Items tagged “physics”

132 results found
Article

Grey scale imaging (ultrasound)

Commonly referred to as B (brightness) mode, the use of grey scale imaging in ultrasound renders a two-dimensional image in which the organs and tissues of interest are depicted as points of variable brightness. The formation of a B-mode image relies on the pulse-echo principle; assuming the spe...
Article

Electron binding energy

The electron binding energy is the minimum energy that is required to remove an electron from an atom, as the negatively charged electrons are held in place by the electrostatic pull of the positively charged nucleus. The electron binding energy is measured in electronvolts (eV), where 1 eV = 1....
Article

X-ray quantity and quality

X-ray spectrum quantity refers to the number of photons within the primary X-ray beam and is measured by mAs (milliampere-seconds) 2. Meanwhile, the intensity of the beam is defined as rate of flow of energy per unit area perpendicular to the beam 3, also known as energy fluence rate, with units...
Article

Specific absorption rate

Specific absorption rate (SAR) is the rate that electromagnetic energy in the radiofrequency pulses is absorbed by tissues during MR image acquisition measured in watts per kilogram (W/kg).  Both the International Electrotechnical Commission and the Food and Drug Administration (in the USA) lim...
Article

Ionization chamber

Ionization chambers measure exposure by detecting liberated electron charge when x-ray photons ionize the gas within the chamber. The chambers need a high positive voltage applied at the collecting anode to attract the liberated electrons. The electron charge is collected and used to determine t...
Article

Film dosimeter

Film dosimeters are used to measure radiation exposure to workers to monitor radiation safety and ensuring that they receive doses below the appropriate limit.  Film badges are the cheapest and most common monitoring device. They consist of a small case with a piece of film situated between fil...
Case

Pseudolayering of urine in the bladder

  Diagnosis certain
Carlos Felipe Teixeira Lôbo
Published 21 Nov 2019
98% complete
MRI
Article

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...
Article

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...
Article

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...
Article

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 (like those used in direct digital radiography) have been replacing t...
Article

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...
Article

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  ...
Article

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...
Article

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...
Article

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...
Article

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 ...
Article

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...
Article

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...
Article

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. ...

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