Musculoskeletal Imaging Original Research

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1 Musculoskeletal Imaging Original Research Subhas et al. Comparison of Fast and Standard Shoulder MRI Protocols Musculoskeletal Imaging Original Research Naveen Subhas 1 Alex Benedick 2 Nancy A. Obuchowski 3 Joshua M. Polster 1 Luis S. Beltran 4 Jean Schils 1 Gina A. Ciavarra 4 Soterios Gyftopoulos 4 Subhas N, Benedick A, Obuchowski NA, et al. Keywords: agreement, interchangeability, MRI, parallel imaging, shoulder, technique DOI: /AJR Received June 23, 2016; accepted after revision October 2, Imaging Institute, Cleveland Clinic, 9500 Euclid Ave, A21, Cleveland, OH Address correspondence to N. Subhas (subhasn@ccf.org). 2 School of Medicine, Case Western Reserve University, Cleveland, OH. 3 Department of Quantitative Health Sciences, Cleveland Clinic, Cleveland, OH. 4 Department of Radiology, NYU Langone Medical Center-Hospital for Joint Diseases, New York, NY. Supplemental Data Available online at AJR 2017; 208: X/17/ American Roentgen Ray Society Comparison of a Fast 5-Minute Shoulder MRI Protocol With a Standard Shoulder MRI Protocol: A Multiinstitutional Multireader Study OBJECTIVE. The purpose of this study was to compare the diagnostic performance of a 5-minute shoulder MRI protocol consisting of multiplanar 2D fast spin-echo (FSE) sequences with parallel imaging to that of a standard shoulder MRI protocol. MATERIALS AND METHODS. A retrospective review of T MRI examinations of shoulders of 147 patients (mean age, years) and T MRI examinations of shoulders of 50 patients (mean age, years) with four fast and five standard sequences from two academic centers between January 2014 and April 2015 was performed by three musculoskeletal radiologists. Interchangeability of fast and standard MRI was tested by comparing interprotocol (fast vs standard) interreader agreement with standard MRI interreader agreement. Interreader agreement was also compared using kappa statistics. The frequency of major findings was compared using an adjusted McNemar test. Sensitivity and specificity of MRI were measured for 51 patients who underwent surgery. RESULTS. Interprotocol reader agreement was essentially equal to reader agreement on standard MRI (mean difference 1%; 95% CI, 3.8% to 3.9%; 61 96% across structures). Interprotocol kappa values ( ) were similar to standard MRI kappa values ( ). Frequencies of major findings on fast and standard MRI were similar ( % across structures; p 0.08). Sensitivities of fast MRI for tendon and labral tears (33 92%) were equivalent or higher than those of standard MRI with similar specificities (77 98%). CONCLUSION. Fast 5-minute shoulder MRI with multiplanar 2D FSE sequences using parallel imaging is interchangeable, with similar interreader agreement and accuracy, with standard shoulder MRI for evaluating shoulder injuries. M RI is the most comprehensive noninvasive imaging test available to evaluate shoulder abnormalities. This modality is highly accurate in diagnosing rotator cuff disease, which is the most common cause of shoulder pain in older adults [1, 2]. Specifically, MRI is effective in detecting partial-thickness and full-thickness rotator cuff tears, glenoid labral abnormalities, and other common causes of shoulder pain, such as biceps tendon tears and osteoarthritis of the glenohumeral or acromioclavicular joints [3 13]. Despite its excellent diagnostic capabilities, the high cost of MRI and limited availability of MRI scanners can deter its use. Cost and availability are directly related to the amount of time required for MRI examinations. A standard shoulder MRI protocol to evaluate rotator cuff disease requires approximately minutes of imaging time and 10 minutes of patient preparation time. To reduce these times with conventional techniques, a limited examination with only a few sequences would need to be performed, or the resolution of the sequences would need to be dramatically lowered. With the emergence of more powerful scanners and better coils, a complete MRI examination can now be performed faster and with a clinically adequate number of sequences and image quality [14]. Multichannel high-field-strength MRI systems (1.5 and 3 T) in combination with multichannel phased-array surface coils improve image quality with a higher signal-to-noise ratio (SNR) [15]. This increase in SNR can be used to obtain higher-resolution images without increasing examination times or to reduce examination time without reducing image resolution with the use of parallel imaging techniques while maintaining acceptable image quality [16 18]. Parallel imaging reduces examination time by obtain- AJR:208, April

2 Subhas et al. ing signal from a reduced FOV with fewer phase-encoding steps, resulting in a raw image with aliasing or wraparound artifacts that are resolved into their correct spatial coordinates using the known location and sensitivities of receiver coil elements. This allows images to be acquired with the same resolution as that obtained with a standard sequence in less time. Using parallel imaging techniques, we developed a 5-minute shoulder MRI protocol for 3- and 1.5-T scanners with standard 2D fast spin-echo (FSE) sequences that we hypothesized to be comparable to the standard protocol. In this study, we compared the diagnostic performance of this 5-minute shoulder MRI protocol consisting of multiplanar 2D FSE sequences with parallel imaging to that of a standard shoulder MRI protocol. Materials and Methods Fast sequences were added to standard sequences for all patients undergoing an unenhanced shoulder MRI at two academic centers: between January 2014 and May 2015 for center 1 and between December 2014 and April 2015 for center 2. A HIPAA-compliant retrospective review of these studies was approved by the institutional review boards of both institutions, with waivers of informed consent. Patients younger than 18 years and patients for whom not all sequences were performed were excluded. At center 1, T shoulder MRI scans were performed for 166 consecutive patients; 20 scans from 20 patients were excluded (eight from patients younger than 18 years and 12 scans that did not contain all sequences). A total of 151 scans for 147 patients (four patients had bilateral scans) were included in the study (mean patient age, years; range, years), including 84 scans of 82 men (mean age, years; range, years) and 67 scans of 65 women (mean age, years; range, years). The primary indications for the MRI were to evaluate for pain not otherwise specified (n = 66), rotator cuff tear (n = 49), labral tear or biceps tendon abnormality (n = 22), instability or dislocation (n = 8), and other (n = 6: adhesive capsulitis, n = 3; rotator cuff arthropathy, n = 2; and pectoralis injury, n = 1). At center 2, T shoulder MRI scans were performed for 70 consecutive patients; 20 scans from 20 patients that did not contain all sequences were excluded. A total of 50 scans for 50 patients were included in the study (mean patient age, years; range, years), including 28 scans of 28 men (mean age, years; range, years) and 22 scans of 22 women (mean age, years; range, years). The primary indications for the MRI were to evaluate for a rotator cuff tear (n = 24), pain not otherwise specified (n = 18), instability or dislocation (n = 4), labral tear or biceps tendon abnormality (n = 2), and other (n = 2: calcific tendinitis, n = 1; and rotator cuff arthropathy, n = 1). MRI Sequence Characteristics MRI studies were performed on an 8-channel 3-T system (Magnetom Verio, Siemens Healthcare) with a 4-channel shoulder array coil (part number [1P] , Invivo) at center 1 or a 64-channel 1.5-T system (Magnetom Aera, Siemens Healthcare) with a 16-channel shoulder array coil (Tim coil , Siemens Healthcare) at center 2. All scans included the standard protocol consisting of five sequences (two coronal oblique fluid-sensitive FSE sequences with TE of and ms, sagittal oblique fluid-sensitive and non T1-weighted FSE sequences, and an axial fluid-sensitive FSE sequence) and four fast sequences using integrated parallel acquisition techniques (ipat, Siemens Healthcare) with an acceleration factor of 2 and slightly larger voxels (coronal oblique, sagittal oblique, and axial fluid-sensitive FSE sequences and a sagittal oblique non T1-weighted sequence). Detailed sequence characteristics, including imaging times for each sequence, are shown in Table 1. Fast and standard sequences were acquired in an alternating fashion. On the 3-T scanner, the mean fast protocol time was 5 minutes 23 seconds (range, 4 minutes 47 seconds to 6 minutes 45 seconds), and the mean standard protocol time was 14 minutes 6 seconds (range, 12 minutes 43 seconds to 16 minutes 34 seconds). On the 1.5-T scanner, the mean fast protocol time was 4 minutes 33 seconds (range, 4 minutes 21 seconds to 4 minutes 51 seconds), and the mean standard protocol time was 15 minutes 40 seconds (range, 13 minutes 43 seconds to 16 minutes 53 seconds). Image Review The standard and fast sequences were separated and anonymized. Cases were reviewed in two reading periods with a minimum of 4 weeks between periods. A different random reading order containing both fast and standard studies was created for each reader and reading period. Fast and standard images from the same patient were never read in the same reading period. The cases were independently reviewed by three fellowshiptrained musculoskeletal radiologists at each site; the readers at center 1 had 9, 11, and 25 years of experience, whereas those at center 2 had 10, 5, and 5 years of experience. Readers were blinded to all patient information except for age. The findings for each case were recorded using a standardized score sheet (see Fig. S1, which can be viewed in the AJR electronic supplement to this article, available at [19]. The following structures were graded using published classification systems: supraspinatus or infraspinatus tendons were graded as normal or tendinosis, low-grade (< 50% tendon thickness) partial-thickness tear, high-grade (> 50% tendon thickness) partial-thickness tear, or full-thickness tear [20]; supraspinatus or infraspinatus fullthickness tear size (anteroposterior) was graded as small (< 1 cm), moderate (1 3 cm), large (3 5 cm), or massive (> 5 cm) [21]; supraspinatus or infraspinatus full-thickness tear retraction was graded as none, mild (< 2 cm), retraction to the top of the humeral head, or retraction to the level of the glenoid [22]; subscapularis tendon was graded as normal or tendinosis, partial-thickness tear, incomplete fullthickness tear, or complete full-thickness tear [23]; supraspinatus, infraspinatus, and subscapularis muscle fatty infiltration was graded as none, minimal, mild, moderate, or marked [24]; biceps tendon was graded as normal, tendinosis or partial tear, or complete tear [13]; labrum by quadrant was graded as intact or torn [12]; glenohumeral articular cartilage was graded as normal, partial-thickness or full-thickness defect less than 1 cm, or partialthickness or full-thickness defect greater than 1 cm; bone or marrow abnormalities (Hill-Sachs and Bankart lesions, fracture, avascular necrosis, marrow lesion) were graded as present or absent; and other abnormalities were graded using free text. Statistical Analysis Primary aim: interchangeability Interchangeability tests the ability of a new imaging technique to replace an established imaging technique by ensuring that the rate of agreement between readers when one of the readers uses the new technique is not significantly lower than the rate of agreement when all readers are using the established technique [25]. For each structure, the proportion of cases in which readers agreed on the abnormality was recorded when both readers were interpreting standard images and when one reader was interpreting standard images and the other was interpreting fast images. Agreement was defined as both readers grading the structure exactly the same (including severity staging). A generalized linear model was fit, in which the dependent variable was the presence or absence of agreement and the independent variables were magnet strength (1.5 or 3 T) and technique (standard images used by both readers or standard images used by one reader and fast images by the other). Generalized estimating equations were used to account for the clustered data (i.e., 2 AJR:208, April 2017

3 TABLE 1: Sequence Characteristics for Studies Performed on 3- and 1.5-T MRI Scanners Matrix Time FOV (cm 2 ) Minimum Maximum Minimum Maximum Minimum Maximum Mean Minimum Maximum No. of Excitations Acceleration Factor Slice (mm) TR (ms) TE (ms) Echo- Train Length Scan, Sequence 3-T fast min 26 s 2 min 8 s 1 min 42 s a Coronal T2-weighted intermediate-weighted min 14 s 2 min 30 s 1 min 27 s a Axial T2-weighted intermediate-weighted min 53 s 1 min 51 s 1 min 27 s a Sagittal T2-weighted intermediate-weighted Comparison of Fast and Standard Shoulder MRI Protocols Sagittal T1-weighted min 42 s 1 min 12 s 0 min 47 s a T standard min 48 s 3 min 58 s 3 min 2 s b Coronal proton density intermediate- weighted blade min 51 s 3 min 25 s 2 min 58 s b Coronal T2-weighted intermediate-weighted blade min 37 s 3 min 34 s 2 min 52 s b Sagittal T2-weighted intermediate-weighted blade min 28 s 3 min 39 s 2 min 51 s b Axial T2-weighted intermediate-weighted blade T1-weighted sagittal min 46 s 2 min 44 s 2 min 23 s b T fast min 13 s 1 min 19 s 1 min 14 s Coronal T2-weighted intermediate-weighted min 29 s 1 min 48 s 1 min 35 s Axial T2-weighted intermediate-weighted min 5 s 1 min 13 s 1 min 8 s Sagittal T2-weighted intermediate-weighted Sagittal T1-weighted min 31 s 0 min 40 s 0 min 33 s T standard min 15 s 3 min 50 s 3 min 6 s b Coronal proton density intermediate- weighted min 57 s 3 min 25 s 3 min 7 s b Coronal T2-weighted intermediate-weighted min 17 s 3 min 22 s 2 min 50 s b Sagittal T2-weighted intermediate-weighted min 15 s 4 min 1 s 3 min 38 s b Axial T2-weighted intermediate-weighted Sagittal T1-weighted min 27 s 3 min 25 s 2 min 58 s b a Matrix used for all but one case in which the matrix was b Default matrix. AJR:208, April

4 multiple interpretations of the same case). The individual equivalence index [25] was then computed as the estimated difference in the proportion of interreader agreement on the standard imaging minus the proportion of interreader agreement on standard and fast imaging; a 95% CI for the difference was constructed. A clinically important difference was defined as greater than 5% additional agreement when both readers were interpreting standard images than when one reader was interpreting standard images and the other was interpreting fast images. Secondary aim 1: weighted kappa interreader agreement Interreader agreement was also assessed using pairwise weighted kappa statistics when both readers were using standard imaging and when one reader was using standard imaging and the other was using fast imaging. Kappa values were estimated only for structures that were graded by the severity of the abnormality. Diagnosis severity differences of one category apart were given partial credit (i.e., half weight) in the weighting scheme. Agreement between fast and standard imaging was compared using the Landis and Koch grading system [26]. Secondary aim 2: frequency of major findings Readers ability to detect major findings using fast imaging was assessed by measuring the frequency that readers reported major findings for each structure only on standard imaging, only on fast imaging, and on both standard and fast imaging. Logistic regression intercept-only models, with generalized estimating equations to account for the clustered data, were built to test whether readers reported more major findings with standard imaging than with fast imaging. Secondary aim 3: accuracy Nine of 50 patients scanned at 1.5 T and 42 of 147 patients scanned at 3 T underwent surgery within 6 months of MRI. Readers sensitivities and specificities for diagnosis on fast and standard MRI were compared for these patients. For this evaluation, highgrade partial- and full-thickness supraspinatus or infraspinatus tears, incomplete and complete fullthickness subscapularis tears, partial and complete biceps tears, and any labral tears on MRI were considered as tears. Both small and large glenohumeral cartilage defects on MRI were considered as cartilage defects. Logistic regression models, using generalized estimating equations, were built to test for the presence of a modality effect; the dependent variable was reader finding, and the independent variable was modality (fast or standard MRI). Separate models were built for sensitivity and specificity. Results Interchangeability Although interreader agreement on standard MRI ranged from 61% to 96% for different structures, the combined (3 and 1.5 T) interreader agreement between fast and stan- TABLE 2: Interchangeability: Interreader Agreement for Standard Versus Subhas et al. Fast MRI Shoulder Abnormality, Modality Interreader Agreement 1.5 T 3 T Combined Supraspinatus and infraspinatus a Standard vs standard 91/150 (60.7) 366/453 (80.8) 457/603 (75.8) Standard vs fast 182/300 (60.7) 746/906 (82.3) 928/1206 (77.0) 95% CI for difference (%) 6.5 to to to 1.0 Subscapularis Standard vs standard 102/150 (68.0) 390/453 (86.1) 492/603 (81.6) Standard vs fast 216/300 (72.0) 789/906 (87.1) 1005/1206 (83.3) 95% CI for difference (%) 10.8 to to to 0.7 Fatty infiltration: supraspinatus and infraspinatus b Standard vs standard 129/150 (86.0) 409/453 (90.3) 538/603 (89.2) Standard vs fast 260/300 (86.7) 823/906 (90.8) 1083/1206 (89.8) 95% CI for difference (%) 6.1 to to to 1.3 Fatty infiltration: subscapularis b Standard vs standard 138/150 (92.0) 421/453 (92.9) 559/603 (92.7) Standard vs fast 286/300 (95.3) 849/906 (93.7) 1135/1206 (94.1) 95% CI for difference (%) 6.1 to to to 0.2 Biceps tendon Standard vs standard 108/150 (72.0) 303/453 (66.9) 411/603 (68.2) Standard vs fast 232/300 (77.3) 604/906 (66.7) 836/1206 (69.3) 95% CI for difference (%) 10.0 to to to 1.1 Labrum: superior Standard vs standard 124/150 (82.7) 359/453 (79.3) 483/603 (80.1) Standard vs fast 248/300 (82.7) 712/906 (78.6) 960/1206 (79.6) 95% CI for difference (%) 5.5 to to to 3.0 Labrum: anterior-superior Standard vs standard 140/150 (93.3) 429/453 (94.7) 569/603 (94.4) Standard vs fast 278/300 (92.7) 856/906 (94.5) 1134/1206 (94.0) 95% CI for difference (%) 3.2 to to to 2.0 Labrum: anterior-inferior Standard vs standard 138/150 (92.0) 421/453 (92.9) 559/603 (92.7) Standard vs fast 280/300 (93.3) 844/906 (93.2) 1124/1206 (93.2) 95% CI for difference (%) 3.1 to % to to 1.1 Labrum: posterior Standard vs standard 144/150 (96.0) 417/453 (92.1) 561/603 (93.0) Standard vs fast 284/300 (94.7) 826/906 (91.2) 1110/1206 (92.0) 95% CI for difference (%) 1.3 to to to 2.6 Glenohumeral cartilage Standard vs standard 102/150 (68.0) 378/453 (83.4) 480/603 (79.6) Standard vs fast 214/300 (71.3) 734/906 (81.0) 948/1206 (78.6) 95% CI for difference (%) 9.2 to to to 3.9 Note Data are number/total (%) except for 95% CIs, which are shown for the excess disagreement with standard versus fast MRI protocol. Agreement was defined as present (readers agreed exactly on the abnormality, including the severity) or absent. a For each patient, the highest-grade lesion of the supraspinatus and infraspinatus identified by the reader was used for analysis. b None and minimal were combined. 4 AJR:208, April 2017

5 Comparison of Fast and Standard Shoulder MRI Protocols dard MRI was nearly identical to that of standard MRI alone (mean excess disagreement 1% with the upper bounds of the 95% CI < 5%) for all of the evaluated structures, indicating that fast MRI and standard MRI are interchangeable (Table 2). The structures were also interchangeable at 1.5 and 3 T, with a few caveats. Although the agreement rate between fast and standard imaging and between standard imaging reads was exactly A A A the same for the supraspinatus or infraspinatus and superior labrum, the upper bounds of the 95% CI for excess disagreement on fast imaging exceeded 5% at 1.5 T because of the smaller sample size. At 3 T, the upper bounds of the 95% CI for excess disagreement on fast imaging for glenohumeral cartilage was 5.2%, minimally exceeding the 5% threshold. Examples of standard and fast 1.5- and 3-T MR images showing supraspinatus, B B B Fig year-old woman with high-grade partialthickness supraspinatus tear. A and B, Coronal T2-weighted multiplanar 2D fast spin-echo unenhanced standard (A) and fast (B) 3-T shoulder MR images show high-grade partialthickness supraspinatus tear (arrows), confirmed at surgery. Two readers classified finding as highgrade partial-thickness supraspinatus tear on both standard and fast MRI; third reader classified finding as full-thickness supraspinatus tear on both standard and fast MRI. Fig year-old man with low-grade partial thickness supraspinatus tear. A and B, Coronal T2-weighted multiplanar 2D fast spin-echo unenhanced standard (A) and fast (B) 1.5-T shoulder MR images show low-grade partialthickness supraspinatus tear (arrows) and fracture (F) of humeral neck, confirmed at surgery. One reader classified finding as normal, one classified finding as high-grade partial-thickness supraspinatus tear, and one classified finding as full-thickness supraspinatus tear on standard MRI; two readers classified finding as high-grade partial-thickness supraspinatus tear and one classified finding as low-grade partialthickness supraspinatus tear on fast MRI. All readers identified humeral neck fracture on both standard and fast MRI. labral, and articular cartilage abnormalities are shown in Figures 1 4. Kappa Interreader Agreement The combined (3 and 1.5 T) interreader agreement with fast and standard MRI ( across structures) was similar to the agreement with just standard MRI ( across structures) [23] (Table 3). In fact, at both 3 T and 1.5 T, the agreement when sub- Fig year-old man with posterior labral tear. A and B, Axial T2-weighted multiplanar 2D fast spin-echo unenhanced standard (A) and fast (B) 3-T shoulder MR images show posterior labral tear (arrows), confirmed at surgery. All three readers classified finding as posterior labral tear on standard MRI; two readers classified finding as posterior labral tear and one classified it as superior labral tear on fast MRI. AJR:208, April

6 Subhas et al. stituting fast imaging did not decrease kappa values by more than 0.1 except for two instances: assessment of supraspinatus or infraspinatus tear size at 1.5 T (0.514 vs 0.382) and supraspinatus or infraspinatus tear retraction at 1.5 T (0.757 vs 0.583) and combined (0.726 vs 0.618). Agreement on tear size and retraction, however, was evaluated only when all of TABLE 3: Interreader Weighted Kappa Statistics for Agreement Between Standard and Fast MRI Weighted κ (Grade a ) Shoulder Abnormality, Modality 1.5 T 3 T Combined A Bootstrap 95% CI Supraspinatus and infraspinatus b Standard vs standard (substantial) Standard vs fast (substantial) Full-thickness supraspinatus and infraspinatus tear size c Standard vs standard (moderate) 0.34 to 1.0 Standard vs fast (moderate) 0.39 to 1.0 Full-thickness supraspinatus and infraspinatus tear retraction c Standard vs standard (substantial) Standard vs fast (substantial) 0.09 to 1.0 Subscapularis d Standard vs standard (fair) Standard vs fast (fair) Biceps tendon e Standard vs standard (moderate) Standard vs fast (moderate) Glenohumeral cartilage d Standard vs standard (moderate) Standard vs fast (moderate) a According to Landis and Koch [26]. b For each patient, the highest-grade lesion of the supraspinatus and infraspinatus identified by the reader was used for the analysis; partial agreement (50%) was assigned for scores one category apart and no agreement was assigned for scores more than one category apart. c Analyses based only on cases in which there was agreement that a full-thickness tear was present; partial agreement (50%) was assigned for scores one category apart and no agreement was assigned for scores more than one category apart. d Partial agreement (50%) was assigned for scores one category apart and no agreement was assigned for scores more than one category apart. e None and minimal were combined; partial agreement (50%) was assigned for scores one category apart and no agreement was assigned for scores more than category apart. B Fig year-old man with articular cartilage defect. A and B, Coronal T2-weighted multiplanar 2D fast spin-echo unenhanced standard (A) and fast (B) 3-T shoulder MR images show articular cartilage defect (arrows), confirmed at surgery. Two readers classified cartilage as normal and one reader classified finding as small articular cartilage defect on standard MRI; two readers classified finding as small articular cartilage defect and one classified cartilage as normal on fast MRI. the readers had graded the tear as a full-thickness tear, resulting in a small sample. Frequency of Major Findings Although the number of major findings reported varied across structures ( %), both fast and standard MRI had similar rates of detecting major abnormalities (p 0.08 for each structure) (Table 4). In other words, readers were not more likely to report major findings on standard MRI compared with fast MRI. The only abnormality for which there was a marginally significant trend for more findings reported on standard imaging was large glenohumeral cartilage defects (p = 0.078). Review of the discordant large glenohumeral cartilage defect cases revealed that the reason for the discrepancy in nearly half of the cases was because of a reader classifying a cartilage defect as large on standard images and as small on fast images. Recall of patients related to poor image quality was rare with both techniques. Accuracy The overall sensitivities, specificities, positive predictive values, and negative predictive values of fast MRI for rotator cuff tears, biceps tears, labral tears, and cartilage defects were not significantly different from those of standard MRI (Table 5). In fact, the sensitivity of fast MRI was equivalent to or higher than the sensitivity of standard MRI for every structure except glenohumeral cartilage defects, which were limited by a small sample size at 1.5 T. Sensitivity was highest for supraspinatus or infraspinatus tears: 93% with the fast protocol versus 88% with the standard protocol. Sensitivity was lowest for subscapularis tears: 33% with both fast and standard protocols. Specificity was fairly high for all of the evaluated structures, ranging from 79% to 99% with both protocols. Positive predictive values ranged from a 6 AJR:208, April 2017

7 Comparison of Fast and Standard Shoulder MRI Protocols TABLE 4: Frequency of Major Findings at 1.5 T and 3 T: Standard Versus Fast MRI Shoulder Abnormality high of 85% for supraspinatus or infraspinatus tears to a low of 47 53% for cartilage defects. Negative predictive values were fairly high for all of the evaluated structures, ranging from 76% to 95% with both protocols. Discussion In this study, we found that the diagnostic performance of fast 5-minute shoulder MRI was comparable to that of standard shoulder MRI at both 3 and 1.5 T using four different methods. First, fast MRI was found to be interchangeable with standard MRI with no significant decrease (< 5%) in the rate of interreader agreement when standard MRI was replaced with fast MRI. Second, fast and standard MRI had similar interreader kappa agreement for all evaluated structures. Third, readers ability to identify major findings on fast and standard MRI was not significantly different. Finally, the sensitivity and specificity of fast MRI in diagnosing rotator cuff and biceps tendon tears, labral tears, and cartilage defects were nearly identical to the accuracy of standard MRI. The fast shoulder MRI protocol was much shorter than the standard MRI protocol, with an average time of 5 minutes 23 seconds compared with 14 minutes 6 seconds (62% reduction) at 3 T and 4 minutes 30 seconds compared with 15 minutes 39 seconds (71% reduction) at 1.5 T. The standard protocol, however, did include Total (n = 1206) a Reported on Both Standard and Fast MRI b one additional sequence compared with the fast protocol with two coronal oblique fatsuppressed fluid-sensitive FSE sequences, one with a shorter TE to evaluate labral abnormalities and another with a longer TE to evaluate rotator cuff abnormalities. Even if the standard protocol were to be shortened by eliminating one coronal oblique fluid-sensitive sequence to make it more comparable to the fast MRI protocol, the fast protocol would still be much shorter, with a reduction in imaging time of 52% at 3 T and 64% at 1.5 T. The mean protocol time at 3 T was longer than 1.5 T because the specific absorption rate limits were exceeded in some patients at 3 T, leading to an increase in the scan time. The main limitation of parallel imaging is loss in SNR as the acceleration factor increases [16]. SNR can, however, still be maintained at sufficiently high levels with the use of high-field strength MRI systems, phasedarray surface coils, low acceleration factors, and slight reductions in the voxel size, as was done in this study. The use of parallel imaging to reduce examination times without sacrificing diagnostic quality has been previously reported. Nael et al. [27] used partially parallel imaging and echo-planar imaging to develop a 6-minute MRI protocol for the evaluation of acute ischemic stroke. Similarly, Zhang et al. [28] described using parallel imaging for rapid abdominal pediatric MRI scans. New Reported on Standard MRI Only b Reported on Fast MRI Only b Full-thickness tear: supraspinatus and infraspinatus 135 (11.2) 102 (75.6) 19 (14.1) 14 (10.4) Incomplete and complete full-thickness subscapularis tear 41 (3.4) 9 (22.2) 15 (36.6) 17 (41.5) Moderate-marked fatty infiltration: supraspinatus and infraspinatus 24 (2.0) 7 (29.2) 10 (41.7) 7 (29.2) Moderate-marked fatty infiltration: subscapularis 9 (0.7) 2 (22.2) 4 (44.4) 3 (33.3) Complete biceps tendon tear 47 (3.9) 32 (68.1) 9 (19.1) 6 (12.8) Labral tear 235 (19.5) 78 (33.2) 76 (32.3) 81 (34.5) Large glenohumeral cartilage defect 88 (7.3) 48 (54.5) 25 (28.4) 15 (17.0) Hill-Sachs lesion 39 (3.2) 20 (51.2) 12 (30.8) 7 (17.9) Bony Bankart lesion 28 (2.3) 10 (35.7) 8 (28.6) 10 (35.7) Greater tuberosity fracture 9 (0.7) 8 (88.9) 0 (0.0) 1 (11.1) Avascular necrosis of humeral head 8 (0.7) 6 (75.0) 2 (25) 0 (0.0) Marrow replacing disease 12 (1.0) 8 (66.7) 4 (33.3) 0 (0.0) Other abnormality 221 (18.4) 119 (53.8) 53 (24.0) 49 (22.2) Patient recalled 3 (0.3) 0 (0.0) 1 (33.3) 2 (66.7) Note Data are number (%) unless otherwise indicated. Dashes ( ) indicate that the number is too small to calculate the p value. a Total no. of observations per structure = 1206 = (201 fast MRI standard MRI) three readers. b Percentage is calculated using the number in the Total column as the denominator. c p for null hypothesis that the proportion of findings reported on the two modalities is the same, versus the alternative hypothesis that the proportions are different. techniques, such as compressed sensing and multiband multislice imaging, allow much higher acceleration factors with parallel imaging while minimizing losses in SNR [29 32]. These techniques, however, are not yet available for routine clinical use [33]. In contrast, the parallel imaging techniques used in this study are clinically available on current-generation MRI systems from most vendors. Aside from parallel imaging, other techniques such as isotropic 3D acquisitions using gradient-echo or FSE techniques with multiplanar reformatting have been proposed for fast imaging [34 36]. Although these 3D techniques have the advantage of acquiring a single sequence and reformatting images in any imaging plane, the major drawback is that the contrast weighting of the images is the same for all imaging planes. The fast protocol used in this study, however, uses the same 2D FSE sequences as are used in most standard protocols, which allowed readers to interpret studies with familiar image contrast. The primary drawback of this protocol was that the image resolution of the fast sequences was somewhat lower than that of the conventional sequences, and the fast protocol consisted of one fewer sequence than the standard protocol. Nevertheless, the fast protocol still provided a complete examination, with both T1-weighted and fluid-sensitive weighted sequences, sequences in all three imaging planes, and images with sufficiently p c AJR:208, April

8 Subhas et al. high image quality to be interchangeable with those obtained with the standard protocol. Furthermore, although the image quality of the fast images may be lower than that of the standard images acquired in this study, many shoulder MRI examinations are still being performed on older scanners and lower field strength systems, where the image quality may not be much different or may be even lower than that of the fast images in this study. Routine use of this protocol could reduce the current 30- to 40-minute time slot for shoulder MRI (20 30 minutes for imaging and 10 minutes for setup) [10] to perhaps a 15-minute time slot (5 minutes for imaging and 10 minutes for setup), effectively doubling the number of shoulder MRI scans that could be performed in a day for better utilization of the scanner. The reduction in examination time may also improve the tolerability and comfort of the examination, especially when imaging anxious or claustrophobic patients. Finally, the fast shoulder protocol could be used as a tool to reduce patient wait times when there is a backlog of cases. Our study was not without limitations. The fast protocol requires current-generation highfield-strength MRI systems and multichannel surface coils. We did not measure SNR or subjective image quality because the purpose of the study was to evaluate diagnostic performance. Although the diagnostic accuracy between the fast and standard protocols was nearly identical, surgical correlation was available only for a subset of the studies and may not have been sufficient to detect a significant difference. Although overall fast MRI was interchangeable with standard MRI for all of the evaluated structures, the smaller sample size at 1.5 T led to wide 95% CIs for some evaluated structures. The study population was older and the results may not be generalizable to a younger patient population, among whom the frequency of labral abnormalities is higher and the frequency of rotator cuff disease is lower [37, 38]. Readers were likely able to discern whether they were interpreting fast or standard images because the fast protocol consisted of one fewer sequence. Verification and recall bias were minimized, however, because interpretations were objective (i.e., grading abnormalities of specific structures) and not subjective (i.e., image quality assessment), images were anonymized and read in a random order, and fast and standard images from the same patient were read in two separate reading sessions. Finally, the low prevalence of some abnormalities, such as subscapularis tears, significant rotator cuff TABLE 5: Comparison of Reader Accuracy on Fast Versus Standard MRI When Correlated With Surgical Findings Shoulder Abnormality Accuracy at 3 T Accuracy at 1.5 T Combined Accuracy Standard MRI Fast MRI Standard MRI Fast MRI Standard MRI Fast MRI 95% CI for Difference a Supraspinatus or infraspinatus tear Sensitivity 86 (44/51) 94 (48/51) 100 (9/9) 89 (8/9) 88 (53/60) 93 (56/60) 0.03 to 0.13 Specificity 92 (69/75) 91 (68/75) 83 (15/18) 83 (15/18) 90 (84/93) 89 (83/93) 0.11 to 0.03 PPV 88 (44/50) 87 (48/55) 75 (9/12) 73 (8/11) 85 (53/62) 85 (56/66) 0.01 to 0.01 NPV 91 (69/76) 96 (68/71) 100 (15/15) 94 (15/16) 92 (84/91) 95 (83/87) 0.01 to 0.02 Subscapularis tear Sensitivity 33 (4/12) 33 (4/12) 33 (4/12) 33 (4/12) 0.33 to 0.33 Specificity 98 (112/114) 99 (113/114) 96 (26/27) 100 (27/27) 98 (138/141) 99 (140/141) 0.01 to 0.04 PPV 67 (4/6) 80 (4/5) 0 (0/1) 57 (4/7) 80 (4/5) No. too small NPV 93 (112/120) 93 (113/121) 100 (26/26) 100 (27/27) 95 (138/146) 95 (140/148) 0.01 to 0.01 Biceps tear Sensitivity 63 (32/51) 57 (29/51) 67 (8/12) 83 (10/12) 63 (40/63) 62 (39/63) 0.14 to 0.10 Specificity 83 (62/75) 84 (63/75) 73 (11/15) 80 (12/15) 81 (73/90) 83 (75/90) 0.05 to 0.09 PPV 71 (32/45) 71 (29/41) 67 (8/12) 77 (10/13) 70 (40/57) 72 (39/54) 0.01 to 0.01 NPV 77 (62/81) 74 (63/85) 90 (18/20) 86 (12/14) 76 (73/96) 76 (75/99) 0.01 to 0.01 Glenohumeral cartilage defect Sensitivity 62 (24/39) 51 (20/39) 33 (1/3) 0 (0/3) 60 (25/42) 48 (20/42) 0.27 to 0.03 Specificity 82 (71/87) 82 (71/87) 75 (18/24) 71 (17/24) 80 (89/111) 79 (88/111) 0.07 to 0.08 PPV 60 (24/40) 56 (20/36) 14 (1/7) 0 (0/7) 53 (25/47) 47 (20/43) 0.27 to 0.15 b NPV 83 (71/86) 79 (71/90) 90 (18/20) 85 (17/20) 84 (89/106) 80 (88/110) 0.01 to 0.01 Labral tear Sensitivity 58 (21/36) 78 (28/36) 87 (13/15) 80 (12/15) 67 (34/51) 78 (40/51) 0.01 to 0.25 Specificity 78 (70/90) 81 (73/90) 100 (12/12) 92 (11/12) 80 (82/102) 83 (84/102) 0.06 to 0.10 PPV 51 (21/41) 62 (28/45) 100 (13/13) 92 (12/13) 63 (34/54) 69 (40/58) 0.01 to 0.01 NPV 82 (70/85) 90 (73/81) 86 (12/14) 79 (11/14) 83 (82/99) 88 (84/95) Note Data are percentage (number/total). Dashes ( ) indicate that no subscapularis tears were identified at surgery. a Numbers indicate the lower and upper bounds of the 95% CI of the difference between fast and standard MRI. b Model did not converge so 95% CI is based on z-value pivotal statistic for difference in proportions. 8 AJR:208, April 2017

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