18F-FDG-PET and MRI in patients with malignancies of the liver and pancreas. Accuracy of retrospective multimodality image registration by using the CT-component of PET/CT.
OBJECTIVE
To evaluate the accuracy of retrospective rigid image registration and fusion between F-18 fluorodeoxyglucose positron emission tomography (FDG-PET) and magnetic resonance imaging (MRI) of the upper abdomen.


METHODS
Image fusion of PET and MRI was performed in 30 patients with suspected malignancy of the liver or pancreas. Using a commercially available image fusion tool capable of rigid manual point-based registration, PET-Images were retrospectively registered and fused by matching eight homologous points in the 3D spoiled gradient echo (GRE) MRI sequences acquired in portal venous phase and in the CT-component of PET/CT. Two separate observers (R1, R2) assessed accuracy of image registration by determining the distances in the x-, y- and z-axis as well as the absolute distance between anatomical landmarks which differed from the landmarks chosen for registration. Quality of fusion was graded using a three point grading scale (1 poorly fused; 2 satisfactory fused; 3 correctly fused) and compared to hybrid PET/CT fusion.


RESULTS
Mean time of registration per patient was less than 2 minutes. Objective registration assessment showed errors between 2.4-6.3 mm in x-axis: mean 3.6 mm (R1); 4.6 mm (R2), 2.3-9.3 mm in y-axis (mean 5.1 mm; 5.5 mm) and 3.3-12.0 mm in z-axis (mean 5.9 mm; 5.9 mm.) The mean error in absolute distance between points was 6.0-16.8 mm (mean 9.9 mm; 10.6 mm). In visual assessment, most fusions were graded to be satisfactory or correctly fused: R1, R2: grade 3, 11/30 (36.7%), 22/30 (73.3%); grade 2, 13/30 (43.3%), 8/30 (26.7%); grade 1, 6/30 (20%), 0/30 (0%). Fusions were mostly comparable to hybrid PET/CT fusions. All of the fusions were defined as diagnostically relevant by both observers.


CONCLUSIONS
Retrospective rigid image fusion of FDG-PET and MRI of the upper abdomen using the CT-component of PET/CT for registration is feasible without adaptation in image acquisition protocols and shows sub-centimeter registration errors in most cases.
Donati
O F
OF
Institute of Diagnostic Radiology, University Hospital Zürich, 8091 Zürich, Switzerland. olivio.donati@usz.ch
Reiner
C S
CS
Hany
T F
TF
Fornaro
J
J
von Schulthess
G K
GK
Marincek
B
B
Weishaupt
D
D
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D049628:Body Size; D003110:Colonic Neoplasms / Q000000981:diagnostic imaging / Q000556:secondary; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008099:Liver / Q000033:anatomy & histology; D008113:Liver Neoplasms / Q000000981:diagnostic imaging*; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D010190:Pancreatic Neoplasms / Q000000981:diagnostic imaging*; D049268:Positron-Emission Tomography / Q000379:methods; D014057:Tomography, X-Ray Computed / Q000379:methods
D019788:Fluorodeoxyglucose F18