Thomas R. McCauley

Magnetic Resonance Imaging of Articular Cartilage

Magnetic resonance imaging is the optimal modality for assessing articular cartilage because of superior soft tissue contrast, direct visualization of articular cartilage, and multiplanar capability. Despite these advantages, there has been disagreement as to the efficacy of magnetic resonance imaging of articular cartilage. The reason for this controversy is multifactorial but in part is attributable to the lack of the use of optimized pulse sequences for articular cartilage. The current authors will review the current state of the art of magnetic resonance imaging of articular cartilage and cartilage repair procedures, discuss future new directions in imaging strategies and methods being developed to measure cartilage thickness and volume measurements, and propose a magnetic resonance imaging protocol to evaluate cartilage that is achievable on most magnetic resonance scanners, vendor independent, practical (time and cost efficient), and accepted and used by a majority of musculoskeletal radiologists.

MR imaging of articular cartilage

Abstract With the advent of new treatments for articular cartilage disorders, accurate noninvasive assessment of articular cartilage, particularly with MR imaging, has become important. Understanding the MR imaging features of articular cartilage has led to the development of two types of routinely available MR imaging techniques which have demonstrated clinical accuracy and interobserver reliability.

Magnetic resonance imaging of articular cartilage of the knee.

Recently developed magnetic resonance (MR) imaging techniques allow accurate detection of moderate- and high-grade articular cartilage defects. There has been increased interest in MR imaging of articular cartilage in part because it is useful in identifying patients who may benefit from new articular cartilage replacement therapies, including chondrocyte transplantation, improved techniques for osteochondral transplantation, chondroprotective agents, and cartilage growth stimulation factors. The modality also has the potential to play an important role in the follow-up of patients during and after treatment. Detection of articular cartilage defects is beneficial for patients undergoing arthroscopy for other injuries, such as meniscal tears, because the presence of articular cartilage injury worsens prognosis and may modify therapy options.

Mechanisms of signal loss in magnetic resonance imaging of stenoses

Some of the factors affecting the signal losses that occur in magnetic resonance images at a stenosis or other region of complex flow have been evaluated. The important determinants of dephasing within a volume element are the net gradient moments, which can be kept small even at long echo times. For compact gradient wave forms, the echo time by itself is unimportant and does not affect signal losses. Reducing the fraction of echo sampled is an alternate method to velocity compensation for reducing gradient moment dephasing that keeps higher moments small. The effects of reducing the fraction of echo sampled on the signal losses in flow distal to a stenosis have been measured experimentally. Another source of signal loss at a stenosis is the variation of the mean phase within a volume element that occurs for flow that varies from one phase encoded view to another. Changes in flow behavior between acquisitions lead to signal displacement in the image. These view to view changes have also been quantified.

Chondroblastoma: MR Characteristics with Pathologic Correlation:

PURPOSE The purpose of this study was to describe the MR findings of chondroblastoma with pathologic correlation. METHOD In 22 patients with pathologically proven chondroblastoma, MR signal characteristics were correlated with pathological findings. RESULTS On T2-weighted images, 12 (55%) lesions were hyperintense with hypointense areas in 9 lesions, whereas 10 (45%) were hypointense. Therefore, 19 of 22 (86%) lesions with pathologic correlation had hypointense areas entirely (n = 10) or partly (n = 9) on T2-weighted images. On gadolinium-enhanced images, 13 (59%) lesions showed lobular enhancement and 9 (41%) showed marginal and septal enhancement. Low signal intensity on T2-weighted MR images was most strongly associated with an abundance of immature chondroid matrix, hypercellularity of the chondroblasts, calcifications, and hemosiderin on histology. CONCLUSION Chondroblastoma was found to show hypointense portions on T2-weighted images. Signal intensity on T1- and T2-weighted MR images in chondroblastoma was dependent on the amounts of histopathological components.

Renal Artery Stenosis Evaluation: Diagnostic Performance of Gadobenate Dimeglumine–enhanced MR Angiography—Comparison with DSA

PURPOSE To prospectively determine diagnostic performance and safety of contrast material-enhanced (CE) magnetic resonance (MR) angiography with 0.1 mmol per kilogram of body weight gadobenate dimeglumine for depiction of significant steno-occlusive disease (> or =51% stenosis) of renal arteries, with digital subtraction angiography (DSA) as reference standard. MATERIALS AND METHODS This multicenter study was approved by local institutional review boards; all patients provided written informed consent. Patient enrollment and examination at centers in the United States complied with HIPAA. Two hundred ninety-three patients (154 men, 139 women; mean age, 61.0 years) with severe hypertension (82.2%), progressive renal failure (11.3%), and suspected renal artery stenosis (6.5%) underwent CE MR angiography with three-dimensional spoiled gradient-echo sequences after administration of 0.1 mmol/kg gadobenate dimeglumine at 2 mL/sec. Anteroposterior and oblique DSA was performed in 268 (91.5%) patients. Three independent blinded reviewers evaluated CE MR angiographic images. Sensitivity, specificity, and accuracy of CE MR angiography for detection of significant steno-occlusive disease (> or =51% vessel lumen narrowing) were determined at segment (main renal artery) and patient levels. Positive and negative predictive values and positive and negative likelihood ratios were determined. Interobserver agreement was analyzed with generalized kappa statistics. A safety evaluation (clinical examination, electrocardiogram, blood and urine analysis, monitoring for adverse events) was performed. RESULTS Of 268 patients, 178 who were evaluated with MR angiography and DSA had significant steno-occlusive disease of renal arteries at DSA. Sensitivity, specificity, and accuracy of CE MR angiography for detection of 51% or greater stenosis or occlusion were 60.1%-84.1%, 89.4%-94.7%, and 80.4%-86.9%, respectively, at segment level. Similar values were obtained for predictive values and for patient-level analyses. Few CE MR angiographic examinations (1.9%-2.8%) were technically inadequate. Interobserver agreement for detection of significant steno-occlusive disease was good (79.9% agreement; kappa = 0.69). No safety concerns were noted. CONCLUSION CE MR angiography performed with 0.1 mmol/kg gadobenate dimeglumine, compared with DSA, is safe and provides good sensitivity, specificity, and accuracy for detection of significant renal artery steno-occlusive disease.

Magnetic Resonance Diagnosis of Meniscal Tears in Patients With Acute Anterior Cruciate Ligament Tears

Objective: To evaluate the accuracy of magnetic resonance imaging in the diagnosis of meniscal tear in patients with acute anterior cruciate ligament tears. Methods: Magnetic resonance images obtained from 41 patients imaged within 6 weeks of injury who had acute anterior cruciate ligament tears identified at arthroscopy were retrospectively reviewed for meniscal tear. Results: With MR imaging the sensitivity, specificity and accuracy for diagnosing meniscal tears in the presence of acute anterior cruciate ligament tears were 71%, 93%, and 88%; for the lateral meniscal tears were 57%, 100% and 85%; and for the medial meniscal tears were 100%, 88%, 90%. All false negative cases (n = 6) involved the posterior horn of the lateral meniscus. Conclusion: In the presence of acute anterior cruciate ligament tears, MRI imaging has relatively low sensitivity for detecting meniscal tears due to missed tears in the lateral meniscus.

Soft tissue edema in osteoid osteoma

Four cases of osteoid osteomas are presented. An uncharacteristic magnetic resonance finding of soft tissue edema is reported. This observation should not be misinterpreted as indicating a more aggressive pathologic process and, thereby, exclude osteoid osteoma from the differential.

Fast spin echo STIR imaging.

Objective Our goal was to evaluate the image quality, contrast characteristics, and possible clinical utility of STIR images obtained using a fast SE (FSE) technique. Materials and Methods The signal and contrast characteristics of FSE STIR images were evaluated using a lipid/water phantom and normal volunteers. Based upon these results, optimal FSE STIR imaging parameters were chosen. Conventional STIR and FSE STIR images were then obtained (while maintaining an equal number of section locations between the two sequences) in a series of 14 patients with known musculoskeletal abnormalities. These images were compared side by side by two experienced MR radiologists for image quality and lesion detection. Results There were no statistically significant differences between the FSE STIR images and conventional STIR images in lesion detection, image quality, motion artifact, or final diagnosis. Conclusion STIR imaging provides optimal contrast for detection of many pathologic abnormalities. This is especially true for musculoskeletal tumors and infection. The long imaging time and reduced number of sections obtainable with conventional SE (CSE) STIR sequences limit their routine use. Our results show that FSE STIR images of the musculoskeletal system can be obtained up to seven times more rapidly than CSE STIR images without compromising lesion detection or image quality.

Clinical magnetic resonance imaging of articular cartilage.

Magnetic resonance (MR) imaging of articular cartilage has recently become of intense interest because of new developments in the treatment of articular cartilage injury. Recent advances in MR imaging technology has allowed the development of imaging sequences tailored to the assessment of articular cartilage. Several clinical studies have validated the accuracy and reliability of high-resolution, fat-suppressed, three-dimensional, spoiled gradient-recalled MR imaging in the assessment of articular cartilage defects of the knee. The use of other MR imaging techniques is evolving, including the use of fast spin-echo imaging and anionic contrast-enhanced T1-weighted imaging. This article describes the background and rationale to MR imaging of articular cartilage and focuses on its clinical application. Because the knee has been the focus of most research in articular cartilage imaging, the discussion in this article will be largely restricted to this joint.