Feasibility of 1 H MR spectroscopy in malignant pulmonary lesions at 3 Tesla: phantom study and clinical verification

Purpose: Primary lung malignancies are the leading cause of cancer death worldwide. In addition to primary lung malignancy, the presence of pulmonary metastases has a critical role in patient prognostication and management. Recently, cellular and molecular imaging, particularly proton magnetic resonance spectroscopy ( 1 H MRS), has been employed for early tumor detection. This article aims to survey the role of 1 H-MRS as a virtual biopsy technique to determine the biological make-up of lung lesions. Methods: NEMA IEC phantom analysis was utilized to acquire free induction decay (FID) of several tumor markers including choline, lactate, and creatine on single-voxel spectroscopy (SVS) at 3 Tesla (T) MRI. Various protocol modifications were performed on acquisition and processing steps. Preliminary in vivo verifications were subsequently performed on MRS datasets of 4 patients with malignant lung pathologies. Results: 1 H MRS of phantom revealed detectable peaks of choline, lactate and creatine in concentrations above the threshold of 1 µ Molar (µM) in patients with lung malignancies. Our result demonstrate that the phantom sphere diameter is the most influential factor on peak detectability with minimum reasonable value of 13mm; with the least acceptable in vitro voxel size of 1 cm 3 and in vivo equivalent of 8 cm 3 . Trading off between acquisition time and signal to noise ratio (SNR), the appreciable number of acquisition (NAS) was equal to 64. A quantitative formula was derived to calculate metabolite concentrations (AUC=0.73). Concordant results were obtained on pilot clinical assessments. Conclusion: This preliminary study provides a one-stop-shop solution for SVS through optimizing acquisition and processing parameters as well as absolute quantification of choline, lactate, and creatine concentrations in malignant pulmonary lesions, with successful clinical verification.