Kevin M. Koch

A multispectral three-dimensional acquisition technique for imaging near metal implants

Metallic implants used in bone and joint arthroplasty induce severe spatial perturbations to the B0 magnetic field used for high‐field clinical magnetic resonance. These perturbations distort slice‐selection and frequency encoding processes applied in conventional two‐dimensional MRI techniques and hinder the diagnosis of complications from arthroplasty. Here, a method is presented whereby multiple three‐dimensional fast‐spin‐echo images are collected using discrete offsets in RF transmission and reception frequency. It is demonstrated that this multi acquisition variable‐resonance image combination technique can be used to generate a composite image that is devoid of slice‐plane distortion and possesses greatly reduced distortions in the readout direction, even in the immediate vicinity of metallic implants. Magn Reson Med 61:381–390, 2009.

Imaging near metal with a MAVRIC-SEMAC hybrid.

The recently developed multi‐acquisition with variable resonance image combination (MAVRIC) and slice‐encoding metal artifact correction (SEMAC) techniques can significantly reduce image artifacts commonly encountered near embedded metal hardware. These artifact reductions are enabled by applying alternative spectral and spatial‐encoding schemes to conventional spin‐echo imaging techniques. Here, the MAVRIC and SEMAC concepts are connected and discussed. The development of a hybrid technique that utilizes strengths of both methods is then introduced. The presented technique is shown capable of producing minimal artifact, high‐resolution images near total joint replacements in a clinical setting. Magn Reson Med, 2010.

Magnetic resonance imaging near metal implants.

The desire to apply magnetic resonance imaging (MRI) techniques in the vicinity of embedded metallic hardware is increasing. The soft‐tissue contrast available with MR techniques is advantageous in diagnosing complications near an increasing variety of MR‐safe metallic hardware. Near such hardware, the spatial encoding mechanisms utilized in conventional MRI methods are often severely compromised. Mitigating these encoding difficulties has been the focus of numerous research investigations over the past two decades. Such approaches include view‐angle tilting, short echo‐time projection reconstruction acquisitions, single‐point imaging, prepolarized MRI, and postprocessing image correction. Various technical advances have also enabled the recent development of two alternative approaches that have shown promising clinical potential. Here, the physical principals and proposed solutions to the problem of MRI near embedded metal are discussed. J. Magn. Reson. Imaging 2010;32:773–787.

New MR Imaging Methods for Metallic Implants in the Knee: Artifact Correction and Clinical Impact

To evaluate two magnetic resonance imaging (MRI) techniques, slice encoding for metal artifact correction (SEMAC) and multiacquisition variable‐resonance image combination (MAVRIC), for their ability to correct for artifacts in postoperative knees with metal.

Quantifying image distortion of orthopedic materials in magnetic resonance imaging.

To determine the magnitude of image distortion between two‐dimensional (2D) fast‐spin‐echo (FSE) images and 3D‐MAVRIC by using a phantom with samples of common materials used in total joint arthroplasty.

Compressed-sensing multispectral imaging of the postoperative spine.

To apply compressed sensing (CS) to in vivo multispectral imaging (MSI), which uses additional encoding to avoid magnetic resonance imaging (MRI) artifacts near metal, and demonstrate the feasibility of CS‐MSI in postoperative spinal imaging.

Imaging near metal: The impact of extreme static local field gradients on frequency encoding processes

Magnetic resonance imaging capabilities in the direct vicinity of metallic devices have substantially improved with the recent development of three‐dimensional multispectral imaging (3D‐MSI) methods. When imaging near metallic hardware, the bulk image distortions in 3D‐MSI techniques are reduced to the single‐pixel level. However, commonly utilized MSI techniques are ultimately limited by frequency‐encoding processes and reveal a class of residual intensity‐based susceptibility artifacts that have yet to be formally analyzed.

In vitro assessment of knee MRI in the presence of metal implants comparing MAVRIC-SL and conventional fast spin echo sequences at 1.5 and 3 T field strength.

To assess lesion detection and artifact size reduction of a multiacquisition variable‐resonance image combination, slice encoding for metal artifact correction (MAVRIC‐SEMAC) hybrid sequence (MAVRIC‐SL) compared to standard sequences at 1.5T and 3T in porcine knee specimens with metal hardware.

Accelerating sequences in the presence of metal by exploiting the spatial distribution of off-resonance.

To demonstrate feasibility of exploiting the spatial distribution of off‐resonance surrounding metallic implants for accelerating multispectral imaging techniques.

Subject-Specific Models of Susceptibility-Induced B0 Field Variations in Breast MRI

To rapidly calculate and validate subject‐specific field maps based on the three‐dimensional shape of the bilateral breast volume.