MR velocity imaging by phase display

The ability of the nuclear magnetic resonance signal to encode information about macroscopic motion has been recognized since the works of Hahn and Carr and Purcell. In the medical imaging setting this ability has led to a variety of ingenious magnetic resonance flow imaging schemes that ultimately may become competitive with X-ray angiography in sensitivity and specificity while remaining radically noninvasive. This work demonstrates that conventional spin-echo Fourier transform image acquisitions naturally encode a component of flow velocity that lies within the image plane. By displacing just the real part of the complex image data (phase display), the velocity distribution within the subject is revealed in image form. This method of flow imaging requires neither special pulse sequences nor image reconstruction and format software for its implementation. Further, images that intersect a flow channel longitudinally, demonstrating in-plane flow, yield an unusually large quantity of physiologic information per image. Phantom and in vivo flow images are presented. Also described is a phantom based on a rotating disk that enables calibration of the velocity/phase-shift constant for an untested pulse sequence.