DW-MRI and MRS to Differentiate Radiation Necrosis and Recurrent

Disease in Gliomas

P100 Exams 4224, SV, 2x2x2cm MV

Thomas Chong

Scans Conducted to Observe MRS Voxel Size Influence on S/N

Single Voxel (SV) Comparisons 1x1x1 (1cm3) 3x3x1 (9cm3) 2x2x2 (8cm3) 3x3x3 (27cm3)

Larger Multi-Voxel (MV) Grid 2x2x2cm voxels 6x6 grid

Single Voxel MRS 1x1x1cm This and subsequent

SV positions selected to be in physical middle of hemisphere, away from voids and boundaries.

No discernible metabolite peaks. Why? Seems inconsistent with MV results.

Could not get results with metabolite peaks using protocol settings on SV

scan. 2-3 attempts

3x3x1cm (9cm3) Single Voxel, S36.6

Exam 4135

3x3x1cm (9cm3) Versus 2x2x2cm (8cm3) Single Voxel, ~S30

Exam 4139Exam 4135

3x3x3cm (27cm3) Single Voxel, ~S26.0

2x2x2cm (8cm3) Versus 3x3x3cm (27cm3) Single Voxel

2x2x2cm SV, Exam 4139 3x3x3cm SV, Exam 4224

Multivoxel Scan with 2x2x2cm Voxels, Exam 4224, S36.6, Vox30

Note: Spectra shows less background noise that 2x2x2cm SV spectra. Why?

Multivoxel Scan with 2x2x2cm Voxels, Exam 4224, S36.6, Vox 10

Multivoxel Scan with 2x2x2cm Voxels, Exam 4224, S36.6, Vox 12 & 27

INTREPRET Study Protocol INTERPRET group MRS data protocol

1.5T GE, Phillips, and Siemens scanners Both short and long TE SV volume 4-8cm3; equivalent to cubes of widths

1.6 – 2cm “whole study protocol took less than 30min”

including MRI set for voxel placement, therefore number of scan averages were higher than in our protocol (2). Averaging helps reduce noise.

“N averages metabolites = 192-128” ? “N averages water = 8-32” ?

Tate A, et al 2006

INTREPRET Study Protocol Voxel Placement: “Whenever possible voxels

were placed entirely within the lesion... avoiding contamination from normal tissue and oedema.”

Data Processing Some SV spectra created by combining MV voxels. Custom program based on MRUI software package

1) Lineshape correction and zero-order phasing using water reference with Klose method

2) 0.8Hz exponential line-broadening 3) FFT processing 4) Water removal by HLSVD; five components removed

within +-0.37ppm of water resonance

INTREPRET Study Protocol

Data Processing, cont'd 4) Water removal by HLSVD; five components removed

within +-0.37ppm of water resonance 5) Residual water suppression; points at 4.2-5.1ppm set

to zero 6) Linear interpolation to 512 points over 1000Hz of

Siemens and Phillips data 7) Spectrum alignment; maximum of choline peak shifted

to 3.21ppm 8) Normalization of spectrum to Euclidian norm of peak

heights.

Data-collection Difference Between INTREPRET and Our Protocol

Highest impact difference between protocols appears to be that their scan focused only on region of lesion INTERPRET used single voxel scans, more

averages, larger voxel sizes These contribute to improve S/N (except maybe

the SV vs MV)

INTERPRET considered mainly glioblastomas, meningiomas, metastases, and astrocytomas

grade II

Re-consideration of Current Scan Protocol

Fact: Based on observations of S/N trends with voxel size and theory, we can say that S/N is improved by: Larger voxel sizes, more averages

Fact: Current protocol gives mostly unusable, low S/N data. We must change it to get data.

Suggestion: Increase voxel size, increase scan averaging Reallocate scan time to focus on region of interest;

can reduce grid size, # of slices; consider SV

Questions to Discuss When Considering Updating Protocol

If switch to SV's, brains with multiple lesions would require multiple SV scans

If switch to SV's, would be useful to collect data for a non-lesioned “control” voxel at consistent location, e.g. contralateral to lesion region.

Switching to SV's would lose spatially changing metabolite ratio information

Comprise with 3x3 MV grid centered at single lesion? E.g. 1.8x1.8x1.8cm, 3 slices, max avgs to fill protocol scan time. Have to consider scan time tradeoffs.

Must answer why the 1x1x1cm SV test scan did not show any peaks

References

Tate, et al, Development of a decision support system for diagnosis and grading of brain tumours using in vivo magnetic resonance single voxel spectra, NMR in Biomedicine, 2006: 19: 411-434.

Tate, et al, Classification of brain tumours using short echo time 1H MR spectra, J of Magn Reson, 2004: 17: 164-175.