3D balanced SSFP UTE MRI for multiple contrasts whole brain imaging.

PURPOSE: This study aimed to develop a new high-resolution MRI sequence for the imaging of the ultra-short transverse relaxation time (uT2) components in the brain, while simultaneously providing proton density (PD) contrast for reference and quantification. THEORY: The sequence combines low flip angle balanced SSFP (bSSFP) and UTE techniques, together with a 3D dual-echo rosette k-space trajectory for readout. METHODS: The expected image contrast was evaluated by simulations. A study cohort of six healthy volunteers and eight multiple sclerosis (MS) patients was recruited to test the proposed sequence. Subtraction between two TEs was performed to extract uT2 signals. In addition, conventional longitudinal relaxation time (T1) weighted, T2-weighted, and PD-weighted MRI sequences were also acquired for comparison. RESULTS: Typical PD-contrast was found in the second TE images, while uT2 signals were selectively captured in the first TE images. The subtraction images presented signals primarily originating from uT2 components, but only if the first TE is short enough. Lesions in the MS subjects showed hyperintense signals in the second TE images but were hypointense signals in the subtraction images. The lesions had significantly lower signal intensity in subtraction images than normal white matter (WM), which indicated a reduction of uT2 components likely associated with myelin. CONCLUSION: 3D isotropic sub-millimeter (0.94 mm) spatial resolution images were acquired with the novel bSSFP UTE sequence within 3 min. It provided easy extraction of uT2 signals and PD-contrast for reference within a single acquisition.

Relationship between CT-Derived Bone Mineral Density and UTE-MR-Derived Porosity Index in Equine Third Metacarpal and Metatarsal Bones.

Fatigue-related subchondral bone injuries of the third metacarpal/metatarsal (McIII/MtIII) bones are common causes of wastage, and they are welfare concerns in racehorses. A better understanding of bone health and strength would improve animal welfare and be of benefit for the racing industry. The porosity index (PI) is an indirect measure of osseous pore size and number in bones, and it is therefore an interesting indicator of bone strength. MRI of compact bone using traditional methods, even with short echo times, fail to generate enough signal to assess bone architecture as water protons are tightly bound. Ultra-short echo time (UTE) sequences aim to increase the amount of signal detected in equine McIII/MtIII condyles. Cadaver specimens were imaged using a novel dual-echo UTE MRI technique, and PI was calculated and validated against quantitative CT-derived bone mineral density (BMD) measures. BMD and PI are inversely correlated in equine distal Mc/MtIII bone, with a weak mean r value of -0.29. There is a statistically significant difference in r values between the forelimbs and hindlimbs. Further work is needed to assess how correlation patterns behave in different areas of bone and to evaluate PI in horses with and without clinically relevant stress injuries.

Design and development of a novel flexible ultra-short echo time (FUSE) sequence.

PURPOSE: To present the validation of a new Flexible Ultra-Short Echo time (FUSE) pulse sequence using a short-T2 phantom. METHODS: FUSE was developed to include a range of RF excitation pulses, trajectories, dimensionalities, and long-T2 suppression techniques, enabling real-time interchangeability of acquisition parameters. Additionally, we developed an improved 3D deblurring algorithm to correct for off-resonance artifacts. Several experiments were conducted to validate the efficacy of FUSE, by comparing different approaches for off-resonance artifact correction, variations in RF pulse and trajectory combinations, and long-T2 suppression techniques. All scans were performed on a 3 T system using an in-house short-T2 phantom. The evaluation of results included qualitative comparisons and quantitative assessments of the SNR and contrast-to-noise ratio. RESULTS: Using the capabilities of FUSE, we demonstrated that we could combine a shorter readout duration with our improved deblurring algorithm to effectively reduce off-resonance artifacts. Among the different RF and trajectory combinations, the spiral trajectory with the regular half-inc pulse achieves the highest SNRs. The dual-echo subtraction technique delivers better short-T2 contrast and superior suppression of water and agar signals, whereas the off-resonance saturation method successfully suppresses water and lipid signals simultaneously. CONCLUSION: In this work, we have validated the use of our new FUSE sequence using a short T2 phantom, demonstrating that multiple UTE acquisitions can be achieved within a single sequence. This new sequence may be useful for acquiring improved UTE images and the development of UTE imaging protocols.

Usefulness of silent magnetic resonance angiography for intracranial aneurysms treated with a flow re-direction endoluminal device.

PURPOSE: Flow re-direction endoluminal device (FRED) is a novel dual-layer flow-diverting stent to treat cerebral aneurysms with high obliteration rates, however, it induces inevitable metal-related artifacts. We compared silent magnetic resonance angiography (MRA), a new MRA method using ultra-short time of echo and arterial spin-labeling, with conventional time-of-flight (TOF)-MRA for imaging aneurysms treated using FRED. METHODS: Between May 2020 and September 2022, 16 patients with unruptured internal carotid aneurysms treated using FRED simultaneously underwent silent MRA and TOF-MRA after treatment, with 36 follow-up sessions in total. Two observers independently graded the quality of intra-aneurysmal flow and stented parent arteries under both types of MRA from 1 (not visible) to 4 (nearly equal to digital subtraction angiography [DSA]), with reference to DSA images as a standard criterion. RESULTS: The mean scores for intra-aneurysmal flow and stented parent arteries were significantly better for silent MRA (3.93 ± 0.21 and 3.82 ± 0.32, respectively) than for TOF-MRA (2.08 ± 0.99 and 1.92 ± 0.79, respectively) (P < 0.01). Intermodality agreements for intra-aneurysmal flow and stented parent arteries were 0.87 and 0.90, respectively. CONCLUSION: Silent MRA is superior to TOF-MRA for assessing patients treated with FRED, with potential as an alternative imaging modality to DSA.

Deep-learning-based biomarker of spinal cartilage endplate health using ultra-short echo time magnetic resonance imaging.

Background: T2* relaxation times in the spinal cartilage endplate (CEP) measured using ultra-short echo time magnetic resonance imaging (UTE MRI) reflect aspects of biochemical composition that influence the CEP's permeability to nutrients. Deficits in CEP composition measured using T2* biomarkers from UTE MRI are associated with more severe intervertebral disc degeneration in patients with chronic low back pain (cLBP). The goal of this study was to develop an objective, accurate, and efficient deep-learning-based method for calculating biomarkers of CEP health using UTE images. Methods: Multi-echo UTE MRI of the lumbar spine was acquired from a prospectively enrolled cross-sectional and consecutive cohort of 83 subjects spanning a wide range of ages and cLBP-related conditions. CEPs from the L4-S1 levels were manually segmented on 6,972 UTE images and used to train neural networks utilizing the u-net architecture. CEP segmentations and mean CEP T2* values derived from manually- and model-generated segmentations were compared using Dice scores, sensitivity, specificity, Bland-Altman, and receiver-operator characteristic (ROC) analysis. Signal-to-noise (SNR) and contrast-to-noise (CNR) ratios were calculated and related to model performance. Results: Compared with manual CEP segmentations, model-generated segmentations achieved sensitives of 0.80-0.91, specificities of 0.99, Dice scores of 0.77-0.85, area under the receiver-operating characteristic curve values of 0.99, and precision-recall (PR) AUC values of 0.56-0.77, depending on spinal level and sagittal image position. Mean CEP T2* values and principal CEP angles derived from the model-predicted segmentations had low bias in an unseen test dataset (T2* bias =0.33±2.37 ms, angle bias =0.36±2.65°). To simulate a hypothetical clinical scenario, the predicted segmentations were used to stratify CEPs into high, medium, and low T2* groups. Group predictions had diagnostic sensitivities of 0.77-0.86 and specificities of 0.86-0.95. Model performance was positively associated with image SNR and CNR. Conclusions: The trained deep learning models enable accurate, automated CEP segmentations and T2* biomarker computations that are statistically similar to those from manual segmentations. These models address limitations with inefficiency and subjectivity associated with manual methods. Such techniques could be used to elucidate the role of CEP composition in disc degeneration etiology and guide emerging therapies for cLBP.

Ultra-short echo time MR imaging in assessing cartilage endplate damage and relationship between its lesion and disc degeneration for chronic low back pain patients.

OBJECTIVE: To investigate the feasibility of ultra-short echo time (UTE) magnetic resonance imaging (MRI) in the assessment of cartilage endplate (CEP) damage and further evaluate the relationship between total endplate score (TEPS) and lumbar intervertebral disc (IVD) degeneration for chronic low back pain patients. MATERIALS AND METHODS: IVD were measured in 35 patients using UTE imaging at 3T MR. Subtracted UTE images between short and long TEs were obtained to depict anatomy of CEP. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated to assess the image quality quantitatively. A new grading criterion for endplate damage evaluation was developed based on Rajasekaran.S grading system in this study. Two radiologists were employed to evaluate CEP and bony vertebral endplates (VEP) using this new grading criterion and assess TEPS, independently. Cohen's kappa analysis was applied to evaluate the inter-observer agreement of endplate damage assessment between two radiologists, and the Kendall's TAU-B analysis was employed to determine the relationship between TEPS and IVD degeneration evaluated with Pfirrmann grading. RESULTS: Well structural CEP was depicted on subtracted UTE images and confirmed by high SNR (33.06±2.92) and CNR values (9.4±2.08). Qualified subtracted UTE images were used by two radiologists to evaluate the degree of CEP and VEP damage. Excellent inter-observer agreement was confirmed by high value in Cohen's kappa test (0.839, P < 0.001). Ensured by this, 138 endplates from 69 IVDs of 35 patients were classified into six grades based on the new grading criterion and TEPS of each endplate was calculated. In addition, the degeneration degree of IVDs were classified into five grades. Finally, using Kendall's TAU-B analysis, significant relationship was obtained between endplate damage related TEPS and IVD degeneration (r = 0.864, P < 0.001). CONCLUSION: Ensured by high image quality, UTE imaging might be considered an effective tool to assess CEP damage. Additionally, further calculated TEPS has shown strong positive association with IVD degeneration, suggesting that the severity of endplate damage is highly linked with the degree of IVD degeneration.

High-resolution 3D ultra-short echo time MRI with Rosette k-space pattern for brain iron content mapping.

BACKGROUND: The iron concentration increases during normal brain development and is identified as a risk factor for many neurodegenerative diseases, it is vital to monitor iron content in the brain non-invasively. PURPOSE: This study aimed to quantify in vivo brain iron concentration with a 3D rosette-based ultra-short echo time (UTE) magnetic resonance imaging (MRI) sequence. METHODS: A cylindrical phantom containing nine vials of different iron concentrations (iron (II) chloride) from 0.5 millimoles to 50 millimoles and six healthy subjects were scanned using 3D high-resolution (0.94 ×0.94 ×0.94 mm3) rosette UTE sequence at an echo time (TE) of 20 µs. RESULTS: Iron-related hyperintense signals (i.e., positive contrast) were detected based on the phantom scan, and were used to establish an association between iron concentration and signal intensity. The signal intensities from in vivo scans were then converted to iron concentrations based on the association. The deep brain structures, such as the substantia nigra, putamen, and globus pallidus, were highlighted after the conversion, which indicated potential iron accumulations. CONCLUSION: This study suggested that T1-weighted signal intensity could be used for brain iron mapping.

Added value of ultra-short echo time and fast field echo using restricted echo-spacing MR imaging in the assessment of the osseous cervical spine.

PURPOSE: To evaluate the added value of ultra-short echo time (UTE) and fast field echo resembling a CT using restricted echo-spacing (FRACTURE) MR sequences in the assessment of the osseous cervical spine using CT as reference. MATERIALS AND METHODS: Twenty-seven subjects underwent postmortem CT and MRI within 48 h. Datasets were anonymized and analyzed retrospectively by two radiologists. Morphological cervical spine alterations were rated on CT, UTE and FRACTURE images. Afterward, neural foraminal stenosis was graded on standard MR and again after viewing additional UTE/FRACTURE sequences. To evaluate interreader and intermodality reliability, intra-class correlation coefficients (ICC) and for stenosis grading Wilcoxon-matched-pairs testing with multiple comparison correction were calculated. RESULTS: Moderate interreader reliability (ICC = 0.48-0.71) was observed concerning morphological findings on all modalities. Intermodality reliability was good between modalities regarding degenerative vertebral and joint alterations (ICC = 0.69-0.91). Compared to CT neural stenosis grades were more often considered as nonsignificant on all analyzed MR sequences. Neural stenosis grading scores differed also significantly between specific bone imaging sequences, UTE and FRACTURE, to standard MR sequences. However, no significant difference was observed between UTE and FRACTURE sequences. CONCLUSION: Compared to CT as reference, UTE or FRACTURE sequence added to standard MR sequences can deliver comparable information on osseous cervical spine status. Both led to changes in clinically significant stenosis gradings when added to standard MR, mainly reducing the severity of neural foramina stenosis.

Ultra-short Echo-time MR Angiography Combined with a Subtraction Method to Assess Intracranial Aneurysms Treated with a Flow-diverter Device.

A flow-diverter (FD) device is a well-established tool for the treatment of unruptured intracranial aneurysms. Time-of-flight (TOF) MR angiography (MRA) is widely used for postoperative assessment after the treatment with FD; however, it cannot fully visualize intra-aneurysmal and intrastent flow signals due to the magnetic susceptibility from the FD. Recently, the utility of MRA with ultra-short TE (UTE) sequence and arterial spin labeling technique in assessing the therapeutic efficacy of intracranial aneurysms treated with metallic devices has been reported, but long image acquisition time is one of the drawbacks of this method. Herein, we introduce a novel UTE MRA using the subtraction method that enables the reduction in susceptibility artifacts with a short image acquisition time.

Ultra-short T2 components imaging of the whole brain using 3D dual-echo UTE MRI with rosette k-space pattern.

PURPOSE: This study aimed to develop a new 3D dual-echo rosette k-space trajectory, specifically designed for UTE MRI applications. The imaging of the ultra-short transverse relaxation time (uT2 ) of brain was acquired to test the performance of the proposed UTE sequence. THEORY AND METHODS: The rosette trajectory was developed based on rotations of a "petal-like" pattern in the kx -ky plane, with oscillated extensions in the kz -direction for 3D coverage. Five healthy volunteers underwent 10 dual-echo 3D rosette UTE scans with various TEs. Dual-exponential complex model fitting was performed on the magnitude data to separate uT2 signals, with the output of uT2 fraction, uT2 value, and long-T2 value. RESULTS: The 3D rosette dual-echo UTE sequence showed better performance than a 3D radial UTE acquisition. More significant signal intensity decay in white matter than gray matter was observed along with the TEs. The white matter regions had higher uT2 fraction values than gray matter (10.9% ± 1.9% vs. 5.7% ± 2.4%). The uT2 value was approximately 0.10 ms in white matter . CONCLUSION: The higher uT2 fraction value in white matter compared to gray matter demonstrated the ability of the proposed sequence to capture rapidly decaying signals.

Ultra-short Echo-time MR Angiography Combined with a Modified Signal Targeting Alternating Radio Frequency with Asymmetric Inversion Slabs Technique to Assess Visceral Artery Aneurysm after Coil Embolization.

Contrast-enhanced CT and MR angiography are widely used for follow-up of visceral artery aneurysms after coil embolization. However, potential adverse reactions to contrast agents and image deterioration due to susceptibility artifacts from the coils are major drawbacks of these modalities. Herein, we introduced a novel non-contrast-enhanced MR angiography technique using ultra-short TE combined with a modified signal targeting alternating radio frequency with asymmetric inversion slabs, which could provide a serial hemodynamic vascular image with fewer susceptibility artifacts for follow-up after coil embolization.

On quantification errors of R2*$$ {R}_2

PURPOSE: To study the effect of field inhomogeneity distributions in trabecularized bone regions on the gradient echo (GRE) signal with short TEs and to characterize quantification errors on R2*$$ {R}_2^{\ast } $$ and proton density fat fraction (PDFF) maps when using a water-fat model with an exponential R2*$$ {R}_2^{\ast } $$ decay model at short TEs. METHODS: Field distortions were simulated based on a trabecular bone micro CT dataset. Simulations were performed for different bone volume fractions (BV/TV) and for different bone-fat composition values. A multi-TE UTE acquisition was developed to acquire multiple UTEs with random order to minimize eddy currents. The acquisition was validated in phantoms and applied in vivo in a volunteer's ankle and knee. Chemical shift encoded MRI (CSE-MRI) based on a Cartesian multi-TE GRE scan was acquired in the spine of patients with metastatic bone disease. RESULTS: Simulations showed that signal deviations from the exponential signal decay at short TEs were more prominent for a higher BV/TV. UTE multi-TE measurements reproduced in vivo the simulation-based predicted behavior. In regions with high BV/TV, the presence of field inhomogeneities induced an R2*$$ {R}_2^{\ast } $$ underestimation in trabecularized bone marrow when using CSE-MRI at 3T with a short TE. CONCLUSION: R2*$$ {R}_2^{\ast } $$ can be underestimated when using short TEs (<2 ms at 3 T) and a water-fat model with an exponential R2*$$ {R}_2^{\ast } $$ decay model in multi-echo GRE acquisitions of trabecularized bone marrow.

Synthetic Time of Flight Magnetic Resonance Angiography Generation Model Based on Cycle-Consistent Generative Adversarial Network Using PETRA-MRA in the Patients With Treated Intracranial Aneurysm.

BACKGROUND: Pointwise encoding time reduction with radial acquisition (PETRA) magnetic resonance angiography (MRA) is useful for evaluating intracranial aneurysm recurrence, but the problem of severe background noise and low peripheral signal-to-noise ratio (SNR) remain. Deep learning could reduce noise using high- and low-quality images. PURPOSE: To develop a cycle-consistent generative adversarial network (cycleGAN)-based deep learning model to generate synthetic TOF (synTOF) using PETRA. STUDY TYPE: Retrospective. POPULATION: A total of 377 patients (mean age: 60 ± 11; 293 females) with treated intracranial aneurysms who underwent both PETRA and TOF from October 2017 to January 2021. Data were randomly divided into training (49.9%, 188/377) and validation (50.1%, 189/377) groups. FIELD STRENGTH/SEQUENCE: Ultra-short echo time and TOF-MRA on a 3-T MR system. ASSESSMENT: For the cycleGAN model, the peak SNR (PSNR) and structural similarity (SSIM) were evaluated. Image quality was compared qualitatively (5-point Likert scale) and quantitatively (SNR). A multireader diagnostic optimality evaluation was performed with 17 radiologists (experience of 1-18 years). STATISTICAL TESTS: Generalized estimating equation analysis, Friedman's test, McNemar test, and Spearman's rank correlation. P < 0.05 indicated statistical significance. RESULTS: The PSNR and SSIM between synTOF and TOF were 17.51 [16.76; 18.31] dB and 0.71 ± 0.02. The median values of overall image quality, noise, sharpness, and vascular conspicuity were significantly higher for synTOF than for PETRA (4.00 [4.00; 5.00] vs. 4.00 [3.00; 4.00]; 5.00 [4.00; 5.00] vs. 3.00 [2.00; 4.00]; 4.00 [4.00; 4.00] vs. 4.00 [3.00; 4.00]; 3.00 [3.00; 4.00] vs. 3.00 [2.00; 3.00]). The SNRs of the middle cerebral arteries were the highest for synTOF (synTOF vs. TOF vs. PETRA; 63.67 [43.25; 105.00] vs. 52.42 [32.88; 74.67] vs. 21.05 [12.34; 37.88]). In the multireader evaluation, there was no significant difference in diagnostic optimality or preference between synTOF and TOF (19.00 [18.00; 19.00] vs. 20.00 [18.00; 20.00], P = 0.510; 8.00 [6.00; 11.00] vs. 11.00 [9.00, 14.00], P = 1.000). DATA CONCLUSION: The cycleGAN-based deep learning model provided synTOF free from background artifact. The synTOF could be a versatile alternative to TOF in patients who have undergone PETRA for evaluating treated aneurysms. EVIDENCE LEVEL: 4 TECHNICAL EFFICACY: Stage 1.

Assessment of pulmonary arteriovenous malformation with ultra-short echo time magnetic resonance imaging.

PURPOSE: The purpose of this study was to evaluate the diagnostic performance of ultra-short echo time magnetic resonance imaging (UTE MRI) in the assessment of pulmonary arteriovenous malformation (PAVM). METHODS: Eighteen consecutive patients (mean [± standard deviation] age, 48.6 ± 16.8 years) with 46 untreated PAVMs who underwent and thin-section computed tomography (CT) and UTE MRI with a 1.5-Tesla and 3-Tesla unit were retrospectively assessed. Two radiologists evaluated the diagnostic capabilities of UTE MRI for the detection and classification of PAVMs with reference to CT. Sensitivity, specificity, and kappa statistics were calculated with reference to CT. We also compared the differences in PAVM measurements between CT and MRI. RESULTS: The sensitivity and specificity of UTE-MRI for the detection of PAVMs were 89.1% and 100%, respectively, for reader 1 and 87.0% and 100%, respectively, for reader 2. In the classification of PAVMs, inter-modality agreement in reader 1 and 2 were both substantial (κ = 0.78 and 0.69, respectively). The measurements of the PAVM feeding artery and sac on CT and MRI were strongly correlated in both readers 1 and 2 (R2 = 0.981 and 0.983, respectively). Both readers 1 and 2 slightly underestimated the diameter of the PAVM feeding artery and sac on UTE MRI (p < 0.001). CONCLUSION: This study indicates that UTE MRI is a feasible and promising modality for noninvasive assessment of PAVMs.

Single point imaging with radial acquisition and compressed sensing.

PURPOSE: To accelerate the Pointwise Encoding Time Reduction with Radial Acquisition (PETRA) sequence using compressed sensing while preserving the image quality for high-resolution MRI of tissue with ultra-short T2∗ values. METHODS: Compressed sensing was introduced in the PETRA sequence (csPETRA) to accelerate the time-consuming single point acquisition of the k-space center data. Random undersampling was applied to achieve acceleration factors up to Acc = 32. Phantom and in vivo images of the knee joint of six volunteers were measured at 3T using csPETRA sequence with Acc = 4, 8, 12, 16, 24, and 32. Images were compared against fully sampled PETRA data (Acc = 1) for structural similarity and normalized-mean-square-error. Qualitative and semi-quantitative analyses were performed to assess the effect of the acceleration on image artifacts, image quality, and delineation of anatomical structures at the knee. RESULTS: Even at high acceleration factors of Acc = 16 no aliasing artifacts were observed, and the anatomical details were preserved compared with the fully sampled data. The normalized-mean-square-error was less than 1% for Acc = 16, in which single point imaging acquisition time was reduced from 165 to 10 s, reducing the total scan time from 7.8 to 5.2 min. Semi-quantitative analyses suggest that Acc = 16 yields comparable diagnostic quality as the fully sampled data for knee imaging at a scan time of 5.2 min. CONCLUSION: csPETRA allows for ultra-short T2∗ imaging of the knee joint in clinically acceptable scan times while maintaining the image quality of original non-accelerated PETRA sequence.

Assessment of vertebral fractures and edema of the thoracolumbar spine based on water-fat and susceptibility-weighted images derived from a single ultra-short echo time scan.

PURPOSE: To develop a methodology to simultaneously perform single echo Dixon water-fat imaging and susceptibility-weighted imaging (SWI) based on a single echo time (TE) ultra-short echo time (UTE) (sUTE) scan to assess vertebral fractures and degenerative bone changes in the thoracolumbar spine. METHODS: A methodology was developed to solve the smoothness-constrained inverse water-fat problem to separate water and fat while removing unwanted low-frequency phase terms. Additionally, the corrected UTE phase was used for SWI. UTE imaging (TE: 0.14 ms, 3T MRI) was performed in the lumbar spine of nine patients with vertebral fractures and bone marrow edema (BME). All images were reviewed by two radiologists. Water- and fat-separated images were analyzed in comparison with short-tau inversion recovery (STIR) and with respect to BME visibility. The visibility of fracture lines and cortical outlining of the UTE magnitude images were analyzed in comparison with computed tomography. RESULTS: Unwanted phase components, dominated by the B1 phase, were removed from the UTE phase images. The rating of the diagnostic quality of BME visualization showed a high preference for the sUTE-Dixon water- and fat-separated images in comparison with STIR. The UTE magnitude images enabled better visualizing fracture lines compared with STIR and slightly better visibility of cortical outlining. With increasing SWI weighting osseous structures and fatty tissues were enhanced. CONCLUSION: The proposed sUTE-Dixon-SWI methodology allows the removal of unwanted low-frequency phases and enables water-fat separation and SWI processing from a single complex UTE image. The methodology can be used for the simultaneous assessment of vertebral fractures and BME of the thoracolumbar spine.

Ultra-short echo time magnetic resonance angiography using a modified signal targeting with alternative radio frequency spin labeling technique for detecting recanalized pulmonary arteriovenous malformation after coil embolization.

Pulmonary arteriovenous malformation (PAVM) is a rare vascular anomaly, for which transcatheter embolization with metallic coils is the standard of care. Although detecting recanalization after embolotherapy is crucial, direct visualization of residual flow with computed tomography or magnetic resonance (MR) imaging is generally difficult due to metal artifacts. We present a case of recanalized PAVM after coil embolization detected by ultra-short echo time MR angiography using a modified signal targeting with an alternative radio frequency spin labeling technique.

Evaluation of the degenerative pattern of PCL in osteoarthritis patients using UTE-T2 mapping.

BACKGROUND: The posterior cruciate ligament (PCL) is one of the essential stabilizers of the knee joint and it was demonstrated that its degenerative change related to the knee osteoarthritis (OA). We aimed to evaluate signal of the PCL in OA patients in comparison with healthy young and elderly volunteers using the ultra-short echo timeenhanced (UTE)-T2∗ mapping, and to validate these findings with histology. METHODS: Thirty asymptomatic volunteers, 13 young people (younger group) and 17 elderly people (elder group), and 27 patients who had undergone total knee arthroplasty (OA group) were enrolled in this study. UTE-T2∗ maps of PCL were obtained from all participants. The PCL was divided into proximal, middle, and distal parts and the UTET2∗ values obtained from each part were compared among the groups. In OA group, the sacrificed PCLs were evaluated histologically in each part corresponding to the part of UTE-T2∗ maps and compared. RESULTS: The UTE-T2∗ values in OA group were significantly higher than those in other groups except in distal part. In elder group, the UTE-T2∗ values were significantly higher than those in younger group only in the proximal part. Moreover, in OA group, the UTE-T2∗ values in proximal and middle parts were significantly higher than those in distal part. There was a moderate correlation between the UTE-T2∗ values and histological scores. CONCLUSIONS: The specific signal intensity pattern of the PCL in patients with OA was demonstrated using UTE-T2∗ mapping, and these findings were related to histological degenerated status of the PCL.

Comparison of MR Ultrashort Echo Time and Optimized 3D-Multiecho In-Phase Sequence to Computed Tomography for Assessment of the Osseous Craniocervical Junction.

BACKGROUND: To assess changes of the craniocervical junction (CCJ), computed tomography (CT) is considered the reference standard. Recent advances in bone depiction on magnetic resonance imaging (MRI) enable high-quality visualization of osseous structures. Consequently, MRI may serve as an alternative to CT, without the use of ionizing radiation. PURPOSE: To compare two MRI sequences optimized for bone visualization to the CT reference standard in the assessment of the osseous CCJ. STUDY TYPE: Prospective. POPULATION/SUBJECTS: Twenty-seven decedents and five healthy volunteers. FIELD STRENGTH/SEQUENCE: 3T/ultrashort-echo time gradient echo (UTE) and optimized 3D-multiecho in-phase gradient echo sequences (FRACTURE). ASSESSMENT: All decedents were scanned with both MRI sequences and CT. Three observers rated degeneration to obtain a score for the upper (atlanto-dental and left/right atlanto-occipital joint) and for the lower part of the CCJ (left and right atlanto-axial joint). Two reader rated the following quantitative parameters: basion-axial-interval, atlanto-dental-interval, atlanto-occipital-interval, Powers-ratio, and signal/contrast-to-noise-ratio. As a proof of concept, five healthy volunteers were scanned with both MRI sequences. STATISTICAL TESTS: Degeneration was assessed on a Likert scale by three independent observers. Interrater and intermodality reliability were calculated using an intraclass correlation coefficient. To compare distance measurements between examination methods, a Friedman test, between-degenerative ratings, and a Kruskal-Wallis test were performed. RESULTS: Degenerative ratings of the CCJ between MRI sequences and CT showed a good interrater and intermodality agreement. MRI sequences tended to underestimate the degree of degeneration compared to CT, and this became more marked with increasing degeneration severity. There were no significant relationships between distance measurements and the degree of degeneration (PCT = 0.62, PUTE = 0.64, PFRACTURE = 0.67). The in vivo examination proved the feasibility of both MRI methods in a clinical setting. DATA CONCLUSION: Quantitative and qualitative ratings on MR images were comparable to CT images; thus, MRI may be a valid alternative to CT assessing the CCJ. LEVEL OF EVIDENCE: 1. TECHNICAL EFFICACY STAGE: 3.

UTE T2* mapping of tendinopathic patellar tendons: an MRI reproducibility study.

BACKGROUND: There is currently a lack of imaging modalities that can be used as a sensitive measure in tendinopathy. Recent findings suggest the applicability of ultra-short echo time (UTE) magnetic resonance imaging (MRI) T2* mapping in tendons, but the reproducibility remains unknown. PURPOSE: To evaluate test-retest reproducibility of UTE MRI T2* mapping of tendinopathic patellar tendons and to evaluate the intra- and inter-observer reproducibility of the measurement. MATERIAL AND METHODS: Fifteen patients with chronic patellar tendinopathy were evaluated with UTE MRI twice in a 3.0-T scanner on the same day. Manual segmentation of the patellar tendon was performed by two blinded investigators and automated T2*map reconstruction was performed in custom-made software. RESULTS: There was a significant and numerically small difference in test-retest T2* values (T2*meandiff = 0.06 ± 0.07 ms ≈ 3.7%; P = 0.006) with an ICC = 0.91 (95% confidence interval [CI] 0.58-0.98; typical error of 3.0%). The intra- and inter-observer reproducibility showed no significant bias (P = 0.493 and P = 0.052), and generally substantial reproducibility was demonstrated for T2* (intra-observer ICC = 0.99; 95% CI 0.98-1.00 and inter-observer ICC = 0.99; 95% CI 0.96-1.00, and typical error 1.3% and 1.3%, respectively). CONCLUSION: These data demonstrate a small bias between repeated measurements for UTE T2*, but with a very low associated mean difference (3.7%) between the two tests. The high ICC values and low typical error % demonstrate reproducibility of repeated T2*-mapping sessions. Further, the method showed substantial intra- and inter-observer reproducibility for T2* values proving feasibility for use of UTE T2* mapping in research and clinical practice.