Methods and apparatus for accurate characterization of signal coil receiver sensitivity in magnetic resonance imaging (mri)

Abstract

A method for estimating receiver sensitivity in a magnetic resonance (MR) system. The method includes steps of acquiring an image SI(x); determining a transmission function T(x) including using Bloch's equation with an estimated transmit field B 1 transmit ; generating an estimate of the bias field B(x); and combining the estimated bias field B(x) and the transmission function T(x) to determine a receiver sensitivity S(x).

What is claimed is: 
     
         1 . A method for estimating receiver sensitivity in a magnetic resonance (MR) system, the method comprising:
 acquiring an image SI(x);   determining a transmission function T(x) comprising using Bloch's equation with an estimated transmit field B 1   transmit ;   generating an estimate of the bias field B(x); and   combining the estimated bias field B(x) and the transmission function T(x) to determine a receiver sensitivity S(x).   
     
     
         2 . The method of  claim 1 , wherein acquiring an image SI(x) comprises acquiring a plurality of signal intensity images using different imaging parameters. 
     
     
         3 . The method of  claim 2 , wherein the estimated transmit field B 1   transmit  is determined by estimating a relative flip angle map using the image SI(x),
 for the plurality of signal intensity images, each acquired using different imaging parameters, estimating a relative transmit field map,   for each nominal flip angle, determining a calibration factor based on a linear relationship between the nominal flip angles and the measured flip angles, and   for each nominal flip angle, calculating an absolute flip angle corresponding to the nominal flip angles.   
     
     
         4 . The method of  claim 3 , wherein determining a transmission function T(x) comprising using Bloch's equation with an estimated transmit field B 1   transmit  is performed for each nominal flip angle. 
     
     
         5 . The method of  claim 1 , wherein generating an estimate of the bias field B(x) comprises generating an estimate using an image SI(x) acquired using a given sequence with minimized TE and geometric distortions. 
     
     
         6 . The method of  claim 1 , wherein generating an estimate of the bias field B(x) comprises generating an estimate using an image SI(x) acquired while minimizing at least one of B 0  inhomogeneity, chemical shift, and magnetic susceptibility artifacts. 
     
     
         7 . The method of  claim 1 , wherein generating an estimate of the bias field B(x) comprises generating an estimate using at least one algorithm selected from an N3, FSL-FMRIB, and SPM algorithms. 
     
     
         8 . The method of  claim 1 , wherein combining the estimated bias field B(x) and the transmission function T(x) to determine a receiver sensitivity S(x) comprises determining a ratio between the estimated bias field B(x) and the transmission function T(x). 
     
     
         9 . The method of  claim 3 , wherein the different imaging parameters for estimating a relative transmit field map include at least one of nominal flip angle, repetition time (TR), number of RF pulses, and excitation frequency. 
     
     
         10 . The method of  claim 3 , wherein estimating a relative flip angle map comprises estimating a relative flip angle map using at least one method selected from a double flip angle method, and an actual flip angle imaging method.