diff --git a/src/modality-specific-files/magnetic-resonance-imaging-data.md b/src/modality-specific-files/magnetic-resonance-imaging-data.md
index 41cacd7e8f..8501651298 100644
--- a/src/modality-specific-files/magnetic-resonance-imaging-data.md
+++ b/src/modality-specific-files/magnetic-resonance-imaging-data.md
@@ -163,6 +163,18 @@ When adding additional metadata please use the CamelCase version of
 whenever possible. See also
 [recommendations on JSON files](../common-principles.md#keyvalue-files-dictionaries).
 
+#### Tissue description
+
+<!-- This block generates a metadata table.
+These tables are defined in
+  src/schema/rules/sidecars
+The definitions of the fields specified in these tables may be found in
+  src/schema/objects/metadata.yaml
+A guide for using macros can be found at
+ https://github.com/bids-standard/bids-specification/blob/master/macros_doc.md
+-->
+{{ MACROS___make_sidecar_table("mri.MRISample") }}
+
 ## Anatomy imaging data
 
 <!--
diff --git a/src/modality-specific-files/positron-emission-tomography.md b/src/modality-specific-files/positron-emission-tomography.md
index d26ba71df6..51842bb11c 100644
--- a/src/modality-specific-files/positron-emission-tomography.md
+++ b/src/modality-specific-files/positron-emission-tomography.md
@@ -151,6 +151,18 @@ A guide for using macros can be found at
 -->
 {{ MACROS___make_sidecar_table("pet.PETScannerHardware") }}
 
+#### Tissue description
+
+<!-- This block generates a metadata table.
+These tables are defined in
+  src/schema/rules/sidecars
+The definitions of the fields specified in these tables may be found in
+  src/schema/objects/metadata.yaml
+A guide for using macros can be found at
+ https://github.com/bids-standard/bids-specification/blob/master/macros_doc.md
+-->
+{{ MACROS___make_sidecar_table("pet.PETSample") }}
+
 #### Radiochemistry
 
 <!-- This block generates a metadata table.
diff --git a/src/schema/rules/sidecars/mri.yaml b/src/schema/rules/sidecars/mri.yaml
index 6833f89a34..3cadec9b63 100644
--- a/src/schema/rules/sidecars/mri.yaml
+++ b/src/schema/rules/sidecars/mri.yaml
@@ -36,6 +36,11 @@ MRIScannerHardware:
     MatrixCoilMode: recommended
     CoilCombinationMethod: recommended
     NumberTransmitCoilActiveElements: optional
+
+MRISample:
+  selectors:
+    - modality == "mri"
+  fields:
     BodyPart: optional
     BodyPartDetails: optional
     BodyPartDetailsOntology: optional
diff --git a/src/schema/rules/sidecars/pet.yaml b/src/schema/rules/sidecars/pet.yaml
index aa942df8fd..4cd85a14a5 100644
--- a/src/schema/rules/sidecars/pet.yaml
+++ b/src/schema/rules/sidecars/pet.yaml
@@ -25,6 +25,12 @@ PETScannerHardware:
     InstitutionalDepartmentName:
       level: recommended
       description_addendum: Corresponds to DICOM Tag 0008, 1040 `Institutional Department Name`.
+
+PETSample:
+  selectors:
+    - modality == "pet"
+    - suffix == "pet"
+  fields:
     BodyPart:
       level: recommended
       description_addendum: Corresponds to DICOM Tag 0018, 0015 `Body Part Examined`.