Quantitative evaluation of metal artifact reduction techniques

Abstract

Purpose: To develop a technique to quantify artifact, and to use it to compare the effectiveness of several approaches to metal artifact reduction, including view angle tilting and increasing the slice select and image bandwidths (BWs), in terms of metal artifact reduction, noise, and blur. Materials and Methods:Nonmetallic replicas of two metal implants (stainless steel and titanium/chromium-cobalt femoral prostheses) were fabricated from wax, and MR images were obtained of each component immersed in water. The differences between the images of each metal prosthesis and its wax counterpart were measured. The contributions from noise and blur were isolated, resulting in a measure of the metal artifact. Several off-resonance artifact reduction techniques were assessed in terms of metal artifact reduction capability, as well as signal to noise ratio and blur.Results: Increasing the image BW from Ϯ16 kHz to Ϯ64 kHz was found to reduce the artifact by an average of 60%, while employing view angle tilting (VAT) alone was found to reduce the artifact by an average of 63%. The metal artifact reduction sequence (MARS), which combines several susceptibility artifact reduction techniques, resulted in the least amount of image distortion, reducing the artifact by an average of 79%. Conclusion:The results indicate that while VAT alone (with an image BW of Ϯ16 kHz) resulted in the smallest amount of total energy and no reduction in the signal-tonoise ratio compared to a conventional spin-echo pulse sequence, MARS resulted in significantly less artifact and dramatically less blur. IMAGE DISTORTIONS caused by differences in magnetic susceptibility have long been a problem in clinical imaging, especially in the presence of metal prostheses. Several techniques are commonly used to reduce the severity of metal susceptibility artifact, including simple concessions such as increasing the frequency encoding bandwidth (BW), or orienting the long axis of the metal along the frequency encoding direction (1). A clever technique still not in common usage is view angle tilting (VAT) (2), which has been demonstrated to be clinically useful for reducing the distortion in images when imaging patients with metal implants (3-5) and during interventional MRI where inserted needles distort the local magnetic field (6). VAT results in a marked reduction in the severity of the metal susceptibility artifact, and can be employed without increasing the imaging time. Unfortunately, it introduces blurring, and only reduces the artifact in one direction. These deficiencies are lessened in the metal artifact reduction sequence (MARS), which involves VAT and increased slice select and image BWs. The effectiveness of MARS in reducing susceptibility artifacts in a clinical scan is illustrated in Fig. 1.It is difficult to evaluate quantitatively the competence of a given metal artifact reduction technique. Each method has drawbacks that can mask its ability to reduce metal artifact, and it is necessary to quantify the disadvantages as well as the advantages ...

Metal artefact reduction in MRI at both 1.5 and 3.0 T using slice encoding for metal artefact correction and view angle tilting

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Phantom based qualitative and quantitative evaluation of artifacts in MR images of metallic hip prostheses

“…More objective phantom-based methods can be useful for systematic comparison of different pulse sequences and for protocol optimization. Methods of varying complexity have been proposed, most of them measuring the total size of the artifact [12,13,14,15]. Recently, Koff et al proposed a method which separates through-plane and in-plane artifacts; however it was restricted to investigation of metallic objects of a fixed, cylindrical shape [16].…”

Improved Late Gadolinium Enhancement MR Imaging for Patients with Implanted Cardiac Devices

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