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Background Center-out radial sampling of k-space in magnetic resonance imaging employs a different direction for each readout. Off-resonance artifacts (including those produced by chemical shift between water and fat) found with this type of sampling are usually described as blurring, however more specific characterization of these artifacts can be ascertained from the fact that their point spread function is ring-shaped. This produces effects that differ from those seen with Cartesian sampling of k-space. Experiments were designed to demonstrate the origin of these artifacts and a volunteer was imaged to show them. Methods Two phantoms containing oil in a syringe and an annulus of oil surrounded by water were scanned with a range of bandwidths from 62.5 down to 4 kHz. In a human volunteer, head, pelvis and spine images were obtained with bandwidths of 62.5 and 4 kHz. Results The two phantoms showed displacement of the oil signal away from the center into the region of the surrounding water. The effect increased as the bandwidth was decreased. In the head of the volunteer, signal from fat in red bone marrow in the skull was displaced centrally and peripherally relative to water within the marrow, and appeared in the region between the skull and the brain, as well as in the surrounding scalp. Displacements of the former type simulated subdural hematomas. Displacement of perivesical fat signal centrally over the wall of the bladder simulated bladder tumor, and displacement of fat signal from red bone marrow in the lumbar spine to the intervertebral discs simulated their cartilaginous endplates. Conclusions Center-out radial artifacts are important to recognize on clinical images since they may mimic anatomy and simulate pathology. The article shows how these artifacts originate, includes examples, and describes how the artifacts differ from Cartesian chemical shift artifacts.

Purpose To describe a new method for accurate T1 measurement of cortical bone that fits the data sets of both 3D UTE actual flip angle imaging (UTE-AFI) and UTE with a single TR (UTE-STR) simultaneously (UTE-AFI-STR). Theory and methods To make both the constant values and longitudinal mapping functions in the signal equations for UTE-AFI and UTE-STR identical, the same RF pulses and flip angles were used. Therefore, there were three unknowns in the three equations. This was sufficient to fit the data. Numerical simulation as well as ex vivo and in vivo cortical bone studies were performed to validate the T1 measurement accuracy with the UTE-AFI-STR method. The original UTE-AFI variable TR (VTR) (ie, combined UTE-AFI and UTE with VTR) and simultaneous fitting (sf) of UTE-AFI and UTE-VTR (sf-UTE-AFI-VTR) methods were performed for comparison. Results The numerical simulation study showed that the UTE-AFI-STR method provided accurate value of T1 when the SNR of the UTE-STR image was higher than 40. The ex vivo study showed that the UTE-AFI-STR method measured the T1 of cortical bone accurately, with difference ratios ranging from -5.0% to 0.4%. The in vivo study showed a mean T1 of 246 ms with the UTE-AFI-STR method, and mean difference ratios of 2.4% and 5.0%, respectively, compared with the other two methods. Conclusion The 3D UTE-AFI-STR method provides accurate mapping of the T1 of cortical bone with improved time efficiency compared with the UTE-AFI-VTR/sf-UTE-AFI-VTR methods.

Background Water signal contamination is a major challenge for direct ultrashort echo time (UTE) imaging of myelin in vivo because water contributes most of the signals detected in white matter. Purpose To validate a new short repetition time (TR) adiabatic inversion recovery (STAIR) prepared UTE (STAIR-UTE) sequence designed to suppress water signals and to allow imaging of ultrashort T2 protons of myelin in white matter using a clinical 3-T scanner. Materials and Methods In this prospective study, an optimization framework was used to obtain the optimal inversion time for nulling water signals using STAIR-UTE imaging at different TRs. Numeric simulation and phantom studies were performed. Healthy volunteers and participants with multiple sclerosis (MS) underwent MRI between November 2018 and October 2019 to compare STAIR-UTE and a clinical T2-weighted fluid-attenuated inversion recovery sequence for assessment of MS lesions. UTE measures of myelin were also performed to allow comparison of signals in lesions and with those in normal-appearing white matter (NAWM) in patients with MS and in normal white matter (NWM) in healthy volunteers. Results Simulation and phantom studies both suggest that the proposed STAIR-UTE technique can effectively suppress long T2 tissues with a broad range of T1s. Ten healthy volunteers (mean age, 33 years ± 8 [standard deviation]; six women) and 10 patients with MS (mean age, 51 years ± 16; seven women) were evaluated. The three-dimensional STAIR-UTE sequence effectively suppressed water components in white matter and selectively imaged myelin, which had a measured T2* value of 0.21 msec ± 0.04 in the volunteer study. A much lower mean UTE measure of myelin proton density was found in MS lesions (3.8 mol/L ± 1.5), and a slightly lower mean UTE measure was found in NAWM (7.2 mol/L ± 0.8) compared with that in NWM (8.0 mol/L ± 0.8) in the healthy volunteers (P < .001 for both comparisons). Conclusion The short repetition time adiabatic inversion recovery-prepared ultrashort echo time sequence provided efficient water signal suppression for volumetric imaging of myelin in the brain and showed excellent myelin signal contrast as well as marked ultrashort echo time signal reduction in multiple sclerosis lesions and a smaller reduction in normal-appearing white matter compared with normal white matter in volunteers. © RSNA, 2020 Online supplemental material is available for this article. See also the editorial by Messina and Port in this issue.

Background Signal contamination from long T2 water is a major challenge in direct imaging of myelin with MRI. Nulling of the unwanted long T2 signals can be achieved with an inversion recovery (IR) preparation pulse to null long T2 white matter within the brain. The remaining ultrashort T2 signal from myelin can be detected with an ultrashort echo time (UTE) sequence. Purpose To develop patient-specific whole-brain myelin imaging with a three-dimensional double-echo sliding inversion recovery (DESIRE) UTE sequence. Materials and Methods The DESIRE UTE sequence generates a series of IR images with different inversion times during a single scan. The optimal inversion time for nulling long T2 signal is determined by finding minimal signal on the second echo. Myelin images are generated by subtracting the second echo image from the first UTE image. To validate this method, a prospective study was performed in phantoms, cadaveric brain specimens, healthy volunteers, and patients with multiple sclerosis (MS). A total of 20 healthy volunteers (mean age, 40 years ± 13 [standard deviation], 10 women) and 20 patients with MS (mean age, 58 years ± 8; 15 women) who underwent MRI between November 2017 and February 2019 were prospectively included. Analysis of variance was performed to evaluate the signal difference between MS lesions and normal-appearing white matter in patients with MS. Results High signal intensity and corresponding T2* and T1 of the extracted myelin vesicles provided evidence for direct imaging of ultrashort-T2 myelin protons using the UTE sequence. Gadobenate dimeglumine phantoms with a wide range of T1 values were selectively suppressed with DESIRE UTE. In the ex vivo brain study of MS lesions, signal loss was observed in MS lesions and was conformed with histologic analysis. In the human study, there was a significant reduction in normalized signal intensity in MS lesions compared with that in normal-appearing white matter (0.19 ± 0.10 vs 0.76 ± 0.11, respectively; P < .001). Conclusion The double-echo sliding inversion recovery ultrashort echo time sequence can generate whole-brain myelin images specifically with a clinical 3-T scanner. © RSNA, 2019 Online supplemental material is available for this article. See also the editorial by Port in this issue.

PURPOSE We describe the measurement of bound water T1 ( T1BW ) of cortical bone in vitro and in vivo with a 3D adiabatic inversion recovery ultrashort echo time (IR-UTE) Cones sequence using a clinical 3T scanner. METHODS A series IR-UTE data from 6 repetition times (TRs) with 5 inversion times (TIs) at each TR were acquired from 12 human tibial bone specimens, and data from 4 TRs with 5 TIs at each TR were acquired from the tibial midshafts of 8 healthy volunteers. The pore water nulling point was calculated from exponential fitting of the inversion recovery curve at each TR. Bone specimens and volunteers were then scanned again with the calculated nulling point at each TR. T1BW was derived through exponential fitting of data from IR-UTE images acquired at different TRs using the calculated pore water nulling point for each TR. RESULTS In vitro pore water nulling TIs were 141.3 ± 11.6, 123.4 ± 8.9, 101.3 ± 6.2, 88.9 ± 5.3, 74.8 ± 4.2, and 59.2 ± 3.9 ms for the 6 TRs of 500, 400, 300, 250, 200, and 150 ms, respectively. In vivo pore water nulling TIs were 132.8 ± 12.8, 110.3 ± 10.0, 80.0 ± 7.2, and 63.9 ± 5.4 ms for the 4 TRs of 400, 300, 200, and 150 ms, respectively. Excellent exponential fitting was achieved for IR-UTE imaging of bound water with pore water nulled at each TR. The mean T1BW was 106.9 ± 6.3 ms in vitro and 112.3 ± 16.4 ms in vivo. CONCLUSION Using the 3D IR-UTE Cones with a variable TR/TI approach, T1BW of cortical bone was calculated after complete nulling of pore water signals.

This paper reviews magnetic resonance (MR) pulse sequences in which the same or different tissue properties (TPs) such as T(1) and T(2) are used to contribute synergistically to lesion contrast. It also shows how synergistic contrast can be created with Multiplied, Added, Subtracted and/or fiTted Inversion Recovery (MASTIR) sequences, and be used to improve the sensitivity, specificity and scope of clinical magnetic resonance imaging (MRI) protocols. Synergistic contrast can be created from: (i) the same TP, e.g., T(1) used twice or more in a pulse sequence; (ii) different TPs such as ρ(m), T(1), T(2), and D* used once or more within a sequence, and (iii) additional suppression or reduction of signals from tissues and/or fluids such as fat, long T(2) tissues and cerebrospinal fluid (CSF). The short inversion time (TI) inversion recovery (IR) (STIR) and double IR (DIR) sequences usually show synergistic positive contrast for lesions which have increases in both T(1) and T(2). The diffusion weighted pulsed gradient spin echo (PGSE) sequence shows synergistic contrast for lesions which have an increase in T(2) and a decrease in D*; the sequence is both positively weighted for T(2) and negatively weighted for D*. In the brain, when an IR sequence nulling white matter has subtracted from it an IR sequence nulling gray matter to form the subtracted IR (SIR) sequence, increases in the single TP T(1) between the two nulling points of the original two sequences generate high synergistic positive contrast. In addition, the subtraction to produce the SIR sequence reduces fat and CSF signals. To provide high sensitivity to changes in TPs in disease the SIR sequence can be used (i) alone to provide synergistic T(1) contrast as above; (ii) with T(2)-weighting to provide synergistic T(1) and T(2) contrast, and (iii) with T(2)- and D*-weighting to provide synergistic T(1), T(2), and D* contrast. The SIR sequence can also be used in reversed form (longer TI form minus shorter TI form) to produce very high positive synergistic T(1) contrast for reductions in T(1), and so increase the positive contrast enhancement produced by clinical gadolinium-based contrast agents (GBCAs) when they reduce T(1). The specificity of MRI examinations can be improved by using the reversed SIR sequence with a long echo time (TE) gradient echo as well as echo subtraction to show synergistic high contrast from T(1) and T(2)* shortening produced by organic iron. Other added and subtracted forms of the MASTIR sequence can be used synergistically to selectively show myelin, myelin water and fluids including blood and CSF. Protocols using MASTIR sequences to provide synergistic contrast in MRI of the brain, prostate and articular cartilage are included as illustrative examples, and the features of synergistic contrast MRI (scMRI) are compared to those of multiparametric MRI (mpMRI) and functional MRI (fMRI).

BACKGROUND AND PURPOSE: MR imaging has been widely used for the noninvasive evaluation of MS. Although clinical MR imaging sequences are highly effective in showing focal macroscopic tissue abnormalities in the brains of patients with MS, they are not specific to myelin and correlate poorly with disability. We investigated direct imaging of myelin using a 2D adiabatic inversion recovery ultrashort TE sequence to determine its value in assessing disability in MS. MATERIALS AND METHODS: The 2D inversion recovery ultrashort TE sequence was evaluated in 14 healthy volunteers and 31 patients with MS. MPRAGE and T2-FLAIR images were acquired for comparison. Advanced Normalization Tools were used to correlate inversion recovery ultrashort TE, MPRAGE, and T2-FLAIR images with disability assessed by the Expanded Disability Status Scale. RESULTS: Weak correlations were observed between normal-appearing white matter volume (R = –0.03, P = .88), lesion load (R = 0.22, P = .24), and age (R = 0.14, P = .44), and disability. The MPRAGE signal in normal-appearing white matter showed a weak correlation with age (R = –0.10, P = .49) and disability (R = –0.19, P = .31). The T2-FLAIR signal in normal-appearing white matter showed a weak correlation with age (R = 0.01, P = .93) and disability (R = 0.13, P = .49). The inversion recovery ultrashort TE signal was significantly negatively correlated with age (R = –0.38, P = .009) and disability (R = –0.44; P = .01). CONCLUSIONS: Direct imaging of myelin correlates with disability in patients with MS better than indirect imaging of long-T2 water in WM using conventional clinical sequences.

Author(s): Ma, Ya-Jun; Lu, Xing; Carl, Michael; Zhu, Yanchun; Szeverenyi, Nikolaus M; Bydder, Graeme M; Chang, Eric Y; Du, Jiang | Abstract: PurposeTo develop an accurate T1 measurement method for short T2 tissues using a combination of a 3-dimensional ultrashort echo time cones actual flip angle imaging technique and a variable repetition time technique (3D UTE-Cones AFI-VTR) on a clinical 3T scanner.MethodsFirst, the longitudinal magnetization mapping function of the excitation pulse was obtained with the 3D UTE-Cones AFI method, which provided information about excitation efficiency and B1 inhomogeneity. Then, the derived mapping function was substituted into the VTR fitting to generate accurate T1 maps. Numerical simulation and phantom studies were carried out to compare the AFI-VTR method with a B1 -uncorrected VTR method, a B1 -uncorrected variable flip angle (VFA) method, and a B1 -corrected VFA method. Finally, the 3D UTE-Cones AFI-VTR method was applied to bovine bone samples (N = 6) and healthy volunteers (N = 3) to quantify the T1 of cortical bone.ResultsNumerical simulation and phantom studies showed that the 3D UTE-Cones AFI-VTR technique provides more accurate measurement of the T1 of short T2 tissues than the B1 -uncorrected VTR and VFA methods or the B1 -corrected VFA method. The proposed 3D UTE-Cones AFI-VTR method showed a mean T1 of 240 ± 25 ms for bovine cortical bone and 218 ± 10 ms for the tibial midshaft of human volunteers, respectively, at 3 T.ConclusionThe 3D UTE-Cones AFI-VTR method can provide accurate T1 measurements of short T2 tissues such as cortical bone. Magn Reson Med 80:598-608, 2018. © 2018 International Society for Magnetic Resonance in Medicine.

In this paper, we aimed to investigate the feasibility of direct visualization of myelin, including myelin lipid and myelin basic protein (MBP), using two-dimensional ultrashort echo time (2D UTE) sequences and utilize phase information as a contrast mechanism in phantoms and in volunteers. The standard UTE sequence was used to detect both myelin and long T2 signal. An adiabatic inversion recovery UTE (IR-UTE) sequence was used to selectively detect myelin by suppressing signal from long T2 water protons. Magnitude and phase imaging and T2* were investigated on myelin lipid and MBP in the forms of lyophilized powders as well as paste-like phantoms with the powder mixed with D 2 O, and rubber phantoms as well as healthy volunteers. Contrast to noise ratio (CNR) between white and gray matter was measured. Both magnitude and phase images were generated for myelin and rubber phantoms as well white matter in vivo using the IR-UTE sequence. T2* values of ~ 300 μs were comparable for myelin paste phantoms and the short T2* component in white matter of the brain in vivo. Mean CNR between white and gray matter in IR-UTE imaging was increased from − 7.3 for the magnitude images to 57.4 for the phase images. The preliminary results suggest that the IR-UTE sequence allows simultaneous magnitude and phase imaging of myelin in vitro and in vivo.

Multiple sclerosis (MS)causes demyelinating lesions in the white matter and increased iron deposition in the subcortical gray matter. Myelin protons have an extremely short T2* (less than 1 ms) and are not directly detected with conventional clinical magnetic resonance (MR) imaging sequences. Iron deposition also reduces T2*, leading to reduced signal on clinical sequences. In this study we tested the hypothesis that the inversion recovery ultrashort echo time (IR-UTE) pulse sequence can directly and simultaneously image myelin and iron deposition using a clinical 3T scanner. The technique was first validated on a synthetic myelinphantom (myelin powder in D2O) and a Feridex iron phantom. This was followed by studies of cadaveric MS specimens, healthy volunteers and MS patients. UTE imaging of the synthetic myelin phantom showed an excellent bi-component signal decay with two populations of protons, one with a T2* of 1.2 ms (residual water protons) and the other with a T2* of 290 μs (myelin protons). IR-UTE imaging shows sensitivity to a wide range of iron concentrations from 0.5 to ∼30 mM. The IR-UTE signal from white matter of the brain of healthy volunteers shows a rapid signal decay with a short T2* of ∼300 μs, consistent with the T2* values of myelin protons in the synthetic myelin phantom. IR-UTE imaging in MS brain specimens and patients showed multiple white matter lesions as well as areas of high signal in subcortical gray matter. This in specimens corresponded in position to Perl's diaminobenzide staining results, consistent with increased iron deposition. IR-UTE imaging simultaneously detects lesions with myelin loss in the white matter and iron deposition in the gray matter.

Author(s): Wan, Lidi; Wu, Mei; Sheth, Vipul; Shao, Hongda; Jang, Hyungseok; Bydder, Graeme; Du, Jiang | Abstract: Background:Dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) has been used to study perfusion in a wide variety of soft tissues including the bone marrow. Study of perfusion in hard tissues such as cortical bone has been much more limited because of the lack of detectable MR signal from them using conventional pulse sequences. However, two-dimensional (2D) ultrashort echo time (UTE) sequences detect signal from cortical bone and allow fast imaging of this tissue. In addition, adiabatic 2D inversion recovery UTE (IR-UTE) sequences can provide excellent signal suppression of soft tissues, such as muscle and marrow, and allow cortical bone to be seen with high contrast and reduced artefacts. We aimed to assess the feasibility of using 2D UTE and 2D IR-UTE sequences to perform DCE-MRI in the cortical bone of rabbits and human volunteers. Methods:Cortical bone perfusion was studied in rabbits (n=12) and human volunteers (n=3) using 2D UTE and 2D IR-UTE sequences on a clinical 3T scanner. Dynamic data with an in-plane resolution of ~0.5×0.5 mm2, single slice thickness of 3 mm for rabbits and 10 mm for human volunteers, and temporal resolution of 23 s for 2D UTE imaging of rabbits, 28 s for 2D UTE imaging of human volunteers, and 60 s for 2D IR-UTE imaging of both the rabbits and human volunteers were acquired before and after the injection of a Gd contrast agent (Gd-BOPTA: Multihance; Bracco Imaging SpA, Milan, Italy). The dose was 0.06 mmol/kg for rabbits and 0.2 mmol/kg for human subjects. Kinetic analyses based on the Brix model, as well as simple calculations of maximum enhancement (ME) and enhancement slope (ES), were performed. Results:The 12 rabbits showed a mean Ktrans of 0.36±0.07 min-1, Kep of 8.42±3.17 min-1, ME of 28.30±6.83, ES of 0.35±0.18 for the femur with the 2D UTE sequence, and a mean Ktrans of 0.45±0.10 min-1, Kep of 9.80±0.50 min-1, ME of 48.84±12.12, and ES of 0.69±0.27 for the femur with the 2D IR-UTE sequence. Lower ME and ES values were observed in the tibial midshaft of healthy human volunteers compared to rabbits. Conclusions:These results show that 2D UTE and 2D IR-UTE sequences are capable of detecting dynamic contrast enhancement in cortical bone in both rabbits and healthy human volunteers. Clinical studies with these techniques are likely to be feasible.

Clinical magnetic resonance imaging of multiple sclerosis (MS) has focused on indirect imaging of myelin in white matter by detecting signal from protons in the water associated with myelin. Here we show that protons in myelin can be directly imaged using ultrashort echo time (UTE) free induction decay (FID) and imaging sequences on a clinical 3T MR scanner. An adiabatic inversion recovery UTE (IR-UTE) sequence was used to detect signal from myelin and simultaneously suppress signal from water protons. Validation studies were performed on myelin lipid and myelin basic protein (MBP) phantoms in the forms of lyophilized powders as well as suspensions in D2O and H2O. IR-UTE sequences were then used to image MS brain specimens, healthy volunteers, and patients. The T2* of myelin was measured using a UTE FID sequence, as well as UTE and IR- UTE sequences at different TEs. T2* values of ~110–330 μs were measured with UTE FID, as well as with UTE and IR-UTE sequences for myelin powders, myelin-D2O and myelin-H2O phantoms, consistent with selective imaging of myelin protons with IR-UTE sequences. Our studies showed myelin selective imaging of white matter in the brains in vitro and in vivo. Complete or partial signal loss was observed in specimens in areas of the brain with histopathologic evidence of myelin loss, and in the brain of patients with MS.

Entheses are regions where tendons and ligaments attach to bone, and are the primary target in seronegative and other diseases of the musculoskeletal (MSK) system. MRI has been widely used for visualizing features of inflammatory and degenerative MSK disease; however, normal tendons and entheses have short transverse relaxation times (T2 ), and show little or no signal with conventional clinical MRI pulse sequences, making it difficult to investigate their MR properties. In this study we examined the normal MR morphology of the cadaveric Achilles tendon and enthesis at 3 T using novel three-dimensional ultrashort echo time (3D UTE) Cones sequences, and at 11.7 T using conventional MRI sequences. We also studied the MR properties of the Achilles tendon and enthesis including T2 *, T1 , and magnetization transfer ratio (MTR). In addition, MT modeling of macromolecular proton fractions was investigated using 3D UTE Cones sequences at 3 T. Indentation testing was performed to investigate the mechanical properties of the tendons and entheses, and this was followed by histological examination. In total five specimens (

Bone water exists in different states with the majority bound to the organic matrix and to mineral, and a smaller fraction in 'free' form in the pores of cortical bone. In this study, we aimed to develop and evaluate ultrashort-TE (UTE) MRI techniques for the assessment of T2*, T1 and concentration of collagen-bound and pore water in cortical bone using a 3-T clinical whole-body scanner. UTE MRI, together with an isotope study using tritiated and distilled water (THO-H2O) exchange, as well as gravimetric analysis, were performed on ten sectioned bovine bone samples. In addition, 32 human cortical bone samples were prepared for comparison between the pore water concentration measured with UTE MRI and the cortical porosity derived from micro-computed tomography (μCT). A short T2* of 0.27 ± 0.03 ms and T1 of 116 ± 6 ms were observed for collagen-bound water in bovine bone. A longer T2* of 1.84 ± 0.52 ms and T1 of 527 ± 28 ms were observed for pore water in bovine bone. UTE MRI measurements showed a pore water concentration of 4.7-5.3% by volume and collagen-bound water concentration of 15.7-17.9% in bovine bone. THO-H2O exchange studies showed a pore water concentration of 5.9 ± 0.6% and collagen-bound water concentration of 18.1 ± 2.1% in bovine bone. Gravimetric analysis showed a pore water concentration of 6.3 ± 0.8% and collagen-bound water concentration of 19.2 ± 3.6% in bovine bone. A mineral water concentration of 9.5 ± 0.6% was derived in bovine bone with the THO-H2O exchange study. UTE-measured pore water concentration is highly correlated (R(2) = 0.72, p

To determine the feasibility of using MR microscopy to characterize the root ligaments of the human knee at both ultra-high-field (11.7 T) and high-field (3 T) strengths. Seven fresh cadaveric knees were used for this study. Six specimens were imaged at 11.7 T and one specimen at 3 T using isotropic or near-isotropic voxels. Histologic correlation was performed on the posteromedial root ligament of one specimen. Meniscal root ligament shape, signal intensity, and ultrastructure were characterized. High-resolution, high-contrast volumetric images were generated from both MR systems. Meniscal root ligaments were predominantly oval in shape. Increased signal intensity was most evident at the posteromedial and posterolateral root ligaments. On the specimen that underwent histologic preparation, increased signal intensity corresponded to regions of enthesis fibrocartilage. Collagen fascicles were continuous between the menisci and root ligaments. Predominantly horizontal meniscal radial tie fibers continued into the root ligaments as vertical endoligaments. MR microscopy can be used to characterize and delineate the distinct ultrastructure of the root ligaments on both ultra-high-field- and high-field-strength MR systems.

Most of the currently available clinical and research magnetic resonance imaging techniques have focused on the more superficial layers of articular cartilage. This has mainly been because the study of early and late alterations to the deeper layers of cartilage, including the deep radial zone and calcified cartilage, has not been possible due to the technical limitations of clinical scanners. In recent years, several types of two- and three-dimensional ultrashort echo time (UTE) sequences have been developed for high-resolution morphological imaging of articular cartilage. Various contrast mechanisms have been used to image the different layers of articular cartilage, especially calcified cartilage. Quantitative UTE imaging sequences have also been developed to measure T1, T1ρ and T2* in the different layers of articular cartilage. Both bound and bulk water components, including their T2*s and relative fractions, can also be assessed using UTE sequences based on multi-component analysis of UTE signal decay.

The background underpinning the clinical use of ultrashort echo-time (UTE) pulse sequences for imaging tissues or tissue components with short T2s is reviewed. Tissues properties are discussed, and tissues are divided into those with a majority of short T2 relaxation components and those with a minority. Features of the basic physics relevant to UTE imaging are described including the fact that when the radiofrequency pulse duration is of the order T2, rotation of tissue magnetization into the transverse plane is incomplete. Consequences of the broad line-width of short T2 components are also discussed including their partial saturation by off-resonance fat suppression pulses as well as multislice and multiecho imaging. The need for rapid data acquisition of the order T2 is explained. The basic UTE pulse sequence with its half excitation pulse and radial imaging from the center of k-space is described together with options that suppress fat and/or long T2 components. Image interpretation is discussed. Clinical features of the imaging of cortical bone, tendons, ligaments, menisci, and periosteum as well as brain, liver, and spine are illustrated. Short T2 components in all of these tissues may show high signals. Possible future developments are outlined as are technical limitations.

Introduction: Ultra Short TE MRI allows signal to be detected from tissues with a very short T2. The aims of this study were to optimize a 2D UTE MRI sequence for imaging and quantification of sclerotic bone metastases, establish T2* values of sclerotic components and investigate the feasibility of using the method to assess changes in T2* of sclerotic metastases and their relation to attenuation values in patients on treatment. Methods: Twenty-two subjects were recruited in 3 cohorts. Cohort 1 was used to optimize the 2-D UTE sequence, cohort 2 was used to establish T2* measurements using a range of TEs and cohort 3 was used to assess T2* changes with treatment response and relate them to changes on electron density as measured by CT Hounsfield Units. Results: Sagittal 2D UTE MRI of the lumbar spine is feasible demonstrating short T2 components in normal volunteers. In patients with bone metastases secondary to prostate carcinoma T2* can be measured and mean T2* of sclerotic metastases measured with TEs of 0.07, 0.27, 0.47 and 0.67 ms was 8.5 ms. T2* shortened by 20.0% in responders and increased by 24.4% in progressors. Discussion: The significant linear relationship between percentage change in T2* as derived from UTE MRI and percentage change in HU from corresponding CT studies is indirect evidence that they are measuring effects of the same process. If the relationship between T2* and electron density holds true in further studies it offers potential for MR guided radiotherapy planning as well as attenuation correction for PET/MRI.

Osteoporosis causes over 1.5 million fractures per year, costing about $15 billion annually in the USA. Current guidelines utilize bone mineral density (BMD) to assess fracture risk; however, BMD alone only accounts for 30-50% of fractures. The other two major components of bone, organic matrix and water, contribute significantly to bone mechanical properties, but cannot be assessed with conventional imaging techniques in spite of the fact that they make up about 57% of cortical bone by volume. Conventional clinical MRI usually detects signals from water in tissues without difficulty, but cannot detect the water bound to the organic matrix, or the free water in the microscopic pores of the Haversian and the lacunar-canalicular system of cortical bone, because of their very short apparent transverse relaxation times (T2 *). In recent years, a new class of sequences, ultrashort-TE (UTE) sequences, with nominal TEs of less than 100 µs, which are much shorter than the TEs available with conventional sequences, have received increasing interest. These sequences can detect water signals from within cortical bone and provide an opportunity to study disease of this tissue in a new way. This review summarizes the recent developments in qualitative UTE imaging (techniques and contrast mechanisms to produce bone images with high contrast) and quantitative UTE imaging (techniques to quantify the MR properties, including T1 , T2 * and the magnetization transfer ratio, and tissue properties, including bone perfusion, as well as total, bound and free water content) of cortical bone in vitro and in vivo. The limitations of the current techniques for clinical applications and future directions are also discussed.

We describe the use of ultrashort echo time (UTE) sequences and fast spin echo sequences to assess cortical bone using a clinical 3T scanner. Regular two- and three-dimensional UTE sequences were used to image both bound and free water in cortical bone. Adiabatic inversion recovery prepared UTE sequences were used to image water bound to the organic matrix. Two-dimensional fast spin echo sequences were used to image free water. Regular UTE sequences were used together with bicomponent analysis to measure T*2s and relative fractions of bound and free water components in cortical bone. Inversion recovery prepared UTE sequences were used to measure the T*2 of bound water. Saturation recovery UTE sequences were used to measure the T1 of bone water. Eight cadaveric human cortical bone samples and a lower leg specimen were studied. Preliminary results show two distinct components in UTE detected signal decay, a single component in inversion recovery prepared UTE detected signal decay, and a single component in saturation recovery UTE detected signal recovery. Regular UTE sequences appear to depict both bound and free water in cortical bone. Inversion recovery prepared UTE sequences appear to depict water bound to the organic matrix. Two-dimensional fast spin echo sequences appear to depict bone structure corresponding to free water in large pores.

To correlate short and long T2* water fractions, derived from ultrashort-echo time (TE) magnetic resonance (MR) imaging, with semiquantitative histopathologic and polarized light microscopic (PLM) assessment of human cadaveric patellae cartilage.Twenty human cadaveric patellae were evaluated by using ultrashort-TE imaging, spin-echo imaging, histopathologic analysis, and PLM, with institutional review board approval. Short and long T2* water components were evaluated for each patella by using bicomponent fitting of ultrashort-TE signal decay. Four to six regions of interest (ROIs) within each patella were chosen for correlation between ultrashort-TE bicomponent analysis, histopathologic grading (Mankin score), and PLM grading (Vaudey score).Ultrashort-TE imaging with bicomponent analysis showed two distinct water components with a short T2* and a longer T2* in all patellae. ROI analysis showed that the short T2* fraction was correlated significantly with the Mankin (ρ = 0.66, P.001) and Vaudey (ρ = 0.68, P.001) scores. The Mankin scores were weakly positively correlated with T2 (ρ = 0.28, P = .13) and short T2* (ρ = 0.24, P = .14) but were negatively correlated with long T2* (ρ = -0.55, P.01). The Vaudey scores were weakly positively correlated with T2 (ρ = 0.18, P = .16) and short T2* (ρ = 0.22, P = .14) but were negatively correlated with long T2* (ρ = -0.55, P.01).Short T2* water fraction derived from ultrashort-TE imaging with bicomponent analysis correlates significantly with both the Mankin and Vaudey scores and may serve as a biomarker of cartilage degeneration.

An ultrashort TE T(1)ρ sequence was used to measure T(1) ρ of the goat posterior cruciate ligament (n = 1) and human Achilles tendon specimens (n = 6) at a series of angles relative to the B(0) field and spin-lock field strengths to investigate the contribution of dipole-dipole interaction to T(1)ρ relaxation. Preliminary results showed a significant magic angle effect. T(1)ρ of the posterior cruciate ligament increased from 6.9 ± 1.3 ms at 0° to 36 ± 5 ms at 55° and then gradually reduced to 12 ± 3 ms at 90°. Mean T(1)ρ of the Achilles tendon increased from 5.5 ± 2.2 ms at 0° to 40 ± 5 ms at 55°. T(1)ρ dispersion study showed a significant T(1)ρ increase from 2.3 ± 0.9 ms to 11 ± 3 ms at 0° as the spin-lock field strength increased from 150 Hz to 1 kHz, and from 30 ± 3 ms to 42 ± 4 ms at 55° as the spin-lock field strength increased from 100 to 500 Hz. These results suggest that dipolar interaction is the dominant T(1)ρ relaxation mechanism in tendons and ligaments.

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.

The effects of water loss on the T1 and T2* of bovine cortical bone were investigated using ultrashort echo time sequences with signals excited either by a short hard pulse or by two longer half pulses. Nine bovine femur samples were prepared and sequentially air- and oven-dried. On average 3.42% of bone by weight was lost after air-drying for 3 days, with another 5.98% of bone weight loss after oven-drying at 100°C for 24 h. T1 and T2* were measured after every 1% decrease in weight, with 9-10% bone weight loss at the termination of the drying process. After both forms of drying, the overall T1 decreased 33% from 153±18 ms to 102±17 ms when measured using the hard pulse and from 186±25 ms to 122±23 ms when using the half pulses. T2* decreased by 45-50% from 368±29 μs to 201±19 μs using the hard pulse and from 379±35 μs to 191±17 μs using the half pulses. A steady decrease of 26-31% was observed in both T1 and T2* with the first 3-4% bone water loss after air-drying. Oven-drying at 100°C for 24 h resulted on an additional 4% T1 reduction but 25% T2* reduction.

Magnetic resonance imaging (MRI) examination of musculoskeletal tissues is being performed routinely for diagnoses of injury and diseases. Although conventional MRI using spin echo sequences has been effective, a number of important musculoskeletal soft tissues remain "magnetic resonance-invisible" because of their intrinsically short T2 values resulting in a rapid signal decay. This makes visualization and quantitative characterization difficult. With the advent and refinement of ultrashort time-to-echo (UTE) MRI techniques, it is now possible to directly visualize and quantitatively characterize these tissues. This review explores the anatomy, conventional MRI, and UTE MRI of articular cartilage, meniscus of the knee, and intervertebral disks and provides a survey of magnetic resonance studies used to better understand tissue structure, composition, and function, as well as subtle changes in diseases.

In this study, we report the use of a novel ultrashort echo time T(1)rhoT(1) sequence that combines a spin-lock preparation pulse with a two-dimensional ultrashort echo time sequence of a nominal echo time 8 microsec. The ultrashort echo time-T(1)rho sequence was employed to quantify T(1)rho in short T(2) tissues including the Achilles tendon and the meniscus. T(1)rho 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-T(1)rho sequence provides high signal and contrast for both the Achilles tendon and the meniscus. The mean T(1)rho of the Achilles tendon ranged from 3.06 +/- 0.51 msec for healthy volunteers to 5.22 +/- 0.58 msec for cadaveric specimens. T(1)rho increased to 8.99 +/- 0.24 msec in one specimen with tendon degeneration. A mean T(1)rho of 7.98 +/- 1.43 msec was observed in the meniscus of the healthy volunteers. There was significant T(1)rho dispersion in both the Achilles tendon and the meniscus. Mean T(1)rho 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.

Short T(2) species such as the Achilles tendon and cortical bone cannot be imaged with conventional MR sequences. They have a much broader absorption lineshape than long T(2) species, therefore they are more sensitive to an appropriately placed off-resonance irradiation. In this work, a technique termed ultrashort TE (UTE) with off-resonance saturation contrast (UTE-OSC) is proposed to image short T(2) species. A high power saturation pulse was placed +1 to +2 kHz off the water peak to preferentially saturate signals from short T(2) species, leaving long T(2) water and fat signals largely unaffected. The subtraction of UTE images with and without an off-resonance saturation pulse effectively suppresses long T(2) water and fat signals, creating high contrast for short T(2) species. The UTE-OSC technique was validated on a phantom, and applied to bone samples and healthy volunteers on a clinical 3T scanner. High-contrast images of the Achilles tendon and cortical bone were generated with a high contrast-to-noise ratio (CNR) of the order of 12 to 20 between short T(2) and long T(2) species within a total scan time of 4 to 10 min.

The objective of our study was to provide a quantitative means of evaluating the intrinsic T1 and T2(*) values of the Achilles tendon through the measurement of T1 recovery and T2(*) relaxation times, respectively, using ultrashort-TE (UTE) MRI at 3 T with histologic correlation.Six cadaveric specimens underwent MRI at 3 T. The MRI protocol included standard MRI and UTE pulse sequences. For T1 measurement, a saturation recovery time method was applied (saturation recovery time range, 10-1,600 milliseconds), and for T2(*) measurements, a constant TR-varying TE method was used (TE, 100 microseconds-15 milliseconds). An analysis algorithm written in Matlab was executed offline on axial DICOM images for the T1 and T2(*) measurements in areas of normal tendon. The cadaveric specimens were subsequently frozen to -40 degrees C. They were sectioned with the slice thickness corresponding to the MR images. Anatomic sections were photographed and visually inspected. Specimens were then processed for histology. MR images, specimen photographs, and histology results were reviewed by two musculoskeletal radiologists and one pathologist.Compared with histology results, the combination of UTE and standard MRI provided an accurate means of identifying normal tendon. The mean T1 measurement was 621 milliseconds and the mean T2(*) measurement was 2.18 milliseconds in histologically proven regions of normal tendon.The UTE MR sequence offers structural information about and allows reproducible quantitative evaluation of tissues with short T2 components, such as tendons, that are inaccessible on conventional MRI. This technique showed T1 and T2(*) measurements in the normal Achilles tendon and allowed correlation with structural status by histology. Because of the small number of specimens, this is considered a feasibility study.

The "magic angle" effect consists of the increase in signal intensity observed at a tendon or cartilage in a magnetic resonance image, when the tissue is oriented at an angle of approximately 55deg with respect to the main magnetic field B0. The exploitation of this phenomenon is often used to assist diagnosis of tendinous and other diseases, although practical difficulties derived from positioning target tissue at the desired orientation inside closed-bore scanners has made this exploitation hard to implement. A 3-DOF MR-compatible mechatronic system has been developed to position a variety of limbs at the magic angle inside a closed- bore scanner, actuated by a custom-developed pneumatic air motor. The system is capable of locating the desired anatomy with high accuracy, and is designed to position the target tissue at a minimal distance from the isocenter. The compatibility of the system is demonstrated, producing negligible artifacts and an insignificant reduction in signal to noise of the image. Preliminary clinical trials scanning the Achilles tendon of healthy volunteers prove the functionality of the device. An increase in signal intensity of up to 21-fold has been recorded in the tendon at the magic angle.

Entheses are the sites of attachment of a tendon, ligament, or joint capsule to bone. Many features of entheses are adapted to disperse stress and accommodate compressive and shear forces at, or near, boundaries between tendons or ligaments and bone. Of particular interest is calcified and uncalcified fibrocartilage, which has mechanical properties that differ from those of tensile regions of tendons or ligaments, and from bone. Ultrashort echo time (UTE) pulse sequences can identify the specific tissue components of entheses and differentiate cortical bone, calcified fibrocartilage, uncalcified fibrocartilage, and fibrous connective tissue. Magic angle imaging can also differentiate tissues, such as fibrocartilage and tendon, which have different fibre orientations. Understanding the magnetic resonance (MR) appearance of entheses involves consideration of tissue properties, fibre-to-field angle, magic angle effects, pulse sequences, and geometrical factors including fibre-to-section orientation and partial volume effects. New approaches using MR imaging, allow entheses to be visualised with much greater detail than previously possible, and this may help in biomechanical studies, diagnosis of disease including overuse syndromes and spondyloarthropathies, as well as monitoring tissue repair and healing.

Owing to their highly ordered structure, tendons and cartilage appear with low signal intensity when imaged using magnetic resonance imaging (MRI) scanners. A significant increase in signal can be observed when these structures are oriented at 55° (termed the magic angle) with respect to the static field B0. There is a clear clinical importance in exploiting this effect as part of the diagnosis of injury. Experimental studies of this phenomenon have been made harder by the practical difficulties associated with tissue positioning and orientation in the confined environment of closed-bore scanners. An MRI-compatible mechatronic system has been developed, which is capable of positioning a number of limbs to a desired orientation inside the scanner, to be used as a diagnostic and research tool. It is actuated with a novel pneumatic motor consisting of a heavily geared-down air turbine, presenting high torques and good accuracy. The system is shown to be magnetic resonance compatible and the results of preliminary trials using the device to image the Achilles tendon of human volunteers at different orientations are presented. An increase of four fold to thirteen fold in signal intensity can be observed at the magic angle.

Author(s): Iwasaki, Kenyu; Tafur, Monica; Chang, Eric Y; Statum, Sheronda; Biswas, Reni; Tran, Betty; Bae, Won C; Du, Jiang; Bydder, Graeme M; Chung, Christine B | Abstract: ObjectiveThis study aimed to implement qualitative and quantitative magnetic resonance sequences for the evaluation of labral pathology.MethodsSix 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.ResultsSpoiled 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 l 0.001).ConclusionsQuantitative T2* measurements acquired with the UTE technique are useful for distinguishing among normal, mildly degenerated, and severely degenerated labra.

Iliotibial band (ITB) syndrome is a common overuse injury in runners and cyclists. It is regarded as a friction syndrome where the ITB rubs against (and 'rolls over') the lateral femoral epicondyle. Here, we re-evaluate the clinical anatomy of the region to challenge the view that the ITB moves antero-posteriorly over the epicondyle. Gross anatomical and microscopical studies were conducted on the distal portion of the ITB in 15 cadavers. This was complemented by magnetic resonance (MR) imaging of six asymptomatic volunteers and studies of two athletes with acute ITB syndrome. In all cadavers, the ITB was anchored to the distal femur by fibrous strands, associated with a layer of richly innervated and vascularized fat. In no cadaver, volunteer or patient was a bursa seen. The MR scans showed that the ITB was compressed against the epicondyle at 30 degrees of knee flexion as a consequence of tibial internal rotation, but moved laterally in extension. MR signal changes in the patients with ITB syndrome were present in the region occupied by fat, deep to the ITB. The ITB is prevented from rolling over the epicondyle by its femoral anchorage and because it is a part of the fascia lata. We suggest that it creates the illusion of movement, because of changing tension in its anterior and posterior fibres during knee flexion. Thus, on anatomical grounds, ITB overuse injuries may be more likely to be associated with fat compression beneath the tract, rather than with repetitive friction as the knee flexes and extends.

Kager's fat pad is a mass of adipose tissue occupying Kager's triangle. By means of a combined magnetic resonance imaging, ultrasound, gross anatomical and histological study, we show that it has three regions that are closely related to the sides of the triangle. Thus, it has parts related to the Achilles and flexor hallucis longus (FHL) tendons and a wedge of fat adjacent to the calcaneus. The calcaneal wedge moves into the bursa during plantarflexion, as a consequence of both an upward displacement of the calcaneus relative to the wedge and a downward displacement of the wedge relative to the calcaneus. During dorsiflexion, the bursal wedge is retracted. The movements are promoted by the tapering shape of the bursal wedge and by its deep synovial infolds. Fibrous connections linking the fat to the Achilles tendon anchor and stabilize it proximally and thus contribute to the motility of its tip. We conclude that the three regions of Kager's fat pad have specialized functions: an FHL part which contributes to moving the bursal wedge during plantarflexion, an Achilles part which protects blood vessels entering this tendon, and a bursal wedge which we suggest minimizes pressure changes in the bursa. All three regions contribute to reducing the risk of tendon kinking and each may be implicated in heel pain syndromes.

The background underpinning the clinical use of ultrashort echo time, SPRITE and other pulse sequences for imaging bone and other connective tissues with short T2 is reviewed. Features of the basic physics relevant to UTE imaging are described, including the consequences when the radiofrequency pulse duration is of the order of T2 so that rotation of tissue magnetization into the transverse plane is incomplete. Consequences of the broad linewidth of short T2 components are also discussed, including partial saturation by off-resonance fat suppression pulses as well as those used in multislice and multiecho imaging. The need for rapid data acquisition of the order of T2 is explained. The basic two-dimensional UTE pulse sequence with its half excitation pulse and radial imaging from the centre of k-space is described, together with options that suppress fat and/or reduce the signal from long T2 components. The basic features of SPRITE and other sequences with very short TE are described. Image interpretation is discussed. Clinical features of the imaging of cortical bone, tendons, ligaments, menisci, periosteum and the spine are illustrated. The source of the short T2 signal in these tissues is predominantly collagen and water tightly bound to collagen. Short T2 components in all of these tissues are detectible and may show high signals. Possible future developments are outlined, as are technical limitations of clinical magnetic resonance systems.

We report muscle MRI findings of 10 patients from 8 families with nemaline myopathy. Patients with involvement of the nebulin (NEB) gene showed a consistent pattern of selective muscle involvement corresponding to clinical severity. In mild cases, there was complete sparing of thigh muscles and selective involvement of tibialis anterior and soleus. In moderate cases, there was predominant involvement of rectus femoris, vastus lateralis and hamstring muscles and diffuse involvement of anterior compartment and soleus. Patients with nemaline myopathy secondary to mutations in the skeletal muscle alpha-actin (ACTA1) gene showed diffuse involvement of thigh and leg muscles with relative sparing of the gastrocnemii. Selective muscle involvement in both genetic categories was distinct from what has been reported in other congenital myopathies. We conclude that muscle MRI may be applied to distinguish nemaline myopathy from other conditions with similar clinical and histopathological features, to supplement clinical assessment in individual patients and to help direct genetic testing.

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.

To assess the Achilles tendon in patients with chronic tendonopathy using magnetic resonance (MR) magic angle imaging, and to compare the appearances and uptake of contrast medium in abnormal tendons with those in normal tendons.Eight patients with chronic Achilles tendonopathy and five normal controls were examined with the long axis of the tendon placed at 55 degrees and at 0 degrees to the main magnetic field. Conventional two-dimensional (2D) multi-slice images were obtained and T1 values were calculated before, and for up to 1h after the administration of intravenous gadodiamide. Both the unenhanced appearance and the pattern of enhancement in the tendon were compared.In the patients with tendonopathy, high signal intensity areas were evident on the short T1 inversion recovery (STIR) images obtained at 55 degrees in all tendons. Contrast medium enhancement was seen in six tendons and was most obvious on the images obtained at the magic angle. This was initially focal and then spread more diffusely within the tendon. After contrast medium administration, T1 values were significantly reduced in the tendonopathy group compared with normal controls (p0.01). On the late post-contrast medium images obtained at 55 degrees, enhancement was evident in most of the tendon and correlated well with high signal intensity seen on STIR images.The use of magic angle MR imaging improved the demonstration of signal changes in the Achilles tendon in chronic tendonopathy. The STIR images obtained at the magic angle showed more obvious signal change than those obtained at 0 degrees. The changes due to enhancement were much more evident on images obtained at 55 degrees than at 0 degrees. The uptake of contrast medium was greater in the patients than in normal controls.

Inversion recovery ultrashort echo time (IR-UTE) imaging holds the potential to directly characterize MR signals from ultrashort T2 tissue components (STCs), such as collagen in cartilage and myelin in brain. The application of IR-UTE for myelin imaging has been challenging because of the high water content in brain and the possibility that the ultrashort T2 * signals are contaminated by water protons, including those associated with myelin sheaths. This study investigated such a possibility in an ovine brain D2 O exchange model and explored the potential of IR-UTE imaging for the quantification of ultrashort T2 * signals in both white and gray matter at 3 T. Six specimens were examined before and after sequential immersion in 99.9% D2 O. Long T2 MR signals were measured using a clinical proton density-weighted fast spin echo (PD-FSE) sequence. IR-UTE images were first acquired with different inversion times to determine the optimal inversion time to null the long T2 signals (TInull ). Then, at this TInull , images with echo times (TEs) of 0.01-4 ms were acquired to measure the T2 * values of STCs. The PD-FSE signal dropped to near zero after 24 h of immersion in D2 O. A wide range of TInull values were used at different time points (240-330 ms for white matter and 320-350 ms for gray matter at TR = 1000 ms) because the T1 values of the long T2 tissue components changed significantly. The T2 * values of STCs were 200-300 μs in both white and gray matter (comparable with the values obtained from myelin powder and its mixture with D2 O or H2 O), and showed minimal changes after sequential immersion. The ultrashort T2 * signals seen on IR-UTE images are unlikely to be from water protons as they are exchangeable with deuterons in D2 O. The source is more likely to be myelin itself in white matter, and might also be associated with other membranous structures in gray matter.

Water is present in cortical bone in different binding states. In this study we aimed to investigate the effects of inversion time (TI) on the signal from bound and pore water in cortical bone using an adiabatic inversion recovery prepared ultrashort echo time (IR-UTE) sequence on a clinical 3 T scanner. In total ten bovine midshaft samples and four human tibial midshaft samples were harvested for this study. Each cortical sample was imaged with the UTE and IR-UTE sequences with a TR of 300 ms and a series of TI values ranging from 10 to 240 ms. Five healthy volunteers were also imaged with the same sequence. Single- and bi-component models were utilized to calculate the T2 * and relative fractions of short and long T2 * components. Bi-component behavior of the signal from cortical bone was seen with the IR-UTE sequence, except with a TI of around 80 ms, where the short T2 * component alone were seen and a mono-exponential decay pattern was observed. In vivo imaging with the IR-UTE sequence provided high contrast-to-noise images with direct visualization of bound water and reduced signal from long T2 muscle and fat. Our preliminary results demonstrate that selective nulling of the pore water component can be achieved with the IR-UTE sequence with an appropriate TI, allowing selective imaging of the bound water component in cortical bone in vivo using clinical MR scanners.

Purpose To quantify changes in bone marrow fat fraction and determine associations with peripheral blood cell counts. Methods and Materials In this prospective study, 19 patients received either highly myelotoxic treatment (radiation therapy plus cisplatin, 5-fluorouracil mitomycin C [FU/MMC], or cisplatin/5-FU/cetuximab) or less myelotoxic treatment (capecitabine-radiation therapy or no concurrent chemotherapy). Patients underwent MR imaging and venipuncture at baseline, midtreatment, and posttreatment visits. We performed mixed effects modeling of the mean proton density fat fraction (PDFF[%]) by linear time, treatment, and vertebral column region (lumbar [L]4-sacral [S]2 vs thoracic [T]10-L3 vs cervical[C]3-T9), while controlling for cumulative mean dose and other confounders. Spearman rank correlations were performed by white blood cell (WBC) counts versus the differences in PDFF(%) before and after treatment. Results Cumulative mean dose was associated with a 0.43% per Gy (P=.004) increase in PDFF(%). In the highly myelotoxic group, we observed significant changes in PDFF(%) per visit within L4-S2 (10.1%, P

Diffusion-weighted imaging (DWI) can readily be performed in the neonate, although currently studies remain a few years behind-those carried out on adults. DWI relies on the random diffusion of water molecules. As for the adult population, a pulsed gradient spin echo sequence (PGSE) with cardiac gating can be used to exploit the effect of diffusion on image contrast and to determine the apparent diffusion coefficient (D*) for tissues or fluids. Anisotropic properties caused by the restriction of the movement of water molecules may be demonstrated. In the neonatal brain restricted motion can be detected in both myelinated and unmyelinated white matter tracts. DWI has been used to study changes in global and focal ischaemic injury to the neonatal brain. A decreased D* may be documented after an ischaemic insult followed by a gradual increase. These changes are consistent with animal data but show a slower time course. Intervention following perinatal ischaemic injury must be started within hours. DWI detects early ischaemic injury and may therefore be a useful tool for identifying those infants who could benefit from intervention.

High-signal artifacts produced by cerebrospinal fluid (CSF) flow can adversely affect fluid-attenuated inversion recovery (FLAIR) imaging of the brain and spinal cord. This study explores the use of a nonslice-selective inversion pulse to eliminate CSF flow artifacts together with a technique called “K-space Reordered by Inversion-time for each Slice Position” (KRISP) to achieve constant contrast in a multislice acquisition. Theory shows that with this method the CSF point spread function (PSF) has a minimum at the center and attenuated side lobes, providing CSF suppression, but residual edge signals remain. The PSF for brain is only mildly attenuated and signals for extended regions are not attenuated. KRISP FLAIR sequences were assessed in 15 patients (10 brain and five spinal cord cases). The images showed reduced CSF and blood flow artifacts and higher conspicuity of the cortex, meninges, ventricular system, brainstem, and cerebellum when compared with conventional FLAIR sequences. Magn Reson Med 46:354–364, 2001. © 2001 Wiley-Liss, Inc.

This study identifies by microautoradiography activated microglia/macrophages as the main cell type expressing the peripheral benzodiazepine binding site (PBBS) at sites of active CNS pathology. Quantitative measurements of PBBS expression in vivo obtained by PET and [(11)C](R)-PK11195 are shown to correspond to animal experimental and human post-mortem data on the distribution pattern of activated microglia in inflammatory brain disease. Film autoradiography with [(3)H](R)-PK11195, a specific ligand for the PBBS, showed minimal binding in normal control CNS, whereas maximal binding to mononuclear cells was found in multiple sclerosis plaques. However, there was also significantly increased [(3)H](R)-PK11195 binding on activated microglia outside the histopathologically defined borders of multiple sclerosis plaques and in areas, such as the cerebral central grey matter, that are not normally reported as sites of pathology in multiple sclerosis. A similar pattern of [(3)H](R)-PK11195 binding in areas containing activated microglia was seen in the CNS of animals with experimental allergic encephalomyelitis (EAE). In areas without identifiable focal pathology, immunocytochemical staining combined with high-resolution emulsion autoradiography demonstrated that the cellular source of [(3)H](R)-PK11195 binding is activated microglia, which frequently retains a ramified morphology. Furthermore, in vitro radioligand binding studies confirmed that microglial activation leads to a rise in the number of PBBS and not a change in binding affinity. Quantitative [(11)C](R)-PK11195 PET in multiple sclerosis patients demonstrated increased PBBS expression in areas of focal pathology identified by T(1)- and T(2)-weighted MRI and, importantly, also in normal-appearing anatomical structures, including cerebral central grey matter. The additional binding frequently delineated neuronal projection areas, such as the lateral geniculate bodies in patients with a history of optic neuritis. In summary, [(11)C](R)-PK11195 PET provides a cellular marker of disease activity in vivo in the human brain.

Iliotibial band (ITB) syndrome is regarded as an overuse injury, common in runners and cyclists. It is believed to be associated with excessive friction between the tract and the lateral femoral epicondyle-friction which 'inflames' the tract or a bursa. This article highlights evidence which challenges these views. Basic anatomical principles of the ITB have been overlooked: (a) it is not a discrete structure, but a thickened part of the fascia lata which envelops the thigh, (b) it is connected to the linea aspera by an intermuscular septum and to the supracondylar region of the femur (including the epicondyle) by coarse, fibrous bands (which are not pathological adhesions) that are clearly visible by dissection or MRI and (c) a bursa is rarely present-but may be mistaken for the lateral recess of the knee. We would thus suggest that the ITB cannot create frictional forces by moving forwards and backwards over the epicondyle during flexion and extension of the knee. The perception of movement of the ITB across the epicondyle is an illusion because of changing tension in its anterior and posterior fibres. Nevertheless, slight medial-lateral movement is possible and we propose that ITB syndrome is caused by increased compression of a highly vascularised and innervated layer of fat and loose connective tissue that separates the ITB from the epicondyle. Our view is that ITB syndrome is related to impaired function of the hip musculature and that its resolution can only be properly achieved when the biomechanics of hip muscle function are properly addressed.

Recent research demonstrates that white matter of the brain contains not only long T2 components, but a minority of ultrashort T2* components. Adiabatic inversion recovery prepared dual echo ultrashort echo time (IR-dUTE) sequences can be used to selectively image the ultrashort T2* components in white matter of the brain using a clinical whole body scanner. The T2*s of the ultrashort T2* components can be quantified using mono-exponential decay fitting of the IR-dUTE signal at a series of different TEs. However, accurate T1 measurement of the ultrashort T2* components is technically challenging. Efficient suppression of the signal from the majority of long T2 components is essential for robust T1 measurement. In this paper we describe a novel approach to this problem based on the use of IR-dUTE data acquisitions with different TR and TI combinations to selectively detect the signal recovery of the ultrashort T2* components. Exponential recovery curve fitting provides efficient T1 estimation, with minimized contamination from the majority of long T2 components. A rubber phantom and a piece of bovine cortical bone were used for validation of this approach. Six healthy volunteers were studied. An averaged T2* of 0.32 ± 0.09 ms, and a short mean T1 of 226 ± 46 ms were demonstrated for the healthy volunteers at 3T.

White matter of the brain contains a majority of long T2 components as well as a minority of short T2 components. These are not detectable using clinical magnetic resonance imaging (MRI) sequences with conventional echo times (TEs). In this study we used ultrashort echo time (UTE) sequences to investigate the ultrashort T2 components in white matter of the brain and quantify their T2*s and relative proton densities (RPDs) (relative to water with a proton density of 100%) using a clinical whole body 3T scanner. An adiabatic inversion recovery prepared dual echo UTE (IR-dUTE) sequence was used for morphological imaging of the ultrashort T2 components in white matter. IR-dUTE acquisitions at a constant TR of 1000 ms and a series of TIs were performed to determine the optimal TI which corresponded to the minimum signal to noise ratio (SNR) in white matter of the brain on the second echo image. T2*s of the ultrashort T2 components were quantified using mono-exponential decay fitting of the IR-dUTE signal at a series of TEs. RPD was quantified by comparing IR-dUTE signal of the ultrashort T2 components with that of a rubber phantom. Nine healthy volunteers were studied. The IR-dUTE sequence provided excellent image contrast for the ultrashort T2 components in white matter of the brain with a mean signal to noise ratio of 18.7 ± 3.7 and a contrast to noise ratio of 14.6 ± 2.4 between the ultrashort T2 white matter and gray matter in a 4.4 min scan time with a nominal voxel size of 1.25 × 1.25 × 5.0mm(3). On average a T2* value of 0.42 ± 0.08 ms and a RPD of 4.05 ± 0.88% were demonstrated for the ultrashort T2 components in white matter of the brain of healthy volunteers at 3T.

While MR imaging has emerged as the imaging method of choice for diagnosis of cartilage disease, the deep radial and calcified layers of cartilage are difficult to image with conventional MRI because of their short T2 relaxation times. The imaging of cartilage injury and osteoarthritis (OA) has therefore focused on the superficial layers of cartilage. We describe herein the implementation of Ultrashort Echo Time (UTE) pulse sequences with Echo Times (TEs) as low as 8 μs on a clinical 3T scanner. Various adaptations were made to the regular UTE acquisition in order to optimize image contrast between the deep layers and superficial layers of cartilage. These modifications included multiple gradient echo UTE acquisition with and without fat saturation, and multiple spin echo UTE acquisition. The efficacy of these techniques in depicting the targeted tissues was demonstrated through imaging of cadaveric samples and healthy volunteers. Excellent depiction of these different regions was obtained, enhanced particularly with fat suppression and later echo subtraction methods. Quantitative measurements showed that while UTE Free Induction Decay (FID) acquisition provided the highest signal-to-noise ratio, both fat suppression and later echo subtraction enhanced the contrast between the deep and superficial layers of cartilage.