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A Protocol for Comprehensive Quantitative 3D Ultrashort Echo Time (UTE) Cones MR Imaging of the Knee Joint with Motion Correction
Mei Wu1,2, Wei Zhao1, Jonathan Lee1, Lidi Wan1, Saeed Jerban1, Eric Y Chang1,3, Jiang Du1, and Yajun Ma1

1Department of Radiology, University of California, San Diego, San Diego, CA, United States, 2Department of Radiology, Guangzhou First People’s Hospital, School of Medicine, South China University of Technology, Guangzhou, China, 3Radiology Service, VA San Diego Healthcare System, San Diego, CA, United States

Synopsis

We propose a protocol for comprehensive quantitative 3D UTE-Cones imaging of the knee joint with motion correction. The protocol includes 3D UTE-Cones actual flip angle imaging (UTE-Cones-AFI) for T1 measurement, UTE-Cones with variable TEs for T2* measurement, UTE-Cones with adiabatic T1ρ preparation for AdiabT1ρ measurement, and UTE-Cones-MT for measuring MTR and modeling of macromolecular fraction (f) for various knee joint tissues including the cartilage, menisci, ligaments, tendons and muscle. An elastix motion registration method was used for motion correction. In our study, three knee specimens and 15 volunteers were evaluated. Mean and standard deviation of the measurements for various knee joint tissues are reported.

Introduction

Knee degeneration involves all the major tissues in the joint (1-3). However, conventional MRI sequences can only detect signals from long T2 tissues such as the superficial cartilage, with little signal from the deep cartilage, menisci, ligaments, tendons, and bone (4). We aimed to develop a comprehensive quantitative 3D Ultrashort Echo Time (UTE) Cones imaging protocol for a truly “whole joint” evaluation of knee degeneration. The protocol includes 3D UTE-Cones actual flip angle imaging (UTE-Cones-AFI) for T1 mapping, multi-echo UTE-Cones with fat suppression for T2* mapping, UTE-Cones with adiabatic T1ρ preparation for AdiabT1ρ mapping, and UTE-Cones magnetization transfer (UTE-Cones-MT) for MT ratio (MTR) and modeling of macromolecular fraction (f) (5-10). An elastix registration technique was used to compensate for motion during the scans (11). Quantitative data analyses were performed on the registered data. Three knee specimens and 15 volunteers were evaluated at 3T.

Method

The 3D UTE-Cones imaging protocol was applied to three human knee specimens (43.3±11.6 years; 2 males) and 15 volunteers (33.2±8.9 years, 6 males). Informed consent was obtained from all subjects in accordance with guidelines of the institutional review board. The UTE-Cones sequences were used to scan the knee joints using the same field of view (FOV)= 15×15×10.8 cm3, slice thickness of 3 mm, and receiver bandwidth of 166 kHz. Other sequence parameters were: 1) UTE-Cones-AFI (8): TR1/TR2=20/100 ms, flip angle (FA)=45°, acquisition matrix=128×128×18, readout duration=924 µs, scan time=4 min 57 sec; 2) UTE-Cones-VFA (9): TR=20 ms; FA=5°,10°,20°, and 30°; matrix=256×256×36; readout duration=1644 µs, scan time=9 min 28 sec; 3) UTE-Cones-AdiabT1ρ (10): TR=500 ms; FOV=15×15×10.8 cm3; bandwidth=166 kHz; FA=10°; matrix=256×256×36, Nsp=25; number of adiabatic inversion pulses NIR=0,2,4,6,8,12, and 16, each with a scan time of 2 min 34 sec; 4) UTE-Cones-T2*: TR=30 ms, FA=10°, matrix=256×256×36, fat saturation, two sets of TEs (set #1=0,2.2,6.6,11 ms; set #2=0.6,4.4,8.8,13 ms), each with a scan time of 2 min 34 sec; 5) UTE-Cones-MT (7): TR=100 ms, TE=32 µs, FA =7°, FOV=14 cm, readout=256×256, 32 slices, number of spokes per MT preparation (Nsp) = 9, three powers (500°,1000°,1500°), and five MT frequency offsets (2,5,10,20 and 50 kHz), with scan time of 58 seconds per acquisition. UTE-MT modeling was performed to calculate macromolecular fraction f. The whole protocol took approximately 50 minutes. The knee specimens were scanned before and after a series of translational and rotational motions. Data processing was performed before and after elastix motion registration, which is based on Insight Segmentation and Registration Toolkit (ITK) (11). The volunteer data were first subjected to the elastix motion registration. Manually drawn regions-of-interest for the ex vivo and in vivo knees were used to measure the mean and standard deviation for T1, AdiabT1ρ, T2*, MTR, and f of various knee joint tissues.

Results and Discussion

Figure 1 shows representative UTE-Cones-AdiabT1ρ imaging of a knee specimen. All main tissues in the knee including the cartilage, menisci, ligaments and tendons were well depicted. Excellent T1ρ fitting was achieved demonstrating a T1ρ of 24.5±1.3ms for the quadriceps tendon, 38.8±3.2ms for the PCL, 33.2±1.3ms for the meniscus and 55.6±5.2ms for the patellar cartilage.

Figure 2 shows UTE-Cones-MT modeling of a knee specimen before and after motion. Without motion, excellent MT modeling was achieved for the quadriceps tendon (f=20.7±1.6%), the PCL (f=15.2±1.0%), the meniscus (f=22.9±1.2%) and the patellar cartilage (f=10.3±0.5%). Poor fitting was achieved when motion was introduced during the scans. After elastix motion registration, very similar macromolecular fractions were achieved for the quadriceps tendon (f=20.4±1.5%), PCL (f=15.0±0.9%), meniscus (f=21.6±1.4%) and cartilage (f=9.7±0.7%).

Table 1 summarizes mean and standard deviation values of AdiabT1ρ and f for cartilage, menisci, PCL, ACL, tendon and muscle over three knee joint specimens before and after elastix motion registration. The results demonstrate the efficiency of the elastix motion registration algorithm.

Figure 3 shows representative UTE-Cones-AdiabT1ρ fitting as well as UTE-Cones-MT modeling of the femoral condyle of a volunteer before and after elastix motion registration. Without motion registration, significant fitting errors were observed. With elastix motion registration, the MT fitting errors were greatly reduced by more than four-fold.

Table 2 summarizes mean and standard deviation of T1, T2*, AdiabT1ρ, MTR and f for cartilage, menisci, quadriceps tendon, patellar tendon, ACL, PCL and muscle over 15 volunteers. The relatively small standard deviation suggests the robustness of the UTE-Cones measurements and of the elastix motion registration algorithm.

Conclusion

The 3D UTE-Cones sequences together with elastix motion correction could robustly measure T1, T2*, AdiabT1ρ, MTR, and macromolecular fraction for both short and long T2 tissues in the knee in vivo.

Acknowledgements

The authors thank the grant support from NIH (R01AR062581).

References

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2. Hunter DJ, Zhang YQ, Niu JB, Tu X, Amin S, Clancy M, Guermazi A, Grigorian M, Gale D, Felson DT. The association of meniscal pathologic changes with cartilage loss in symptomatic knee osteoarthritis. Arthritis Rheum 2006; 54:795-801.

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4. Chang EY, Du J, Chung CB. UTE imaging in the musculoskeletal system. J Magn Reson Imaging. 2015;41(4):870-83.

5. Ma Y, Shao H, Du J, Chang EY. Ultrashort Echo Time Magnetization Transfer (UTE-MT) Imaging and Modeling: Magic Angle Independent Biomarkers of Tissue Properties. NMR Biomed 2016; 29:1546-1552. 6. Carl M, Bydder GM, Du J. UTE imaging with simultaneous water and fat signal suppression using a time-efficient multispoke inversion recovery pulse sequence. Magn Reson Med 2016;76:577–582.

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8. Ma YJ, Lu X, Carl M, Zhu Y, Szeverenyi N, Bydder GM, Chang E, Du J. Accurate T1 mapping of short T2 tissues using a three-dimensional ultrashort echo time cones actual flip angle – variable TR (3D UTE-Cones AFI-VTR) method. Magn Reson Med 2018; 80:598-608.

9. Ma YJ, Zhao W, Wan L, Guo T, Searleman A, Jang H, Chang EY, Du J. Whole knee joint T1 values measured in vivo at 3T by combined 3D ultrashort echo time cones actual flip angle and variable flip angle methods. Magn Reson Med 2018 (in press).

10. Ma YJ, Carl M, Searleman A, Lu X, Chang EY. Du J. 3D adiabatic T1r prepared ultrashort echo time cones sequence for whole knee imaging. Magn Reson Med 2018; 80:1429-1439.

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Figures

Figure 1. Representative 3D UTE-Cones-AdiabT1ρ imaging of an ex vivo knee sample from a 63y old female donor without motion artifact. Selected AdiabT1ρ images with regions of interest (red circles) and corresponding fitting curves of quadriceps tendon, PCL, meniscus and patellar cartilage are shown in the first and second rows, respectively. The T1ρ values of quadriceps tendon, PCL, meniscus and patellar cartilage were 24.5±1.3, 38.8±3.2, 33.2±1.3 and 55.6±5.2 ms, respectively.

Figure 2. 3D UTE-Cones-MT imaging of a cadaveric knee joint with representative regions of interest (red circles) (A-D), the corresponding fitting curves for quadriceps tendon, PCL, meniscus, and patellar cartilage before motion (E-H), after motion without elastix motion correction (I-L), and after motion with elastix motion correction (M-P). UTE-MT modeling parameters obtained using elastic motion correction are comparable to the still condition.

Figure 3. 3D UTE-Cones-AdiabT1ρ fitting for femoral condyle of a healthy volunteer before (A) and after (B) elastix motion registration, as well as 3D UTE-MT modeling before elastix motion registration (C) and after elastix motion registration (D). Significant motion artifacts were observed in the fitting curves (A, C), while excellent fitting was achieved for both AdiabT1ρ (B) and MT modeling (D), demonstrating an AdiabT1ρ value of 39.1±3.9 ms and macromolecular fraction of 9.8±0.9% for articular cartilage in the femoral condyle.

Table 1. Mean 3D UTE-Cones-AdiabT1ρ and MT modeling of macromolecular fraction (f) for various cadaveric human knee joint tissues including cartilage, menisci, ligaments, tendons and muscle before and after elastix motion registration.

Table 2. Mean 3D UTE AFI-VFA T1, AdiabT1ρ, MTR, MT modeling of macromolecular fraction (f) and T2* for various knee joint tissues including meniscus, femoral cartilage, tibial cartilage, patellar cartilage, quadriceps tendon, patellar tendon, ACL, PCL and muscle of 15 healthy volunteers after elastix motion registration.

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