DEPENDENCE OF MAGNETIC-RESONANCE IMAGE (MRI) INTENSITY VALUES ON RELAXATION-TIMES, PULSE INTERVALS AND OTHER SIGNAL ATTENUATION FACTORS

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  • 1 January 1985
    • journal article
    • research article
    • Vol. 17  (1) , 81-100
Abstract
Magnetic resonance image (MRI) pixel intensities were investigated using a phantom containing several uniform size chambers filled with solutions of known relaxation times, and scans of patients and volunteers. Intensities were measured with a variety of pulse intervals typically used for imaging with spin echo (SE) and inversion recovery (IR) sequences at 0.15 Tesla using the back projection (R-THETA) method and at 0.27 Tesla using the 2-dimensional Fourier transform (2DFT)technique. Results were compared with the calculated dependence of MRI signal intensity on relaxation times and pulse interval parameters using the well known functions containing exponential forms. The experimental and the calculated pixel intensity time dependence did not always agree. Factors other than the conventional functions for T1 [spin-lattice relaxation time] and T2 [spin-spin relaxation time] signal decay are important. These factors may include the attenuation of the radiofrequency (RF) signals through inhomogenious lossy dielectric materials (e.g., tissues and organs), the location (coordinate) of the portion of the sample to be imaged relative to the RF coils and the timing and amplitude of gradient pulses relative to the RF input and the detected signals. The flow velocity and diffusions are also important determinants of the signal from blood vessels and body fluids. Further investigation toward more comprehensive understanding of MRI intensities is needed.