simulateSpectrum {Cardinal} | R Documentation

## Simulate a mass spectrum or MS imaging experiment

### Description

Simulate mass spectra or complete MS imaging experiments, including a possible baseline, spatial and spectral noise, mass drift, mass resolution, and multiplicative variation, etc.

A number of preset imaging designs are available for quick-and-dirty simulation of images.

These functions are designed for small proof-of-concept examples and testing, and may not scale well to simulating larger datasets.

### Usage

    simulateSpectrum(n = 1L, peaks = 50L,
        mz = rlnorm(peaks, 7, 0.3), intensity = rlnorm(peaks, 1, 0.9),
        from = 0.9 * min(mz), to = 1.1 * max(mz), by = 400,
        sdpeaks = sdpeakmult * log1p(intensity), sdpeakmult = 0.2,
        sdnoise = 0.1, sdmz = 10, resolution = 1000, fmax = 0.5,
        baseline = 0, decay = 10, units=c("ppm", "mz"),
        representation = c("profile", "centroid"), ...)

    simulateImage(pixelData, featureData, preset,
        from = 0.9 * min(mz), to = 1.1 * max(mz), by = 400,
        sdrun = 1, sdpixel = 1, spcorr = 0.3, sptype = "SAR",
        representation = c("profile", "centroid"), units=c("ppm", "mz"),
        as = c("MSImagingExperiment", "SparseImagingExperiment"),
        BPPARAM = bpparam(), ...)

    addShape(pixelData, center, size, shape=c("circle", "square"), name=shape)

    presetImageDef(preset = 1L, nruns = 1, npeaks = 30L,
        dim = c(20L, 20L), peakheight = 1, peakdiff = 1,
        sdsample = 0.2, jitter = TRUE, ...)

### Arguments

`n` | The number of spectra to simulate.
`peaks, npeaks` | The number of peaks to simulate. Not used if `mz` and `intensity` are provided.
`mz` | The theoretical m/z values of the simulated peaks.
`intensity` | The mean intensities of the simulated peaks.
`from` | The minimum m/z value used for the mass range.
`to` | The maximum m/z value used for the mass range.
`by` | The step-size used for the observed m/z-values of the profile spectrum.
`sdpeaks` | The standard deviation(s) for the distributions of observed peak intensities on the log scale.
`sdpeakmult` | A multiplier used to calculate `sdpeaks` based on the mean intensities of peaks; used to simulate multiplicative variance. Not used if `sdpeaks` is provided.
`sdnoise` | The standard deviation of the random noise in the spectrum on the log scale.
`sdmz` | The standard deviation of the mass error in the observed m/z values of peaks, in units indicated by `units`.
`resolution` | The mass resolution as defined by `m / dm`, where `m` is the observed mass and `dm` is the width of the peak at a proportion of its maximum height defined by `fmax` (defaults to full-width-at-half-maximum – FWHM – definition). Note that this is NOT the same as the definition of `resolution` in the `readImzML` function.
`fmax` | The proportion of the maximum peak height to use when defining the mass resolution.
`baseline` | The maximum intensity of the baseline. Note that `baseline=0` means there is no baseline.
`decay` | A constant used to calculate the exponential decay of the baseline. Larger values mean the baseline decays more sharply at the lower mass range of the spectrum.
`units` | The units for `by` and `sdmz`. Either parts-per-million or absolute m/z units.
`representation` | Should a profile spectrum be returned or only the centroided peaks?
`BPPARAM` | An optional instance of `BiocParallelParam`. See documentation for `bplapply`.
`pixelData` | A `PositionDataFrame` giving the pixel design of the experiment. The names of the columns should match the names of columns in `featureData`. Each column should be a logical vector corresponding to a morphological substructure, indicate which pixels belong to that substructure.
`featureData` | A `MassDataFrame` giving the feature design of the experiment. Each row should correspond to an expected peak. The names of the columns should match the names of columns in `pixelData`. Each column should be a numeric vector corresponding to a morphological substructure, giving the mean intensity of that peak for that substructure.
`preset` | A number indicating a preset image definition to use.
`nruns` | The number of runs to simulate for each condition.
`sdrun` | A standard deviation giving the run-to-run variance.
`sdpixel` | A standard deviation giving the pixel-to-pixel variance.
`spcorr` | The spatial autocorrelation. Must be between 0 and 1, where `spcorr=0` indicates no spatial autocorrelation.
`sptype` | The type of spatial autocorrelation.
`as` | The class of object to be returned.
`...` | Additional arguments to pass to `simulateSpectrum` or `presetImageDef`.
`dim` | The dimensions of the preset image.
`peakheight` | Reference intensities used for peak heights by the preset.
`peakdiff` | A reference intensity difference used for the mean peak height difference between conditions, for presets that simulate multiple conditions.
`sdsample` | A standard deviation giving the amount of variation from the true peak heights for this simulated sample.
`jitter` | Should random noise be added to the location and size of the shapes?
`center` | The center of the shape.
`size` | The size of the shape (from the center).
`shape` | What type of shape to add.
`name` | The name of the added column.

### Details

The `simulateSpectrum()` and `simulateImage()` functions are used to simulate mass spectra and MS imaging experiments. They provide a great deal of control over the parameters of the simulation, including all sources of variation.

For `simulateImage()`, the user should provide the design of the simulated experiment via matching columns in `pixelData` and `featureData`, where each column corresponds to different morphological substructures or differing conditions. These design data frames are returned in the `metadata()` of the returned object for later reference.

A number of presets are defined by `presetImageDef()`, which returns only the `pixelData` and `featureData` necessary to define the experiment for `simulateImage()`. These can be referenced for help in understanding how to define experiments for `simulateImage()`.

The preset images are:

- 1: a centered circle

- 2: a topleft circle and a bottomright square

- 3: two corner squares and a centered circle

- 4: a centered circle with conditions A and B in different runs

- 5: a topleft circle and a bottomright square with conditions A and B in different runs

- 6: two corner squares and a centered circle; the circle has conditions A and B in different runs

- 7: matched pairs of circles with conditions A and B within the same runs; includes reference peaks

- 8: matched pairs of circles inside squares with conditions A and B within the same runs; includes reference peaks

- 9: a small sphere inside a larger sphere (3D)

The `addShape()` function is provided for convenience when generating the `pixelData` for `simulateImage()`, as a simple way of adding morphological substructures using basic shapes such as squares and circles.

### Value

For `simulateSpectrum`, a `list` with elements:

- `mz`: a numeric vector of the observed m/z values

- `intensity`: a numeric vector or matrix of the intensities

For `simulateImage`, a `MSImagingExperiment` or a `SparseImagingExperiment`.

For `addShape`, a new `PositionDataFrame` with a logical column added for the corresponding shape.

For `presetImageDef`, a list with two elements: the `pixelData` and `featureData` to be used as input to `simulateImage()`.

### Author(s)

Kylie A. Bemis

### See Also

`simulateSpectrum`, `simulateImage`

### Examples

    register(SerialParam())
    set.seed(1)

    # generate a spectrum
    s <- simulateSpectrum(1)
    plot(intensity ~ mz, data=s, type="l")

    # generate a noisy low-resolution spectrum with a baseline
    s <- simulateSpectrum(1, baseline=2, sdnoise=0.3, resolution=100)
    plot(intensity ~ mz, data=s, type="l")

    # generate a high-resolution spectrum
    s <- simulateSpectrum(1, peaks=100, resolution=10000)
    plot(intensity ~ mz, data=s, type="l")

    # generate an image
    x <- simulateImage(preset=1, npeaks=10, dim=c(10,10))
    m <- mz(metadata(x)$design$featureData)

    image(x, mz=m[5])

    plot(x, coord=c(x=3, y=3))

[Package Cardinal version 2.4.0 Index]