Figure 1. Sequence Options window.

Once you have chosen the pulse sequence required there are several extra Sequence Options you can select from. The choice of options is dependent on compatibility with the Pulse Sequence and so the actual options available will be a subset of the panel shown in Figure 1.

Make your selection using the left-hand mouse on the diamond button.

Number of Echoes

This option determines how many echoes will be collected within a single Repetition Time. Select the number of echoes required from the options available. The effective echo times you require are then set on the Sequence Parameters page.

Number of Interleaves

This option allows you to determine different methods of K-Space filling.

When using Echo Planar Imaging (EPI) you can chose between a Single Shot approach, where K-Space is filled in one Repetition Time (TR), or a multi-shot approach where several TRs are used. Choose the number of shots by highlighting one interleave for Single Shot and from the other options for multi-shot.

Flow Compensation

Flow compensation helps to minimise artefacts caused by flow using a technique of gradient moment rephasing, or nulling, which compensates for the altered phase values of nuclei flowing along a gradient direction. This option should be chosen when flow artefacts are possible, in order to improve image quality.

Fat Saturation

Fat saturation applies a frequency selective 90 degree RF pulse to pre-excite and dephase the signal from fat. When an imaging pulse sequence is then played out the signal from fat becomes saturated. This option is useful, particularly when using EPI sequences, to avoid the large chemical shift artefact that is otherwise present when imaging at high magnetic field.

Inversion Recovery

Inversion recovery utilises a 180-degree inverting pulse at the beginning of a standard pulse sequence in order to null out specific signal from the MR image. By altering the time between the 180 degree pulse and the start of the imaging portion of the pulse sequence (the inversion time or TI time) signal from different tissue can be nulled out depending on their T1 relaxation times. E.g., Fat, CSF etc. This option also allows for good contrast manipulation between the different tissues being imaged (e.g., grey and white matter). Once this option has been selected the invert (TI) time can be entered in the Sequence Parameters page.

Use the NEXT button to move to the next menu page