High resolution T1ρ mapping of in vivo human knee cartilage at 7T.
OBJECTIVE
Spin lattice relaxation time in rotating frame (T1ρ) mapping of human knee cartilage has shown promise in detecting biochemical changes during osteoarthritis. Due to higher field strength, MRI at 7T has advantages in term of SNR compared to clinical MR scanners and this can be used to increase in image resolution. Objective of current study was to evaluate the feasibility of high resolution T1ρ mapping of in vivo human knee cartilage at 7T MR scanner.


METHODS
In this study we have used a T1ρ prepared GRE pulse sequence for obtaining high resolution (in plan resolution  = 0.2 mm2) T1ρ MRI of human knee cartilage at 7T. The effect of a global and localized reference frequency and reference voltage setting on B0, B1 and T1ρ maps in cartilage was evaluated. Test-retest reliability results of T1ρ values from asymptomatic subjects as well as T1ρ maps from abnormal cartilage of two human subjects are presented. These results are compared with T1ρ MRI data obtained from 3T.


RESULTS
Our approach enabled acquisition of 3D-T1ρ data within allowed SAR limits at 7T. SNR of cartilage on T1ρ weighted images was greater than 90. Off-resonance effects present in the cartilage B0, B1 and T1ρ maps obtained using global shim and reference frequency and voltage setting, were reduced by the proposed localized reference frequency and voltage setting. T1ρ values of cartilage obtained with the localized approach were reproducible. Abnormal knee cartilage showed elevated T1ρ values in affected regions. T1ρ values at 7T were significantly lower (p<0.05) compared to those obtained at 3T.


CONCLUSIONS
In summary, by using proposed localized frequency and voltage setting approach, high-resolution 3D-T1ρ maps of in vivo human knee cartilage can be obtained in clinically acceptable scan times (<30 min) and SAR constraints, which provides the ability to characterize cartilage molecular integrity.
CMROI, Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America; Center for Biomedical Engineering, Indian Institute of Technology Delhi, Delhi, India.
Anup
A
Singh
CMROI, Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America; Research Branch, Sidra Medical and Research Center, Doha, Qatar.
Mohammad
M
Haris
CMROI, Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America; Radiology, University of Illinois at Chicago, Chicago, Illinois, United States of America.
Kejia
K
Cai
CMROI, Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.
Feliks
F
Kogan
CMROI, Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.
Hari
H
Hariharan
CMROI, Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.
Ravinder
R
Reddy
D000328:Adult; D002358:Cartilage, Articular / Q000033:anatomy & histology* / Q000473:pathology; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional; D007717:Knee / Q000473:pathology; D007719:Knee Joint / Q000473:pathology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000175:diagnosis / Q000503:physiopathology*; D015203:Reproducibility of Results; D059629:Signal-To-Noise Ratio; D055815:Young Adult