Metamaterial Internal Receivers for Magnetic Resonance Imaging
Abstract: Cancer of the biliary ductal system (cholangiocarcinoma) is rare in the West but one of the major disease problems in South-East Asian countries such as Cambodia, Laos, Myanmar, Thailand, and Vietnam. The cause is endemic liver fluke infestation, which follows from the consumption of raw and partly cooked river fish according to local dietary customs. The disease typically presents late and has a very poor prognosis. Currently surgical resection offers the only possibility of a cure, but staging and pre-operative planning are difficult because of the low resolution offered by computed tomography and magnetic resonance imaging (MRI) with external receiver coils. Internal receivers potentially offer higher signal-to-noise ratio (SNR) and resolution in MRI. Their limited reception pattern reduces the field-of-view for thermal noise from the body, the dominant noise source, but may be compensated by employing T2 mapping rather than imaging. The receivers must be low cost, disposable, compatible with endoscopes and catheters, and intrinsically MRI-safe. This talk will describe the development of receivers based on magneto-inductive waveguides, a form of one-dimensional metamaterial. The waveguides are batch-fabricated as smooth, flexible thin film circuits by lithographically patterning copper clad Kapton, and need no additional components. The use of figure-of-eight coils and the segmentation inherent in MI waveguides provide decoupling from magnetic and electric fields during excitation. The design principles will be outlined, and the local SNR advantage will be explained and demonstrated using phantoms. High-resolution 1H T2 maps will be presented at 3T for ex-vivo specimens from Thai cholangiocarcinoma patients and correlated with histopathology.