Assessment of tumoural ADC’s in Assessment of tumoural ADC’s in rectal Tumours using Burst:rectal Tumours using Burst:

New methodological DevelopmentsNew methodological Developments

SJ DoranSJ Doran11, ASK Dzik-Jurasz, ASK Dzik-Jurasz22, J Wolber, J Wolber22,,

C DomenigC Domenig11, MO Leach, MO Leach22

22 CRC Clinical Magnetic Resonance CRC Clinical Magnetic Resonance Research GroupResearch Group Institute of Cancer ResearchInstitute of Cancer Research Sutton, UKSutton, UK

11 University of Surrey University of Surrey Department of PhysicsDepartment of Physics Guildford, UKGuildford, UK

Purpose of the clinical StudyPurpose of the clinical Study

• Assessment of locally advanced rectal tumours andAssessment 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 treatmenttherapy and after treatment

• Changes in ADC may precede conventionalChanges in ADC may precede conventional morphologicalmorphological measures of tumour responsemeasures of tumour response

The original Burst SequenceThe original Burst Sequence

(J. Hennig, M. Hodapp, 1993; L. Zha, I. J. Lowe, 1995)(J. Hennig, M. Hodapp, 1993; L. Zha, I. J. Lowe, 1995)

Main Components of Burst-type Main Components of Burst-type SequencesSequences

• excitation with a series of N low-flip-angel RF pulsesexcitation with a series of N low-flip-angel RF pulses (DANTE pulse train)(DANTE pulse train)

• consecutive acquisition of the N echoesconsecutive acquisition of the N echoes

• constant gradient during excitation/acquisition in theconstant gradient during excitation/acquisition in the readout directionreadout direction

• Intrinsic characteristics:Intrinsic characteristics: decay of successive echoes due to T2 and diffusion

Our first Burst-Diffusion SequenceOur first Burst-Diffusion Sequence

(C. A. Wheeler-Kingshott et al., 2000(C. A. Wheeler-Kingshott et al., 2000))

• Excitation/readout gradient = diffusion gradientExcitation/readout gradient = diffusion gradient transverse magnetisation dephases during exitation,

rephases during readout dephasing = rephasing due to diffusion motion

• Stepped phase-encoding gradient Stepped phase-encoding gradient diffusion gradient diffusion gradient

• M repetitions of the sequenceM repetitions of the sequence

Main Components of the Burst-Diffusion Main Components of the Burst-Diffusion SequenceSequence

Calculation of ADC and TCalculation of ADC and T22 map map

• Data acquisitionData acquisition N echoes, M repetitions, R points in readout direction

per echo data matrix [M x N x R]

• Post processingPost processing reformation of the data in N separate matrices FT set of N images of the same slice but with increased

diffusion and T2 weighting

double exponential fit ADC and T2 map

First clinical ResultsFirst clinical Results

• Clinical study:Clinical study: 1.5T Siemens Magnetom Vision MR Scanner

• Scanning parameters:Scanning parameters: N = 16 echoes FOV = 180 x 180 mm2

matrix = 128 x 128

Burst-diffusion MR images:Burst-diffusion MR images:

TR = 2000 ms TA = 4 min. 16 sec.

TT22-weighted SE images:-weighted SE images:

TR = 1500 ms TA = 1 min. 54 sec.

TT22-weighted SE-weighted SE

imageimage

TT22 map mapADC mapADC map

Burst-diffusion imageBurst-diffusion imagelow b-valuelow b-value

ProblemsProblems

• Images suffer from low signal-to-noise ratioImages suffer from low signal-to-noise ratio

• Field-of-view and diffusion sensitisation are coupledField-of-view and diffusion sensitisation are coupled

• Need of different sequence for correcting echo-decayNeed of different sequence for correcting echo-decay due to Tdue to T22-relaxation-relaxation

• Only single-slice data can be obtainedOnly single-slice data can be obtained

• Motion during and between scans leads to ghostingMotion during and between scans leads to ghosting artifacts in the phase-encode directionartifacts in the phase-encode direction

Problem SolvingProblem Solving

• Increasing the SNRIncreasing the SNR by: 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 gradientUncoupling of readout- and diffusion gradient diffusion gradient independent of FOV

• Sequence can be used to Sequence can be used to correct for Tcorrect for T22-decay-decay

• PhantomPhantom:: 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 Phantom Study: Comparison of the old and new Sequence in Terms of SNRnew Sequence in Terms of SNR

low b-valuelow b-value(2 s/mm(2 s/mm22))

higher b-valuehigher b-value(310 s/mm(310 s/mm22))

(b(bjj-b-b00) vs. ln(S) vs. ln(Sjj/S/S00))

-1.6

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0 50 100 150 200 250 300 350(bj-b0) [s/mm2]

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j/S0)

H2O

Acetonitrile

H2O

DMSO -1.6

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0 50 100 150 200 250 300 350(bj-b0) [s/mm2]

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Single pixel fit Signal averaged

• GGdiffdiff = G = Greadread

Gdiff = 3.67 mT/m

b-values: 0.95 - 100 s/mm2

• GGdiffdiff G Greadread

Gdiff = 10 mT/m

b-values: 0.11 - 1272 s/mm2

• Acquisition parameters:Acquisition parameters: FOV = 160 x 160 mm2

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-Coupled and uncoupled FOV and Diffusion-GradientGradient

Coupled and uncoupled FOV and Diffusion-Coupled and uncoupled FOV and Diffusion-GradientGradient

0

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0 1 2 3 4 5 6 7 8

Image No.

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mp

litu

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coupled FOV and DiffusionGradient

uncoupled FOV andDiffusion Gradient

The new single-slice Burst-Diffusion The new single-slice Burst-Diffusion SequenceSequence

First abdominal ImagesFirst abdominal Images

Left: Image obtained with the old sequenceRight: Image obtained with the new sequence

Comparison in terms of SNRComparison in terms of SNR4 differently diffusion-weighted images4 differently diffusion-weighted images

Multi-slice Burst-Diffusion SequenceMulti-slice Burst-Diffusion Sequence

• ReplacingReplacing the the non-selectice non-selectice -pulses-pulses by slice-selective by slice-selective onesones

ConclusionsConclusions

• Burst can be used for Burst can be used for abdominal imagingabdominal imaging (regions with (regions with short Tshort T22))

• More More b-values over a wide rangeb-values over a wide range can be obtained can be obtained (G(GDiffDiff = 6 mT/m: b-values from 0.05 to 522 s/mm = 6 mT/m: b-values from 0.05 to 522 s/mm22))

• Although longer than EPI the Burst-diffusion sequencesAlthough longer than EPI the Burst-diffusion sequences are much are much shorter thanshorter than the conventional the conventional PGSE MethodPGSE Method

Future WorkFuture Work

• Further testing and clinical evaluation of the newFurther testing and clinical evaluation of the new Burst-diffusion sequencesBurst-diffusion sequences

• Introduction of Introduction of navigator echoesnavigator echoes in both, the single- in both, the single- slice and multi-slice Burst-diffusion sequenceslice and multi-slice Burst-diffusion sequence

AcknowledgementsAcknowledgements

• Simon J DoranSimon J Doran

• Andrzej SK Dzik-JuraszAndrzej SK Dzik-Jurasz

• Jan WolberJan Wolber

• Martin O LeachMartin O Leach