Medical Screening Images With Gradient Echo Pulse Sequences
GE T1 weighted
GE T1 weighted images usually use the following order depending on the scanner used: SPGR (General Electric), RF-FAST (Marconi, formerly Picker), FLASH (Siemens), and T1-FFE (Philips). The flip angle should be considered when you want to obtain T1 weighted images. Small flip angles, normally those less than 90, are normally used in GE sequences and also short TRs, which are approximately 150ms. This will produce a small signal-to-noise ratio (SNR) through short repetition periods. 30 RF pulse can be used to avoid loss of signal, and it will also increase magnetization to 86% of equilibrium value. At this rate, the recovery of T1 is almost complete and in a short period of time, full relaxation will be obtained.
Gradient-echo T2* weighted images
GE T2* weighted images normally use the following order depending on the scanner being used, for example, T2-FFE (Philips), FISP (Siemens), CE-FAST (Marconi) and GRE (General Electric). It is important to keep small whenever you are using one of these scanners in order to prevent T1 weighting. Multiple slices can be obtained if TR is short for quick scanning or scanning is done long enough. This will increase TE and T2* weighted images will be achieved. The T2* weighted images are mainly used in imaging musculoskeletal or haemorrhage detection.
Gradient-echo T2 weighted images
To obtain GE T2 weighted images, it is fundamental to have spin-spin time for relaxation. This will enable you to describe the speed of transverse magnetization decays. The homogeneous magnetic field can also produce GE T2 weighted images in a perfect way. Different magnetic field strengths caused by inhomogeneities or susceptibility in different parts of the body and in the main magnetic field can cause the transverse relaxation to speed up. However, this will not affect the relaxation of spin-lattice.
Gradient-echo PD-weighted images
The same type of sequence used in the GE T1 weighted image can be used to obtain PD-weighted images. The TR should be set to be as short as possible, especially for a 3D scan, or it can also be set long enough to be able to obtain the required slices. The echo time should be short to avoid T2 decay, and it should also be small to prevent the formation of T1 contrast.