《Principles Of Magnetic Resonance Imaging》教学AppendixB.pdfVIP

AppendixB Glossary This appendix presents a glossary of technical terms used in this book. Note that some of the terms have broader meanings than are described here in the context of MRI applications. For a comprehensive glossary of MR terms, the reader is referred to a publication by the American College of Radiology: Glossary ofMR terms (4th ed., ACR, Reston, VA, 1995). Aliasing: Image error due to undersampling of k-space. In Fourier reconstruc- tion, aliasing manifests itself as folding over (ghosting) of some parts of the ob- ject. In projection reconstruction, angular undersampling results in streaking arti- facts. Angiography: Application of MRI techniques to produce images of blood ves- sels. Angular frequency: Frequency of oscillation or rotation commonly measured in radians/second. Angular momentum: Inertial property of a rotating body that, in the absence of external forces (torques), tends to maintain the same axis of rotation. When an external torque is applied to a rotating body, the angular momentum changes, resulting in precession. Angular velocity: Vector quantity specifying both the speed and direction of object rotation. Artifacts: Spurious image features caused by imperfections in the imaging in- strumentation and/or technique. Asymmetric k-space sampling: Collection of more data points on one side of the k-space origin than on the other. This data acquisition scheme is often used in half-Fourier imaging experiments. 371 372 Appendix B Glossary Bandlimited function: A function is called frequency bandlimited if its Fourier transform has nonzero values only inside a finite frequency band, whereas a func- tion is said to be space bandli