Abstract
Chemical exchange saturation transfer (CEST) MRI is a promising molecular imaging tool which allows the specific detection of metabolites that contain exchangeable amide, amine, and hydroxyl protons. Decades of development have progressed CEST imaging from an initial concept to a clinical imaging tool that is used to assess tumor metabolism. The first translation efforts involved brain imaging, but this has now progressed to imaging other body tissues. In this review, we summarize studies using CEST MRI to image a range of tumor types, including breast cancer, pelvic tumors, digestive tumors, and lung cancer. Approximately two thirds of the published studies involved breast or pelvic tumors which are sites that are less affected by body motion. Most studies conclude that CEST shows good potential for the differentiation of malignant from benign lesions with a number of reports now extending to compare different histological classifications along with the effects of anti-cancer treatments. Despite CEST being a unique ‘label-free’ approach with a higher sensitivity than MR spectroscopy, there are still some obstacles for implementing its clinical use. Future research is now focused on overcoming these challenges. Vigorous ongoing development and further clinical trials are expected to see CEST technology become more widely implemented as a mainstream imaging technology.
Highlights
Magnetization transfer (MT) technology in magnetic resonance imaging (MRI), referring to the transfer of longitudinal magnetization between two proton groups, was first proposed by Wolff and Balaban et al in 1989 [1]
Where S0 refers to the water signal intensity that is obtained. Another prevailing method of separating pure chemical exchange saturation transfer (CEST) signals is to subtract the experwhen no pre-saturation pulse is applied, S(+∆ω) and S(−∆ω) refer to the signal intensities imental from the reference values that are free from CEST at a certain frequency offset that are obtained after applying pre-saturation pulses at + ∆ω and –∆ω, respectively [13,14]
MTRasym is unable to separate the CEST signals that are resonating down-field of water (∆ω between 1–3.5 ppm), from the nuclear Overhauser effect (NOE) that is resonating up-field of water (∆ω between −1.6 to −4 ppm). Another prevailing method of separating pure CEST signals is to subtract the experimental from the reference values that are free from CEST at a certain frequency offset (i.e., MTR = Zre f − Zexp )
Summary
Magnetization transfer (MT) technology in magnetic resonance imaging (MRI), referring to the transfer of longitudinal magnetization between two proton groups, was first proposed by Wolff and Balaban et al in 1989 [1]. In the year 2000, by combining magnetization transfer and chemical exchange, Wolff and Balaban first obtained the MR contrast images of several small molecules and named this novel molecular imaging technique chemical exchange saturation transfer (CEST) [3]. This imaging technology has attracted a number of preclinical and clinical research studies [4,5], becoming a promising molecular imaging tool that is available in the clinic [6,7].
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