*4.8. Magnetic Resonance Spectroscopy*

Magnetic resonance spectroscopy (MRS) allows the identification of different atomic nuclei, such as hydrogen, carbon, phosphorus, and fluorine, in specific regions of interest; thus, providing functional and biochemical information on a wide range of biological processes. For example, among the cellular metabolites measured with MRS, there is choline contained in cell membranes, creatine and glucose involved in energy production, and alanine and lactate that are typically increased in some tumors [83]. In clinical applications, it is a noninvasive method for the assessment of tumor biochemistry and physiology to identify the early changes in response to therapy, as well as for grading and staging of cancer [93,151,152]. In many preclinical studies, e.g., in breast or colon cancer, this method is used to track intra-tumor changes during therapy, and the levels of the metabolites measured may represent a potential noninvasive marker to check tumor response [153–155].

#### 4.8.1. Thyroid

Proton (H) MRS and DWI-ADC mapping (see 4.6 Diffusion-Weighted Imaging, [145]) were performed on 14 patients with malignant thyroid nodules diagnosed by ultrasonography and verified by biopsy. In these patients, 13 nodules were malignant with biopsy evidence, and five nodules were benign. Intra-nodular choline (Cho) peak, Cho/creatine (Cr) ratio, and ADC values of malignant nodules were evaluated and compared to those of benign nodules. Malignant nodules had significantly higher Cho peak amplitudes and a higher Cho/Cr ratio than benign ones. Hence, the use of H-MRS may be added to other imaging approaches in the evaluation of thyroid nodules and the determination of their nature. It might help to establish adequate treatments at an early stage, reducing the morbidity and mortality of the disease, and, at the same time, avoiding unnecessary surgical interventions in patients with benign lesions. Nonetheless, there are technical difficulties in performing MRS on thyroid glands, or other neck structures, concerning tumor movement due to swallowing and breathing, substantial differences in magnetic susceptibility between the neck and the air in the trachea, and the contamination of spectra by adjacent fat [145].
