# Basic analyses with SPIAT

Yuzhou Feng

#### 2024-07-31

#### Package

SPIAT 1.6.2

    library(SPIAT)

In this vignette we will use an inForm data file that’s already been formatted for SPIAT with `format_image_to_spe()`, which we can load with `data()`. We will use `define_celltypes()` to define the cells with certain combinations of markers.

    data("simulated_image")

    # define cell types
    formatted_image <- define_celltypes(
        simulated_image,
        categories = c("Tumour_marker","Immune_marker1,Immune_marker2",
                       "Immune_marker1,Immune_marker3",
                       "Immune_marker1,Immune_marker2,Immune_marker4", "OTHER"),
        category_colname = "Phenotype",
        names = c("Tumour", "Immune1", "Immune2", "Immune3", "Others"),
        new_colname = "Cell.Type")

We will be performing some basic analyses on this image. Here is the visualisation of the cell coordinates.

    my_colors <- c("red", "blue", "darkcyan", "darkgreen")

    plot_cell_categories(spe_object = formatted_image,
                         categories_of_interest =
                           c("Tumour", "Immune1", "Immune2", "Immune3"),
                         colour_vector = my_colors,
                         feature_colname = "Cell.Type")

# 1 Cell percentages

We can obtain the number and proportion of each cell type with `calculate_cell_proportions()`. We can use `reference_celltypes` to specify cell types to use as the reference. For example, “Total” will calculate the proportion of each cell type against all cells. We can exclude any cell types that are not of interest e.g. “Undefined” with `celltypes_to_exclude`.

    p_cells <- calculate_cell_proportions(formatted_image,
                                          reference_celltypes = NULL,
                                          feature_colname ="Cell.Type",
                                          celltypes_to_exclude = "Others",
                                          plot.image = TRUE)

    p_cells

    ##   Cell_type Number_of_celltype Proportion Percentage Proportion_name
    ## 5    Tumour                819 0.41679389  41.679389          /Total
    ## 3   Immune3                630 0.32061069  32.061069          /Total
    ## 1   Immune1                338 0.17201018  17.201018          /Total
    ## 2   Immune2                178 0.09058524   9.058524          /Total

Alternatively, we can also visualise cell type proportions as barplots using `plot_cell_percentages()`.

    plot_cell_percentages(cell_proportions = p_cells,
                          cells_to_exclude = "Tumour", cellprop_colname="Proportion_name")

# 2 Cell distances

## 2.1 Pairwise cell distances

We can calculate the pairwise distances between two cell types (cell type A and cell type B) with `calculate_pairwise_distances_between_cell_types()`. This function calculates the distances of all cells of type A against all cells of type B.

This function returns a data frame that contains all the pairwise distances between each cell of cell type A and cell type B.

    distances <- calculate_pairwise_distances_between_celltypes(
      spe_object = formatted_image,
      cell_types_of_interest = c("Tumour", "Immune1", "Immune3"),
      feature_colname = "Cell.Type")

The pairwise distances can be visualised as a violin plot with `plot_cell_distances_violin()`.

    plot_cell_distances_violin(distances)

We can also calculate summary statistics for the distances between each combination of cell types, the mean, median, min, max and standard deviation, with `calculate_summary_distances_between_celltypes()`.

    summary_distances <- calculate_summary_distances_between_celltypes(distances)

    summary_distances

    ##              Pair      Mean      Min      Max    Median  Std.Dev Reference
    ## 1 Immune1/Immune1 1164.7096 10.84056 2729.120 1191.3645 552.0154   Immune1
    ## 2 Immune1/Immune3 1034.4960 10.23688 2691.514 1026.4414 442.2515   Immune1
    ## 3  Immune1/Tumour 1013.3697 13.59204 2708.343 1004.6579 413.7815   Immune1
    ## 4 Immune3/Immune1 1034.4960 10.23688 2691.514 1026.4414 442.2515   Immune3
    ## 5 Immune3/Immune3  794.7765 10.17353 2645.302  769.9948 397.8863   Immune3
    ## 6  Immune3/Tumour  758.2732 10.02387 2670.861  733.4501 380.7703   Immune3
    ## 7  Tumour/Immune1 1013.3697 13.59204 2708.343 1004.6579 413.7815    Tumour
    ## 8  Tumour/Immune3  758.2732 10.02387 2670.861  733.4501 380.7703    Tumour
    ## 9   Tumour/Tumour  711.2657 10.00348 2556.332  703.9096 380.3293    Tumour
    ##    Target
    ## 1 Immune1
    ## 2 Immune3
    ## 3  Tumour
    ## 4 Immune1
    ## 5 Immune3
    ## 6  Tumour
    ## 7 Immune1
    ## 8 Immune3
    ## 9  Tumour

An example of the interpretation of this result is: “average pairwise distance between cells of Immune3 and Immune1 is 1034.496”.

These pairwise cell distances can then be visualised as a heatmap with `plot_distance_heatmap()`. This example shows the average pairwise distances between cell types. Note that the pairwise distances are symmetrical (the average distance between cell type A and cell type B is the same as the average distance between cell Type B and cell Type A).

    plot_distance_heatmap(phenotype_distances_result = summary_distances, metric = "mean")

This plot shows that Tumour cells are interacting most closely with Tumour cells and Immune3 cells.

## 2.2 Minimum cell distances

We can also calculate the minimum distances between cell types with `calculate_minimum_distances_between_celltypes()`. Unlike the pairwise distance where we calculate the distances between all cell types of interest, here we only identify the distance to the closest cell of type B to each of the reference cells of type A.

    min_dist <- calculate_minimum_distances_between_celltypes(
      spe_object = formatted_image,
      cell_types_of_interest = c("Tumour", "Immune1", "Immune2","Immune3", "Others"),
      feature_colname = "Cell.Type")

    ## [1] "Markers had been selected in minimum distance calculation: "
    ## [1] "Others"  "Immune1" "Tumour"  "Immune3" "Immune2"

The minimum distances can be visualised as a violin plot with `plot_cell_distances_violin()`. Visualisation of this distribution often reveals whether pairs of cells are evenly spaced across the image, or whether there are clusters of pairs of cell types.

    plot_cell_distances_violin(cell_to_cell_dist = min_dist)

We can also calculate summary statistics for the distances between each combination of cell types, the mean, median, min, max and standard deviation, with `calculate_summary_distances_between_celltypes()`.

    min_summary_dist <- calculate_summary_distances_between_celltypes(min_dist)

    # show the first five rows
    min_summary_dist[seq_len(5),]

    ##              Pair     Mean      Min       Max   Median  Std.Dev Reference
    ## 1 Immune1/Immune2 63.65211 10.33652 158.80504 59.01846 32.58482   Immune1
    ## 2 Immune1/Immune3 88.46152 10.23688 256.30328 77.21765 53.73164   Immune1
    ## 3  Immune1/Others 19.24038 10.05203  49.86409 17.49196  7.19293   Immune1
    ## 4  Immune1/Tumour 85.84773 13.59204 223.15809 80.80592 40.72454   Immune1
    ## 5 Immune2/Immune1 48.45885 10.33652 132.31086 43.71936 27.43245   Immune2
    ##    Target
    ## 1 Immune2
    ## 2 Immune3
    ## 3  Others
    ## 4  Tumour
    ## 5 Immune1

Unlike the pairwise distance, the minimum distances are not symmetrical, and therefore we output a summary of the minimum distances specifying the reference and target cell types used.

An example of the interpretation of this result is: “average minimum distance between cells of Immune1 and Tumour is 85.84773”.

Similarly, the summary statistics of the minimum distances can also be visualised by a heatmap. This example shows the average minimum distance between cell types.

    plot_distance_heatmap(phenotype_distances_result = min_summary_dist, metric = "mean")

# 3 You can access the vignettes for other modules of SPIAT here:

- Overview of SPIAT
- Data reading and formatting
- Quality control and visualisation
- Cell colocalisation
- Spatial heterogeneity
- Tissue structure
- Cellular neighborhood

# 4 Reproducibility

    sessionInfo()

    ## R version 4.4.1 (2024-06-14 ucrt)
    ## Platform: x86_64-w64-mingw32/x64
    ## Running under: Windows Server 2022 x64 (build 20348)
    ##
    ## Matrix products: default
    ##
    ##
    ## locale:
    ## [1] LC_COLLATE=C
    ## [2] LC_CTYPE=English_United States.utf8
    ## [3] LC_MONETARY=English_United States.utf8
    ## [4] LC_NUMERIC=C
    ## [5] LC_TIME=English_United States.utf8
    ##
    ## time zone: America/New_York
    ## tzcode source: internal
    ##
    ## attached base packages:
    ## [1] stats4    stats     graphics  grDevices utils     datasets  methods
    ## [8] base
    ##
    ## other attached packages:
    ##  [1] SPIAT_1.6.2                 SpatialExperiment_1.14.0
    ##  [3] SingleCellExperiment_1.26.0 SummarizedExperiment_1.34.0
    ##  [5] Biobase_2.64.0              GenomicRanges_1.56.1
    ##  [7] GenomeInfoDb_1.40.1         IRanges_2.38.1
    ##  [9] S4Vectors_0.42.1            BiocGenerics_0.50.0
    ## [11] MatrixGenerics_1.16.0       matrixStats_1.3.0
    ## [13] BiocStyle_2.32.1
    ##
    ## loaded via a namespace (and not attached):
    ##  [1] tidyselect_1.2.1        viridisLite_0.4.2       dplyr_1.1.4
    ##  [4] farver_2.1.2            fastmap_1.2.0           spatstat.geom_3.3-2
    ##  [7] spatstat.explore_3.3-1  RANN_2.6.1              digest_0.6.36
    ## [10] lifecycle_1.0.4         spatstat.data_3.1-2     magrittr_2.0.3
    ## [13] compiler_4.4.1          rlang_1.1.4             sass_0.4.9
    ## [16] tools_4.4.1             utf8_1.2.4              yaml_2.3.10
    ## [19] knitr_1.48              S4Arrays_1.4.1          labeling_0.4.3
    ## [22] DelayedArray_0.30.1     plyr_1.8.9              abind_1.4-5
    ## [25] withr_3.0.1             grid_4.4.1              polyclip_1.10-7
    ## [28] fansi_1.0.6             colorspace_2.1-1        ggplot2_3.5.1
    ## [31] gtools_3.9.5            scales_1.3.0            spatstat.utils_3.0-5
    ## [34] tinytex_0.52            cli_3.6.3               rmarkdown_2.27
    ## [37] crayon_1.5.3            generics_0.1.3          httr_1.4.7
    ## [40] reshape2_1.4.4          rjson_0.2.21            cachem_1.1.0
    ## [43] stringr_1.5.1           zlibbioc_1.50.0         BiocManager_1.30.23
    ## [46] XVector_0.44.0          vctrs_0.6.5             Matrix_1.7-0
    ## [49] jsonlite_1.8.8          bookdown_0.40           tensor_1.5
    ## [52] magick_2.8.4            spatstat.univar_3.0-0   jquerylib_0.1.4
    ## [55] goftest_1.2-3           glue_1.7.0              spatstat.random_3.3-1
    ## [58] stringi_1.8.4           gtable_0.3.5            deldir_2.0-4
    ## [61] UCSC.utils_1.0.0        munsell_0.5.1           tibble_3.2.1
    ## [64] pillar_1.9.0            htmltools_0.5.8.1       GenomeInfoDbData_1.2.12
    ## [67] R6_2.5.1                evaluate_0.24.0         lattice_0.22-6
    ## [70] apcluster_1.4.13        highr_0.11              bslib_0.8.0
    ## [73] Rcpp_1.0.13             gridExtra_2.3           SparseArray_1.4.8
    ## [76] nlme_3.1-165            spatstat.sparse_3.1-0   xfun_0.46
    ## [79] pkgconfig_2.0.3

# 5 Author Contributions

AT, YF, TY, ML, JZ, VO, MD are authors of the package code. MD and YF wrote the vignette. AT, YF and TY designed the package.