Molecular modeling and simulation studies of SELEX-derived high-affinity DNA aptamers to the Ebola virus nucleoprotein

Ebola viral disease (EVD) is a highly infectious and potentially fatal illness with a case fatality rate ranging from 25% to 90%. To effectively control its spread, there is a need for rapid, reliable and lowcost point-of-care (P OC) diagnostic tests. While various EVD diagnostic tests exist, few are P OC tests, and many are not cost-effective. The use of antibodies in these tests has limitations, prompting the exploration of aptamers as potential alternatives. Various proteins from the Ebola virus (EBOV) proteome, including EBOV nucleoprotein (NP), are considered viable targets for diagnostic assays. A previous study identified three aptamers (Apt1. Apt2 and Apt3) with high affinity for EBOV NP using systemic evolution of ligands by exponential enrichment (SELEX). This study aimed to employ in silico methods, such as Phyre2, RNAfold, RNAComposer, HADDOCK and GROMACS, to model the structures of EBOV NP and the aptamers, and to investigate their binding. The in silico analysis revealed successful binding of all the three aptamers to EBOV NP, with a suggested ranking of Apt1 > Apt2 > Apt3 based on binding affinity. Microscale thermophoresis (MST) analysis confirmed the binding, providing dissociation constants of 25 ± 2.84, 56 ± 2.76 and 140 ±3.69 nM for Apt1, Apt2 and Apt3, respectively. The study shows that the findings of the in silico analysis was in agreement with the MST analysis. Inclusion of these in silico approaches in diagnostic assay development can expedite the selection of candidate aptamers, potentially overcoming challenges associated with aptamer application in diagnostics.Communicated by Ramaswamy H. Sarma.

Characterization, Bioactivity, and Biodistribution of 35 kDa Hyaluronan Fragment

It has been reported that hyaluronic acid (HA) with a 35 kDa molecular weight (HA35) acts biologically to protect tissue from injury, but its biological properties are not yet fully characterized. This study aimed to evaluate the cellular effects and biodistribution of HA35 compared to HA with a 1600 kDa molecular weight (HA1600). We assessed the effects of HA35 and HA1600 on cell migration, NO and ROS generation, and gene expression in cultured macrophages, microglia, and lymphocytes. HA35 was separately radiolabeled with 99mTc and 125I and administered to C57BL/6J mice for in vivo biodistribution imaging. In vitro studies indicated that HA35 and HA1600 similarly enhanced cell migration through HA receptor binding mechanisms, reduced the generation of NO and ROS, and upregulated gene expression profiles related to cell signaling pathways in immune cells. HA35 showed a more pronounced effect in regulating a broader range of genes in macrophages and microglia than HA1600. Upon intradermal or intravenous administration, radiolabeled HA35 rapidly accumulated in the liver, spleen, and lymph nodes. In conclusion, HA35 not only exhibits effects on cellular bioactivity comparable to those of HA1600 but also exerts biological effects on a broader range of immune cell gene expression. The findings herein offer valuable insights for further research into the therapeutic potential of HA35 in inflammation-mediated tissue injury.

An eNAMPT-neutralizing mAb reduces post-infarct myocardial fibrosis and left ventricular dysfunction

Myocardial infarction (MI) triggers adverse ventricular remodeling (VR), cardiac fibrosis, and subsequent heart failure. Extracellular nicotinamide phosphoribosyltransferase (eNAMPT) is postulated to play a significant role in VR processing via activation of the TLR4 inflammatory pathway. We hypothesized that an eNAMPT specific monoclonal antibody (mAb) could target and neutralize overexpressed eNAMPT post-MI and attenuate chronic cardiac inflammation and fibrosis. We investigated humanized ALT-100 and ALT-300 mAb with high eNAMPT-neutralizing capacity in an infarct rat model to test our hypothesis. ALT-300 was 99mTc-labeled to generate 99mTc-ALT-300 for imaging myocardial eNAMPT expression at 2 hours, 1 week, and 4 weeks post-IRI. The eNAMPT-neutralizing ALT-100 mAb (0.4 mg/kg) or saline was administered intraperitoneally at 1 hour and 24 hours post-reperfusion and twice a week for 4 weeks. Cardiac function changes were determined by echocardiography at 3 days and 4 weeks post-IRI. 99mTc-ALT-300 uptake was initially localized to the ischemic area at risk (IAR) of the left ventricle (LV) and subsequently extended to adjacent non-ischemic areas 2 hours to 4 weeks post-IRI. Radioactive uptake (%ID/g) of 99mTc-ALT-300 in the IAR increased from 1 week to 4 weeks (0.54 ± 0.16 vs. 0.78 ± 0.13, P < 0.01). Rats receiving ALT-100 mAb exhibited significantly improved myocardial histopathology and cardiac function at 4 weeks, with a significant reduction in the collagen volume fraction (%LV) compared to controls (21.5 ± 6.1% vs. 29.5 ± 9.9%, P < 0.05). Neutralization of the eNAMPT/TLR4 inflammatory cascade is a promising therapeutic strategy for MI by reducing chronic inflammation, fibrosis, and preserving cardiac function.

Observations about declining fertility in a feline breeding colony

Feline breeding colonies are important to the feline industry by preserving traits desirable for a particular breed or in research settings by maintaining medically valuable genetic traits. As breeding females age, their reproductive efficiency declines. The objective of this study was to determine the most common causes of infertility in breeding females that were producing fewer kittens. Knowing the cause and average age of infertility would allow management decisions to be made for the betterment of the colony. The medical records of 70 queens retired from breeding from a single research colony were examined for litter size and number, fertility over their lifespan, and age and reason for removal from breeding stock. Sections of uterus and ovaries were evaluated using gross and histopathological examination for a subset of these queens (46). The data suggests that mature, continuously breeding female cats may show signs of reduced fertility (infertile matings or reduced litter size) as early as 3 years of age and may be a result of undiagnosed Cystic Endometrial Hyperplasia (CEH), endometritis, pyometra and/or ovarian cysts. Evaluation of breeding queens should include periodic ultrasounds to monitor for ovarian cysts and evidence of CEH. Retiring animals from breeding once signs of infertility become apparent is recommended.

Involvement of eNAMPT/TLR4 inflammatory signaling in progression of non-alcoholic fatty liver disease, steatohepatitis, and fibrosis

Although the progression of non-alcoholic fatty liver disease (NAFLD) from steatosis to steatohepatitis (NASH) and cirrhosis remains poorly understood, a critical role for dysregulated innate immunity has emerged. We examined the utility of ALT-100, a monoclonal antibody (mAb), in reducing NAFLD severity and progression to NASH/hepatic fibrosis. ALT-100 neutralizes eNAMPT (extracellular nicotinamide phosphoribosyltransferase), a novel damage-associated molecular pattern protein (DAMP) and Toll-like receptor 4 (TLR4) ligand. Histologic and biochemical markers were measured in liver tissues and plasma from human NAFLD subjects and NAFLD mice (streptozotocin/high-fat diet-STZ/HFD, 12 weeks). Human NAFLD subjects (n = 5) exhibited significantly increased NAMPT hepatic expression and significantly elevated plasma levels of eNAMPT, IL-6, Ang-2, and IL-1RA compared to healthy controls, with IL-6 and Ang-2 levels significantly increased in NASH non-survivors. Untreated STZ/HFD-exposed mice displayed significant increases in NAFLD activity scores, liver triglycerides, NAMPT hepatic expression, plasma cytokine levels (eNAMPT, IL-6, and TNFα), and histologic evidence of hepatocyte ballooning and hepatic fibrosis. Mice receiving the eNAMPT-neutralizing ALT-100 mAb (0.4 mg/kg/week, IP, weeks 9 to 12) exhibited marked attenuation of each index of NASH progression/severity. Thus, activation of the eNAMPT/TLR4 inflammatory pathway contributes to NAFLD severity and NASH/hepatic fibrosis. ALT-100 is potentially an effective therapeutic approach to address this unmet NAFLD need.

PEGylated and Non-PEGylated TCP-1 Probes for Imaging of Colorectal Cancer

PURPOSE

Previous studies indicate that 99mTc- and fluorescent-labeled c[Cys-Thr-Pro-Ser-Pro-Phe-Ser-His-Cys]OH (TCP-1) peptides were able to detect colorectal cancer (CRC) and tumor-associated vasculature. This study was designed to characterize the targeting properties of PEGylated and non-PEGylated TCP-1 peptides for CRC imaging.

PROCEDURES

Cell uptake of cyanine 7 (Cy7)-labeled TCP-1 probes (Cy7-PEG4-TCP-1 and Cy7-TCP-1) was investigated in three CRC cell lines (human, HCT116 and HT29; mouse, CT26). Xenograft and orthotopic CRC tumor models with HCT116 and CT26 cells were used to characterize biodistribution and CRC tumor-targeting properties of TCP-1 fluorescence and radioligand with and without PEGylation, [99mTc]Tc-HYNIC-PEG4-TCP-1 vs. [99mTc]Tc-HYNIC-TCP-1.

RESULTS

Fluorescence images showed that TCP-1 probes were distributed in the cytoplasm and nucleus of CRC cells. When CT26 cells were treated with unlabeled TCP-1 peptide prior to the cell incubation with Cy7-PEG4-TCP-1, cell fluorescent signals were significantly reduced relative to the cells without blockade. Relative to Cy7-TCP-1, superior brilliance and visibility of fluorescence was observed in the tumor with Cy7-PEG4-TCP-1 and maintained up to 18 h post-injection. [99mTc]Tc-HYNIC-PEG4-TCP-1 images in xenograft and orthotopic CRC models demonstrated that TCP-1 PEGylation preserved tumor-targeting capability of TCP-1, but its distribution (%ID/g) in the liver and intestine was higher than that of [99mTc]Tc-HYNIC-TCP-1 (1.51 ± 0.29 vs 0.53 ± 0.12, P < 0.01). Better tumor visualization by [99mTc]Tc-HYNIC-TCP-1 was observed in the orthotopic CRC model due to lower intestinal radioactivity.

CONCLUSIONS

TCP-1-based probes undergo endocytosis and localize in the cytoplasm and nucleus of human and mouse CRC cells. Tumor detectability of fluorescent TCP-1 peptide with a PEG4 spacer is promising due to its enhanced tumor binding affinity and rapid clearance kinetics from nontumor tissues. Non-PEGylated [99mTc]Tc-HYNIC-TCP-1 exhibits lower nonspecific accumulation in the liver and gastrointestinal tract and might have better capability for detecting CRC lesions in clinical sites. TCP-1 may represent an innovative targeting molecule for detecting CRC noninvasively.

Use of radiolabeled hyaluronic acid for preclinical assessment of inflammatory injury and acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is accompanied by a dramatic increase in lung hyaluronic acid (HA), leading to a dose-dependent reduction of pulmonary oxygenation. This pattern is associated with severe infections, such as COVID-19, and other important lung injury etiologies. HA actively participates in molecular pathways involved in the cytokine storm of COVID-19-induced ARDS. The objective of this study was to evaluate an imaging approach of radiolabeled HA for assessment of dysregulated HA deposition in mouse models with skin inflammation and lipopolysaccharide (LPS)-induced ARDS using a novel portable intensified Quantum Imaging Detector (iQID) gamma camera system.

METHODS

HA of 10 kDa molecular weight (HA10) was radiolabeled with 125I and 99mTc respectively to produce [125I]I-HA10 and [99mTc]Tc-HA10, followed by comparative studies on stability, in vivo biodistribution, and uptake at inflammatory skin sites in mice with 12-O-tetradecanoylphorbol-13-acetate (TPA)-inflamed ears. [99mTc]Tc-HA10 was used for iQID in vivo dynamic imaging of mice with ARDS induced by intratracheal instillation of LPS.

RESULTS

[99mTc]Tc-HA10 and [125I]I-HA10 had similar biodistribution and localization at inflammatory sites. [99mTc]Tc-HA10 was shown to be feasible in measuring skin injury and monitoring skin wound healing. [99mTc]Tc-HA10 dynamic pulmonary images yielded good visualization of radioactive uptake in the lungs. There was significantly increased lung uptake and slower lung washout in mice with LPS-induced ARDS than in control mice. Postmortem biodistribution measurement of [99mTc]TcHA10 (%ID/g) was 11.0 ± 3.9 vs. 1.3 ± 0.3 in the ARDS mice (n = 6) and controls (n = 6) (P < 0.001), consistent with upregulated HA expression as determined by enzyme-linked immunosorbent assay (ELISA) and immunohistochemistry (IHC) staining.

CONCLUSIONS

[99mTc]Tc-HA10 is promising as a biomarker for evaluating HA dysregulation that contributes to pulmonary injury in ARDS. Rapid iQID imaging of [99mTc]Tc-HA10 clearance from injured lungs may provide a functional template for timely assessment and quantitative monitoring of pulmonary pathophysiology and intervention in ARDS.

eNAMPT Neutralization Preserves Lung Fluid Balance and Reduces Acute Renal Injury in Porcine Sepsis/VILI-Induced Inflammatory Lung Injury

Background: Numerous potential ARDS therapeutics, based upon preclinical successful rodent studies that utilized LPS challenge without mechanical ventilation, have failed in Phase 2/3 clinical trials. Recently, ALT-100 mAb, a novel biologic that neutralizes the TLR4 ligand and DAMP, eNAMPT (extracellular nicotinamide phosphoribosyltransferase), was shown to reduce septic shock/VILI-induced porcine lung injury when delivered 2 h after injury onset. We now examine the ALT-100 mAb efficacy on acute kidney injury (AKI) and lung fluid balance in a porcine ARDS/VILI model when delivered 6 h post injury.

Methods/Results: Compared to control PBS-treated pigs, exposure of ALT-100 mAb-treated pigs (0.4 mg/kg, 2 h or 6 h after injury initiation) to LPS-induced pneumonia/septic shock and VILI (12 h), demonstrated significantly diminished lung injury severity (histology, BAL PMNs, plasma cytokines), biochemical/genomic evidence of NF-kB/MAP kinase/cytokine receptor signaling, and AKI (histology, plasma lipocalin). ALT-100 mAb treatment effectively preserved lung fluid balance reflected by reduced BAL protein/tissue albumin levels, lung wet/dry tissue ratios, ultrasound-derived B lines, and chest radiograph opacities. Delayed ALT-100 mAb at 2 h was significantly more protective than 6 h delivery only for plasma eNAMPT while trending toward greater protection for remaining inflammatory indices. Delayed ALT-100 treatment also decreased lung/renal injury indices in LPS/VILI-exposed rats when delivered up to 12 h after LPS.

Conclusions: These studies indicate the delayed delivery of the eNAMPT-neutralizing ALT-100 mAb reduces inflammatory lung injury, preserves lung fluid balance, and reduces multi-organ dysfunction, and may potentially address the unmet need for novel therapeutics that reduce ARDS/VILI mortality.

Abdominal T2-Weighted Imaging and T2 Mapping Using a Variable Flip Angle Radial Turbo Spin-Echo Technique

BACKGROUND

T2 mapping is of great interest in abdominal imaging but current methods are limited by low resolution, slice coverage, motion sensitivity, or lengthy acquisitions.

PURPOSE

Develop a radial turbo spin-echo technique with refocusing variable flip angles (RADTSE-VFA) for high spatiotemporal T2 mapping and efficient slice coverage within a breath-hold and compare to the constant flip angle counterpart (RADTSE-CFA).

STUDY TYPE

Prospective technical efficacy.

SUBJECTS

Testing performed on agarose phantoms and 12 patients. Focal liver lesion classification tested on malignant (N = 24) and benign (N = 11) lesions.

FIELD STRENGTH/SEQUENCE

1.5 T/RADTSE-VFA, RADTSE-CFA.

ASSESSMENT

A constrained objective function was used to optimize the refocusing flip angles. Phantom and/or in vivo data were used to assess relative contrast, T2 estimation, specific absorption rate (SAR), and focal liver lesion classification. STATISTICAL TESTS: t-Tests or Mann-Whitney Rank Sum tests were used.

RESULTS

Phantom data did not show significant differences in mean relative contrast (P = 0.10) and T2 accuracy (P = 0.99) between RADTSE-VFA and RADTSE-CFA. Adding noise caused T2 overestimation predominantly for RADTSE-CFA and low T2 values. In vivo results did not show significant differences in mean spleen-to-liver (P = 0.62) and kidney-to-liver (P = 0.49) relative contrast between RADTSE-VFA and RADTSE-CFA. Mean T2 values were not significantly different between the two techniques for spleen (T2VFA  = 109.2 ± 12.3 msec; T2CFA  = 110.7 ± 11.1 msec; P = 0.78) and kidney-medulla (T2VFA  = 113.0 ± 8.7 msec; T2CFA  = 114.0 ± 8.6 msec; P = 0.79). Liver T2 was significantly higher for RADTSE-CFA (T2VFA  = 52.6 ± 6.6 msec; T2CFA  = 60.4 ± 8.0 msec) consistent with T2 overestimation in the phantom study. Focal liver lesion classification had comparable T2 distributions for RADTSE-VFA and RADTSE-CFA for malignancies (P = 1.0) and benign lesions (P = 0.39). RADTSE-VFA had significantly lower SAR than RADTSE-CFA increasing slice coverage by 1.5.

DATA CONCLUSION

RADTSE-VFA provided noise-robust T2 estimation compared to the constant flip angle counterpart while generating T2-weighted images with comparable contrast. The VFA scheme minimized SAR improving slice efficiency for breath-hold imaging.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY STAGE: 1.

Above and Beyond Age: Prediction of Major Postoperative Adverse Events in Head and Neck Surgery

OBJECTIVE

Major postoperative adverse events (MPAEs) following head and neck surgery are not infrequent and lead to significant morbidity. The objective of this study was to ascertain which factors are most predictive of MPAEs in patients undergoing head and neck surgery.

METHODS

A cohort study was carried out based on data from patients registered in the National Surgical Quality Improvement Program (NSQIP) from 2006 to 2018. All patients undergoing non-ambulatory head and neck surgery based on Current Procedural Terminology codes were included. Perioperative factors were evaluated to predict MPAEs within 30-days of surgery. Age was classified as both a continuous and categorical variable. Retained factors were classified by attributable fraction and C-statistic. Multivariate regression and supervised machine learning models were used to quantify the contribution of age as a predictor of MPAEs.

RESULTS

A total of 43 701 operations were analyzed with 5106 (11.7%) MPAEs. The results of supervised machine learning indicated that prolonged surgeries, anemia, free tissue transfer, weight loss, wound classification, hypoalbuminemia, wound infection, tracheotomy (concurrent with index head and neck surgery), American Society of Anesthesia (ASA) class, and sex as most predictive of MPAEs. On multivariate regression, ASA class (21.3%), hypertension on medication (15.8%), prolonged operative time (15.3%), sex (13.1%), preoperative anemia (12.8%), and free tissue transfer (9%) had the largest attributable fractions associated with MPAEs. Age was independently associated with MPAEs with an attributable fraction ranging from 0.6% to 4.3% with poor predictive ability (C-statistic 0.60).

CONCLUSION

Surgical, comorbid, and frailty-related factors were most predictive of short-term MPAEs following head and neck surgery. Age alone contributed a small attributable fraction and poor prediction of MPAEs.

LEVEL OF EVIDENCE

3.

Rapid high-resolution volumetric T1 mapping using a highly accelerated stack-of-stars Look Locker technique

PURPOSE

To develop a fast volumetric T1 mapping technique.

MATERIALS AND METHODS

A stack-of-stars (SOS) Look Locker technique based on the acquisition of undersampled radial data (>30× relative to Nyquist) and an efficient multi-slab excitation scheme is presented. A principal-component based reconstruction is used to reconstruct T1 maps. Computer simulations were performed to determine the best choice of partitions per slab and degree of undersampling. The technique was validated in phantoms against reference T1 values measured with a 2D Cartesian inversion-recovery spin-echo technique. The SOS Look Locker technique was tested in brain (n = 4) and prostate (n = 5). Brain T1 mapping was carried out with and without kz acceleration and results between the two approaches were compared. Prostate T1 mapping was compared to standard techniques. A reproducibility study was conducted in brain and prostate. Statistical analyses were performed using linear regression and Bland Altman analysis.

RESULTS

Phantom T1 values showed excellent correlations between SOS Look Locker and the inversion-recovery spin-echo reference (r2 = 0.9965; p < 0.0001) and between SOS Look Locker with slab-selective and non-slab selective inversion pulses (r2 = 0.9999; p < 0.0001). In vivo results showed that full brain T1 mapping (1 mm3) with kz acceleration is achieved in 4 min 21 s. Full prostate T1 mapping (0.9 × 0.9 × 4 mm3) is achieved in 2 min 43 s. T1 values for brain and prostate were in agreement with literature values. A reproducibility study showed coefficients of variation in the range of 0.18-0.2% (brain) and 0.15-0.18% (prostate).

CONCLUSION

A rapid volumetric T1 mapping technique was developed. The technique enables high-resolution T1 mapping with adequate anatomical coverage in a clinically acceptable time.

Improving subspace constrained radial fast spin echo MRI using block matching driven non-local low rank regularization

Subspace-constrained reconstruction methods restrict the relaxation signals (of size M) in the scene to a pre-determined subspace (of size K≪M) and allow multi-contrast imaging and parameter mapping from accelerated acquisitions. However, these constraints yield poor image quality at some imaging contrasts, which can impact the parameter mapping performance. Additional regularization such as the use of joint-sparse (JS) or locally-low-rank (LLR) constraints can help improve the recovery of these images but are not sufficient when operating at high acceleration rates. We propose a method, non-local rank 3D (NLR3D), that is built on block matching and transform domain low rank constraints to allow high quality recovery of subspace-coefficient images (SCI) and subsequent multi-contrast imaging and parameter mapping. The performance of NLR3D was evaluated using Monte-Carlo (MC) simulations and compared against the JS and LLR methods. In vivo T 2 mapping results are presented on brain and knee datasets. MC results demonstrate improved bias, variance, and MSE behavior in both the multi-contrast images and parameter maps when compared to the JS and LLR methods. In vivo brain and knee results at moderate and high acceleration rates demonstrate improved recovery of high SNR early TE images as well as parameter maps. No significant difference was found in the T2 values measured in ROIs between the NLR3D reconstructions and the reference images (Wilcoxon signed rank test). The proposed method, NLR3D, enables recovery of high-quality SCI and, consequently, the associated multi-contrast images and parameter maps.

Quantitative metric for assessment of pancreatic ductal adenocarcinoma treatment response in T1-weighted gadolinium-enhanced magnetic resonance imaging

Background:

We theoretically derived a new quantitative metric reflecting the product of T1 signal intensity and contrast media concentration (T1C) using first principles for the signal provided by the gradient echo sequence. This metric can be used with conventional gadolinium contrast-enhanced magnetic resonance imaging (CE-MRI) exams. We used this metric to test our hypothesis that gadolinium enhancement changes with pancreatic ductal adenocarcinoma (PDA) treatment response, and that this metric may differentiate responders from non-responders.

Methods:

Out of 264 initially identified patients, a final total of 35 patients with PDA were included in a retrospective study of responders (n=24) and non-responders (n=11), which used changes in cancer antigen 19–9 (CA 19–9) and tumor size as reference standards. T1C was computed for the pancreatic mass in the arterial, portal venous, and delayed phases in pre-treatment and post-treatment MRIs. Changes in measurements and correlations with treatment response were assessed by repeated measures analysis of variance and paired t-tests.

Results:

In the treatment responder group, T1C significantly increased in the arterial, portal venous, and delayed phases (P=7.57e–5, P=3.25e–4, P=1.75e–4). In the non-responder group, T1C did not significantly change in any phase (P>0.58). Post-treatment T1C significantly differed between responders and non-responders (P=0.044) by repeated measures analysis of variance.

Conclusions:

T1C significantly increases in all phases of CE-MRI in responders to treatment, but does not change in non-responders. T1C correlates with treatment response, can be computed from clinical MRI exams, and may be useful as an additional metric to stratify patients undergoing treatment.

A multi-scale residual network for accelerated radial MR parameter mapping

A deep learning MR parameter mapping framework which combines accelerated radial data acquisition with a multi-scale residual network (MS-ResNet) for image reconstruction is proposed. The proposed supervised learning strategy uses input image patches from multi-contrast images with radial undersampling artifacts and target image patches from artifact-free multi-contrast images. Subspace filtering is used during pre-processing to denoise input patches. For each anatomy and relaxation parameter, an individual network is trained. in vivo T1 mapping results are obtained on brain and abdomen datasets and in vivo T2 mapping results are obtained on brain and knee datasets. Quantitative results for the T2 mapping of the knee show that MS-ResNet trained using either fully sampled or undersampled data outperforms conventional model-based compressed sensing methods. This is significant because obtaining fully sampled training data is not possible in many applications. in vivo brain and abdomen results for T1 mapping and in vivo brain results for T2 mapping demonstrate that MS-ResNet yields contrast-weighted images and parameter maps that are comparable to those achieved by model-based iterative methods while offering two orders of magnitude reduction in reconstruction times. The proposed approach enables recovery of high-quality contrast-weighted images and parameter maps from highly accelerated radial data acquisitions. The rapid image reconstructions enabled by the proposed approach makes it a good candidate for routine clinical use.

An efficient 3D stack-of-stars turbo spin echo pulse sequence for simultaneous T2-weighted imaging and T2 mapping

PURPOSE

To design a pulse sequence for efficient 3D T2-weighted imaging and T2 mapping.

METHODS

A stack-of-stars turbo spin echo pulse sequence with variable refocusing flip angles and a flexible pseudorandom view ordering is proposed for simultaneous T2-weighted imaging and T2 mapping. An analytical framework is introduced for the selection of refocusing flip angles to maximize relative tissue contrast while minimizing T2 estimation errors and maintaining low specific absorption rate. Images at different echo times are generated using a subspace constrained iterative reconstruction algorithm. T2 maps are obtained by modeling the signal evolution using the extended phase graph model. The technique is evaluated using phantoms and demonstrated in vivo for brain, knee, and carotid imaging.

RESULTS

Numerical simulations demonstrate an improved point spread function with the proposed pseudorandom view ordering compared to golden angle view ordering. Phantom experiments show that T2 values estimated from the stack-of-stars turbo spin echo pulse sequence with variable refocusing flip angles have good concordance with spin echo reference values. In vivo results show the proposed pulse sequence can generate qualitatively comparable T2-weighted images as conventional Cartesian 3D SPACE in addition to simultaneously generating 3D T2 maps.

CONCLUSION

The proposed stack-of-stars turbo spin echo pulse sequence with pseudorandom view ordering and variable refocusing flip angles allows high resolution isotropic T2 mapping in clinically acceptable scan times. The optimization framework for the selection of refocusing flip angles improves T2 estimation accuracy while generating T2-weighted contrast comparable to conventional Cartesian imaging.

Radial streak artifact reduction using phased array beamforming

PURPOSE

A new method for streak artifact reduction in radial MRI based on phased array filtering.

THEORY

Radial imaging in applications that require large fields-of-view can be susceptible to streaking artifacts due to gradient nonlinearities. Coil removal methods prune the coils contributing the most to streaking artifacts at the expense of signal loss. Phased array beamforming is a form of spatial filtering used to suppress unwanted signals. The proposed method uses interference covariance generated from the streaking artifact samples which are manually extracted with phased array beamforming to suppress streaking in the images.

METHODS

The performance of the proposed method was evaluated on abdomen radial fast spin echo images acquired on a 1.5T Siemens scanner and compared with previously proposed methods.

RESULTS

Our results demonstrate that the proposed method can effectively suppress streaking artifacts without any noticeable loss in signal levels. Coil removal methods can suppress streaks as well but they may incur significant signal loss due to coil pruning. Quantitative metrics also demonstrate the superiority of the proposed method over earlier methods.

CONCLUSION

The use of interference covariance with phased array beamforming can help reduce streaking artifacts.

First-Line Diagnostic Evaluation with MRI of Children Suspected of Having Acute Appendicitis

Background Advances in abdominal MRI have enabled rapid, free-breathing imaging without the need for intravenous or oral contrast material. The use of MRI as the primary imaging modality for suspected appendicitis has not been previously studied. Purpose To determine the diagnostic performance of MRI as the initial imaging modality in children suspected of having acute appendicitis. Materials and Methods The study included consecutive patients 18 years of age and younger presenting with acute abdominal pain at a tertiary care institution from January 2013 through June 2016 who subsequently underwent an unenhanced MRI examination as the primary diagnostic imaging modality. Electronic medical records and radiology reports were retrospectively evaluated for the feasibility and diagnostic performance of MRI, with surgical pathology and follow-up electronic records as reference standards. Statistical analyses were performed by using simple binomial proportions to quantify sensitivity, specificity, and accuracy, and exact 95% confidence intervals (CIs) were obtained. Results After exclusions, 402 patients (median age: 13 years; interquartile range [IQR], 9-15 years; 235 female patients; 167 male patients) were included. Sedation for MRI was required in 13 of 402 patients (3.2%; 95% CI: 1.7%, 5.5%). The appendix was visualized in 349 of 402 patients (86.8%; 95% CI: 83.1%, 90%); for the remaining patients, a diagnosis was provided on the basis of secondary signs of appendicitis. The sensitivity, specificity, and accuracy of MRI as the primary diagnostic imaging modality for the evaluation of acute appendicitis were 97.9% (95 of 97; 95% CI: 92.8%, 99.8%), 99% (302 of 305; 95% CI: 97.2%, 99.8%), and 98.8% (397 of 402; 97.1%, 99.6%), respectively. Among patients with negative findings for appendicitis at MRI, an alternate diagnosis was provided in 113 of 304 patients (37.2%; 95% CI: 31.7%, 42.9%). Conclusion When performed as the initial imaging modality in children suspected of having acute appendicitis, MRI examinations had high diagnostic performance for the diagnosis of acute appendicitis and in providing alternative diagnoses. © RSNA, 2019 See also the editorial by Dillman and Trout in this issue.

Imaging assessment of cardioprotection mediated by a dodecafluoropentane oxygen-carrier administered during myocardial infarction

INTRODUCTION

The objective of this study was to investigate the cardioprotective effects of a dodecafluoropentane (DDFP)-based perfluorocarbon emulsion (DDFPe) as an artificial carrier for oxygen delivery to ischemic myocardium, using ^99mTc-duramycin SPECT imaging.

METHODS

Rat hearts with Ischemia-reperfusion (I/R) was prepared by coronary ligation for 45-min followed by reperfusion. The feasibility of ^99mTc-duramycin in detecting myocardial I/R injury and its kinetic profile were first verified in the ischemic hearts with 2-h reperfusion (n = 6). DDFPe (0.6 mL/kg) was intravenously administered at 10 min after coronary ligation in fifteen rats and saline was given in thirteen rats as controls. ^99mTc-duramycin SPECT images were acquired in the DDFPe-treated hearts and saline controls at 2-h (DDFPe-2 h, n = 7 and Saline-2 h, n = 6) or 24-h (DDFPe-24 h, n = 8 and Saline-24 h, n = 7) of reperfusion.

RESULTS

SPECT images, showing "hot-spot" ^99mTc-duramycin uptake in the ischemic myocardium, exhibited significantly lower radioactive retention and smaller hot-spot size in the DDFPe-2 h and DDFPe-24 h hearts compared to controls. The infarcts in the Saline-24 h hearts extended significantly relative to measurements in the Saline-2 h. The extension of infarct size did not reach a statistical difference between the DDFPe-2 h and DDFPe-24 h hearts. Ex vivo measurement of ^99mTc-duramycin activity (%ID/g) was lower in the ischemic area of DDFPe-2 h and DDFPe-24 h than that of the Saline-2 h and Saline-24 h hearts (P < 0.05). The area of injured myocardium, delineated by the uptake of ^99mTc-duramycin, extended more substantially outside the infarct zone in the controls.

CONCLUSIONS

Significant reduction in myocardial I/R injury, as assessed by ^99mTc-duramycin cell death imaging and histopathological analysis, was induced by DDFPe treatment after acute myocardial ischemia. ^99mTc-duramycin imaging can reveal myocardial cell death in ischemic hearts and may provide a tool for the non-invasive assessment of cardioprotective interventions.

Classification and Diagnosis of Cystic Renal Tumors: Role of MR Imaging Versus Contrast-Enhanced Ultrasound

Superior soft tissue and contrast resolution of MR imaging benefits sensitivity to kidney cyst features and classification, which may have an impact on patient management and outcomes. Contrast-enhanced ultrasound (CEUS) may have nearly similar sensitivity for detection of cyst features yet is dependent on patient body habitus and adequacy of visualization windows for the kidneys, which does not have the same impact on MR imaging results. Both MR imaging and CEUS may provide superior kidney cyst assessment compared with contrast-enhanced CT; however, further research is needed, particularly for the identification of role of CEUS.

Rapid high-resolution T1 mapping using a highly accelerated radial steady-state free-precession technique

BACKGROUND

T₁ mapping is often used in some clinical protocols. Existing techniques are limited in slice coverage, and/or spatial-temporal resolution, or require long acquisitions. Here we present a multi-slice inversion-recovery (IR) radial steady-state free precession (radSSFP) pulse sequence combined with a principal component (PC) based reconstruction that overcomes these limitations.

PURPOSE

To develop a fast technique for multi-slice high-resolution T₁ mapping.

STUDY TYPE

Technical efficacy study done prospectively.

PHANTOM/SUBJECTS

IR-radSSFP was tested in phantoms, five healthy volunteers, and four patients with abdominal lesions.

FIELD STRENGTH/SEQUENCE

IR-radSSFP was implemented at 3T.

ASSESSMENT

Computer simulations were performed to optimize the flip angle for T₁ estimation; testing was done in phantoms using as reference an IR spin-echo pulse sequence. T₁ mapping with IR-radSSFP was also assessed in vivo (brain and abdomen) and T₁ values were compared with literature. T₁ maps were also compared with a radial IR-FLASH technique.

STATISTICAL TESTS

A two-tailed t-test was used to compare T₁ values in phantoms. A repeatability study was carried out in vivo using Bland-Altman analysis.

RESULTS

Simulations and phantom experiments showed that a flip angle of 20˚ was optimal for T₁ mapping. When comparing single to multi-slice experiments in phantoms there were no significant differences between the means T₁ values (P = 0.0475). In vivo results show that T₁ maps with spatial resolution as high as 0.69 mm × 0.69 mm × 2.00 mm (brain) and 0.83 mm × 0.83 mm × 3.00 mm (abdomen) can be generated for 84 brain slices in 3 min and 10 abdominal slices in a breath-hold; T₁ values were comparable to those reported in literature. The coefficients of variation from the repeatability study were 1.7% for brain and 2.5-2.7% in the abdomen.

DATA CONCLUSION

A multi-slice IR-radSSFP technique combined with a PC-based reconstruction was demonstrated for higher resolution T₁ mapping. This technique is fast, motion-insensitive and yields repeatable T₁ values comparable to those in literature.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;49:239-252.

Improved Detection of Pelvic Organ Prolapse: Comparative Utility of Defecography Phase Sequence to Nondefecography Valsalva Maneuvers in Dynamic Pelvic Floor Magnetic Resonance Imaging

PURPOSE

To evaluate the utility of a defecography phase (DP) sequence in dynamic pelvic floor MRI (DPMRI), in comparison to DPMRI utilizing only non-defecography Valsalva maneuvers (VM).

MATERIALS AND METHODS

Inclusion criteria identified 237 female patients with symptoms and/or physical exam findings of pelvic floor prolapse. All DPMRI exams were obtained following insertion of ultrasound gel into the rectum and vagina. Steady-state free-precession sequences in sagittal plane were acquired in the resting state, followed by dynamic cine acquisitions during VM and DP. In all phases, two experienced radiologists performed blinded review using the H-line, M-line, Organ prolapse (HMO) system. The presence of a rectocele, enterocele and inferior descent of the anorectal junction, bladder base, and vaginal vault were recorded in all patients using the pubococcygeal line as a fixed landmark.

RESULTS

DPMRI with DP detected significantly more number of patients than VM (p<0.0001) with vaginal prolapse (231/237, 97.5% vs. 177/237, 74.7%), anorectal prolapse (227/237, 95.8% vs. 197/237, 83.1%), cystocele (197/237, 83.1% vs. 108/237, 45.6%), and rectocele (154/237, 65% vs. 93/237, 39.2%). The median cycstocele (3.2cm vs. 1cm), vaginal prolapse (3cm vs. 1.5cm), anorectal prolapse (5.4cm vs. 4.2cm), H-line (8cm vs. 7.2cm) and M-line (5.3cm vs. 3.9cm) were significantly higher with DP than VM (p<0.0001).

CONCLUSIONS

Addition of DP to DPMRI demonstrates a greater degree of pelvic floor instability as compared to imaging performed during VM alone. Pelvic floor structures may show mild descent or appear normal during VM, with marked prolapse on subsequent DP images.

A multi-band double-inversion radial fast spin-echo technique for T2 cardiovascular magnetic resonance mapping of the heart

BACKGROUND

Double inversion recovery (DIR) fast spin-echo (FSE) cardiovascular magnetic resonance (CMR) sequences are used clinically for black-blood T2-weighted imaging. However, these sequences suffer from slice inefficiency due to the non-selective inversion pulses. We propose a multi-band (MB) encoded DIR radial FSE (MB-DIR-RADFSE) technique to simultaneously excite two slices. This sequence has improved signal-to-noise ratio per unit time compared to a single slice excitation. It is also motion robust and enables the reconstruction of high-resolution black-blood T2-weighted images and T2 maps for the excited slices.

METHODS

Hadamard encoded MB pulses were used in MB-DIR-RADFSE to simultaneously excite two slices. A principal component based iterative reconstruction was used to jointly reconstruct black-blood T2-weighted images and T2 maps. Phantom and in vivo experiments were performed to evaluate T2 mapping performance and results were compared to a T2-prepared balanced steady state free precession (bSSFP) method. The inter-segment variability of the T2 maps were assessed using data acquired on healthy subjects. A reproducibility study was performed to evaluate reproducibility of the proposed technique.

RESULTS

Phantom experiments show that the T2 values estimated from MB-DIR-RADFSE are comparable to the spin-echo based reference, while T2-prepared bSSFP over-estimated T2 values. The relative contrast of the black-blood images from the multi-band scheme was comparable to those from a single slice acquisition. The myocardial segment analysis on 8 healthy subjects indicated a significant difference (p-value < 0.01) in the T2 estimates from the apical slice when compared to the mid-ventricular slice. The mean T2 estimate from 12 subjects obtained using T2-prepared bSSFP was significantly higher (p-value = 0.012) compared to MB-DIR-RADFSE, consistent with the phantom results. The Bland-Altman analysis showed excellent reproducibility between the MB-DIR-RADFSE measurements, with a mean T2 difference of 0.12 ms and coefficient of reproducibility of 2.07 in 15 clinical subjects. The utility of this technique is demonstrated in two subjects where the T2 maps show elevated values in regions of pathology.

CONCLUSIONS

The use of multi-band pulses for excitation improves the slice efficiency of the double inversion fast spin-echo pulse sequence. The use of a radial trajectory and a joint reconstruction framework allows reconstruction of TE images and T2 maps for the excited slices.

Accelerated MR parameter mapping with a union of local subspaces constraint

PURPOSE

A new reconstruction method for multi-contrast imaging and parameter mapping based on a union of local subspaces constraint is presented.

THEORY

Subspace constrained reconstructions use a predetermined subspace to explicitly constrain the relaxation signals. The choice of subspace size ( K ) impacts the approximation error vs noise-amplification tradeoff associated with these methods. A different approach is used in the model consistency constraint (MOCCO) framework to leverage the subspace model to enforce a softer penalty. Our proposed method, MOCCO-LS, augments the MOCCO model with a union of local subspaces (LS) approach. The union of local subspaces model is coupled with spatial support constraints and incorporated into the MOCCO framework to regularize the contrast signals in the scene.

METHODS

The performance of the MOCCO-LS method was evaluated in vivo on T₁ and T₂ mapping of the human brain and with Monte-Carlo simulations and compared against MOCCO and the explicit subspace constrained models.

RESULTS

The results demonstrate a clear improvement in the multi-contrast images and parameter maps. We sweep across the model order space ( K ) to compare the different reconstructions and demonstrate that the reconstructions have different preferential operating points. Experiments on T₂ mapping show that the proposed method yields substantial improvements in performance even when operating at very high acceleration rates.

CONCLUSIONS

The use of a union of local subspace constraints coupled with a sparsity promoting penalty leads to improved reconstruction quality of multi-contrast images and parameter maps.

MRI of patients with implanted cardiac devices

Cardiac implanted electronic devices (CIEDs) have historically been regarded as a contraindication for performing magnetic resonance imaging (MRI), limiting the availability of this exam for large numbers of patients who may have otherwise benefited from the unique diagnostic capabilities of MRI. Interactions between CIEDs and the magnetic field associated with MRI systems have been documented, and include potential effects on CIED function, lead heating, and force/torque on the generator. Several device manufacturers have developed "MR-Conditional" CIEDs with specific hardware and software design changes to optimize the device for the MR environment. However, a substantial body of evidence has been accumulating that suggests that MRI may be safely performed in patients with either conditional or nonconditional CIEDs. Institutional policies and procedures, including preexam screening and assessment by skilled electrophysiology personnel and intraexam monitoring, allow MRI to be safely performed in CIED patients, as evidenced by at least two, large multicenter prospective studies and multiple smaller, single-institution studies. Cross-departmental collaboration and a robust safety infrastructure at sites that perform MRI should allow for the safe imaging of CIED patients who have a clinical indication for the study, regardless of the conditionality status of the device.

LEVEL OF EVIDENCE

5 Technical Efficacy: Stage 5 J. Magn. Reson. Imaging 2018;47:595-603.

Trophoblast Glycoprotein (TPGB/5T4) in Human Placenta: Expression, Regulation, and Presence in Extracellular Microvesicles and Exosomes

BACKGROUND

Many parallels exist between growth and development of the placenta and that of cancer. One parallel is shared expression of antigens that may have functional importance and may be recognized by the immune system. Here, we characterize expression and regulation of one such antigen, Trophoblast glycoprotein (TPGB; also called 5T4), in the placenta across gestation, in placentas of preeclamptic (PE) pregnancies, and in purified microvesicles and exosomes.

METHODS

Trophoblast glycoprotein expression was analyzed by real-time reverse transcription-polymerase chain reaction (RT-PCR), Western blot, and immunohistochemistry. Regulation of 5T4 in cytotrophoblast cells was examined under either differentiating conditions of epidermal growth factor or under varying oxygen conditions. Microvesicles and exosomes were purified from supernatant of cultured and perfused placentas.

RESULTS

Trophoblast glycoprotein expression was prominent at the microvillus surface of syncytiotrophoblast and on the extravillous trophoblast cells, with minimal expression in undifferentiated cytotrophoblasts and normal tissues. Trophoblast glycoprotein expression was elevated in malignant tumors. In cytotrophoblasts, 5T4 was induced by in vitro differentiation, and its messenger RNA (mRNA) was increased under conditions of low oxygen. PE placentas expressed higher 5T4 mRNA than matched control placentas. Trophoblast glycoprotein was prominent within shed placental microvesicles and exosomes.

CONCLUSION

Given the potential functional and known immunological importance of 5T4 in cancer, these studies reveal a class of proteins that may influence placental development and/or sensitize the maternal immune system. In extravillous trophoblasts, 5T4 may function in epithelial-to-mesenchymal transition during placentation. The role of syncytiotrophoblast 5T4 is unknown, but its abundance in shed syncytial vesicles may signify route of sensitization of the maternal immune system.

Multiresolution imaging using golden angle stack-of-stars and compressed sensing for dynamic MR urography

PURPOSE

To develop a novel multiresolution MRI methodology for accurate estimation of glomerular filtration rate (GFR) in vivo.

MATERIALS AND METHODS

A three-dimensional golden-angle radial stack-of-stars (SoS) trajectory was used for data acquisition on a 3 Tesla MRI scanner. Multiresolution reconstruction and analysis was performed using arterial input function reconstructed at 1-s. temporal resolution and renal dynamic data reconstructed using compressed sensing (CS) with 4-s temporal resolution. The method was first validated using simulations and the clinical utility of the technique was evaluated by comparing the GFR estimates from the proposed method to the estimated GFR (eGFR) obtained from serum creatinine for 10 subjects.

RESULTS

The 4-s temporal resolution CS images minimized streaking artifacts and noise while the 1-s temporal resolution AIF minimized errors in GFR estimates. A paired t-test showed that there was no statistically significant difference between MRI based total GFR values and serum creatinine based eGFR estimates (P = 0.92).

CONCLUSION

We have demonstrated the feasibility of multiresolution MRI using a golden angle radial stack-of-stars scheme to accurately estimate GFR as well as produce diagnostic quality dynamic images in vivo.

LEVEL OF EVIDENCE

1 Technical Efficacy: Stage 3 J. MAGN. RESON. IMAGING 2017;46:303-311.

Hepatic epithelioid hemangioendothelioma: a report from three university centers

Objective

To determine common imaging findings of hepatic epithelioid hemangioendothelioma on magnetic resonance images.

Materials and Methods

A search was made of three institutional databases between January 2000 and August 2012. Seven patients (mean age, 47 years; range, 21-66 years; 6 women) with pathology-confirmed diagnosis of hepatic epithelioid hemangioendothelioma who had undergone magnetic resonance imaging were identified. None of the patients had received any treatment for hepatic epithelioid hemangioendothelioma at the time of the initial magnetic resonance imaging examination.

Results

Hepatic epithelioid hemangioendothelioma tumors appeared as focal masses in 7/7 patients, greater than 5 in number, with a coalescing lesion in 1/5, and peripheral localization in 6/7. Capsular retraction was present in 4/7, and was associated with peripherally located lesions. Early ring enhancement was appreciated in the majority of lesions in 7/7 patients. Centripetal progressive enhancement was shown in 5/7 patients on venous phase that exhibited a distinctive thick inner border of low signal on venous phase images, and a central core of delayed enhancement. Small lesions did not show this.

Conclusion

The combination of multifocal round-configuration lesions that are predominantly peripheral and exhibit early peripheral ring enhancement and late appearance of an inner thick border of low signal and central core of high signal may represent an important feature for hepatic epithelioid hemangioendothelioma.

Task-based optimization of flip angle for fibrosis detection in T1-weighted MRI of liver

Chronic liver disease is a worldwide health problem, and hepatic fibrosis (HF) is one of the hallmarks of the disease. The current reference standard for diagnosing HF is biopsy followed by pathologist examination; however, this is limited by sampling error and carries a risk of complications. Pathology diagnosis of HF is based on textural change in the liver as a lobular collagen network that develops within portal triads. The scale of collagen lobules is characteristically in the order of 1 to 5 mm, which approximates the resolution limit of in vivo gadolinium-enhanced magnetic resonance imaging in the delayed phase. We use MRI of formalin-fixed human ex vivo liver samples as phantoms that mimic the textural contrast of in vivo Gd-MRI. We have developed a local texture analysis that is applied to phantom images, and the results are used to train model observers to detect HF. The performance of the observer is assessed with the area-under-the-receiver-operator-characteristic curve (AUROC) as the figure-of-merit. To optimize the MRI pulse sequence, phantoms were scanned with multiple times at a range of flip angles. The flip angle that was associated with the highest AUROC was chosen as optimal for the task of detecting HF.

MRI of diffuse liver disease: characteristics of acute and chronic diseases

Diffuse liver disease, including chronic liver disease, affects tens of millions of people worldwide, and there is a growing need for diagnostic evaluation as treatments become more readily available, particularly for viral liver diseases. Magnetic resonance imaging (MRI) provides unique capabilities for noninvasive characterization of the liver tissue that rival or surpass the diagnostic utility of liver biopsies. There has been incremental improvement in the use of standardized MRI sequences, acquired before and after administration of a contrast agent, for the evaluation of diffuse liver disease and the study of the liver parenchyma and blood supply. More recent developments have led to methods for quantifying important liver metabolites, including lipids and iron, and liver fibrosis, the hallmark of chronic liver disease. Here, we review the MRI techniques and diagnostic features associated with acute and chronic liver disease.

MRI of hepatocellular carcinoma: an update of current practices

Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide, and liver transplantation is the optimal treatment for selected patients with HCC and chronic liver disease (CLD). Accurate selection of patients for transplantation is essential to maximize patient outcomes and ensure optimized allocation of donor organs. Magnetic resonance imaging (MRI) is a powerful tool for the detection, characterization, and staging of HCC. In patients with CLD, the MRI findings of an arterial-enhancing mass with subsequent washout and enhancing capsule on delayed interstitial phase images are diagnostic for HCC. Major organizations with oversight for organ donor distribution, such as The Organ Procurement and Transplantation Network (OPTN), accept an imaging diagnosis of HCC, no longer requiring tissue biopsy. In patients that are awaiting transplantation, or are not candidates for liver transplantation, localized therapies such as transarterial chemoembolization and radiofrequency ablation may be offered. MRI can be used to monitor treatment response. The purpose of this review article is to describe the role of imaging methods in the diagnosis, staging, and follow-up of HCC, with particular emphasis on established and evolving MRI techniques employing nonspecific gadolinium chelates, hepatobiliary contrast agents, and diffusion weighted imaging. We also briefly review the recently developed Liver Imaging Reporting and Data System (LI-RADS) formulating a standardized terminology and reporting structure for evaluation of lesions detected in patients with CLD.

Measurement of liver fat fraction and iron with MRI and MR spectroscopy techniques

Diffuse liver disease is a widespread global healthcare burden, and the abnormal accumulation of lipid and/or iron is common to important disease processes. Developing the improved methods for detecting and quantifying liver lipid and iron is an important clinical need. The inherent risk, invasiveness, and sampling error of liver biopsy have prompted the development of noninvasive imaging methods for lipid and iron assessment. Ultrasonography and computed tomography have the ability to detect diffuse liver disease, but with limited accuracy. The purpose of this review is to describe the current state-of-the-art methods for quantifying liver lipid and iron using magnetic resonance imaging and spectroscopy, including their implementation, benefits, and potential pitfalls. Imaging- and spectroscopy-based methods are naturally suited for lipid and iron quantification. Lipid can be detected and decomposed from the inherent chemical shift between lipid and water signals, whereas iron imparts significant paramagnetic susceptibility to tissue, which accelerates proton relaxation. However, measurements of these biomarkers are confounded by technical and biological effects. Current methods must address these factors to allow a precise correlation between the lipid fraction and iron concentration. Although this correlation becomes increasingly challenging in the presence of combined lipid and iron accumulation, advanced techniques show promise for delineating these quantities through multi-lipid peak analysis, T2 water mapping, and fast single-voxel water-lipid spectroscopy.

Partitioned edge-function-scaled region-based active contour (p-ESRAC): automated liver segmentation in multiphase contrast-enhanced MRI

PURPOSE

In multiphase contrast-enhanced magnetic resonance imaging (CE-MRI), liver segmentation is an important preprocessing step for the computer-aided evaluation of liver disease. However, because of the liver's irregular shape, proximity to surrounding organs, and large intensity variation, and peripheral contrast enhancement in the kidney, liver segmentation has been very challenging. This paper presents a novel hybrid active contour model and overall procedures that are specific to liver segmentation.

METHODS

The authors introduced an edge-function-scaled (weighted) region-based active contour model (ESRAC) and utilization of registered, multiphase sequences to address leakage-to-kidney and oversegmentation problems. The model incorporated weighted regional information with a compactly supported edge map, computed from a combination of images obtained during arterial and delayed phases, and it was coupled with a geodesic edge term. To cope with signal-inhomogeneity on MRI, all of the axial slices were partitioned into eight sectors with an angular span of 45°, centered on the inferior vena cava, each in the superior and inferior regions and the regional information regarding ESRAC was computed for each partition, henceforth the so-called partitioned ESRAC (p-ESRAC). Initialization of the active contour was performed by thresholding with a range of [200, +∞) and simple morphological operation during the delayed phase. At the end, to fill the holes in the segmented images caused by high gradients around the vasculature, noise, or outstanding texture features, iterative morphological operations were performed until convergence. The authors compared the segmentation accuracy of p-ESRAC to that with geodesic active contour, region-based active contour, geodesic active region, and localized region-based active contour using quantitative and visual assessments.

RESULTS

In three-dimensional experimental studies conducted on 30 subjects (14 normal or benign cases and 16 malignant cases), compared with other active contours, p-ESRAC achieved the highest dice similarity coefficients of 93.9 ± 1.6% (normal) and 91.6 ± 2.2% (malignant), respectively. In addition, p-ESRAC resulted in the lowest false positive rates of 4.5 ± 3.2% (normal) and 7.9 ± 3.0% (malignant), demonstrating it to be the most effective in reducing oversegmentation. The partition scheme improved segmentation accuracy by 5.4 ± 9.2% (normal) and 22.2 ± 27.6% (malignant) of the true segmentation that was missed by ESRAC. Visual assessment confirmed that p-ESRAC prevented leakage of the segmentation results of the liver into the kidney.

CONCLUSIONS

A novel active-contour model was developed, allowing for accurate liver segmentation on multiphase CE-MRI, with conditions that include signal inhomogeneity and weak boundary conditions. Such a technique could be useful for applications that involve computer-aided diagnosis of liver disease.

MRI of diffuse liver disease: the common and uncommon etiologies

Diffuse liver disease, including all causes of chronic liver disease, affects tens of millions of people worldwide. There is a growing need for diagnostic evaluation as treatments become more readily available, particularly for viral liver disease. Magnetic resonance imaging (MRI) provides unique capabilities for noninvasive characterization of liver tissue that rival or surpass the diagnostic utility of liver biopsies. There has been incremental improvement in the use of standardized MRI sequences, acquired before and after administration of contrast for the evaluation of diffuse liver disease, and this includes study of the liver parenchyma and blood supply. More recent developments have led to methods for quantifying important liver metabolites, including fat and iron, and liver fibrosis, which is the hallmark for chronic liver disease. In this study, we review the MRI techniques and diagnostic features associated with common and uncommon etiologies of diffuse liver diseases, including processes that lead to abnormal perfusion (e.g. Budd-Chiari syndrome, congestive hepatomegaly), deposition diseases (e.g. fatty liver, hemochromatosis, Wilson's disease), and abnormalities that are related to inflammation and fibrosis (e.g. primary sclerosing cholangitis, sarcoidosis).

Correcting partial volume effects in biexponential T2 estimation of small lesions

PURPOSE

T2 mapping provides a quantitative approach for focal liver lesion characterization. For small lesions, a biexponential model should be used to account for partial volume effects (PVE). However, conventional biexponential fitting suffers from large uncertainty of the fitted parameters when noise is present. The purpose of this work is to develop a more robust method to correct for PVE affecting small lesions.

METHODS

We developed a region of interest-based joint biexponential fitting (JBF) algorithm to estimate the T2 of lesions affected by PVE. JBF takes advantage of the lesion fraction variation among voxels within a region of interest. JBF is compared to conventional approaches using Cramér-Rao lower bound analysis, numerical simulations, phantom, and in vivo data.

RESULTS

JBF provides more accurate and precise T2 estimates in the presence of PVE. Furthermore, JBF is less sensitive to region of interest drawing. Phantom and in vivo results show that JBF can be combined with a reconstruction method for highly undersampled data, enabling the characterization of small abdominal lesions from data acquired in a single breath hold.

CONCLUSION

The JBF algorithm provides more accurate and stable T2 estimates for small structures than conventional techniques when PVE is present. It should be particularly useful for the characterization of small abdominal lesions.

MR imaging for acute nontraumatic abdominopelvic pain: rationale and practical considerations

Medical imaging is becoming an increasingly vital component of patient care in the emergency department. Computed tomography has been the diagnostic imaging method of choice for emergency department patients with acute abdominopelvic pain; however, the use of ionizing radiation and the potential need for exogenous contrast material adversely affect patient safety and work flow efficiency, respectively. Magnetic resonance (MR) imaging holds promise as an alternative for the evaluation of acute abdominopelvic pain. Critical causes of abdominopelvic pain may be detected with MR imaging without exogenous contrast material. MR imaging is sensitive for depicting tissue or fluid changes related to inflammation, a common process in causes of acute abdominopelvic pain. Fat suppression allows the detection of abnormal signal caused by inflamed tissue. MR imaging has proved sensitive in the detection of acute inflammatory diseases of the gallbladder and bile ducts, liver, pancreas, kidneys, collecting system, bowel, and pelvic soft tissues. Moreover, MR imaging without exogenous contrast material may be safely used in pregnant patients. Evolving roles for emergency department MR imaging include the assessment of vascular disease (including thromboembolic disease) and right upper quadrant pain. Emergency department MR imaging currently has limited availability, and its continued use will require further education regarding operation and image interpretation as well as further validation of cost-effectiveness. Nevertheless, current understanding of the diagnostic utility of this imaging method warrants continued study and the increased use of MR imaging in the evaluation of emergency department patients with acute abdominopelvic pain.

Paraduodenal pancreatitis: clinical performance of MR imaging in distinguishing from carcinoma

PURPOSE

To evaluate the diagnostic performance of contrast material-enhanced magnetic resonance (MR) imaging for distinguishing paraduodenal pancreatitis (PDP) from pancreatic head duct adenocarcinoma (CA) in patients with diagnoses confirmed by histopathologic analysis.

MATERIALS AND METHODS

This retrospective study was approved by the institutional review board and is HIPAA compliant. Between July 2007 and July 2010, 47 patients who underwent Whipple procedure and MR imaging less than 60 days before surgery were identified retrospectively. Two relatively inexperienced fellowship trainees with 9 months of body fellowship training were asked to record the presence or absence of three MR imaging features: focal thickening of the second portion of the duodenum; abnormal enhancement of the second portion of the duodenum; and cystic focus in the expected region of the accessory pancreatic duct. Strict criteria for diagnosis of PDP included presence of all three imaging features. Any case that did not fulfill the criteria was classified as CA. Sensitivity, specificity, positive predictive value, and negative predictive value for characterization of PDP was calculated for each reader with 95% confidence intervals. A κ test assessed level of agreement between readers.

RESULTS

Each reader correctly categorized 15 of 17 (88.2%) PDP cases when all three imaging criteria were met. Alternatively, 26 of 30 (86.7%) pancreatic duct CA were correctly categorized as inconsistent with PDP. Four patients with histopathologic diagnosis of CA were incorrectly classified as PDP by each reader. Agreement between the two readers showed substantial κ agreement for the diagnosis of PDP and differentiation from pancreatic duct CA.

CONCLUSION

Contrast-enhanced MR imaging may help accurately identify PDP and distinguish it from CA when strict diagnostic criteria are followed.

SUPPLEMENTAL MATERIAL

http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.13112056/-/DC1.

Paraduodenal pancreatitis: clinical performance of MR imaging in distinguishing from carcinoma

PURPOSE

To evaluate the diagnostic performance of contrast material-enhanced magnetic resonance (MR) imaging for distinguishing paraduodenal pancreatitis (PDP) from pancreatic head duct adenocarcinoma (CA) in patients with diagnoses confirmed by histopathologic analysis.

MATERIALS AND METHODS

This retrospective study was approved by the institutional review board and is HIPAA compliant. Between July 2007 and July 2010, 47 patients who underwent Whipple procedure and MR imaging less than 60 days before surgery were identified retrospectively. Two relatively inexperienced fellowship trainees with 9 months of body fellowship training were asked to record the presence or absence of three MR imaging features: focal thickening of the second portion of the duodenum; abnormal enhancement of the second portion of the duodenum; and cystic focus in the expected region of the accessory pancreatic duct. Strict criteria for diagnosis of PDP included presence of all three imaging features. Any case that did not fulfill the criteria was classified as CA. Sensitivity, specificity, positive predictive value, and negative predictive value for characterization of PDP was calculated for each reader with 95% confidence intervals. A κ test assessed level of agreement between readers.

RESULTS

Each reader correctly categorized 15 of 17 (88.2%) PDP cases when all three imaging criteria were met. Alternatively, 26 of 30 (86.7%) pancreatic duct CA were correctly categorized as inconsistent with PDP. Four patients with histopathologic diagnosis of CA were incorrectly classified as PDP by each reader. Agreement between the two readers showed substantial κ agreement for the diagnosis of PDP and differentiation from pancreatic duct CA.

CONCLUSION

Contrast-enhanced MR imaging may help accurately identify PDP and distinguish it from CA when strict diagnostic criteria are followed.

SUPPLEMENTAL MATERIAL

http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.13112056/-/DC1.

Liver steatosis assessment: correlations among pathology, radiology, clinical data and automated image analysis software

Quantitating hepatic steatosis is important in many liver diseases and liver transplantation. Since steatosis estimation by pathologists has inherent intra- and inter-observer variability, we compared and contrasted computerized techniques with magnetic resonance imaging measurements, pathologist visual scoring, and clinical parameters. Computerized methods applied to whole slide images included a commercial positive pixel count algorithm and a custom algorithm programmed at our institution. For all liver samples (n=59), including pediatric, adult, frozen section, and permanent specimens, statistically significant correlations were observed between pathology, radiology, and each image analysis modality (r=0.75-0.97, p<0.0001), with the strongest correlations in the pediatric cohort. Statistically significant relationships were observed between each method and with body mass index (r=0.37-0.56, p from <0.0001 to <0.05) and with albumin (r=0.55-0.64, p<0.05) but not with alanine aminotransferase or aspartate aminotransferase. Although pathologist assessments correlated (r=0.64-0.86, 0.92-0.97, and 0.78-0.91 for microvesicular, macrovesicular, and overall steatosis, respectively), the absolute values of hepatic steatosis visual assessment were susceptible to intra- and inter-observer variability, particularly for microvesicular steatosis. Image analysis, pathologist assessments, radiology measurements, and several clinical parameters all showed correlations in this study, providing evidence for the utility of each method in different clinical and research settings.

MR imaging of pulmonary embolism: diagnostic accuracy of contrast-enhanced 3D MR pulmonary angiography, contrast-enhanced low-flip angle 3D GRE, and nonenhanced free-induction FISP sequences

PURPOSE

To evaluate relative detection of pulmonary embolism (PE) with standard bolus-triggered contrast-enhanced breath-hold magnetic resonance (MR) pulmonary angiography, contrast-enhanced recirculation-phase breath-hold low-flip angle three-dimensional (3D) gradient-echo (GRE), and nonenhanced free-induction cardiac- and respiratory-triggered true fast imaging with steady-state precession (FISP) MR sequences.

MATERIALS AND METHODS

The study was HIPAA compliant and institutional review board approved. Twenty-two patients with a computed tomographic (CT) angiography diagnosis of PE underwent MR imaging within 48 hours of CT. MR included three complementary techniques: MR pulmonary angiography, 3D GRE, and triggered true FISP. Each sequence was analyzed separately by two independent reviewers who recorded presence of emboli in categorized pulmonary artery anatomic territories. CT angiography results were analyzed by a third independent reviewer, who retrospectively recorded presence of emboli using the same format; these results served as the reference standard. Sensitivity, specificity, and positive and negative predictive values for PE detection were calculated for each MR technique on a per-embolus basis, and 95% confidence intervals were calculated according to the efficient-score method. A two-sample t test was used to compare values among MR techniques.

RESULTS

Sensitivities for PE detection were 55% for MR pulmonary angiography, 67% for triggered true FISP, and 73% for 3D GRE MR imaging. Combining all three MR sequences improved overall sensitivity to 84%. Specificity was 100% for all detection methods except for MR pulmonary angiography (one false-positive). Agreement between readers was high (κ = 0.87). Embolus detection rates were lowest in the lingula branch for all MR sequences compared with remainder of the vascular territories (P = .07).

CONCLUSION

There are complementary benefits to combining standard MR pulmonary angiography, 3D GRE, and triggered true FISP MR examinations for evaluation of PE.

Liver MRI and histological correlates in chronic liver disease on multiphase gadolinium-enhanced 3D gradient echo imaging

PURPOSE

To evaluate intrinsic hepatic enhancement patterns on multiphase, gadolinium-enhanced, fat-suppressed, 3D T1-weighted, gradient echo magnetic resonance imaging (MRI) as a quantitative correlate for severity of pathological changes in chronic liver disease (CLD).

MATERIALS AND METHODS

This study was HIPAA-compliant and Institutional Review Board-approved. In all, 75 patients were studied by contrast-enhanced multiphase abdominal MRI. CLD patients had liver histology correlation derived from right lobe liver biopsies. Contrast-enhanced arterial- and delayed-phase 3D gradient recalled echo (GRE) liver MRI were scored using feature categorization templates to quantify enhancement patterns by three independent readers. Liver histopathology was staged/graded for fibrosis/inflammation using the Scheuer system. Statistical testing for MRI histology correlates used a Pearson's product moment correlation and a Wilcoxon-Mann-Whitney two-sample rank-sum test. Reader agreement was analyzed by a modified Fleiss' kappa test.

RESULTS

MRI histology correlation was high for delayed-phase MRI versus fibrosis stage (95% confidence interval [CI] 0.941 < r < 0.976, P = 5 × 10(-7)), but lower for all other comparisons (delayed-phase vs. inflammation and arterial-phase vs. inflammation or fibrosis all showed a CI no greater than 0.64). Paired testing between delayed-phase MRI score and histology fibrosis staging incremental levels was significant (from P < 10(-2) to P < 10(-5)).

CONCLUSION

A standard gadolinium-enhanced liver MRI may provide a correlate measure of hepatic fibrosis over a spectrum of severity.

Magnetic resonance enterography in Crohn's disease: techniques, interpretation, and utilization for clinical management

Crohn's disease treatment has improved significantly with the development of immunosuppressive and immunomodulatory agents, while surgery remains an important option in selected patients. However, a relative lag in diagnostics has become apparent with a growing need for the capacity to noninvasively and safely evaluate the tissue changes of Crohn's disease within the bowel wall and deeper tissues. We have noted marked technical improvements in magnetic resonance enterography (MRE) and in our understanding of the different facets of Crohn's disease that can be elucidated by optimized MRE, in contrast to other diagnostics. This review will provide an integrated understanding of MRE related to other available tests and recommendations for the optimal use of MRE for the clinical management of Crohn's disease. We will review the relative strengths and limitations of MRE as applied to clinical evaluation and therapeutic decisions, including the use of the unique capacity to delineate active inflammation and fibrosis in the submucosal and deeper enteric tissues, which is beyond the diagnostic reach of endoscopy and biopsy.