Intro Flashcards
Refers to imaging in which the energy source is outside the body
Transmission imaging
Refers to each point on the image corresponds to information along a straight line trajectory thru the patient
Projection imaging
Mammography system in which the xray tube (in some cases the detector) moves in an arc from approximately 7 to 40 degrees around the breast
Tomosynthesis
Tomography means
Picture (graph)
Slice (tomo)
MRI is approximately _____ times stronger than the earth’s magnetic field
10,000 to 60,000 times stronger
Nuclear medicine produces ______ images, because the radioisotopes emit their energy from inside the patient
Emission
2D maps of 3D radioisotope distribution and are helpful in evaluation of a large number of disorders
Planar nuclear images
Roentgen discovered xray in year
1895
Refers to continuous acquisition of a sequence of xray images over time, essentially a real time xray movie of a patient
Fluoroscopy
_____ energy xrays are used to reduce conspicuity of the ribs and other bones to permit better visualization of air spaces and soft tissue structures in the thorax
High energy xrays
Dark areas (high film optical density) correspond to ____ attenuation
Low
Bright areas (low film optical density) correspond to _____ attenuation
High
First imaging modality made possible by the computer
Computed tomography
Produced by passing xrays thru the body at a large number of angles, by rotating the xray tube around the body
CT
Modern CT scanners can acquire _____ mm-thick tomographic images along a ___ cm length of patient in ____ seconds
0.50 - 0.62 mm
50 cm
5 seconds
In MRI, proton has a magnetic moment, and when placed in a 1.5 T magnetic field, proton ______ (wobbles) about its axis, and preferentially absorbs radio wave energy at the resonance frequency of about ___ million cycles per second
Precesses
64 million
In MRI, Pulse of radio waves is generated by _____ positioned around the patient
Antennas/coils
By slightly changing the strength of the magnetic field as a function of position in the patient using magnetic field gradients, the proton resonancr frequency varies as a function of position, since frequency is _______ to magnetic field strength
Proportional
An area of MR data collection that allows for analysis of metabolic products in the tissue is _____, whereby a single voxel or multiple voxels may be analyzed using specialized MRI sequences
MR spectroscopy
Tomographic counterpart of nuclear medicine planar imaging
Single photon emission computed tomography
Positively charged electrons
Positrons
Similar to gamma rat emission, except that 2 photons are produced, and they are emitted simultaneously in almost exactly opposite directions
Annihilation radiation
Ultilizes rings of detectors that surround the patient, and has special circuitry that is capable of identifying the photon pairs produced during annihilation
Positron emission tomography
More sensitive to the presence of radioisotopes than SPECT cameras
PET detector system
Contrast in _____ imaging depends upon the tissues ability to concentrate the radioactive material
Nuclear imaging
Contrast in ____ imaging is related primarily to the proton density and to relaxation phenomena
MRI
Contrast in ______ imaging is largely determined by the acoustic properties of the tissues being imaged, the difference between acoustic impedances
Ultrasound
Imaging that shows the amplitude and direction of blood flow by analyzing the frequency shift in the reflected signal and thus motion is the source of contrast
Doppler ultrasound
Ability to see small detail
Spatial resolution
Size of the smallest object that an imaging system can resolve
Limiting spatial resolution
Highest resolution modality
Mammography
At 3.5 mHz, the wavelength of sound in soft tissue is about
500 um
At 10 Mhz, the wavelength is
150 um
Energy that travels thru space or matter
Radiation
No mass, unaffected by either electric or magnetic fields, and has a constant speed in a given medium. It does not require matter to propagate
Electromagnetic radiation
Interaction of EM radiation can occur by
Scattering
Absorption
Transformation
EM radiation is commonly characterized by
Wavelength, frequency, energy per photon
Emitted by the nuclei of radioactive atoms
Gamma rays
Produced outside the nuclei of atoms. Used in radiography, fluoroscopy and CT
Xrays
Produced when xrays or gamma rays interact with various scintillators in the detectors used in several imaging modalities and is also used to display images
Visible light
There are two correct ways pf describing EM radiation, as ____ and as discrete particle-like packers or quanta of energy called ______
Waves and photon
“Billiard-ball” type of collision between an xray photon and an orbital electron during a _______ scattering event
Compton
Xrays photon’s energy is completely absorbed by, and results in the ejection of an orbital electron (a photoelectron), in the _______ effect
Photoelectric effect
Intensity of the wave
Amplitude
Distance between any two identical points on adjacent cycles
Wavelength
Time required to complete one cycle of a wave
Period
Number of periods that occur per second is the
Frequency
Temporal shift of one wave with respect to the other
Phase
Because the speed of EM radiation is constant in a given medium, its frequency and wavelength are ______ proportional
Inversely
Wavelengths of xrays and gamma rays are typically measured in fractions of
Nanometers
Frequency is expressed in
Hertz (Hz)
Planck’s constant represents the
Energy of a photon
Energies of photons are commonly expressed in
Electron volts
Defined as the energy acquired by an electron as it traverses an electrical potential difference (voltage) of one volt in a vacuum
One electron volt
An atom or molecule that has lost or gained one or more electrons has a net electrical charge and is called
Ion
Photons of higher frequency than the far UV region of the spectrum (wavelengths greater than 200nm) have sufficient energy per photon to remove bound electrons from atomic shells, thereby producing ionized atoms and molecules. Radiation in this portion of the spectrum is called
Ionizing radiation
Minimum energies necessary to remove an electron
Ionization energy
Electrons emitted by the nuclei of radioactive atoms are referred to as
Beta particles
Negatively charge beta-minus particles or
Negatrons
Positively charge electrons, referred to as
Beta-plus particles or positrons
An uncharged nuclear particle that has a mass slightly greater than that of a proton. They are released by nuclear fission and are used for radionuclide production
Neutrons
Consists of 2 protons and 2 neutrons, it has +2 charge and is identical to the nucleus of a helium atom
Alpha particle
Emitted by many high atomic number radioactive elements such as uranium, thorium and radium
Alpha particles
The smallest division of an element in which the chemical identity of the element is maintained
Atom
The outer electron shell of an atom called _______, Determines the chemical properties of the element
Valence shell
Energy required to remove an orbital electron completely from the atom is called its
Orbital binding energy
Emissions from transitions exceeding ____ eV are called characteristic or fluorescent xray
100
An electron cascade does not always result in the production of a characteristic xray or xrays. A competing process that predominates in low Z elements is
Auger electron emision
The probability that the electron transition will result in the emission of a characteristic xray is called
Fluorescent yield
Number of protons in nucleus
Atomic number (Z)
Total number of protons and neutrons within the nucleus is the
Mass number (A)
Excited states that exist longer than 10-12 s are referred to as
Metastable or isomeric states
Species of atoms characterized by the number of protns and neutrons and the energy content of the atomic nuclei are called
Nuclides
Number of protons
Isotopes
Same atomic mass number
Isobars
Same number of neutrons
Isotones
Different nuclear energy states
Isomer
EM radiation emitted from the nucleus as the excited state transitions to a lower (more stable) energy state is called
Gamma ray
An alternative form of de-excitation is______, in which the de-excitation energy is completely transferred to an orbital electron
Internal conversion
Energy required to separate an atom into its constituent parts is the
Atomic binding energy
Sum of the orbital electron binding energy and the nuclear binding energy
Atomic binding energy
The energy necessary to disassociate a nucleus into its constituent parts and is the result of the strong forces acting between the nucleons
Nuclear binding energy
The binding energy can be calculated by subtracting the mass of the atom from the total mass of its constituent protons, neutrons and electrons; this mass difference is called the
Mass defect
During nuclear _______, a nucleus with a large atomic mass splits into two usually unequal parts called fission fragments, each with an average binding energy per nucleon greater than that pf the original nucleus
Fission fragments
Examples of heavy charged particles
Alpha particles and protons
Examples of lighter charged particles
Electrons and positrons
Particles of ionizing radiation include charged particles and uncharged particles such as
Charged particles such as Alpha particles, protons, beta particles, positrons, energetic extranuclear electrons
And uncharged particles such as neutrons
Refer to coulombic forces exerted on charged particles when they pass in proximity to the electric field generated by the atom’s electron and protons
Interactional or collisional losses
Energetic charged particles interact with matter by electrical forces and lose kinetic energy via
Excitation, ionization and radiative losses
Transfer of some of the incident particles energy to electrons in the absorbing material, promotung them to electron orbits farther from the nucleus
Excitation
In _______, the energy transferred to an electron does not exceed its binding energy
Excitation
If the transferred energy exceeds the binding energy of the electron, ________ occurs, whereby the electron is ejected electron and the positively charged atom
Ionization
An ion pair consists of
Ejected electron and positively charged atom
Ejected electrons posses sufficient energy to produce further ionizations called secondary ionization. These electrons are called
Delta rays
70% of the energy deposition of energetic electrons in soft tissue occurs via
Ionization
Average number of primary and secondary ion pairs produced per unit length of the charged particle’s path is called ________ expressed in ion pairs
Specific ionization
As the alpha particle slows, the specific ionization increases to a maximum called, ______ beyond which it decreases rapidly as the alpha particle acquires electrons and becomes electrically neutral, thus losing its capacity for further ionization
Bragg peaks
Electrons follow tortuous paths in matter as the result of multiple scattering events caused by ______
Coulombic deflections (repulsion and/or attraction
Electron particle track follows a
Tortuous path due to coulombic deflections
Charged particles follow a ______
Linear ionization track
Distance the particle travels
Path length
Defined as the depth of penetration of the particle in matter
Range
The path length of the _______ almost always exceeds its range
Electron
The path length and range of ______ is nearly equal
Charged particles
Measure of the average amount of energy deposited locally (near the incident particle track) in the absorber per unit path length
Linear energy transfer
Reflects all energy losses that occurs before an ion pair is produced
Specific ionization
Linear energy transfer of a charged particle is proportional to the square of the charge and _______ proportional to the particle kinetic energy
Inversely proportional
Alpha particles and protons have high/low LET radiation
High
Low LET radiation includes
Energetic electrons and ionizing electromagnetic radiation (gamma rays and xrays)
Interaction that deflects a particle or photon from its original trajectory
Scattering
A scattering event in which the total kinetic energy of the colliding particles is unchanged is called
Elastic
When scattering occurs with a loss of kinetic energy, the interaction is said to be
Inelastic
Radiation emission accompanying electron deceleration
Braking radiation or bremsstrahlung
Total bremsstrahlung emission per atom is ________ to Z2, where Z is the atomic number of the absorber and _______ proportional to the squatr of the mass of the incident particle that i Z2/M2
Proportional to Z2
Inversely proportional to square of mass
Responsible for the majority of the xrays produced by xray tubes
Radiative energy loss
These particles cannot cause excitation and ionization via coulombic interactions but can interact with atomic nuclei, sometimes liberating charged particles or nuclear fragments that can directly cause excitation and ionization
Neutrons
Xray and gamma ray major interactions with matter include
Rayleigh scattering
Compton scattering
Photoelectric absorption
Pair production
In _____ scattering, the incident photon interacts with and excites the total atom
Rayleigh
This interaction occurs mainly with very low energy xrays such as those used in mammography
Rayleigh scattering
In this interaction, electrons are not ejected and thus, ionization does not occur
Rayleigh
Also referred to as coherent or classical scattering
Rayleigh
Also called inelastic or nonclassical scattering, it is the predominant interaction of xray and gamma ray photons in the diagnostic energy range with soft tissue
Compton scattering
Results in the ionization of the at and a division of the incident photon’s energy between the scattered photon and the ejected electron
Compton scattering
In _______ effect, all of the incident photon energy is transferred to an electron, which is ejected from the atom
Photoelectric
Primary mode of interaction of diagnostic xrays with image receptors, radiographic contrast materials and radiation shielding, all of which have much higher atomic numbers than soft tissue
Photoelectric absorption
In ______, an xray or gamma ray interacts with the electric field of the nucleus of an atom. The photon’s energy is transformed into an electron-positron pair
Pair production
Removal of photons from a beam of xrays or gamma rays as it passes thru matter
Attenuation
At low photon energies (less than 26 keV), the ________ effect dominates the attenuation processes in soft tissue
Photoelectric
The fraction of photons removed from a monoenergetic beam of xrays or gamma rays per unit thickness of material is called
Linear attenuation coefficient
The probability of interaction is proportional to the
Number of atoms per volume
Defined as thickness of material required to reduce the intensity of an xray or gamma ray beam to one half of its initial value
Half value layer
Thickness of material that is necessary to reduce the intensity of the beam to a tenth of its initial value. It is often used in xray room shielding design calculations
Tenth-value layer
Xray beams in radiology are _______, meaning that they are composed of a spectrum of xray energies
Polyenergetic
It is a way of characterizing the penetrability of the xray beam
Half value layer
An estimate of the penetration power of the xray beam, expressed as the energy of a monoenergetic beam that would exhibit the same “effective” penetrability
Effective energy
Shift of xray spectrum to higher effective energies as the beam transverses matter is called
Beam hardening
Number of photons or particles passing thru a unit cross-sectional area is referred to as the
Fluence
The fluence rate is called the _____. It is useful in situations in which the photon beam is on for extended periods of time such as in fluoroscopy
Flux
Amount of energy passing through a unit cross-sectional area is referred to as the
Energy fluence
It is an acronym for kinetic energy released in matter
Kerma
SI unit for Kerma
Joule per kilogram
Gray (Gy)
Mass attenuation coefficient multiplied by the fraction of the energy pf the interacting photons that is transferred to charged particles as kinetic energy
Mass energy transfer coefficient
Energy imparted by ionizing radiation per unit mass of irradiated material
Absorbed dose
Kerma is defined using ______ coefficient, whereas dose is defined using ______ coefficient
Mass energy transfer-kerma
Mass energy absorption-dose
Amount of electrical charge (Q) produced by ionizing electromagnetic radiation per mass is called
Exposure
Total amount of energy deposited in matter.
Product of dose and the mass over which the energy is imparted.
Imparted energy
Product of absorbed dose and radiation weighing factor is the
Equivalent dose
Traditional unit for both dose equivalent and the equivalent dose is the
Rem
A sievert is equal to ____ rem
100
Amount of ionization per mass of air due to xrays and gamma rays
Exposure
Amount of energy imparted by radiation per mass
Absorbed dose
Kinetic energy transfered to charged particles per unit mass
Kerma
Kinetic energy transferred to charged particles per unit mass of air
Air kerma
Total radiation energy imparted to matter
Imparted energy
A measure of absorbed dose weighted for the biological effectiveness of the type of radiation (relative to low LET photons and electrons) to produce stochastic health effects in humans
Equivalent dose
A measure of dose equivalent, weighted for the biological sensitivity of the exposed tissues and organs (relative to whole body exposure) to stochastic health effects in humans
Effective dose equivalent
A measure of equivalent dose, weighted for the biological sensitivity of the exposed tissues and organs (relative to whole body exposure) to stochastic health effects in humans
Effective dose
Describes the level of detail that can be seen on an image
Spatial resolution
Most basic measure of the resolution properties of an imaging system
Point spread function
An imaging system with the same PSF at all locations in the field of view is called
Stationary or shift invariant
PSFs that vary depending on the position in the field of view is called
Nonstationary
Describes the extent of blurring that is introduced by an imaging system
Point spread function
This is particularly useful when the spatial distribution characteristics of glare or scatter phenomenon are the subject of interest
Edge spread function
An integral calculus procedure that accurately describes mathematically what the blurring process does physically. It is also an important mathematical component of image reconstruction
Convolution
An algorithm that decomposes a spatial or time domain signal into a series of sine waves that when summed, replicate that signal
Fourier transform
Once a spatial domain signal is fourier transformed, the resulting data are considered to be in the
Frequency domain
Sets the upper bound on the spatial frequency that can be detected for a digital detector system with detector pitch
Nyquist frequency
Ability to detect very subtle changes in gray scale and distinguish them from the noise in the image
Contrast resolution
Relates more to anatomical structures that produce small changes in signal intensity (image grayscale)
Contrast resolutiom
Relates to how close one gets tl the truth
Accuracy
Description of the variation, scatter or reproducibility in a measurement
Precision
In medical imaging, it has to do with amount of noise in the image
Precision
Observed darkness
Optical density
Electronic noise can be from
Thermal noise, shot noise
Any number of particles or objects than can be counted such as electrons, xray photons, optical photons or even brush strokes on impressionist paintings
Quanta
Uncorrelated noise is called
White noise
An object size-independent measure of the signal level in the presence of noise
Contrast to noise ratio
One of the most meaningful metrics that describes the conspicuity of an object— how well it be seen by the typical observer
Signal-to-noise ratio
Describes the overall frequency-dependent SNR performance of the system
Detective quantum efficiency
