Felix Bloch and the Nuclear Magnetic Resonance Method

Felix Bloch
Image: Stanford University / Courtesy Stanford News Service

On October 23, 1905, Swiss-born American physicist Felix Bloch was born. He is best known for his investigations into nuclear induction and nuclear magnetic resonance, which are the underlying principles of MRI. He was awarded the 1952 Nobel Prize in Physics for developing the nuclear magnetic resonance (NMR) method of measuring the magnetic field of atomic nuclei.

Felix Bloch was educated at the Eidgenössische Technische Hochschule in Zurich, starting out in engineering. Later on, he increased his interest in physics and attended the lectures of Peter Debye and Hermann Weyl at ETH Zürich and Erwin Schrödinger at the University of Zurich.

One of his fellow students was also John von Neumann. Bloch graduated in 1927 and continued his studies at the University of Leipzig. There, he met and studied with Werner Heisenberg, he received his Ph.D. in 1928. His doctoral thesis established the quantum theory of solids, using Bloch waves to describe the electrons.

Bloch remained in Europe in the following period. He studied with Wolfgang Pauli in Zürich, Niels Bohr in Copenhagen and Enrico Fermi in Rome. He was then appointed privatdozent in Leipzig and had to leave Germany due to the rise of the Nazi party. Bloch continued his career at Stanford University and later Berkeley. He became a citizen of the United States and worked on nuclear power at Los Alamos National Laboratory during World War II before resigning to join the radar project at Harvard University. Felix Bloch focused on his research on nuclear magnetic resonance and nuclear induction. Nuclear magnetic resonance was first described and measured in molecular beams by Isidor Rabi around 1938. In 1944, Rabi was awarded the Nobel Prize in physics for this work on the topic. About two years later, Felix Bloch and Edward Mills Purcell expanded the technique for use on liquids and solids, for which they shared the Nobel Prize in Physics in 1952. The three scientists, Rabi, Bloch, and Purcell observed that magnetic nuclei could absorb RF energy when placed in a magnetic field and when the RF was of a frequency specific to the identity of the nuclei. When this absorption occurs, the nucleus is described in resonance. Different atomic nuclei within a molecule resonate at different frequencies for the same magnetic field strength. The observation of such magnetic resonance frequencies of the nuclei present in a molecule allows any trained user to discover essential chemical and structural information about the molecule. The development of Nuclear Magnetic Resonance as a technique in analytical chemistry and biochemistry parallels the development of electromagnetic technology and advanced electronics and their introduction into civilian use.

At yovisto, you may be interested in a video lecture on MRI-Driven Turbulence – MRI-driven Turbulence with Resistivity by Professor Takayoshi Sano at Princeton.

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