What is magic angle phenomenon?
The “magic angle” effect in magnetic resonance (MR) imaging is caused by changes in the dipolar interactions between water hydrogen protons that are loosely bound along collagen fibrils in organized tissue such as tendon or articular cartilage.
What is the magic angle in NMR?
In solid-state NMR spectroscopy, magic-angle spinning (MAS) is a technique routinely used to produce better resolution NMR spectra. MAS NMR consists in spinning the sample (usually at a frequency of 1 to 130 kHz) at the magic angle θm (ca. 54.74°, where cos2θm=1/3) with respect to the direction of the magnetic field.
What is magic angle artifact in MRI?
The magic angle is an MRI artifact which occurs on sequences with a short TE (less than 32ms; T1W sequences, PD sequences and gradient echo sequences).
What causes chemical shift artifact in MRI?
Chemical shift is due to the differences between resonance frequencies of fat and water. It occurs in the frequency-encode direction where a shift in the detected anatomy occurs because fat resonates at a slightly lower frequency than water.
What is an aliasing artifact?
Aliasing artifact, otherwise known as undersampling, in CT refers to an error in the accuracy proponent of analog to digital converter (ADC) during image digitization. Image digitization has three distinct steps: scanning, sampling, and quantization.
What is cross talk in MRI?
Cross-talk refers to interference between adjacent slices in MR imaging. Cross-talk arises because the slice profiles generated by RF- pulses are not perfectly rectangular. The simplest solution is to introduce small gaps on the order of 10-20% between slices so that the “tails” of the slice profiles do not overlap.
What is Cpmas NMR?
Solid-state CP/MAS -NMR spectroscopy is a powerful tool for the investigation of cellulose structure. If it is used in conjunction with spectral fitting, it is possible to study and monitor changes in the structural characteristics of cellulose introduced by chemical, mechanical and thermal treatments.
What is spinning sidebands NMR?
Spinning sidebands (SSBs) in the MAS NMR spectrum of a polycrystalline solid are related to the principal values of the chemical shift or quadrupole coupling tensors. At present, 2D methods are widely used to sort out the SSBs for each isotropic peak.
How do you correct a chemical shift artifact?
Remedies. The chemical shift artifacts are reduced by fat suppression techniques (saturation, inversion-recovery). The reduced signal from fat thereby minimizes the chemical shift artifact.
How do you fix a chemical shift MRI?
One simple way to work around the chemical-shift artifact is to swap the frequency- and phase-encode axes prior to imaging. Doing so will not eliminate the chemical-shift artifact but will rotate it to a different anatomical area.
What is photon starvation?
When too few photons reach detector elements, strong streaks appear through paths of high X-ray attenuation and an image becomes completely useless. This photon starvation artifact phenomenon occurs frequently when a pelvis or shoulder is scanned with thin slices.
How do you avoid aliasing?
The solution to prevent aliasing is to band limit the input signals—limiting all input signal components below one half of the analog to digital converter’s (ADC’s) sampling frequency. Band limiting is accomplished by using analog low-pass filters that are called anti-aliasing filters.