Al Parker
Transcription
Al Parker
Linear and non-linear Bayesian models of 3-D Confocal Microscope Movies of Biofilms Al Parker MUQ, Missoula, MT June 26, 2015 Talk Outline: 1. Describe the problem of estimating biofilm characteristics from confocal scanning laser microscope (CSLM) movies using a linear statistical model of biofilm heights. 2. Apply polynomial accelerated iterative samplers to solve this large (> 108-dim) Bayesian linear inverse problem. 3. Overcome some limitations of the linear approach by constructing a non-linear model. Center for Biofilm Engineering Betsey Pitts www.biofilm.montana.edu Phil Stewart In vitro methods to grow relevant biofilms Rotating Disk Reactor Moderate shear - CSTR ASTM Method E2196 Drip Flow Biofilm Reactor Low shear - Plug flow ASTM Method E2647 CDC Biofilm Reactor MBEC Assay High shear - CSTR ASTM Method E2562 Gentle shear - Batch ASTM Method E2799 “Traditional way” to quantify microbial abundances http://www.hypertextbookshop.com/biofilmbook/v004/r003/ Colony forming units (CFU) Microbiologists in my lab usually want to kill biofilms: 3 Michaelis-Menten, Monod, lethality model: 𝑉 𝑐 ∆abundance = log(CFUratio) = 𝐾𝑚𝑎𝑥 +𝑐 𝑚 2 1 Lauchnor et al., JAM, 2015 Inference via the posterior Check model fit via residuals Using confocal images to quantify microbial abundances CDC Biofilm Reactor After growing a Staph. aureus biofilm that has been genetically modified to express a green fluorescent protein … … apply real-time, microscopy-based analysis of biofilm accumulation. High shear - CSTR ASTM Method E2562 The confocal microscope Cartoon from A. Constans, The Confocal Microscope, The Scientist, November 22, 2004, http://www.thescientist.com/?articles.view/articleNo/16043/title/TheConfocal-Microscope/ The data: The biofilm movies, y є R4.5 x 10^8, are stored as uint8 (i.e., 0255), with dimension calculated by: ( planar slice ) x (depth) x (time) = (620μm x 620μm) x (119μm) x (4 f/m over hours) =( 512 pixels )2 x (17 z-slices) x (100’s) = 5122 x 17 x 100 = 4.5 x 108 Linear model assumptions: 1. The height of the biofilm is modeled as a surface over a 2-D domain at each time point (Sheppard & Shotton 1997), i.e., z є R512^2 = R2.6 x 10^5 Independent cryosectioning of biofilm suggests that there is biofilm all the way through Linear model assumptions: 1. The height of the biofilm is modeled as a surface over a 2-D domain at each time point (Sheppard & Shotton 1997), i.e., z є R512^2 = R2.6 x 10^5 Linear model assumptions: 2. The biofilm’s height changes smoothly: each point on the biofilm surface is assumed to be dependent on its neighbors (1st order), and conditionally independent the rest of the surface Figure 14 from D. Higdon, A primer on space-time modelling from a Bayesian perspective, in Statistical Methods for Spatio-Temporal Systems, B. Finkenstadt, L. Held, and V. Isham, eds., Chapman & Hall/CRC, Boca Raton, FL, 2007, pp. 217–279. 3. Assume a locally linear structure: z(i) | (neighbors) ~ N(mean of the neighbors, 1/ [λz(# of neighbors)]) The linear statistical model: The assumptions 1-3 are encapsulated by the prior in the following locally linear Gauss-Markov Random Field: y = Az + ε, , A = I, ε ~ N(0,λyI); likelihood: priors: y|z z λy λz ~ N(z, λyI); ~ N(0, λzW-1); ~ Gamma(ay, by) ~ Gamma(az, bz) W is a Laplacian (a sparse singular precision matrix) with bandwidth b = 512: There are 3 parameters to estimate at each time t: * true image: * SD of the data: * SD of the prior: z є R512^2 = R2.6 x 10^5 1/sqrt(λy) 1/sqrt(λz) W= Estimation procedure: The posterior is straightforward to calculate: Page 32 from D. Higdon, A primer on space-time modelling from a Bayesian perspective, in Statistical Methods for Spatio-Temporal Systems, B. Finkenstadt, L. Held, and V. Isham, eds., Chapman & Hall/CRC, Boca Raton, FL, 2007, pp. 217–279. To get a sample from the posterior, after sampling λy and λz, it is expensive to sample this R2.6 x 10^5 Gaussian (this is an expensive step for any linear Bayesian model y = Az + ε) : Apply iterative samplers from a MASSIVE Gaussian N(µ, Λ-1) Solving Λx=b: Gauss-Seidel Chebyshev-GS CG Sampling y ~ N(µ, Λ-1): Gibbs Chebyshev-Gibbs CG-Lanczos sampler The sampler error decreases according to a polynomial, (E(yk) - µ)= Pk(I-G) (E(y0) – µ) (Λ -1 - Var(yk)) = Pk(I-G) (Λ-1 - Var(y0)) Pk(I-G)T Gibbs Pk(I-G) = for any Krylov vector v CG-Lanczos Chebyshev-Gibbs Gk, with error reduction factor p(G)2 (Λ-1 - Var(yk))v = 0 Pk(I-G) Var(yk) is the kth order CG polynomial kth order Chebyshev polyomial, optimal variance asymptotic average reduction factor is 1 cond ( I G ) 2 1 cond ( I G ) 2 converges in a finite number of steps* in a Krylov space depending on eig(I-G) In theory and on a computer (finite precision), a Chebyshev accelerated sampler is faster than a Gibbs sampler but slower than a Cholesky sampler Example: In 10x10 domain, N(µ, Covariance matrix convergence, ||A-1 – Var(yk)||2 /||A-1 ||2 Benchmark for cost in finite precision is the cost of a Cholesky factorization Benchmark for convergence in finite precision is 105 Cholesky samples -1 ) in R100 … but in R2.6 x 10^5, iterative sampling is much faster than Cholesky sampling Each Gaussian sample of a single movie frame costs: 1. 6.9x1010 flops for a Cholesky factorization [O(b2n) = O(5124)] 2. 9.7x107 flops for an iterative Chebyshev sampler [O(#iters x 2n) = O(185x2x5122)] 3. 2.2x107 flops for an iterative CG sampler [O(#iters x n) = O(85x5122)] These iterative samplers of N(0, Λ-1) are of the form: 1. Split Λ = M - N for M invertible. 2. Sample ck ~ N(0, (2-vk)/vk ( (2 – uk)/ uk M + N) 3. xk+1 = (1- vk) xk-1 + vk xk + vk uk M-1 (b- Λ xk) 4. yk+1 = (1- vk) yk-1 + vk yk + vk uk M-1 (ck - Λyk) 5. Check for convergence: Quit if ||b - Λ xk+1 || is small. Otherwise, update linear solver parameters vk and uk, go to step 2. Examples of matrix splittings … yk+1 = (1- vk) yk-1 + vk yk + vk uk M-1 (ck - Λ yk) ck ~ N(0, (2-vk)/vk ( (2 – uk)/ uk MT + N) Gibbs MGS = D + L, vk = uk = 1 Chebyshev-Gibbs M = MGS D MTGS, vk and uk are functions of the 2 extreme eigenvalues of I-G=M-1Λ CG-Lanczos M = I, vk , uk are functions of the residuals b - Λ xk My attempt at the historical development of iterative Gaussian samplers: Type Stationary (vk = uk = 1) Sampler Matrix Splittings Gibbs (Gauss-Seidel) Literature Adler 1981, Goodman & Sokal 1989, Amit & Grenander 1991 BF (SOR) Barone & Frigessi 1990 REGS (SSOR) Roberts & Sahu 1997 Chen & Oliver 1996 Bardsley, Solonen, Haario & Laine 2014 RML or linear RTO Generalized Non-stationary Multi-Grid Lanczos Krylov subspace Krylov sampling CD Sampler with conjugate directions CG Sampler Krylov sampling with Lanczos Lanczos sampler vectors Chebyshev Fox & P 2014 Goodman & Sokal 1989 Liu & Sabatti 2000 Schneider & Wilsky 2003 Fox 2007 Ceriotti, Bussi & Parrinello 2007 P & Fox 2012 Simpson, Turner, & Pettitt 2008 Aune, Eidsvik, & Pokern 2014 Chow & Saad 2014 Fox & P 2014 Posterior based on linear model: Mean(z) SD(z) med(λy-1/2) med(λz-1/2) Cholesky sampler 0.3717 0.1 Chebyshev sampler 0.3715 0.1 0.7130 10 1. extreme e-vals of M-1Λ 2. CG sample CG sampler Bayesian UQ with iterative samplers using a linear model of heights Salt water added here 25-27% reduction based on 99% credible interval Bayesian UQ with iterative samplers using a linear model of heights These blips in volume are due to peristaltic pump rate (2mL/m) en.wikipedia.org/wiki/File:Peristal tic_pump.gif Model assessment and tweaking Joint work with Colin Fox “Assess and Tweak” approach resembles Doug Nichka’s (director of Computational & Information System Lab's (CISL) Institute for Mathematics Applied to Geosciences (IMAGe) at the National Center for Atmospheric Research (NCAR)) SIAMUQ2014 workshop Hierarchical models of tropical ocean winds given high-resolution satellite scatterometer observations and low-resolution assimilated model output. (Wikle, Milliff, Nychka, Berliner, JASA, 2001) Assessing the Linear Model’s Image Reconstruction: Linear model yields samples z є R512^2 over 2-D domain that do not: capture holes or over-hanging biofilm features allow an accurate reconstruction of the CSLM images Instead, consider a non-linear model 3D binary τ є {0,1}17x512^2 over 3-D domain (Lewandowski & Beyenal 2014; Higdon 2002) Let τ(𝑖, 𝑗, 𝑘) = 0ifnobiofilm 1ifbiofilm l (τ) = min(255, 𝐹(l0τ 𝑟 𝑑 ))= blurred attenuated light profile 𝐹implementssmoothinginthezdirection, l0isluminescenseoftopofthebiofilm, 𝑟 < 1modelsattentationoflightatbiofilmdepth𝑑 Example: A 2D vertical slice from CSLM The CSLM user typically thresholds images before quantitation, i.e., only bright pixels are included Example: A 2D vertical slice from CSLM One might ‘fill in’ below the bright pixels to estimate where the biofilm is …. Nonlinear Bayesian model with 1 Gaussian layer: Let τ(𝑖, 𝑗, 𝑘) = 0ifnobiofilm 1ifbiofilm l (τ) = min(255, 𝐹(l0τ 𝑟 𝑑 ))= blurred attenuated light profile 𝐹implementssmoothinginthe𝑧direction, l0isluminescenseoftopofthebiofilm, 𝑟 < 1modelsattentationoflightatbiofilmdepth𝑑 y = l (τ) + ε, ε ~ N(0,λyI) likelihood: y|τ ~ N(l (τ) , λyI) prior: τ ~ Ising(J) hyperparameters: l0, r, λy, J Apply MCMC to estimate p(τ|y) Example: A 2D vertical slice from CSLM An MCMC sample from the posterior using 1 Gaussian layer ... y τ|y Nonlinear Bayesian model with 2 Gaussian layers: Let τ(𝑖, 𝑗, 𝑘) = 0ifnobiofilm 1ifbiofilm l (𝑥|τ) = min(255, 𝐹(𝑥 𝑟 𝑑 ))= blurred attenuated light profile 𝐹implementssmoothinginthezdirection, 𝑥isluminescensethroughoutthebiofilm, 𝑟 < 1modelsattentationoflightatbiofilmdepth𝑑 y = l (𝑥|τ) + ε, ε ~ N(0,λyI); likelihood: y|τ, 𝑥 ~ N(l (𝑥|τ) , λyI) x|τ ~ N(l0τ, λxI) priors: l0 ~ Unif(0, L0) τ ~ Ising(J) hyperparameters: r, λy, λx, L0, J Example: A 2D vertical slice from CSLM An MCMC sample from the posterior using 2 Gaussian layers ... y τ x|τ Example: A 2D vertical slice from CSLM An MCMC sample from the posterior using 2 Gaussian layers ... y Example: A 2D vertical slice from CSLM Assess residuals to further fine-tune the model ... Next steps: MCMC implementation: Devise efficient schemes for sampling hyperparameters, esp. variance components Can be slow due to single or paired pixel moves in proposal Model correlation across time Alternative to 3D binary model is to model each of N cells by points or ellipsoids, z є R3N or R10N (Al-Awadhi, Hurn & Jennison 2011) Construct posterior for θ|… and model y = l (θ) + ε, where the vector of unknowns θ are directly related to biofilm and confocal microscope parameters like limiting nutrients, wavelength of laser light Devise sampling schemes over time (trade-off with spatial resolution) Compare with other estimation methods (Lewandowski & Beyenal 2014; Jonkman & Stelzer 2002; COMSTAT (Heydorn et al. 2000); Errington & White 1999) References: Iterative Sampling Fox & P. Convergence in variance of Chebyshev accelerated Gibbs samplers. SIAM Journal on Scientific Computing, 36(1):A124-A147, 2014. Bardsley, Solonen, Haario, & Laine. Randomize-then-Optimize: a method for sampling from posterior distributions in nonlinear inverse problems," SIAM Journal on Scientific Computing 36(4): A1359-C399, 2014. P & Fox. Sampling Gaussian Distributions in Krylov Spaces with Conjugate Directions. SIAM Journal on Scientific Computing, 34(3), 2012. Confocal image analysis Lewandowski & Beyenal. Fundamentals of Biofilm Research, 2nd ed. 2014. Jonkman & Stelzer. Resolution and Contrast in Confocal and Two-Photon Microscopy. Confocal and Two-Photon Microscopy, Diaspro ed., 2002. Heydorn, Nielsen, Hentzer, Sternberg, Givskov, Ersboll & Molin. Quantification of biofilm structures by the novel computer program COMSTAT, Microbiology 146, 2000. (MATLAB package) Rodenacker, Bruhl, Hausner, Kuhn, Liebscher, Wagner, Winkler & Wuertz. Quantification of biofilms in multi-spectral digital volumes from confocal laser-scanning microscopes. Image Anal. Stereo 19:151-156, 2000. (math morphology, watershed algorithm) Errington & White. Measuring Dynamic Volume In Situ by Confocal Microscopy. Confocal Microscopy, Paddock ed., 1999 Lewandowski, Webb, Hamilton & Harkin. Quantifying biofilm structure. Water Sci Tech., 1999. Sheppard & Shotton, Microscopy Handbooks 38: Confocal Laser Scanning Microscopy, 1997. (surface representation) Van Der Voort & Strasters, Restoration of confocal images for quantitative image analysis. J. Microscopy 178: 1995. (PSF individual cells) estimation, volumes of Bloem, Veninga & Shephard. Fully Automated Determination of Soil Bacterium Numbers, cell volumes, and frequencies of dividing cells by confocal laser scanning microscopy and image analysis. AEM. 1995. (math morphology) Stewart, Peyton, Drury & Murga. Quantitative Observations of heterogeneities in Pseudomonas aeruginosa biofilms. AEM 59: 1993. Bayesian image analysis Al-Awadhi, Hurn & Jennison. Three-dimensional Bayesian analysis and confocal microscopy. Journal of Applied Statistics, 38(1), 2011 (applied to cartilage cells). Higdon. A primer on space-time modelling from a Bayesian perspective, in Statistical Methods for Spatio-Temporal Systems, B. Finkenstadt, L. Held, & V. Isham, eds., 2007. Geman & Geman. Stochastic relaxation, Gibbs distributions and the Bayesian restoration of images. Advances in Applied Statistics, 1993.
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