Metal Artifact Reduction Sequence: Early Clinical Applications1
Randall V. Olsen, MD,
Peter L. Munk, MD,
Mark J. Lee, BSc,
Dennis L. Janzen, MD,
Alex L. MacKay, PhD,
Qing-San Xiang, PhD and
Bassam Masri, MD
1 From the Departments of Radiology (R.V.O., P.L.M., M.J.L., D.L.J., A.L.M., Q.S.X.), Orthopedic Surgery (P.L.M., B.M.), and Physics and Astronomy (A.L.M., Q.S.X.), University of British Columbia, Vancouver General Hospital, 855 W 12th Ave, Vancouver, British Columbia, Canada V5Z 1M9; the Vancouver Musculoskeletal Tumor Group, Vancouver, British Columbia, Canada (P.L.M., M.J.L., B.M.); and the Department of Radiology, Surrey Memorial Hospital, Surrey, British Columbia, Canada (D.L.J.). Presented as a scientific exhibit at the 1998 RSNA scientific assembly. Received March 22, 1999; revision requested May 3 and received May 28; accepted June 1. Address reprint requests to P.L.M. (e-mail: plmunk@interchange.ubc.ca).
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Figure 1. Diagram of a conventional spin-echo sequence modified for the MARS technique. Gx = frequency-encoding gradient, Gy = phase-encoding gradient, Gz = section-selection gradient, RF = radio frequency.
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Figure 2a. Phantom study of a femoral component from total hip arthroplasty with a titanium alloy. The component was suspended in grease. (a) Coronal T1-weighted spin-echo MR image (repetition time msec/echo time msec = 500/15, 3-mm section thickness, 1.5-mm gap, 30-cm FOV) shows extensive distortion and artifact of mixed high and low signal intensity, especially around the proximal portion of the component. (b) Corresponding MR image obtained with the MARS technique shows some residual distortion, especially around the femoral head. However, a dramatic reduction in artifact is apparent, and the remaining signal void is now easily recognized as representing a femoral component.
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Figure 2b. Phantom study of a femoral component from total hip arthroplasty with a titanium alloy. The component was suspended in grease. (a) Coronal T1-weighted spin-echo MR image (repetition time msec/echo time msec = 500/15, 3-mm section thickness, 1.5-mm gap, 30-cm FOV) shows extensive distortion and artifact of mixed high and low signal intensity, especially around the proximal portion of the component. (b) Corresponding MR image obtained with the MARS technique shows some residual distortion, especially around the femoral head. However, a dramatic reduction in artifact is apparent, and the remaining signal void is now easily recognized as representing a femoral component.
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Figure 3a. Avascular necrosis in a 56-year-old man with hip pain 4 months after a femoral neck fracture, which was transfixed with three screws. (a) Frog-leg radiograph of the hip shows the screws in position. The fracture is in satisfactory alignment and appears well healed. The femoral head is intact with no evidence of sclerosis or collapse. (b) Coronal T1-weighted spin-echo MR image (600/15) through the hip shows extensive artifact, which precludes evaluation of the femoral head and joint space. (c) Corresponding MR image obtained with the MARS technique shows diminished artifact. A focus of avascular necrosis is clearly seen in the superior aspect of the femoral head (arrow); this finding presumably accounted for the patient's persistent and increasing hip pain despite the normal radiographic appearance.
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Figure 3b. Avascular necrosis in a 56-year-old man with hip pain 4 months after a femoral neck fracture, which was transfixed with three screws. (a) Frog-leg radiograph of the hip shows the screws in position. The fracture is in satisfactory alignment and appears well healed. The femoral head is intact with no evidence of sclerosis or collapse. (b) Coronal T1-weighted spin-echo MR image (600/15) through the hip shows extensive artifact, which precludes evaluation of the femoral head and joint space. (c) Corresponding MR image obtained with the MARS technique shows diminished artifact. A focus of avascular necrosis is clearly seen in the superior aspect of the femoral head (arrow); this finding presumably accounted for the patient's persistent and increasing hip pain despite the normal radiographic appearance.
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Figure 3c. Avascular necrosis in a 56-year-old man with hip pain 4 months after a femoral neck fracture, which was transfixed with three screws. (a) Frog-leg radiograph of the hip shows the screws in position. The fracture is in satisfactory alignment and appears well healed. The femoral head is intact with no evidence of sclerosis or collapse. (b) Coronal T1-weighted spin-echo MR image (600/15) through the hip shows extensive artifact, which precludes evaluation of the femoral head and joint space. (c) Corresponding MR image obtained with the MARS technique shows diminished artifact. A focus of avascular necrosis is clearly seen in the superior aspect of the femoral head (arrow); this finding presumably accounted for the patient's persistent and increasing hip pain despite the normal radiographic appearance.
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Figure 4a. Persistent drainage from the lateral aspect of the superior thigh in a 68-year-old woman 5 years after femoral hemiarthroplasty. (a) Axial T1-weighted spin-echo MR image (800/12) shows considerable artifact around the prosthesis. (b) Corresponding MR image obtained with the MARS technique shows marked reduction of artifact, thus allowing much better assessment of the surrounding soft tissues. Note that the anterior and posterior columns of the acetabulum can be readily visualized, whereas they were completely obscured on the conventional MR image (a). (c) MR image obtained with the MARS technique several centimeters inferior to b shows the site of the drainage, which can be seen extending laterally in a low-signal-intensity track (arrows) traversing the higher-signal-intensity fat. No abnormal soft-tissue collection is apparent directly around the hip joint because spontaneous decompression has occurred. Note that the soft tissues of the thigh around the femoral component are well seen.
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Figure 4b. Persistent drainage from the lateral aspect of the superior thigh in a 68-year-old woman 5 years after femoral hemiarthroplasty. (a) Axial T1-weighted spin-echo MR image (800/12) shows considerable artifact around the prosthesis. (b) Corresponding MR image obtained with the MARS technique shows marked reduction of artifact, thus allowing much better assessment of the surrounding soft tissues. Note that the anterior and posterior columns of the acetabulum can be readily visualized, whereas they were completely obscured on the conventional MR image (a). (c) MR image obtained with the MARS technique several centimeters inferior to b shows the site of the drainage, which can be seen extending laterally in a low-signal-intensity track (arrows) traversing the higher-signal-intensity fat. No abnormal soft-tissue collection is apparent directly around the hip joint because spontaneous decompression has occurred. Note that the soft tissues of the thigh around the femoral component are well seen.
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Figure 4c. Persistent drainage from the lateral aspect of the superior thigh in a 68-year-old woman 5 years after femoral hemiarthroplasty. (a) Axial T1-weighted spin-echo MR image (800/12) shows considerable artifact around the prosthesis. (b) Corresponding MR image obtained with the MARS technique shows marked reduction of artifact, thus allowing much better assessment of the surrounding soft tissues. Note that the anterior and posterior columns of the acetabulum can be readily visualized, whereas they were completely obscured on the conventional MR image (a). (c) MR image obtained with the MARS technique several centimeters inferior to b shows the site of the drainage, which can be seen extending laterally in a low-signal-intensity track (arrows) traversing the higher-signal-intensity fat. No abnormal soft-tissue collection is apparent directly around the hip joint because spontaneous decompression has occurred. Note that the soft tissues of the thigh around the femoral component are well seen.
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Figure 5a. Recurrent synovial osteochondromatosis in an obese 50-year-old woman who underwent total hip arthroplasty 2 years earlier at the time of complete synovectomy for synovial osteochondromatosis. She presented with gradually increasing hip pain. (a) Anteroposterior radiograph is unremarkable. (b) CT scan through the hip joint is of poor quality, with marked beam hardening and spray artifact precluding adequate evaluation of the periarticular soft tissues. (c) Axial T1-weighted spin-echo MR image (600/15) through the hip shows extensive artifact. Although some bowing of the soft tissues medial to the hip can be seen (arrows), a discrete mass is hard to appreciate. (d) Corresponding MR image obtained with the MARS technique clearly shows a large soft-tissue mass (arrows). The mass, which was later diagnosed as recurrent synovial osteochondromatosis, compresses the bladder, vagina, and rectum and extends posteriorly to almost come in contact with the gluteus maximus muscle. Note that the cup liner can even be partially visualized within the joint.
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Figure 5b. Recurrent synovial osteochondromatosis in an obese 50-year-old woman who underwent total hip arthroplasty 2 years earlier at the time of complete synovectomy for synovial osteochondromatosis. She presented with gradually increasing hip pain. (a) Anteroposterior radiograph is unremarkable. (b) CT scan through the hip joint is of poor quality, with marked beam hardening and spray artifact precluding adequate evaluation of the periarticular soft tissues. (c) Axial T1-weighted spin-echo MR image (600/15) through the hip shows extensive artifact. Although some bowing of the soft tissues medial to the hip can be seen (arrows), a discrete mass is hard to appreciate. (d) Corresponding MR image obtained with the MARS technique clearly shows a large soft-tissue mass (arrows). The mass, which was later diagnosed as recurrent synovial osteochondromatosis, compresses the bladder, vagina, and rectum and extends posteriorly to almost come in contact with the gluteus maximus muscle. Note that the cup liner can even be partially visualized within the joint.
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Figure 5c. Recurrent synovial osteochondromatosis in an obese 50-year-old woman who underwent total hip arthroplasty 2 years earlier at the time of complete synovectomy for synovial osteochondromatosis. She presented with gradually increasing hip pain. (a) Anteroposterior radiograph is unremarkable. (b) CT scan through the hip joint is of poor quality, with marked beam hardening and spray artifact precluding adequate evaluation of the periarticular soft tissues. (c) Axial T1-weighted spin-echo MR image (600/15) through the hip shows extensive artifact. Although some bowing of the soft tissues medial to the hip can be seen (arrows), a discrete mass is hard to appreciate. (d) Corresponding MR image obtained with the MARS technique clearly shows a large soft-tissue mass (arrows). The mass, which was later diagnosed as recurrent synovial osteochondromatosis, compresses the bladder, vagina, and rectum and extends posteriorly to almost come in contact with the gluteus maximus muscle. Note that the cup liner can even be partially visualized within the joint.
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Figure 5d. Recurrent synovial osteochondromatosis in an obese 50-year-old woman who underwent total hip arthroplasty 2 years earlier at the time of complete synovectomy for synovial osteochondromatosis. She presented with gradually increasing hip pain. (a) Anteroposterior radiograph is unremarkable. (b) CT scan through the hip joint is of poor quality, with marked beam hardening and spray artifact precluding adequate evaluation of the periarticular soft tissues. (c) Axial T1-weighted spin-echo MR image (600/15) through the hip shows extensive artifact. Although some bowing of the soft tissues medial to the hip can be seen (arrows), a discrete mass is hard to appreciate. (d) Corresponding MR image obtained with the MARS technique clearly shows a large soft-tissue mass (arrows). The mass, which was later diagnosed as recurrent synovial osteochondromatosis, compresses the bladder, vagina, and rectum and extends posteriorly to almost come in contact with the gluteus maximus muscle. Note that the cup liner can even be partially visualized within the joint.
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Figure 6a. Bone staples and metallic crystals in a 36-year-old man 4 years after anterior cruciate ligament reconstruction with a hamstring tendon and an "over the top" technique (ie, stapling the cranial aspect of the neoligament to the distal femur). (a) Sagittal T1-weighted spin-echo MR image (500/14) clearly shows artifact from bone staples at the top of the image. In addition, numerous small areas of low signal intensity can be seen in the posterior aspect of the suprapatellar bursa (arrows), which represent small metallic crystals deposited at the time of previous surgery (these could not be seen on radiographs). (b) Corresponding MR image obtained with the MARS technique shows marked reduction of artifact from both bone staples and metallic crystals.
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Figure 6b. Bone staples and metallic crystals in a 36-year-old man 4 years after anterior cruciate ligament reconstruction with a hamstring tendon and an "over the top" technique (ie, stapling the cranial aspect of the neoligament to the distal femur). (a) Sagittal T1-weighted spin-echo MR image (500/14) clearly shows artifact from bone staples at the top of the image. In addition, numerous small areas of low signal intensity can be seen in the posterior aspect of the suprapatellar bursa (arrows), which represent small metallic crystals deposited at the time of previous surgery (these could not be seen on radiographs). (b) Corresponding MR image obtained with the MARS technique shows marked reduction of artifact from both bone staples and metallic crystals.
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Figure 7a. Ligament tear in a 34-year-old woman who had undergone two anterior cruciate ligament reconstructions. She presented with symptoms suggestive of neoligament failure. (a) Lateral radiograph shows two bone staples in the distal femur and an unusual wide tunnel with sclerotic margins in the anterior aspect of the superior tibia. (b) Sagittal gradient-echo MR image (400/14, 30° flip angle) shows marked susceptibility artifact obscuring the entire intraarticular portion of the neoligament. (c) Sagittal T1-weighted spin-echo MR image (400/12) clearly shows the portion of the neoligament within the osseous tunnel (straight arrow). However, metallic crystals obscure the more cranial portion (curved arrow). (d) Corresponding MR image obtained with the MARS technique shows reduction of artifact, thus allowing more of the ligament to be assessed. The cranial portion of the ligament is noted to be torn; this finding was confirmed at surgery.
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Figure 7b. Ligament tear in a 34-year-old woman who had undergone two anterior cruciate ligament reconstructions. She presented with symptoms suggestive of neoligament failure. (a) Lateral radiograph shows two bone staples in the distal femur and an unusual wide tunnel with sclerotic margins in the anterior aspect of the superior tibia. (b) Sagittal gradient-echo MR image (400/14, 30° flip angle) shows marked susceptibility artifact obscuring the entire intraarticular portion of the neoligament. (c) Sagittal T1-weighted spin-echo MR image (400/12) clearly shows the portion of the neoligament within the osseous tunnel (straight arrow). However, metallic crystals obscure the more cranial portion (curved arrow). (d) Corresponding MR image obtained with the MARS technique shows reduction of artifact, thus allowing more of the ligament to be assessed. The cranial portion of the ligament is noted to be torn; this finding was confirmed at surgery.
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Figure 7c. Ligament tear in a 34-year-old woman who had undergone two anterior cruciate ligament reconstructions. She presented with symptoms suggestive of neoligament failure. (a) Lateral radiograph shows two bone staples in the distal femur and an unusual wide tunnel with sclerotic margins in the anterior aspect of the superior tibia. (b) Sagittal gradient-echo MR image (400/14, 30° flip angle) shows marked susceptibility artifact obscuring the entire intraarticular portion of the neoligament. (c) Sagittal T1-weighted spin-echo MR image (400/12) clearly shows the portion of the neoligament within the osseous tunnel (straight arrow). However, metallic crystals obscure the more cranial portion (curved arrow). (d) Corresponding MR image obtained with the MARS technique shows reduction of artifact, thus allowing more of the ligament to be assessed. The cranial portion of the ligament is noted to be torn; this finding was confirmed at surgery.
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Figure 7d. Ligament tear in a 34-year-old woman who had undergone two anterior cruciate ligament reconstructions. She presented with symptoms suggestive of neoligament failure. (a) Lateral radiograph shows two bone staples in the distal femur and an unusual wide tunnel with sclerotic margins in the anterior aspect of the superior tibia. (b) Sagittal gradient-echo MR image (400/14, 30° flip angle) shows marked susceptibility artifact obscuring the entire intraarticular portion of the neoligament. (c) Sagittal T1-weighted spin-echo MR image (400/12) clearly shows the portion of the neoligament within the osseous tunnel (straight arrow). However, metallic crystals obscure the more cranial portion (curved arrow). (d) Corresponding MR image obtained with the MARS technique shows reduction of artifact, thus allowing more of the ligament to be assessed. The cranial portion of the ligament is noted to be torn; this finding was confirmed at surgery.
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Figure 8a. Normal findings in an asymptomatic 59-year-old man 2 years after tricompartment total knee arthroplasty. (a) Lateral radiograph is unremarkable. (b, c) Sagittal (b) and axial (c) T1-weighted spin-echo MR images (500/12) show large areas of signal void and distortion, as well as accompanying regions of high signal intensity. (d, e) Corresponding sagittal (d) and axial (e) MR images obtained with the MARS technique show dramatic reduction of artifact, thus allowing better resolution of the soft tissues adjacent to the arthroplasty. The improved resolution is especially evident on the axial image (e).
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Figure 8b. Normal findings in an asymptomatic 59-year-old man 2 years after tricompartment total knee arthroplasty. (a) Lateral radiograph is unremarkable. (b, c) Sagittal (b) and axial (c) T1-weighted spin-echo MR images (500/12) show large areas of signal void and distortion, as well as accompanying regions of high signal intensity. (d, e) Corresponding sagittal (d) and axial (e) MR images obtained with the MARS technique show dramatic reduction of artifact, thus allowing better resolution of the soft tissues adjacent to the arthroplasty. The improved resolution is especially evident on the axial image (e).
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Figure 8c. Normal findings in an asymptomatic 59-year-old man 2 years after tricompartment total knee arthroplasty. (a) Lateral radiograph is unremarkable. (b, c) Sagittal (b) and axial (c) T1-weighted spin-echo MR images (500/12) show large areas of signal void and distortion, as well as accompanying regions of high signal intensity. (d, e) Corresponding sagittal (d) and axial (e) MR images obtained with the MARS technique show dramatic reduction of artifact, thus allowing better resolution of the soft tissues adjacent to the arthroplasty. The improved resolution is especially evident on the axial image (e).
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Figure 8d. Normal findings in an asymptomatic 59-year-old man 2 years after tricompartment total knee arthroplasty. (a) Lateral radiograph is unremarkable. (b, c) Sagittal (b) and axial (c) T1-weighted spin-echo MR images (500/12) show large areas of signal void and distortion, as well as accompanying regions of high signal intensity. (d, e) Corresponding sagittal (d) and axial (e) MR images obtained with the MARS technique show dramatic reduction of artifact, thus allowing better resolution of the soft tissues adjacent to the arthroplasty. The improved resolution is especially evident on the axial image (e).
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Figure 8e. Normal findings in an asymptomatic 59-year-old man 2 years after tricompartment total knee arthroplasty. (a) Lateral radiograph is unremarkable. (b, c) Sagittal (b) and axial (c) T1-weighted spin-echo MR images (500/12) show large areas of signal void and distortion, as well as accompanying regions of high signal intensity. (d, e) Corresponding sagittal (d) and axial (e) MR images obtained with the MARS technique show dramatic reduction of artifact, thus allowing better resolution of the soft tissues adjacent to the arthroplasty. The improved resolution is especially evident on the axial image (e).
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Figure 9a. Multiple loose bodies within a Baker cyst in a 62-year-old man who had undergone total knee arthroplasty. (a) Lateral radiograph shows a knee arthroplasty with accompanying joint effusion and several slightly calcified areas of increased opacity (arrows) at the posterior aspect of the joint.
(b) Sagittal T1-weighted spin-echo MR image (500/15) shows extensive artifact involving the metal components. At the posterior aspect of the joint, some high-signal-intensity lesions (arrows) are noted around the hamstring and gastrocnemius tendons. (c) Corresponding MR image obtained with the MARS technique shows greatly decreased artifact, thus allowing visualization of the high-signal-intensity fat within the marrow in the ossified loose bodies (arrows).
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Figure 9b. Multiple loose bodies within a Baker cyst in a 62-year-old man who had undergone total knee arthroplasty. (a) Lateral radiograph shows a knee arthroplasty with accompanying joint effusion and several slightly calcified areas of increased opacity (arrows) at the posterior aspect of the joint.
(b) Sagittal T1-weighted spin-echo MR image (500/15) shows extensive artifact involving the metal components. At the posterior aspect of the joint, some high-signal-intensity lesions (arrows) are noted around the hamstring and gastrocnemius tendons. (c) Corresponding MR image obtained with the MARS technique shows greatly decreased artifact, thus allowing visualization of the high-signal-intensity fat within the marrow in the ossified loose bodies (arrows).
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Figure 9c. Multiple loose bodies within a Baker cyst in a 62-year-old man who had undergone total knee arthroplasty. (a) Lateral radiograph shows a knee arthroplasty with accompanying joint effusion and several slightly calcified areas of increased opacity (arrows) at the posterior aspect of the joint.
(b) Sagittal T1-weighted spin-echo MR image (500/15) shows extensive artifact involving the metal components. At the posterior aspect of the joint, some high-signal-intensity lesions (arrows) are noted around the hamstring and gastrocnemius tendons. (c) Corresponding MR image obtained with the MARS technique shows greatly decreased artifact, thus allowing visualization of the high-signal-intensity fat within the marrow in the ossified loose bodies (arrows).
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Figure 10a. Vertebral displacement in a 39-year-old man who underwent posterior fixation for progressive back pain secondary to spondylolysis and spondylolisthesis. (a) Lateral radiograph shows the posterior fixation device extending from L4 to S1 with grade II anterior displacement of L5 over S1. (b) Sagittal T1-weighted spin-echo MR image (500/15) shows geometric distortion. (c) Corresponding MR image obtained with the MARS technique shows marked improvement in the degree of distortion.
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Figure 10b. Vertebral displacement in a 39-year-old man who underwent posterior fixation for progressive back pain secondary to spondylolysis and spondylolisthesis. (a) Lateral radiograph shows the posterior fixation device extending from L4 to S1 with grade II anterior displacement of L5 over S1. (b) Sagittal T1-weighted spin-echo MR image (500/15) shows geometric distortion. (c) Corresponding MR image obtained with the MARS technique shows marked improvement in the degree of distortion.
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Figure 10c. Vertebral displacement in a 39-year-old man who underwent posterior fixation for progressive back pain secondary to spondylolysis and spondylolisthesis. (a) Lateral radiograph shows the posterior fixation device extending from L4 to S1 with grade II anterior displacement of L5 over S1. (b) Sagittal T1-weighted spin-echo MR image (500/15) shows geometric distortion. (c) Corresponding MR image obtained with the MARS technique shows marked improvement in the degree of distortion.
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Figure 11a. Anterior fixation of the cervical spine from C3 to C5 in a 74-year-old man. (a) Sagittal T1-weighted spin-echo MR images (500/15) show artifact produced by the screws transfixing the anterior plate. The artifact extends into the anterior aspect of the spinal canal and distorts the anterior contours of the cord. (b) Corresponding MR images obtained with the MARS technique (500/12) show marked improvement in the demonstration of the anterior spinal canal.
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Figure 11b. Anterior fixation of the cervical spine from C3 to C5 in a 74-year-old man. (a) Sagittal T1-weighted spin-echo MR images (500/15) show artifact produced by the screws transfixing the anterior plate. The artifact extends into the anterior aspect of the spinal canal and distorts the anterior contours of the cord. (b) Corresponding MR images obtained with the MARS technique (500/12) show marked improvement in the demonstration of the anterior spinal canal.
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Figure 12a. Normal findings in a 35-year-old man who underwent wrist fusion with multiple bone staples. (a) Coronal T1-weighted spin-echo MR image (400/12) shows multiple areas of artifact with distortion and poor visualization of carpal bones and joints. (b) Corresponding MR image obtained with the MARS technique shows some increased blurring but a dramatic reduction in distortion and improved demonstration of the bone around the midcarpal space.
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Figure 12b. Normal findings in a 35-year-old man who underwent wrist fusion with multiple bone staples. (a) Coronal T1-weighted spin-echo MR image (400/12) shows multiple areas of artifact with distortion and poor visualization of carpal bones and joints. (b) Corresponding MR image obtained with the MARS technique shows some increased blurring but a dramatic reduction in distortion and improved demonstration of the bone around the midcarpal space.
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Copyright © 2000 by the Radiological Society of North America.
