J. R. Singer

Blood Flow Rates by Nuclear Magnetic Resonance Measurements

Blood flow rates may be determined by nuclear magnetic resonance relaxation time measurements. A set of experiments carried out on the flow of blood in mice tails has demonstrated the feasibility of the scheme. Two simple measurement methods are described, and the pertinent equations are given. In addition, some procedures for using nuclear magnetic resonance and electron paramagnetic resonance for tracing the flow of specific materials in the body are outlined.

Image Reconstruction of the Interior of Bodies That Diffuse Radiation

A method for reconstructing images from projections is described. The unique aspect of the procedure is that the reconstruction of the internal structure can be carried out for objects that diffuse the incident radiation. The method may be used with photons, phonons, neutrons, and many other kinds of radiation. The procedure has applications to medical imaging, industrial imaging, and geophysical imaging.

NMR diffusion and flow measurements and an introduction to spin phase graphing

Diffusion and flow can be measured very delicately and accurately using an NMR system. The essence of the method is that motion of magnetic nuclei in a magnetic field and a magnetic gradient results in those nuclei changing their Larmor precession frequency and their phase angle in the field. Since NMR can be set up to measure the number of nuclei at specific phase angles, the motion of groups of nuclei can be determined very accurately. Self-diffusion of molecules was first measured by Hahn in 1950. Self-diffusion of molecules and flow of molecules can be separated in an NMR measurement as was shown by Carr and Purcell in 1954. This review describes some techniques of NMR diffusion and flow measurements, and a method of plotting phase angles of isochromatic spin groups for theoretical analyses and simulations of NMR experiments.

Some Magnetic Studies of Normal and Leukemic Blood

Blood samples from out-patients of Donner Laboratory and Alta Bates Hospital were studied through measurements of the nuclear magnetic resonance (NMR) relaxation times (T1‘s). Non-leukemic whole blood showed a very nearly linear relationship between 1/T1 values and the hemoglobin concentrations. Blood samples from leukemic patients exhibited a marked departure from the non-leukemic T1 values with corresponding hemoglobin concentrations. Further measurements on blood plasma, packed red cells and whole blood are described. Discussions of the causes of the NMR proton relaxation time variations are given with reference to the basic theories of oxygenation of blood. Proton relaxation times are also affected strongly by protein concentration levels.

Resolution and signal-to-noise relationships in NMR imaging in the human body

When nuclear magnetic resonance techniques are applied to the imaging of structures deep inside the human body, it becomes important to consider the degrading effects of the surrounding body tissues on the signal-to-noise ratio of the received resonance signal. The passage of the NMR signal through the surrounding conductive tissue casues an appreciable loss of signal strength at high frequencies. Also, the presence of a large resistive medium, such as a portion of the body, inside the receiving coil causes a significant amount of thermal noise to be detected. The levels of the signal-to-noise ratio and the corresponding spatial resolution are quantitatively discussed in this paper. Expressions are obtained which enable the resolution to be estimated for a variety of medical imaging systems.

Tomographic imaging with nuclear magnetic resonance.

A technique is described for obtaining tomographic images of hydrogen distribution in animals using nuclear magnetic resonance (NMR). Resonant frequency is proportional to magnetic field strength, so that spatial resolution is achieved by frequency selection and magnetic field shaping. The results of scanning a phantom and two rats are presented.

Transistorized Nuclear Resonance Magnetic Field Probe

A transistorized marginal oscillator type of nuclear resonance probe is described. The main advantages of transistor use are in obtaining portability, eliminating external power sources, and low cost. The sensitivity and stability equaled that of a standard transition vacuum tube circuit when compared using protons in water.

Tomography Of Hydrogen With Nuclear Magnetic Resonance (NMR), And The Potential For Imaging Other Body Constituents

Nuclear magnetic resonance (NMR) imaging has already attracted a great deal of attention because it is non-hazardous and because the intrinsic NMR contrast appears to be considerably higher than x-ray contrast. On the other hand, the in-vivo NMR characteristics of normal tissues are not well understood, and no reliable data exist on the potential for differentiating normal from abnormal tissues, or benign from malignant lesions.

Radiation Damping Effects in Two Level Maser Oscillators

Several experiments [1,2] have noted recently that when an inverted two-level spin system was permitted to radiate spontaneously, the resulting oscillation was characterized by an appreciable amplitude modulation. The phenomenon was first believed to be the result of interference of different spin packets in an inhomogeneously broadened spectrum [1]. A theoretical analysis (which will be reported separately) shows that this is not the case. The spins are not independent but are coupled together by means of their radiation field. This explanation has since been by its original authors.

Paramagnetic Maser Oscillator Analysis

A physical and mathematical description of maser oscillator is given with particular emphasis upon explaining the structure of the output line shape. Several approaches to the problem are taken. A qualitative description of the motion of the spin vector is followed by a derivation of the equations pertinent to the interaction of a tuned circuit (microwave cavity) and precessing spins. The resultant equation is nonlinear. Approximate solutions are given and these are plotted as output amplitude vs time. In addition, the equations are solved with numerical solutions for specific experimental conditions by means of a digital computer. The numerical results are compared with experimental data including that taken in our laboratory. The field‐swept oscillator line shapes are explained by the analysis, and the steady state oscillator is described as well.