## 7 Conclusions  
Whole-body imaging mass spectrometry was developed for the study of spatially resolved immunometabolism within a murine corticosteroid administration model. Metabolic effects of corticosteroid administration in mice were reflected in thymus-centric alterations in purine and pyrimidine metabolites. Applying a machine learning method with dimensionality reduction technology, we demonstrated that the metabolic profile in thymus was consistent with histological compartments such as cortex, medulla and the corticomedullary junction of the control thymus. Applying the aforementioned technology into corticosteroid induced thymus evidenced massive apoptotic changes in the thymic cortex, which was extracted as a common metabolic profile, as well as single specific biomarker metabolites. The following are available online at [[https://www.mdpi.com/article/10.3390/app112211038/s1](https://www.mdpi.com/article/10.3390/app112211038/s1)]([https://www.mdpi.com/article/10.3390/app112211038/s1](https://www.mdpi.com/article/10.3390/app112211038/s1)). Figure S1: HE staining of the serial sections of murine thymus, coronal sections. Upper panels are from left lobe and lower panels are from right lobe of the thymus. Cortex and medulla of the thymus can easily be defined by the current HE staining. Marked points are the arterial branches of the internal thoracic artery, which enter into the thymus. Blood vessels are marked as #, and juxtaposed with major organs and the heart. Scales are 2.5 mm; Figure S2: Control mouse. HE staining of the control murine thoracic transverse tissue section for tMSI. Multiple organs  
Figure 8: **Differentially detected ionic images from mouse thorax by DEX administration. ** Images at \(m/z\) 558.04 (**a**,**e**), 579.03 (**b**,**f**), \(m/z\) 625.16 (**c**,**d**), and 640.12 (**e**,**f**) were shown. (**a**–**d**) are from control mouse and (**e**–**h**) from DEX-treated mouse. Ionic intensity was visualized with heat map mode. \(m/z\) 558.04 is annotated as ADP-ribose by MS/MS analysis (Supplementary Table S1). Color scale for each ion is between 0 and 28.543% (**a**,**e**), 0 to 24.954% (**b**,**f**), 0 to 20.334% (**c**,**d**), and 0 to 13.687% (**e**,**f**), respectively. in the thorax from normal mouse were shown. Each dotted square area was enlarged as numbered: (1) Bone marrow and thymus, (2) A branch from the internal thoracic artery enters the thymus, (3) Adipose tissues surrounding and juxtaposed to the thymus and aorta, (4) Lymph node; several follicle structures are apparently observed as a concentric circle, (5) Enlarged view of bone marrow; typical bone marrow hematopoietic cells such as megakaryocytes are shown. Figure S3: HE staining of the DEX-treated murine thoracic transverse tissue section for tMSI. Figure S4: Results of single mass spectrometry imaging, annotated as purine metabolites, are shown: (a,c,e) are from control mouse and (b,d,f) are from DEX treated mouse, (a,b) GMP at \(m/z\) 362.04, (c,d) GDP at \(m/z\) 442.00, (e,f) GTP at \(m/z\) 521.96. Color scale for each ion is the same as between 0 and 47.023%. Figure S5: Results of single mass spectrometry imaging annotated as pyrimidine metabolites are shown: (a,b,c) and (g,h,i) are from control mouse and (d,e,f) and (j,k,l) are from DEX treated mouse, (a,d) dTMP at \(m/z\) 321.03, (b,e) dTDP at \(m/z\) 401.00, (c,f) dTTP at \(m/z\) 480.96, (g,j) CMP at \(m/z\) 322.04, (h,k) CDP at \(m/z\) 402.00, (i,l) CTP at \(m/z\) 481.98. Color scale for deoxythymidine nucleotides is the same as between 0 and 47.023% and cytidine nucleotides is the same as between 0 and 39.715%, respectively. Figure S6: Ionic images of inosine mono phosphate (IMP), an intermediate metabolite in purine synthesis are shown. IMP as \(m/z\) 347.03. tMSI of normal (left) and DEX treated (right) mice. Color scale for IMP is the same as that between 0 and 30.22%. Figure S7: UMAP analysis from MSI data. Three independent experiments support a definite metabolic compartment shift induced by DEX treatment in mice.