Quantitative assessment of susceptibility‐weighted imaging processing methods

Abstract

Purpose To evaluate different susceptibility weighted imaging (SWI) phase processing methods and parameter selection, thereby improving understanding of potential artifacts, as well as facilitating choice of methodology in clinical settings. Materials and Methods Two major phase processing methods, Homodyne-filtering and phase unwrapping-high pass (HP) filtering, were investigated with various phase unwrapping approaches, filter sizes, and filter types. Magnitude and phase images were acquired from a healthy subject and brain injury patients on a 3T clinical Siemens MRI system. Results were evaluated based on image contrast to noise ratio and presence of processing artifacts. Results When using a relatively small filter size (32 pixels for the matrix size 512 × 512 pixels), all Homodyne-filtering methods were subject to phase errors leading to 2% to 3% masked brain area in lower and middle axial slices. All phase unwrapping-filtering/smoothing approaches demonstrated fewer phase errors and artifacts compared to the Homodyne-filtering approaches. For performing phase unwrapping, Fourier-based methods, although less accurate, were 2–4 orders of magnitude faster than the PRELUDE, Goldstein and Quality-guide methods. Conclusion Although Homodyne-filtering approaches are faster and more straightforward, phase unwrapping followed by HP filtering approaches perform more accurately in a wider variety of acquisition scenarios.

Artifactual microhemorrhage generated by susceptibility weighted image processing

“…Fortunately, global phase shift or low frequency deviations may not be critical in SWI processing as the HP filtering substantially reduces the effects of low frequency phase deviation, leaving only the high frequency information in focus. The final SWI images using the Fourier based method appear very similar to SWI images processed using the traditional path‐following phase unwrapping approaches .…”

SWI post processing using granularity controlled edge‐preserved denoising of multichannel GRE images

“…Since the phase information is directly proportional to the susceptibility variations and echo time, the phase contrast of small vessels and micro‐hemorrhages increases with extensive phase wraps at higher echoes. Thus in order to extract the susceptibility‐related field information, phase unwrapping followed by background suppression is usually performed . For the current work, we have used the Laplacian based fast unwrapping method .…”

“…Thus in order to extract the susceptibility-related field information, phase unwrapping followed by background suppression is usually performed. 21,22 For the current work, we have used the Laplacian based fast unwrapping method. 23,24 Other forms of unwrapping such as the Goldstein 25 or PRE-LUDE 26 can also be used.…”

Characterizing the spatial distribution of microhemorrhages resulting from Traumatic Brain Injury (TBI)

“…SWI images were processed for phase enhancement using in-house developed SWI processing software and included three steps. 10,11 First, a Fourier-based phase unwrapping algorithm was performed, followed by one minus Gaussian filtering to remove unwanted artifacts of the raw phase signal obtained directly from the scanner. Then a normalized phase mask was used with values between zero and one in areas of negative phase, and with a value of one elsewhere.…”