• Object ID: 00000018WIA30D45970GYZ
  • Topic ID: id_40021706 Version: 1.3
  • Date: Feb 25, 2022 3:53:33 PM

PROBE SVQ

Consider this information when modifying PROBE SVQ scan parameters. For specific scan parameter values, select a protocol from your GE or Site library.

The prescription of a PROBE/SVQ data acquisition is rather restricted. Only a limited number of scan prescription parameters may be selected for optimization. For specific scan parameter values, select a protocol from your GE or Site library.

  • Scan selections: MRS Mode, Spectroscopy family, PROBE-P or PROBE-S pulse.

General

  • Graphic Rx allows you to determine the size and location of the PROBE/SVQ voxel. See Single Voxel spectroscopy procedure for details.
  • Sixteen non-water suppressed excitations are acquired to create the reference data. Similarly, PROBE/SVQ data processing or reconstruction follows a fixed path:
    • Creatine (Cr) is the chemical species used as the reference for the calculated ratios and for data processing. The reference resonance is used to establish the frequency and line width deviations of the spectrum from a standard frequency and line width. This information is used to preprocess the spectrum before fitting.
    • The spectrum is reconstructed (processed) with water subtraction, and quantitative analysis is performed as described in more detail just below.
    • The frequency of the water resonance is temperature dependent. To correctly locate the four metabolite frequencies relative to the water frequency (a system frequency reference), the frequency differences between water and the four metabolites are defined for 37° C (the normal human temperature). The automatic quantitative analysis of PROBE/SVQ data acquired from a phantom not at 37° C will fail.

Scan parameter

  • Frequency direction: Selecting Freq DIR choice other than default reorders the slice selection in the pulse sequences by swapping the gradients normally associated with the frequency and phase gradients; e.g., if the default order is X and Y, the swapped order would be Y and X.
  • NEX: It determines how many excitations are summed to form a single frame of raw data and sets the RF phase cycling method; when the phase cycle is 2, the phase of the first slice selective RF pulse is alternated from excitation to excitation; when the phase cycle is 8, the phase of each of the 3 slice selective RF pulses is alternated during the acquisition of 8 excitations.
  • TE: Typical longer echo time selections are 144 ms and 288 ms (these times are related to the 7 Hz coupling between the two peaks in the lactate doublet).
  • TR: For voxel imaging, use a much shorter TR (e.g., < 300 ms).

User CVs

Click the Advance tab to view the available User CVs. The CVs may vary based on the field strength and selected scan and imaging parameters.

  • Scan Mode
    • Set to 0 (to acquire an image from the voxel).
    • Set to 1 (to acquire a spectrum from the voxel).
  • Total Number of Scans
    • It is water suppressed excitations acquired to create the “signal” data set.
    • For PROBE-P, for an 8 cc voxel, set it to 64.
    • For PROBE-S, for an 8 cc voxel, set it to 128.
  • A number of the PROBE/SVQ data acquisition parameters are set to fixed values, and can not be changed during the prescription:

Post-process tasks

There are multiple compatible post-process tasks. For details, see Add post-process task.

  • Brain Spectroscopy (2D & 3D CSI)
  • Image Enhancement Filters