MRI: 造影原理

Quick Overview of MR Imaging Principle

From Pixel to Images

MR is very simple… U 65 % H2O N S

Image Formation MR Image Fourier Transform K-Space Data Acquisition

Resonance & Relaxation Data Acquisition MR Signal T1 & T2 Relaxation Mxy Decay Mz Recovery Resonant RF Pulse

Magnetic Field Alignment of H Nuclei Spinning H Nuclei ( In Direction of Bo ) External Static Magnetic Field Bo Spinning H Nuclei ( Random Directions )

In Magnetic Field Spinning H Nuclei Alignment of H Nuclei ( Random Directions ) External Static Magnetic Field Bo Magnet Alignment of H Nuclei ( In Direction of Bo )

Resonance & Relaxation MR Signal Acquisition Mxy Decay Mz Recovery Resonant RF Pulse T1 & T2 Relaxation RF Transmitting System Gradient System RF Receiving System

MR Image K-Space Data Acquisition Fourier Transform Computer Array Processor

Patient + Magnet Without magnetic field : With magnetic field : B = 0 x y B = 0 M = 0 x y B M No net magnetization Low net magnetization

Slice Selection B = B0 + Gz * z Slice Excitation at 0 B  B0 Weaker Field 0 lower field, 0 higher field, 0 Stronger Field 0 z -z +z

Spatial Resolution within the Slice Raw Data p256f1 p256f256 p2f1 p1f1 p1f2 p1f256 (Phase und Frequency Encoding)

Raw Data Matrix (k-Space) ky 1                2                                 N                Raw data matrix or k-space is filled line by line by variation of the Phase Encoding Gradient kx Line Information = Frequencies of the Readout Gradient

Fourier Transformation Frequency Phase x y

Zusammenhang von Orts- und k-Raum Ortsraum FFT FFT-1

3D Sequences 2D 3D No Slice Gaps Thinner Slices Rectangular Slice Profiles Postprocessing with MPR

Segmentierte k-Raumabtastung ky Aufteilung des k-Raums in Segmente 180° 180° 180° 90° RF kx Gs Gp Gr ADC Segment 1 Segment 2 Segment 3