0927

Simultaneous 1H MRF / 23Na MRI in knee cartilage at 7 T
Anne Adlung1,2, Zoe Pursel1,3, Baptiste Busi1,2, Gonzalo Gabriel Rodriguez1,4, and Guillaume Madelin1,2
1Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University Grossman School of Medicine, New York, NY, United States, 2Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University Grossman School of Medicine, New York, NY, United States, 3Pelham Memorial High School, Pelham, NY, United States, 4NMR Signal Enhancement, Max Planck for Multidisciplinary Sciences, Göttingen, Germany

Synopsis

Keywords: Non-Proton, Non-Proton

Motivation: Sodium MRI can provide tissue sodium concentration (TSC) and enable assessment of knee cartilage degradation.

Goal(s): We aim to quantify TSC, proton density (PD) and 1H T1 and T2 in the knee from multinuclear simultaneous acquisition.

Approach: We acquired 23Na-only FLORET and simultaneous 1H MRF/23Na MRI data in the knee of four healthy volunteers. We calculated TSC maps from both 23Na acquisitions for comparison, and PD, T1 and T2 maps from 1H MRF.

Results: Mean TSC in patellar and femorotibial cartilage, and gastrocnemius muscle showed no significant differences between both sodium acquisitions. Mean TSC, PD, T1 and T2 values were within previously-reported range.

Impact: We showed that a 3D simultaneous 1H MRF/23Na MRI acquisition at 7 T can provide reliable quantitative maps of TSC, PD, and 1H T1 and T2 relaxation times in cartilage.

Introduction

Quantitative sodium MRI provides tissue sodium concentration (TSC), changes of which have been linked to various pathologies in brain, muscle or cartilage, among others [1,2,3]. Sodium MRI could benefit from being acquired simultaneously with 1H MRI in terms of image coregistration and measurement time [4,5]. Magnetic resonance fingerprinting (MRF) enables simultaneous quantification of multiple tissue properties, such as proton density and relaxation times [6], with a single MR sequence.

Proteoglycans are a crucial component of articular cartilage and loss thereof is an early sign of osteoarthritis. A linear relationship between TSC and proteoglycan concentration in knee cartilage has been observed [7,8]. Thus, TSC quantification in cartilage might enable assessment of cartilage degradation in osteoarthritis [9,10,11]. Additionally, changes in 1H relaxation times (T1, T2) have also been associated with changes in the knee cartilage with aging [12] and osteoarthritis [13,14,15].

We suggest using a recently-developed multinuclear fingerprinting (MNF) sequence that acquires 1H MRF / 23Na MRI data simultaneously [4,5,16] to quantify TSC, proton density (PD) and 1H T1- and T2 relaxation times in the knee region. In this pilot study, we measured T1, T2, PD and TSC in multiple regions-of-interest (ROIs) within cartilage and the gastrocnemius muscle (GNM) in 4 healthy subjects, and compared the TSC measurements with standard FLORET 23Na acquisition.

Methods

We acquired 1H and 23Na MR data in the right knee of four healthy volunteers (two males, mean age: 27±3 years) at 7 T (Siemens Magnetom scanner) using an in-house built dual-tuned 1H/23Na knee coil with four 1H channels and eight 23Na channels.

The protocol included one 23Na-only FLORET sequence [17] (TR/TE = 120/0.2 ms, isotropic resolution = 2.3×2.3×2.3 mm3, FoV = 300 mm3, TA = 9:30 min) and one 3D simultaneous 1H MRF / 23Na MRI sequence [4,5] (MNF, TR/TE = 15/1.2ms, FoV = 240×240 mm2, in-plane resolution 1H = 1.5×1.5 mm2, resolution 23Na = 2.84×2.84 mm2, slice thickness = 5.0 mm, 9 shots, TA = 21 min). The MNF sequence enables calculation of TSC, PD, 1H T1 and T2 maps (Figure 1).
For each acquisition, reference phantoms were placed on both sides of the volunteer’s knee. These phantoms contained 150 mM NaCl and 3% agar to mimic physiological relaxation times for TSC quantification.
All 1H MRF and 23Na MRI data were reconstructed offline in MATLAB. Both 23Na images were corrected for B1- inhomogeneities by estimating the coil’s receive field through application of a Gaussian low pass filter on the masked object [18].

TSC maps were generated from MNF and FLORET 23Na images by linear regression from the signal intensity in the reference phantoms, including a correction factor for the phantom’s relaxation times. Mean TSC was calculated within four ROIs (patellar (PT), femorotibial medial (FTM) and -lateral (FTL) cartilage, and gastrocnemius muscle (GNM), Figure 1) on both TSC maps. A paired student t-test was performed to evaluate differences between ROI measurements from both TSC maps. Values for PD, and 1H T1 and T2 were also measured in the same ROIs.

Results

One slice of each orientation of the FLORET and 23Na MNF are shown in Figure 2.
The student t-test showed no significant difference (p>0.05) between mean TSC values from both maps in all ROIs.
Examples of the four MNF maps are shown in Figure 3.
All ROI values are listed in Table 1, and the corresponding boxplots are depicted in Figure 4.

Discussion

The mean TSC values measured in all ROIs were similar when quantified based on FLORET versus MNF. Previous studies have reported TSC to be around 158-271 mM [19] within different regions in the knee cartilage. In this study we observed values on the lower end of this range, (178-187)±8 mM. Cartilage is surrounded by synovial fluid, which has TSC values around 140 mM. Due to the relatively large voxel sizes of 23Na images, TSC values are a volume-weighted average of TSC in synovial fluid and cartilage (TSC around 250-300 mM [20]).

However, TSC within the GNM was around 69±8 (FLORET) and 76±5 mM (MNF), which is overall significantly higher than previously reported TSC values in human muscles [19]. Mean T1 (972±217, 1012±112, and 986±189 ms) and T2 (31±6, 31±9, and 31±6 ms) in cartilage were in agreement with literature values [12]. Mean T1 (1209±67ms) and T2 (24±2 ms) in GNM were also similar to previously-reported values [21,22].

Conclusion

We showed that a 3D simultaneous 1H MRF / 23Na MRI acquisition at 7 T provides reliable quantitative maps of TSC, PD, and 1H T1 and T2 in cartilage.

Acknowledgements

This work was supported in part by the NIH R01 AR079182, and was performed under the rubric of the Center for Advanced Imaging Innovation and Research (CAI2R, www.cai2r.net), an NIBIB National Center for Biomedical Imaging and Bioengineering (NIH P41 EB017183).

References

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  18. Lachner, Sebastian, et al. "Comparison of optimized intensity correction methods for 23Na MRI of the human brain using a 32-channel phased array coil at 7 Tesla." Zeitschrift für Medizinische Physik 30.2 (2020): 104-115.
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Figures

Table 1: Mean proton density (PD), 1H T1 and T2 relaxation times, and tissue sodium concentration (TSC) based on the FLORET and the MNF sequence, in ROIs within the patellar (PT) cartilage, the femorotibial medial (FTM) and -lateral (FTL) cartilage, and the gastrocnemius muscle (GNM).

Figure 1: Example of the ROIs within the patellar cartilage (A), the femorotibial medial and -lateral cartilage (B), and within the gastrocnemius muscle (C).

Figure 2: One representative sagittal (left), transversal (middle), and coronal (right) slice of the 3D data from FLORET (resolution = 2.3×2.3×2.3 mm3, FoV = 300 mm3) and MNF (resolution = 2.84×2.84×5 mm3, FoV = 240×240×180 mm3) sequences of the same volunteer.

Figure 3: One representative slice from one healthy volunteer with its four quantitative maps from the MNF sequence: TSC (23Na), proton density (PD), 1H T1, and 1H T2.

Figure 4: Boxplots depicting the quantitative assessment of TSC based on the 23Na FLORET (F) and the MNF (M) sequences, proton density (PD), 1H T1, and 1H T2. All four quantitative parameters were evaluated within the four ROIs: patellar cartilage (PT), the femorotibial medial (FTM), and -lateral (FTL) cartilage, and within the gastrocnemius muscle (GNM).

Proc. Intl. Soc. Mag. Reson. Med. 32 (2024)
0927
DOI: https://doi.org/10.58530/2024/0927