Ultrashort Echo Time MRI Research Articles

Direct imaging of white matter ultrashort [formula omitted] components at 7 Tesla

PurposeTo demonstrate direct imaging of the white matter ultrashort T2∗ components at 7 Tesla using inversion recovery (IR)-enhanced ultrashort echo time (UTE) MRI. To investigate its characteristics, potentials and limitations, and to establish a clinical protocol. Material and methodsThe IR UTE technique suppresses long T2∗ signals within white matter by using adiabatic inversion in combination with dual-echo difference imaging. Artifacts arising at 7 T from long T2∗ scalp fat components were reduced by frequency shifting the IR pulse such that those frequencies were inverted likewise. For 8 healthy volunteers, the T2∗ relaxation times of white matter were then quantified. In 20 healthy volunteers, the UTE difference and fraction contrast were evaluated. Finally, in 6 patients with multiple sclerosis (MS), the performance of the technique was assessed. ResultsA frequency shift of −1.2 ppm of the IR pulse (i.e. towards the fat frequency) provided a good suppression of artifacts. With this, an ultrashort compartment of (68 ± 6) % with a T2∗ time of (147 ± 58) μs was quantified with a chemical shift of (−3.6 ± 0.5) ppm from water. Within healthy volunteers' white matter, a stable ultrashort T2∗ fraction contrast was calculated. For the MS patients, a significant fraction reduction in the identified lesions as well as in the normal-appearing white matter was observed. ConclusionsThe quantification results indicate that the observed ultrashort components arise primarily from myelin tissue. Direct IR UTE imaging of the white matter ultrashort T2∗ components is thus feasible at 7 T with high quantitative inter-subject repeatability and good detection of signal loss in MS.

CKD Stages, Bone Metabolism Markers, and Cortical Porosity Index: Associations and Mediation Effects Analysis

Chronic kidney disease (CKD) has a significant negative impact on bone health. However, the mechanisms of cortical bone deterioration and cortical porosity enlargement caused by CKD have not been fully described. We therefore examined the association of CKD stages with cortical porosity index (PI), and explored potential mediators of this association. Double-echo ultrashort echo-time magnetic resonance imaging (UTE MRI) provides the possibility of quantifying cortical porosity in vivo. A total of 95 patients with CKD stages 2-5 underwent 3D double-echo UTE-Cones MRI (3.0T) of the midshaft tibia to obtain the PI. PI was defined as the ratio of the image signal intensity of a sufficiently long echo time (TE) to the shortest achievable TE. Parathyroid hormone (PTH), β-CrossLaps (β-CTX), total procollagen type I amino-terminal propeptide (T-P1NP), osteocalcin (OC), 25-hydroxyvitamin D (25OHD), and lumbar bone mineral density (BMD) were measured within one week of the MRI. Partial correlation analysis was performed to address associations between PI, eGFR and potential mediators (PTH, β-CTX, T-P1NP, OC, 25OHD, BMD, and T-score). Multiple linear regression models were used to assess the association between CKD stages and PI value. Then, a separate exploratory mediation analysis was carried out to explore the impact of CKD stages and mediators on the PI value. The increasing CKD stages were associated with a higher PI value (Ptrend < 0.001). The association of CKD stages and PI mediated 34.4% and 30.8% of the total effect by increased PTH and β-CTX, respectively. Our study provides a new idea to monitor bone health in patients with CKD, and reveals the internal mechanism of bone deterioration caused by CKD to some extent.

Pentafluorosulfanyl (SF5) as a Superior 19F Magnetic Resonance Reporter Group: Signal Detection and Biological Activity of Teriflunomide Derivatives.

Fluorine (19F) magnetic resonance imaging (MRI) is severely limited by a low signal-to noise ratio (SNR), and tapping it for 19F drug detection in vivo still poses a significant challenge. However, it bears the potential for label-free theranostic imaging. Recently, we detected the fluorinated dihydroorotate dehydrogenase (DHODH) inhibitor teriflunomide (TF) noninvasively in an animal model of multiple sclerosis (MS) using 19F MR spectroscopy (MRS). In the present study, we probed distinct modifications to the CF3 group of TF to improve its SNR. This revealed SF5 as a superior alternative to the CF3 group. The value of the SF5 bioisostere as a 19F MRI reporter group within a biological or pharmacological context is by far underexplored. Here, we compared the biological and pharmacological activities of different TF derivatives and their 19F MR properties (chemical shift and relaxation times). The 19F MR SNR efficiency of three MRI methods revealed that SF5-substituted TF has the highest 19F MR SNR efficiency in combination with an ultrashort echo-time (UTE) MRI method. Chemical modifications did not reduce pharmacological or biological activity as shown in the in vitro dihydroorotate dehydrogenase enzyme and T cell proliferation assays. Instead, SF5-substituted TF showed an improved capacity to inhibit T cell proliferation, indicating better anti-inflammatory activity and its suitability as a viable bioisostere in this context. This study proposes SF5 as a novel superior 19F MR reporter group for the MS drug teriflunomide.

Ultrashort echo time MRI of the lung in children and adolescents: comparison with non-enhanced computed tomography and standard post-contrast T1w MRI sequences

ObjectivesTo compare the diagnostic value of ultrashort echo time (UTE) magnetic resonance imaging (MRI) for the lung versus the gold standard computed tomography (CT) and two T1-weighted MRI sequences in children.MethodsTwenty-three patients with proven oncologic disease (14 male, 9 female; mean age 9.0 + / − 5.4 years) received 35 low-dose CT and MRI examinations of the lung. The MRI protocol (1.5-T) included the following post-contrast sequences: two-dimensional (2D) incoherent gradient echo (GRE; acquisition with breath-hold), 3D volume interpolated GRE (breath-hold), and 3D high-resolution radial UTE sequences (performed during free-breathing). Images were evaluated by considering image quality as well as distinct diagnosis of pulmonary nodules and parenchymal areal opacities with consideration of sizes and characterisations.ResultsThe UTE technique showed significantly higher overall image quality, better sharpness, and fewer artefacts than both other sequences. On CT, 110 pulmonary nodules with a mean diameter of 4.9 + / − 2.9 mm were detected. UTE imaging resulted in a significantly higher detection rate compared to both other sequences (p < 0.01): 76.4% (84 of 110 nodules) for UTE versus 60.9% (67 of 110) for incoherent GRE and 62.7% (69 of 110) for volume interpolated GRE sequences. The detection of parenchymal areal opacities by the UTE technique was also significantly higher with a rate of 93.3% (42 of 45 opacities) versus 77.8% (35 of 45) for 2D GRE and 80.0% (36 of 45) for 3D GRE sequences (p < 0.05).ConclusionThe UTE technique for lung MRI is favourable in children with generally high diagnostic performance compared to standard T1-weighted sequences as well as CT.Key Points• Due to the possible acquisition during free-breathing of the patients, the UTE MRI sequence for the lung is favourable in children.• The UTE technique reaches higher overall image quality, better sharpness, and lower artefacts, but not higher contrast compared to standard post-contrast T1-weighted sequences.• In comparison to the gold standard chest CT, the detection rate of small pulmonary nodules small nodules ≤ 4 mm and subtle parenchymal areal opacities is higher with the UTE imaging than standard T1-weighted sequences.

Pulmonary Imaging of Immunocompromised Patients during Hematopoietic Stem Cell Transplantation using Non-Contrast-Enhanced Three-Dimensional Ultrashort Echo Time (3D-UTE) MRI.

To evaluate the feasibility of non-contrast-enhanced three-dimensional ultrashort echo time (3D-UTE) MRI for pulmonary imaging in immunocompromised patients during hematopoietic stem cell transplantation (HSCT). MRI was performed using a stack-of-spirals 3D-UTE sequence (slice thickness: 2.34mm; matrix: 256 × 256; acquisition time: 12.7-17.6 seconds) enabling imaging of the entire thorax within single breath-holds. Patients underwent MRI before HSCT initiation, in the case of periprocedural pneumonia, before discharge, and in the case of re-hospitalization. Two readers separately assessed the images regarding presence of pleural effusions, ground glass opacities (GGO), and consolidations on a per lung basis. A T2-weighted (T2w) multi-shot Turbo Spin Echo sequence (BLADE) was acquired in coronal orientation during breath-hold (slice thickness: 6.00mm; matrix: 320 × 320; acquisition time: 3.1-5.5 min) and read on a per lesion basis. Low-dose CT scans in inspiration were used as reference and were read on a per lung basis. Only scans performed within a maximum of three days were included in the inter-method analyses. Interrater agreement, sensitivity, specificity, positive and negative predictive values, and diagnostic accuracy of 3D-UTE MRI were calculated. 67 MRI scans of 28 patients were acquired. A reference CT examination was available for 33 scans of 23 patients. 3D-UTE MRI showed high sensitivity and specificity regarding pleural effusions (n = 6; sensitivity, 92 %; specificity, 100 %) and consolidations (n = 22; sensitivity 98 %, specificity, 86 %). Diagnostic performance was lower for GGO (n = 9; sensitivity, 63 %; specificity, 84 %). Accuracy rates were high (pleural effusions, 98 %; GGO, 79 %; consolidations 94 %). Interrater agreement was substantial for consolidations and pleural effusions (κ = 0.69-0.82) and moderate for GGO (κ = 0.54). Compared to T2w imaging, 3D-UTE MRI depicted the assessed pathologies with at least equivalent quality and was rated superior regarding consolidations and GGO in ~50 %. Non-contrast 3D-UTE MRI enables radiation-free assessment of typical pulmonary complications during HSCT procedure within a single breath-hold. Yet, CT was found to be superior regarding the identification of pure GGO changes. · 3D-UTE MRI of the thorax can be acquired within a single breath-hold.. · 3D-UTE MRI provides diagnostic imaging of pulmonary consolidations and pleural effusions.. · 3D-UTE sequences improve detection rates of ground glass opacities on pulmonary MRI.. · 3D-UTE MRI depicts pulmonary pathologies at least equivalent to T2-weighted Blade sequence.. · Metz C, Böckle D, Heidenreich JF et al. Pulmonary Imaging of Immunocompromised Patients during Hematopoietic Stem Cell Transplantation using Non-Contrast-Enhanced Three-Dimensional Ultrashort Echo Time (3D-UTE) MRI. Fortschr Röntgenstr 2022; 194: 39 - 48.

Ultra-short echo-time magnetic resonance imaging lung segmentation with under-Annotations and domain shift.

Ultra-short echo-time (UTE) magnetic resonance imaging (MRI) provides enhanced visualization of pulmonary structural and functional abnormalities and has shown promise in phenotyping lung disease. Here, we describe the development and evaluation of a lung segmentation approach to facilitate UTE MRI methods for patient-based imaging. The proposed approach employs a k-means algorithm in kernel space for pair-wise feature clustering and imposes image domain continuous regularization, coined as continuous kernel k-means (CKKM). The high-order CKKM algorithm was simplified through upper bound relaxation and solved within an iterative continuous max-flow framework. We combined the CKKM with U-net and atlas-based approaches and comprehensively evaluated the performance on 100 images from 25 patients with asthma and bronchial pulmonary dysplasia enrolled at Robarts Research Institute (Western University, London, Canada) and Centre Hospitalier Universitaire (Sainte-Justine, Montreal, Canada). For U-net, we trained the network five times on a mixture of five different images with under-annotations and applied the model to 64 images from the two centres. We also trained a U-net on five images with full and brush annotations from one centre, and tested the model on 32 images from the other centre. For an atlas-based approach, we employed three atlas images to segment 64 target images from the two centres through straightforward atlas registration and label fusion. We applied the CKKM algorithm to the baseline U-net and atlas outputs and refined the initial segmentation through multi-volume image fusion. The integration of CKKM substantially improved baseline results and yielded, with minimal computational cost, segmentation accuracy, and precision that were greater than some state-of-the-art deep learning models and similar to experienced observer manual segmentation. This suggests that deep learning and atlas-based approaches may be utilized to segment UTE MRI datasets using relatively small training datasets with under-annotations.

Neonates With Tracheomalacia Generate Auto-Positive End-Expiratory Pressure via Glottis Closure

In pediatrics, tracheomalacia is an airway condition that causes tracheal lumen collapse during breathing and may lead to the patient requiring respiratory support. Adult patients can narrow their glottis to self-generate positive end-expiratory pressure (PEEP) to raise the pressure in the trachea and prevent collapse. However, auto-PEEP has not been studied in newborns with tracheomalacia. The objective of this study was to measure the glottis cross-sectional area throughout the breathing cycle and to quantify total pressure difference through the glottis in patients with and without tracheomalacia. Do neonates with tracheomalacia narrow their glottises? How does the glottis narrowing affect the total pressure along the airway? Ultrashort echo time MRI was performed in 21 neonatal ICU patients (11 with tracheomalacia, 10 without tracheomalacia). MRI scans were reconstructed at four different phases of breathing. All patients were breathing room air or using noninvasive respiratory support at the time of MRI. Computational fluid dynamics simulations were performed on patient-specific virtual airway models with airway anatomic features and motion derived via MRI to quantify the total pressure difference through the glottis and trachea. The mean glottis cross-sectional area at peak expiration in the patients with tracheomalacia was less than half that in patients without tracheomalacia (4.0 ± 1.1mm2 vs10.3 ± 4.4mm2; P= .002). The mean total pressure difference through the glottis at peak expiration was more than 10 times higher in patients with tracheomalacia compared with patients without tracheomalacia (2.88 ± 2.29cm H2O vs0.26 ± 0.16cm H2O; P= .005). Neonates with tracheomalacia narrow their glottises, which raises pressure in the trachea during expiration, thereby acting as auto-PEEP.

Ultrashort echo time adiabatic T1ρ (UTE-Adiab-T1ρ) is sensitive to human cadaveric knee joint deformation induced by mechanical loading and unloading

PurposeThe development of ultrashort echo time (UTE) MRI sequences has led to improved imaging of tissues with short T2 relaxation times, such as the deep layer cartilage and meniscus. UTE combined with adiabatic T1ρ preparation (UTE-Adiab-T1ρ) is an MRI measure with low sensitivity to the magic angle effect. This study aimed to investigate the sensitivity of UTE-Adiab-T1ρ to mechanical load-induced deformations in the tibiofemoral cartilage and meniscus of human cadaveric knee joints. MethodsEight knee joints from young (42 ± 12 years at death) donors were evaluated on a 3 T scanner using the UTE-Adiab-T1ρ sequence under four sequential loading conditions: load = 0 N (Load0), load = 300 N (Load1), load = 500 N (Load2), and load = 0 N (Unload). UTE-Adiab-T1ρ was measured in the meniscus (M), femoral articular cartilage (FAC), tibial articular cartilage (TAC), articular cartilage regions uncovered by meniscus (AC-UC), and articular cartilage regions covered by meniscus (AC-MC) within region of interests (ROIs) manually selected by an experienced MR scientist. The Kruskal–Wallis test, with corrected significance level for multiple comparisons, was used to examine the UTE-Adiab-T1ρ differences between different loading conditions. ResultsUTE-Adiab-T1ρ decreased in all grouped ROIs under both Load1 and Load2 conditions (−18.7% and − 16.9% for M, −18.8% and − 12.6% for FAC, −21.4% and − 10.7% for TAC, −26.2% and − 13.9% for AC-UC, and − 16.9% and − 10.7% for AC-MC). After unloading, average UTE-Adiab-T1ρ increased across all ROIs and within a lower range compared with the average UTE-Adiab-T1ρ decreases induced by the two previous loading conditions. The loading-induced differences were statistically non-significant. ConclusionsWhile UTE-Adiab-T1ρ reduction by loading is likely an indication of tissue deformation, the increase of UTE-Adiab-T1ρ within a lower range by unloading implies partial tissue restoration. This study highlights the UTE-Adiab-T1ρ technique as an imaging marker of tissue function for detecting deformation patterns under loading.

Preclinical MRI to quantify pulmonary disease severity and trajectories in poorly characterized mouse models: A pedagogical example using data from novel transgenic models of lung fibrosis

Structural remodeling in lung disease is progressive and heterogeneous, making temporally and spatially explicit information necessary to understand disease initiation and progression. While mouse models are essential to elucidate mechanistic pathways underlying disease, the experimental tools commonly available to quantify lung disease burden are typically invasive (e.g., histology). This necessitates large cross-sectional studies with terminal endpoints, which increases experimental complexity and expense. Alternatively, magnetic resonance imaging (MRI) provides information noninvasively, thus permitting robust, repeated-measures statistics. Although lung MRI is challenging due to low tissue density and rapid apparent transverse relaxation (T2* <1 ms), various imaging methods have been proposed to quantify disease burden. However, there are no widely accepted strategies for preclinical lung MRI. As such, it can be difficult for researchers who lack lung imaging expertise to design experimental protocols—particularly for novel mouse models. Here, we build upon prior work from several research groups to describe a widely applicable acquisition and analysis pipeline that can be implemented without prior preclinical pulmonary MRI experience. Our approach utilizes 3D radial ultrashort echo time (UTE) MRI with retrospective gating and lung segmentation is facilitated with a deep-learning algorithm. This pipeline was deployed to assess disease dynamics over 255 days in novel, transgenic mouse models of lung fibrosis based on disease-associated, loss-of-function mutations in Surfactant Protein-C. Previously identified imaging biomarkers (tidal volume, signal coefficient of variation, etc.) were calculated semi-automatically from these data, with an objectively-defined high signal volume identified as the most robust metric. Beyond quantifying disease dynamics, we discuss common pitfalls encountered in preclinical lung MRI and present systematic approaches to identify and mitigate these challenges. While the experimental results and specific pedagogical examples are confined to lung fibrosis, the tools and approaches presented should be broadly useful to quantify structural lung disease in a wide range of mouse models.

Evaluation of pulmonary ventilation in COVID-19 patients using oxygen-enhanced three-dimensional ultrashort echo time MRI: a preliminary study

AIMTo evaluate the lung function of coronavirus disease 2019 (COVID-19) patients using oxygen-enhanced (OE) ultrashort echo time (UTE) MRI.MATERIALS AND METHODSForty-nine patients with COVID-19 were included in the study. The OE-MRI was based on a respiratory-gated three-dimensional (3D) radial UTE sequence. For each patient, the percent signal enhancement (PSE) map was calculated using the expression PSE = (S100% – S21%)/S21%, where S21% and S100% are signals acquired during room air and 100% oxygen inhalation, respectively. Agreement of lesion detectability between UTE-MRI and computed tomography (CT) was performed using the kappa test. The Mann–Whitney U-test was used to evaluate the difference in the mean PSE between mild-type COVID-19 and common-type COVID-19. Spearman's test was used to assess the relationship between lesion mean PSE and lesion size. Furthermore, the Mann–Whitney U-test was used to evaluate the difference in region of interest (ROI) mean PSE between normal pulmonary parenchyma and lesions. The Kruskal–Wallis test was applied to test the difference in the mean PSE between different lesion types.RESULTSCT and UTE-MRI reached good agreement in lesion detectability. Ventilation measures in mild-type patients (5.3 ± 5.5%) were significantly different from those in common-type patients (3 ± 3.9%). Besides, there was no significant correlation between lesion mean PSE and lesion size. The mean PSE of COVID-19 lesions (3.2 ± 4.9%) was significantly lower than that of the pulmonary parenchyma (5.4 ± 3.9%). No significant difference was found among different lesion types.CONCLUSIONOE-UTE-MRI could serve as a promising method for the assessment of lung function or treatment management of COVID-19 patients.

A Useful Combination of Quantitative Ultrashort Echo Time MR Imaging and a Probing Device for Biomechanical Evaluation of Articular Cartilage.

In this study, we combined quantitative ultrashort echo time (UTE) magnetic resonance (MR) imaging and an investigation by a probing device with tri-axial force sensor to seek correlations with mechanical properties of human patellar cartilage for in situ evaluation of biomechanical properties. Cartilage blocks (15 × 20 × 5 mm3) were dissected from the patella of six donors; 5 mm square regions of interest from the cartilage blocks were imaged using UTE-MR imaging sequences (T2* and magnetization transfer ratio (MTR)), and mechanical properties were measured using a micro indentation device. Then, the vertical reaction force on the cartilage surface was measured while push-probing forward 3 mm with the probing device at a 30° tilt to the horizontal plane. The results showed a positive correlation between stiffness/elastic modulus and each predictor variable (UTE-T2* (r = 0.240 and 0.255, respectively, UTE-MTR (r = 0.378 and 0.379, respectively), and probing device force (r = 0.426 and 0.423, respectively). Furthermore, multiple linear regression analysis showed the combination of the three predictors had stronger correlation (adjusted r2 = 0.314 (stiffness), 0.323 (elastic), respectively). Our results demonstrate the potential for these non- and less- invasive methods for in situ evaluation of the mechanical properties of cartilage tissue.

CT-like images based on T1 spoiled gradient-echo and ultra-short echo time MRI sequences for the assessment of vertebral fractures and degenerative bone changes of the spine

ObjectivesTo evaluate the performance of 3D T1w spoiled gradient-echo (T1SGRE) and ultra-short echo time (UTE) MRI sequences for the detection and assessment of vertebral fractures and degenerative bone changes compared with conventional CT.MethodsFractures (n = 44) and degenerative changes (n = 60 spinal segments) were evaluated in 30 patients (65 ± 14 years, 18 women) on CT and 3-T MRI, including CT-like images derived from T1SGRE and UTE. Two radiologists evaluated morphological features on both modalities: Genant and AO/Magerl classifications, anterior/posterior vertebral height, fracture age; disc height, neuroforaminal diameter, grades of spondylolisthesis, osteophytes, sclerosis, and facet joint degeneration. Diagnostic accuracy and agreement between MRI and CT and between radiologists were assessed using crosstabs, weighted κ, and intraclass correlation coefficients. Image quality was graded on a Likert scale.ResultsFor fracture detection, sensitivity, specificity, and accuracy were 0.95, 0.98, and 0.97 for T1SGRE and 0.91, 0.96, and 0.95 for UTE. Agreement between T1SGRE and CT was substantial to excellent (e.g., Genant: κ, 0.92 [95% confidence interval, 0.83–1.00]; AO/Magerl: κ, 0.90 [0.76–1.00]; osteophytes: κ, 0.91 [0.82–1.00]; sclerosis: κ, 0.68 [0.48–0.88]; spondylolisthesis: ICCs, 0.99 [0.99–1.00]). Agreement between UTE and CT was lower, ranging from moderate (e.g., sclerosis: κ, 0.43 [0.26–0.60]) to excellent (spondylolisthesis: ICC, 0.99 [0.99–1.00]). Inter-reader agreement was substantial to excellent (0.52–1.00), respectively, for all parameters. Median image quality of T1SGRE was rated significantly higher than that of UTE (p < 0.001).ConclusionsMorphologic assessment of bone pathologies of the spine using MRI was feasible and comparable to CT, with T1SGRE being more robust than UTE.Key Points• Vertebral fractures and degenerative bone changes can be assessed on CT-like MR images, with 3D T1w spoiled gradient-echo–based images showing a high diagnostic accuracy and agreement with CT.• This could enable MRI to precisely assess bone morphology, and 3D T1SGRE MRI sequences may substitute additional spinal CT examinations in the future.• Image quality and robustness of T1SGRE sequences are higher than those of UTE MRI for the assessment of bone structures.

Effects of neonatal lung abnormalities on parenchymal R2 * estimates.

Infants admitted to the neonatal intensive care unit (NICU) often suffer from multifaceted pulmonary morbidities that are not well understood. Ultrashort echo time (UTE) magnetic resonance imaging (MRI) is a promising technique for pulmonary imaging in this population without requiring exposure to ionizing radiation. The aims of this study were to investigate the effect of neonatal pulmonary disease on R2 * and tissue density and to utilize numerical simulations to evaluate the effect of different alveolar structures on predicted R2 *.This was a prospective study, in which 17 neonatal human subjects (five control, seven with bronchopulmonary dysplasia [BPD], five with congenital diaphragmatic hernia [CDH]) were enrolled. Twelve subjects were male and five were female, with postmenstrual age (PMA) at MRI of 39.7 ± 4.7 weeks. A 1.5T/multiecho three-dimensional UTE MRI was used. Pulmonary R2 * and tissue density were compared across disease groups over the whole lung and regionally. A spherical shell alveolar model was used to predict the expected R2 * over a range of tissue densities and tissue susceptibilities. Tests for significantly different mean R2 * and tissue densities across disease groups were evaluated using analysis of variance, with subsequent pairwise group comparisons performed using t tests. Lung tissue density was lower in the ipsilateral lung in CDH compared to both controls and BPD patients (both p < 0.05), while only the contralateral lung in CDH (CDHc) had higher whole-lung R2 * than both controls and BPD (both p < 0.05). R2 * differences were significant between controls and CDHc within all tissue density ranges (all p < 0.05) with the exception of the 80%-90% range (p=0.17). Simulations predicted an inverse relationship between alveolar tissue density and R2 * that matches empirical human data. Alveolar wall thickness had no effect on R2 * independent of density (p=1). The inverse relationship between R2 * and tissue density is influenced by the presence of disease globally and regionally in neonates with BPD and CDH in the NICU. LEVEL OF EVIDENCE: 2. TECHNICAL EFFICACY STAGE: 2.

Novel Thoracic MRI Approaches for the Assessment of Pulmonary Physiology and Inflammation.

Excessive pulmonary inflammation can lead to damage of lung tissue, airway remodelling and established structural lung disease. Novel therapeutics that specifically target inflammatory pathways are becoming increasingly common in clinical practice, but there is yet to be a similar stepwise change in pulmonary diagnostic tools. A variety of thoracic magnetic resonance imaging (MRI) tools are currently in development, which may soon fulfil this emerging clinical need for highly sensitive assessments of lung structure and function. Given conventional MRI techniques are poorly suited to lung imaging, alternate strategies have been developed, including the use of inhaled contrast agents, intravenous contrast and specialized lung MR sequences. In this chapter, we discuss technical challenges of performing MRI of the lungs and how they may be overcome. Key thoracic MRI modalities are reviewed, namely, hyperpolarized noble gas MRI, oxygen-enhanced MRI (OE-MRI), ultrashort echo time (UTE) MRI and dynamic contrast-enhanced (DCE) MRI. Finally, we consider potential clinical applications of these techniques including phenotyping of lung disease, evaluation of novel pulmonary therapeutic efficacy and longitudinal assessment of specific patient groups.

Three Dimensional Ultra-short Echo Time MRI Can Depict Cholesterol Components of Gallstones Bright.

PurposeNon-calcified cholesterol stones that are small in size are hard to be depicted on CT or magnetic resonance cholangiopancreatography. This institutional review board (IRB)-approved retrospective in vitro study aims to characterize contrast behaviors of 3 main components of the gallstones, i.e., cholesterol component (CC), bilirubin calcium component (BC) and CaCO3 (CO) on 3D radial scan with ultrashort TE (UTE) MRI, and to test the capability of depicting CC of gallstones as bright signals as compared to background saline.MethodsFourteen representative gallstones from 14 patients, including 15 CC, 6 BC and 4 CO, were enrolled. The gallstones underwent MRI including fat-saturated T1-weighted image (fs-T1WI) and UTE MRI with dual echoes. The contrast-to-noise ratio (CNR) and the chemical analysis for the 25 portions of the stones were compared.ResultsBC was bright on fs-T1WI, which did not change dramatically on UTE MRI and the signal did not remain on UTE subtraction image between dual echoes. Whereas the CC was negative or faintly positive signal on fs-T1WI, bright signal on UTE MRI and the contrast remained even higher on the UTE subtraction, which reflected their short T2 values. Median CNRs and standard errors of the segments on each imaging were as follows: on fs-T1WI, −10.2 ± 4.2 for CC, 149.7 ± 27.6 for BC and 37.9 ± 14.3 for CO; on UTE MRI first echo, 16.7 ± 3.3 for CC, 74.9 ± 21.3 for BC and 17.7 ± 8.4 for CO; on UTE subtraction image, 30.2 ±2.0 for CC, −11.2 ± 5.4 for BC and 17.8 ± 10.7 for CO. Linear correlations between CNRs and cholesterol concentrations were observed on fs-T1WI with r = −0.885, (P < 0.0001), UTE MRI first echo r = −0.524 (P = 0.0072) and UTE subtraction with r = 0.598 (P = 0.0016).ConclusionUTE MRI and UTE subtraction can depict CC bright.

Sensitive structural and functional measurements and 1-year pulmonary outcomes in pediatric cystic fibrosis

BackgroundTwo functional measurements (multiple breath washout [MBW] and hyperpolarized 129Xe ventilation magnetic resonance imaging [129Xe MRI]) have been shown to be more sensitive to cystic fibrosis (CF) lung obstruction than traditional spirometry. However, functional techniques may be sensitive to different underlying structural abnormalities. The purpose of this study was to determine relationships between these functional markers, their pathophysiology, and 1-year clinical outcomes. MethodsSpirometry, MBW, 129Xe MRI, and ultrashort echo-time (UTE) MRI were obtained in a same-day assessment of 27 pediatric CF patients (ages 11.5±5.0) who had not begun CFTR modulator therapies. UTE MRI was scored for structural abnormalities and functional metrics obtained via spirometry, MBW and 129Xe MRI. 1-year outcomes (ΔFEV1 and pulmonary exacerbations), during which ≈50% initiated modulator therapy, were obtained from the electronic medical record. ResultsMBW, 129Xe MRI, and UTE MRI detected clinically significant disease in more subjects (>78%) compared to spirometry (<30%). UTE MRI suggests increased odds of bronchial changes when mucus plugging is present in the same lobe. MBW and 129Xe MRI correlated best with mucus plugging, while spirometry correlated best with consolidations. Bronchial abnormalities were associated with future pulmonary exacerbations. ConclusionsMBW, 129Xe MRI, and UTE MRI are more sensitive for detection of pediatric CF lung disease when compared to spirometry. MBW and 129Xe MRI correlated with structural abnormalities which occur in early CF disease, suggesting MBW and 129Xe MRI are valuable tools in mild CF lung disease that can guide clinical decision making.

Assessment of mechanical properties of articular cartilage with quantitative three-dimensional ultrashort echo time (UTE) cones magnetic resonance imaging

Conventional magnetic resonance imaging (MRI) is not capable of detecting signal from the deep cartilage due to its short transverse relaxation time (T2). Moreover, several quantitative MRI techniques are significantly influenced by the magic angle effect. The combinations of ultrashort echo time (UTE) MRI with magnetization transfer (UTE-MT) and Adiabatic T1ρ (UTE-AdiabT1ρ) imaging allow magic angle-insensitive assessments of all regions of articular cartilage. The purpose of this study was to investigate the correlations between quantitative three-dimensional UTE MRI biomarkers and mechanical properties of human tibiofemoral cartilage specimens. In total, 40 human tibiofemoral cartilage specimens were harvested from three male and four female donors (64 ± 18 years old). Cartilage samples were scanned using a series of quantitative 3D UTE Cones T2* (UTE-T2*), T1 (UTE-T1), UTE-AdiabT1ρ, and UTE-MT sequences in a standard knee coil on a clinical 3T scanner. UTE-MT data were acquired with a series of MT powers and frequency offsets to calculate magnetization transfer ratio (MTR), as well as macromolecular fraction (MMF) and macromolecular T2 (T2mm) through modeling. Cartilage stiffness and Hayes elastic modulus were measured using indentation tests. Correlations of 3D UTE Cones MRI measurements in the superficial layer, deep layer, and global regions of interest (ROIs) with mechanical properties were investigated. Cartilage mechanical properties demonstrated highest correlations with UTE measures of the superficial layer of cartilage. AdiabT1ρ, MTR, and MMF in superficial layer ROIs showed significant correlations with Hayes elastic modulus (p < 0.05, R = −0.54, 0.49, and 0.66, respectively). These UTE measures in global ROIs showed significant, though slightly lower, correlations with Hayes elastic modulus (p < 0.05, R = −0.37, 0.52, and 0.60, respectively). Correlations between other UTE MRI measurements (T2*, T1, and T2mm) and mechanical properties were non-significant. The 3D UTE-AdiabT1ρ and UTE-MT sequences were highlighted as promising surrogates for non-invasive assessment of cartilage mechanical properties. MMF from UTE-MT modeling showed the highest correlations with cartilage mechanics.

Subglottic Stenosis Position Affects Work of Breathing.

Subglottic stenosis (SGS) is the most common type of laryngeal stenosis in neonates. SGS severity is currently graded based on percent area of obstruction (%AO) via the Myer-Cotton grading scale. However, patients with similar %AO can have widely different clinical courses. Computational fluid dynamics (CFD) based on patient-specific imaging can quantify the relationship between airway geometry and flow dynamics. We investigated the effect of %AO and axial position of SGS on work of breathing (WOB) in neonates using magnetic resonance imaging. High-resolution ultrashort echo-time MRI of the chest and airway was obtained in three neonatal patients with no suspected airway abnormalities; images were segmented to construct three-dimensional (3D) models of the neonatal airways. These models were then modified with virtual SGSs of varying %AO and axial positioning. CFD simulations of peak inspiratory flow were used to calculate patient-specific WOB in nonstenotic and artificially stenosed airway models. CFD simulations demonstrated a relationship between stenosis geometry and WOB increase. WOB rapidly increased with %AO greater than about 70%. Changes in axial position could also increase WOB by approximately the same amount as a 10% increase in %AO. Increased WOB was particularly pronounced when the SGS lumen was misaligned with the glottic jet. The results indicate a strong, predictable relationship between WOB and axial position of the stenotic lumen relative to the glottis, which has not been previously reported. These findings may lead to precision diagnosis and treatment prediction tools in individual patients. 4 Laryngoscope, 131:E1220-E1226, 2021.

Quantitative Ultrashort Echo Time (UTE) Magnetic Resonance Imaging of Bone: An Update.

Bone possesses a highly complex hierarchical structure comprised of mineral (~45% by volume), organic matrix (~35%) and water (~20%). Water exists in bone in two forms: as bound water (BW), which is bound to bone mineral and organic matrix, or as pore water (PW), which resides in Haversian canals as well as in lacunae and canaliculi. Magnetic resonance (MR) imaging has been increasingly used for assessment of cortical and trabecular bone. However, bone appears as a signal void on conventional MR sequences because of its short T2*. Ultrashort echo time (UTE) sequences with echo times (TEs) 100–1,000 times shorter than those of conventional sequences allow direct imaging of BW and PW in bone. A series of quantitative UTE MRI techniques has been developed for bone evaluation. UTE and adiabatic inversion recovery prepared UTE (IR-UTE) sequences have been developed to quantify BW and PW. UTE magnetization transfer (UTE-MT) sequences have been developed to quantify collagen backbone protons, and UTE quantitative susceptibility mapping (UTE-QSM) sequences have been developed to assess bone mineral.

Detecting small pulmonary nodules with spiral ultrashort echo time sequences in 1.5T MRI.

This study investigated ultrashort echo time (UTE) sequences in 1.5T magnetic resonance imaging (MRI) for small lung nodule detection. A total of 120 patients with 165 small lung nodules before video-associated thoracoscopic resection were enrolled. MRI sequences included conventional volumetric interpolated breath-hold examination (VIBE, scan time 16s), spiral UTE (TE 0.05ms) with free-breathing (scan time 3.5-5min), and breath-hold sequences (scan time 20s). Chest CT provided a standard reference for nodule size and morphology. Nodule detection sensitivity was evaluated on a lobe-by-lobe basis. The nodule detection rate was significantly higher in spiral UTE free-breathing (> 78%, p < 0.05) and breath-hold sequences (> 75%, p < 0.05) compared with conventional VIBE (> 55%), reaching 100% when nodule size was > 16mm, and reaching 95% when nodules were in solid morphology, regardless of size. The inter-sequence reliability between free-breathing and breath-hold spiral UTE was good (κ > 0.80). Inter-reader agreement was also high (κ > 0.77) for spiral UTE sequences. Nodule size measurements were consistent between CT and spiral UTE MRI, with a minimal bias up to 0.2mm. Spiral UTE sequences detect small lung nodules that warrant surgery, offers realistic scan times for clinical work, and could be implemented as part of routine lung MRI.