Corduroy Artifacts

Cord Artifacts

Corduroy Artifacts, which are also known as Spike Noise or White Pixels, is one of the most common artifacts in MRI imaging. "Corduroy" refers to the parallel line patterns that are frequently seen in the produced image. These lines are caused by pronounced or bright areas in raw data "White Pixels". These accented areas are typically created by arcs or "Spike Noise" received by the system. The source of these arcs can be any current carrying conductor. This includes Lights, Blowers, Cables and electronic components. Remember also that any conductor in a changing magnetic field (i.e. gradient fields) or any conductor moving in a magnetic field will have eddy currents flowing in it. This could include the rear pedestal, magnet enclosure frame, or any loose metal object. The arcing is usually happening in the magnet room. Interior room lighting is suspect. As long as the RF shield is working, any arcing outside the room should not be a problem as long as the RF shield and filters are good. The only exceptions are the RF transmit and receive chains since the RF cables are not filtered. Although this happens very rarely, it is possible for digital data handling problems during the data acquisition to create corduroy. Corduroy artifacts require a thorough troubleshooting method when first discovered. Many times these Cord Artifacts will disappear and return at the most inopportune times. It is better to have a firm method to employ at the outset. A good solid troubleshooting technique will reduce the time and cost of repair.

Also, Corduroy can appear very different from image to image. It may only be show on one image in the series, on every other image, or in every image. It may appear different throughout the image series. It may be just subtle fine lines that are hardly noticeable or it may completely envelope the entire image. I have seen them appear as tire tracks. It could even look like an SNR problem where the image is "grainy". The magnitude of the arc and where it happens in raw data "K-space" determines how it will affect the image. Arcs or white pixels near the center of K-space have more effect on the image. This is because most of the SNR for the image comes from the central portion of K-space due to the Fermi filtering. There are many variations of corduroy artifacts that can appear at the same time, which could lead a field engineer to believe there are multiple problems, but chances are they are all coming from one source.

Developing a Good Solid Troubleshooting Procedure comes with experience. I always duplicate the problem. Then change the environment as much as possible by turning off all lights, blowers, air conditioners, and anything powered just inside or outside the scanning room. The following Flow Chart is a Good place to Start.

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