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.

410 results found
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Piezoelectric effect

The Piezoelectric effect converts kinetic or mechanical energy, due to crystal deformation, into electrical energy. This is how ultrasound transducers receive the sound waves. The same effect can be used in reverse – inverse piezoelectric effect – whereby the application of an electric field to...
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Pitch

Pitch (P) is a term used in helical CT. It has two terminologies depending on whether single slice or multislice CT scanners are used 1-3. Single slice CT (SSCT) The term detector pitch is used and is defined as table distance traveled in one 360° gantry rotation divided by beam collimation 2....
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Pixel

A pixel (or pel or picture element) may refer to either the smallest discrete element of the physical display or to the smallest element of the image. Voxel is its 3-dimensional equivalent, as employed in CT and other cross-sectional imaging modalities. History and etymology The history of the...
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Portosystemic shunt ratio

The portosystemic shunt ratio is a measure performed using ultrasound to quantify the abnormal flow of portal venous blood that is shunted away from the hepatic sinusoidal circulation in the context of a congenital portosystemic shunt 1. Ultrasound The ratio is determined using the following e...
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Positron emission tomography

Positron emission tomography (PET) is a modern non-invasive imaging technique for quantification of radioactivity in vivo. It involves the intravenous injection of a positron-emitting radiopharmaceutical, waiting to allow for systemic distribution, and then scanning to detect and quantification ...
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Power Doppler

Power Doppler is a technique that uses the amplitude of Doppler signal to detect moving matter. Power Doppler: is independent of velocity and direction of flow, so there is no possibility of signal aliasing is independent of angle, allowing detection of smaller velocities than colour Doppler, ...
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Production of radioactive nuclei

Naturally occurring radioactive nuclei have a physical half life time of  about 108 to 1010 years which makes them unsuitable for use in medical imaging. Thus radioactive nuclei used in medical practice are artificially made. Production of these nuclei involve bombarding stable nuclei with prot...
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Propagation speed

The propagation speed of sound waves through tissue is an important element of ultrasound scans. Ultrasound machines assume sound waves travel at a speed of 1540 m/sec through tissue 1. In reality, the speed of sound is affected by the density and elasticity of the medium through which it is tr...
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Pseudoenhancement

Pseudoenhancement is an artifact in postcontrast CT evaluation of renal cysts. The distinction between cystic and solid lesions visualised in CT is primarily made on the basis of whether the lesion enhances with contrast administration. A renal cystic lesion is considered "enhancing" when there...
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Pulsatile portal venous flow

Pulsatile portal venous flow pattern can result from both physiological and pathological causes. Usually, mild pulsatility or in rare situations even marked pulsatility has been described, particularly in thin subjects with a venous pulsatility index of >0.5 with an inverse correlation to body ...
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Quantitative computed tomography

Quantitative computed tomography (QCT) is a bone mineral density (BMD) measurement technique in which the CT scanner is calibrated using solid phantoms (made of calcium hydroxyapatite, representing various bone mineral densities) placed under the patient in a pad. With this calibration, the Houn...
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Quenching

Quenching refers to rapid expulsion of the liquid cryogen used to maintain the MRI magnet in a superconducting state. Discussion Modern MRI scanners contain superconducting magnets which have very low energy consumption, made possible by maintaining internal subzero temperatures by way of a 'c...
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Radiation damage (biomolecular)

Biomolecular radiation damage can result when biological tissues are exposed to ionising radiation from direct exposure or via Compton scattering. Ionisation is known to lead to the production of free radicals; free radicals are uncharged molecules that possess an unpaired valence electron. Con...
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Radiation damage (skin injury)

Radiation-induced skin injuries can occur in both radiotherapy and fluoroscopic procedures such as interventional radiology.  Acute radiation doses above 2 Gy are known to result in erythema, permanent epilation will occur at 7 Gy and delayed skin necrosis transpires above doses of 12 Gy.  The...
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Radiation-induced carcinogenesis

Radiation-induced carcinogenesis is widely but not universally believed to occur at exposures from ionising radiation used in medical imaging. It is thought to be a stochastic effect of ionising radiation, with the linear no-threshold theory (LNT) proposing no "safe" level of radiation exposure,...
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Radiation-induced lung cancer

Radiation-induced lung cancers have been reported as a rare late complication of radiation therapy in both post-operative breast cancer and Hodgkin lymphoma patients. These occur 5-10 years (or later) after treatment 1-4. There appears to be increased risk of lung cancer in these patients if the...
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Radiation protection

Radiation protection is based on the three fundamental principles of justification of exposure, keeping doses as low as reasonably achievable (optimisation) and the application of dose limits. The International Commission on Radiological Protection (ICRP) is responsible for the development of th...
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Radiofrequency coils

Radiofrequency coils (RF coils) are the "antennae" of the MRI system, broadcasting the RF signal to the patient and/or receiving the return signal. RF coils can be receive-only, in which case the body coil is used as a transmitter; or transmit and receive (transceiver). Surface coils are the si...
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Radiofrequency receiver

Radiofrequency coils are the radiofrequency receivers (as well as sometimes the transmitters) of the electromagnetic signal used in MRI. Radiofrequency coils can be either receive-only, or both receivers and transmitters of the radiofrequency signal. The receiver coils detect the electromagnetic...
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Radiofrequency shielding

Radiofrequency shielding serves to both prevent external interference and ensure signals generated by MR imaging do not escape the room.  MRI systems utilise electromagnetic waves to produce the soft tissue contrast characteristic to the modality. Given the ubiquity of similar waves in the exte...
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Radiofrequency transmitter

The radiofrequency transmitter is the generator of the radiofrequency current which is delivered to the transmitting coil. This creates a signal which is used to excite protons in the imaging field. Radiofrequency coils can be both transmitters and receivers of the radiofrequency signal or recei...
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Radiograph

Radiograph (or plain radiograph although the word plain is strictly superfluous) is the radiologist's preferred term for the static image generated following the passage of x-rays through the patient. Non-imaging clinicians and the lay population generally use the term "x-ray" to refer to a radi...
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Radioisotope spills

Radioisotope spills are classified as major or minor Examples of major spills include quantities equal to or larger than: 1mCi I-131 100 mCi Tc-99m or Tl-201 10 mCi Ga-67, In-111, or I-123
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Radiopharmaceuticals

Radiopharmaceuticals are drugs that are bound to radioactive substances.  The pharmaceutically active portion determines the activity that will be measured and the radioactive portion emits radiation that can be measured by the scanner. A number of radiopharmaceuticals are used in human imaging...
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RadLex

RadLex is a lexicon of radiological information that has been produced by the RSNA.  It is an ontological system whose principle aim is to develop a useful vocabulary for radiologists.  In the words of the RSNA "As images, imaging reports, and medical records move online, radiologists need a u...
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Rad (unit)

The rad (symbol rad) is a legacy unit in the cgs system for the absorbed dose of ionising radiation, although it remains in widespread use in the United States.  The rad is defined as the dose represented by 100 ergs of energy being absorbed by one gramme of matter. The erg is the unit of energ...
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Receiver operating characteristic curve

The receiver operating characteristic (ROC) curve is a statistical relationship used frequently in radiology, particularly with regards to limits of detection and screening. The curves on the graph demonstrate the inherent trade-off between sensitivity and specificity: y-axis: sensitivity x-a...
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Rectal cancer protocol (MRI)

Pelvic MRI protocol for rectal cancer includes: through tumour (always ensure planes are exactly perpendicular to the wall) three-plane T2 axial T1 narrow field of view images to be included overviews axial T2FS axial T1 See also MRI protocols
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Reflection

Reflection of a sound wave occurs when the wave passes between two tissues of different acoustic speeds and a fraction of the wave 'bounces' back. This forms one of the major principles of ultrasound imaging as the ultrasound probe detects these reflected waves to form the desired image. Angle ...
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Refraction

Refraction of a sound wave occurs if it travels between tissues with different propagation speeds. As the incident pulse or returning echo strikes an interface of different density or elasticity and therefore a different propagation speed, the direction of the wave changes according to Snell’s l...
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Refraction artifact

Refraction artifact can occur when a transmitted ultrasound pulse strikes an interface at a non-perpendicular angle. The difference in propagation speeds between the two tissues can cause refraction to occur. Should the refracted incident sound wave strike a reflector and cause an echo to return...
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Relaxation

MRI image contrast is influenced by several characteristics of tissues and other materials including: T1, T2 and T2* relaxation as well as spin density, susceptibility effects and flow effects. This page and the following detailed pages on relaxation parameters will introduce properties and effe...
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Relaxometry

Relaxometry is measurement of relaxation times from MR images. T1, T2 and T2* can be estimated using the appropriate pulse sequence and parameters. T2 relaxometry has found useful in quantitating signal changes on T2-weighted images as in evaluating mesial temporal sclerosis. Details T2 rela...
Article

Rem (unit)

The rem (an acronym for roentgen equivalent man) was the cgs unit of effective dose and was officially replaced by the sievert many years ago.  One rem was a large quantity of radiation, and therefore for practical day to day use the millirem (mrem), representing one-thousandth of a rem, was us...
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Repetition time

The repetition time (TR) is the time from the application of an excitation pulse to the application of the next pulse. It determines how much longitudinal magnetization recovers between each pulse. It is measured in milliseconds.
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Resonance and radiofrequency

Protons in a magnetic field have a microscopic magnetisation and act like tiny toy tops that wobble as they spin.The rate of the wobbling or precession is the resonance or Larmor frequency. In the magnetic field of an MRI scanner at room temperature, there is approximately the same number of pro...
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Reticuloendothelial MRI contrast agents

Reticuloendothelial MRI contrast agents can best be discussed in terms of those used for liver and spleen imaging and those for lymph node imaging. NOTE: This article has been transferred from mritutor.org and was last updated in March 5, 1996. Review and edit pending.  Liver and spleen The u...
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Reverberation artifact

Reverberation artifact occurs when an ultrasound beam encounters two strong parallel reflectors. When the ultrasound beam reflects back and forth between the reflectors ("revereberates"), the ultrasound transducer interprets the sound waves returning from the reverbration as deeper structures s...
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RF overflow artifact

RF overflow artefact cause a nonuniform, washed-out appearance to an image. This artifact occurs when the signal received by the scanner from the patient is too intense to be accurately digitized by the analog-to-digital converter. Autoprescanning usually adjusts the receiver gain to prevent thi...
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Ring artifact

Ring artifacts are a CT phenomenon that occur due to miscalibration or failure of one or more detector elements in a CT scanner. They occur close to the isocentre of the scan and are usually visible on multiple slices at the same location. They are a common problem in cranial CT. The remedy is ...
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Ring down artifact

Ring down artifact is a special type of resonance artifact. Its appearance is similar to the ladder-like reverberation of comet-tail artifact, but it is produced by a completely different mechanism. The artifact is only associated with gas bubbles, and occurs when an ultrasound pulse encounters...
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Roentgen (unit)

The roentgen (symbol R) or röntgen (in German) is a legacy unit to measure radiation exposure. It was defined as the quantity of x-rays that produces 2.580 × 10-4 coulombs of charge collected per unit mass (kilograms) of air at standard temperature and pressure (STP): 1 R = 0.000258 coulombs per...
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Rutherford (unit)

The rutherford (symbol Rd) is an obsolete unit of radioactivity which was superseded by the introduction of the becquerel in 1975. One rutherford was equivalent to 1,000,000 nuclear disintegrations per second, or alternatively one becquerel equated to one microrutherford (μRd).  Terminology As...
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Saturation recovery sequences

Saturation recovery (SR) sequences are rarely used for imaging now. Their primary use at this time is as a technique to measure T1 times more quickly than an inversion recovery pulse sequence. Saturation recovery sequences consist of multiple 90 degree RF pulses at relatively short repetition ti...
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Scattering (ultrasound)

Scattering occurs when a sound wave strikes a structure with both a different acoustic impedance to the surrounding tissue and a wavelength less than that of the incident sound wave. Such structures are known as “diffuse reflectors,” with examples being red blood cells and non-smooth surfaces of...
Article

SeHCAT

SeHCAT (23-seleno-25-homo-tauro-cholic acid) is a radiopharmaceutical used in the investigation of bile salt malabsorption, which is a cause of chronic diarrhoea.  Characteristics physical half-life: 118 days Uses, dosage and timings A capsule containing SeHCAT is ingested with water. The pa...
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Sensitivity

Sensitivity of a test/investigation is defined as the ability of the test to identify true positive cases of the disease under question. Calculation Sensitivity = true positives detected by test / total cases of the disease where, total cases with the disease = true positive + false negative
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Sensitivity and specificity

Sensitivity and specificity are fundamental characteristics of diagnostic imaging tests. The two characteristics derive from a 2x2 box of basic, mutually exclusive outcomes from a diagnostic test (Figure 1): true positive (TP): an imaging test is positive and the patient has the disease/condit...
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Sensitivity and specificity of multiple tests

Sensitivity and specificity of multiple tests is a common statistical problem in radiology because frequently two tests (A and B) with different sensitivities and specificities are combined to diagnose a particular disease or condition. These two tests can be interpreted in an "and" or an "or" ...
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Shading artifact

Shading artifact in MRI refers to loss of signal intensity in one part of the image, leading to dark shading in this portion of the image. Causes uneven excitation of nuclei within the field; due to RF pulses applied at flip angles other than 90 and 180 degrees abnormal loading of coil or cou...
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Shear wave elastography

Shear wave elastography is a developing variation of ultrasound imaging. The concept is similar to strain elastography, but instead of using transducer pressure to compare a shift in an ultrasound A-line (thereby measuring changes in strain), a higher intensity pulse is transmitted to produce s...
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Short tau inversion recovery

Short tau inversion recovery (STIR), also known as short TI inversion recovery, is a fat suppression technique with an inversion time TI = ln(2)·T1fat,where the signal of fat is zero. This equates to approximately 140 ms at 1.5 T. To distinguish two tissue components with this technique, their ...
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Side lobe artifact

Side lobe artifacts occur where side lobes reflect sound from strong reflector that is outside of the central beam, and where the echoes are displayed as if they originated from within the central beam. Ultrasound transducer crystals expand and contract to produce primary ultrasound beams in th...
Article

Sievert (SI unit)

The sievert (symbol Sv) is the SI unit of dose equivalent and is dimensionally-equivalent to one joule per kilogram. The sievert represents the stochastic effects of ionising radiation as adjusted by a tissue weighting factor to account for differing responses of different human tissues to ionis...
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Signal-to-noise ratio

Signal-to-noise ratio (SNR) is a generic term which, in radiology, is a measure of true signal (i.e. reflecting actual anatomy) to noise (e.g. random quantum mottle). A lower signal-to-noise ratio generally results in a grainy appearance to images.  Each modality has its own source(s) of noise ...
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Size specific dose estimate

Size specific dose estimate (SSDE) is a method of estimating CT radiation dose that takes a patient's size into account.  CTDIvol and DLP are common methods to estimate a patient's radiation exposure from a CT procedure. The exposures are the same regardless of patient size, but the size of the...
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Slew rate

Slew rate refers to the speed at which a gradient can be turned on and off, and is defined as the maximum gradient strength of the gradient divided by the rise time.  MR imaging is a product of magnetic field gradients which are created by magnetic gradient coils. The quality and performance of...
Article

Space charge and space charge effect

Space charge refers to the collection of electrons which are emitted from the metal surface, after the application of tube current, at a short distance away from the metal surface. These electrons collect and form a cloud of charge around the metal surface. This space charge limits the further ...
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Spatial resolution

Spatial resolution in radiology refers to the ability of the imaging modality to differentiate two objects. Low spatial resolution techniques will be unable to differentiate between two objects that are relatively close together. See also spatial resolution (CT) spatial resolution (MRI) cont...
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Spatial resolution (CT)

Spatial resolution in CT is the ability to distinguish between object or structures that differ in density. A high spatial resolution is important for one to discriminate between structures that are located within a small proximity to each other.  Factors affecting CT spatial resolution field...
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Spatial resolution MRI

Spatial resolution determines how "sharp" the image looks. Low resolution will give either fuzzy edges, or a pixelly appearance to the image. In MRI, spatial resolution is defined by the size of the imaging voxels. Since voxels are three dimensional rectangular solids, the resolution is frequen...
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Specificity

Specificity of a test/investigation is the ability of a test to be correctly negative (true negative) in persons without the disease in question. Calculation Specificity = true negatives detected by test / total cases without the disease where, total cases without the disease = true negative ...
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Speckle artifact

Speckle artifact may be encountered in ultrasound. It is caused by the scattering of waves from the surface of small structures within a certain tissue. The artifact produces a textured appearance. See also ultrasound artifacts
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Speckle tracking echocardiography

Speckle tracking echocardiography is a new player in the cardiac arena which is rapidly making its mark in cardiac and radiology circles alike. It is an objective, robust, semiautomatic and reproducible technique with a short post processing time. Traditionally, left ventricular function is mea...
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Speed displacement artifact

Speed displacement artifact is a gray scale ultrasound finding that can be identified as an area of focal discontinuity and displacement of an echo deeper than that its actual position in an imaged structure.  The artifact is due to the image processor's assumption that the velocity of the ultra...
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Spin echo sequences

Spin-echo pulse sequences are one of the earliest developed and still widely used (in the form of fast spin-echo) of all MRI pulse sequences. The pulse sequence timing can be adjusted to give T1-weighted, proton density, and T2-weighted images. Dual echo and multiecho sequences can be used to ob...
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Spiral pulse sequences

Spiral scanning in MRI is unlike spiral scanning in CT where the x-ray tube is continuously rotating and data is continuously being acquired. In MRI the word "spiral" refers to the pattern of sampling k-space. In conventional imaging sequences including spin echo and gradient echo and in fast im...
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Spoiled gradient echo MRI

Spoiled gradient echo MRI is an MRI technique which destroys residual transverse magnetization at the end of each excitation cycle. 
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Standard uptake value

The standard uptake value (SUV) is a simple way of determining activity in PET imaging, most commonly used in fluorodeoxyglucose (FDG) imaging. It is also known as the dose uptake ratio (DUR). As the name suggests it is a mathematically derived ratio of tissue radioactivity concentration at a po...
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Steady-state free precession MRI

Steady-state free precession MRI (SSFP) is a type of gradient echo MRI pulse sequence in which a steady, residual transverse magnetisation (Mxy) is maintained between successive cycles. The sequence is noted for its superiority in dynamic/cine assessment of cardiac function. Discussion To unde...
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Step-and-shoot tomosynthesis (breast)

Step-and-shoot is a technology of image acquisition in digital breast tomosynthesis characterised by stop scanning at every single angle during images acquisition. Step-and-shoot technology allows advantages in microcalcifications conspicuity, spatial resolution, signal-to-noise Ratio improveme...
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Stochastic effects

Stochastic effects occur by chance and can be compared to deterministic effects which result in a direct effect. Cancer induction as a result of exposure to radiation is thought by most to occur in a stochastic manner: there is no threshold point and risk increases in a linear-quadratic fashion...
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Strain elastography

Strain elastography (also known as tissue strain elastography/static elastography/compression elastography) is a developing form of ultrasound that assesses tissues' macroscopic structure through the strain modulus. This is different from normal B-mode grayscale ultrasound which characterizes a ...
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Structure of the atom

The structure of the atom is key to the majority of the techniques used in radiology, and a general understanding of atomic structure is worthwhile. The following is an uncomplicated overview of the structure of the atom. Nucleus The composition of an atom is principally 'empty space'. Its ma...
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Superparamagnetism

Superparamagnetic materials consist of individual domains of elements that have ferromagnetic properties in bulk. Their magnetic susceptibility is between that of ferromagnetic and paramagnetic materials.  The figure illustrates the effect of a superparamagnetic material (grey circle) on the ma...
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Surface coil

Surface coils are a type of receive-only radiofrequency coil used in MRI to receive the radiofrequency signal (transmitted by the body coil). Surface coils are small and are shaped so that they can be placed near the part of anatomy being imaged. By their nature, surface coils have good signal-t...
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Susceptibility weighted imaging

Susceptibility weighted imaging (SWI) is an MRI sequence which is particularly sensitive to compounds which distort the local magnetic field and as such make it useful in detecting blood products, calcium, etc. Physics SWI is a 3D high-spatial resolution fully velocity corrected gradient echo ...
Article

Synthetic MRI

Synthetic MRI is a technique that generates contrast weighted images based on measurements of tissue properties from a single acquisition. Basic principles With synthetic MRI, different contrast weighted images can be obtained based on quantifications of a single multiple dynamic and multiple...
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T1 rho

T1 rho, also referred to as T1ρ or "spin lock", is an MRI sequence that is being developed for use in musculoskeletal imaging. At the moment it is mostly investigational and does not yet have widespread clinical use. The "rho" in the sequence name refers to a "ro"tating frame and the sequence h...
Article

T1 values (1.5 T)

T1 values are a few hundred milliseconds for most tissues examined. The following are approximate T1 values (ms) of several tissues for B = 1.5 T fat = 260 liver = 500 muscle = 870 brain white matter = 780 brain grey matter = 920 CSF = 2500 Tissues that will have high signal in T1 weight...
Article

T2 relaxation

T2 relaxation refers to the progressive dephasing of spinning dipoles following the 90° pulse as seen in a spin-echo sequence due to tissue-particular characteristics, primarily those that affect the rate of movement of protons, most of which are found in water molecules. This is alternatively k...
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T2* relaxation

T2* decay refers to an exponential decrease in Mxy  (i.e. signal strength) following the initial excitation pulse as a function of time constant T2*. A picture of the signal or free induction decay (FID) is shown on the right, occurring immediately after a 90o RF excitation pulse in a liquid pha...
Article

T2 shine through

T2 shine-through refers to high signal on DWI images that is not due to restricted diffusion, but rather to high T2 signal which 'shines through' to the DWI image. T2 shine through occurs because of long T2 decay time in some normal tissue. This is most often seen with subacute infarctions due ...
Article

T2 washout

T2 washout is a phenomenon encountered on diffusion weighted imaging (DWI) which results in DWI images (e.g. B = 1000) appearing normal despite abnormal ADC maps.  For the phenomenon to occur a particular combination of ADC and T2 signal intensity is required.  increased T2 signal facilitated...
Article

Tc-99m HMPAO labelled WBC

Tc-99m HMPAO (hexamethylpropyleneamine oxime) labelled WBC is one of the technetium radiopharmaceuticals used in WBC imaging. Characteristics photon energy: 140 KeV physical half life: 6 hours biological half life: 4 hours normal distribution: spleen, liver, kidney, bone marrow pha...
Article

Tc-99m labeled RBC

Tc-99m labelled RBC is one of the technetium radiopharmaceuticals used in renal imaging. Characteristics photon energy: 140 KeV physical half life: 6 hours biological half life:  normal distribution: heart, vessels, spleen miscellaneous facts: threshold for detection is 0.05-0.1 m...
Article

Tc-99m MAG3

Tc-99m MAG3 (mercaptoacetyltriglycine) is one of the technetium radiopharmaceuticals used in renal imaging. Characteristics photon energy: 140 KeV physical half life: 6 hours biological half life: 4 hours normal distribution: kidneys (100%) pharmacokinetics: uptake by tubular secretion (9...
Article

Tc-99m pertechnetate

Tc-99m pertechnetate is one of the technetium radiopharmaceuticals used in imaging of thyroid, colon, bladder and stomach. Characteristics photon energy: 140 keV physical half-life biological half-life: 6 hours normal distribution: stomach, thyroid, salivary glands, (testicles) excretion: ...
Article

Tc-99m sulfur colloid

Technetium-99m sulfur colloid is one of the technetium radiopharmaceuticals. Characteristics photon energy: 140 keV physical half-life: 6 hours biological half-life normal distribution: liver: 85% spleen: 10% bone marrow: 5% excretion: hepatic target organ: liver, spleen pharmacokinet...
Article

Technetium 99m-methyl diphosphonate

Technetium 99m-methyl diphosphonate (99mTc MDP) is a radioisotope used in nuclear medicine especially for bone scans. Any disease process which results in extracellular fluid expansion will lead to accumulation of this isotope. Radionuclide profile photon energy: 140 keV physical half life: 6...
Article

Temporal resolution

Temporal resolution relates to the duration of time for acquisition of a single frame of a dynamic process, i.e., cine imaging. Discussion The concept of temporal resolution is fundamental to cardiac CT and MRI, in which a rapidly beating heart is imaged over the order of milliseconds into mul...
Article

Tesla (SI unit)

The tesla (symbol T) is the derived SI unit of magnetic flux density, which represents the strength of a magnetic field. One tesla represents one weber per square metre. The equivalent, and superseded, cgs unit is the gauss (G); one tesla equals 10,000 gauss.  Terminology As for all eponymous ...
Article

Thallium-201 chloride

Thallium-201 chloride is a radiopharmaceutical used primarily in cardiac imaging. Characteristics photon energy: 80 keV physical half life: 73 hours biological half life rest: 3 minutes exercise: 30 seconds normal distribution: myocardium, skeletal muscle, GI tract, liver, kidneys excret...

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