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Brain spectroscopy in ependymoma

Case Study
Güran, Salih, M.D. Istanbul, Sonomed Imaging Center Turkey
de Kok, Wendy Philips Healthcare Philips Global
Unlu, Melahat Philips Medical Systems Philips Global

Patient history:

A 48-year-old female patient was referred to Sonomed Private Imaging center in Istanbul, Turkey, for an MR imaging and MR spectroscopy examination.


On a conventional MR image a tumorous tissue was identified within the lateral ventricle. MR spectroscopy was done to determine the tissue origin and the grade of the tumor.

MR spectroscopy examination:

The examination was started with fast T2-weighted scans in three orthogonal directions.

(Selected preset procedure: Head_CNS/FastBrain/T2W_TSE)

The images of these scans were used for optimal planning of the spectroscopy scans.

 

A single voxel scan was planned in the ventricular tumor and repeated three times, using different echo times. (Selected preset procedure: Head_CNS/Brain/1VOI_23_exc):

 

  • volume size 20 x 20 x 20 mm
  • repetition time 2000 ms, for sufficient T1-relaxation
  • echo time 1 = 23 ms: for visualisation of short-T2 metabolites
  • echo time 2 = 144 ms: optimal for detection of the lactate doublet at ~ 1.3 ppm, having a 180 degree phase, leading to a negative doublet
  • echo time 3 = 288 ms: leading to a positive doublet of the lactate signal at ~ 1.3 ppm
  • Bandwidth 1000 Hz, nr. of samples 512 (zerofilled to 1024) = spectral resolution ~ 2 Hz
  • 128 measurements: scan time = 4:55 min

 

The spectra were all processed using SpectroView:

SVS TE = 23 ms SVS TE = 144 ms SVS TE = 288 ms
SVS TE = 23 ms
SVS TE = 144 ms
SVS TE = 288 ms

 

Screen captures of the processed spectra show that the NAA-level is reduced in all spectra. Choline levels are increased.

 

Script parameters:

  • initial baseline subtraction = no
  • analysis range = 4.35 - -1.0 ppm
  • baseline terms = 5
  • Gaussian percentage = 90
  • real signal aspect
  • lock relative frequencies / widths = no

 

Additionally, turbo-spectroscopic imaging (TSI) was performed to collect information on the spatial distribution of metabolite concentrations. The planning of this scan was equal to the planning of the transverse T2-weighted TSE sequence, to allow overlay of the metabolite and ratio maps on the anatomical scans.

(Selected preset procedure: Head_CNS/Brain/TSI3_288_exc):

 

  • SI FOV = 230 mm
  • scan matrix = 24 x24
  • slice thickness = 22 mm
  • repetition time = 2000 ms
  • echo time / eco spacing = 288 ms
  • TSI factor = 3
  • BW / samples = 1000 / 256: spectral resolution ~ 4 Hz
  • scan time = 6:19 min

 

The scan was processed using SpectroView:

TSI TE 288 ms, TSI factor 3
TSI TE 288 ms, TSI factor 3

 

A screen capture of SpectroView shows the planscan image and the acquired spectral grid, the ratio map of Choline and NAA and the Choline metabolite map. The maps are presented as transparent color overlays onto the anatomical image.

Four spectra in the tumorous tissue were selected from the grid for display.

 

NAA levels are reduced in all spectra and elevated choline levels are seen. Lactate signal is clearly detected in two of the spectra.

 

Script parameters:

    • initial baseline subtraction = no
    • analysis range = 4.35 - 0.0 ppm
    • baseline terms = 5
    • Gaussian percentage = 90
    • modulus signal aspect
    • lock relative frequencies / widths = no
    • correct for DSA-filter = NAA/Lac

 

Metabolite maps of the fitted area of Choline, Creatine and NAA were generated. Additionally, ratio maps of Cho/NAA, Cho/Cre and Cre/NAA were generated.

 

As it was clearly seen from the T2-weighted images that a larger region of brain tissue was affected, single voxel scans were also performed in the left frontal lobe and in the right occipital lobe. The preset procedure with TE = 288 ms as previously described was used for both scans.

Both scans were processed in SpectroView:

SVS TE = 288 ms SVS in left frontal lobeSVS TE = 288 ms SVS in right occipital lobe
SVS TE = 288 ms
SVS TE = 288 ms
SVS in left frontal lobe
SVS in right occipital lobe

 

The spectrum in the left frontal lobe shows reduced NAA and slightly increased choline, but the Cho/Cre ratio is < 1, which is much lower than the Cho/Cre ratio in the ventricular tumor (>2.1).

The Cho/Cre ratio in the right occipital lobe is ~1.2.

Diagnosis:

Diagnosis is made on the outcome of both conventional MRI findings and MR spectroscopy findings. The difference in Cho/Cre ratio indicate tumoral process.

The processed spectra show tha NNA is present. This indicates glial origin of the tumor.

 

The post-operative diagnosis was ependymoma.



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Oct 20, 2005

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