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Jun 20, 2024 | 
radiopaedia.org | Usman Bashir |Lachlan McKay
Gibbs artifact, also known as truncation artifact or ringing artifact, is a type of MRI artifact. It refers to 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. The MR image is reconstructed from k-space which is a finite sampling of the signal subjected to inverse Fourier transform in order to obtain the final image.
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Jun 9, 2024 | 
radiopaedia.org | Ayush Goel |Lachlan McKay
Compton effect or Compton scatter is one of principle forms of photon interaction. It is the main cause of scattered radiation in a material. It occurs due to the interaction of the photon (x-ray or gamma) with free electrons (unattached to atoms) or loosely bound valence shell (outer shell) electrons. The resultant incident photon is scattered (changes direction) and imparts energy to the electron (recoil electron).
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Jun 7, 2024 | 
radiopaedia.org | Bálint Botz |Lachlan McKay
Aliasing is a phenomenon inherent to Doppler modalities which utilize intermittent sampling in which an insufficient sampling rate results in an inability to record direction and velocity accurately. PhysicsUnlike continuous wave Doppler, pulsed wave and color flow Doppler modalities alternate between rapid emission of ultrasound waves (at a rate termed the pulse repetition frequency) and reception of incident ultrasound waves.
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Jun 7, 2024 | 
radiopaedia.org | Bálint Botz |Lachlan McKay
Pulse repetition frequency (PRF) indicates the number of ultrasound pulses emitted by the transducer over a designated period of time. It is typically measured as pulses per second or hertz (Hz). In medical ultrasound the typically used range of PRF varies between 1 and 10 kHz 1. PRF is defined by using the formula below 3:PRF = 1/period between pulses (or pulse repetition period, PRP)Pulse repetition period (PRP) consists of pulse duration and receiving time.
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Jun 6, 2024 | 
radiopaedia.org | Lachlan McKay
Citation: McKay L, Panoramic ultrasound. Reference article, Radiopaedia.org (Accessed on 07 Jun 2024) https://radiopaedia.org/articles/190760 DOI: - rID: 190760 Article created: 7 Jun 2024, Lachlan McKay ◉ Disclosures: At the time the article was created Lachlan McKay had no financial relationships to ineligible companies to disclose.
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Jun 3, 2024 | 
radiopaedia.org | Sonam Vadera |Lachlan McKay
Spatial pulse length (SPL) in ultrasound imaging describes the length of time that an ultrasound pulse occupies in space. Mathematically, it is the product of the number of cycles in a pulse and the wavelength. A shorter SPL results in higher axial resolution. The minimum distance between two tissues that can be resolved in the axial dimension is equal to 1/2 * SPL 2. To improve axial resolution, SPL can be reduced by heavier damping or use of a higher frequency transducer 1.
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Jun 2, 2024 | 
radiopaedia.org | Ayush Goel |Lachlan McKay
Harmonic imaging is a technique in ultrasonography that provides images of better quality as compared with conventional ultrasound technique. PhysicsHarmonic imaging exploits non-linear propagation of ultrasound through the body tissues. The high pressure portion of the wave travels faster than the low pressure portion resulting in distortion of the shape of the wave. This change in waveform leads to the generation of harmonics (multiples of the fundamental or transmitted frequency) from a tissue.
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Jun 1, 2024 | 
radiopaedia.org | Lachlan McKay
Spatial compounding is an advanced ultrasound technique that utilizes multiple angles of insonation to create a single averaged image 1. The advantages of spatial compounding are that angle dependent artefacts are reduced, curved surfaces appear more continuous and background speckle is reduced, improving the signal to noise ratio 1. The primary disadvantage of spatial compounding is the increased likelihood of movement artifact and loss of temporal resolution 1.
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May 29, 2024 | 
radiopaedia.org | Matt Morgan |Lachlan McKay
The mechanical index (MI) is an attempt to measure part of an ultrasound beam's bioeffects. The mechanical index is found on most ultrasound display screens, along with the thermal index. Mechanical index is an indication of an ultrasound beam's ability to cause cavitation-related bioeffects, and this is currently thought to be a reasonable proxy for micromechanical damage. It is "strictly a cavitation index," but is meant to be interpreted more broadly as tissue mechanical stress/damage.
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May 28, 2024 | 
radiopaedia.org | Marcin Czarniecki |Lachlan McKay
Speckle artifact may be encountered in ultrasound. It is caused by the scattering of waves from the surface of small structures within a certain tissue. The artifact produces a textured appearance. Because speckle can make it harder to distinguish soft tissue differences, modern ultrasound machines are able to reduce speckle through various techniques known as 'despeckling' 2. See also
