Root data energy information is converted to keV instead of MeV (#736)

* Root data energy information is converted to keV instead of MeV

This is done only in the when reading energy information.

* Remove unnecessary #include

* get energy information in keV functions. Update ROOT documentation

Clean up the conversion of energy information to keV using methods. Updates the documentation regarding ROOT energy units and the conversion

* Updates release notes [ci skip]

documentation/STIR-UsersGuide.tex

@@ -774,6 +774,10 @@ \subsubsection{ROOT files as output by OpenGATE}
 
 See \texttt{examples/samples/root\_headerECAT.hroot} for an example using the ECAT system.
 
+OpenGATE energy information is recorded in MeV units into the ROOT file.
+For STIR files, e.g. \texttt{.hroot} and \texttt{.hs}, should use keV units.
+STIR assumes this convention and will convert this automatically.
+
 There are some unfinished classes
 available on the \textit{STIR} web-site to read \textit{LMF} format files,
 in conjunction with the \textit{LMF} library. However, these might be obsolete

documentation/release_4.1.htm

@@ -119,6 +119,10 @@ <h3>Minor bug fixes</h3>
   Changes to GATE/root cylindrical PET geometry interpretation,
   see <a href="https://github.com/UCL/STIR/pull/569">PR 569</a>.</li>
 </li>
+<li>
+    OpenGATE energy information is MeV. Added a method to convert between MeV to (STIR convention) keV units when
+    reading root files.
+</li>
 </ul>
 
 <h3>Documentation changes</h3>

src/IO/InputStreamFromROOTFileForCylindricalPET.cxx

@@ -81,10 +81,11 @@ get_next_record(CListRecordROOT& record)
             continue;
         if ( (this->eventID1 != this->eventID2) && this->exclude_randoms)
             continue;
-        if (this->energy1 < this->low_energy_window ||
-                 this->energy1 > this->up_energy_window ||
-                 this->energy2 < this->low_energy_window ||
-                 this->energy2 > this->up_energy_window)
+      //multiply here by 1000 to convert the list mode energy from MeV to keV
+        if (this->get_energy1_in_keV() < this->low_energy_window ||
+                this->get_energy1_in_keV() > this->up_energy_window ||
+                this->get_energy2_in_keV() < this->low_energy_window ||
+                this->get_energy2_in_keV() > this->up_energy_window)
             continue;
 
         break;

src/IO/InputStreamFromROOTFileForECATPET.cxx

@@ -77,10 +77,11 @@ get_next_record(CListRecordROOT& record)
             continue;
         if ( eventID1 != eventID2 && exclude_randoms )
             continue;
-        if (energy1 < low_energy_window ||
-                 energy1 > up_energy_window ||
-                 energy2 < low_energy_window ||
-                 energy2 > up_energy_window)
+        //multiply here by 1000 to convert the list mode energy from MeV to keV
+        if (this->get_energy1_in_keV() < low_energy_window ||
+                this->get_energy1_in_keV() > up_energy_window ||
+                this->get_energy2_in_keV() < low_energy_window ||
+                this->get_energy2_in_keV() > up_energy_window)
             continue;
 
         break;

src/include/stir/IO/InputStreamFromROOTFile.h

@@ -204,6 +204,12 @@ class InputStreamFromROOTFile : public RegisteredObject< InputStreamFromROOTFile
     //! (<a href="http://wiki.opengatecollaboration.org/index.php/Users_Guide_V7.2:Digitizer_and_readout_parameters">here</a> )
     //! > the readout depth depends upon how the electronic readout functions.
     int singles_readout_depth;
+
+    //! OpenGATE output ROOT energy information is given in MeV, these methods convert to keV
+    float get_energy1_in_keV() const
+    { return energy1 * 1e3; };
+    float get_energy2_in_keV() const
+    { return energy2 * 1e3; };
 };
 
 END_NAMESPACE_STIR