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Introduction of Targeted Rapid Knee MRI exam using T2 Shuffling into Clinical Practice: Retrospective Analysis on Image Quality, Charges, and Scan Time
Jonathan I Tamir1, Michael Lustig1, Valentina Taviani2, Marcus T Alley3, Kendall O'Brien4, Becki Perkins4, Lori Hart4, Fida Wishah3, Jesse K Sandberg3, Michael J Anderson5, Javier Turek6, Theodore L Willke6, and Shreyas S Vasanawala3

1Electrical Engineering and Computer Sciences, University of California, Berkeley, Berkeley, CA, United States, 2MR Applications & Workflow, GE Healthcare, Menlo Park, CA, United States, 3Radiology, Stanford University, Stanford, CA, United States, 4Radiology, Lucile Packard Children’s Hospital, Palo Alto, CA, United States, 5Intel Labs, Santa Clara, CA, United States, 6Intel Labs, Hillsboro, OR, United States

Synopsis

Volumetric fast spin echo (FSE) of the knee using T2 Shuffling (T2Sh) has previously been described as comparable to traditional 2D imaging. T2Sh has the added advantage of being a rapid single-scan 4D multi-plane reformattable sequence for pediatric knee examinations. This study investigates the feasibility and effectiveness of a targeted rapid pediatric knee MRI exam after introduction into clinical practice, with the goal of reducing cost and enabling same-day MRI access.

Introduction

Magnetic resonance imaging (MRI) is commonly used to evaluate musculoskeletal pathologies. Despite its advantages, MRI of the pediatric knee presents several challenges due to requirements for sub-millimeter spatial resolution and multiple contrasts$$$^{1,2}$$$, leading to lengthy scan and exam times. The long exams often lead to a high cost, limiting the value of the MRI exam in the context of clinical care. Volumetric fast-spin-echo (3D FSE) alternatives to the standard knee protocol are attractive because they theoretically provide isotropic resolution and larger slice coverage, enabling multi-planar reformats and eliminating the need to separately scan at multiple orientations with additional technologist planning$$$^{3-8}$$$. The primary challenge with 3D FSE acquisitions is the tradeoff between scan time and image blurring due to long echo trains$$$^{3,9}$$$.

Recently, an acquisition based on 3D FSE was proposed that permits volumetric reconstruction of images with contrast varying from proton-density (PD) weighting to increasing T2 weighting$$$^7$$$. This seven-minute scan, termed T2 Shuffling (T2Sh), uses ideas from compressed sensing$$$^10$$$ to accelerate the acquisition and mitigate blurring due to T2 decay by accounting for relaxation behavior. A prior study with 30 consecutive patients investigating a single sequence protocol using T2Sh, compared against the conventional protocol, indicated that missing clinically relevant pathology is unlikely$$$^8$$$. The use of T2Sh in a targeted exam is attractive because it provides images at multiple clinical contrasts, obviating the need for numerous conventional 2D scans$$$^11$$$. The purpose of this study is to investigate the feasibility and effectiveness of a targeted rapid pediatric knee MRI exam after introduction into clinical practice, with the goal of reducing cost and enabling same-day MRI access.

Materials and Methods


In an Institutional Review Board approved study with informed consent/assent, we implemented a targeted pediatric knee MRI exam on three 3T scanners (GE MR750) for assessing pediatric knee pain. The 10-minute protocol consisted of a 7-minute fat-suppressed T2Sh scan followed by a 3-minute T1 2D FSE sequence (scan parameters in Figure 1). To enable clinically feasible image reconstruction times, a distributed, compressed sensing-based iterative reconstruction was implemented on a local four-node high-performance compute cluster and integrated into the clinical scanner and PACS$$$^12$$$. Pediatric patients were sub-selected for the exam based on insurance plan and clinical indication. Over a two-year period, 47 subjects were recruited for the study and 49 MRIs were ordered. Date and time information was recorded for MRI referral, registration, and completion, and descriptive statistics were analyzed. Image quality was also assessed from 0 (non-diagnostic) to 5 (best anatomy delineation) by two radiologists, and consensus was subsequently reached.

Results

Of the 47 subjects, 18 completed the exam on the same day as their referral (Figure 2). Median time from registration to exam completion was 18.7 minutes. Median end-to-end reconstruction time for the T2 Shuffling sequence was reduced from 18.9 minutes to 95 seconds using the distributed implementation. Technical fees charged for the targeted exam were one third that of the routine clinical knee exam. Figure 3 shows a 14-year-old male evaluated for internal derangement of the knee. The T2Sh image formatted into axial PD weighting is annotated to demarcate the patellar tendon, ACL fibers, meniscus, and MCL. Edema and partial tearing/sprain of the MCL is visualized in the T2Sh coronal and sagittal images. Figure 4 shows two patients referred for meniscal tear. Image quality assessment is shown in Figure 5. Greater than 85% of the cases were rated as very good to outstanding. No exams were deemed non-diagnostic or poor quality. No subject had to return for additional imaging.

Discussion

As the imaging time for the targeted exam was reduced compared to the conventional knee MRI, a reduced charge modifier code was used for insurance billing, lowering the technical fees to one third of the conventional knee MRI fee. In this study, about 38% of the exams were completed on the same day. In comparison, our institution had no instances of same-day scheduling for routine knee MRI prior to the introduction of the targeted knee exam. The distributed reconstruction enabled a streamlined workflow for the technologists, as the images were available on the scanner console before the T1 scan finished.

A limitation of this study was that arthroscopic data was not available to corroborate the MRI findings, though the focus of this study was on scheduling feasibility. A second limitation was the relatively small number of participants. The targeted knee exam was intentionally limited to a small subset of clinical indications and insurance pre-authorizations during its initial implementation, but further evaluation is required at a multi-site level.

Conclusion

The targeted knee MRI exam is feasible and reduces imaging time, cost, and barrier to same-day MRI access for pediatric patients.

Acknowledgements

We thank the following funding sources: National Institutes of Health (NIH) grants R01EB009690, P41RR09784; Sloan Research Fellowship; Bakar Fellowship; GE Healthcare, and Intel Labs.

References

  1. Laor T, Jaramillo D. Pediatric musculoskeletal MRI: basic principles to optimize success. Pediatr Radiol 2008;38(4): 379-391.
  2. Strouse P, Koujok K. Magnetic resonance imaging of the pediatric knee. Top Magn Reson Imaging 2002; 3(4):277-294.
  3. Mugler JP. Optimized three-dimensional fast-spin-echo MRI. J Magn Reson Imaging 2014;39(4):745-767.
  4. Fritz J, Raithel E, Thawait GK, Gilson W, Papp DF. Six-Fold Acceleration of High-Spatial Resolution 3D SPACE MRI of the Knee Through Incoherent k-Space Undersampling and Iterative Reconstruction-First Experience. Invest Radiol 2016;51(6):400-409.
  5. Kijowski R, Rosas H, Samsonov A, King K, Peters R, Liu F. Knee imaging: Rapid three-dimensional fast spin-echo using compressed sensing. J Magn Reson Imaging 2017;45(6):1712-1722.
  6. Fritz J, Ahlawat S, Fritz B, et al. 10‐Min 3D Turbo Spin Echo MRI of the Knee in Children: Arthroscopy‐Validated Accuracy for the Diagnosis of Internal Derangement. J Magn Reson Imaging 2018; in press. doi: 10.1002/jmri.26241.
  7. Tamir JI, Uecker M, Chen W, et al. T2 shuffling: Sharp, multicontrast, volumetric fast spin-echo imaging. Magn Reson Med 2016;77(1):180-195.
  8. Bao S, Tamir JI, Young JL, et al. Fast comprehensive single-sequence four-dimensional pediatric knee MRI with T2 shuffling. J Magn Reson Imaging 2016;45(6):1700-1711.
  9. Busse RF, Brau ACS, Vu A, et al. Effects of refocusing flip angle modulation and view ordering in 3D fast spin echo. Magn Reson Med 2008;60(3):640-649
  10. Lustig M, Donoho D, Pauly JM. Sparse MRI: The application of compressed sensing for rapid MR imaging. Magn Reson Med 2007;58(6):1182-1195.
  11. Tamir JI, Anderson MJ, Turek J, Roh A, Alley MT, Lustig M, Vasanawala SS. Targeted Rapid MRI Exams and Reconstructions using T2 Shuffling. ISMRM-RSNA Co-Provided Workshop on High-Value MRI, Washington, DC, 2008.
  12. Anderson MJ, Tamir JI, Turek J, et al. Clinically Deployed Distributed Magnetic Resonance Imaging Reconstruction: Application to Pediatric Knee Imaging. Arxiv 2018; preprint. doi: arXiv:1809.04195v1.

Figures

Figure 1. Targeted knee MRI typical scan parameters.

Figure 2. (a) Histogram and (b) cumulative distribution of number of days between exam order and exam completion for targeted knee MRI exam. Mean and median number of days are shown with solid red and dashed black lines, respectively. (c) Histogram and (d) cumulative distribution of exam times for targeted knee MRI exam. Mean and median exam times are shown with solid red and dashed black lines, respectively.

Figure 3. A 14-year-old male evaluated for internal derangement of the right knee. (top left) Annotated T2Sh image reformatted axially with PD contrast. The T2Sh images reformatted into intermediate and T2 weighted coronal planes (top middle and top right, respectively) show bone bruise (white arrow) and partial tearing/sprain of the medial collateral ligament (red arrows). T2Sh sagittal source images with (bottom left) PD, (bottom middle) intermediate weighting, and (bottom right) T2 weighting show the bone bruise (white arrow).

Figure 4. Two patients with clinical indication of meniscal tear. (a) A 13-year-old female patient evaluated for internal derangement of the left knee. T2Sh images reformatted into (left) sagittal PD, (middle) coronal T2, and (right) axial intermediate weighting. Clinical suspicion of lateral meniscal tear was confirmed with MRI (yellow arrows). Additional related findings were medial discoid meniscus (red arrow) and bone marrow edema (white arrow). (b) Patient presented with knee pain and clinical suspicion of meniscal tear; (left) coronal nonfat-suppressed T1, and (right) T2Sh reformatted to coronal T2 weighted images are shown. Note the bone bruise, marked by the yellow arrows.

Figure 5. Frequency of image quality ratings after consensus by two radiologists. Images were rated using the scale 0 (non-diagnostic), 1 (poor), 2 (limited), 3 (good), 4 (very good), and 5 (outstanding). There was one case with a score of limited and no cases with scores of non-diagnostic and poor.

Proc. Intl. Soc. Mag. Reson. Med. 27 (2019)
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