Detection of early gamma-postirradiation effects in murine spleen by proton NMR relaxation times.

BACKGROUND: It was our aim to evaluate the potential of proton relaxation times for the early detection of radiation-induced spleen changes. MATERIALS AND METHODS: Female Swiss mice were irradiated with doses ranging from 0.05 Gy to 4 Gy. The body weight, the spleen weight and the spleen water content of single animals were determined. Measurements of longitudinal (T1) and transversal (T2) proton relaxation times of the spleen samples were performed in a 0.47 T spectrometer. Histological examinations of the control and irradiated organs were performed. RESULTS: NMR measurements during the first five days after irradiation showed that total body gamma-irradiation with doses from 1.5 Gy to 4 Gy results in decreasing T1 of the murine spleen. Significant shortening in T2 was observed for the spleen of animals irradiated with a dose of 4 Gy. Histological examinations demonstrated subnormal architecture in slices derived from animals irradiated with 2 Gy and 4 Gy. CONCLUSION: The fluctuations of the spleen T1 and T2 of irradiated mice are correlated with relative spleen weight and can be used to estimate radiation induced changes in this organ.

A new fast and unsynchronized method for MRI of viscoelastic properties of soft tissues.

Quantitative measurement of mechanical properties of biologic tissues may have several applications for diagnosis or biomechanic modeling in sports medicine, traumatology, or computer-guided surgery. The magnetic resonance imaging (MRI) methods previously tested for these applications all required synchronization between MRI acquisition pulses and the mechanical stimulation. A new unsynchronized method operating with no prior knowledge of intensity, direction, and frequency of the mechanical waves is proposed. A specifically modified SPAMM (SPAtial Modulation of Magnetization) sequence has been used, operating on a 0.2-T MRI system. The experimental results obtained on test objects fit well with theoretical calculations. The new proposed method is very fast (a less than 5-second acquisition time) for routine clinical use.

Viscoelastic property detection by elastic displacement NMR measurements.

An attempt was undertaken to analyze the phase changes in the transverse magnetization component, M[perp], determined in NMR response by an elastic wave in the presence of two pulses with opposite magnetic field gradient directions. The obtained theoretical results indicate that such changes are significant in biologic tissues. Their measurement by NMR opens up new possibilities for detecting the displacement and some viscoelastic properties such as the adiabatic compressibility coefficient, amplitude wave damping coefficient, frequency and dispersion strength of elastic relaxation processes, etc. The method may be useful in basic applied research and in medical diagnosis of some diseases resulting in the variation of elastic properties of biological tissues, eg, atherosclerosis.

Proton nuclear magnetic resonance spectroscopy of plasma lipoprotein: technical problems and potential interest in cancer disease.

This paper reviews several methods presently available for analysing lipoprotein NMR spectra. Two main steps can be distinguished: NMR signal processing and data analysis. Time domain (wavelet transform) and frequency domain (curve fitting) signal processing methods are compared. Statistical methods of data analysis (Ascending Hierarchical Classification, Correspondence Analysis and Principal Component Analysis) have been tested on simulated NMR data of plasma lipoprotein with different numbers of sampling points and different noise levels. These few examples clearly attest that the NMR approach to complex "mixture" (such as body fluids) analysis is emerging from its infancy. New interest in plasma lipoprotein analysis in cancer biology is finally discussed in the light of previous clinical and experimental results and of understanding of lipid metabolism in cancer.

In vivo evidence of abnormal mechanical and oxidative functions in the exercised muscle of dystrophic hamsters by 31P-NMR.

Mechanical properties and metabolic adaptation to exercise in skeletal muscle of dystrophic hamsters were studied with an in vivo 31P-NMR multistep fatigue test. Three successive 20-min steps with increasing rhythms of tetanic stimulation were followed by a 20-min recovery period. Fatigue in dystrophic hamsters (DH) developed more rapidly and was greater than in normal hamsters (NH); total mechanical performance per min increased step by step in NH while it decreased in DH, showing a progressive mechanical impairment of the dystrophic muscles. ADP and PCr recovery rates were significantly reduced in DH muscles. Acidosis appeared in both DH and NH and persisted in DH throughout the test, suggesting reduced mitochondrial oxidative capacity of the dystrophic muscle. The pH recovery rate was reduced in DH muscles suggesting a reduction in export protons capacity. These results provide evidence of impaired mitochondrial function and intracellular ionic regulation in the dystrophic muscle, associated with the lack of dystrophin and dystrophin-associated glycoproteins in the DH.

Measurements of the effect of storage at various temperatures on the T1 of ex vivo tissues.

The detailed measurements of the effects of storage at various temperatures on the nuclear magnetic resonance (NMR) spin-lattice relaxation time T1 are reported. On the basis of the results, a method to monitor tissue transformation in hyperthermia of biological systems using magnetic resonance imaging (MRI) techniques is discussed. The method was found on proton relaxation time spin-lattice T1 variation measurements. Parameter F described as tissue structure transformation and/or protein denaturation rate index is discussed.

MR imaging of viscoelastic properties.

Mechanical waves in magnetic resonance imaging, which have been suggested for possible clinical applications, were analyzed with regard to imaging of the viscoelastic properties of large objects. The method is based on the Larmor frequency modulation caused by the application of mechanical waves. Possible clinical applications include all diseases that result in a change in the mechanical properties of biologic tissues (eg, atherosclerosis).

Temperature relationships of proton spin-lattice relaxation time T1 in biological tissues.

Temperature relationships of the proton spin-lattice relaxation time T1 for animal and human tissues, both healthy and tumorous, are presented. An irreversible decrease in time T1 within the temperature range TT1max less than T less than TT1min, was found. The temperature relationships of T1 for healthy and tumorous tissues were of a similar nature. The relationships obtained are discussed on the basis of the FETS model.

Magnetic transverse relaxation time of the protons in transplantable melanotic and amelanotic melanoma and in some inner organs of golden hamster Mesocricetus auratus, Waterhouse.

The proton magnetic relaxation time T2 was measured in transplantable melanotic and amelanotic melanoma as well as in some organs of golden hamsters of agouti and albino strains. These measurement indicate that the proton relaxation rate depends upon the properties of the biopolymers contained in the tissues, such as melanin, upon the age of the animals, but also on pathological changes different from the neoplastic transformation of the tissues, such as oedema.