diff --git a/Plugins/org.mitk.gui.qt.photoacoustics.pausmotioncompensation/src/internal/PAUSMotionCompensation.cpp b/Plugins/org.mitk.gui.qt.photoacoustics.pausmotioncompensation/src/internal/PAUSMotionCompensation.cpp
index 932c8800a6..9179a10ae4 100644
--- a/Plugins/org.mitk.gui.qt.photoacoustics.pausmotioncompensation/src/internal/PAUSMotionCompensation.cpp
+++ b/Plugins/org.mitk.gui.qt.photoacoustics.pausmotioncompensation/src/internal/PAUSMotionCompensation.cpp
@@ -1,102 +1,111 @@
 /*===================================================================
 
 The Medical Imaging Interaction Toolkit (MITK)
 
 Copyright (c) German Cancer Research Center,
 Division of Medical and Biological Informatics.
 All rights reserved.
 
 This software is distributed WITHOUT ANY WARRANTY; without
 even the implied warranty of MERCHANTABILITY or FITNESS FOR
 A PARTICULAR PURPOSE.
 
 See LICENSE.txt or http://www.mitk.org for details.
 
 ===================================================================*/
 
-
 // Blueberry
 #include <berryISelectionService.h>
 #include <berryIWorkbenchWindow.h>
 
 // Qmitk
 #include "PAUSMotionCompensation.h"
 
 // Qt
 #include <QMessageBox>
 
 // mitk image
 #include <mitkImage.h>
 
 const std::string PAUSMotionCompensation::VIEW_ID = "org.mitk.views.pausmotioncompensation";
 
 void PAUSMotionCompensation::SetFocus()
 {
   m_Controls.buttonPerformImageProcessing->setFocus();
 }
 
 void PAUSMotionCompensation::CreateQtPartControl(QWidget *parent)
 {
   // create GUI widgets from the Qt Designer's .ui file
   m_Controls.setupUi(parent);
-  connect(m_Controls.buttonPerformImageProcessing, &QPushButton::clicked, this, &PAUSMotionCompensation::DoImageProcessing);
+  connect(
+    m_Controls.buttonPerformImageProcessing, &QPushButton::clicked, this, &PAUSMotionCompensation::DoImageProcessing);
 }
 
 void PAUSMotionCompensation::OnSelectionChanged(berry::IWorkbenchPart::Pointer /*source*/,
                                                 const QList<mitk::DataNode::Pointer> &nodes)
 {
-  // iterate all selected objects, adjust warning visibility
-  foreach (mitk::DataNode::Pointer node, nodes)
+  // Make sure that there are exactle 2 nodes selected
+  if (nodes.size() == 2)
   {
-    if (node.IsNotNull() && dynamic_cast<mitk::Image *>(node->GetData()))
+    // iterate all selected objects, adjust warning visibility
+    foreach (mitk::DataNode::Pointer node, nodes)
     {
-      m_Controls.labelWarning->setVisible(false);
-      m_Controls.buttonPerformImageProcessing->setEnabled(true);
-      return;
+      if (node.IsNotNull() && dynamic_cast<mitk::Image *>(node->GetData()))
+      {
+        m_Controls.labelWarning->setVisible(false);
+        m_Controls.buttonPerformImageProcessing->setEnabled(true);
+        return;
+      }
     }
   }
-
   m_Controls.labelWarning->setVisible(true);
   m_Controls.buttonPerformImageProcessing->setEnabled(false);
 }
 
 void PAUSMotionCompensation::DoImageProcessing()
 {
   QList<mitk::DataNode::Pointer> nodes = this->GetDataManagerSelection();
-  if (nodes.empty())
+
+  // Make sure that there are two images selected
+  if (nodes.empty() || nodes.size() != 2)
+  {
+    QMessageBox::information(nullptr, "Warning", "Please select two images before starting image processing.");
     return;
+  }
 
+  //TODO: I need to process two nodes and get the BaseData.
   mitk::DataNode *node = nodes.front();
 
   if (!node)
   {
     // Nothing selected. Inform the user and return
     QMessageBox::information(nullptr, "Template", "Please load and select an image before starting image processing.");
     return;
   }
 
   // here we have a valid mitk::DataNode
 
   // a node itself is not very useful, we need its data item (the image)
   mitk::BaseData *data = node->GetData();
   if (data)
   {
     // test if this data item is an image or not (could also be a surface or something totally different)
     mitk::Image *image = dynamic_cast<mitk::Image *>(data);
     if (image)
     {
       std::stringstream message;
       std::string name;
       message << "Performing image processing for image ";
       if (node->GetName(name))
       {
         // a property called "name" was found for this DataNode
         message << "'" << name << "'";
       }
       message << ".";
       MITK_INFO << message.str();
 
       // actually do something here...
     }
   }
 }