Reni Biswas

Ultrashort echo time (UTE) imaging with bi-component analysis: Bound and free water evaluation of bovine cortical bone subject to sequential drying

Recent proton magnetic resonance (MR) spectroscopy studies have shown that cortical bone exists as different components which have distinct transverse relaxation times (T2s). However, cortical bone shows zero or near zero signal with all conventional MR sequences on clinical scanners and the different water components cannot be assessed with this approach. In order to detect signal in this situation a two-dimensional (2D) non-slice selective ultrashort echo time (UTE) pulse sequence with a nominal TE of 8 μs was used together with bi-component analysis to quantify bound and free water in bovine cortical bone at 3T. Total water concentration was quantified using a 3D UTE sequence together with a reference water phantom. 2D and 3D UTE imaging were performed on 14 bovine bone samples which were subjected to sequential air drying to evaluate free water loss, followed by oven drying to evaluate bound water loss. Sequential bone weight loss was measured concurrently using a precision balance. Bone porosity was measured with micro computed tomography (μCT) imaging. UTE measured free water loss was higher than the volume of cortical pores measured with μCT, but lower than the gravimetric bone water loss measured during air drying. UTE assessed bound water loss was about 82% of gravimetric bone water loss during oven drying. On average bovine cortical bone showed about 13% free water and 87% bound water. There was a high correlation (R=0.91; P<0.0001) between UTE MR measured free water loss and gravimetric bone weight loss during sequential air drying, and a significant correlation (R=0.69; P<0.01) between UTE bound water loss and gravimetric bone weight loss during oven drying. These results show that UTE bi-component analysis can reliably quantify bound and free water in cortical bone. The technique has potential applications for the in vivo evaluation of bone porosity and organic matrix.

Ultrashort echo time magnetization transfer (UTE‐MT) imaging of cortical bone

Magnetization transfer (MT) imaging is one way to indirectly assess pools of protons with fast transverse relaxation. However, conventional MT imaging sequences are not applicable to short T2 tissues such as cortical bone. Ultrashort echo time (UTE) sequences with TE values as low as 8 µs can detect signals from different water components in cortical bone. In this study we aim to evaluate two‐dimensional UTE‐MT imaging of cortical bone and its application in assessing cortical bone porosity as measured by micro‐computed tomography (μCT) and biomechanical properties. In total, 38 human cadaveric distal femur and proximal tibia bones were sectioned to produce 122 rectangular pieces of cortical bone for quantitative UTE‐MT MR imaging, μCT, and biomechanical testing. Off‐resonance saturation ratios (OSRs) with a series of MT pulse frequency offsets (Δf) were calculated and compared with porosity assessed with μCT, as well as elastic (modulus, yield stress, and strain) and failure (ultimate stress, failure strain, and energy) properties, using Pearson correlation and linear regression. A moderately strong negative correlation was observed between OSR and μCT porosity (R2 = 0.46–0.51), while a moderate positive correlation was observed between OSR and yield stress (R2 = 0.25–0.30) and failure stress (R2 = 0.31–0.35), and a weak positive correlation (R2 = 0.09–0.12) between OSR and Youngs modulus at all off‐resonance saturation frequencies. OSR determined with the UTE‐MT sequence provides quantitative information on cortical bone and is sensitive to μCT porosity and biomechanical function. Copyright

Single‐ and Bi‐component T2* analysis of tendon before and during tensile loading, using UTE sequences

To determine if the application of tensile force alters the single‐ or bi‐component T2* values of human tendons as measured on a clinical MRI scanner with ultrashort echo time (UTE sequences and if single‐ or bi‐component T2* values differ when measured with 2D‐UTE, 3D‐UTE, or 3D‐UTE‐Cones sequences.

UTE MRI of the Osteochondral Junction.

The osteochondral junction is composed of numerous tissue components and serves important functions relating to structural stability and proper nutrition in joints such as the knee and spine. Conventional MR techniques have been inadequate at imaging the tissues of the osteochondral junction primarily because of the intrinsically short T2 nature of these tissues, rendering them “invisible” with the standard acquisitions. Ultrashort time to echo (UTE) MR techniques acquire sufficient MR signal of osteochondral tissues, thereby allowing direct evaluation. This article reviews the anatomy of the osteochondral junction of the knee and the spine, technical aspects of UTE MRI, and the application of UTE MRI for evaluation of the osteochondral junction.

Ultrashort time to echo magnetic resonance techniques for the musculoskeletal system

Magnetic resonance (MR) imaging has been widely implemented as a non-invasive modality to investigate musculoskeletal (MSK) tissue disease, injury, and pathology. Advancements in MR sequences provide not only enhanced morphologic contrast for soft tissues, but also quantitative biochemical evaluation. Ultrashort time to echo (UTE) sequence, in particular, enables novel morphologic and quantitative evaluation of previously unseen MSK tissues. By using short minimum echo times (TE) below 1 msec, the UTE sequence can unveil short T2 properties of tissues including the deepest layers of the articular cartilage, cartilaginous endplate at the discovertebral junction, the meniscus, and the cortical bone. This article will discuss the application of UTE to evaluate these MSK tissues, starting with tissue structure, MR imaging appearance on standard versus short and ultrashort TE sequences, and provide the range of quantitative MR values found in literature.

Off‐resonance saturation ratio obtained with ultrashort echo time‐magnetization transfer techniques is sensitive to changes in static tensile loading of tendons and degeneration

To determine if off‐saturation ratio (OSR) measured with the ultrashort echo time magnetization transfer (UTE‐MT) sequence could differentiate between tendons under different states of tensile load and to compare these changes between normal versus degenerated tendons.

High-Resolution Qualitative and Quantitative Magnetic Resonance Evaluation of the Glenoid Labrum.

Objective This study aimed to implement qualitative and quantitative magnetic resonance sequences for the evaluation of labral pathology. Methods Six glenoid labra were dissected, and the anterior and posterior portions were divided into normal, mildly degenerated, or severely degenerated groups using gross and magnetic resonance findings. Qualitative evaluation was performed using T1-weighted, proton density-weighted, spoiled gradient echo and ultrashort echo time (UTE) sequences. Quantitative evaluation included T2 and T1rho measurements as well as T1, T2*, and T1rho measurements acquired with UTE techniques. Results Spoiled gradient echo and UTE sequences best demonstrated labral fiber structure. Degenerated labra had a tendency toward decreased T1 values, increased T2/T2* values, and increased T1rho values. T2* values obtained with the UTE sequence allowed for delineation among normal, mildly degenerated, and severely degenerated groups (P < 0.001). Conclusions Quantitative T2* measurements acquired with the UTE technique are useful for distinguishing among normal, mildly degenerated, and severely degenerated labra.

High-resolution morphologic and ultrashort time-to-echo quantitative magnetic resonance imaging of the temporomandibular joint.

ObjectiveTo implement high-resolution morphologic and quantitative magnetic resonance imaging (MRI) of the temporomandibular joint (TMJ) using ultrashort time-to-echo (UTE) techniques in cadavers and volunteers.MethodsThis study was approved by the institutional review board. TMJs of cadavers and volunteers were imaged on a 3-T MR system. High-resolution morphologic and quantitative sequences using conventional and UTE techniques were performed in cadaveric TMJs. Morphologic and UTE quantitative sequences were performed in asymptomatic and symptomatic volunteers.ResultsMorphologic evaluation demonstrated the TMJ structures in open- and closed-mouth position. UTE techniques facilitated the visualization of the disc and fibrocartilage. Quantitative UTE MRI was successfully performed ex vivo and in vivo, reflecting the degree of degeneration. There was a difference in the mean UTE T2* values between asymptomatic and symptomatic volunteers.ConclusionsMRI evaluation of the TMJ using UTE techniques allows characterization of the internal structure and quantification of the MR properties of the disc. Quantitative UTE MRI can be performed in vivo with short scan times.

Evaluation of the disco-vertebral junction using ultrashort time-to-echo magnetic resonance imaging: inter-reader agreement and association with vertebral endplate lesions

ObjectiveTo evaluate ultrashort time to echo (UTE) magnetic resonance (MR) morphology of the cartilaginous endplates (CEP) in cadaveric lumbar spines with bony vertebral endplate (VEP) lesions, to determine inter-reader agreement as well as associations between the CEP morphology and VEP lesions as well as other abnormalities.Materials and methodsMR imaging of cadaveric lumbar spines from 10 donors was performed at 3T using a UTE MR sequence. Two musculoskeletal radiologists identified the location of vertebral endplate lesions in consensus. The morphology of the CEP overlying the lesions and in the adjacent normal regions was assessed individually. A total of 55 vertebral lesions and 55 normal regions were assessed. The presence of osteophytosis, morphological changes of the anterior and posterior longitudinal ligament, and intervertebral disc signal and morphology was also assessed. Agreement between observers was determined using Cohen’s kappa analysis, and association between CEP and vertebral endplate lesions was determined using the chi square test.ResultsFifty-five vertebral endplate lesions were identified and the morphology of CEP evaluated by two readers was in substantial agreement with Cohen’s kappa of 0.78. The presence of vertebral endplate abnormality was associated with the presence of osteophytes (39 out of 55 levels), altered morphology and signal of the anterior longitudinal ligament (23 out of 55 levels) and intervertebral discs (30 out of 55 levels).ConclusionUTE MRI enables evaluation of the CEP with substantial inter-reader agreement. Abnormal changes of the CEP may facilitate formation of lesions of vertebral endplate over time and are associated with degenerative changes of the lumbar spine.

Thickness of the Meniscal Lamellar Layer: Correlation with Indentation Stiffness and Comparison of Normal and Abnormally Thick Layers by Using Multiparametric Ultrashort Echo Time MR Imaging

Purpose To determine the relationship between lamellar layer thickness on ultrashort echo time (UTE) magnetic resonance (MR) images and indentation stiffness of human menisci and to compare quantitative MR imaging values between two groups with normal and abnormally thick lamellar layers. Materials and Methods This was a HIPAA-compliant, institutional review board-approved study. Nine meniscal pieces were obtained from seven donors without gross meniscal pathologic results (mean age, 57.4 years ± 14.5 [standard deviation]). UTE MR imaging and T2, UTE T2*, and UTE T1ρ mapping were performed. The presence of abnormal lamellar layer thickening was determined and thicknesses were measured. Indentation testing was performed. Correlation between the thickness and indentation stiffness was assessed, and mean quantitative MR imaging values were compared between the groups. Results Thirteen normal lamellar layers had mean thickness of 232 μm ± 85 and indentation peak force of 1.37 g ± 0.87. Four abnormally thick lamellar layers showed mean thickness of 353.14 μm ± 98.36 and peak force 0.72 g ± 0.31. In most cases, normal thicknesses showed highly positive correlation with the indentation peak force (r = 0.493-0.912; P < .001 to .05). However, the thickness in two abnormal lamellar layers showed highly negative correlation (r = -0.90, P < .001; and r = -0.23, P = .042) and no significant correlation in the others. T2, UTE T2*, and UTE T1ρ values in abnormally thick lamellar layers were increased compared with values in normal lamellar layers, although only the UTE T2* value showed significant difference (P = .010). Conclusion Variation of lamellar layer thickness in normal human menisci was evident on two-dimensional UTE images. In normal lamellar layers, thickness is highly and positively correlated with surface indentation stiffness. UTE T2* values may be used to differentiate between normal and abnormally thickened lamellar layers. (©) RSNA, 2016.