共查询到20条相似文献,搜索用时 11 毫秒
1.
Jiang Du Atsushi M. Takahashi Won C. Bae Christine B. Chung Graeme M. Bydder 《Magnetic resonance in medicine》2010,63(2):447-455
Imaging of short‐T2 species requires not only a short echo time but also efficient suppression of long‐T2 species in order to maximize the short‐T2 contrast and dynamic range. This paper introduces a method of long‐T2 suppression using two long adiabatic inversion pulses. The first adiabatic inversion pulse inverts the magnetization of long‐T2 water and the second one inverts that of fat. Short‐T2 species experience a significant transverse relaxation during the long adiabatic inversion process and are minimally affected by the inversion pulses. Data acquisition with a short echo time of 8 μs starts following a time delay of inversion time (TI1) for the inverted water magnetization to reach a null point and a time delay of TI2 for the inverted fat magnetization to reach a null point. The suppression of long‐T2 species depends on proper combination of TI1, TI2, and pulse repetition time. It is insensitive to radiofrequency inhomogeneities because of the adiabatic inversion pulses. The feasibility of this dual inversion recovery ultrashort echo time technique was demonstrated on phantoms, cadaveric specimens, and healthy volunteers, using a clinical 3‐T scanner. High image contrast was achieved for the deep radial and calcified layers of articular cartilage, cortical bone, and the Achilles tendon. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc. 相似文献
2.
Chappell KE Patel N Gatehouse PD Main J Puri BK Taylor-Robinson SD Bydder GM 《Journal of magnetic resonance imaging : JMRI》2003,18(6):709-713
PURPOSE: To assess the feasibility of imaging the liver in volunteers and patients with ultrashort echo time (UTE) pulse sequences. MATERIALS AND METHODS: Seven normal controls as well as 12 patients with biopsy-proven generalized liver disease and three patients with focal disease were examined using pulse sequences with initial TEs of 0.08 msec followed by three later echoes, with or without frequency-based fat suppression. T(2)* values were calculated from regions of interest in the liver. RESULTS: Good image quality was obtained in each subject. There was a highly significant difference in the mean T(2)* values between the normal controls and patients with generalized liver disease (P = 0.001). T(2)* was significantly decreased in hemochromatosis (P = 0.002) and increased in cirrhosis (P = 0.04), compared with controls. T(2)* also correlated with functional status assessed by Child's grade (P = 0.001). A hepatocellular carcinoma showed reduced short T(2) components in the region of thermal ablation and evidence of a subcapsular hematoma which were not apparent with conventional imaging. CONCLUSIONS: Imaging of the liver with UTE sequences showed good image quality and tolerance of abdominal motion. T(2)* was specifically correlated with the presence of hemochromatosis, cirrhosis, and functional grade. Imaging of short T(2) relaxation components may provide useful information in disease. 相似文献
3.
Biological tissues frequently contain different water compartments, and these often have distinct transverse relaxation times. Quantification of these may be problematic on clinical scanners because spin echo sequences usually have initial echo times that are too long to accurately quantify shorter relaxation time components. In this study, an ultrashort echo time pulse sequence was used together with bicomponent analysis to quantify both the short and long T(2) components in tissues of the musculoskeletal system. Feasibility studies were performed using numerical simulation, and on phantoms and in vitro tissues including bovine cortical bone, ligaments, menisci, tendons, and articular cartilage. The simulation and phantom studies demonstrated that this technique can quantify T(2) * and fractions of the short and long T(2) components. The tissues studies showed two distinct components with short T(2) *s ranging from 0.3 ms for bovine cortical bone to 2.1 ms for menisci, and long T(2) *s ranging from 2.9 ms for bovine cortical bone to 35.0 ms for articular cartilage. The short T(2) * fraction ranged from 18.5% for patella cartilage to 80.9% for ligaments. The results show that ultrashort echo time imaging with bicomponent analysis can quantify the short and long T(2) water components in vitro in musculoskeletal tissues. 相似文献
4.
Jiang Du Michael Carl Eric Diaz Atsushi Takahashi Eric Han Nikolaus M. Szeverenyi Christine B. Chung Graeme M. Bydder 《Magnetic resonance in medicine》2010,64(3):834-842
In this study, we report the use of a novel ultrashort echo time T1rhoT1 sequence that combines a spin‐lock preparation pulse with a two‐dimensional ultrashort echo time sequence of a nominal echo time 8 μsec. The ultrashort echo time‐T1rho sequence was employed to quantify T1rho in short T2 tissues including the Achilles tendon and the meniscus. T1rho dispersion was investigated by varying the spin‐lock field strength. Preliminary results on six cadaveric ankle specimens and five healthy volunteers show that the ultrashort echo time‐T1rho sequence provides high signal and contrast for both the Achilles tendon and the meniscus. The mean T1rho of the Achilles tendon ranged from 3.06 ± 0.51 msec for healthy volunteers to 5.22 ± 0.58 msec for cadaveric specimens. T1rho increased to 8.99 ± 0.24 msec in one specimen with tendon degeneration. A mean T1rho of 7.98 ± 1.43 msec was observed in the meniscus of the healthy volunteers. There was significant T1rho dispersion in both the Achilles tendon and the meniscus. Mean T1rho increased from 2.06 ± 0.23 to 7.85 ± 0.74 msec in normal Achilles tendon and from 7.08 ± 0.64 to 13.42 ± 0.93 msec in normal meniscus when the spin‐lock field was increased from 250 to 1,000 Hz. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc. 相似文献
5.
MRI has become the modality of choice for many diagnostic questions in musculoskeletal radiology. Naturally, with the increasing role of MRI in diagnosis of musculoskeletal conditions, clinicians have been eager to explore the possibility of using MR guidance for musculoskeletal procedures. Researchers are actively investigating the utility and practicality of MRI compared with more established modalities for procedure guidance such as computed tomography, fluoroscopy, and ultrasound. Early studies have demonstrated the safety and feasibility of MR guidance for biopsies, spine procedures, cyst aspirations, therapeutic injections, and tumor ablation. Applications in the musculoskeletal system are likely to expand as technology improves and clinicians gain more experience. Hybrid X-ray fluoroscopy/MR imaging systems hold great promise for the future of musculoskeletal intervention by combining the excellent temporal and spatial resolution of X-ray with the anatomic detail provided by MRI. 相似文献
6.
Single‐ and Bi‐component T2* analysis of tendon before and during tensile loading,using UTE sequences 下载免费PDF全文
Eric Y. Chang MD Jiang Du PhD Kenyu Iwasaki MD PhD Reni Biswas BS Sheronda Statum MS Qun He PhD Won C. Bae PhD Christine B. Chung MD 《Journal of magnetic resonance imaging : JMRI》2015,42(1):114-120
7.
Jiang Du Atsushi M. Takahashi Christine B. Chung 《Journal of magnetic resonance imaging : JMRI》2009,29(2):412-421
Purpose
To investigate ultrashort TE spectroscopic imaging (UTESI) of short T2 tissues in the musculoskeletal (MSK) system.Materials and Methods
Ultrashort TE pulse sequence is able to detect rapidly decaying signals from tissues with a short T2 relaxation time. Here a time efficient spectroscopic imaging technique based on a multiecho interleaved variable TE UTE acquisition is proposed for high‐resolution spectroscopic imaging of the short T2 tissues in the MSK system. The projections were interleaved into multiple groups with the data for each group being collected with progressively increasing TEs. The small number of projections in each group sparsely but uniformly sampled k‐space. Spectroscopic images were generated through Fourier transformation of the time domain images at variable TEs. T2* was quantified through exponential fitting of the time domain images or line shape fitting of the magnitude spectrum. The feasibility of this technique was demonstrated in volunteer and cadaveric specimen studies on a clinical 3T scanner.Results
UTESI was applied to six cadaveric specimens and four human volunteers. High spatial resolution and contrast images were generated for the deep radial and calcified layers of articular cartilage, menisci, ligaments, tendons, and entheses, respectively. Line shape fitting of the UTESI magnitude spectroscopic images show a short T2* of 1.34 ± 0.56 msec, 4.19 ± 0.68 msec, 3.26 ± 0.34 msec, 1.96 ± 0.47 msec, and 4.21 ± 0.38 msec, respectively.Conclusion
UTESI is a time‐efficient method to image and characterize the short T2 tissues in the MSK system with high spatial resolution and high contrast. J. Magn. Reson. Imaging 2009;29:412–421. © 2009 Wiley‐Liss, Inc.8.
Koenig CW Duda SH Truebenbach J Schott UG Maurer F Claussen CD Pereira PL 《Journal of magnetic resonance imaging : JMRI》2001,13(5):761-768
Thirty magnetic resonance (MR)-guided biopsies were obtained from 20 skeletal and 10 soft-tissue lesions in 31 patients using an open 0.2 T MR system equipped with interventional accessories. The results from aspiration (N = 3), core biopsy (N = 15), and transcortical trephine biopsy (N = 12) were evaluated for accuracy and clinical efficacy. Specimens were successfully obtained from 29 patients. Results were clinically effective in 23 patients, rated definitive in 16, nonconclusive in 9, and unspecific in 2 patients. A false diagnosis due to sampling error occurred in 2 patients, and biopsy sampling was impossible in one case. The best diagnostic yield was achieved from nontranscortical biopsies of osteolytic or soft-tissue masses. Results from transcortical biopsies were less specific due to the predominance of benign lesions. MR fluoroscopy for needle guidance was applied in 13 patients. Complete needle placement inside the magnet could be performed in 16 patients. MR-guided biopsy using an open low-field MR imager is feasible and clinically effective and will become a valuable tool in the management of musculoskeletal lesions. J. Magn. Reson. Imaging 2001;13:761-768. 相似文献
9.
Sonal Josan John M. Pauly Bruce L. Daniel Kim Butts Pauly 《Magnetic resonance in medicine》2009,61(5):1083-1089
Ultrashort echo time imaging with half RF pulse excitation is challenging as eddy currents induced by the slice‐select gradient distort the half pulse slice profile. This work presents two pulses with T2‐dependent slice profiles that are less sensitive to eddy currents. The double half pulse improves the slice selectivity for long T2 components, while the inverted double half pulse suppresses the unwanted long T2 signal. Thus, both approaches prevent imperfect cancellation of out‐of‐slice signal from contaminating the desired slice. Experimental results demonstrate substantially improved slice selectivity and R2* quantitation accuracy with these pulses. These pulses are effective in making short T2 imaging and quantitation less sensitive to eddy currents and provide an alternative to time‐consuming gradient characterization. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc. 相似文献
10.
Diffusion-weighted imaging of the musculoskeletal system in humans 总被引:18,自引:4,他引:18
This article reviews the principles of diffusion-weighted imaging (DWI) and recent results in DWI of the musculoskeletal system.
The potential of DWI in the diagnosis of pathology of the musculoskeletal system is discussed. DWI is a relatively new MR
imaging technique that has already been established in neuroradiology, especially in the early detection of brain ischemia.
The random motion of water protons on a molecular basis can be measured with DWI. To date DWI of the abdomen and of the musculoskeletal
system has only been employed in scientific studies, but first results indicate that it may also be beneficial in these fields.
Different diffusion characteristics have been found in normal tissues such as muscle, fat and bone marrow. Also, pathologic
entities such as neoplasms, post-therapeutic soft tissue changes and inflammatory processes can be differentiated. Normal
muscle shows significantly higher diffusion values than subcutaneous fat and bone marrow, due to a higher mobility of water
protons within muscle. Soft tissue tumors exhibit a significantly lower diffusion value compared with post-therapeutic soft
tissue changes and inflammatory processes. Necrotic tumor tissue can be distinguished from viable tumor due to significantly
higher diffusion of water protons within necrotic tissue.
Received: 10 February 2000 Revision requested: 4 April 2000 Revision received: 10 May 2000 Accepted: 12 May 2000 相似文献
11.
12.
13.
14.
Two fat-suppressed three-dimensional gradient echo pulse sequences, FLASH and DESS (Double Echo in Steady-State), that have significantly reduced scan time compared with conventional chemical shift fat-suppression sequences are presented. This fat-suppression technique is based on selectively exciting water spins using a time-optimized binomial RF pulse pair at the water resonance frequency with a null in the excitation profile at the fat frequency. To minimize the total pulse length, the delay between the binomial components of the RF pulse is decreased from a standard jump-return implementation. To maintain the proper null frequency, the phase of the second RF pulse is shifted such that it returns the fat resonance back to its initial z position while further tipping the water spins. Nonselective phase-modulated RF pulse pairs can be implemented in 1.20 ms at 1.0 T, significantly reducing the minimum TR. 相似文献
15.
Origins of the ultrashort‐T2 1H NMR signals in myelinated nerve: A direct measure of myelin content?
Recently developed MRI techniques have enabled clinical imaging of short‐lived 1H NMR signals with T2 < 1 ms. Using these techniques, novel signal enhancement has been observed in myelinated tissues, although the source of this enhancement has not been identified. Herein, we report studies of the nature and origins of ultrashort T2 (uT2) signals (50 μs < T2 < 1 ms) from amphibian and mammalian myelinated nerves. NMR measurements and comparisons with myelin phantoms and expected myelin components indicate that these uT2 signals arise predominantly from methylene 1H on/in the myelin membranes, which suggests that direct measurement of uT2 signals can be used as a new means for quantitative myelin mapping. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc. 相似文献
16.
17.
18.
AIM: To assess the potential value of imaging the Achilles tendon with ultrashort echo time (UTE) pulse sequences. MATERIALS AND METHODS: Four normal controls and four patients with chronic Achilles tendinopathy were examined in the sagittal and transverse planes. Three of the patients were examined before and after intravenous gadodiamide. RESULTS: The fascicular pattern was clearly demonstrated within the tendon and detail of the three distinct fibrocartilaginous components of an "enthesis organ" was well seen. T2* measurements showed two short T2* components. Increase in long T2 components with reduction in short T2 components was seen in tendinopathy. Contrast enhancement was much more extensive than with conventional sequences in two cases of tendinopathy but in a third case, there was a region of reduced enhancement. CONCLUSION: UTE pulse sequences provide anatomical detail not apparent with conventional sequences, demonstrate differences in T2* and show patterns of both increased and decreased enhancement in tendinopathy. 相似文献
19.