Faculty Bibliography

This study compares two potential magnetic resonance imaging (MRI) indices for noninvasive early detection of tumor response to chemotherapy: the spin-lattice relaxation in the rotating frame (T1rho) and the transverse relaxation time (T2). Measurements of these relaxation parameters were performed on a s.c. murine radiation-induced fibrosarcoma (RIF-1) model before and after cyclophosphamide treatment. The number of pixels exhibiting T1rho values longer than controls in viable regions of the tumor increased significantly as early as 18 h after drug administration and remained elevated up to 36 h after treatment (P < 0.005). Although a trend of increasing T2s relative to controls was noted in viable regions of the tumor 36 h after treatment, the changes were not statistically significant. Histological examination indicated a decrease in mitotic index that paralleled the changes in T1rho. We conclude that T1rho measurements may be useful for noninvasive monitoring of early response of tumors to chemotherapy.

(17)O-decoupled (1)H spin-echo imaging has been reported as a means of indirect (17)O detection, with potential application to measurement of blood flow and metabolism. In its current form, (17)O decoupling requires large RF amplitudes and a 180 degrees refocusing pulse, complicating its application in volume and surface coils, respectively. To overcome this problem, we have developed an (17)O-decoupled proton stimulated echo sequence ("STEAM decoupling") to allow (17)O detection with a surface coil. A high B(1) amplitude is easily generated, allowing complete decoupling of (17)O and (1)H. Slice-selective, (17)O-decoupled (1)H imaging is readily performed and the sequence is easily adapted for localized spectroscopy. Intrinsic correction for variations in B(1) and further compensation for B(1) inhomogeneity are discussed.

Sodium multiple quantum (MQ) spectroscopy of the human breast in vivo was performed. Double quantum (DQ) filtered spectra were used to demonstrate the existence of a non-vanishing (residual) quadrupolar interaction in the tissue. Triple quantum (TQ) filtered spectra were used to measure the two time constants associated with the biexponential transverse relaxation times of sodium in biological tissues. The two time constants were found to be 0.64 and 26.57 msec. The potential applications of this finding are discussed.

The preliminary results of magnetization transfer (MT) imaging on a whole body 4.0 T system are presented. Cooked egg phantoms and several volunteers were imaged on 1.5 and 4.0 T magnets interfaced to GE Signa scanners. The MT ratio (MTR), signal difference to noise ratio (SDNR), and contrast parameters were measured at both fields and compared. Furthermore, single-shot Z-spectroscopy was used to characterize the frequency dependence of the MT phenomenon. The results show that MT imaging can be safely performed at 4.0 T without exceeding limitations of radio frequency power. The MT effect is more pronounced at the higher field, leading to better quality images with higher contrast and SDNR. The Z-spectra are not markedly different at the higher field although the MTR is greater. The potential applications of this technique to study neurodegenerative diseases, as well as, perfusion imaging and angiography are discussed. J. Magn. Reson. Imaging 1999;10:527-532.

The effects of mechanical compression on the multiple quantum coherences generated from sodium ions in articular cartilage were investigated. Cartilage samples obtained from bovine patellae were studied during compression at 0.7 MPa (100 psi) for 1 hour. The double quantum filtered spectra showed marked lineshape changes in the compressed samples. Compression did not seem to influence the lineshapes of the single quantum and triple quantum filtered spectra significantly. We found that the residual quadrupolar interaction was reduced in the compressed samples. Changes in the ordering of collagen fibers may be responsible for the observed effect.

Spin-lattice relaxation in the rotating frame (T1rho) dispersion spectroscopy and imaging were used to study normal and enzymatically degraded bovine articular cartilage. Normal specimens demonstrate significant T1rho "dispersion" (approximately 60 to approximately 130 ms) in the 100 Hz to 9 kHz frequency range. Proteoglycan-degraded specimens have 33% greater T1rho values than collagen-degraded or normal samples. T1rho-weighted images reveal structure not found in conventional T1- or T2-weighted images. Our results suggest that T1rho measurements are selectively sensitive to proteoglycan content. The potential of this method in distinguishing the early degenerative changes in cartilage associated with osteoarthritis is discussed.