Multiple Echo, Caesar Cipher Acquisition and Model-Based Reconstruction (ME-CAMBREC): a Novel Accelerated T2 Mapping Method

Abstract

Due to the need to acquire a series of T2-weighted images, quantitative T2 mapping protocols in magnetic resonance imaging (MRI) suffer from long scan times. In order to alleviate this problem, fast spin-echo (FSE) imaging protocols can be employed, but the resulting images contain errors in the form of smoothing and ghosting artifacts which propagate to T2 maps. This dissertation presents a new method, dubbed Multiple Echo, Caesar Cipher Acquisition and Model-Based Reconstruction (ME-CAMBREC), which explicitly accounts for k-space signal attenuation during the reconstruction step. T2 maps generated by ME-CAMBREC contained reduced artifact compared to those generated by FSE methods, while requiring only a fraction of the scan time of a multiple spin-echo protocol. For moderate-to-high acceleration factors, ME-CAMBREC outperformed parallel imaging and steady-state T2 mapping techniques. Data suitable for ME-CAMBREC can be acquired in multi-slice mode using pulse sequence interleafs, but a slice gap should be employed to limit T2 bias caused by radiofrequency profile effects. Although ME-CAMBREC can be used to generate accurate T2s in the presence of flip angle errors, it was shown that the use of an independent measure of the transmit field (B1+) will improve fitted T2 precision.