High Spatiotemporal Resolution Dynamic Contrast-Enhanced MR Enterography in Crohn Disease Terminal Ileitis Using Continuous Golden-Angle Radial Sampling, Compressed Sensing, and Parallel Imaging

Comparison of golden-angle radial sparse parallel (GRASP) and conventional cartesian sampling in 3D dynamic contrast-enhanced mri for bladder cancer: a preliminary study

PURPOSE

To compare the image quality, inter-reader agreement, and diagnostic capability for muscle-invasive bladder cancer (MIBC) of the reconstructed images in sections orthogonal to the bladder tumor obtained by 3D Dynamic contrast-enhanced (DCE)-MRI using the Golden-angle Radial Sparse Parallel (GRASP) technique with the images directly captured using the Cartesian sampling.

MATERIALS AND METHODS

This study involved 68 initial cases of bladder cancer examined with DCE-MRI (GRASP: n = 34, Cartesian: n = 34) at 3 Tesla. Four radiologists conducted qualitative evaluations (overall image quality, absence of motion artifact, absence of streak artifact, and tumor conspicuity) using a five-point Likert scale (5 = Excellent/None) and quantitative signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) measurements. The areas under the receiver-operating characteristic curves (AUCs) for the Vesical Imaging-Reporting and Data System (VI-RADS) DCE score for MIBC assessment were calculated. Inter-reader agreement was also assessed.

RESULTS

GRASP notably enhanced overall image quality (pooled score: GRASP 4 vs. Cartesian 3, P < 0.0001), tumor conspicuity (5 vs. 3, P < 0.05), SNR (Median 38.2 vs. 19.0, P < 0.0001), and CNR (7.9 vs. 6.0, P = 0.005), with fewer motion artifacts (5 vs. 3, P < 0.0001) and minor streak artifacts (5 vs. 5, P > 0.05). Although no significant differences were observed, the GRASP group tended to have higher AUCs for MIBC (pooled AUCs: 0.92 vs. 0.88) and showed a trend toward higher inter-reader agreement (pooled kappa-value: 0.70 vs. 0.63) compared to the Cartesian group.

CONCLUSIONS

Using the GRASP for 3D DCE-MRI, the reconstructed images in sections orthogonal to the bladder tumor achieved higher image quality and improve the clinical work flow, compared to the images directly captured using the Cartesian. GRASP tended to have higher diagnostic ability for MIBC and showed a trend toward higher inter-reader agreement compared to the Cartesian.

Correlation between imaging findings on outpatient MR enterography (MRE) in adult patients with Crohn disease and progression to surgery within 5 years

PURPOSE

To retrospectively evaluate which key imaging features described by SAR-AGA on outpatient surveillance MRE correlate with progression to surgery in adults with CD.

METHODS

52 CD patients imaged with outpatient MRE from 10/2015 to 12/2016 and with available clinical information were included. Two abdominal radiologists reviewed the MRE for the presence of active inflammation, intramural edema, restricted diffusion, stricture, probable stricture, ulceration, sacculation, simple fistula, complex fistula, sinus tract, inflammatory mass, abscess, perienteric inflammation, engorged vasa recta, fibrofatty proliferation, and perianal disease. Bowel wall thickness, length of bowel involvement, and degree of upstream dilation in strictures were quantified. Subsequent bowel resection, prior bowel surgery, and available laboratory values were recorded. The association between progression to surgery and imaging features was evaluated using a logistic regression model adjusting for demographics, prior bowel surgery, medication usage, and body mass index.

RESULTS

19.2% (10/52) of patients progressed to surgery. Restricted diffusion, greater degree of upstream dilation from stricture, complex fistula, perienteric inflammation, and fibrofatty proliferation were significantly more common in patients progressing to surgery (all p < 0.05). κ for these significant findings ranged 0.568-0.885. Patients progressing to surgery had longer length bowel involvement (p = 0.03). Platelet count, ESR, and fecal calprotectin were significantly higher, and serum albumin was significantly lower in patients progressing to surgery. Prior bowel surgery, sex, age, and all other parameters were similar.

CONCLUSION

Radiologists should carefully describe bowel dilation upstream from strictures, penetrating and perienteric findings on outpatient MRE in CD patients, as these findings may herald progression to surgery.

Comparison of Sensitivity Encoding (SENSE) and Compressed Sensing-SENSE for Contrast-Enhanced T1-Weighted Imaging in Patients With Crohn Disease Undergoing MR Enterography

Please see the Editorial Comment by Tyler J. Fraum discussing this article. Background: Long acquisition times for breath-hold contrast-enhanced T1-weighted (CE-T1W) imaging in MR enterography (MRE) protocols result in reduced image quality. Objective: To compare CE-T1W imaging performed using sensitivity encoding (SENSE) and compressed-sensing SENSE (CS-SENSE) in terms of image quality and diagnostic performance for active inflammation in Crohn disease (CD). Methods: This retrospective study included 41 patients (31 men, 10 women; mean age, 34±12 years) who underwent MRE for known or suspected CD between June 2020 and September 2020. MRE was performed in one of two scanning rooms based on scheduling availability. Per institutional protocol, in one room, the enteric phase was acquired using SENSE (acceleration factor 3), and the portal phase was acquired using CS-SENSE (acceleration factor 5); this order was reversed in the other room. Two radiologists independently assessed sequences for subjective image quality measures at the patient level and for active inflammation at the bowel-segment level. Mean image quality scores between readers were computed. Diagnostic performance for active inflammation was compared using generalized estimating equations; a separate experienced radiologist reviewed the full MRE protocol to establish the reference standard. Results: The mean acquisition time of CE-T1W imaging was 17.2 ± 1.1 seconds for SENSE versus 11.5 ± 0.8 seconds for CS-SENSE (P<.001). CS-SENSE was significantly better than SENSE in overall image quality (4.2±0.7 vs 3.7±1.1; P=.02), motion artifacts (4.0±0.8 vs 3.6±1.2; P=.006), and aliasing artifacts (4.8±0.4 vs 4.2±0.6; P<.001). CSSENSE was significantly worse than SENSE in synthetic appearance (4.6±0.5 vs 4.8±0.4; P=.003). Contrast, sharpness, and blurring were not different between sequences (P>.05). For reader 1, CS-SENSE, compared with SENSE, demonstrated sensitivity of 86% versus 81% (P=.09), specificity of 88% versus 83% (P=.08), and accuracy of 87% versus 82% (P=.56). For reader 2, CS-SENSE, compared with SENSE, demonstrated sensitivity of 92% versus 80% (P=.006), specificity of 91% versus 98% (P=.16), and accuracy of 91% versus 86% (P=.002). Conclusion: Use of CS-SENSE for CE-T1W imaging in MRE protocols results in reduced scan times with reduced artifact and improved image quality. Clinical impact: The benefits of CS-SENSE in MRE protocols may improve the diagnostic performance for active inflammation in CD.

Crohn Disease Active Inflammation Assessment with Iodine Density from Dual-Energy CT Enterography: Comparison with Histopathologic Analysis

Background Dual-energy CT enterography (DECTE) has been shown to be useful in characterizing Crohn disease activity compared with clinical markers of inflammation but, to the knowledge of the authors, comparison has not been made with histopathologic specimens. Purpose To compare mucosal iodine density obtained at DECTE from Crohn disease-affected bowel with histopathologic specimens from surgically resected ileocolectomy bowel segments or terminal ileum colonoscopic biopsies in the same patients. Materials and Methods This was a retrospective study. Bowel segments in adults with Crohn disease who underwent DECTE from January 2017 to April 2019 within 90 days of ileocolectomy or colonoscopy were retrospectively evaluated with prototype software allowing the semiautomatic determination of inner hyperdense bowel wall (mucosal) mean iodine density, normalized to the aorta. Mean normalized iodine density and clinical activity indexes (Crohn Disease Activity Index [CDAI] and Harvey-Bradshaw Index [HBI]) were compared with histologic active inflammation grades by using two-tailed t tests. Receiver operating characteristic curves were generated for mean normalized iodine density, CDAI, and HBI to determine sensitivity, specificity, and accuracy. A P value less than .05 was considered to indicate statistical significance. Results The following 16 patients were evaluated (mean age, 41 years ± 14 [standard deviation]): 10 patients (five men, five women; mean age, 41 years ± 15) with 19 surgical resection specimens and six patients with terminal ileum colonoscopic mucosal biopsies (four men, two women; mean age, 43 years ± 14). Mean normalized iodine density was 16.5% ± 5.7 for bowel segments with no active inflammation (n = 8) and 34.7% ± 9.7 for segments with any active inflammation (n = 17; P < .001). A 20% mean normalized iodine density threshold had sensitivity, specificity, and accuracy of 17 of 17 (100%; 95% CI: 80.5, 100), six of eight (75%; 95% CI: 35, 97), and 23 of 25 (92%; 95% CI: 74, 99), respectively, for active inflammation. Clinical indexes were similar for patients with and without active inflammation at histopathologic analysis (CDAI score, 261 vs 251, respectively [P = .77]; HBI score, 7.8 vs 6.4, respectively [P = .36]). Conclusion Iodine density from dual-energy CT enterography may be used as a radiologic marker of Crohn disease activity as correlated with histopathologic analysis. © RSNA, 2021 See also the editorial by Ohliger in this issue.

Emerging Imaging Biomarkers in Crohn Disease

ABSTRACT

In this review article, we present the latest developments in quantitative imaging biomarkers based on magnetic resonance imaging (MRI), applied to the diagnosis, assessment of response to therapy, and assessment of prognosis of Crohn disease. We also discuss the biomarkers' limitations and future prospects. We performed a literature search of clinical and translational research in Crohn disease using diffusion-weighted MRI (DWI-MRI), dynamic contrast-enhanced MRI (DCE-MRI), motility MRI, and magnetization transfer MRI, as well as emerging topics such as T1 mapping, radiomics, and artificial intelligence. These techniques are integrated in and combined with qualitative image assessment of magnetic resonance enterography (MRE) examinations. Quantitative MRI biomarkers add value to MRE qualitative assessment, achieving substantial diagnostic performance (area under receiver-operating curve = 0.8-0.95). The studies reviewed show that the combination of multiple MRI sequences in a multiparametric quantitative fashion provides rich information that may help for better diagnosis, assessment of severity, prognostication, and assessment of response to biological treatment. However, the addition of quantitative sequences to MRE examinations has potential drawbacks, including increased scan time and the need for further validation before being used in therapeutic drug trials as well as the clinic.

Crohn Disease Prognostication With Semiautomatic Dual-Energy Computed Tomography Enterography-Derived Iodine Density

OBJECTIVE

The objective of this study was to determine if dual-energy computed tomography enterography (DECTE)-obtained iodine density can predict medical management change or surgery in Crohn disease patients.

METHODS

The most active-appearing bowel segment on DECTE in 21 Crohn disease patients was retrospectively interrogated with prototype software determining the percentage of bowel wall (I) in specified ranges. Patients were categorized into 3 groups after DECTE: (1) no management change, (2) outpatient medication change, and (3) inpatient admission or surgery. Crohn's disease activity index was calculated. Group 3's percentage iodine density of >3 mg/mL and Crohn's disease activity index were compared with group 1/2. Crohn's disease activity index and percentage iodine density of >2 mg/mL were compared for groups 2/3 versus group 1 patients.

RESULTS

There were 5 group 1, 6 group 2, and 10 group 3 patients. Group 3 patients had higher frequency of iodine density >3 mg/mL (27%) compared with groups 1/2 patients (12.6%) (P < 0.05). Crohn's disease activity index was similar (P = 0.98). Groups 2/3 patients had 60.5% iodine density of >2 mg/mL, whereas group 1 patients had 31.7% iodine density of >2 mg/mL (P < 0.05). Crohn's disease activity index was similar (P = 0.12).

CONCLUSIONS

Iodine density from DECTE may predict medical or surgical Crohn disease management.

Novel Dual-Energy Computed Tomography Enterography Iodine Density Maps Provide Unique Depiction of Crohn Disease Activity

OBJECTIVE

To create a map of iodine densities within affected segments of small-bowel Crohn disease (CD) derived from contrast-enhanced dual-energy computed tomography enterography (DECTE) studies.

METHODS

Twenty CD patients imaged with intravenous contrast-enhanced DECTE between June 2016 and December 2017 were retrospectively identified. Ten patients without clinical evidence of CD and 8 normal-appearing jejunal segments in CD patients were controls. Using prototype software, 8 manual contours were drawn along the mucosa of affected segments. Relatively normal-appearing bowel was included at the edges. These contours served as a basis for iodine density calculation and 3-dimensional iodine density map rendering. Color-coded iodine densities allowed detection and quantification of the most and least dense portion of each segment and also permitted relative comparison between segments.

RESULTS

The average iodine density per CD involved segment ranged 1.0 to 3.3 mg/mL, which differed significantly from normal ileum (P < 0.0001) and normal-appearing jejunum in patients with CD (P = 0.0009). Standard deviations ranged from 0.8 to 1.7 mg/mL, which differed significantly from normal ileum (P = 0.0039) and normal-appearing jejunum in patients with CD (P = 0.0056). The amplitude of the power spectrum ranged from 0.66 to 3.3 demonstrating patches of iodine rather than uniform distribution. This differed significantly from normal ileum (P = 0.0005) and normal-appearing jejunum in patients with CD (P = 0.0004).

CONCLUSIONS

Heterogeneous CD activity and distribution can be displayed as iodine density maps created from DECTE.

Magnetic resonance enterography perfusion parameters reveal complex changes in affected and unaffected segments in Crohn's disease

OBJECTIVES

To compare dynamic contrast-enhanced (DCE)-MRI parameters in affected and unaffected segments of CD patients with those of a control group, and to assess the correlation between DCE-MRI parameters and clinical index of activity (HBI) as well as biomarkers (CRP and faecal calprotectin).

METHODS

We performed a single-center prospective study of CD patients and control subjects who underwent DCE-MRI. Regions of interest were drawn in segments and the program (Olea Medical - Canon) provided values for transfer constant (Ktrans), fractional volume of extravascular-extracellular space (Ve), slope of enhancement (SoE), time to maximum enhancement (TME), maximum enhancement (ME) and enhancement ratio (ER) which were determined and compared.

RESULTS

Fifteen CD patients (mean age 42 years; 10 women) and 7 healthy subjects (mean age 40.4 years; 6 women) were included. Paired comparisons of affected and unaffected segments in CD showed a significant increase of all parameters in affected segments, except for ER and TME. When comparing to controls, the affected segments did not show any significant difference, while a significant decrease in most of the parameters (except for ER and TME) was observed when comparing unaffected segments of CD patients to controls. In CD, significant correlations between DCE-MRI parameters and biomarkers (CRP, faecal calprotectin) were more frequent in unaffected segments than in affected segments.

CONCLUSIONS

Significant differences in perfusion parameters were observed between affected and unaffected segments of CD patients and between unaffected segments and those of control subjects. This suggests complex perfusion changes in both unaffected and affected intestinal segments in CD.

Improving dynamic contrast-enhanced MRI of the lung using motion-weighted sparse reconstruction: Initial experiences in patients

PURPOSE

The purpose of this study was to evaluate the performance of motion-weighted Golden-angle RAdial Sparse Parallel MRI (motion-weighted GRASP) for free-breathing dynamic contrast-enhanced MRI (DCE-MRI) of the lung.

METHODS

Motion-weighted GRASP incorporates a soft-gating motion compensation algorithm into standard GRASP reconstruction, so that motion-corrupted motion k-space (e.g., k-space acquired in inspiratory phases) contributes less to the final reconstructed images. Lung MR data from 20 patients (mean age = 57.9 ± 13.5) with known pulmonary lesions were retrospectively collected for this study. Each subject underwent a free-breathing DCE-MR scan using a fat-statured T₁-weighted stack-of-stars golden-angle radial sequence and a post-contrast breath-hold MR scan using a Cartesian volumetric-interpolated imaging sequence (BH-VIBE). Each radial dataset was reconstructed using GRASP without motion compensation and motion-weighted GRASP. All MR images were visually evaluated by two experienced radiologists blinded to reconstruction and acquisition schemes independently. In addition, the influence of motion-weighted reconstruction on dynamic contrast-enhancement patterns was also investigated.

RESULTS

For image quality assessment, motion-weighted GRASP received significantly higher visual scores than GRASP (P < 0.05) for overall image quality (3.68 vs. 3.39), lesion conspicuity (3.54 vs. 3.18) and overall artifact level (3.53 vs. 3.15). There was no significant difference (P > 0.05) between the breath-hold BH-VIBE and motion-weighted GRASP images. For assessment of temporal fidelity, motion-weighted GRASP maintained a good agreement with respect to GRASP.

CONCLUSION

Motion-weighted GRASP achieved better reconstruction performance in free-breathing DCE-MRI of the lung compared to standard GRASP, and it may enable improved assessment of pulmonary lesions.

Evaluation of compressed sensing MRI for accelerated bowel motility imaging

Background

To investigate the feasibility of compressed sensing and parallel imaging (CS-PI)-accelerated bowel motility magnetic resonance imaging (MRI) and to compare its image quality and diagnostic quality to conventional sensitivity encoding (SENSE) accelerated scans.

Methods

Bowel MRI was performed in six volunteers using a three-dimensional balanced fast field-echo sequence. Static scans were performed after the administration of a spasmolytic agent to prevent bowel motion artefacts. Fully sampled reference scans and multiple prospectively 3× to 7× undersampled CS-PI and SENSE scans were acquired. Additionally, fully sampled CS-PI and SENSE scans were retrospectively undersampled and reconstructed. Dynamic scans were performed using 5× to 7× accelerated scans in the presence of bowel motion. Retrospectively, undersampled scans were compared to fully sampled scans using structural similarity indices. All reconstructions were visually assessed for image quality and diagnostic quality by two radiologists.

Results

For static imaging, the performance of CS-PI was lower than that of fully sampled and SENSE scans: the diagnostic quality was assessed as adequate or good for 100% of fully sampled scans, 95% of SENSE, but only for 55% of CS-PI scans. For dynamic imaging, CS-PI image quality was scored similar to SENSE at high acceleration. Diagnostic quality of all scans was scored as adequate or good; 55% of CS-PI and 83% of SENSE scans were scored as good.

Conclusion

Compared to SENSE, current implementation of CS-PI performed less or equally good in terms of image quality and diagnostic quality. CS-PI did not show advantages over SENSE for three-dimensional bowel motility imaging.

Free-breathing dynamic contrast-enhanced MRI for assessment of pulmonary lesions using golden-angle radial sparse parallel imaging

BACKGROUND

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) has been shown to be a promising technique for assessing lung lesions. However, DCE-MRI often suffers from motion artifacts and insufficient imaging speed. Therefore, highly accelerated free-breathing DCE-MRI is of clinical interest for lung exams.

PURPOSE

To test the performance of rapid free-breathing DCE-MRI for simultaneous qualitative and quantitative assessment of pulmonary lesions using Golden-angle RAdial Sparse Parallel (GRASP) imaging.

STUDY TYPE

Prospective.

POPULATION

Twenty-six patients (17 males, mean age = 55.1 ± 14.4) with known pulmonary lesions.

FIELD STRENGTH/SEQUENCE

3T MR scanner; a prototype fat-saturated, T₁ -weighted stack-of-stars golden-angle radial sequence for data acquisition and a Cartesian breath-hold volumetric-interpolated examination (BH-VIBE) sequence for comparison.

ASSESSMENT

After a dual-mode GRASP reconstruction, one with 3-second temporal resolution (3s-GRASP) and the other with 15-second temporal resolution (15s-GRASP), all GRASP and BH-VIBE images were pooled together for blind assessment by two experienced radiologists, who independently scored the overall image quality, lesion delineation, overall artifact level, and diagnostic confidence of each case. Perfusion analysis was performed for the 3s-GRASP images using a Tofts model to generate the volume transfer coefficient (K^trans ) and interstitial volume (V_e ).

STATISTICAL TESTS

Nonparametric paired two-tailed Wilcoxon signed-rank test; Cohen's kappa; unpaired Student's t-test.

RESULTS

15s-GRASP achieved comparable image quality with conventional BH-VIBE (P > 0.05), except for the higher overall artifact level in the precontrast phase (P = 0.018). The K^trans and V_e in inflammation were higher than those in malignant lesions (K^trans : 0.78 ± 0.52 min^-1 vs. 0.37 ± 0.22 min^-1 , P = 0.020; V_e : 0.36 ± 0.16 vs. 0.26 ± 0.1, P = 0.177). Also, the K^trans and V_e in malignant lesions were also higher than those in benign lesions (K^trans : 0.37 ± 0.22 min^-1 vs. 0.04 ± 0.04 min^-1 , P = 0.001; V_e : 0.26 ± 0.12 vs. 0.10 ± 0.00, P = 0.063).

DATA CONCLUSION

This feasibility study demonstrated the performance of high spatiotemporal resolution free-breathing DCE-MRI of the lung using GRASP for qualitative and quantitative assessment of pulmonary lesions.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2018;48:459-468.

Detection of prostate cancer local recurrence following radical prostatectomy: assessment using a continuously acquired radial golden-angle compressed sensing acquisition

PURPOSE

To compare image quality and diagnostic performance for detecting local recurrence (LR) of prostate cancer after radical prostatectomy (RP) between standard dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) and a high spatiotemporal resolution, continuously acquired Golden-angle RAdial Sparse Parallel acquisition employing compressed sensing reconstruction ("GRASP").

METHODS

A search was conducted for prostate MRI examinations performed in patients with PSA ≥0.2 ng/mL after RP in whom follow-up evaluation allowed classification as positive (≥50% PSA reduction after pelvic radiation or positive biopsy) or negative (<50% PSA reduction after pelvic radiation; spontaneous PSA normalization) for LR, yielding 13 patients with standard DCE (11 LR+) and 12 with GRASP (10 LR+). Standard DCE had voxel size 3.0 × 1.9 × 1.9 mm and temporal resolution 5.5 s. GRASP had voxel size 1.0 × 1.1 × 1.1 cm and was retrospectively reconstructed at 2.3 s resolution. Two radiologists evaluated DCE sequences for image quality measures (1-5 scale) and the presence of LR.

RESULTS

GRASP achieved higher scores than standard DCE from both readers (p < 0.001-0.136) for anatomic clarity (R1: 4.4 ± 0.8 vs. 2.8 ± 0.67 R2: 4.8 ± 0.5 vs. 3.2 ± 0.6), sharpness (3.6 ± 0.9 vs. 2.5 ± 0.7; 4.6 ± 0.5 vs. 2.6 ± 0.5), confidence in interpretation (3.8 ± 0.8 vs. 3.1 ± 0.9; 3.8 ± 1.0 vs. 3.1 ± 1.2), and conspicuity of detected lesions (4.7 ± 0.5 vs. 3.8 ± 1.1; 4.5 ± 0.5 vs. 3.8 ± 1.0). For detecting LR, GRASP also achieved higher sensitivity (70% vs. 36%; 80% vs. 45%), specificity (R1 and R2: 100% vs. 50%), and accuracy (75% vs. 38%; 83% vs. 46%) for both readers.

CONCLUSION

Although requiring larger studies, high spatiotemporal resolution GRASP achieved substantially better image quality and diagnostic performance than standard DCE for detecting LR in patients with elevated PSA after prostatectomy.

Compressed sensing for body MRI

The introduction of compressed sensing for increasing imaging speed in magnetic resonance imaging (MRI) has raised significant interest among researchers and clinicians, and has initiated a large body of research across multiple clinical applications over the last decade. Compressed sensing aims to reconstruct unaliased images from fewer measurements than are traditionally required in MRI by exploiting image compressibility or sparsity. Moreover, appropriate combinations of compressed sensing with previously introduced fast imaging approaches, such as parallel imaging, have demonstrated further improved performance. The advent of compressed sensing marks the prelude to a new era of rapid MRI, where the focus of data acquisition has changed from sampling based on the nominal number of voxels and/or frames to sampling based on the desired information content. This article presents a brief overview of the application of compressed sensing techniques in body MRI, where imaging speed is crucial due to the presence of respiratory motion along with stringent constraints on spatial and temporal resolution. The first section provides an overview of the basic compressed sensing methodology, including the notion of sparsity, incoherence, and nonlinear reconstruction. The second section reviews state-of-the-art compressed sensing techniques that have been demonstrated for various clinical body MRI applications. In the final section, the article discusses current challenges and future opportunities.

LEVEL OF EVIDENCE

5 J. Magn. Reson. Imaging 2017;45:966-987.

Hyaluronic acid-modified manganese-chelated dendrimer-entrapped gold nanoparticles for the targeted CT/MR dual-mode imaging of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most common malignant tumor of the liver. The early and effective diagnosis has always been desired. Herein, we present the preparation and characterization of hyaluronic acid (HA)-modified, multifunctional nanoparticles (NPs) targeting CD44 receptor-expressing cancer cells for computed tomography (CT)/magnetic resonance (MR) dual-mode imaging. We first modified amine-terminated generation 5 poly(amidoamine) dendrimers (G5.NH2) with an Mn chelator, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), fluorescein isothiocyanate (FI), and HA. Then, gold nanoparticles (AuNPs) were entrapped within the above raw product, denoted as G5.NH2-FI-DOTA-HA. The designed multifunctional NPs were formed after further Mn chelation and purification and were denoted as {(Au0)100G5.NH2-FI-DOTA(Mn)-HA}. These NPs were characterized via several different techniques. We found that the {(Au0)100G5.NH2-FI-DOTA(Mn)-HA} NPs exhibited good water dispersibility, stability under different conditions, and cytocompatibility within a given concentration range. Because both AuNPs and Mn were present in the product, {(Au0)100G5.NH2-FI-DOTA(Mn)-HA} displayed a high X-ray attenuation intensity and favorable r1 relaxivity, which are advantageous properties for targeted CT/MR dual-mode imaging. This approach was used to image HCC cells in vitro and orthotopically transplanted HCC tumors in a unique in vivo model through the CD44 receptor-mediated endocytosis pathway. This work introduces a novel strategy for preparing multifunctional NPs via dendrimer nanotechnology.

Sparse Reconstruction Techniques in Magnetic Resonance Imaging: Methods, Applications, and Challenges to Clinical Adoption

The family of sparse reconstruction techniques, including the recently introduced compressed sensing framework, has been extensively explored to reduce scan times in magnetic resonance imaging (MRI). While there are many different methods that fall under the general umbrella of sparse reconstructions, they all rely on the idea that a priori information about the sparsity of MR images can be used to reconstruct full images from undersampled data. This review describes the basic ideas behind sparse reconstruction techniques, how they could be applied to improve MRI, and the open challenges to their general adoption in a clinical setting. The fundamental principles underlying different classes of sparse reconstructions techniques are examined, and the requirements that each make on the undersampled data outlined. Applications that could potentially benefit from the accelerations that sparse reconstructions could provide are described, and clinical studies using sparse reconstructions reviewed. Lastly, technical and clinical challenges to widespread implementation of sparse reconstruction techniques, including optimization, reconstruction times, artifact appearance, and comparison with current gold standards, are discussed.