Image Synthesis in the Image Synthesiser

Image Synthesis

First, choose which pulse sequence contrast you want to emulate:

. A conventional spin-echo pulse sequence.
. An inversion-recovery pulse sequence, such as a FLAIR or a STIR.
. A double inversion-recovery pulse sequence.

For the IR and DIR pulse sequences, you can also select Synthesise a spin-echo sequence

. If selected, the magnitude of the signal intensity will calculated, rather than the signed (phase-sensitive) signal intensity.

Next, set the scan timing parameters:

. The scan repetition time. Applicable to all pulse sequences. Set the TR in milliseconds by typing in the value (and pressing the return key) or moving the slider.
. The scan echo time (time between the excitation pulse and the image acquisition). Applicable to all pulse sequences. Set the TE in milliseconds by typing in the value (and pressing the return key) or moving the slider.
. The inversion time. For the IR pulse sequence, this is the time between the inversion pulse and the excitation pulse. For the DIR pulse sequence, this is the time between the inversion pulse and the second inversion pulse. Visible and applicable only when the inversion-recovery or double inversion-recovery pulse sequence is selected. Set the TI in milliseconds by typing in the value (and pressing the return key) or moving the slider.
. The second inversion time (time between the second inversion pulse and the excitation pulse). Visible and applicable only when the double inversion-recovery pulse sequence is selected. Set TI2 in milliseconds by typing in the value (and pressing the return key) or moving the slider.

As you change the pulse sequence or timing parameters, the synthetic image is updated in Jim's display.

Note: as you change one of the timing parameters, adjustment may be made automatically to others to preclude infeasible combinations. For example, TE can never be longer than TR, so if you are reducing TR, the TE may also be shortened.

By default, the Image Synthesiser expects the units of intensity in the input images to be seconds. This, inevitably, requires the images to be in floating-point format or to have intensity rescaling applied in the image header. If the image units of intensity are milliseconds, then select:

Input image units are milliseconds for the Image Synthesiser input images

If the data for the PD map, T₁ map or T₂ map were collected using more than one pulse sequence, then the images may be slightly out of alignment. To automatically bring them into register, you can select:

Checkbox to bring the input images into register

When selected, the T₁ map and T₂ map will be registered to the PD map, and when the registration is complete, the synthetic image will be loaded into the display. Depending on the speed of your computer, registration may take several minutes, but will only need to be redone if you select new input image(s).

Below is an example synthetic FLAIR image.

FLAIR image synthesised using the Image
Synthesiser
Synthetic FLAIR image. TR=8000 ms; TE=140 ms; TI=2320 ms

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