Imaging and T₂ relaxometry of short‐T₂ connective tissues in the knee using ultrashort echo‐time double‐echo steady‐state (UTEDESS)

Abstract

Purpose To develop a radial, double-echo steady-state (DESS) sequence with ultra-short echo-time (UTE) capabilities for T2 measurement of short-T2 tissues along with simultaneous rapid, SNR-efficient, and high-isotropic-resolution morphological knee imaging. Methods 3D radial UTE readouts were incorporated into DESS, termed UTEDESS. Multiple-echo-time UTEDESS was used for performing T2 relaxometry for short-T2 tendons, ligaments, and menisci; and for Dixon water-fat imaging. In vivo T2 estimate repeatability and SNR efficiency for UTEDESS and Cartesian DESS were compared. The impact of coil combination methods on short-T2 measurements was evaluated via simulations. UTEDESS T2 measurements were compared to T2 measurements from Cartesian DESS, multi-echo spin-echo (MESE), and fast spin-echo (FSE). Results UTEDESS produced isotropic resolution images with high SNR efficiency in all short-T2 tissues. Simulations and experiments demonstrated that sum-of-squares coil combinations overestimated short-T2 measurements. UTEDESS measurements of meniscal T2 were comparable to DESS, MESE, and FSE measurements while the tendon and ligament measurements were less biased than those from Cartesian DESS. Average UTEDESS T2 repeatability variation was under 10% in all tissues. Conclusions The T2 measurements of short-T2 tissues and high-resolution morphological imaging provided by UTEDESS makes it promising for studying the whole knee, both in routine clinical examinations and longitudinal studies.

Biexponential T2 relaxation estimation of human knee cartilage in vivo at 3T

“…The smaller slice thickness (2 mm) in our study compared to 3 mm or 4 mm of other studies, decreases the PVE. Moreover, 10 TE points were acquired in our study to model the T 2 decay behavior, which leads to more accurate estimation in comparison with other studies in which only 4 or 5 data points were used or only two echoes in the case of using a DESS sequence . Furthermore, using different MR pulse sequences for T 2 relaxation time measurements in articular cartilage can lead to different results.…”

A simple analytic method for estimating T2 in the knee from DESS

“…This could include T 2 mapping in breast cancer patients, which to date is impractical due to the time consuming nature of spin-echo-based T 2 measurements [26]. Also, this methodology has been used to perform relaxometry of short-T 2 tissues in the knee [27]. …”

Five‐minute knee MRI for simultaneous morphometry and T2 relaxometry of cartilage and meniscus and for semiquantitative radiological assessment using double‐echo in steady‐state at 3T

“…These simulations were performed to compromise between adequate SNR for T 2 relaxometry of meniscus and cartilage, low B 1 sensitivity, and sufficient contrast for segmentation. Reference T 1 and T 2 values for the simulated tissues were obtained from previously established results . The simulations were performed with numerical computations using a matrix representation of the EPG formalism with six transverse magnetization states according to methods described previously .…”

“…DESS fluid‐nulled images were used to help guide segmentation in regions with large synovial fluid signal. Reference T 2 measurements to evaluate DESS‐EXP reproducibility were obtained from a previously‐optimized Cartesian DESS sequence (scan parameters in Table ) achieving high SNR through thick slices, low in‐plane resolution, and a low sampling bandwidth . DESS‐EXP images were downsampled to a 0.6 × 0.6 × 3.0 mm 3 resolution to increase SNR and to match the DESS‐T2S resolution.…”

“…DESS‐EXP images were downsampled to a 0.6 × 0.6 × 3.0 mm 3 resolution to increase SNR and to match the DESS‐T2S resolution. Reference T 1 values for cartilage were 1.2 seconds and for the meniscus were 1.0 seconds . The reported T 2 values were averages of all pixel T 2 values in the entire segmented region of interest (ROI).…”