Proton reference frequency method

In Section 3.1.1, the dependence of the water chemical shift on temperature was described. The same dependence is found for water in tissue in vivo, and methods and applications based on the proton reference frequency (PRF) are involved in the vast majority of current in vivo temperature imaging studies. 

Figure 3.2. The increase in proton resonance frequency since the introduction of NMR spectroscopy as an analytical method (adapted with permission from reference [1] and extended Copyright 1995, Elsevier).

Then in 1913 Moseley, working in Manchester, discovered what we now call atomic number (Moseley, 1913). He began by photographing the X-ray spectrum of 12 elements, 10 of which occupied consecutive places in the periodic table. He discovered that the frequencies of features called K-lines in the spectrum of each element were directly proportional to the square of the integer representing the position of each successive element in the table. As Moseley put it, here was proof that "there is in the atom a fundamental quantity, which increases by regular steps as we pass from one element to the next." This fundamental quantity, first referred to as "atomic number" in 1920 by Ernest Rutherford, is now identified as the munber of protons in the nucleus of an atom. Moseley s work provided a method that could be used to determine exactly how many empty spaces remained in the periodic table. 

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