diff --git a/PyrexReader.py b/PyrexReader.py
index ee5d5d9..b4909d5 100644
--- a/PyrexReader.py
+++ b/PyrexReader.py
@@ -102,7 +102,8 @@ def Img_Bimask(img_path,rtstruct_path,ROI_name): # generating image array and bi
 
     ROI_id = match_ROIid(rtstruct_path,ROI_name)
     #Check DICOM file Modality
-    if IM.Modality == 'CT' or 'PT':
+    # Check for the modalities 'CT' or 'PET'
+    if IM.Modality == 'CT' or IM.Modality == 'PT':
         for k in range(len(M.ROIContourSequence[ROI_id].ContourSequence)):
             Cpostion_rt = M.ROIContourSequence[ROI_id].ContourSequence[k].ContourData[2]
             for i in range(num_slice):