Apparatus and method for non-invasive measurement of cardiac output

Abstract

A comparatively light and compact permanent magnet arrangement for an MRI apparatus has a pair of opposed permanent magnet arrays with a shimming system to adjust the uniformity and strength of a magnetic field in a central chamber of the apparatus. The MRI apparatus is used to examine the extremities of a patient to determine cardiovascular characteristics from an analysis of the blood flow through selected arteries in the extremity. The information collected can be used to calculate such characteristics as total cardiac output, blood flow, arterial wall thickness and elasticity and the presence of plaque.

1 - 11 . (canceled) 
     
     
         12 . An apparatus comprising:
 two permanent magnet assemblies which are opposite in polarity and are set within a hollow steel sleeve to provide an air gap with a magnetic flux between the two permanent magnet assemblies, wherein the two permanent magnet assemblies and the hollow steel sleeve have an axis that is common to each and wherein a diagnostic zone is defined within the air gap,   at least one steel shim enclosed within at least one of the two permanent magnet assemblies and the hollow steel sleeve, wherein the at least one steel shim has a position which is adjustable along a direction that is parallel to the axis and wherein the adjusting of the at least one steel shim is configured to enhance a strength and a linearity of the magnetic flux in the diagnostic zone.   
     
     
         13 . The diagnostic apparatus of  claim 12 , wherein at least one of the two permanent magnet assemblies comprises a central cylindrical main steel magnet, a cylindrical steel pole piece of a same diameter as the main magnet placed in face-to-face contact thereto, and a coaxially positioned toroidal side magnet. 
     
     
         14 . The diagnostic apparatus of  claim 13 , wherein the toroidal side magnet has a rectangular cross section. 
     
     
         15 . The diagnostic apparatus of  claim 13 , wherein both permanent magnet assemblies have an identical structure. 
     
     
         16 . The diagnostic apparatus of  claim 13 , wherein the at least one steel shim is adjustably positioned within a cavity in the cylindrical steel pole piece. 
     
     
         17 . The diagnostic apparatus of  claim 16 , wherein the at least one steel shim is adjustably positioned in the cavity by a threaded fastener. 
     
     
         18 . The diagnostic apparatus of  claim 16 , wherein the at least one of the two permanent magnet assemblies comprises a plurality of steel shims, each positioned in a corresponding cavity in the respective pole piece and each having an adjustable position within the cavity. 
     
     
         19 . The diagnostic apparatus of  claim 12 , wherein the hollow steel sleeve comprises removable side walls. 
     
     
         20 . The diagnostic apparatus of  claim 12 , wherein the hollow steel sleeve comprises a circumferential channel with at least one toroidal steel shim having a position which is adjustable parallel to the common axis to enhance a strength and a linearity of the magnetic flux in the diagnostic zone. 
     
     
         21 . The diagnostic apparatus of  claim 20 , wherein the at least one toroidal steel shim comprises a plurality of concentric sleeve shims positioned within the circumferential channel and wherein each sleeve shim has an adjustable position within the circumferential channel. 
     
     
         22 . An MRI device comprising the apparatus of  claim 12 , at least one RF coil configured to deliver a pulsed signal and at least one pick up coil configured to receive a corresponding signal, both with respect to a part of a patient which is placed within the diagnostic zone.