7 Tesla Multinuclear MRI: Sodium Imaging

Groupleader : Dr. Tanja Platt

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Dr. Tanja Platt
Medical Physics in Radiology
Project Group:
7 Tesla Multinuclear MRI:
Sodium Imaging

Tel:  +49 6221 42 3066
Fax: +49 6221 42 3058
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Besides conventional magnetic resonance imaging (MRI), where the magnetization of 1H nuclei is measured, other atomic nuclei with spin I > 0 can be used for signal detection. In our department we are developing methods to acquire in-vivo MR signals of sodium (23Na), potassium (39K), chloride (35Cl), oxygen (17O), magnesium (25Mg), phosphorus (31P) and carbon (13C). These nuclei are of special interest in clinical research because of their crucial role in many cellular processes. For instance, 23Na, 39K, and 35Cl concentrations strongly depend on the physiologic condition of a cell. And 17O MRI can be used to directly access the oxygen consumption non-invasively (7 Tesla Multinuclear MRI: Oxygen imaging).

The requirements for X-nuclei imaging are strongly associated with their atomic properties. Due to the nucleus specific gyromagnetic ratio the different nuclei have differing resonance frequencies at 7 Tesla (1H: ca. 297 MHz, 23Na: ca. 79 MHz, 35Cl: ca. 29 MHz, 39K: ca. 14 MHz). As a result, the MR scanner must support these frequencies in addition to the proton frequency and special coils are required for the respective nuclei (e.g. 23Na head coil, 23Na body coil). In collaboration with the research groups ‘7 Tesla MR: RF Systems and Concepts’ and ‘Electromagnetic Simulations’ we are developing and building MR coils for X-nuclei imaging in-house such as a sodium body coil (Platt et al., 2018).

Furthermore, 23Na, 39K, and 35Cl have a spin of 3/2 and thus exhibit very short relaxation times. This necessitates the use of dedicated pulse sequences such as a density-adapted radial sequence (Nagel et al., 2009). Furthermore, the in vivo concentration of X-nuclei is orders of magnitude lower compared to the concentration of 1H. X-nuclei imaging therefore greatly benefits from ultrahigh static magnetic fields such as 7 Tesla. Image quality of X-nuclei MRI can be further improved via iterative image reconstruction techniques (Gnahm et al., 2014, Behl et al., 2016). Additionally, the physical properties of the quadrupolar nuclei (e.g. 23Na, 35Cl, 39K) can be utilized to generate special imaging contrasts such as triple quantum filtered imaging (Benkhedah et al., 2013).

The aim of this project group is to develop innovative imaging and post processing techniques for X-nuclei MRI, especially sodium, considering the criteria mentioned above. Due to a large number of commercial and in-house developed MR coils we are able to perform sodium MR examinations of the head, torso and extremities.

References

Platt et al., 2018: Platt, T., Umathum, R., Fiedler, T. M., Nagel, A. M., Bitz, A. K., Maier, F., ... & Behl, N. G. (2018). In vivo self‐gated 23Na MRI at 7 T using an oval‐shaped body resonator. Magnetic Resonance in Medicine, 80(3), 1005-1019.

Nagel et al., 2009: Nagel, A. M., Laun, F. B., Weber, M. A., Matthies, C., Semmler, W., & Schad, L. R. (2009). Sodium MRI using a density‐adapted 3D radial acquisition technique. Magnetic Resonance in Medicine, 62(6), 1565-1573.

Gnahm et al., 2014: Gnahm, C., Bock, M., Bachert, P., Semmler, W., Behl, N. G., & Nagel, A. M. (2014). Iterative 3D projection reconstruction of 23Na data with an 1H MRI constraint. Magnetic Resonance in Medicine, 71(5), 1720-1732.

Behl et al., 2016: Behl, N. G., Gnahm, C., Bachert, P., Ladd, M. E., & Nagel, A. M. (2016). Three‐dimensional dictionary‐learning reconstruction of 23Na MRI data. Magnetic Resonance in Medicine, 75(4), 1605-1616.

Benkhedah et al., 2013: Benkhedah, N., Bachert, P., Semmler, W., & Nagel, A. M. (2013). Three‐dimensional biexponential weighted 23Na imaging of the human brain with higher SNR and shorter acquisition time. Magnetic Resonance in Medicine, 70(3), 754-765.

Figure: ²³Na MR reconstruction for the full dataset and motion-separated ²³Na MR reconstructions (exhaled, inhaled) of the abdomen at B0 = 7 Tesla demonstrate the large field of view (FOV) of the developed body coil with FOV = (40 cm)³ (nominal spatial resolution = (4 mm)³, measurement time: 30 min 20 s). The separation into two respiratory states reduces motion blurring caused by breathing (see white lines and arrows), while the image quality in the motion-separated, iteratively reconstructed images is not markedly reduced compared to the iterative reconstruction of the full dataset.

Research Topics

-    23Na MRI of the human brain
-    23Na MRI of the human torso (e.g. lung, heart, kidneys, liver, prostate)
-    Correction methods for quantification (field inhomogeneities, relaxation,
      motion, partial volume correction)
-    Pulse sequence and reconstruction techniques

Job Offers

If you are interested in writing a Bachelor, Master, or Ph.D. thesis in our project group, we are happy to discuss potential projects with you. Please do not hesitate to contact us.

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