A post-processing method for correction and enhancement of chemical shift images Yu-Che Cheng a , Jyh-Horng Chen b , Tsu-Tsuen Wang c , Ta-Te Lin a, ⁎ a Department of Bio-Industrial Mechatronics Engineering, National Taiwan University, Taipei 106, Taiwan, ROC b Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan 106, ROC c Department of Horticulture, National Taiwan University, Taipei, Taiwan 106, ROC Received 8 August 2008; revised 8 February 2009; accepted 10 May 2009 Abstract Chemical shift imaging (CSI) relies on a strong and homogeneous main field. Field homogeneity ensures adequate coherence between the precessions of individual spins within each voxel. Variation of field strength between different voxels causes geometric distortion and intensity variation in chemical shift images, resulting in errors when analyzing the spatial distribution of specific chemical compounds. A post-processing method, based on detection of the spectral peak of water and baseline subtraction with Lorentzian functions, was developed in this study to automatically correct spectra offsets caused by field inhomogeneity, thus enhancing the contrast of the chemical shift images. Because this method does not require prior field plot information, it offers advantages over existing correction methods. Furthermore, the method significantly reduces geometric distortion and enhances signals of chemical compounds even when the water suppression protocol was applied during the CSI data acquisition. The experimental results of the water and glucose phantoms showed a considerable reduction of artifacts in the spectroscopic images when this post-processing method was employed. The significance of this method was also demonstrated by an analysis of the spatial distributions of sugar and water contents in ripe and unripe bananas. © 2009 Elsevier Inc. All rights reserved. Keywords: Chemical shift imaging; Field inhomogeneity; Spectrum; Sugar content 1. Introduction Magnetic resonance imaging (MRI) is a powerful tool widely used in biological research and diagnostics, providing a nondestructive means of assessing characteristics of biological materials qualitatively and quantitatively. One area of strength of the MRI is its ability to generate high- quality diagnostic images reflecting internal characteristics of biological materials within a reasonable measurement time. The magnetic resonance signal from protons results from the interactions between an external magnetic field and a nucleus that possesses spin. Image contrast is created by selecting image acquisition parameters that weight signals according to the time constants of relaxation processes following the radiofrequency (RF) excitation of protons [1]. Since an MRI reveals the spatial distribution of different chemical components internal to a sample, this technique has proved useful for describing anatomic development and for monitoring physiological processes in various biological materials [2–7]. Chemical shift imaging (CSI), a branch of MRI technique, has been applied to many areas of chemical, medical, and psychological studies [8–11]. With CSI, images from test samples containing a range of chemical components can be displayed by analyzing its spectroscopic data. Because it gives both spatial and spectroscopic information, CSI has also become the preeminent tool for studying the internal physicochemical characteristics of biological materials. Furthermore, its applications in food and agricultural science have increased in recent years [12,13]. CSI is a nuclear magnetic resonance (NMR) spectroscopic method from which a matrix of spectra is acquired with a frequency- selective excitation to achieve cross-sectional imaging of specific compounds. It offers the advantage that many Available online at www.sciencedirect.com Magnetic Resonance Imaging 27 (2009) 1420 – 1429 ⁎ Corresponding author. Tel.: +886 2 33665331; fax: +886 2 23929416. E-mail address: m456@ntu.edu.tw (T.-T. Lin). 0730–725X/$ – see front matter © 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.mri.2009.05.035