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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.

The image quality limitations of echo-planar diffusion-weighted imaging (DWI) are an obstacle to its widespread adoption in the breast. Steady-state DWI is an alternative DWI method with more robust image quality but its contrast for imaging breast cancer is not well-understood. The aim of this study was to develop and evaluate diffusion-weighted double-echo steady-state imaging with a three-dimensional cones trajectory (DW-DESS-Cones) as an alternative to conventional DWI for non-contrast-enhanced MRI in the breast. This prospective study included 28 women undergoing clinically indicated breast MRI and six asymptomatic volunteers. In vivo studies were performed at 3 T and included DW-DESS-Cones, DW-DESS-Cartesian, DWI, and CE-MRI acquisitions. Phantom experiments (diffusion phantom, High Precision Devices) and simulations were performed to establish framework for contrast of DW-DESS-Cones in comparison to DWI in the breast. Motion artifacts of DW-DESS-Cones were measured with artifact-to-noise ratio in volunteers and patients. Lesion-to-fibroglandular tissue signal ratios were measured, lesions were categorized as hyperintense or hypointense, and an image quality observer study was performed in DW-DESS-Cones and DWI in patients. Effect of DW-DESS-Cones method on motion artifacts was tested by mixed-effects generalized linear model. Effect of DW-DESS-Cones on signal in phantom was tested by quadratic regression. Correlation was calculated between DW-DESS-Cones and DWI lesion-to-fibroglandular tissue signal ratios. Inter-observer agreement was assessed with Gwet’s AC. Simulations predicted hyperintensity of lesions with DW-DESS-Cones but at a 3% to 67% lower degree than with DWI. Motion artifacts were reduced with DW-DESS-Cones versus DW-DESS-Cartesian (p < 0.05). Lesion-to-fibroglandular tissue signal ratios were not correlated between DW-DESS-Cones and DWI (r = 0.25, p = 0.38). Concordant hyperintensity/hypointensity was observed between DW-DESS-Cones and DWI in 11/14 lesions. DW-DESS-Cones improved sharpness, distortion, and overall image quality versus DWI. DW-DESS-Cones may be able to eliminate motion artifacts in the breast allowing for investigation of higher degrees of steady-state diffusion weighting. Malignant breast lesions in DW-DESS-Cones demonstrated hyperintensity with respect to surrounding tissue without an injection of contrast. LEVEL OF EVIDENCE: 2. TECHNICAL EFFICACY STAGE: 1.

Purpose To evaluate the 3-dimensional (3D) zero echo time (ZTE) magnetic resonance imaging (MRI) technique and compare it with 3D computed tomography (CT) for the assessment of the glenoid bone. Methods ZTE MRI using multiple resolutions and multislice CT were performed in 6 shoulder specimens before and after creation of glenoid defects and in 10 glenohumeral instability patients. Two musculoskeletal radiologists independently generated 3D volume-rendered images of the glenoid en face. Post-processing times and glenoid widths were measured. Inter-modality and inter-rater agreement was assessed. Results Intraclass correlation coefficients (ICCs) for inter-modality assessment showed almost perfect agreement for both readers, ranging from 0.949 to 0.991 for the ex vivo study and from 0.955 to 0.987 for the in vivo patients. Excellent interobserver agreement was found for both the ex vivo (ICCs ≥ 0.98) and in vivo (ICCs ≥ 0.92) studies. For the ex vivo study, Bland-Altman analyses for CT versus MRI showed a mean difference of 0.6 to 1 mm at 1.0-mm3 MRI resolution, 0.3 to 0.6 mm at 0.8-mm3 MRI resolution, and 0.3 to 0.6 mm at 0.6-mm3 MRI resolution for both readers. For the in vivo study, Bland-Altman analyses for CT versus MRI showed a mean difference of 0.6 to 0.8 mm at 1.0-mm3 MRI resolution, 0.5 to 0.6 mm at 0.8-mm3 MRI resolution, and 0.4 to 0.8 mm at 0.7-mm3 MRI resolution for both readers. Mean post-processing times to generate 3D images of the glenoid ranged from 32 to 46 seconds for CT and from 33 to 64 seconds for ZTE MRI. Conclusions Three-dimensional ZTE MRI can potentially be considered as a technique to determine glenoid width and can be readily incorporated into the clinical workflow. Level of Evidence Level II, development of diagnostic criteria (consecutive patients with consistently applied reference standard and blinding).

Author(s): Wan, Lidi; Zhao, Wei; Ma, Yajun; Jerban, Saeed; Searleman, Adam C; Carl, Michael; Chang, Eric Y; Tang, Guangyu; Du, Jiang | Abstract: PurposeTo investigate the effect of stretching sampling window on quantitative 3D ultrashort TE (UTE) imaging of cortical bone at 3 T.MethodsTen bovine cortical bone and 17 human tibial midshaft samples were imaged with a 3T clinical MRI scanner using an 8-channel knee coil. Quantitative 3D UTE imaging biomarkers, including T1 , T2∗ , magnetization transfer ratio and magnetization transfer modeling, were performed using radial or spiral Cones sampling trajectories with various durations. Errors in UTE-MRI biomarkers as a function of sampling time were evaluated using radial sampling as a reference standard.ResultsFor both bovine and human cortical bone samples, no significant differences were observed for all UTE biomarkers (single-component T2∗ , bicomponent T2∗ and relative fractions, T1 , magnetization transfer ratio, and magnetization transfer modeling of macromolecular fraction) for spiral sampling windows of 992 µs to 1600 µs compared with a radial sampling window of 688 µs.ConclusionThe total scan time can be reduced by 76% with quantification errors less than 5%. Quantitative UTE-MRI techniques can be greatly accelerated using longer sampling windows without significant quantification errors.

Ultrashort echo time (UTE) sequences can image tissues with transverse T(2)/T(2)* relaxations too short to be efficiently observed on routine clinical MRI sequences, such as the vertebral body cartilaginous endplate (CEP). Here, we describe a 3D adiabatic inversion recovery-prepared fat-saturated ultrashort echo time (3D IR-FS-UTE) sequence to highlight the CEP of vertebral bodies in comparison to the intervertebral disc (IVD) and bone marrow fat (BF) at 3T. The IR-FS-UTE sequence used a 3D UTE sequence combined with an adiabatic IR preparation pulse centered in the middle of the water and fat peaks, while a fat saturation module was used to suppress the signal from fat. A slab-selective half pulse was used for signal excitation, and a 3D center-out cones trajectory was used for more efficient data sampling. The 3D IR-FS-UTE sequence was applied to an ex vivo human spine sample, as well as the spines of six healthy volunteers and of three patients with back pain. Bright continue lines representing signal from CEP were found in healthy IVDs. The measured contrast-to-noise ratio (CNR) was 18.5±4.9 between the CEP and BF, and 20.3±4.15 between the CEP and IVD for the six volunteers. Abnormal IVDs showed CEP discontinuity or irregularity in the sample and patients’ studies. In conclusion, the proposed 3D IR-FS-UTE sequence is feasible for imaging of the vertebral body’s CEP in vivo with high contrast.

Psychosis is a rare manifestation of neuropsychiatric systemic lupus erythematosus (NPSLE). Current guidelines do not make a recommendation regarding the use of antinuclear antibody (ANA) testing in the assessment of patients with psychosis. The present study was undertaken to determine the prevalence of NPSLE in patients with psychosis who were positive for ANAs.A retrospective review of patients who were admitted to the mental health service of 2 metropolitan tertiary referral centers with a diagnosis of psychosis and had been tested for ANAs was conducted. A diagnosis of SLE was made when the 2019 American College of Rheumatology (ACR)/European Alliance of Associations for Rheumatology (EULAR) classification criteria were fulfilled. Attribution of psychosis-related events to NPSLE were made according to validated criteria.There were 10,205 mental health admissions with diagnoses of psychosis representing 4,766 individual patients, 911 patients (19%) were tested for ANAs, 135 (15%) of those tests returned a positive result with a titer of ≥1:160. The mean ± SD follow-up time was 47 ± 26 months. At discharge, there were 4 patients who met 2019 ACR/EULAR criteria for SLE, 2 of whom met criteria for NPSLE (2 patients had other manifestations of SLE), yielding an NPSLE prevalence of 1.5% (2 of 135) among patients who were positive for ANAs, and 0.2% (2 of 911) among all patients who underwent testing for ANAs.The prevalence of NPSLE in patients with psychosis who were positive for ANAs was low, at 1.5%. The low rate of clinically significant positive results would argue against routine testing for ANAs in patients with psychosis.

The purpose of this study is to investigate the effect of extending the spiral sampling window on quantitative 3D ultrashort echo time (UTE) Cones imaging of major knee joint tissues including articular cartilage, menisci, tendons and ligaments at 3 T. Nine cadaveric human whole knee specimens were imaged on a 3 T clinical MRI scanner. A series of quantitative 3D UTE Cones imaging biomarkers including T2 *, T1 , adiabatic T1ρ , magnetization transfer ratio (MTR) and macromolecular fraction (MMF) were estimated using spiral sampling trajectories with various durations. Errors in UTE MRI biomarkers as a function of sampling time were evaluated using a nonstretched spiral trajectory as a reference standard. No significant differences were observed by increasing the spiral sampling window from 1116 to 2232 μs in the calculated T2 *, T1 , adiabatic T1ρ , MTR and MMF, as all P-values were over .05 as assessed by ANOVA with two-sided Dunnett's test. Although extending the sampling window results in signal loss for short T2 components, there was limited effect on the calculated quantitative biomarkers, with error percentages typically smaller than 5% in all the evaluated tissues. The total scan time can be reduced by up to 54% with quantification errors of less than 5% in any evaluated major tissue in the knee joint, suggesting that 3D UTE Cones MRI techniques can be greatly accelerated by using a longer spiral sampling window without causing additional quantitative bias.

Introduction:corneal transplantation is a surgical procedure requiring consistent long-term follow-up to maximize the chance of graft survival. The purpose of this study was to explore patient characteristics and reasons for being lost to follow-up (LTFU). Methods:a retrospective review of clinical records from January 2012 to October 2014 was conducted of patients who received corneal transplantation at Tenwek Hospital. At the time of chart review, all patients who provided a mobile phone number were contacted to answer a phone questionnaire. Logistic regression was used to assess the association of each patient characteristic, separately, with the outcome of LTFU. Results:of the 118 patients that met inclusion criteria, 40 (33.9%) were considered LTFU by failing to follow up at Tenwek Hospital to at least one year postoperatively. The odds of LTFU for patients age 60 and older were 3.78 times that of those who were 18-59 (95% CI: 1.21-11.80]; p-value=0.02). The odds of LTFU for patients with a preoperative diagnosis of pseudophakic bullous keratopathy were 3.83 times that of those with a preoperative diagnosis of keratoconus (95% CI: [1.13-12.94]; p-value=0.03). Education level, employment status, distance from the hospital, and possession of a mobile contact number appeared marginally associated with follow-up status, though not statistically significant at the 0.05 significance level. Financial barriers were the most commonly cited reason for LTFU (42.4%, n=14). Conclusion:certain reasons and patient characteristics may be associated with follow-up adherence. Identifying these factors may help providers identify patients who are at a higher risk of LTFU and influence providers in medical decision-making and system-based interventions when offering corneal transplantation.

Background Myelin alteration is closely associated with neurological diseases such as multiple sclerosis (MS). Unfortunately, due to myelin's extremely short T2* (~0.3 ms or shorter at 3T), it cannot be directly imaged with conventional MR imaging techniques. Recently, ultrashort echo time (UTE) imaging-based methods have been proposed for direct imaging of myelin. In this study, we explore the feasibility and efficacy of inversion recovery prepared zero echo time (IR-ZTE) imaging for direct volumetric imaging of myelin in white matter of the brain in vivo. Methods In the proposed method, an adiabatic IR preparation pulse is used to suppress long T2 white matter signal, followed by dual echo ZTE imaging where the remaining long T2 components, including gray matter, are suppressed by dual echo subtraction. In the implementation of ZTE, the sampling strategy introduced in Water- and Fat-Suppressed Proton Projection MRI (WASPI) was incorporated to acquire the k-space data missing due to the radiofrequency (RF) transmit/receiver switching time. The IR-ZTE sequence was implemented on a 3T clinical MR system and evaluated using a myelin phantom composed of six different myelin concentrations (0% to 20%), a cadaveric human brain, four healthy volunteers, and seven MS patients. Results In the myelin phantom experiment, the ZTE signal intensity showed high linearity to the myelin concentrations (R2=0.98). In the ex vivo and in vivo experiments, the IR-ZTE sequence provided high contrast volumetric imaging of myelin in human brains. The IR-ZTE sequence was able to detect demyelinated foci lesions in all MS patients. Conclusions Adiabatic IR prepared dual echo ZTE imaging allows for direct, volumetric imaging of myelin in white matter of the brain in vivo.

Purpose Off-resonance saturation (ORS) is a tool which can be used in ultrashort echo time (UTE) magnetic resonance imaging to selectively reduce short T2 signals. When these ORS prepared UTE images are subtracted from a non-suppressed UTE acquisition, the short T2 signals are highlighted. The aim of this paper is to develop a theoretical ORS model and optimize short T2 contrast. Theory Using a theoretical model the sequence parameters such as saturation flip angle and off-resonance frequency were optimized to maximize short T2 contrast. Bloch simulations were performed to demonstrate the accuracy of the theoretical model. Methods Volunteer imaging was performed on the knee using different saturation flip angles and off-resonance frequencies using a Fermi RF pulse with a 3D UTE Cones acquisition. Results The off-resonance saturation method showed good long T2 suppression, and highlighted short T2 signals such as the patella tendon. The theoretical signal curves generally agreed with simulated and experimentally measured signals. Conclusion Off-resonance saturation 3D UTE imaging can be used to effectively suppress long T2 signals and highlight short T2 signals. Theoretical modeling can be used to optimize sequence parameters to maximize long T2 suppression and short T2 contrast. Experimental results confirmed the theoretical predictions.

Author(s): Ma, Ya-Jun; Carl, Michael; Searleman, Adam; Lu, Xing; Chang, Eric Y; Du, Jiang | Abstract: PurposeTo develop a 3D adiabatic T1ρ prepared ultrashort echo time cones (3D AdiabT1ρ UTE-Cones) sequence for whole knee imaging on a clinical 3T scanner.MethodsA train of adiabatic full passage pulses were used for spin locking, followed by time-efficient multispoke UTE acquisition to detect signals from both short and long T2 tissues in the whole knee joint. A modified signal model was proposed for multispoke UTE data fitting. The feasibility of this 3D AdiabT1ρ UTE-Cones technique was demonstrated through numerical simulation, phantom, and ex vivo knee sample studies. The 3D AdiabT1ρ UTE-Cones technique was then applied to 6 in vivo knee joints of healthy volunteers to measure T1ρ values of quadriceps tendon, patellar tendon, anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), meniscus, patellar cartilage, and muscle.ResultsNumerical simulation, phantom and ex vivo knee sample studies demonstrated the feasibility of whole knee imaging using the proposed multispoke 3D AdiabT1ρ UTE-Cones sequence. The healthy volunteer knee study demonstrated an averaged T1ρ of 13.9 ± 0.7 ms for the quadriceps tendon, 9.7 ± 0.8 ms for the patellar tendon, 34.9 ± 2.8 ms for the ACL, 21.6 ± 1.4 ms for the PCL, 22.5 ± 1.9 ms for the meniscus, 44.5 ± 2.4 ms for the patellar cartilage, and 43.2 ± 1.1 ms for the muscle.ConclusionThe 3D AdiabT1ρ UTE-Cones sequence allows volumetric T1ρ assessment of both short and long T2 tissues in the knee joint on a clinical 3T scanner.

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.

Author(s): Ma, Ya-Jun; Zhu, Yanchun; Lu, Xing; Carl, Michael; Chang, Eric Y; Du, Jiang | Abstract: PurposeTo investigate high contrast imaging of short T2 tissues with a three-dimensional double adiabatic inversion recovery prepared ultrashort echo time Cones (3D DIR-UTE-Cones) sequence.MethodsThe sequence used two sequential adiabatic inversion pulses to suppress signals from long T2 tissues, followed by multispoke UTE acquisition to detect signals from short T2 tissues. The two adiabatic inversion pulses are identical with a center frequency located at the water peak, but the spectral width is broad enough to cover both water and fat frequencies. The feasibility of this technique was demonstrated through numerical simulation and phantom studies. Finally, DIR-UTE-Cones was applied to three healthy volunteers to image cortical bone, patellar tendon, and Achilles tendon. T2* was also measured via single-component exponential fitting.ResultsNumerical simulation suggests that the DIR technique provides perfect nulling of muscle and fat as well as efficient suppression of other long T2 tissues with T1 values between fat and water or those above water. Excellent image contrast can be achieved with DIR-UTE-Cones for the short T2 tissues, with fitted T2* values of 0.28-0.38 ms for cortical bone, 0.56 ± 0.07 ms for the patella tendon, and 0.45 ± 0.06 ms for the Achilles tendon, respectively.ConclusionThe 3D DIR-UTE-Cones sequence provides robust suppression of long T2 tissues and allows selective imaging as well as T2* measurement of short T2 tissues such as cortical bone, patellar tendon, and the Achilles tendon. Magn Reson Med 79:2555-2563, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Purpose To assess the feasibility and performance of conical k-space trajectory free-breathing ultrashort echo time (UTE) chest magnetic resonance imaging (MRI) versus four-dimensional (4D) flow and effects of 50% data subsampling and soft-gated motion correction. Materials and Methods Thirty-two consecutive children who underwent both 4D flow and UTE ferumoxytol-enhanced chest MR (mean age: 5.4 years, range: 6 days to 15.7 years) in one 3T exam were recruited. From UTE k-space data, three image sets were reconstructed: 1) one with all data, 2) one using the first 50% of data, and 3) a final set with soft-gating motion correction, leveraging the signal magnitude immediately after each excitation. Two radiologists in blinded fashion independently scored image quality of anatomical landmarks on a 5-point scale. Ratings were compared using Wilcoxon rank-sum, Wilcoxon signed-ranks, and Kruskal–Wallis tests. Interobserver agreement was assessed with the intraclass correlation coefficient (ICC). Results For fully sampled UTE, mean scores for all structures were ≥4 (good-excellent). Full UTE surpassed 4D flow for lungs and airways (P 93% scans for all techniques (P = 0.27). Interobserver agreement was excellent for combined scores (ICC = 0.83). Conclusion High-quality free-breathing conical UTE chest MR is feasible, surpassing 4D flow for lungs and airways, with equivalent PA visualization. Data subsampling only mildly degraded images, favoring lesser scan times. Soft-gating motion correction overall did not improve image quality. Level of Evidence: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2017.

Purpose To accelerate the quantitative ultrashort echo time imaging using a time-efficient 3D multispoke Cones sequence with magnetization transfer (3D UTE-Cones-MT) and signal modeling. Theory and Methods A 3D UTE-Cones-MT acquisition scheme with multispoke per MT preparation and a modified rectangular pulse (RP) approximation was developed for two-pool MT modeling of macromolecular and water components including their relative fractions, relaxation times and exchange rates. Numerical simulation and cadaveric specimens, including human Achilles tendon and bovine cortical bone, were investigated using a clinical 3T scanner. Results Numerical simulation showed that the modified RP model provided accurate estimation of MT parameters when multispokes were acquired per MT preparation. For the experiment with the Achilles tendon and cortical bone samples, the macromolecular fractions were 20.4 ± 2.0% and 59.4 ± 5.3%, respectively. Conclusion The 3D multispoke UTE-Cones-MT sequence can be used for fast volumetric assessment of macromolecular and water components in short T2 tissues. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

Objective To assess differences in biochemical composition of the deep cartilage layer in subjects with type 2 diabetes mellitus (T2DM) and nondiabetic controls using UTE (ultra-short echo time) T2* mapping and to investigate the association of vascular health and UTE T2* measurements. Design Ten subjects with T2DM matched for age, sex, and body mass index with 10 nondiabetic controls. A 3D UTE sequence with 6 echo times was acquired using 3T magnetic resonance imaging of the knee. For UTE T2* analysis, the deep cartilage layer was segmented and analyzed in 5 compartments (patella, medial, and lateral femur and tibia). The ankle brachial index (ABI) was obtained in all subjects. Linear regression analyses were used to assess associations of T2DM and UTE T2* relaxation times and the associations of ABI measurements and UTE measurements. Results Compared with nondiabetic controls, T2DM subjects had significantly lower mean T2*-UTE in the patella (mean difference 4.87 ms; 95% confidence interval [CI] 1.09-8.65; P = 0.015), the lateral tibia (mean difference 2.26 ms; 95% CI 0.06-4.45; P = 0.045), and the lateral femur (mean difference 4.96 ms; 95% CI 0.19-9.73; P = 0.043). Independent of diabetic status, subjects with higher ABI values, indicating better vascular health, had higher T2*-UTE of the patella (coefficient 15.2; 95% CI 3.3-21.4; P = 0.017), the medial tibia (coefficient 9.8; 95% CI 1.0-18.6; P = 0.031), and the lateral femur (coefficient 18.8; 95% CI 3.3-34.3; P = 0.021). Conclusions T2*-UTE measurements of the deep cartilage layer were consistently lower in subjects with T2DM and in subjects with impaired vascular health, likely indicating increased mineralization of this layer.

BACKGROUND Flow visualization in time-of-flight magnetic resonance angiography (TOF MRA) is limited for treated intracranial aneurysms owing to magnetic susceptibility and radiofrequency shielding. OBJECTIVE To assess the clinical usefulness of noncontrast-enhanced magnetic resonance angiography (MRA) using a silent scan (silent MRA) as a follow-up imaging modality in patients with treated intracranial aneurysms. METHODS A total of 119 patients with 126 treated aneurysms underwent silent MRA and TOF MRA during the same scan session. Two neuroradiologists independently assessed overall image quality and visualization of the treated site using a 5-point Likert scale to compare the 2 image sets. We used receiver operating characteristic (ROC) curve analysis to investigate the diagnostic performance of the 2 MRA methods in evaluating aneurysm occlusion. Interobserver reliability was also assessed using weighted kappa statistics. RESULTS The overall image quality scores of silent MRA and TOF MRA were 4.04 ± 0.22 and 4.64 ± 0.48, respectively (P

Purpose Direct myelin imaging can improve the characterization of myelin-related diseases such as multiple sclerosis. In this study, we explore a novel method to directly image myelin using inversion recovery-prepared hybrid encoding (IR-HE) UTE MRI. Methods The IR-HE sequence uses an adiabatic inversion pulse to suppress the long T2 white matter signal, followed by 3D dual-echo HE utilizing both single point imaging and radial frequency encoding, for which the subtraction image between 2 echoes reveals the myelin signal with high contrast. To reduce scan time, it is common to obtain multiple spokes per IR. Here, we invented a novel method to improve the HE, adapted for the multi-spoke IR imaging-termed interleaved HE-for which single point imaging encoding is interleaved between radial frequency encodings near nulling point to allow more efficient IR-signal suppression. To evaluate the proposed approach, a computer simulation, myelin phantom experiment, an ex vivo experiment with a cadaveric multiple sclerosis brain, and an in vivo experiment with 8 healthy volunteers and 13 multiple sclerosis patients were performed. Results The computer simulation showed that IR-interleaved HE allows for improved contrast of myelin signal with reduced imaging artifacts. The myelin phantom experiment showed IR-interleaved HE allows direct imaging of myelin lipid with excellent suppression of water signal. In the ex vivo and in vivo experiments, the proposed method demonstrated highly specific imaging of myelin in white matter of the brain. Conclusion IR-interleaved HE allows for time-efficient, high-contrast direct myelin imaging and can detect demyelinated lesions in multiple sclerosis patients.

We report the three-dimensional ultrashort-TE (3D UTE) and adiabatic inversion recovery UTE (IR-UTE) sequences employing a radial trajectory with conical view ordering for bi-component T2* analysis of bound water (T2*BW) and pore water (T2*PW) in cortical bone. An interleaved dual-echo 3D UTE acquisition scheme was developed for fast bi-component analysis of bound and pore water in cortical bone. A 3D IR-UTE acquisition scheme employing multiple spokes per IR was developed for bound water imaging. Two-dimensional UTE (2D UTE) and IR-UTE sequences were employed for comparison. The sequences were applied to bovine bone samples (n = 6) and volunteers (n = 6) using a 3-T scanner. Bi-component fitting of 3D UTE images of bovine samples showed a mean T2*BW of 0.26 ± 0.04 ms and T2*PW of 4.16 ± 0.35 ms, with fractions of 21.5 ± 3.6% and 78.5 ± 3.6%, respectively. The 3D IR-UTE signal showed a single-component decay with a mean T2*BW of 0.29 ± 0.05 ms, suggesting selective imaging of bound water. Similar results were achieved with the 2D UTE and IR-UTE sequences. Bi-component fitting of 3D UTE images of the tibial midshafts of healthy volunteers showed a mean T2*BW of 0.32 ± 0.08 ms and T2*PW of 5.78 ± 1.24 ms, with fractions of 34.2 ± 7.4% and 65.8 ± 7.4%, respectively. Single-component fitting of 3D IR-UTE images showed a mean T2*BW of 0.35 ± 0.09 ms. The 3D UTE and 3D IR-UTE techniques allow fast volumetric mapping of bound and pore water in cortical bone. Copyright © 2016 John Wiley & Sons, Ltd.

Author(s): Chen, Jun; Chang, Eric Y; Carl, Michael; Ma, Yajun; Shao, Hongda; Chen, Bimin; Wu, Zhihong; Du, Jiang | Abstract: PurposeWe present three-dimensional ultrashort echo time Cones (3D UTE Cones) techniques for quantification of total water T1 ( T1TW), bound water T1 ( T1BW), and pore water T1 ( T1PW) in vitro and in vivo using a 3 Tesla (T) scanner.MethodsT1TW, T1BW, and T1PW were measured with three-dimensional (3D) Cones and adiabatic inversion recovery Cone (IR-Cone) sequences. Two-dimensional (2D) nonselective ultrashort echo time (UTE) techniques, including saturation recovery, variable repetition times (TRs), and inversion recovery (IR) preparation approaches were compared with 3D-Cones techniques on bovine cortical bone samples (n = 8). The 3D Cones sequences were used to measure T1TW, T1BW, and T1PW in the tibial midshaft of healthy volunteers (n = 8).ResultsComparable T1 images were achieved for cortical bone between 3D Cones and 2D UTE techniques as well as those published in the literature. The 3D Cones sequences showed a mean T1TW of 208 ± 22 ms, a mean T1PW of 545 ± 28 ms, and a mean T1BW of 131 ± 12 ms for bovine cortical bone; and a mean T1TW of 246 ± 32 ms, a mean T1PW of 524 ± 46 ms, and a mean T1BW of 134 ± 11 ms for the tibial midshaft of healthy volunteers.ConclusionsThe 3D Cones sequences can be used for fast volumetric assessment of bound and pore water T1 images in vitro and in vivo. Magn Reson Med 77:2136-2145, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Background: Radiation exposure during nuclear cardiology procedures has received much attention and has prompted citations for radiation reduction. In 2010, the American Society of Nuclear Cardiology recommended reducing the average patient study radiation exposure to Methods and Results: This was an analysis of nuclear cardiology studies submitted to the Intersocietal Accreditation Commission for either or both cardiac PET and SPECT accreditation. Cardiac SPECT data represented year 2015 while PET data combined years 2013 to 2015. Data was analyzed with χ 2 and Mann-Whitney U tests (reported as median, 25th percentile, and 75th percentile). Reported PET MPI radiation exposure for 111 laboratories (532 patient cases) was 3.7 (3.2–4.1) mSv per study with no geographic variation. Reported SPECT MPI radiation exposure for 665 laboratories (3067 patient studies) was 12.8 (12.2–14.3) mSv. Highest radiation exposure was found in the South region. Technetium-only studies resulted in a median of 12.2 mSv per study. Conclusions: Radiation exposure from cardiac PET MPI in US laboratories applying for Intersocietal Accreditation Commission accreditation is low (111 laboratories, 3.7 mSv) and substantially lower than cardiac SPECT (665 laboratories, 12.8 mSv).

ObjectivesThe objective of this study was to compare the diagnostic performance and confidence of conventional, optimized, and ultrashort time to echo (UTE) magnetic resonance (MR) protocols for detection of simulated lumbar spondylolysis in human cadavers. In addition, we sought to demonstrate the feasibility of the UTE technique in subjects with and without spondylolysis.Materials and methodsFour human lumbar spine specimens with 46 individual pars interarticularis were randomly left intact (n = 26) or received experimental osteotomy (n = 20) using a microsurgical saw to simulate spondylolysis. The specimens were imaged using a computed tomography (CT) scan along with 3 "Tiers" of MR protocols at 3 T: Tier 1, conventional lumbar MR protocol; Tier 2, optimized conventional protocol consisting of a sagittal oblique spoiled gradient recall echo and axial oblique T1 and short tau inversion recovery sequences; and Tier 3, a sagittal UTE MR sequence. Two blinded readers evaluated the images using a 4-point scale (1 = spondylolysis certainly absent, 2 = probably absent, 3 = probably present, 4 = certainly present) at each individual pars. For each imaging protocol, diagnostic performance (sensitivity, specificity, and area under the receiver operating characteristic curve, using the surgical osteotomy as the reference) and confidence were assessed and compared using the McNemar test. Furthermore, 2 human subjects were imaged with the conventional and UTE MR protocols to demonstrate feasibility in vivo.ResultsDiagnostic performance was moderate for Tiers 1 and 2, with a moderate sensitivity (0.70 to 0.75) and high (1.00) specificity. In contrast, CT and Tier 3 UTE MR imaging had both high sensitivity (1.00) and specificity (1.00). The sensitivities of CT or Tier 3 were statistically greater than Tier 1 sensitivity (P = 0.041) and neared statistical significance when compared with Tier 2 sensitivity (P = 0.074). Area under the receiver operating characteristic curve was also significantly greater for CT and Tier 3 (each area = 1.00), compared with the areas for Tier 1 (0.89, P = 0.037) or Tier 2 (0.873, P = 0.024). Diagnostic confidences of CT or Tier 3 were much greater than other Tiers: Both Tiers 1 and 2 had a large percentage of uncertain (>60%, P < 0.001) or wrong interpretations (>10%, P < 0.001), unlike CT or Tier 3 (0% uncertain or wrong interpretations). Preliminary in vivo UTE images clearly depicted intact and fractured pars.ConclusionsOur study demonstrated that the detection of pars fractures using a single sagittal UTE MR sequence is superior in performance and confidence to conventional and optimized MR protocols at 3 T, whereas matching those from CT evaluation. Furthermore, we demonstrated the feasibility of in vivo application of the UTE sequence in subjects with and without spondylolysis.

In early stages of tendon disease, mechanical properties may become altered prior to changes in morphological anatomy. Ultrashort echo time (UTE) magnetic resonance imaging (MRI) can be used to directly detect signal from tissues with very short T2 values, including unique viscoelastic tissues such as tendons. The purpose of this study was to use UTE sequences to measure T2*, T1 and magnetization transfer ratio (MTR) variations of tendon samples under static tensile loads. Six human peroneal tendons were imaged before and under static loading using UTE sequences on a clinical 3T MRI scanner. Tendons were divided into two static tensile loading groups: group A that underwent one-step loading (15 N) and group B that underwent two-step loading (15 and 30 N). The T2*, T1 and MTR variations were investigated in two selected ROIs, including whole and core sections. Mean T2* values for the first step of loading (groups A and B) in both whole section and core section regions of interest (ROIs) were significantly decreased by 13 ± 7% (P=0.028) and 16 ± 5% (P=0.017), respectively. For the second loading step (group B), there was a consistent, but non-significant reduction in T2* value by 9 ±2% (P=0.059) and 7 ± 5% (P=0.121) for whole and core sections, respectively. Mean T1 did not show any consistent changes for either loading steps (P>0.05). Mean MTR increased slightly, but not significantly for both loading steps (P>0.05). Significant differences were found only in T2* values of tendons by static tensile load application. Therefore, T2* monitoring during loading is suggested for quantitative investigation of the tendons biomechanics.

Purpose We present three-dimensional adiabatic inversion recovery prepared ultrashort echo time Cones (3D IR-UTE-Cones) imaging of cortical bone in the hip of healthy volunteers using a clinical 3T scanner. Methods A 3D IR-UTE-Cones sequence, based on a short pulse excitation followed by a 3D Cones trajectory, with a nominal TE of 32 μs, was employed for high contrast morphological imaging of cortical bone in the hip of heathy volunteers. Signals from soft tissues such as muscle and marrow fat were suppressed via adiabatic inversion and signal nulling. T2⁎ value of the cortical bone was also calculated based on 3D IR-UTE-Cones acquisitions with a series of TEs ranging from 0.032 to 0.8 ms. A total of four healthy volunteers were recruited for this study. Average T2⁎ values and the standard deviation for four regions of interests (ROIs) at the greater trochanter, the femoral neck, the femoral head and the lesser trochanter were calculated. Results The 3D IR-UTE-Cones sequence provided efficient suppression of soft tissues with excellent image contrast for cortical bone visualization in all volunteer hips. Exponential single component decay was observed for all ROIs, with averaged T2⁎ values ranging from 0.33 to 0.45 ms, largely consistent with previously reported T2⁎ values of cortical bone in the tibial midshaft. Conclusions The 3D IR-UTE-Cones sequence allows in vivo volumetric imaging and quantitative T2⁎ measurement of cortical bone in the hip using a clinical 3T scanner.

Introduction Shear-wave elastographic ultrasound (SW-EUS) assesses the stiffness of human tissues. It is used in liver, thyroid and breast imaging but has not been studied in synovium. Soft tissues have a slower shear-wave velocity (SWV) than stiff tissues. We hypothesised that rheumatoid arthritis (RA) patients would have softer synovium than controls and this could be quantified with a slower SWV. We also assessed whether SWV varied with disease activity. Methods Nine patients with RA were consecutively recruited and matched with five controls. Participants underwent clinical assessment, blood sampling, grey scale ultrasound (GSUS), power Doppler ultrasound and SW-EUS of MCP joints 2–5 on the dominant hand. Results Average age was 60. Mean RA disease activity (DAS28-ESR) was moderate at 3.65. Patients with RA had lower maximum synovial SWV than controls (6.38 m/s vs. 6.99 m/s P = 0.042). Negative Pearson's correlation coefficients (PCC) were observed between maximum SWV and disease activity markers including GSUS graded synovial thickness (PCC = −0.57, P = 0.03) and ESR (PCC = −0.46, P = 0.095). Intra- and interobserver reliability was good with intraclass correlation coefficients (ICC) of 0.66 and 0.58, respectively, for quantitative maximum SWV and ICC > 0.80 for colour scale rated SWV. Conclusion This is the first pilot study of SW-EUS in synovium. Maximum synovial SWV was significantly lower in RA than controls. There was a negative correlation between maximum SWV and GSUS synovial thickening. Further study is warranted to confirm the role of SW-EUS in diagnosing and assessing disease activity in RA.

The purpose of this study is to develop a 3D adiabatic inversion recovery prepared ultrashort echo time Cones (3D IR-UTE-Cones) sequence for high resolution and contrast imaging of the region of osteochondral junction (OCJ) of human knee joint using a clinical 3 T scanner. A feasibility study on direct imaging of the OCJ region was performed on a human patellar cartilage sample and on eight cadaveric knee joints using T1 -weighted, proton density (PD)-weighted and short-T2 -weighted 3D IR-UTE-Cones sequences. Contrast to noise ratio was measured to evaluate the effectiveness of the 3D IR-UTE-Cones sequences for selective imaging of the OCJ region. Computed tomography imaging was performed in parallel for the cadaveric knee joints. The optimized T1 -weighted 3D IR-UTE-Cones sequence was used to image the knee joints of eight healthy volunteers and six patients with osteoarthritis (OA) to evaluate morphological changes in the OCJ region. Clinical PD- and T2 -weighted FSE sequences were also performed for comparison. The T1 -weighted 3D IR-UTE-Cones sequence showed high resolution and contrast bright band of the normal OCJ region in the cadaveric joints. Normal OCJ appearances were also seen in healthy volunteers. Abnormal OCJ regions, manifested as ill-defined, focal loss or non-visualization of the high intensity band adjacent to the subchondral bone plate, were observed in the knee joints of both ex vivo and in vivo OA patients. The 3D IR-UTE-Cones sequence can image OCJ regions ex vivo and in vivo, with abnormalities depicted with high resolution and contrast. The technique may be useful for demonstrating involvement of OCJ regions in early OA.

Purpose Magnetic resonance imaging capabilities in the direct vicinity of metallic devices have substantially improved with the recent development of three-dimensional multispectral imaging (3D-MSI) methods. When imaging near metallic hardware, the bulk image distortions in 3D-MSI techniques are reduced to the single-pixel level. However, commonly utilized MSI techniques are ultimately limited by frequency-encoding processes and reveal a class of residual intensity-based susceptibility artifacts that have yet to be formally analyzed. Methods Empirical measurements and simulation techniques are utilized to study the static local magnetic field gradients induced by metal implants and their general impact on frequency-encoding processes. The specific consequences of these gradients on 3D-MSI approaches are also analyzed using empirical and simulated approaches. Results Close agreements between empirical and simulated measurements clearly demonstrate the effects of strong local gradients on frequency-encoded imaging capabilities near metallic implants. Conclusions 3D-MSI techniques can enable substantially enhanced magnetic resonance imaging capabilities near metallic implants. However, strong local static field gradients generate residual artifacts whose direct mitigation are ultimately limited by frequency encoding processes. Applications of 3D encoding strategies or additional post processing may be required to further reduce residual artifacts in multispectral images near metal implants. Magn Reson Med 71:2024–2034, 2014. © 2013 Wiley Periodicals, Inc.

Impedance measurements have been used to quantify changes in vascular function associated with hypertension. Fourier analysis based solely on the arterial flow wave may provide a useful alternative to traditional techniques. Therefore the utility of blood flow frequency analysis in differentiating vascular changes in hypertension is tested. A frequency-based method was developed to evaluate the aortic pulse wave under conditions of spontaneous hypertension, sodium nitroprusside (SNP) induced normotension in spontaneously hypertensive rats (SHR), and phenylephrine (PE) induced hypertension in Wistar–Kyoto rats (WKY). Under anesthesia, animals were instrumented and signals were digitized for measurement of arterial blood pressure, aortic blood flow, and electrocardiogram. Hemodynamic parameters were extracted and the aortic flow signal was processed via Fourier analysis to produce a fingerprint of pulse transmission. Results demonstrated significant fingerprint differences between SHR and WKY at baseline pressures. Fingerprint differences are simulated by PE-induced hypertension, however, they did not match the SHR fingerprint despite similar flow-based biomarkers. Conversely, administration of SNP to the SHR creates differences in the fingerprint, however, SNP did not approximate the WKY fingerprint despite similar hemodynamics. Furthermore, characteristic fingerprint differences between SHR and WKY vasculature are maintained regardless of the intervention. In conclusion, results suggest Fourier analysis can be used to reveal functional vascular states regardless of pressure. Data presented demonstrates functional differences in the hypertensive vasculature that cannot be ameliorated with SNP, or reproduced with PE in normotensive vasculature. This may be useful clinically, to identify vascular dysfunction prior to overt hypertension.

Recently developed techniques such as the multiple acquisition with variable resonance image combination and slice encoding for metal artifact correction techniques have improved the ability of clinical magnetic resonance scanners to image near metal implants. These sequences are based on fast spin echo sequences which preclude detection of short T(2) tissues such as tendons, ligaments, and cortical bone. Ultrashort echo time sequences have the potential to detect signals from these tissues. In this study, we investigate the potential of combining ultrashort echo time with multiple acquisition with variable resonance image combination to image short T(2) musculoskeletal tissues adjacent to metallic implants. Different radio frequency excitation pulse types and spectral binning strategies were studied. We found that ultrashort echo time-multiple acquisition with variable resonance image combination sequences were able to significantly reduce typical artifacts near metal, as well as detect very short T(2) signals that are usually not visualized using clinical pulse sequences.

Stress cardiomyopathy (SCM) also referred to as the “broken heart syndrome” is a condition in which intense emotional or physical stress can cause fulminant and reversible cardiac muscle weakness. SCM most commonly involves the apical segment of left ventricle but newer and rare variants have recently been seen reported. We here report a case of rare midventricular variant of stress related cardiomyopathy. A 72-year-old female with past medical history, only significant for SVT, presented with an episode of severe substernal chest pain while hiking with her husband. She felt a significant heaviness in her chest and was short of breath. During her hospitalization she was found to have positive cardiac enzymes. EKG showed 1 mm downsloping ST segment changes. Ventriculogram during left heart catheterization revealed dyskinetic midventricle. Patient was diagnosed with midventricular SCM. The patient was placed on ACE inhibitor and beta-blocker and discharged in a well-compensated state. We suggest identifying these patients by standard lab testing, electrocardiography, echocardiography, and left heart coronary angiography and ventriculography. Management of this unique entity is similar to the other variants with close observation and treatment of accompanying heart failure, valvular dysfunction, and any arrhythmias that may develop.

Bone stress injury (BSI) incidents have been increasing amongst athletes in recent years as a result of more intense sporting activities. Cortical bone in the tibia and fibula is one of the most common BSI sites. Nowadays, clinical magnetic resonance imaging (MRI) is the recommended technique for BSI diagnosis at an early stage. However, clinical MRI focuses on edema observations in surrounding soft tissues, rather than the injured components of the bone. Specifically, both normal and injured bone are invisible in conventional clinical MRI. In contrast, ultrashort echo time (UTE)-MRI is able to detect the rapidly decaying signal from the bone. This study aimed to employ UTE-MRI for fatigue fracture detection in fibula cortical bone through an ex vivo investigation. Fourteen human fibular samples (47 ± 20 years old, four women) were subjected to cyclic loading on a four-point bending setup. The loading was displacement controlled to induce -5000 ± 1500 μ-strain at 4 Hz. Loading was stopped when bone stiffness was reduced by 20%. Fibula samples were imaged twice, using UTE-MRI and micro-computed tomography (μCT), first pre-loading and second post-loading. After loading, the macromolecular fraction (MMF) from UTE-MT modeling demonstrated a significant decrease (12% ± 20%, P = 0.02) on average. Single-component T2 * also decreased significantly by BSI (12% ± 11%, P = 0.01) on average. MMF reduction is hypothesized to be a result of collagenous matrix rupture and water increase. However, faster T2 * decay might be a result of water shifts towards newly developed microcracks with higher susceptibility. Despite this good sensitivity level of the UTE-MRI technique, the μCT-based porosity at a voxel size of 9 μm was not affected by loading. UTE-MRI shows promise as a new quantitative technique to detect BSI.

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.

Reduction of radiation exposure during nuclear cardiology procedures is a great concern. The American Society of Nuclear Cardiology (ASNC) recommends reducing radiation exposure to

The American Society of Nuclear Cardiology (ASNC) has recommended reducing the radiation exposure to

Caffeine is a widely popular, naturally occurring plant alkaloid that is classified as a methylated xanthine derivative. It is found in a variety of products, most notably coffee, carbonated beverages, and so-called energy drinks. Previous studies have confirmed that typical caffeine consumption is not generally associated with an increased risk of arrhythmias.1 Even at moderate doses (defined as 10 g, has been associated with tachydysrhythmias, including organized supraventricular tachycardia, ventricular tachycardia, and ventricular fibrillation (VF). Because of the increasing popularity of caffeinated energy drinks, there is an increased risk for caffeine toxicity, and as a result, the clinical entity of acute caffeine toxicity may become a more common pathology. Therefore, it is important to not only recognize the effects of caffeine on the cardiovascular system at toxic doses but also to be aware of management strategies. See Editor’s Perspective by Asirvatham and Stevenson A 29-year-old female patient with a history of severe depression and prior suicide attempts presented to the Emergency Department after ingestion of ≈36 to 40 g of caffeine. Before arrival, she admitted to taking 180 to 200 pills of NoDoz brand caffeine, each pill containing ≈200 mg of caffeine. She denied taking any additional prescription medications or substances other than the caffeine pills. On presentation to the emergency room, the patient …

We report a novel three-dimensional (3D) ultrashort echo time (UTE) sequence employing Cones trajectory and T1ρ preparation (UTE-Cones-T1ρ ) for quantitative T1ρ assessment of short T2 tissues in the musculoskeletal system. A basic 3D UTE-Cones sequence was combined with a spin-locking preparation pulse for T1ρ contrast. A relatively short TR was used to decrease the scan time, which required T1 measurement and compensation using 3D UTE-Cones data acquisitions with variable TRs. Another strategy to reduce the total scan time was to acquire multiple Cones spokes (Nsp ) after each T1ρ preparation and fat saturation. Four spin-locking times (TSL = 0-20 ms) were acquired over 12 min, plus another 7 min for T1 measurement. The 3D UTE-Cones-T1ρ sequence was compared with a two-dimensional (2D) spiral-T1ρ sequence for the imaging of a spherical CuSO4 phantom and ex vivo meniscus and tendon specimens, as well as the knee and ankle joints of healthy volunteers, using a clinical 3-T scanner. The CuSO4 phantom showed a T1ρ value of 76.5 ± 1.6 ms with the 2D spiral-T1ρ sequence, as well as 85.7 ± 3.6 and 89.2 ± 1.4 ms for the 3D UTE-Cones-T1ρ sequences with Nsp of 1 and 5, respectively. The 3D UTE-Cones-T1ρ sequence provided shorter T1ρ values for the bovine meniscus sample relative to the 2D spiral-T1ρ sequence (10-12 ms versus 16 ms, respectively). The cadaveric human Achilles tendon sample could only be imaged with the 3D UTE-Cones-T1ρ sequence (T1ρ = 4.0 ± 0.9 ms), with the 2D spiral-T1ρ sequence demonstrating near-zero signal intensity. Human studies yielded T1ρ values of 36.1 ± 2.9, 18.3 ± 3.9 and 3.1 ± 0.4 ms for articular cartilage, meniscus and the Achilles tendon, respectively. The 3D UTE-Cones-T1ρ sequence allows volumetric T1ρ measurement of short T2 tissues in vivo.

Re-expression of the developmental gene Pax-2 during experimental acute tubular necrosis in mice. Background The transcription factor Pax-2 is known to play a key regulatory role during embryonic development of the nervous and excretory systems in mammals and flies. During mouse kidney development, Pax-2 is expressed in the undifferentiated mesenchyme in response to ureter induction and continues to be expressed in the developing comma- and s-shaped bodies. These structures harbor the immediate precursors of the proximal tubular epithelial cells. Pax-2 expression is down-regulated as the differentiation of the functional units of the nephron proceeds. In the adult mammalian kidney, the Pax-2 protein is detectable exclusively in the epithelium of the collecting ducts. We sought to test the hypothesis that tissue regeneration is characterized by re-expression of developmentally important regulatory genes such as Pax-2. Methods The expression pattern of Pax-2 in kidneys after experimentally-induced acute tubular necrosis caused by intraperitoneally injected folic acid in mice was tested by indirect immunofluorescence, Western blotting, reverse transcriptase-polymerase chain reaction, and in situ hybridization analysis. Results A transient, temporally and locally restricted re-expression of Pax-2 in regenerating proximal tubular epithelial cells was observed following kidney damage. Conclusions These data indicate that during the regeneration processes, developmental paradigms may be recapitulated in order to restore mature kidney function.

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.

Ultrashort-echo-time (UTE) sequences have been proposed in the past for MR-based attenuation correction of PET data, because of their ability to image cortical bone. In the present work we assessed the limitations of dual-echo UTE imaging for bone segmentation in head and neck imaging. Sequentially acquired MR and PET/CT clinical data were used for this purpose. Methods: Twenty patients referred for a clinical oncology examination were scanned using a trimodality setup. Among the MR sequences, a dual-echo UTE acquisition of the head was acquired and used to create tissue R2 maps. The different undesired structures present in these maps were identified by an experienced radiologist. Global and local measurements of the overlap between R2-based and CT-based bone masks were computed. Results: UTE R2 maps displayed a nonfunctional relation with CT data. The obtained bone masks showed acceptable overlap with the corresponding CT data, in the case of the skull itself (e.g., 47% mismatch for the parietal region), with decreased performance in the base of the skull and in the neck (e.g., 78% for the maxillary region). Unwanted structures were detected, both anatomic (e.g., sternocleidomastoid, temporal, and masseter muscles) and artifactual (e.g., dental implants and air–tissue interfaces). Conclusion: It is indeed possible to estimate the anatomic location of bone tissue using UTE sequences. However, using pure parametric maps for attenuation correction may lead to bias close to certain anatomic structures and areas of high magnetic field inhomogeneity. More sophisticated approaches are necessary to compensate for these effects.

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.

Ultrashort TE (UTE) is a relatively new MRI technique that allows for the visualization of tissue structures with short T2 components that show little or no signal on all conventional MR imaging sequences. This technique, to the best of our knowledge, has been described only in adults and uses a half excitation pulse and radial k-space data acquisition to produce echo times of less than 100 microseconds with no need for additional hardware modifications. We describe the feasibility of using a 2-D UTE sequence in vivo on a routine 1.5 T clinical MR scanner to depict various musculoskeletal structures in children.

Summary Objective To develop ultrashort echo time (UTE) magnetic resonance imaging (MRI) techniques to image the zone of calcified cartilage (ZCC), and quantify its T2*, T1 and T1ρ. Design In this feasibility study a dual inversion recovery UTE (DIR-UTE) sequence was developed for high contrast imaging of the ZCC. T2* of the ZCC was measured with DIR-UTE acquisitions at progressively increasing TEs. T1 of the ZCC was measured with saturation recovery UTE acquisitions at progressively increasing saturation recovery times. T1ρ of the ZCC was measured with spin-locking prepared DIR-UTE acquisitions at progressively increasing spin-locking times. Results The feasibility of the qualitative and quantitative DIR-UTE techniques was demonstrated on phantoms and in six cadaveric patellae using a clinical 3 T scanner. On average the ZCC has a short T2* ranging from 1.0 to 3.3 ms (mean ± standard deviation = 2.0 ± 1.2 ms), a short T1 ranging from 256 to 389 ms (mean ± standard deviation = 305 ± 45 ms), and a short T1ρ ranging from 2.2 to 4.6 ms (mean ± standard deviation = 3.6 ± 1.2 ms). Conclusion UTE MR based techniques have been developed for high resolution imaging of the ZCC and quantitative evaluation of its T2*, T1 and T1ρ relaxation times, providing non-invasive assessment of collagen orientation and proteoglycan content at the ZCC and the bone cartilage interface. These measurements may be useful for non-invasive assessment of the ZCC, including understanding the involvement of this tissue component in osteoarthritis.

Recently developed sequences such as slice encoding for metal artifact correction (SEMAC) and multiacquisition with variable resonance image combination (MAVRIC) have improved the ability of clinical magnetic resonance scanners to image near metal implants. Since these sequences are based on fast spin echo sequences, little or no signal from short T2 tissues such as tendons, ligaments, and cortical bone is detected. Ultrashort echo time (UTE) sequences do have the capacity to detect signals from these tissues. Here, we explore the potential of combining UTE with MAVRIC to image short T2 musculoskeletal tissues adjacent to metallic implants. Keywords: metal implants; short T2 tissue; UTE; MAVRIC

Purpose: To use a tissue specific algorithm to numerically optimize UTE sequence parameters to maximize contrast within temporomandibular joint (TMJ) donor tissue. Materials and Methods: A TMJ specimen tissue block was sectioned in a true sagittal plane and imaged at 3 Tesla (T) using UTE pulse sequences with dual echo subtraction. The MR tissue properties (PD, T2, T2*, and T1) were measured and subsequently used to calculate the optimum sequences parameters (repetition time [TR], echo time [TE], and θ). Results: It was found that the main contrast available in the TMJ could be obtained from T2 (or T2*) contrast. With the first echo time fixed at 8 μs and using TR = 200 ms, the optimum parameters were found to be: θ ≈ 60°, and TE2 ≈ 15 ms, when the second echo is acquired using a gradient echo and θ ≈ 120°, and TE2 ≈ 15 ms, when the second echo is acquired using a spin echo. Conclusion: Our results show that MR signal contrast can be optimized between tissues in a systematic manner. The MR contrast within the TMJ was successfully optimized with facile delineation between disc and soft tissues. J. Magn. Reson. Imaging 2011;. © 2011 Wiley Periodicals, Inc.