tissues (e.g. due to respiration), or the transducer, which genera...

Cybersecurity

Cybersecurity is the protection of digital data, software and hardware from risks including attacks or other problems related to their integrity and/or data confidentiality. Cybersecurity may utilize many different types of tools and protocols including encryption, firewalls and other infrastruc...

MR elastography

MR elastography (MRE) is an MRI technique that can be used to assess liver stiffness. This is useful not only to detect the development of fibrosis in diffuse liver disease but also to quantify it and monitor liver fibrosis change with (or without) therapy. The main advantage over ultrasound el...

Electrical interference artifact (ultrasound)

Electrical interference artifact is an ultrasound artifact usually caused by the ultrasound machine being too close to the unshielded electrical equipment. The disturbance appears as arc-like moving bands in the ultrasound image. While the presence of electrical equipment (e.g unshielded vent...

International Union of Pure and Applied Chemistry

The International Union of Pure and Applied Chemistry (IUPAC) is the world authority on the nomenclature of chemical elements and compounds. The nomenclature is designed to provide an unambiguous representation of a molecule. However, the systematic names are often not used in scientific or clin...

F-18 fluorodeoxyglucose

F-18 fluorodeoxyglucose (FDG) is the most common PET radiotracer. Structure The radiopharmaceutical consists of the fluorine-18 radionuclide substituting the hydroxyl group at the C-2 position of glucose. The IUPAC chemical name is 2-deoxy-2-[F-18]fluoroglucose. Production F-18 fluoride ion ...

Kernel (image reconstruction for CT)

The kernel, also known as a convolution algorithm, refers to the process used to modify the frequency contents of projection data prior to back projection during image reconstruction in a CT scanner 1. This process corrects the image by reducing blurring 1. The kernel affects the appearance of i...

Noise reduction

Noise reduction, also known as noise suppression or denoising, commonly refers to the various algorithmic techniques to reduce noise in digital images once they are created although a few sources use the term more broadly to imply anything that reduces noise. In digital image processing various ...

NIfTI (file format)

NIfTI is a type of file format for neuroimaging. Technically there are NIfTI-1 and NIfTI-2 file formats. The NIfTI-2 format is an update on NIfTI-1 that allows more data to be stored. NIfTI files are used very commonly in imaging informatics for neuroscience and even neuroradiology research. In ...

Filtered (1)Done (clear)

+Systems

×Article Sections

+Sort By

ADVERTISEMENT: Supporters see fewer/no ads

Updating… Please wait.

Unable to process the form. Check for errors and try again.

Thank you for updating your details.