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DOI:10.2214/AJR.05.0487
AJR 2006; 187:371-375
© American Roentgen Ray Society

Original Research

3.0-T MRI of Meniscal Tears

Thomas Magee1 and David Williams1

1 Both authors: Department of Radiology, Neuroskeletal Imaging, 255 N Sykes Creek Pkwy., Merritt Island, FL 32953.

Received March 19, 2005; accepted after revision June 21, 2005.

 
Address correspondence to T. Magee (tmageerad{at}cfl.rr.com).


Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
OBJECTIVE. The sensitivity and specificity of 3.0-T MRI of the knee for meniscal tears have not been specifically assessed. We undertook a retrospective review of 100 consecutive MR examinations of the knee followed by arthroscopy to evaluate the sensitivity and specificity of 3.0-T MRI compared with arthroscopy in the detection of meniscal tears.

MATERIALS AND METHODS. Two experienced musculoskeletal radiologists retrospectively reviewed MR scans of the knees of 100 patients who underwent consecutive knee arthroscopic procedures after MRI examinations. Interpretations were performed by consensus review with the reviewers blinded to arthroscopic results at the time of consensus review. All patients underwent complete MRI of the knee on a 3.0-T unit. All patients underwent fast spin-echo proton density sagittal imaging at 2-mm slice thickness. Fat-saturated fast spin-echo T2 axial, coronal, and sagittal imaging and T1 coronal imaging also were performed. All 100 patients underwent arthroscopy, and the results were compared with MR interpretations.

RESULTS. Consensus retrospective review of the 100 knee MR examinations revealed 111 meniscal tears. Four meniscal tears seen on arthroscopy were not seen on MR examination. There were three false-positive MR interpretations of meniscal tear compared with arthroscopy. In this study, the sensitivity of MRI in the detection of meniscal tears was 96%, and the specificity was 97%.

CONCLUSION. MRI of the knee at 3.0 T is sensitive and specific compared with arthroscopy in the detection of meniscal tears. Findings at 3.0 T compare favorably with results at 1.5-T or lower field strength.

Keywords: arthroscopy • injury • meniscal tear • musculoskeletal imaging • 3-T MRI


Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
MRI of the knee has been found to be highly accurate in the diagnosis of meniscal tears. In previous studies, the sensitivity of MRI in the detection of meniscal tears has been reported to be between 80% and 100% [1-7]. Kelly et al. [1] reported 94% accuracy of MRI compared with arthroscopy in the detection of meniscal tears. Mink et al. [2] reported 92% accuracy for MRI compared with arthroscopy. None of these studies were performed with a 3.0-T MR scanner. To our knowledge, the sensitivity and specificity of 3.0-T MRI of the knee compared with arthroscopy in the detection of meniscal tears have not been specifically assessed. To examine the sensitivity and specificity of 3.0-T MRI in the detection of meniscal tears, we undertook a retrospective review of 100 MRI knee examinations that were followed by arthroscopy.


Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Two experienced musculoskeletal radiologists retrospectively reviewed 3.0-T MR images of the knee from consecutive examinations of 100 patients who later underwent arthroscopy. Interpretations were performed by consensus review. MR examinations were performed between March and May 2004. The age range of the 100 patients was 15-74 years (mean, 41 years). There were 73 male patients and 27 female patients. All arthroscopic procedures were performed within 30 days of the MR examination (minimum time after MR examination, 1 day; maximum time after MR examination, 30 days; mean time after MR examination, 8 days).

All patients underwent MRI of the knee in the coronal, axial, and sagittal planes on a 3.0-T scanner (Signa, GE Healthcare). Coronal fast spin-echo T1-weighted (TR/TE, 750/10); coronal, sagittal, and axial fast spin-echo fat-saturated T2-weighted (3,950/51); and fast spin-echo proton density sagittal (1,800/12) sequences with a field of view of 15 cm on all images were used. Slice thickness was 3 mm with a 10% interslice gap on all sequences except for the fast spin-echo proton density sagittal sequence, which had a 2-mm slice thickness with a 10% interslice gap. The matrix on the sagittal proton density sequence was 416 x 288, and the matrix on all other sequences was 320 x 320. The echotrain lengths were 3 for the T1 coronal sequence, 6 for the fast spin-echo sagittal proton density sequence, and 12 for all other sequences. One excitation was used in the T1 coronal sequence, and two excitations were used in all other sequences. Imaging times were as follows: 3 minutes 5 seconds for T2 coronal and axial sequences, 3 minutes 45 seconds for T2 sagittal sequences, 6 minutes for thin-section proton density sagittal sequences, and 1 minute 30 seconds for T1 coronal sequences. A quadrature extremity coil was used.

The MR images of all 100 patients were retrospectively reviewed by two experienced musculoskeletal radiologists at one sitting. At the time of review, the reviewers were blinded to the results of arthroscopy. Consensus interpretation was achieved when both reviewers agreed that a meniscal tear was present or not present on MR images. Retrospective MR interpretations were then correlated with arthroscopic findings for the 100 patients. MR images were assessed for location of meniscal tears. MR criteria used for diagnosis of meniscal tears were abnormal meniscal signal touching an articular surface or abnormal morphologic features of the meniscus on one or more MR images. If signal was definitively seen to touch a surface in one view, a meniscal tear was reported.


Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
Consensus retrospective interpretation of the images from 100 MR examinations of the knee revealed 111 meniscal tears in 100 patients (Figs. 1, 2, 3, 4, 5, 6, 7A, 7B, 8, and 9). Four meniscal tears seen at arthroscopy had not been seen on MR examination. Two of these four meniscal tears were not seen on retrospective review after results of arthroscopy were known (Fig. 3). Two of these four meniscal tears were seen on retrospective review after arthroscopic results were known. One was a horizontal tear seen only on coronal images (Figs. 7A and 7B). The second was a radial tear seen only on one coronal image (Fig. 5).


Figure 1
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  		Fig. 1 —28-year-old man with knee pain who had surgically proven meniscal tear. Proton density sagittal MR image (TR/TE, 1,800/12) shows findings consistent with meniscal tear (arrow).

 

Figure 2
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  		Fig. 2 —45-year-old man with knee pain who had surgically proven meniscal radial tear. Proton density sagittal MR image (TR/TE, 1,800/12) shows findings consistent with radial tear (arrow) in body of lateral meniscus.

 

Figure 3
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  		Fig. 3 —15-year-old boy with knee pain who had meniscal tear found at arthroscopy. Proton density sagittal MR image (TR/TE, 1,800/12) shows area of intrasubstance signal in posterior horn of meniscus but no meniscal tear (arrow).

 

Figure 4
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  		Fig. 4 —42-year-old woman with knee pain who had meniscal tears of medial and lateral menisci found at arthroscopy. T1-weighted coronal MR image (TR/TE, 750/10) shows horizontal meniscal tear (down arrow) in posterior horn of medial meniscus. Horizontal tear (up arrow) also is present in lateral meniscus.

 

Figure 5
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  		Fig. 5 —42-year-old man with knee pain. Meniscal radial tear was found at arthroscopy. T2-weighted coronal MR image (TR/TE, 3,950/51) shows MRI findings consistent with meniscal radial tear (arrow). This tear was not seen by either reviewer at blinded retrospective review but was seen in retrospect after arthroscopic results were known.

 

Figure 6
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  		Fig. 6 —15-year-old boy with knee pain who had surgically proven meniscal tear. Proton density sagittal MR image (TR/TE, 1,800/12) shows findings consistent with meniscal tear (arrow).

 

Figure 7
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  		Fig. 7A —39-year-old woman with knee pain who had surgically proven meniscal tear. T2-weighted coronal MR image (TR/TE, 3,950/51) shows linear area of abnormal increased signal touching superior articular surface of meniscus (arrow). This finding was not interpreted as meniscal tear by either reviewer at retrospective blinded review.

 

Figure 8
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  		Fig. 7B —39-year-old woman with knee pain who had surgically proven meniscal tear. T1-weighted coronal MR image (684/9.5) shows abnormal increased signal touching superior articular surface of meniscus (arrow). This finding was seen only in retrospect after results of arthroscopy were known. This meniscal tear was seen only on coronal images and was not seen in sagittal or axial planes.

 

Figure 9
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  		Fig. 8 —23-year-old man with knee pain. Proton density sagittal MR image (TR/TE, 1,800/12) shows MRI findings consistent with meniscal tear (arrow). Meniscal tear was not seen at arthroscopy.

 

Figure 10
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  		Fig. 9 —34-year-old man with knee pain. Proton density sagittal MR image (TR/TE, 1,800/12) shows MRI findings consistent with meniscal tear (arrow). Meniscal tear was not seen at arthroscopy.

 
Compared with arthroscopic findings, there were three false-positive MR interpretations of meniscal tear. In all of these cases, signal was seen to touch the inferior articular surface in the periphery of the posterior horn of the medial meniscus (Figs. 8 and 9). In six cases, signal was seen to touch a meniscal surface in one view only. Four of these patients had meniscal radial tears. Two patients had horizontal tears seen to touch a surface in only one view. In all six cases, meniscal tear was seen at arthroscopy.

In this study, the sensitivity of MR detection of meniscal tears in the knee was 96% (108 of 112 meniscal tears seen at arthroscopy were seen on MRI) (95% CI, 92.8-98.2%). The specificity was 97% (95% CI, 93-98.3%). Twelve of the 100 patients had two meniscal tears in the same knee. Ten of these 12 patients had meniscal tears in both the medial and lateral menisci, and two of these patients had two meniscal tears in the medial meniscus.

The locations of arthroscopically detected meniscal tears were as follows: anterior horn medial meniscus (n = 2), body of the medial meniscus (n = 16), posterior horn of the medial meniscus (n = 48), anterior horn of the lateral meniscus (n = 26), body of the lateral meniscus (n = 14), and posterior horn of the lateral meniscus (n = 6).


Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
MRI of the knee at 3.0 T is sensitive and specific compared with arthroscopy in the detection of meniscal tears. Results of previous studies have shown MRI at 1.5-T field strength or less to be highly sensitive in the detection of meniscal tears [1-6]. Results of our study compare favorably with results at 1.5-T or less field strength.

In this study four meniscal tears were seen at arthroscopy that were not seen at retrospective blinded consensus MR interpretation. Two of these meniscal tears were not seen at retrospective review even after arthroscopic results were known (Fig. 3). Two of these meniscal tears were subtle but were seen on retrospective review after the arthroscopic results were known. One was a horizontal tear seen only on coronal images (Figs. 7A and 7B). The second was a radial tear seen only on one coronal image (Fig. 5). Both tears were in the far posterior horn of the meniscus and only visible on T2 coronal images. Both reviewers found this area difficult to assess. Sensitivity for detection of meniscal tears in this study was affected by perceptual errors of the consensus reviewers in these two cases.

There were three false-positive interpretations of meniscal tears on MR images compared with arthroscopy. In all of these cases there was evidence that signal was touching the inferior articular surface in the periphery of the posterior horn of the medial meniscus (Figs. 8 and 9). These tears were within the vascularized red zone of the meniscus. It is possible that these MRI findings that had the appearance of a tear were healed tears. This area also can be difficult to visualize at arthroscopy. It is possible meniscal tears were present in these areas that were not seen at arthroscopy. Even in retrospect, after arthroscopic results were known to the consensus reviewers, these three injuries had the appearance of meniscal tear on MR images. These three cases affected the specificity of detection of meniscal tears in this study.

MRI at 3 T allows a higher signal-to-noise ratio (SNR) than 1.5-T MRI. The spin-spin TR, T2, remains fairly constant at different field strengths. However, the spin-lattice TR, T1, increases as field strength increases. Therefore, at 3.0 T the TR must be longer than in 1.5-T MRI to maximize the SNR gain. At 3.0 T, the TR must be longer to attain the same type of contrast on T1-weighted images as seen with 1.5-T MRI. In addition, in 3.0-T MRI, the TE must be slightly shorter than in 1.5-T MRI to account for decreased T2 TR [8, 9]. The parameters used in our knee imaging have an increased TR and a decreased TE in all sequences compared with parameters previously used on our 1.5-T MR scanner. This adjustment was made to optimize our SNR in 3.0-T MRI.

Imaging at 3 T allows a higher SNR than does 1.5-T imaging. This feature can be used to improve imaging speed and resolution. However, T1 TR is longer and T2 TR is shorter at 3.0 T than at 1.5 T. Also, at 3.0 T there is more sensitivity to magnetic susceptibility artifacts and chemical shift artifacts than at 1.5 T. To reduce chemical shift artifact, we have doubled our bandwidth on 3.0 T compared with the bandwidth used at 1.5 T. Doubling the bandwidth has resulted in a reduction of SNR by the square root of 2. The increase in SNR allows faster imaging at 3.0 T, with improved resolution and thinner slice thickness compared with 1.5 T [9]. Since changing to 3.0-T imaging from 1.5-T imaging in our practice, we have faster throughput and higher-resolution imaging and are more confident in making a diagnosis of a meniscal tear. We seldom need to equivocate about whether a meniscal tear is present. Some authors have advocated equivocating on the diagnosis of meniscal tear in as many as 10% of cases in the use of 1.5-T MRI [10]. We believe that MRI of the knee at 3 T allows more accurate and definitive diagnoses compared with imaging at 1.5 T.

Results of a previous study indicated that for a definitive report of meniscal tear on MR examinations, signal should touch a surface on two images [6]. In our study, if signal was definitively seen to touch a surface in one view, a meniscal tear was reported. Using this criterion in our study did not decrease specificity (97%) compared with that in previous studies performed at 1.5 T or lower field strength. This result may have been be due to the high resolution of 3-T images. Another explanation may be the use of thin-section (2 mm) proton density sagittal images. In previous studies, slice thickness on sagittal proton density images was at least 3 mm. The thinner sections may make it clearer to see whether signal touches a surface. In six cases, signal was seen to touch a meniscal surface in one view only. Four of these injuries were meniscal radial tears, which sometimes are seen only in one view. Two of these injures were horizontal tears seen to touch a surface in only one view. In all six cases, a meniscal tear was seen at arthroscopy.

Fast spin-echo proton density sagittal imaging with an echo-train length of 6 was used in this study. Some authors have indicated that fast spin-echo imaging can cause blur, affecting the diagnosis of meniscal tears on MRI [10]. Neither of the two reviewers in this study perceived blurring of images at retrospective interpretation. Our sensitivity and specificity for detection of meniscal tears with the use of fast spin-echo imaging compared favorably with results reported in previous studies [1-7]. In one previous study, 100% sensitivity was reported for detection of meniscal tears, degeneration, or both. A significant limitation was that only 20 patients were enrolled in that study [7].

Limitations of our study were its retrospective nature and the fact MR images were interpreted by consensus rather than independently. Most of our referrals come from orthopedic surgeons, and the patients have a high prevalence of positive findings on MRI. The surgeons were aware of the prospective MR review before arthroscopy, and this knowledge may have biased their arthroscopic findings.

We conclude that MRI of the knee performed at 3.0 T compares favorably in sensitivity and specificity with studies performed at 1.5-T field strength or lower.


References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

  1. Kelly MA, Flock TJ, Kimmel JA, et al. MR imaging of the knee: clarification of its role. Arthroscopy1991; 7:78 -85[Medline]
  2. Mink JH, Deutsch AL, Crues JV, et al. MR imaging of the knee: technical factors, diagnostic accuracy, and further pitfalls. Radiology 1987;165 : 175
  3. Crues JV, Mink J, Levy TL, et al. Meniscal tears of the knee: accuracy of MR imaging. Radiology 1987;164 : 445-448[Abstract/Free Full Text]
  4. DeSmet AA, Norris MA, Yandow DR, et al. Diagnosis of meniscal tears of the knee with MR imaging: effect of observer variation and sample size on sensitivity and specificity. AJR 1993;160 : 555-559[Abstract/Free Full Text]
  5. DeSmet AA, Tuite MJ, Norris MA, et al. MR diagnosis of meniscal tears: analysis of causes of errors. AJR1994; 163:1419 -1423[Abstract/Free Full Text]
  6. DeSmet AA, Norris MA, Yandow DR, et al. MR diagnosis of meniscal tears of the knee: importance of high signal in the meniscus that extends to the surface. AJR 1993;161 : 101-107[Abstract/Free Full Text]
  7. Tyrell RL, Gluckert K, Pathria M, et al. Fast three-dimensional MR imaging of the knee: a comparison with arthroscopy. Radiology 1988;166 : 865-872[Abstract/Free Full Text]
  8. Gold GE, Han E, Stainsby J, et al. Musculoskeletal MRI at 3.0 T: relaxation times and image contrast. AJR2004; 183:343 -351[Abstract/Free Full Text]
  9. Gold GE, Suh B, Sawyer-Glover A, et al. Musculoskeletal MRI at 3.0 T: initial clinical experience. AJR 2004;183 : 1479-1486[Free Full Text]
  10. Kaplan PA, Dussault R, Helms CA, et al. Knee. In: Kaplan PA, ed. Musculoskeletal MRI. Philadelphia, PA: Saunders,2001 : 363-391

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