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Related Concept Videos

Aliasing01:18

Aliasing

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Accurate signal sampling and reconstruction are crucial in various signal-processing applications. A time-domain signal's spectrum can be revealed using its Fourier transform. When this signal is sampled at a specific frequency, it results in multiple scaled replicas of the original spectrum in the frequency domain. The spacing of these replicas is determined by the sampling frequency.
If the sampling frequency is below the Nyquist rate, these replicas overlap, preventing the original...
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Downsampling01:20

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When considering a sampled sequence with zero values between sampling instants, one can replace it by taking every N-th value of the sequence. At these integer multiples of N, the original and sampled sequences coincide. This process, known as decimation, involves extracting every N-th sample from a sequence, thereby creating a more efficient sequence.
The Fourier transform of the decimated sequence reveals a combination of scaled and shifted versions of the original spectrum. This...
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Upsampling01:22

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Managing signal sampling rates is essential in digital signal processing to maintain signal integrity. A decimated signal, characterized by a reduced frequency range due to its lower sampling rate, can be upsampled by inserting zeros between each sample. This upsampling process expands the original spectrum and introduces repeated spectral replicas at intervals dictated by the new Nyquist frequency. To refine this zero-inserted sequence, it is passed through a lowpass filter with a cutoff...
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Reducing Line Loss01:18

Reducing Line Loss

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In a three-phase circuit, line loss is an indicator of energy dissipated as heat due to the resistance of transmission lines. To address this, incorporating transformers into the system—a step-up transformer at the source and a step-down transformer at the load—is a strategic solution. Two three-phase transformers are introduced to improve this.
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Reconstruction of Signal using Interpolation01:10

Reconstruction of Signal using Interpolation

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Signal processing techniques are essential for accurately converting continuous signals to digital formats and vice versa. When a continuous signal is sampled with a period T, the resulting sampled signal exhibits replicas of the original spectrum in the frequency domain, spaced at intervals equal to the sampling frequency. To handle this sampled signal, a zero-order hold method can be applied, which creates a piecewise constant signal by retaining each sample's value until the next...
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The Doppler effect has several practical, real-world applications. For instance, meteorologists use Doppler radars to interpret weather events based on the Doppler effect. Typically, a transmitter emits radio waves at a specific frequency toward the sky from a weather station. The radio waves bounce off the clouds and precipitation and travel back to the weather station. The radio frequency of the waves reflected back to the station appears to decrease if the clouds or precipitation are moving...
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Related Experiment Video

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OPERA: a novel method to reduce ghost and aliasing artifacts.

Andrea Dell'Orso1, Vincenzo Positano2, Giovanni Arisi3

  • 1Department of Radiology, San Giuseppe Hospital, Empoli AO Toscana Centro, Viale Boccaccio 14, Florence, Italy. dellorsoandrea@gmail.com.

Magma (New York, N.Y.)
|August 14, 2020
PubMed
Summary

A new method called Orthogonal Phase Encoding Reduction of Artifact (OPERA) effectively reduces MR imaging artifacts. This technique improves perceived image quality without significantly impacting signal-to-noise or contrast-to-noise ratios.

Keywords:
AliasingGhost artifactImage qualityMRIPhase-encoding direction

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Area of Science:

  • Medical Imaging
  • Image Processing
  • Magnetic Resonance Imaging (MRI)

Background:

  • MRI is susceptible to artifacts like ghosting and aliasing, which can degrade image quality.
  • Predictable artifact patterns along rows or columns necessitate targeted correction methods.

Purpose of the Study:

  • To develop and evaluate a novel method, Orthogonal Phase Encoding Reduction of Artifact (OPERA), for reducing MRI artifacts.
  • To assess OPERA's efficacy, robustness, and reproducibility in artifact reduction and its impact on image quality metrics.

Main Methods:

  • OPERA combines intensity values from two MRI scans with swapped phase-encoding directions to correct artifacts.
  • Simulations and phantom experiments were performed to validate the method's performance.
  • Clinical validation involved 1003 images, comparing OPERA-corrected scans with standard images for Signal-to-Noise Ratio (SNR) and Contrast-to-Noise Ratio (CNR), alongside radiologist assessments.

Main Results:

  • Simulations and phantom studies confirmed OPERA's effectiveness and robustness in reducing artifact strength.
  • OPERA application showed no significant changes in SNR (+4.16%) and CNR (+4.30%).
  • Radiologists reported an 82-84% reduction in perceived artifacts and an 83-89% improvement in perceived SNR and CNR in 893 images.

Conclusions:

  • The developed OPERA method successfully reduces MRI artifacts.
  • OPERA significantly improves the perceived image quality without compromising essential quantitative metrics like SNR and CNR.