Image contrast is normally described as proton density: T1-weighted or T2-weighted - Essay Example

Fat has a rapid T1 recovery time, and hence the T1 time of fat is short. Water, however, takes much longer to recover, and the T1 time of water, therefore, is long. In order to achieve maximum contrast between fat and water, it is advisable to make the selected TR shorter in order for the tissue to regain the longitudinal magnetization and the subsequent RF pulses are affected by the partial saturation. This makes the fat vector gain more longitudinal magnetization as compared to water and create fat to appear brighter on the T1weighted image.

T2 weighted image After the RF pulses are applied to the spins, the spin interaction appears. This causes the T2 to decay due to the nuclei interaction in the magnetic fields in the region. This also reduces the transverse magnetization. It is also imperative to note that the water and the fat have varying T2 decay. This is mainly caused by the rapid exchange of energy. The fat have very short T2 TIME, on the other hand, the processing of water has very long T2 TIME DUE TO ITS INEFICINCY. The TE is responsible for controlling the amount of decay (T2) appearing before the reception of the signals.

Therefore to acquire a very clear difference between the water and the fat, it is advisable to increase TE and TR. . On the other hand, there are tissues that have a lot of proton contents. These classes of tissues include the brain and are manually characterised by high ability to of creating a high. The proton density and the T2 images can be easily acquired in a single sequence (double echo). This process uses the long TR and short TE. The first echo is achieved by use of the long TR and the short TE, while the second echo is achieved by long TE and long TR to acquire the T2 weighted images.

Proton density is just a representation if the number of hydrogen atoms that are in the tissue, for example, the CSF contains higher proton density as compared to the bone. For the proton density that occurs, it is important to reduce the impact of the T1 weighting imaging and THE T2 weighting imaging through making the TR longer and TE shorter (McRobbie 2007). b) Describe how images proton density, T1-weighted or T2-weighted contrast, plus T2* contrast, are acquired with gradient echo pulse sequences.

The flip angle of the gradient echo pulse sequence is adjusted over a range of close to 80m degrees to get a larger tip angle in order to acquire more T1 weighting to the formed image; this will also give a smaller tip angle to provide more T2 and T2* weighting to the so formed images. Proton density images On the other hand, the proton density images can be acquired by the use of low flip angles and fast image acquisition, short TR and TE times. T1 weighted images This can only acquired by the GE pulse sequence through the use of mid range pulse angles, short TR and TE times.

The flip angles are enlarged (70 -110 degrees), the TE are shortened (5-10 ms) and the TR approximately less than 50 ms T2 weighted images This is acquired with the GE through mid-range pulse angles with