The collagen density is not detected in the patellar tendon (PT), posterior cruciate ligament (PCL), and anterior cruciate ligament (ACL) in clinic. We assess the technical feasibility of three-dimension multiecho fat saturated ultrashort echo time cones (3D FS-UTE-Cones) acquisitions for single- and bicomponent T2
Many of the degenerate tendons and ligaments from cadavers and biopsies from patients had a decreased collagen concentration and this change may predispose the tendons and ligaments to rupture, as a reduction in the collagen density has been correlated with the tensile strength of tendons and ligaments. If we can detect the reduction in the collagen density in the degenerate patellar tendon (PT), posterior cruciate ligament (PCL), and anterior cruciate ligament (ACL) in clinic, some medical methods might be used to prevent PT, PCL, and ACL from being ruptured. However, tendons and ligaments typically have very short transverse relaxation times (T2s or T2
Ultrashort echo time (UTE) techniques, which use nominal TEs about 10-200 times shorter than those of conventional clinical MR sequences, can directly detect signal from short T2 tissues and might be used for diagnosis of these diseases at early stages [
Most knee joint tissues, including PT, PCL, and ACL, have two components, namely, bound water (BW) and free water (FW). Free water has a longer T2
However, bicomponent analysis typically requires a long scan time to allow acquisition of all images at different TEs [
Five heathy volunteers (4 males, aging from 25 to 30; one female, 46 years old) were enrolled to investigate the clinical feasibility of 3D multiecho FS-UTE-Cones imaging techniques using a clinical whole-body 3T scanner. Written informed consent and approval from the institutional review board (IRB) of our hospital were obtained before the in vivo scans. The inclusion criteria for the volunteers were as follows: no history of knee joints pain, no nontraumatic joint pain history, and no metal implants or pacemakers.
Six sets of PCL, ACL, and PT samples from cadaveric knees of six donors (2 males, 4 females, age range = 24–65 years, and mean ± standard deviation of 47.5 ± 14.5 years) were obtained from University California, San Diego morgue. A transverse cut at the proximal one-third of the samples and a longitudinal cut through the center of the ligament stored in -20°C refrigerator. A transverse slab of ~10 mm thickness and a longitudinal slab of ~5mm thickness were cut and stored in a phosphate buffered saline (PBS) soaked gauze at 4°C prior to MR imaging. After the ex vivo scans, the samples from the center of the PCL, ACL, and PT substance were immediately fixed in Z-Fix (Anatech, Battle Creek, MI) for histology. Samples were embedded in paraffin, and five micrometer thick sections were cut and stained with hematoxylin and eosin (H&E).
An 8-channel transmit-receive knee coil and a 3-inch coil was used for all volunteer and cadaveric samples acquisitions, respectively. The 3D FS-UTE-Cones sequence employs a short rectangular pulse excitation (pulse duration = 32
The 3D UTE Cones sequence (a). After excitation with a short rectangular pulse, a 3D Cones trajectory (b) is used to allow time-efficient sampling with a minimal TE of 32
To save scan time, a multiecho FS-UTE-Cones acquisition scheme was designed for mapping of T2
Both single- and bicomponent T2
Selected 3D UTE Cones images and region-of-interest (ROI) shown in a patella tendon (PT) sample with red lines, a posterior cruciate ligament (PCL) sample with yellow lines, and anterior cruciate ligament (ACL) sample with blue lines (a), followed by histology in the ROI of the PT (b), PCL (c), and ACL (d), where collagen is arranged in tightly cohesive well-demarcated bundles (stain: hematoxylin and eosin; original magnification,
Selected 3D UTE Cones images and region-of-interest (ROI) shown with red lines in patella tendon (PT) (a), posterior cruciate ligament (PCL) (c), and anterior cruciate ligament (ACL) (e), as well as single- and bicomponent fitting (b, d, f) of interleaved multiecho UTE image acquired at TE (0.032/4.4/20/40 ms, 0.4/6.6/25/50 ms, 0.8/1/30/60 ms, and 2.2/16/35/70 ms of a 29 years old male volunteer). All bicomponent fitting shows superior over single-component fitting. Dashed lines represent the estimated T2
Both single- and biexponential fitting procedures were performed on the selected ROIs, for all MR data sets. For single-exponential fitting, a three-parameter function (see (
For the T2
As a result, the bicomponent fitting model can estimate T2
All statistical analyses were analyzed in SPSS Statistics version 13.0 for Windows. Calculated values, including T2
Table
T-test of RMSE between bi- and single-component.
Parameters | Knee joint samples (RMSE) | Knee joints in Volunteer (RMSE) | ||||
---|---|---|---|---|---|---|
Bi-component (%) | Single-component (%) | P values | Bi-component (%) | Single-component (%) | P values | |
PT | 0.08±0.04 | 0.91±0.41 | 0.01 | 1.63±0.15 | 2.56±0.12 | 0.01 |
PCL | 0.12±0.02 | 1.38±0.25 | 0.01 | 1.34±0.13 | 2.57±0.25 | 0.01 |
ACL | 0.33±0.09 | 1.91±0.71 | 0.01 | 3.23±0.33 | 3.62±0.33 | 0.29 |
Figure
Simulation results are shown in Figure
Table
Bi- and single-component T2
parameters | Samples | Volunteer | |||||
---|---|---|---|---|---|---|---|
PT | PCL | ACL | PT | PCL | ACL | ||
Bi-component | | 80.44±8.31 | 75.50±6.49 | 79.24±7.43 | 90.54±2.69 | 87.02±3.85 | 21.91±9.05 |
T2 | 1.53±0.31 | 1.86±0.45 | 1.63±0.31 | 1.40±0.50 | 1.56±0.71 | 2.01±0.45 | |
| 19.56±8.31 | 24.50±6.49 | 21.30±7.44 | 9.45±2.69 | 13.04±3.91 | 78.62±8.17 | |
T2 | 11.83±4.63 | 13.53±3.46 | 13.58±6.59 | 12.96±1.08 | 12.81±3.47 | 13.08±3.38 | |
Single-component | T2 | 2.17±0.49 | 2.64±0.46 | 2.18±0.49 | 2.05±0.27 | 2.21±0.96 | 7.65±1.29 |
SD: standard deviation; PCL: posterior cruciate ligament; ACL: anterior cruciate ligament; PT: patellar tendon.
However, for volunteer, T2
Table
parameters | Sample | Volunteer | |||||
---|---|---|---|---|---|---|---|
PT_PCL | PCL_ACL | PT_ACL | PT_PCL | PCL_ACL | PT_ACL | ||
Bi-component | | 0.24 | 0.73 | 0.45 | 0.01 | 0.01 | 0.01 |
T2 | 0.21 | 0.28 | 0.46 | 0.63 | 0.47 | 0.01 | |
| 0.24 | 0.69 | 0.47 | 0.01 | 0.01 | 0.01 | |
T2 | 0.28 | 0.18 | 0.61 | 0.88 | 0.41 | 0.04 | |
Single-component | T2 | 0.58 | 0.23 | 0.06 | 0.05 | 0.06 | 0.01 |
PCL: posterior cruciate ligament, ACL: anterior cruciate ligament, and PT: patella tendon. P values < 0.05 indicate significant difference; 0.01 < P values < 0.001 are highly statistically significant.
Box plots of
Our results suggest that the 3D Cones FS-UTE sequences, together with an interleaved multiecho acquisition strategy, allow mapping of bound and free water T2
As shown in Table
The T2
Our results for T2
For the first time, we performed T2
In summary, our results suggest that multiecho 3D UTE Cones acquisitions have some advantages over existing technologies. First, the multiecho 3D FS-UTE-Cones acquisition allows highresolution 2D T2
Our study has several limitations. First, 3D UTE requires longer scan times. The increased likelihood of patient movement increases susceptibility to motion artifacts and could introduce errors in biexponential T2
This study confirms that interleaved multiecho 3D UTE Cones acquisitions allow T2
The data used to support the findings of this study are available from the corresponding author upon request.
An earlier version of our study has been presented as meeting in Joint 2018 ISMRM-ESMRMB (E-poster).
The authors declare that they no conflicts of interest.
The authors thank Niloofar Shojaeiadib for the statistical analysis and Rose Luo for proofreading the manuscript. This study has received grants from the National Scientific Foundation of China (nos. 81871510 and 81471810), the Tianhe District Science and Technology Project of Guangzhou City, Guangdong Provincial, China (no. 201704KW026), and the Public Welfare Research and Capacity Building of Science and Technology Projects of Guangdong Province, China (nos. 2014A020212399 and 2014A020211018).