Fast Field-Cycling Magnetic Resonance Imaging (FFC-MRI)

Transcription

1 Fast Field-Cycling Magnetic Resonance Imaging (FFC-MRI) David J. Lurie Aberdeen Biomedical Imaging Centre University of Aberdeen

2 Summary of talk Short introduction to MRI Physics Field-Cycling MRI Field-Cycling MRI Scanners Applications of Field-Cycling MRI

3 Physics of MRI

4 Central idea behind MRI:

5 Magnetic field gradient Magnetic field gradient is: linear variation of the strength of the applied magnetic field with position across the sample Without gradient: B z = B 0 everywhere With x-gradient (for example): B z (x) = B 0 + x.g x position (m) gradient (T/m)

6 Magnetic field gradient Main Field B z = B 0 PLUS Gradient Field B z (x) = x.g x EQUALS Total Field B z (x) = B 0 + x.g x 0 x (position)

7 Magnetic field gradient B z B 0 B z (x) = B 0 + x.g x 0 x ω ω 0 ω(x) = γ B z (x) = γ(b 0 + x.g x ) 0 x = ω 0 + γ.x.g x

8 Magnetic Resonance Imaging What is the effect of a gradient in the x-direction? 0 x (position)

9 Magnetic Resonance Imaging e.g. applied gradient G x = 0.5 mt/m Centre: B z = B 0 = 1.0 T f = 42.6 MHz 25 cm left: B z = T f = MHz 25 cm right: B z = T f = MHz 0 x (position)

10 Magnetic Resonance Imaging e.g. applied gradient G x = 0.5 mt/m 0 x (position)

11 Magnetic Resonance Imaging e.g. applied gradient G x = 0.5 mt/m Centre: B z = B 0 = 1.0 T f = 42.6 MHz 25 cm left: B z = T f = MHz 25 cm right: B z = T f = MHz 0 x (position)

12 Magnetic field Frequency encoding Observe NMR signal with gradient on 0 Position Bottles of water in the scanner NMR signal from bottle low frequency, large size medium frequency, small size high frequency, medium size total signal

13 Frequency encoding NMR Signals Amount of signal Frequency of signal This gives a one-dimensional projection of the objects

14 Frequency encoding NMR Signals Amount of signal Frequency of signal Moving a bottle changes its frequency & the projection

15 Frequency encoding NMR Signals Amount of signal Frequency of signal Moving a bottle changes its frequency & the projection

16 Magnetic Resonance Imaging Frequency analysis of NMR signals (Fourier transform) allows images to be produced Gradients are used in 3 dimensions

17 Main parts of an MRI scanner Very strong magnet (usually 1.5 or 3 tesla) Radiofrequency coil (a head coil in this case)

18 Main parts of an MRI scanner

19 Motivation for Field-Cycling MRI

20 Standard MRI vs Field-Cycling MRI Standard MRI The patient is placed inside a large magnet with a strong, fixed magnetic field (e.g. 1.5 T or 3.0 T) Field-Cycling MRI Instead of being constant, the magnetic field (B 0 ) is switched (cycled) between different levels during the collection of a scan The hypothesis is that this can provide extra information, especially about proteins in the body Could improve diagnosis of a wide range of diseases

21 T 1 based image contrast Standard MRI Much of the contrast in conventional MRI arises from differences in the T 1 relaxation time of tissues Typical T 1 -weighted proton MR image

22 Extra information: T 1 Dispersion Studies on small tissue samples have shown that the way in which T 1 changes with field strength ( T 1 dispersion ) could also be a marker of disease However, this information is completely hidden to conventional MRI scanners, because each scanner can only operate at its own fixed value of magnetic field, e.g. 1.5 tesla 3.0 tesla 7.0 tesla

23 T 1 Dispersion a new kind of contrast Our idea is to measure T 1 dispersion in patients, and use it as a completely new marker of disease FFC-MRI Normal Field strength

24 Motivation for FC-MRI So how can we measure T 1 vs field? (a) Buy 100 MRI scanners covering a large range of magnetic fields 0.01 T 0.02 T 0.03 T 0.04 T 0.05 T

25 Motivation for FC-MRI So how can we measure T 1 vs field? (b) Buy one MRI scanner with a variable field (if it was available) B 0

26 Motivation for FC-MRI So how can we measure T 1 vs field? (b) Buy one MRI scanner with a variable field (if it was available)

27 Motivation for FC-MRI So how can we measure T 1 vs field? (b) Buy one MRI scanner with a variable field (if it was available) But the RF coil(s) would have to be retuned at every field...

28 Motivation for FC-MRI So how can we measure T 1 vs field? (c) Use magnetic field cycling! and first, build the equipment

29 How does Field-Cycling work?

30 Introduction to Field-Cycling In Field-Cycling MRI, the magnetic field is switched between two (or more) levels during the MRI procedure

31 Low Field

32 High Field

33 Two fields in one experiment Prepare at low field Detect at higher field

34 Generalised FC method POLARISATION EVOLUTION DETECTION B 0 field B 0 P field B 0 D field B 0 E time Relaxation Relaxation occurs during the Evolution period, usually at low magnetic field The result is read out during the detection period, always at the same (higher) field

35 FFC-MRI imaging pulse sequence T ev B 0 B 0 typically 500 ms B 0 E D RF 90 Gradients Signal

36 FFC-MRI Scanners

37 FFC-MRI Scanners It is not (yet) possible to buy an FFC-MRI scanner from medical imaging companies So we have built our own scanners Most of the FFC-MRI scanner is the same as a standard scanner, except for the magnet, which is very different The magnet in a standard clinical MRI scanner cannot be switched to different magnetic fields (Though field-offset insert coils can be used, as presented by Ludovic de Rochefort yesterday)

38 Double magnet system (0.06 T) Primary Magnet (permanent) Vertical field 59 mt Secondary Magnet (resistive) Vertical field 55 mt Cancellation of magnetic fields: 4 mt at the patient

39 Whole-body FFC-MRI scanner (0.06 T)

40 Single magnet system (0.2 T) Higher detection field (better SNR) More flexible free choice of magnetic fields during the whole pulse sequence But field (in)stability can be problematic

41 Single magnet system (0.2 T) International Electric Company (Finland) 3 circuits, each supplied with 650 A

42 Images from 0.2 T FFC-MRI system

43 Information from T 1 dispersion

44 Remember the dispersion concept? The dispersion curve contains important disease-dependent information

45 The wiggles in the curves are Quadrupolar Dips Arise due to the coincidence of NMR and NQR interaction frequencies in immobile proteins T 1 (ms) T 1 NMR poly-l-alanine (-1 C) 14 N 1 H Frequency (MHz) Kimmich et al., J. Magn. Reson. 68, 263 (1986) H NMR 14 N Nuclear Quadrupole Resonance Magnetic Field (mt)

46 Quadrupolar Dips The quadrupolar dips are sensitive to protein concentration and motion By fitting the dispersion curves to theoretical models, we can extract parameters to use as quantitative biomarkers of disease

47 Biomedical applications

48 Biomedical applications Lionel Broche has led the biomedical applications work in our lab Lionel will give a talk on the applications tomorrow (14:30) I will give one example

49 Cartilage in Osteoarthritis Osteoarthritis is a debilitating disease of joints Can FFC-NMR or FFC-MRI detect disease at an early stage, and monitor treatment? First step was in vitro measurements of T 1 dispersion in normal and osteoarthritic cartilage

50 FFC-MRI results in osteoarthritis Patients undergoing joint-replacement surgery agreed to have FFC measurements made on their joints after they had been removed Relaxation rate (s -1 ) osteoarthritis OA cartilage data Lorentzian fit: R 2 = Healthy cartilage data Lorentzian fit: R 2 = healthy cartlilage Evolution field (MHz 1 H)

51 Conclusions

52 Conclusions Fast Field-cycling MRI can give new types of endogenous contrast, based on T 1 dispersion & Quadrupole peaks Initial results show that FFC-NMR relaxometry and FFC-MRI can give useful information about disease processes That information is invisible to conventional MRI, so represents a new type of image contrast for MRI We are currently investigating FFC-MRI applications in osteoarthritis, cancer, liver disease (fibrosis) and neurodegeneration (Alzheimer s and Parkinson s)

53 Members of the FFC-MRI group Dr. Lionel Broche Dr. Gareth Davies Dr. James Ross Nick Payne Vasilis Zampetoulas

54 Sources of Funding

55 The IDentIFY H2020 project

56 The IDentIFY H2020 project Improving Diagnosis by Fast Field-Cycling MRI Consortium of 7 universities/ research institutes and 2 SMEs in 6 countries Aberdeen is coordinating partner 4-year project started in January 2016 Total funding of 6.60m

57 IDentIFY Partners International Electric Company University of Aberdeen Technical University of Ilmenau University of Warmia and Mazury in Olsztyn INSERM, CEA, CNRS in Grenoble Stelar, S.r.l. University of Turin

58 IDentIFY: Aims & Objectives Improve the FFC-MRI technology Stabilise magnetic field Correct for environmental fields Speed up acquisition Develop FFC-tailored contrast agents Develop relaxation theory Understand the quadrupolar effects Fit data to reliable models Extract quantitative biomarkers of disease Demonstrate effectiveness of FFC-MRI On tissue samples (biobanks and from surgery) On small numbers of patients Bring FFC-MRI closer to the marketplace and to adoption in clinical radiology & research

59 Thanks for your attention! This project has received funding from the European Union s Horizon 2020 research and innovation programme under grant agreement No (project IDentIFY )

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