Ultrashort echo time spectroscopic imaging (UTESI): an efficient method for quantifying bound and free water

Abstract

Biological tissues usually contain distinct water compartments with different transverse relaxation times. In this study, two-dimensional, multi-slice, ultrashort echo time spectroscopic imaging (UTESI) was used with bi-component analysis to detect bound and free water components in musculoskeletal tissues. Feasibility studies were performed using numerical simulation. Imaging was performed on bovine cortical bone, human cadaveric menisci and the Achilles' tendons of volunteers. The simulation study demonstrated that UTESI, together with bi-component analysis, could reliably quantify both T(2)* and fractions of the short and long (2)* components. The in vitro and in vivo studies each took less than 14 min. The bound water components showed a short T(2)* of ~0.3 ms for bovine bone, ~1.8 ms for meniscus and ~0.6 ms for the Achilles' tendon. The free water components showed about an order of magnitude longer T(2)* values, with ~2 ms for bovine bone, ~14 ms for meniscus and ~8 ms for the Achilles' tendon. Bound water fractions of up to ~76% for bovine bone, 50% for meniscus and ~75% for the Achilles' tendon were measured. The corresponding free water components were up to ~24% for bovine bone, 50% for meniscus and ~25% for the Achilles' tendon by volume. These results demonstrate that UTESI, combined with bi-component analysis, can quantify the bound and free water components in musculoskeletal tissues in clinically realistic times.

Ultrashort–Echo Time MR Imaging of the Patella with Bicomponent Analysis: Correlation with Histopathologic and Polarized Light Microscopic Findings

“…Recent nuclear MR spectroscopy of simple collagen-water systems shows that water molecules exist either as bulk water, which does not interact with collagen, or as interior hydration water molecules (9,29). The existence of bound and free water pools has also been confirmed by findings in recent cross-relaxation imaging experiments (30), as well as results from MR spectroscopy studies and our own study (10,16).…”

“…(25,26). Because only three parameters, namely short T2*, long T2*, and the short or long T2* fraction, were fitted in this bicomponent model, robust fitting could be achieved with clinically achievable signal-to-noise ratios (16).…”

“…Ultrashort-TE sequences have been developed to image short-T2 tissues or tissue components in vitro and in vivo and have been implemented on clinical MR imaging units (11)(12)(13)(14)(15). Recently, we reported the use of ultrashort-TE imaging together with bicomponent analysis to evaluate short T2* (predictive of bound water) and longer T2* (predictive of free water) components in joint tissues (16). In this study, we aimed to correlate Red-stained sections centered on a ro tating stage of a microscope (Olympus BX60; Shinjuku, Tokyo, Japan).…”

Achillodynia - Radiological Imaging of Acute and Chronic Overuse Injuries of the Achilles Tendon

“…On the other hand, UTE sequences also allow quantitative evaluation of different MRspecific tissue characteristics. Essentially, known methods have been applied to UTE imaging so that in particular T1, T1rho, T2* and magnetization transfer (MT) effects can be evaluated [70][71][72][73][74][75]. In a number of studies, the effective transverse relaxation time (T2*) of healthy and degenerative tendons was examined.…”

“…However, more recent studies regarding the T2* effect assume a biexponential signal decay from which a long and short T2* component can be derived [70,73]. In healthy tendons, the fractional portion of the short T2* component at 3 T (0.5 -1.3 ms depending on the region and study) is approximately 50 -80 % and that of the long T2* component (7.9 -31.8 ms) is 20 -50 % [70,73]. The longitudinal relaxation time of the Achilles tendon was also determined in vivo via UTE sequences and is approx.…”