title: Masked volume wise Principal Component Analysis of small adrenocortical tumours in dynamic [11C]-metomidate Positron Emission Tomography.
abstract: BACKGROUND
  In previous clinical Positron Emission Tomography (PET) studies novel approaches for application of Principal Component Analysis (PCA) on dynamic PET images such as Masked Volume Wise PCA (MVW-PCA) have been introduced. MVW-PCA was shown to be a feasible multivariate analysis technique, which, without modeling assumptions, could extract and separate organs and tissues with different kinetic behaviors into different principal components (MVW-PCs) and improve the image quality.
  
  
  METHODS
  In this study, MVW-PCA was applied to 14 dynamic 11C-metomidate-PET (MTO-PET) examinations of 7 patients with small adrenocortical tumours. MTO-PET was performed before and 3 days after starting per oral cortisone treatment. The whole dataset, reconstructed by filtered back projection (FBP) 0-45 minutes after the tracer injection, was used to study the tracer pharmacokinetics.
  
  
  RESULTS
  Early, intermediate and late pharmacokinetic phases could be isolated in this manner. The MVW-PC1 images correlated well to the conventionally summed image data (15-45 minutes) but the image noise in the former was considerably lower. PET measurements performed by defining "hot spot" regions of interest (ROIs) comprising 4 contiguous pixels with the highest radioactivity concentration showed a trend towards higher SUVs when the ROIs were outlined in the MVW-PC1 component than in the summed images. Time activity curves derived from "50% cut-off" ROIs based on an isocontour function whereby the pixels with SUVs between 50 to 100% of the highest radioactivity concentration were delineated, showed a significant decrease of the SUVs in normal adrenal glands and in adrenocortical adenomas after cortisone treatment.
  
  
  CONCLUSIONS
  In addition to the clear decrease in image noise and the improved contrast between different structures with MVW-PCA, the results indicate that the definition of ROIs may be more accurate and precise in MVW-PC1 images than in conventional summed images. This might improve the precision of PET measurements, for instance in therapy monitoring as well as for delineation of the tumour in radiation therapy planning.
authors.affiliation: Molecular Imaging & CT Research, GE Healthcare, Waukesha, Wisconsin, USA. pasha.razifar@ge.com
authors.forename: Pasha
authors.initials: P
authors.lastname: Razifar
authors.forename: Joakim
authors.initials: J
authors.lastname: Hennings
authors.forename: Azita
authors.initials: A
authors.lastname: Monazzam
authors.forename: Per
authors.initials: P
authors.lastname: Hellman
authors.forename: Bengt
authors.initials: B
authors.lastname: Långström
authors.forename: Anders
authors.initials: A
authors.lastname: Sundin
mesh_terms: D000306:Adrenal Cortex Neoplasms / Q000000981:diagnostic imaging*; D000328:Adult; D000368:Aged; D000465:Algorithms; D001185:Artificial Intelligence; D005045:Etomidate / Q000031:analogs & derivatives*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008297:Male; D008875:Middle Aged; D010363:Pattern Recognition, Automated / Q000379:methods*; D049268:Positron-Emission Tomography / Q000379:methods*; D025341:Principal Component Analysis; D019275:Radiopharmaceuticals; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D019275:Radiopharmaceuticals; C084586:metomidate; D005045:Etomidate