1. Assessment of tumoural ADC’s in rectal Tumours using Burst: New methodological Developments SJ Doran 1, ASK Dzik-Jurasz 2, J Wolber 2, C Domenig 1, MO Leach 2 2 CRC Clinical Magnetic Resonance Research Group Research Group Institute of Cancer Research Institute of Cancer Research Sutton, UK Sutton, UK 1 University of Surrey Department of Physics Department of Physics Guildford, UK Guildford, UK

2. Purpose of the clinical Study Assessment of locally advanced rectal tumours and Assessment of locally advanced rectal tumours and surrounding normal tissue prior to chemo- and radio- surrounding normal tissue prior to chemo- and radio- therapy and after treatment therapy and after treatment Changes in ADC may precede conventional Changes in ADC may precede conventional morphological measures of tumour response morphological measures of tumour response

3. The original Burst Sequence (J. Hennig, M. Hodapp, 1993; L. Zha, I. J. Lowe, 1995)

4. Main Components of Burst-type Sequences excitation with a series of N low-flip-angel RF pulses excitation with a series of N low-flip-angel RF pulses (DANTE pulse train) (DANTE pulse train) consecutive acquisition of the N echoes consecutive acquisition of the N echoes constant gradient during excitation/acquisition in the constant gradient during excitation/acquisition in the readout direction readout direction Intrinsic characteristics: Intrinsic characteristics:  decay of successive echoes due to T 2 and diffusion

5. Our first Burst-Diffusion Sequence (C. A. Wheeler-Kingshott et al., 2000)

6. Excitation/readout gradient = diffusion gradient Excitation/readout gradient = diffusion gradient  transverse magnetisation dephases during exitation, rephases during readout  dephasing = rephasing due to diffusion motion Stepped phase-encoding gradient  diffusion gradient Stepped phase-encoding gradient  diffusion gradient M repetitions of the sequence M repetitions of the sequence Main Components of the Burst-Diffusion Sequence

7. Calculation of ADC and T 2 map Data acquisition Data acquisition  N echoes, M repetitions, R points in readout direction per echo  data matrix [M x N x R] Post processing Post processing  reformation of the data in N separate matrices  FT  set of N images of the same slice but with increased diffusion and T 2 weighting  double exponential fit  ADC and T 2 map

8. First clinical Results Clinical study: Clinical study:  1.5T Siemens Magnetom Vision MR Scanner Scanning parameters: Scanning parameters:  N = 16 echoes  FOV = 180 x 180 mm 2  matrix = 128 x 128 Burst-diffusion MR images:  Burst-diffusion MR images:  T R = 2000 ms  T A = 4 min. 16 sec. T 2 -weighted SE images:  T 2 -weighted SE images:  T R = 1500 ms  T A = 1 min. 54 sec. T 2 -weighted SE image T 2 map ADC map Burst-diffusion image low b-value

9. Problems Images suffer from low signal-to-noise ratio Images suffer from low signal-to-noise ratio Field-of-view and diffusion sensitisation are coupled Field-of-view and diffusion sensitisation are coupled Need of different sequence for correcting echo-decay Need of different sequence for correcting echo-decay due to T 2 -relaxation due to T 2 -relaxation Only single-slice data can be obtained Only single-slice data can be obtained Motion during and between scans leads to ghosting Motion during and between scans leads to ghosting artifacts in the phase-encode direction artifacts in the phase-encode direction

10. Problem Solving Increasing the SNR by: Increasing the SNR by:  reducing the number of pulses: 16  9  increasing the flip angle: 16   21   reducing the acquisition bandwidth: 100 kHz  25 kHz (12.5kHz) Uncoupling of readout- and diffusion gradient Uncoupling of readout- and diffusion gradient  diffusion gradient independent of FOV Sequence can be used to correct for T 2 -decay Sequence can be used to correct for T 2 -decay

11. Phantom : Phantom :  Tubes with Acetonitrile, DMSO, H2O and Glycerol Old Sequence: Old Sequence:  N = 16  BW = 100 kHz  SNR = 7:1 New Sequence: New Sequence:  N = 9  BW = 12.5 kHz  SNR = 30:1 Phantom Study: Comparison of the old and new Sequence in Terms of SNR low b-value (2 s/mm 2 ) higher b-value (310 s/mm 2 )

12. (b j -b 0 ) vs. ln(S j /S 0 ) Single pixel fitSignal averaged

13. G diff = G read G diff = G read  G diff = 3.67 mT/m  b-values: 0.95 - 100 s/mm 2 G diff  G read G diff  G read  G diff = 10 mT/m  b-values: 0.11 - 1272 s/mm 2 Acquisition parameters: Acquisition parameters:  FOV = 160 x 160 mm 2  matrix = 128 x 128  TR = 2000 ms  TA = 4 min. 16 sec. Sequence parameters: Sequence parameters:  N = 9  BW = 25 kHz Coupled and uncoupled FOV and Diffusion- Gradient

15. The new single-slice Burst-Diffusion Sequence

16. First abdominal Images Left: Image obtained with the old sequence Right: Image obtained with the new sequence Comparison in terms of SNR 4 differently diffusion-weighted images

17. Multi-slice Burst-Diffusion Sequence Replacing the non-selectice  -pulses by slice-selective Replacing the non-selectice  -pulses by slice-selective ones ones

18. Conclusions Burst can be used for abdominal imaging (regions with Burst can be used for abdominal imaging (regions with short T 2 ) short T 2 ) More b-values over a wide range can be obtained More b-values over a wide range can be obtained (G Diff = 6 mT/m: b-values from 0.05 to 522 s/mm 2 ) (G Diff = 6 mT/m: b-values from 0.05 to 522 s/mm 2 ) Although longer than EPI the Burst-diffusion sequences Although longer than EPI the Burst-diffusion sequences are much shorter than the conventional PGSE Method are much shorter than the conventional PGSE Method

19. Future Work Further testing and clinical evaluation of the new Further testing and clinical evaluation of the new Burst-diffusion sequences Burst-diffusion sequences Introduction of navigator echoes in both, the single- Introduction of navigator echoes in both, the single- slice and multi-slice Burst-diffusion sequence slice and multi-slice Burst-diffusion sequence

20. Acknowledgements Simon J Doran Simon J Doran Andrzej SK Dzik-Jurasz Andrzej SK Dzik-Jurasz Jan Wolber Jan Wolber Martin O Leach Martin O Leach