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


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.


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.


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.


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.


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


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


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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)