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Definition
| An RF pulse that rotates the magnetization by 90 degrees. Also known as saturation pulse |
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| An RF pulse that rotates the magnetization by 180 degrees. Also known as inversion pulse or refocusing pulse |
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| Features in MR images produced by various complications of the imaging process |
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| What are some examples of sources of artifacts? |
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Definition
| Subject motion, magnetic field inhomogeneities, blood flow, and partial voluming |
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Definition
| The main static magnetic field |
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Definition
| Phenomenological equations that describe the time dependency of the magnetization vector in presence of an externally applied magnetic field and subject to relaxation processes |
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Definition
| Blood oxygen level dependent effect. The change in T2* that is caused by changes in the amount of oxygenated hemoglobin in the venous circulation of the brain |
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Definition
| Cerebral blood flow. The flow of capillary blood per unit mass through the cortex |
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| Cerebral blood volume. The volume of blood in a given portion of cerebral cortex |
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| Refers to the loss of net magnetization in the transverse plane due to the fact that the individual nuclei are precessing around the main field B0 at different rates |
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| Diffusion weighted imaging |
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Definition
| Images designed to detect the random movement of water through tissues by diffusion |
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Definition
| Refers to the regrowth of the transverse component of magnetization after it has disappeared due to dephasing |
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| An MRI technique in which a single saturation pulse is used to generate NMR data that is sufficient to define a two-dimensional planar image |
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| What is the main advantage of EPI? |
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Definition
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Definition
| An induced spurious electrical current produced by time-varying magnetic fields |
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| What are some problems with eddy currents? |
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Definition
| They can cause artifacts in images and may seriously degrade overall magnet performance |
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Definition
| Fast fourier transform. A particularly fast and efficient computational method of performing a Fourier Transform, which is the mathematical process by which raw data is processed into a usable image |
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Definition
| The decomposition of an arbitrary mathematical function into a sum of weighted sinusoidal functions |
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| How is Fourier analysis critical in MRI? |
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Definition
| It permits the analysis of a mixture of NMR signals at slightly different frequencies into their component frequencies |
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Term
| What are component frequencies specified? |
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Definition
| They are specified by the frequency-encode gradient, and thus permit the correspondence of frequencies with position |
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Definition
| This refers to the use of a magnetic field gradient to cause different rates of precession along the direction of the gradient during the time that data is acquired |
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Definition
| A form of magnetic resonance signal from the refocusing of transverse magnetization caused by the application of a specific magnetic field gradient |
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Definition
| The ratio of the resonance frequency to the magnetic field strength for a given nucleus |
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Definition
| The changes in blood flow, blood volume, and blood oxygenation in response to local neural activity |
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Definition
| A volume element with equal dimensions in x, y, and z |
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Definition
| The Fourier transform domain of ordinary space |
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Definition
| The net macroscopic magnetization in the sample at thermal equilibrium. It is defined by the spin population excess in the lower energy state |
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| Perfusion-weighted imaging |
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Definition
| Refers to images designed to detect the movement of fluids through vessels |
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Term
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Definition
| This refers to the use of a magnetic field gradient to cause different rates of precession for a brief period of time, resulting in phase differences across space in the direction of the gradient |
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Definition
| A single number in a two-dimensional array of numbers that is used to create and image |
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Definition
| The density of water protons in a given volume of tissue |
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Definition
| Coils positioned near the main magnetic field that carry a relatively small current that is used to provide localized auxiliary magnetic fields in order to improve field homogeneity |
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Definition
| The NMR signal resulting from the refocusing of magnetization after the application of 90 and 180 rf pulses |
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Term
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Definition
| This refers to the loss of NMR signal or to image distortion that arise when two substances of differing magnetic susceptibility are adjacent to one another. |
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Term
| What processes induce T2* relaxation? |
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Definition
| Signal dephasing arising from both macrosopic magnetic field inhomogeneities and microscopic spin-spin interactions |
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Term
| What tissues are bright in a T1-weighted image? |
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Definition
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Term
| What parameters are used for a T1-weighted image? |
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Definition
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| What parameters are used for a T2-weighted image? |
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Definition
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| What tissues are bright in a T2-weighted image? |
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Definition
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Definition
| The time between the presentation of the saturating rf pulse and the time that an NMR echo signal is detected |
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Definition
| The time between consecutive presentations of the rf pulses that flips the longitudinal magnetization |
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Definition
| A single number in a three-dimensional array of numbers. In MRI, a pixel in the image of a single slice through the body corresponds to a voxel in that body |
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Definition
| Number of independent data samples in each direction |
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Definition
| Time in the MR pulse sequence during which the MR signal is recorded |
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Definition
| Consequence of sampling the MR signal in which any components of the signal that are at a higher frequency than the Nyquist limit will be folded in the spectrum so that they appear to be at a lower frequency |
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Definition
| A conventional symbol for the radiofrequency magnetic induction field used in an MR system |
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Definition
| A gradient waveform which will act on any stationary spin on resonance between two consecutive RF pulses and return it to the same phase it had before the gradients were applied |
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Definition
| A general term referring to a range of frequencies |
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Definition
| A generally smooth background curve with respect to which either the integrals or peak heights are measured |
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Definition
| Sequence of a 90 RF pulse followed by repeated 180 RF pulses to produce a train of spin echos. Useful for measuring T2 |
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