GE MRI No Phase Wrap

Key concepts for GE MRI No Phase Wrap imaging option. This article is a step-by-step guide to help you avoid phase wrap artifact in MRI. Visit our MRI Technologist resources page for additional operator manual procedures and technical documentation.

We know you are looking for quick resolutions and we are always glad to help. Click here to jump directly to the GE MRI no phase wrap solutions section. We urge you to read the rest of the article when you have time. Learn all about NPW scan considerations, limitations and how scan parameters affect image quality or scan times.

GE MRI No Phase Wrap Imaging Option (NPW)

GE MRI systems offer a scan feature known as “No phase wrap” which minimizes phase wrap artifacts in the images. This feature utilizes advanced algorithms to correct for phase wrap and guarantee accurate and reliable images.

What is Phase Wrap and Why Does it Happen?

No Phase Wrap (NPW) imaging option prevents phase wraparound artifacts. The phase wraparound artifact, or aliasing, occurs when anatomy extends beyond the imaging field of view (FOV) in the phase direction.

The RF pulses delivered excite the nuclei outside the area of interest, causing them to emit signals. As a result, the system collects this data and mismaps the signal, folding it back into the reconstructed image. This causes the system to artificially reconstructthe signal from the anatomy outside of the FOV in the opposite side of the image. (as seen below).

Why is No Phase Wrap Important?

The accuracy of MRI images is critical for successful diagnosis and treatment of medical conditions. Image artifacts caused by phase wrap can make it difficult to accurately interpret the images, leading to incorrect diagnoses and inappropriate treatments. With no phase wrap, the GE MRI provides accurate and reliable images, which can help to improve the quality of patient care.

How Does ‘No Phase Wrap’ Work?

NPW is designed to eliminate wrap-around artifact by doubling the FOV in the phase encoding direction. The enlarged FOV now encompasses all anatomy to prevent this artifact.

When NPW is selected, the system automatically saves the central half of this larger image and discards data collected from the outside of the specified FOV. Although you are acquiring a FOV twice the size as you prescribed, you only see your prescribed FOV in
the final image.

When using NPW, both the FOV and number of phase encoding steps are doubled, so the pixel size remains constant. Doubling the number of phase encoding steps would double the acquisition time, so the number of excitations (NEX) value is halved. Therefore, no change in resolution, signal-to-noise, or acquisition time occurs.

NOTE: NPW is compatible with most pulse sequences. However, it is not compatible with Square Pixel, Echo Planar Imaging (EPI), Phase FOV less than one, or Respiratory Compensation high-sort method.

When to Use No Phase Wrap Option

Use NPW when the FOV selected in the phase direction is smaller than the anatomy being scanned. Common applications include pituitary, coronal hips or shoulders, and axial spine imaging.

Swapping phase and frequency on a sagittal or coronal image places phase in the long axis of the body, resulting in aliasing. NPW can help to correct the problem.

Step-by-Step Procedure: Avoid MRI Wrap Around

Quick solutions to keep you MRI scanning reliably. Step-by-step-procedure to avoid MRI aliasing and wraparound artifact.

1. Enable GE MRI NPW Scan Option

Enabling the GE MRI no phase wrap scan option is a great method of removing aliasing artifact from images. Please make sure to read the scan considerations detailed below to understand how scan parameters affect image quality and scan times.

2. Manually Increase Scan Field of View

Phase wrap or aliasing artifact occurs when there is anatomy outside of the scan FOV. Another method of avoiding aliasing artifact is manually increasing the scan field of view. Increasing FOV (e.g. 16cm to 24cm, or 24 cm to 30 cm) will minimize the likelihood of anatomy outside the scan windows causing image artifact.

3. Reduce Number of Receiver Channels

Another method of reducing artifact due to signal outside the scan window is to reduce the number of receiver channels in use during the scan sequence. To manually reduce number of channel, start by clicking on the Coil Selection window. Select a new coil configuration with reduced number of receivers in use. For example NVPA123 to NVPA12, or CTLBOT to CTL234.

NPW Scan Considerations

There are several factors you should consider when using GE MRI ‘No Phase Wrap’ imaging option.

1. When using NPW, motion artifacts become more noticeable. To reduce these artifacts, higher NEX values can be used to average the data. However, when NPW is activated, the programmed NEX value is cut in half, resulting in a loss of the benefits of data averaging that comes with higher NEX values. To mitigate this, an alternative approach is to keep the NEX value greater than 1 or position saturation (SAT) pulses next to the FOV, instead of using NPW, to reduce aliasing.
2. NPW with 1 NEX extends the scan time slightly.
3. The NEX value with NPW must be greater than or equal to one
4. Phase wraparound occurs if anatomy exists outside the new, reduced FOV. SAT pulses placed in the phase direction can reduce the aliasing artifact.

No Phase Wrap Limitations

• No Phase Wrap is not compatible with Respiratory Compensation high sort, ZIP1024, and Square Pixel.
• Scan sequence must have a NEX greater than or equal to 1.
• Scans with a NEX of 1 or 2 may be more susceptible to motion artifact.

Conclusion

No phase wrap is an important feature of the GE MRI system. By correcting for phase wrap artifacts, this feature ensures that the images produced by the GE MRI are of the highest quality and accuracy. View the additional resources section for more information.

Related Resources

• GE MRI ZIP 512 Explained
• GE Signa Voyager Artifact Solutions Guide
• GE MRI ARC vs ASSET
• Medical Imaging Source Radiology Blog
• MRIPETCTSOURCE YouTube Channel

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