Contrast Simulations:

SpinEcho SpinEcho is a magnetic resonance contrast simulator. Given knowledge of the magnetic properties, T1 and T2, it is possible to predict the signal intensity produced by a given tissue when imaged. Technically, this involves solving the Bloch equations for the particular tissue and imaging sequence. The contrast visible in MR images is a function of the intrinsic differences in the the magnetic properties of human tissue; in particular its characteristic longitudinal (T1) and transverse (T2) relaxation rates as well as the proton density of the tissues. In addition, the field strength of the imaging magnet strongly affects the contrast behavior, through both its influence on the tissue T1 and T2 and by the change in effective contrast resulting from the differences in the background noise level and its consequent effect on the "contrast to noise ratio. Spin Echo is available (only) as a standalone Macintosh program. The user manual is supplied with the program.

IRsim pc version This Excel (for Macintosh) spreadsheet simulates the contrast behavior of Inversion Recovery imaging, according to the formula: SI = |exp(-TE/T2){1 - 2exp(-TI/T1) + exp(-(TR-TE)/T1) }|. where TI is the inversion time, TR the repetition time, and TE the echo time. Note: Some instruments present the signed, rather than the absolute signal value The tissue signals are calculated from the inputs in the upper left corner of the spreadsheet. The contrast as a function of each of the major parameters, TR, TE and TI is displayed in graphic form. To use: Enter values for the T1 and T2 of the tissues of interest, as well as starting pulse sequence parameters. The graphs will update immediately. You can alter the x axis of the graphs by putting in different values for MaxTR, MaxTE and MaxTI. The file is supplied as a "protected" Excel spreadsheet with no password; password protection may therefore be freely turned on and off. I hope that you find this useful.

FLASHsim This Spreadsheet simulates the contrast behavior of FLASH imaging, according to the formula: SI =sin(a)*exp(-TE/T2)*(1-exp(-TR/T1)/(1-cos(a)*exp(-TR/T1), where a is the flip angle, TR the repetition time, and TE the echo time. The tissue signals are calculated from the inputs in the upper left corner of the spreadsheet. The contrast as a function of each of the major parameters, TR, TE and TI is displayed in graphic form. To use: Enter values for the T1 and T2 of the tissues of interest, as well as starting pulse sequence parameters, including TR, TE and Flip Angle. The graphs will update immediately. You can alter the x axis of the graphs by putting in different values for MaxTR, MaxTE and MaxFlip. The file is supplied as a "protected" Excel spreadsheet with no password; password protection may therefore be freely turned on and off.

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©1997-1999 Mark S. Cohen, Ph.D.