High resolution T1ρ mapping of in vivo human knee cartilage at 7T.

Anup Singh,Hari Hariharan,Kejia Cai,Ravinder Reddy,Mohammad Haris,Feliks Kogan,Amir A Zadpoor

doi:10.1371/journal.pone.0097486

Abstract

PurposeSpin 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.Materials and MethodsIn 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.ResultsOur 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.ConclusionIn 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.

Highlights

Cartilage is a thin tissue with a thickness varying between 1 and 6 mm [1] and consists of multiple zones, superficial, transitional or middle and deep zones
T1r values of cartilage obtained with the localized approach were reproducible
In summary, by using proposed localized frequency and voltage setting approach, high-resolution 3D-T1r maps of in vivo human knee cartilage can be obtained in clinically acceptable scan times (,30 min) and specific absorption ratio (SAR) constraints, which provides the ability to characterize cartilage molecular integrity

Summary

Introduction

Cartilage is a thin tissue with a thickness varying between 1 and 6 mm [1] and consists of multiple zones, superficial, transitional or middle and deep zones. High resolution MRI is always desirable for better characterization of focal aberrations in cartilage molecular integrity. Several T1r mapping studies of very high resolution in ex vivo cartilage tissue have shown exquisite cartilage classification [9,10,11]. T1r mapping has been used to characterize in vivo human articular cartilage at clinical MR field strengths (1.5 T and 3T) [9,12,13,14,15,16,17,18,19,20,21,22]. At clinical field strengths (1.5 T and 3T), planar resolution of in vivo 3D-T1r maps has been limited due to a combination of issues related to adequate SNR, appropriate RF coils and scanning time constraints

Methods

Results

Conclusion