Selecting the reference image for registration of CEST series.
BACKGROUND
To compare different reference images selected for registration among chemical exchange saturation transfer (CEST) series.


METHODS
Five normal volunteers and eight brain tumor patients were studied on a 3 Tesla scanner. Image registration was performed by choosing each of the acquired CEST saturation or unsaturation dynamic images as the reference. CEST images at 3.5 ppm (amide proton transfer, APT) were computed for each motion-corrected data set after main magnetic field inhomogeneity correction. A uniformity index was defined to quantify the efficacy of image registration using different reference images. Joint histograms and the structural similarity index (SSIM) were used to analyze the intrinsic image similarity between various dynamic images.


RESULTS
Image registration increased the average uniformity index by 18% if the 3.5 ppm saturated image was selected as the reference image. However, registering to the unsaturated dynamic image reduced the uniformity index by 13% on average. The joint histogram analysis showed that the saturated dynamic images were highly similar (SSIM = 0.89 ± 0.01), and were considerably different from the unsaturated dynamic image (SSIM = 0.58 ± 0.03).


CONCLUSIONS
The selection of the 3.5 ppm dynamic image as the reference image generated the highest uniformity index for APT imaging though other saturated images were equally suited as reference images.
Division of MR Research, Department of Radiology, Johns Hopkins University, Baltimore, Maryland, USA.
Yi
Y
Zhang
Division of MR Research, Department of Radiology, Johns Hopkins University, Baltimore, Maryland, USA.
Hye-Young
HY
Heo
Division of MR Research, Department of Radiology, Johns Hopkins University, Baltimore, Maryland, USA.
Dong-Hoon
DH
Lee
Division of MR Research, Department of Radiology, Johns Hopkins University, Baltimore, Maryland, USA.
Xuna
X
Zhao
Division of MR Research, Department of Radiology, Johns Hopkins University, Baltimore, Maryland, USA.
Shanshan
S
Jiang
Division of MR Research, Department of Radiology, Johns Hopkins University, Baltimore, Maryland, USA.
Kai
K
Zhang
Division of MR Research, Department of Radiology, Johns Hopkins University, Baltimore, Maryland, USA.
Haiyun
H
Li
Division of MR Research, Department of Radiology, Johns Hopkins University, Baltimore, Maryland, USA.|F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland, USA.
Jinyuan
J
Zhou
D001932:Brain Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology*; D016022:Case-Control Studies; D003287:Contrast Media / Q000737:chemistry; D064368:Healthy Volunteers; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D007091:Image Processing, Computer-Assisted / Q000379:methods; D060526:Magnetic Fields; D008279:Magnetic Resonance Imaging; D015233:Models, Statistical; D009038:Motion; D012016:Reference Values
D003287:Contrast Media
APT imaging; CEST imaging; brain tumor; image registration