Term
| 3D volumetric acquisition |
|
Definition
| acquisition where the whole imaging volume is excited so that the images can be viewed in any plane |
|
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Term
|
Definition
| the time between the echo and the next RF pulse in SSFP |
|
|
Term
|
Definition
| artefact produced when anatomy outside the FOV is mismapped inside the FOV |
|
|
Term
|
Definition
| when nuclei are placed in an external magnetic field their magnetic moments line up with the magnetic field flux lines |
|
|
Term
|
Definition
| alloy that is used to make permanent magnets |
|
|
Term
|
Definition
| determines the magnitude and direction of the magnetic field due to a current; if you point your right thumb along the direction of the current, then the magnetic field points along the direction of the curled fingers |
|
|
Term
| Analogue to digital conversion (ADC) |
|
Definition
| process by which a waveform is sampled and digitized |
|
|
Term
|
Definition
| the spin of MRI active nuclei that depends on the balance between the number of protons and neutrons in the nucleus |
|
|
Term
|
Definition
| describes the alignment of magnetic moments in the opposite direction of the main field |
|
|
Term
| Apparent diffusion coefficient (ADC) |
|
Definition
| net displacement of molecules due to diffusion |
|
|
Term
|
Definition
| sum of PROTONS in the nucleus |
|
|
Term
|
Definition
| the main magnetic field measured in Tesla |
|
|
Term
|
Definition
| strength and duration of diffusion gradients |
|
|
Term
| Balanced gradient echo (BGE) |
|
Definition
| gradient echo sequence that uses balanced gradients and alternating RF pulses |
|
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Term
|
Definition
| describes a magnet with tow poles, north and south |
|
|
Term
|
Definition
| where the phase encoding gradient slope is slightly altered to jump from K space line to the next. Used in EPI to step down through phasing encoding steps |
|
|
Term
|
Definition
| additional solenoid magnets to adjust field homogeneity |
|
|
Term
|
Definition
| voxels that are not the same dimension in all three planes |
|
|
Term
|
Definition
| also called no phase wrap oversamples along the phase encoding axis by increasing the number of phase encodings performed |
|
|
Term
|
Definition
| a tiny element that is the basis for all things |
|
|
Term
|
Definition
|
|
Term
|
Definition
| acquisitions in which blood vessels are black |
|
|
Term
| Blood Oxygen Level Dependent imaging (BOLD) |
|
Definition
| a functional MRI technique that used the differences in magnetic susceptibility between oxyhemoglobin and deoxyhemoglobin to image areas of activated cerebral cortex |
|
|
Term
|
Definition
| internal motion of molecules |
|
|
Term
|
Definition
| the result of T2* decay during the course of the EPI acquisition |
|
|
Term
|
Definition
| acquisitions in which blood vessels are bright |
|
|
Term
|
Definition
| monitors cardiac electrical activity during the sequence to reduce cardiac wall motion artefact |
|
|
Term
|
Definition
| Continuous Arterial Spin Labeling- attenuates arterial spins by inversion or saturation pulses outside the FOV |
|
|
Term
|
Definition
|
|
Term
| Central lines/Centric K space filling |
|
Definition
| area of K space filled with the shallowest phase encoding slopes |
|
|
Term
|
Definition
| along the frequency axis caused by the frequency difference between fat and water |
|
|
Term
|
Definition
| aretfact along the phase axis caused by the phase difference between fat and water |
|
|
Term
|
Definition
| the precessional frequency difference between fat and water |
|
|
Term
|
Definition
| uses the direction of the magnetic moments to illustrate alginment |
|
|
Term
|
Definition
| flow int he same direction as slice excitation |
|
|
Term
|
Definition
| the magnetic moments of hydrogen are at the same place on the precessional path |
|
|
Term
|
Definition
| a matrix with a low number of frequency encodings and/or phase encodings and results in a low number of pixels in the FOV |
|
|
Term
|
Definition
| symmetry of data in K space |
|
|
Term
| Contrast to noise ratio (CNR) |
|
Definition
| difference in SNR between to adjacent structures |
|
|
Term
|
Definition
| flow in the opposite direction to slice excitation |
|
|
Term
|
Definition
| energy given to nuclei in adjacent slices by the RF pulse |
|
|
Term
|
Definition
| energy given to nuclei in adjacent slices due to spin lattice relaxation |
|
|
Term
|
Definition
| area around the coils of wire in which cryogens are placed |
|
|
Term
|
Definition
| substances used to supercool the coils of wire in a superconducting magnet |
|
|
Term
|
Definition
| point in K space that contains digitized information from spatial encoding |
|
|
Term
|
Definition
| loss of coherent transverse magnetization |
|
|
Term
|
Definition
| the magnetic moments of hydrogen are at a different place on their precessional path |
|
|
Term
|
Definition
| property that shows a small magnetic moment that opposes the applied field |
|
|
Term
|
Definition
| the movement of molecules due to random thermal motion |
|
|
Term
| Diffusion tensor imaging (DTI) |
|
Definition
| DWI sequence that uses very strong multidirectional gradients |
|
|
Term
| Diffusion weighted imaging (DWI) |
|
Definition
| sequence that uses gradients to sensitize the sequence to diffusion. technique that produces images whose contrast is due to the differences in ADC between tissues. |
|
|
Term
| Dipole-Dipole interaction |
|
Definition
| the phenomenon by which excited protons are affected by nearby excited protons and electrons |
|
|
Term
|
Definition
| technique that uses a TE when fat and water are out of phase with each other to null the signal from fat |
|
|
Term
|
Definition
| sequence in which two 180 degree pulses are used to saturate blood in black blood imaging |
|
|
Term
|
Definition
| Driven Equlilibrium- a pulse sequence that achieves a very high signal intensity from water even when using short TRs |
|
|
Term
|
Definition
| a sequence that uses additional pulses to drive any remaining transverse magnetization into the longitudinal plane |
|
|
Term
|
Definition
| the percentage of time a gradient is at maximum amplitude |
|
|
Term
|
Definition
| digital subtraction MR angiography-contrast is selectively produced for moving spins during two acquisitions. These are then subtracted to remove the signal from the stationary spins, leaving behind an image of only the moving spins |
|
|
Term
|
Definition
| Diethylene Triaminepentaacetic Acid, a gadolinium chelate |
|
|
Term
|
Definition
| time in milliseconds from the application of the RF pulse to the peak of the signal induced in the coil- TE determines how much decay of transverse magnetization is allowed to occur |
|
|
Term
| Echo Planar Imaging (EPI) |
|
Definition
| sequence that uses single and multi-shot K space filling techniques with sampling of gradient echoes |
|
|
Term
|
Definition
| spacing between each echo in TSE/FSE |
|
|
Term
|
Definition
| series of 180 degree rephasing pulse and echoes in a fast/turbo spine echo pulse sequence |
|
|
Term
|
Definition
| the number of 180 degree rephasing pulse/echoes/phase encodings per TR in fast/turbo spine echo |
|
|
Term
|
Definition
| the time between the echo and the RF pulse that initiated it in SSFP, also the TE used in FSE |
|
|
Term
|
Definition
| orbit the nucleus in distinct shells and are negatively charged |
|
|
Term
|
Definition
| drives a current in a circuit and is the result of a changing magnetic field inducing an electric field |
|
|
Term
|
Definition
| once a slice is selected, the signal is located or encoded along both axes of the image |
|
|
Term
|
Definition
| contrast difference of flowing nuclei relative to the stationary nuclei because the are fresh |
|
|
Term
|
Definition
| the flip angle that results in the highest signal intensity in a tissue with a particular T1 relaxation time and at a particular TR |
|
|
Term
|
Definition
| technique that uses two echoes to reduce flow artefact |
|
|
Term
|
Definition
| application of RF pulse that transfers energy to the spins and causes resonance to occur |
|
|
Term
| Extrinsic contrast parameters |
|
Definition
| contrast parameters that are controlled by the system operator |
|
|
Term
| Faradays law of induction |
|
Definition
| las that states that a change of magnetic flux induces an emf in a closed circuit |
|
|
Term
| Fast fourier transform (FFT) |
|
Definition
| mathmatical conversion of frequency/time domain to frequency/amplitude |
|
|
Term
|
Definition
| FSE sequence that uses an additional RF pulse to drive any residual transverse magnetization into the longitudinal plane (also called DRIVE) |
|
|
Term
| Fast/Turbo Spine Echo (FSE or TSE) |
|
Definition
| spin echo sequence that decreases scan time by filling multiple lines of K space ever TR |
|
|
Term
|
Definition
| property of a substance that ensures that it remains magnetic, is permanently magnetized and subsequently becomes a permanent magnet |
|
|
Term
|
Definition
| area of anatomy covered in an image |
|
|
Term
|
Definition
| matrix where there are a high number of frequency encodings and/or phase encodings and results in a large number of pixels in the FOV |
|
|
Term
| First order motion compensation |
|
Definition
|
|
Term
| FLAIR (Fluid attenuated inversion recovery) |
|
Definition
| IR sequences that nulls the signal from CSF |
|
|
Term
|
Definition
| the angle of the NMV to Bo |
|
|
Term
|
Definition
| axes along which bipolar gradients axt in order to sensitize flow along the axis of the gradient; used in Phase Contrast (PC) MRA |
|
|
Term
|
Definition
| artefacts produced by flowing nuclei |
|
|
Term
|
Definition
| decrease in flow enhancement due to a decrease in the velocity of flow |
|
|
Term
| Free Induction Decay (FID) |
|
Definition
| loss of signal due to relaxation |
|
|
Term
|
Definition
| the speed with which a spin precesses or a waveform oscillates |
|
|
Term
|
Definition
| locating a signal according to its frequency |
|
|
Term
|
Definition
| aliasing along the frequency encoding axis |
|
|
Term
|
Definition
| number of pixels in the frequency direction of an image |
|
|
Term
|
Definition
| difference in frequency between spins located along a gradient |
|
|
Term
|
Definition
| nuclei that have not been beaten down by repeated RF pulses |
|
|
Term
|
Definition
| stray magnetic field outside the bore of the magnet |
|
|
Term
| Functional MR Imaging (fMRI) |
|
Definition
| a rapid MR imaging technique that acquires images of the brain during activity or stimulus and at rest |
|
|
Term
|
Definition
|
|
Term
|
Definition
|
|
Term
|
Definition
|
|
Term
|
Definition
|
|
Term
|
Definition
|
|
Term
|
Definition
|
|
Term
|
Definition
| unit of field strength 1Tesla=10,000FGauss |
|
|
Term
|
Definition
| motion artefact in the phase axis |
|
|
Term
|
Definition
| a series of lines in the MR image parallel to abrupt and intense changes in the object at this location, such as the CSF-spinal cord and the skull-brain interface. |
|
|
Term
|
Definition
| supplies power to the gradient coils |
|
|
Term
|
Definition
| echo produced as a result of gradient rephasing |
|
|
Term
| Gradient Echo pulse sequence |
|
Definition
| one that uses a gradient to regenerate an echo |
|
|
Term
Gradient Echo-Echo planar imaging
EPI (GE-EPI) |
|
Definition
| gradient echo sequence with EPI readout |
|
|
Term
|
Definition
| a system of gradients that compensates for intra-voxel dephasing and reduce flow artefact |
|
|
Term
|
Definition
| coils of wire that alter the magnetic field strength in a linear fashion when a current is passed through them |
|
|
Term
|
Definition
| the use of gradients to dephase magnetic moments; the opposite of rewinding |
|
|
Term
|
Definition
| Gradient echo and spin echo |
|
|
Term
|
Definition
| the precessional frequency of an element at 1T |
|
|
Term
|
Definition
| echoes formed when any two 90 degree RF pulses are used in steady state sequences |
|
|
Term
| High velocity signal loss |
|
Definition
| increase in time of flight due to an increase in the velocity of flow |
|
|
Term
|
Definition
| evenness of the magnetic field |
|
|
Term
|
Definition
| combination of fast spine echo and EPI sequences where a series of gradient echoes are interspersed with spin echoes or 180 degree rephasing pulses in this way susceptibility artefacts are reduced |
|
|
Term
|
Definition
| high signal intensity- bright |
|
|
Term
|
Definition
| low signal intensity- dark |
|
|
Term
|
Definition
| the most abundant atom in the body |
|
|
Term
|
Definition
| International society for MR in medicine |
|
|
Term
|
Definition
| Institute for MR safety, education and research |
|
|
Term
|
Definition
| the magnetic moments of hydrogen are at different places on the precessional path- out of phase |
|
|
Term
| Incoherent gradient echoe |
|
Definition
| gradient echo sequence that uses RF spoiling for T1 weighting |
|
|
Term
|
Definition
| oscillating current that occurs when a magnet is moved in a closed circuit |
|
|
Term
|
Definition
| another term for entry slice phenomenon |
|
|
Term
|
Definition
| areas where the magnetic field strength is not exactly the same as the main field strength- magnetic field unevenness |
|
|
Term
|
Definition
| magnetic moments that are in the same place on the precessional path around Bo at any given time |
|
|
Term
|
Definition
| a method of acquiring data from alternate slices and dividing the sequence into two acquisitions- no slice gap is required |
|
|
Term
|
Definition
| phase difference between flow and stationary nuclei in a voxel |
|
|
Term
| Intrinsic contrast parameters |
|
Definition
| those parameters that cannot be changed because they are inherent to the body tissues |
|
|
Term
|
Definition
| sequence that uses an inverting pulse to saturate or null tissue |
|
|
Term
|
Definition
| atoms with an excess or deficit of electrons |
|
|
Term
|
Definition
|
|
Term
|
Definition
| atoms of the same element with an odd mass number |
|
|
Term
|
Definition
| voxels that have the same dimension in all three planes |
|
|
Term
|
Definition
| a process that describes the reduction the spin spin interactions cause in fat, caused by multiple RF pulses as in fast spin echo, thereby increasing its T2 decay time |
|
|
Term
|
Definition
| unit of field strength 1000 gauss |
|
|
Term
|
Definition
| an area in the array processor where data on spatial frequencies are stored |
|
|
Term
|
Definition
| used to caculate the frequency or speed of precession for a specific nucleus in a specific magnetic field strength |
|
|
Term
|
Definition
|
|
Term
|
Definition
| states that induced emf is in a direction so that it opposes the change in magnetic field that causes it |
|
|
Term
|
Definition
| field created by passing current through a gradient coil |
|
|
Term
|
Definition
| number of flux lines per unit area |
|
|
Term
| Magneto-hemodynamic effect |
|
Definition
| effect that causes elevation of the T wave of the ECG of the patient when placed in a magnetic field. this is due to the conductivity of blood |
|
|
Term
|
Definition
| the centre of the bore of the magnet in all plances |
|
|
Term
|
Definition
| lines of force running from the magnetic south to the north poles of the magnet |
|
|
Term
|
Definition
| denotes the direction of the north/south axis of a magnet and the amplitude of the magnetic field |
|
|
Term
|
Definition
| ability of a substance to become magnetized |
|
|
Term
| Magnetization transfer contrast/coherence (MTC) |
|
Definition
| technique used to suppress background tissue and increase CNR |
|
|
Term
|
Definition
| a property of all matter that depends on the magnetic susceptibility of the atom |
|
|
Term
|
Definition
| a prepulse applied before the main sequence to null the signal from certain tissues in fast gradient echo |
|
|
Term
|
Definition
| transfer of RF energy from free to bound protons |
|
|
Term
|
Definition
| un-subtracted image combination of flow sensitized data |
|
|
Term
|
Definition
| sum of neutrons and protons in the nucleus |
|
|
Term
| Maximum intensity projection (MIP) |
|
Definition
| technique that uses a ray passed through an imaging volume to assign signal intensity according to their proximity to the observer |
|
|
Term
|
Definition
| used in perfusion imaging to indicate the transit time of blood through a tissue |
|
|
Term
|
Definition
| where two or more atoms are arranged together |
|
|
Term
|
Definition
| nuclei that possess an odd number of protons |
|
|
Term
|
Definition
| method of visualizing vessels that contain flowing nuclei by producing a contrast between them and the stationary nuclei |
|
|
Term
|
Definition
| the voltage induced in the receiver coil |
|
|
Term
| Multiple overlapping thin section angiography (MOTSA) |
|
Definition
| method combining a number of high resolution 3D acquisitions to produce an image that has good resolution and a large area of coverage |
|
|
Term
|
Definition
| technique that fills K space in multiple sections. K space is divided into segments and one segment is acquired per TR |
|
|
Term
|
Definition
| technique that acquires multiple voxels by encoding in K space in MR signal |
|
|
Term
| Net Magnetization Vector (NMV) |
|
Definition
| the magnetic vector produced as a result of the alignment of excess hydrogen nuclei with Bo |
|
|
Term
|
Definition
| particles in the nucleus that have no charge |
|
|
Term
| NEX/Number of excitations, NSA/Number of signal averages |
|
Definition
| number of excitations, the number of times an echo is encoded with the same slope of phas encoding gradient |
|
|
Term
|
Definition
| frequencies that exist randomly in time and space |
|
|
Term
|
Definition
|
|
Term
|
Definition
| the point at which there is no longitudinal magnetization in a tissue in an inversion recovery sequence |
|
|
Term
|
Definition
| states that frequencies must be sampled at a rate at least twice that of the highest frequency in the echo in order to reliably reproduce it |
|
|
Term
|
Definition
basic law of electricity-
voltage(V)=current(I)x(R)resistance |
|
|
Term
|
Definition
| RF pulses applied at a frequency slightly different to the larmor frequency of a tissue |
|
|
Term
|
Definition
| RF pulses applied at the larmor frequency of a particular tissue |
|
|
Term
|
Definition
| area of K space filled with the steepest phase encoding gradient slopes |
|
|
Term
|
Definition
| when magnetic moments are not in the same place on the precessional path |
|
|
Term
|
Definition
| artefact along the phase axis caused by the phase difference between fat and water |
|
|
Term
|
Definition
| describes the alignment of magnetic moments in the same direction as the main field |
|
|
Term
|
Definition
| a technique that uses multiple coils to fill segments of K space |
|
|
Term
|
Definition
| property whereby substances affect external magnetic fields in a positive way, resulting in a local increase in the magnetic field |
|
|
Term
|
Definition
| filling only a proportion of K space with data and putting zeros in the remainder |
|
|
Term
|
Definition
| sampling only part of the echo and extrapolating the remainder in K space |
|
|
Term
|
Definition
| occurs when the NMV is flipped beyond 90 degrees (91-179 degrees) |
|
|
Term
|
Definition
| loss of spatial resolution when large voxels are used |
|
|
Term
|
Definition
| shielding accomplished by surrounding the magnet with steel plates |
|
|
Term
|
Definition
| a measure of the quality of vascular supply to a tissue |
|
|
Term
|
Definition
| uses metal discs/plates at installation to adjust for large changes in field homogeneity |
|
|
Term
|
Definition
| achieved in IR pulse sequence with a long TE, pathology appears bright even though the image is T1 weighted |
|
|
Term
|
Definition
| the time interval between the magnetic moments of fat and water being in phase |
|
|
Term
|
Definition
| magnets that retain their magnetism |
|
|
Term
|
Definition
| the position of a magnetic moment on its precessional path at any given time |
|
|
Term
| Phase Contrast Angiography (PCMRA) |
|
Definition
| technique that generates vascular contrast by applying a bipolar gradient using the phase difference between stationary and flowing spins |
|
|
Term
|
Definition
| a waveform derived from plotting different phase postions over a distance in the patient |
|
|
Term
|
Definition
| locating a signal according to its phase |
|
|
Term
|
Definition
| Subtracted image combination of flow sensitized data |
|
|
Term
|
Definition
| aliasing along the phase encoding axis |
|
|
Term
|
Definition
| number of pixels in the phase direction of an image |
|
|
Term
|
Definition
| the order that lines of K space are filled is altered from linear to non linear |
|
|
Term
|
Definition
| difference in phase between spins located along a gradient |
|
|
Term
|
Definition
| picture element in the FOV |
|
|
Term
|
Definition
| the direction of a gradietn which end is greater then Bo and which is lower th\an Bo; depends on the direction of the current through the gradient coil |
|
|
Term
| Point Resolved Spectroscopy Spin Echo (PRESS) |
|
Definition
| single voxel technique in MRS |
|
|
Term
|
Definition
| the secondary spin of the magnetic moments around Bo |
|
|
Term
| Precessional (Larmor) frequency |
|
Definition
| The speed of precession; frequency with which MR active nuclei precess when exposed to an external magnetic field |
|
|
Term
|
Definition
| the circular pathway of magnetic moments as they precess around Bo |
|
|
Term
|
Definition
| technique that uses RF pulses before the sequence to null the signal from moving spins or from certain types of tissue |
|
|
Term
|
Definition
| isotope of hydrogen that has a mass and atomic number of 1, MR active nucleus used in MRI |
|
|
Term
|
Definition
| number of protons per unit volume of that tissue |
|
|
Term
|
Definition
| image that demonstrates the differences in the proton densities of the tissues |
|
|
Term
|
Definition
| positively charged element of an atomic nucleus |
|
|
Term
|
Definition
| the frequency that is indirectly derived from a change of phase. from a waveform that represents the change of phase of spins within a voxel across the whole acquisition |
|
|
Term
|
Definition
| coordinates the switching on and off of the gradient and RF transmitter coils at appropriate times during the pulse sequence |
|
|
Term
|
Definition
| a series of RF pulses, gradient applications and intervening time periods, used to control contrast |
|
|
Term
|
Definition
| uses the energy level of the nuclei to illustrate alignment |
|
|
Term
|
Definition
| process by which there is a sudden loss of the superconductivity of the magnet coils so that the magnet becomes resistive |
|
|
Term
|
Definition
|
|
Term
|
Definition
| waves of electromagnetic radiation that oscillate with a radiofrequency |
|
|
Term
|
Definition
| emission of energy caused by a deficit in the number of electrons compared with protons |
|
|
Term
|
Definition
| low energy, low frequency electromagnetic radiation. Used to excite hydrogen nuclei in MRI |
|
|
Term
|
Definition
| where sampling data points are collected when the gradient rise time is almost complete-sampling occurs while the gradient is still reaching max amplitude, while the gradient is at max amplitude and as it begins to decline |
|
|
Term
|
Definition
| the frequency encoding gradient |
|
|
Term
|
Definition
| range of frequencies that are sampled during readout- determines sampling rate |
|
|
Term
|
Definition
| growth of longitudinal magnetisation |
|
|
Term
|
Definition
| also known as asymmetric FOV uses a FOC in the phase direction that is different to that in the frequency direction of the image- where the phase FOV is smaller then the frequency FOV |
|
|
Term
|
Definition
| process by which the NMV loses energy |
|
|
Term
|
Definition
| process by which relaxation rates of a tissue are altered by administering contrast agents |
|
|
Term
|
Definition
| the factor by which the scan time is reduced using parallel imaging. Equals the number of coils used. |
|
|
Term
|
Definition
| time between each excitation pulse |
|
|
Term
|
Definition
| creating in phase magnetization, usually by using and RF pulse or a gradient |
|
|
Term
| Residual transverse magnetization |
|
Definition
| transverse magnetization left over from previous RF pulses in steady state conditions |
|
|
Term
|
Definition
| another term for solenoid magnet, an electromagnet created by passing current through loops of wire |
|
|
Term
|
Definition
| an energy transition that occurs when an object is subjected to a frequency the same as its own |
|
|
Term
|
Definition
| uses mechanical motion of air in bellows to order K space filling and reduce respiratory motion |
|
|
Term
| Respiratory gating/triggering |
|
Definition
| scan initiated when the patient is not breathing |
|
|
Term
|
Definition
| the use of a gradient to rephase magnetic moments |
|
|
Term
|
Definition
| supplies power to the RF transmitter coil |
|
|
Term
|
Definition
| short burst of RF energy that excites nuclei into a high energy state |
|
|
Term
|
Definition
| the use of digitized RF to transmit and receive at a certain phase |
|
|
Term
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Definition
| coil that transmits RF at the resonant frequency of hydrogen to excite nuclei and move them into a high energy state |
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Term
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Definition
| the time it takes a gradient to switch on, achieve the required gradient slope and switch off again |
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Term
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Definition
| time between each R wave in gated studies |
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Term
| Rotating time frame of reference |
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Definition
| where you, the observer, ride along with the object that is moving |
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Term
| Sampling rate or frequency |
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Definition
| rate at which samples are taken during readout |
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Term
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Definition
| the time for which the readout gradient is switched on |
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Term
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Definition
| Standardized absorbtion rate a way of measuring the usa food and drug admin limit for RF exposure. Specific Absorption Rate |
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Term
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Definition
| time between each pre-sat pulse |
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Term
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Definition
| occurs when the NMV is flipped to a full 180 degrees |
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Term
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Definition
| acq where all the data from each slice is acquired before going on to the next |
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Term
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Definition
| extra coils used to make the magnetic field as homogeneous as possible |
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Term
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Definition
| process whereby the evenness of the magnetic field is optimized |
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Term
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Definition
| voltage induced in the receiver coil |
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Term
| Signal to Noise Ratio (SNR) |
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Definition
| ratio of signal relative to noise |
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Term
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Definition
| a fast spin echo sequence where all the lines of K space are acquired during a single TR period |
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Term
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Definition
| techniques that use three intersecting slices to locate a single voxel in MR |
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Term
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Definition
| function of gradient rise time and amplitude, the strength of a gradient over distance |
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Term
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Definition
| the separation of individual slice locations b phase in volume acquisitions |
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Term
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Definition
| selecting a slice using a gradient |
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Term
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Definition
| spatially locating a signal in three dimensions |
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Term
| Spatial modulation of Magnetisation (SPAMM) |
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Definition
| creates a saturation effect which produces a cross hatching of stripes on the image. these can be compared with moving anatomy to determine its function |
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Term
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Definition
| the ability to distinguish two points as separate |
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Term
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Definition
| provides a frequency spectrum of a given tissue based on the molecular and chemical structures of that tissue |
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Term
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Definition
| the population of high energy hydrogen nuclei that align their magnetic moments anti parallel to the main field Bo |
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Term
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Definition
| echo produced as a result of a 180 degree rephasing pulse |
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Term
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Definition
| process by which energy is given up to the surrounding lattice |
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Term
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Definition
| process by which interactions between the magnetic fields of adjacent nuclei causes dephasing |
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Term
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Definition
| the population of low energy hydrogen nuclei that align their magnetic moments parallel to Bo |
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Term
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Definition
| a process of dephasing spins either with a gradient or RF pulse |
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Term
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Definition
| a situation when the TR is shorter than both the T1 and T2 relaxation times of all tissues |
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Term
| Steady State Free Precession (SSFP) |
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Definition
| gradient echo sequence that uses echo shifting for T2 weighting |
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Term
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Definition
| two gradients of equal polarity and amplitude are applied on each side of a 180 degree RF pulse |
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Term
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Definition
| echo produced by previous RF pulse in a steady state sequence by rephasing residual transverse magnetization |
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Term
| Stimulated Echo Aquisition Mode (STEAM) |
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Definition
| technique used in spectroscopy- single voxel MRS |
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Term
| STIR (Short TI Inversion Recovery) |
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Definition
| sequence used to suppress fat |
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Term
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Definition
| solenoid electromagnet that uses super cooled coils of wire so that there is no inherent resistance in the system through which the current flows, and therefore the magnetism is generated without a driving voltage |
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Term
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Definition
| a paramagnetic contrast agent- shortens T1 relaxtion in tissues that take up the agent. Gadolinium. |
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Term
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Definition
| growth of longitudinal magnetization as a result of spin lattice relaxtion |
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Term
| T1 relaxtion/recovery time |
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Definition
| time taken for 63% of the longitudinal magnetization to recover |
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Term
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Definition
| image that demonstrates the differences in the T1 of the tissues |
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Term
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Definition
| dephasing due to magnetic field inhomogeneities |
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Term
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Definition
| loss of coherent transverse magnetization as a result of spin spin relaxation |
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Term
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Definition
| time taken for 63% of the transverse magnetization to decay |
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Term
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Definition
| agents that shorten T2 relaxation times in tissues that take up the agent |
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Term
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Definition
| image that demonstrate the differences in the T2 times of the tissues |
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Term
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Definition
| acquisition where the whole imaging volume is excited so that the images can be viewed in any place |
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Term
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Definition
| the time between the excitation pulse and the 180 degree rephasing pulse and the time between this and the echo. sometimes used in STIR sequences as an alternative to the TI |
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Term
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Definition
| assumes patients temperature is constant and therefore does not influence the thermal energy of hydrogen during the MR experiment |
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Term
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Definition
| curve produce in perfusion imaging to show perfusion kinetics of a tissue |
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Term
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Definition
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Term
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Definition
| rate of flow in a given time , causes some flowing nuclei to receive on RF pulse only and therefore produce a signal void |
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Term
| Time of flight MR angiography |
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Definition
| technique that generates vascula contrast by using the inflow effect |
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Term
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Definition
| time from 180 degree inverting pulse to 90 degree excitation pulse in inversion recovery pulse sequences |
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Term
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Definition
| rate of flow in a given time, causes some flowing nuclei to receive one RF pulse only and therefore produce a signal void |
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Term
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Definition
| time between the excitation pulse and the echo |
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Term
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Definition
| image in DWI where abnormal tissue is brighter than normal tissue |
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Term
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Definition
| coil that both transmits RF and received the MR signal |
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Term
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Definition
| range of frequencies transmitted in an RF pulse |
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Term
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Definition
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Term
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Definition
| waiting period before each R wave in gated studies |
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Term
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Definition
| artefact caused by undersampling so that edges of high and low signal are not properly mapped into the image |
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Term
| Turbo factor/ Echo train length |
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Definition
| the number of 180 degree rephasing pulse/echoes/phase encodings per TR in FSE |
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Term
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Definition
| sensitizes the sequence to blood flow in PC MRA |
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Term
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Definition
| coil that transmits and receives signal over a large volume of the patient |
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Term
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Definition
| volume of tissue in the patient |
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Term
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Definition
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Term
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Definition
| technique that nulls signal from water by applying a RF pulse at the frequency of water to the imaging volume before slice excitation |
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Term
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Definition
| FSE sequence using very long TRs, TEs, and turbo factors to produce very heavy T2 weighting |
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Term
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Definition
| process by which parameters are manipulated so that one intrinsic contrast mechanism is more dominant then the others |
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Term
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Definition
| settings that control brightness and contrast in MR Images. |
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