Theoretical considerations for optimizing intensity differences between primary XXXX and normal tissue with spin-echo magnetic resonance imaging.

@entity1 @entity3884 @entity5 @entity2967 @entity1492 @entity421 @entity85
In the radiographic assessment of primary @entity85 , it is important for therapy planning to accurately define the extent of a @entity5 . Using a double spin-echo pulse sequence, the T1 and T2 relaxation times and relative @entity3884 densities of several neoplastic tissues and of several normal tissues in four @entity1 were measured. @entity5 measured included one @entity1492 , two @entity421 , and one @entity2967 . Normal tissues measured included normal muscle, fat, and bone marrow. Using a mathematical model of the double spin-echo pulse sequence, the intensity difference between each @entity5 and each normal tissue for multiple values of TR and TE was calculated. These calculated intensity differences were then used to plot isodifference contour curves for each tissue pair. These plots enabled us to pick combinations of TR and TE that optimized the signal difference between @entity5 and normal tissue. When comparing @entity5 with predominantly fatty tissue such as marrow or subcutaneous fat, optimal signal difference in our imager occurred at a TR of 600 to 800 msec and a very short TE. When comparing @entity5 with muscle, optimal signal difference occurred with very long TR times, and TE times ranging from 30 to 90 msec. These preliminary results suggest that an optimal scanning protocol for primary @entity85 should contain at least two different pulse sequences with widely separated TR values (500 and 2000 msec in our instrument), and short to intermediate values of TE (28 and 56 msec in our instrument). It is believed that analysis of isodifference contour plots is a useful method for optimizing intensity differences between any two tissue types.
