A formalism is presented that concisely describes the magnetization of a sample subjected to a periodic series of RF pulses. In this formalism, the steady state of the magnetization is shown to be a sum of magnetic substates, each with unique contrast characteristics. When more than one substate contributes to a given image, the substates interfere with each other, producing ghosts and other artifacts. Properly designed gradient protocols can image single substates, producing ghost-free images. The contrast of the image depends largely on the choice of the imaged substate. Analytic solutions for unspoiled, RF spoiled, and gradient spoiled magnetizations are presented.

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Data from existing tables of normalized glandular doses in mammography were parametrized to determine analytical expressions that match tabulated results within known uncertainties. The parametrization was performed for three different target/filter combinations (molybdenum target-molybdenum filter, molybdenum target-rhodium filter, and rhodium target-rhodium filter) and three different breast compositions (100% adipose, 50% adipose-50% glandular, and 100% glandular). The analytical expressions provide the normalized glandular dose for any breast composition within stated ranges of tabulated input parameters (kVp, half-value layer, and breast thickness). The maximum difference between tabulated and parametrized data is 1.29%, which is smaller than the stated 2% uncertainty in tabulated dose data due to uncertainties in the x-ray spectra models used to generate the tables. Analytical expressions are easily coded to create custom functions that return the normalized glandular dose for the set of input parameters. Examples of implementation are presented in Microsoft Visual Basic for Applications (VBA).

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The purpose of this paper is to present basic functional principles of high frequency x-ray generators. The emphasis is put on physical concepts that determine the engineering solutions to the problem of efficient generation and control of high voltage power required to drive the x-ray tube. The physics of magnetically coupled circuits is discussed first, as a background for the discussion of engineering issues related to high-frequency power transformer design. Attention is paid to physical processes that influence such factors as size, efficiency, and reliability of a high voltage power transformer. The basic electrical circuit of a high frequency generator is analyzed next, with focus on functional principles. This section investigates the role and function of basic components, such as power supply, inverter, and voltage doubler. Essential electronic circuits of generator control are then examined, including regulation of voltage, current and timing of electrical power delivery to the x-ray tube. Finally, issues related to efficient feedback control, including basic design of the AEC circuitry are reviewed.