MR Spectroscopic imaging of collagen: Tendons and knee menisci

Gold, Garry E.; Pauly, John M.; Macovski, Albert; Herfkens, Robert J.

doi:10.1002/mrm.1910340502

Cited by 130 publications

(135 citation statements)

References 21 publications

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“…Using ultrashort echo time (UTE) sequences it is possible to directly visualize short T 2 tissues such as tendons (T 2 % 2 ms), ligaments (T 2 % 4-10 ms), menisci (T 2 % 4-10 ms), and cortical bone (T 2 % 0.5 ms) (1)(2)(3)(4). This is usually achieved by acquiring the free induction decay of the MR signal as soon after the end of the radiofrequency (RF) excitation pulse as possible, and is frequently accomplished with a radial center-out k-space trajectory and data sampling of a few hundred microseconds.…”

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confidence: 99%

Investigations of the origin of phase differences seen with ultrashort TE imaging of short T2 meniscal tissue

Carl¹,

Chiang

2011

Magnetic Resonance in Med

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Ultrashort echo time MRI requires specialized pulse sequences with nominal echo times as low as a few microseconds to detect signals from the short T2 tissues frequently encountered in the musculoskeletal system. Usually, magnitude images are reconstructed and these often show low tissue contrast. Ultrashort echo time phase images of the meniscus show surprisingly high contrast despite their very short echo time. In this article, we investigated the source of this contrast using the Bloch equations, simulations, phantom experiments, and tissue studies. Phase evolution was shown to occur in ultrashort echo time sequences during the finite radiofrequency pulse and readout periods, and previously unrecognized susceptibility differences between fiber groups were observed in the meniscus. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.

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confidence: 99%

Investigations of the origin of phase differences seen with ultrashort TE imaging of short T2 meniscal tissue

Carl¹,

Chiang

2011

Magnetic Resonance in Med

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“…With the development of ultrashort TE (UTE) sequences, one is able to directly visualize tissues containing highly ordered structures (1)(2)(3)(4)(5)(6)(7). Other potential applications of UTE are imaging of the lung parenchyma, brain, or liver (8)(9)(10)(11).…”

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confidence: 99%

Optimization of RF excitation to maximize signal and T₂ contrast of tissues with rapid transverse relaxation

Carl¹,

Bydder

et al. 2010

Magnetic Resonance in Med

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Ultrashort echo time MRI requires specialized pulse sequences to overcome the short T 2 of the MR signal encountered in tissues such as ligaments, tendon, or cortical bone. Theoretical work is presented, supported by simulations and experimental data on optimizing the radiofrequency excitation to maximize signal-to-noise ratio and contrast-to-noise ratio. The theoretical calculations and simulations are based on the classic Bloch equations and lead to a closed form expression for the optimal radiofrequency pulse parameters to maximize the MR signal in the presence of rapid T 2 decay. In the steady state, the spoiled gradient recalled echo signal amplitude in response to the radiofrequency excitation pulses is not maximized by the classic Ernst angle but by a more general criterion we call ''generalized Ernst angle.'' Finally, it is shown that T 2 contrast is maximized by flipping the magnetization at the Ernst angle with a radiofrequency pulse duration proportional to the targeted T 2 . Experimental studies on short T 2 phantoms confirm these optimization criteria for both signal-to-noise ratio and contrast-to-noise ratio. Clinical MRI is predominantly geared toward long T 2 species (greater than a few milliseconds). However, tissues containing highly ordered structures such as ligaments (T 2 % 4-10 ms), tendons (T 2 % 2 ms), or cortical bone (T 2 % 0.5 ms) appear dark in images acquired using clinical MR sequences (1,2). This is because the minimum echo times (TEs) for spin echo and gradient echo sequences are approximately 8-10 ms and 1-2 ms, respectively (2). Anomalies in such tissues typically only become apparent when pathology leads to increased signal (e.g., edema) set against the dark signal from short T 2 tissues.With the development of ultrashort TE (UTE) sequences, one is able to directly visualize tissues containing highly ordered structures (1-7). Other potential applications of UTE are imaging of the lung parenchyma, brain, or liver (8-11). Imaging short T 2 tissues is achieved in UTE by acquiring the free induction decay of the MR signal as soon after the end of the radiofrequency (RF) pulse as possible. This is typically accomplished by using a radial center-out k-space trajectory and data sampling of only a few hundred microseconds. Magnitude images are then reconstructed from the (regridded) k-space data. For the special case of UTE imaging, the time between the end of the RF pulse and the beginning of the read gradient (k ¼ 0) is typically defined in the literature as the TE (see for example Rahmer et al. (5)). Typical minimum TE values for clinical scanners, which depend on the RF transmit-receive switching and settling times, are 40-200 ms (12), while the shortest TE reported is 8 ms (13). In order to achieve a better delineation of the morphology within short T 2 tissues, several long T 2 suppression techniques have been developed, including dual echo subtraction techniques (1,5,14), and long T 2 preparation clusters using either long-duration hard pulses (15-17) or adiabatic pulses (12,18)...

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“…124 MRI is currently used to study the cartilage regeneration and restoration in animal models and in human patients, and there have been attempts to incorporate MRS information as well. [125][126][127] In vivo studies using bioreactors (incubators) and animal models are important for validating new approaches of tissue engineering. MR compatible bioreactors allow the investigator to continuously monitor tissue regeneration over a period of days to weeks, which is important for optimizing growth conditions and viewing developing tissue structures.…”

Section: In Vivo Mr Techniques For Monitoring Of Cartilage Tissue Engmentioning

confidence: 99%

Monitoring Cartilage Tissue Engineering Using Magnetic Resonance Spectroscopy, Imaging, and Elastography

Kotecha

Klatt

Magin

2013

Tissue Engineering Part B: Reviews

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A key technical challenge in cartilage tissue engineering is the development of a noninvasive method for monitoring the composition, structure, and function of the tissue at different growth stages. Due to its noninvasive, three-dimensional imaging capabilities and the breadth of available contrast mechanisms, magnetic resonance imaging (MRI) techniques can be expected to play a leading role in assessing engineered cartilage. In this review, we describe the new MR-based tools (spectroscopy, imaging, and elastography) that can provide quantitative biomarkers for cartilage tissue development both in vitro and in vivo. Magnetic resonance spectroscopy can identify the changing molecular structure and alternations in the conformation of major macromolecules (collagen and proteoglycans) using parameters such as chemical shift, relaxation rates, and magnetic spin couplings. MRI provides high-resolution images whose contrast reflects developing tissue microstructure and porosity through changes in local relaxation times and the apparent diffusion coefficient. Magnetic resonance elastography uses low-frequency mechanical vibrations in conjunction with MRI to measure soft tissue mechanical properties (shear modulus and viscosity). When combined, these three techniques provide a noninvasive, multiscale window for characterizing cartilage tissue growth at all stages of tissue development, from the initial cell seeding of scaffolds to the development of the extracellular matrix during construct incubation, and finally, to the postimplantation assessment of tissue integration in animals and patients.

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MR Spectroscopic imaging of collagen: Tendons and knee menisci

Cited by 130 publications

References 21 publications

Investigations of the origin of phase differences seen with ultrashort TE imaging of short T2 meniscal tissue

Investigations of the origin of phase differences seen with ultrashort TE imaging of short T2 meniscal tissue

Optimization of RF excitation to maximize signal and T₂ contrast of tissues with rapid transverse relaxation

Monitoring Cartilage Tissue Engineering Using Magnetic Resonance Spectroscopy, Imaging, and Elastography

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MR Spectroscopic imaging of collagen: Tendons and knee menisci

Cited by 130 publications

References 21 publications

Investigations of the origin of phase differences seen with ultrashort TE imaging of short T2 meniscal tissue

Investigations of the origin of phase differences seen with ultrashort TE imaging of short T2 meniscal tissue

Optimization of RF excitation to maximize signal and T2 contrast of tissues with rapid transverse relaxation

Monitoring Cartilage Tissue Engineering Using Magnetic Resonance Spectroscopy, Imaging, and Elastography

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Optimization of RF excitation to maximize signal and T₂ contrast of tissues with rapid transverse relaxation