Anatomical Distribution of Hyperpolarized. He and 129 Xe MRI Apparent Diffusion Coefficients in Asthma

Transcription

1 Computer # 19 Anatomical Distribution of Hyperpolarized He and 129 Xe MRI Apparent Diffusion Coefficients in Asthma Sarah Svenningsen 1,2, Miranda Kirby 1,2, Andrew Wheatley 1, Adam Farag 1, Alexei Ouriadov 1, Giles Santyr 1,2, David G McCormack, and Grace Parraga 1,2 1 Imaging Research Laboratories, Robarts Research Institute, 2 Department of Medical Biophysics, Department of Medicine, The University of Western Ontario, London, Ontario, CANADA May 9, 2012

2 Declaration of Relevant Financial Interests or Relationships Sarah Svenningsen: I have no relevant financial interest or relationship to disclose with regard to the subject matter of this presentation.

3 Asthma Asthma is a chronic respiratory disease characterized by reversible airway inflammation Healthy Smooth muscle constriction Asthma Mucus Thickened airway wall

4 Hyperpolarized Gas MRI Apparent Diffusion Coefficient (ADC) Diffusion weighted (DW) imaging measures the distance (r) the atoms diffuse during a period of time: Healthy 1 r ADC Emphysema 2, ADC=apparent diffusion coefficient, r=distance the atoms diffuse, t=diffusion time. 1. Evans A et al. JAP, Mathew L et al. EJR, Kirby M et al. JAP, 2012 r ADC

5 He ADC: Asthma ADC ADC No obstruction No gas trapping Partial obstruction Gas trapping 1. Wang C et al. JMRI, 2008 Asthma He ADC > Healthy He ADC 1

6 He ADC: Asthma Asthma (n=25) Healthy (n=8) Baseline Post-methacholine Recovery PA G No significant difference in ADC between asthma and healthy Significant volunteers at Significant at all time-points all time-points Significant anterior-to-poster ADC gradients in asthma and healthy volunteers 1. Costella et al. Respirology, 2012

7 Motivation High cost and limited availability of He gas worldwide Restricted clinical translation Necessary transition of hyperpolarized noble gas MRI to 129-xenon ( 129 Xe) gas Important differences between the physical characteristics of He and 129 Xe that must be explored Polarized Agent Gyromagnetic ratio (ƴ) [MHz/T] Natural abundance (%) Self diffusion coefficient [cm 2 /s] Blood solubility (%) Typical polarization levels (%) He Xe Fain et al Zhou et al. 2011

8 Objective To quantitatively compare He and 129 Xe MRI apparent diffusion coefficients (ADC) in asthma and the relationship of anterior-to-posterior (AP) ADC gradients. We hypothesize that a similar anterior-toposterior ADC gradient will be observed with 129 Xe and He MRI in asthma

9 Methods: Subjects and Study Design He DW MRI days Mild to moderate asthma subjects years Baseline FEV 1 > 60% pred 129 Xe DW MRI

10 Methods: Hyperpolarized Noble Gas MRI He MRI 129 Xe MRI Poster #: 12

11 Methods: DW Imaging Parameters b = ƴ 2 G 2 δ 2 ( - δ/) Ƴ = gyromegnetic ratio G = gradient strength Δ = diffusion time δ = gradient duration 2D fast gradient-echo (FGRE) sequence 16 sec data acquisition FOV = 40 x 40 cm Matrix = 128 x slices, 0 mm slice thickness, 0 gap He 129 Xe TR/TE/flip angle = 7.6 ms/.7 ms/ 8 TR/TE/flip angle = 1.5 ms/ 10 ms/ 9 b = 1.6 sec/cm 2 (n=6) G = 1.94 G/cm = 2.9 ms δ = 0.46 ms rise fall time = 0.5 ms b = 20 sec/cm 2 (n=2) G =.75 G/cm = 5 ms δ = 2.0 ms rise fall time = 0.5 ms b = 0 sec/cm 2 (n=4) G = 4.59 G/cm = 5 ms δ = 2.0 ms rise fall time = 0.5 ms

12 Results: Subject Demographics Asthma (n=6) Male sex Age (SD) (yrs) 46 (8) BMI (SD) (kg/m 2 ) 27 (5) FEV 1 % pred 69 (6) FVC % pred 91 (8) FEV 1 /FVC (%) 76 (4) FRC % pred 107 (11) RV % pred 140 (15) TLC % pred 107 (6) RV/TLC (%) 11 (12) DLCO % pred 108 (1)

13 He and 129 Xe ADC 129 Xe ADC (cm 2 /s) r = 0.66 r=0.66 r 2 r 2 = 0.44 p = = p= He ADC (cm 2 /s) Significant relationship between He and 129 Xe ADC

14 He and 129 Xe ADC He ADC 0.69 (0.240) 0.25 (0.162) 0.11 (0.12) (0.1) Higher cm 2 /s He and 129 cmxe 2 /s ADC values cm 2 /s in the anterior cm 2 /s slices 129 Xe ADC of a representative asthma subject (0.0210) cm 2 /s Anterior (0.0192) cm 2 /s (0.0164) cm 2 /s Acquisition Direction (0.0187) cm 2 /s Posterior

15 Regional He and 129 Xe ADC Maps He (n=6) 129 Xe (n=6) WL ADC cm 2 /s 0.28 (0.055) (0.0051) WL SNR 51 (28) 28 (11) Anterior (0.065) (0.0048) Posterior (0.062) (0.0062) He ADC (cm 2 /s) 0.4 ΔAP cm 2 /s (0.022) (0.004) AP G cm/s 1.x10 - (0.4x10 - ) 0.076x10 - (0.065x10 - ) *p=0.00 **p= Significant and similar He and Xe anterior-to-posterior Anterior Posterior Anterior Posterior 129 Xe ADC (cm 2 /s) ADC gradient * ** * Xe SNR was significantly lower than He SNR *p=0.005

16 Correlation with Established Parameters He ADC Pearson r (p-value) [n=6] 129 Xe ADC Pearson r (p-value) [n=6] FEV 1 % pred 0. (0.5) 0.2 (0.5) FVC % pred (0.72) 0.0 (0.57) FEV 1 /FVC (%) 0.87 (0.02) * (0.82) FRC % pred (0.69) 0.6 (0.25) RV % pred -0.0 (0.96) 0.08 (0.90) TLC % pred (0.7) 0.21 (0.7) RV/TLC (%) (0.22) (0.4) Raw % pred 0.55 (0.) (0.9) DLCO % pred -0. (0.5) - Statistically significant relationship between He ADC and FEV 1 /FVC

17 Results Summary Significant relationship between He and 129 Xe ADC 129 Xe SNR was significantly lower than He SNR Significant and similar He and 129 Xe anterior-toposterior ADC gradient Significant relationship between He ADC and FEV 1 /FVC

18 Conclusion Six asthmatics performed He and 129 Xe MRI diffusion weighted imaging: the relationship between anatomical location and ADC was statistically significant for both gases Despite having a lower diffusion coefficient and larger atomic mass, 129 Xe MRI anatomical ADC gradients are similar to He MRI which bodes well for clinical translation

19 Acknowledgements and Disclosures Investigators Grace Parraga PhD David G McCormack MD Nigel Paterson MD Giles Santyr PhD Roya Etemad-Rezai MD Research Team Andrew Wheatley BSc Adam Farag MSc Alexei Ouriadov PhD Shayna McKay BSc Sandra Halko CCRC, RPT Trevor Szekeres RTMR Miranda Kirby BSc Stephen Costella BEng Dan Buchanan BHSc Amir Owrangi MEng Nikhil Kanhere BE Lauren Villemaire BMSc

20 London Lung Imaging Research Team