Mask-Adapted Background Field Removal for Artifact Reduction in Quantitative Susceptibility Mapping of the Prostate.

Sina Straub,Heinz-Peter Schlemmer,David Bonekamp,Frederik B. Laun,Matthias C. Röthke,Mark E. Ladd,Klaus H. Maier-Hein,Julian Emmerich

doi:10.18383/j.tom.2017.00005

Abstract

We propose an alternative processing method for quantitative susceptibility mapping of the prostate that reduces artifacts and enables better visibility and quantification of calcifications and other lesions. Three-dimensional gradient-echo magnetic resonance data were obtained from 26 patients at 3 T who previously received a planning computed tomography of the prostate. Phase images were unwrapped using Laplacian-based phase unwrapping. The background field was removed with the V-SHARP method using tissue masks for the entire abdomen (Method 1) and masks that excluded bone and the rectum (Method 2). Susceptibility maps were calculated with the iLSQR method. The quality of susceptibility maps was assessed by one radiologist and two physicists who rated the data for visibility of lesions and data quality on a scale from 1 (poor) to 4 (good). The readers rated susceptibility maps computed with Method 2 to be, on average, better for visibility of lesions with a score of 2.9 ± 1.1 and image quality with a score of 2.8 ± 0.8 compared with maps computed with Method 1 (2.4 ± 1.2/2.3 ± 1.0). Regarding strong artifacts, these could be removed using adapted masks, and the susceptibility values seemed less biased by the artifacts. Thus, using an adapted mask for background field removal when calculating susceptibility maps of the prostate from phase data reduces artifacts and improves visibility of lesions.

Highlights

IntroductionIn magnetic resonance imaging (MRI), prostate cancer detection can be hampered by postbiopsy hemorrhage and/or calcifications [2]; in particular, the detection of intraprostatic calcifications is difficult because of variations in signal intensity and the small size of the lesions [3]
Prostate cancer is the most common cancer among males in the Western world [1]
We propose an alternative processing method for quantitative susceptibility mapping of the prostate that reduces artifacts and enables better visibility and quantification of calcifications and other lesions

Summary

Introduction

In magnetic resonance imaging (MRI), prostate cancer detection can be hampered by postbiopsy hemorrhage and/or calcifications [2]; in particular, the detection of intraprostatic calcifications is difficult because of variations in signal intensity and the small size of the lesions [3]. It has recently been shown that QSM can be a valuable tool to detect intra- and periprostatic calcifications [16], but in cases of intestinal movement or air in the rectum, severe artifacts can occur when inverting unreliable phase information because of nonlocality of the inversion kernel [17,18,19,20,21]. For QSM and can render the detection of calcifications difficult. Because streaking artifacts in susceptibility maps corrupt image quality and hamper detection of lesions (calcifications or hemorrhage), and bias the accurate quantification of susceptibility values, the reduction or elimination of artifacts is crucial

Objectives

Methods

Results

Conclusion