Gradient echo

Speck O, Chang L, DeSilva NM, Ernst T. Perfusion MRI of the human brain with dynamic susceptibility contrast gradient-echo versus spin-echo techniques. J Magn Reson Imaging 2000 12 381-387. 

Donahue KM, Krouwer HG, Rand SD, Pathak AP, Marszalkowski CS, Censky SC, Pros RW. Utility of simultaneously acquired gradient-echo and spin-echo cerebral blood volume and morphology maps in brain tumor patients. Magn Reson Med 2000 43 845-853. 

Fig. 1.20 Gradient-echo based pulse sequences based on low flip angles. When low flip angles and short image repetition times are employed at the expense of transverse magnetization during the course of the complete image acquisition, this represents a FLASH sequence (without ). The combination of flip angle and repetition time can be adjusted in...

Fig. 1.21 Echo Planar Imaging (EPI) pulse sequence. Gradient-echo based multiple echoes are used for fast single-shot 2D imaging. Slice selection along Gs and frequency encoding along C, are utilized. Phase encoding is realized using short blipped gradient pulses along Gp.

Figure 2.2.14 shows cross-sections of salmon acquired with a gradient echo sequence (TR = 30 ms, TE = 15 ms, slice thickness = 4 cm, image matrix = 128 x 128, total acquisition time = 3.84 s). For the female salmon, roe were clearly visualized as dark regions because the T2 is shorter than that of the surrounding tissues. For the male salmon, milt was observed instead of roe. However, the image intensity of the milt was similar to that of the surrounding tissues. 

NMR diffusometry Decay of spin echoes in the presence of a magnetic field gradient (echo attenuation curve) Price (1996, 1997, 1998a)... 

J. B. Weaver, E. E. Van Houten, M. I. Miga, F. E. Kennedy and K. D. Paulsen, Magnetic resonance elastography using 3D gradient echo measurements of steady-state motion, Med. Rhys., 2001, 28, 1620-1628. 

Fig. 10. Sequence for the assessment of magnetization transfer (MT) effects. Images recorded without (a) and with MT prepulses (b) have to be subtracted. In the presented example a standard gradient-echo sequence is used for MT imaging. The MT prepulse is Gaussian-shaped with a flip angle of 600° and 1.5 kHz off-resonance frequency.

Abbreviations D, self-diffusion coefficient ge, gradient-echo IR, inversion recovery IRFT, inversion recovery fourier transform MRS, magnetic resonance spectroscopy PD, proton density PFGSE, pulsed field gradient spin echo se, spin-echo. 

Abbreviations ge, gradient-echo IR, inversion recovery PD, proton density se, spin-echo. 

Hall and co-workers have imaged overripe melons suffering from internal necrosis with both spin-echo and gradient-echo sequences at 2 T (86 MHz). 

The spin-echo images showed no obvious differences between ripe and overripe samples, but the gradient-echo images of the over-ripe melons showed decreased intensity. It was surmised that the increased air spaces in the overripe tissue intensified the internal magnetic susceptibility gradients, whose dephasing effects can be refocused by a spin-echo but not by a gradient-echo. 

The Pulsed Field Gradient Echo (PFGE) NMR Experiment... 

THE PULSED FIELD GRADIENT ECHO (PFGE) NMR EXPERIMENT... 

Fig. 1. The pulse sequences for the pulsed field gradient echo NMR experiment (a) Hahn echo, (b) stimulated or three-pulse sequence.

Figure 4. Accumulation of iron-labeled MSC in the renal cortex. Animals were anesthetized and coronal T 2-weighted gradient echo in vivo magnetic resonance images (MRl) were obtained before (A) and immediately (B) or 3 days (C) after injection of magnetically labeled (iron-dextran) syngeneic mesenchymal stem cells.

Figure 11 shows the i 2 dependence on the particle size for systems containing a constant amount of magnetized material, without refocusing pulse (like in a gradient echo sequence), and with 7 different echo times used in CPMG sequences. 

---