Isotropic 3D black blood MRI of abdominal aortic aneurysm wall and intraluminal thrombus

Direct angiographic comparison of different velocity-selective saturation, inversion, and DANTE labeling modules on cerebral arteries

PURPOSE

This study evaluated the velocity-selective (VS) MRA with different VS labeling modules, including double refocused hyperbolic tangent, eight-segment B1-insensitive rotation, delay alternating with nutation for tailored excitation, Fourier transform-based VS saturation, and Fourier transform-based inversion.

METHODS

These five VS labeling modules were evaluated first through Bloch simulations, and then using VSMRA directly on various cerebral arteries of healthy subjects. The relative signal ratios from arterial ROIs and surrounding tissues as well as relative arteria-tissue contrast ratios of different methods were compared.

RESULTS

Double refocused hyperbolic tangent and eight-segment B1-insensitive rotation showed very similar labeling effects. Delay alternating with nutation for tailored excitation yielded high arterial signal but with residual tissue signal due to the spatial banding effect. Fourier transform-based VS saturation with half the time of other techniques serves as an efficient nonsubtractive VSMRA method, but the remaining tissue signal still obscured some small distal arteries that were delineated by other subtraction-based VSMRA, allowing more complete cancelation of static tissue. Fourier transform-based inversion produced the highest arterial signal in VSMRA with minimal tissue background.

CONCLUSION

This is the first study that angiographically compared five different VS labeling modules. Their labeling characteristics on arteries and tissue and implications for VSMRA and VS arterial spin labeling are discussed.

Value of Non-Contrast-Enhanced Vessel Wall MR Imaging in Assessing Vascular Invasion of Retroperitoneal Tumors

BACKGROUND

Due to their location and growth patterns, retroperitoneal tumors often involve the surrounding blood vessels. Clinical decisions on a proper treatment depend on the information on this condition. Evaluation of blood vessels using non-contrast-enhanced vessel wall MRI may provide noninvasive assessment of the extent of tumor invasion to assist clinical decision-making.

PURPOSE

To investigate the performance and potential of non-contrast-enhanced vessel wall MRI in evaluating the degree of vessel wall invasion of retroperitoneal tumors.

STUDY TYPE

Prospective.

POPULATION

Thirty-seven participants (mean age: 60.59 ± 11.77 years, 59% male) with retroperitoneal tumors close to vessels based on their diagnostic computer tomography.

FIELD STRENGTH/SEQUENCES

3 T; vessel wall MRI sequences: two-dimensional T2-weighted MultiVane XD turbo spin-echo (2D-T2-MVXD-TSE) and three-dimensional T1-weighted motion sensitized driven equilibrium fat suppression turbo spin-echo (3D-T1-MSDE-TSE) sequences; conventional MRI sequences: T2-weighted fat suppression turbo spin-echo (T2-FS-TSE), T2-weighted turbo spin-echo (T2-TSE), modified Dixon T1-weighted fast field echo (T1-mDixon-FFE), and diffusion-weighted echo planar imaging (DWI-EPI) sequences.

ASSESSMENT

All patients underwent preoperative imaging using both non-contrast conventional and vessel wall MRI sequences. Images obtained from conventional and vessel wall MRI sequences were evaluated independently by three junior radiologists (3 and 2 years of experience in reading MRI) and reviewed by one senior radiologist (25 years of experience in reading MRI) to assess the degree of vessel wall invasion. MRI were validated results from the clinical standard diagnosis based on surgical confirmation or histopathological reports. Interobserver agreement was determined based on the reports from three readers with similar years of experiences. Intraobserver variability was assessed based on categorizing and recategorizing the vessels of 37 patients 1 month apart.

STATISTICAL TESTS

Intra-class correlation efficient (ICC), Chi-square test, McNemar test, area under the receiver-operating characteristic curve (AUC), Delong test, P < 0.05 was considered significant.

RESULTS

The accuracy of vessel wall MRI (91.96%, 95% CI: 85.43-95.71; 103 of 112) in detecting the degree of vessel wall invasion was significantly higher than that of conventional MRI (75%, 95% CI: 66.24-82.10; 84 of 112). The interobserver variability or reproducibility in categorization of the degree of vascular wall invasion was good in evaluating images from conventional and vessel wall MRI sequences (ICC = 0.821, 95% CI: 0.765-0.867 and ICC = 0.881, 95% CI: 0.842-0.913, respectively).

DATA CONCLUSION

Diagnosis of vessel wall invasion of retroperitoneal tumors and assessment of its severity can be improved by using non-contrast-enhanced vessel wall MRI.

EVIDENCE LEVEL

1 TECHNICAL EFFICACY: Stage 3.

Simultaneous Highly Efficient Contrast-Free Lumen and Vessel Wall MR Imaging for Anatomical Assessment of Aortic Disease

BACKGROUND

Bright-blood lumen and black-blood vessel wall imaging are required for the comprehensive assessment of aortic disease. These images are usually acquired separately, resulting in long examinations and potential misregistration between images.

PURPOSE

To characterize the performance of an accelerated and respiratory motion-compensated three-dimensional (3D) cardiac MRI technique for simultaneous contrast-free aortic lumen and vessel wall imaging with an interleaved T2 and inversion recovery prepared sequence (iT2Prep-BOOST).

STUDY TYPE

Prospective.

POPULATION

A total of 30 consecutive patients with aortopathy referred for a clinically indicated cardiac MRI examination (9 females, mean age ± standard deviation: 32 ± 12 years).

FIELD STRENGTH/SEQUENCE

1.5-T; bright-blood MR angiography (diaphragmatic navigator-gated T2-prepared 3D balanced steady-state free precession [bSSFP], T2Prep-bSSFP), breath-held black-blood two-dimensional (2D) half acquisition single-shot turbo spin echo (HASTE), and 3D bSSFP iT2Prep-BOOST.

ASSESSMENT

iT2Prep-BOOST bright-blood images were compared to T2prep-bSSFP images in terms of aortic vessel dimensions, lumen-to-myocardium contrast ratio (CR), and image quality (diagnostic confidence, vessel sharpness and presence of artifacts, assessed by three cardiologists on a 4-point scale, 1: nondiagnostic to 4: excellent). The iT2Prep-BOOST black-blood images were compared to 2D HASTE images for quantification of wall thickness. A visual comparison between computed tomography (CT) and iT2Prep-BOOST was performed in a patient with chronic aortic dissection.

STATISTICAL TESTS

Paired t-tests, Wilcoxon signed-rank tests, intraclass correlation coefficient (ICC), Bland-Altman analysis. A P value < 0.05 was considered statistically significant.

RESULTS

Bright-blood iT2Prep-BOOST resulted in significantly improved image quality (mean ± standard deviation 3.8 ± 0.5 vs. 3.3 ± 0.8) and CR (2.9 ± 0.8 vs. 1.8 ± 0.5) compared with T2Prep-bSSFP, with a shorter scan time (7.8 ± 1.7 minutes vs. 12.9 ± 3.4 minutes) while providing a complementary 3D black-blood image. Aortic lumen diameter and vessel wall thickness measurements in bright-blood and black-blood images were in good agreement with T2Prep-bSSFP and HASTE images (<0.02 cm and <0.005 cm bias, respectively) and good intrareader (ICC > 0.96) and interreader (ICC > 0.94) agreement was observed for all measurements.

DATA CONCLUSION

iT2Prep-BOOST might enable time-efficient simultaneous bright- and black-blood aortic imaging, with improved image quality compared to T2Prep-bSSFP and HASTE imaging, and comparable measurements for aortic wall and lumen dimensions.

EVIDENCE LEVEL

2.

TECHNICAL EFFICACY

Stage 2.

Reproducibility between three-dimensional turbo spin-echo and two-dimensional dual inversion recovery turbo spin-echo for coronary vessel wall imaging in Kawasaki disease

Magnetic resonance vessel wall imaging is desirable for evaluating Kawasaki disease (KD)-associated coronary arterial lesions. To evaluate the reproducibility of three-dimensional turbo spin-echo (3D-TSE) and two-dimensional dual inversion-recovery turbo spin-echo (2D-DIR-TSE) for coronary vessel wall imaging in KD. Ten patients were prospectively enrolled. Coronary vessel wall imaging with axial-slice orientation 3D-TSE and 2D-DIR-TSE were acquired for cross-sectional images in aneurysmal and normal regions. Lumen area (LA), wall area (WA), and normalized wall index (NWI) of cross-sectional images were measured in both regions. Reproducibility between 3D-TSE and 2D-DIR-TSE was evaluated via intraclass correlation coefficients (ICCs) and Bland–Altman plots. 48 points (aneurysmal, 27; normal, 21) were evaluated. There were high ICCs between 3D-TSE and 2D-DIR-TSE in LA (0.95) and WA (0.95). In aneurysmal regions, 95% limits of agreement were LA, WA, and NWI of − 29.9 to 30.4 mm², − 18.8 to 15.0 mm², and − 0.22 to 0.20, respectively. In normal regions, the 95% limits of agreement were LA, WA, and NWI of − 4.44 to 4.38 mm², − 3.51 to 4.30 mm², and − 0.14 to 0.16, respectively. No fixed and proportional biases between 3D-TSE and 2D-DIR-TSE images in aneurysmal and normal regions were noted. 3D-TSE was reproducible with conventional 2D-DIR-TSE for coronary vessel wall assessment on KD.

Dark blood cardiovascular magnetic resonance of the heart, great vessels, and lungs using electrocardiographic-gated three-dimensional unbalanced steady-state free precession

BACKGROUND

Recently, we reported a novel neuroimaging technique, unbalanced T1 Relaxation-Enhanced Steady-State (uT1RESS), which uses a tailored 3D unbalanced steady-state free precession (3D uSSFP) acquisition to suppress the blood pool signal while minimizing bulk motion sensitivity. In the present work, we hypothesized that 3D uSSFP might also be useful for dark blood imaging of the chest. To test the feasibility of this approach, we performed a pilot study in healthy subjects and patients undergoing cardiovascular magnetic resonance (CMR).

MAIN BODY

The study was approved by the hospital institutional review board. Thirty-one adult subjects were imaged at 1.5 T, including 5 healthy adult subjects and 26 patients (44 to 86 years, 10 female) undergoing a clinically indicated CMR. Breath-holding was used in 29 subjects and navigator gating in 2 subjects. For breath-hold acquisitions, the 3D uSSFP pulse sequence used a high sampling bandwidth, asymmetric readout, and single-shot along the phase-encoding direction, while 3 shots were acquired for navigator-gated scans. To minimize signal dephasing from bulk motion, electrocardiographic (ECG) gating was used to synchronize the data acquisition to the diastolic phase of the cardiac cycle. To further reduce motion sensitivity, the moment of the dephasing gradient was set to one-fifth of the moment of the readout gradient. Image quality using 3D uSSFP was good-to-excellent in all subjects. The blood pool signal in the thoracic aorta was uniformly suppressed with sharp delineation of the aortic wall including two cases of ascending aortic aneurysm and two cases of aortic dissection. Compared with variable flip angle 3D turbo spin-echo, 3D uSSFP showed improved aortic wall sharpness. It was also more efficient, permitting the acquisition of 24 slices in each breath-hold versus 16 slices with 3D turbo spin-echo and a single slice with dual inversion 2D turbo spin-echo. In addition, lung and mediastinal lesions appeared highly conspicuous compared with the low blood pool signals within the heart and blood vessels. In two subjects, navigator-gated 3D uSSFP provided excellent delineation of cardiac morphology in double oblique multiplanar reformations.

CONCLUSION

In this pilot study, we have demonstrated the feasibility of using ECG-gated 3D uSSFP for dark blood imaging of the heart, great vessels, and lungs. Further study will be required to fully optimize the technique and to assess clinical utility.

Double delay alternating with nutation for tailored excitation facilitates banding-free isotropic high-resolution intracranial vessel wall imaging

The purpose of this study was to evaluate the use of a double delay alternating with nutation for tailored excitation (D-DANTE)-prepared sequence for banding-free isotropic high-resolution intracranial vessel wall imaging (IC-VWI) and to compare its performance with regular DANTE in terms of signal-to-noise ratio (SNR) as well as cerebrospinal fluid (CSF) and blood suppression efficiency. To this end, a D-DANTE-prepared 3D turbo spin echo sequence was implemented by interleaving two separate DANTE pulse trains with different RF phase-cycling schemes, but keeping all other DANTE parameters unchanged, including the total number of pulses and total preparation time. This achieved a reduction of the banding distance compared with regular DANTE enabling banding-free imaging up to higher resolutions. Bloch simulations assuming static vessel wall and flowing CSF spins were performed to compare DANTE and D-DANTE in terms of SNR and vessel wall/CSF contrast. Similar image quality measures were assessed from measurements on 13 healthy middle-aged volunteers. Both simulation and in vivo results showed that D-DANTE had only slightly lower vessel wall/CSF and vessel wall/blood contrast-to-noise ratio values compared with regular DANTE, which originated from a 10%-15% reduction in vessel wall SNR but not from reduced CSF or blood suppression efficiency. As anticipated, IC-VWI acquisitions showed that D-DANTE can successfully remove banding artifacts compared with regular DANTE with equal scan time or DANTE preparation length. Moreover, application was demonstrated in a patient with an intracranial aneurysm, indicating improved robustness to slow flow artifacts compared with clinically available 3D turbo spin echo scans. In conclusion, D-DANTE provides banding artifact-free IC-VWI up to higher isotropic resolutions compared with regular DANTE. This allows for a more flexible choice of DANTE preparation parameters in high-resolution IC-VWI protocols.

Detection and Prediction of Peripheral Arterial Plaque Using Vessel Wall MR in Patients with Diabetes

Objectives

To evaluate the predictive performance of a newly developed delay alternating with nutation for tailored excitation (DANTE) pulse sequence for detecting lower extremity artery wall morphology and distribution in patients with peripheral artery disease (PAD) with diabetes.

Methods

Seventy-four PAD patients diagnosed according to 2011 WHO criteria were enrolled, who has diabetic diagnosis by 1999 WHO diabetes criteria. All patients received sequential DANTE, T2WI, DANTE-enhance, and CE-MRA scans. The images consisted of three parts: the iliac artery (segment 1), femoral artery (segment 2), and popliteal artery (segment 3). Regions of interest (ROIs) were drawn on vessels, muscle, and background, and multiple imaging metrics compared between modalities, including image quality score, image noise, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). In the images with a score greater than 2, the lumen area (LA), total vessel area (TVA), and vessel thickness (VT) can be identified using semiautomatic image analysis vessel morphology parameters.

Results

All 222 arterial segments were successfully analyzed from 71 patients, after exclusion of three subjects with poor image quality (IQ < 2) in segment 3. There were 54 diabetic and 17 nondiabetic patients. Quantitative analysis shows that the CNR difference between diabetic patients and nondiabetic patients was statistically significant for the same segment, while there was no significant difference among the three segments of SNR and CNR. There were a total of 54 diabetics with plaque distribution data, which showed that LA of segments 1 and 2 was higher than that of segment 3. The VWI of segments 1 and 2 was lower than segment 3. Diabetic was associated with vascular WT 3 and WA3, which increased by 0.23 and 0.83 units on average compared without diabetic foot, respectively. Diabetic foot was associated with vascular WT 3, which increased by 0.37 units on average compared without diabetic foot. The incidence of segment 3 plaques was higher than that of segment 1. The incidence of the left and right plaques was different.

Conclusions

MR imaging using the DANTE and multicontrast sequence could evaluate plaque morphology, and distribution of lower extremities and the occurrence of diabetic foot development are closely related; it may predict occurrence of PAD with diabetic foot.

Loan sharking: changing patterns in, and challenging perceptions of, an abuse of deprivation

BACKGROUND

Illegal high interest lending or 'loan sharking' exploits the vulnerable and has profound negative impacts on individuals and communities. The 2008 UK financial crash and subsequent austerity programme coupled with changes in the consumer credit market have fuelled an increase in predatory lending.

METHODS

The study is a descriptive analysis of demographic, financial, health and behavioural data on 753 victims (2011-2017). A review of the causative factors and potential political, economic and public health responses is analysed.

RESULTS

Most victims were female but males were considerably more indebted. Illegal loans are largely taken out for routine living expenses and over 70% of victims reported other serious debts. Victims are disproportionately poor, unemployed and on benefits but fewer than half have had financial or benefits advice. Despite 90% reporting they would not borrow illegally again, 30% had previously done so from the same shark and over half considered them a friend.

CONCLUSIONS

The increase in loan sharking has coincided with the withdrawal of traditional sub-prime lenders and local welfare assistance schemes, and the low penetration of Credit Unions in many areas. Conventional perceptions of loan sharks and their relationships with victims are largely incorrect. A range of coordinated financial, political and social interventions is required.

Abdominal aortic aneurysm measurement at CT/MRI: potential clinical ramifications of non-standardized measurement technique and importance of multiplanar reformation

Accurate and reproducible measurement of abdominal aortic aneurysm (AAA) size is an essential component of patient management, and most reliably performed at CT using a multiplanar reformat (MPR) strategy. This approach is not universal, however. This study aims to characterize the measurement error present in routine clinical assessment of AAAs and the potential clinical ramifications. Patients were included if they had AAA assessed by CT and/or MRI at two time points at least 6 months apart. Clinical maximal AAA diameter, assessed by non-standardized methods, was abstracted from the radiology report at each time point and compared to the reference aneurysm diameter measured using a MPR strategy. Discrepancies between clinical and reference diameters, and associated aneurysm enlargement rates were analyzed. Two hundred thirty patients were included, with average follow-up 3.3±2.5 years. When compared to MPR-derived diameters, clinical aneurysm measurement inaccuracy was, on average, 3.3 mm. Broad limits of agreement were found for both clinical diameters [-6.7 to +6.5 mm] and aneurysm enlargement rates [-4.6 to +4.2 mm/year] when compared to MPR-based measures. Of 78 AAAs measuring 5-6 cm by the MPR method, 21 (26.9%) were misclassified by the clinical measurement with respect to a common repair threshold (5.5 cm), of which 5 were misclassified as below, and 16 were misclassified as above the threshold. The clinical use of non-standardized AAA measurement strategies can lead to incorrect classification of AAAs as larger or smaller than the commonly accepted repair threshold of 5.5 cm and can induce large errors in quantification of aneurysm enlargement rate.

Computer-aided quantification of non-contrast 3D black blood MRI as an efficient alternative to reference standard manual CT angiography measurements of abdominal aortic aneurysms

BACKGROUND

Non-contrast 3D black blood MRI is a promising tool for abdominal aortic aneurysm (AAA) surveillance, permitting accurate aneurysm diameter measurements needed for patient management.

PURPOSE

To evaluate whether automated AAA volume and diameter measurements obtained from computer-aided segmentation of non-contrast 3D black blood MRI are accurate, and whether they can supplant reference standard manual measurements from contrast-enhanced CT angiography (CTA).

MATERIALS AND METHODS

Thirty AAA patients (mean age, 71.9 ± 7.9 years) were recruited between 2014 and 2017. Participants underwent both non-contrast black blood MRI and CTA within 3 months of each other. Semi-automatic (computer-aided) MRI and CTA segmentations utilizing deformable registration methods were compared against manual segmentations of the same modality using the Dice similarity coefficient (DSC). AAA lumen and total aneurysm volumes and AAA maximum diameter, quantified automatically from these segmentations, were compared against manual measurements using Pearson correlation and Bland-Altman analyses. Finally, automated measurements from non-contrast 3D black blood MRI were evaluated against manual CTA measurements using the Wilcoxon test, Pearson correlation and Bland-Altman analyses.

RESULTS

Semi-automatic segmentations had excellent agreement with manual segmentations (lumen DSC: 0.91 ± 0.03 and 0.94 ± 0.03; total aneurysm DSC: 0.92 ± 0.02 and 0.94 ± 0.03, for black blood MRI and CTA, respectively). Automated volume and maximum diameter measurements also had excellent correlation to their manual counterparts for both black blood MRI (volume: r = 0.99, P < 0.001; diameter: r = 0.97, P < 0.001) and CTA (volume: r = 0.99, P < 0.001; diameter: r = 0.97, P < 0.001). Compared to manual CTA measurements, bias and limits of agreement (LOA) for automated MRI measurements (lumen volume: 1.49, [-4.19 7.17] cm³; outer wall volume: -2.46, [-14.05 9.13] cm³; maximal diameter: 0.08, [-6.51 6.67] mm) were largely equivalent to those of manual MRI measurements, particularly for maximum AAA diameter (lumen volume: 0.73, [-6.47 7.93] cm³; outer wall volume: 0.98, [-10.54 12.5] cm³; maximal diameter: 0.08, [-3.67 3.83] mm).

CONCLUSION

Semi-automatic segmentation of non-contrast 3D black blood MRI efficiently provides reproducible morphologic AAA assessment yielding accurate AAA diameters and volumes with no clinically relevant differences compared to either automatic or manual measurements based on CTA.

Growth of common iliac artery aneurysms coexisting with abdominal aortic aneurysms: associated factors and potential role of intraluminal thrombus

BACKGROUND

The factors influencing common iliac artery aneurysm (CIA) growth are not fully known. Intraluminal thrombus (ILT) has been studied as a marker of growth in abdominal aortic aneurysms (AAA), but its role in CIAs is unknown. This study aims to examine the factors associated with growth of CIAs coexistent with AAA using serial cross-sectional imaging (CT and MRI) with multiplanar reconstruction (MPR).

METHODS

Patients with synchronous AAA and CIA observed at contrast-enhanced CT or MRI were included. The maximal diameters of both CIA and AAA were measured using MPR. Correlation of the baseline aneurysm diameter and growth rate between CIA and AAA was evaluated. Multivariate regression analysis was used to investigate the factors associated with CIA growth.

RESULTS

Seventy-five AAA patients (age 74±9 years; all male) with 100 CIAs were followed for an average of 2.2±1.2 years. CIA and AAA growth were positively correlated (r=0.39, P<0.001). Multivariate analysis showed that CIA baseline diameter, AAA baseline diameter, and smoking were positively related to CIA growth. In 2-3 cm CIAs (n=59), ILT tends to be an independent predictor of AAA growth (P=0.076), and CIAs with ILT grow at more than twice the rate of CIAs without ILT (1.7 vs. 0.8 mm/year, P=0.036), despite similar baseline diameters.

CONCLUSIONS

CIA baseline diameter, coexisting AAA baseline diameter, and smoking are associated with CIA growth. In CIAs measuring 2-3 cm, the presence of ILT is associated with faster growth, and should be taken into account when determining surveillance intervals and timing of intervention for patients being considered for AAA repair.

Magnetic resonance imaging assessment of proteolytic enzyme concentrations and biologic properties of intraluminal thrombus in abdominal aortic aneurysms

OBJECTIVE

The aim of the study was to determine whether magnetic resonance imaging (MRI) can be used in assessment of biologic activity of intraluminal thrombus (ILT) and proteolytic processes of the abdominal aortic aneurysm wall.

METHODS

Using MRI, 50 patients with asymptomatic infrarenal abdominal aortic aneurysm were analyzed at the maximum aneurysm diameter on T1-weighted images in the arterial phase after administration of contrast material. Relative ILT signal intensity (SI) was determined as the ratio between ILT SI and psoas muscle SI. During surgery, the full thickness of the ILT and the adjacent part of the aneurysm wall were harvested at the maximal diameter for biochemical analysis. The concentrations of matrix metalloproteinase 9 and neutrophil elastase (NE/ELA) were analyzed in harvested thrombi, and the concentrations of collagen type III, elastin, and proteoglycans were analyzed in harvested aneurysm walls.

RESULTS

A significant positive correlation was found between the NE/ELA concentration of the ILT and the relative SI (ρ = 0.309; P = .029). Furthermore, a negative correlation was observed between the elastin content of the aneurysm wall and the relative SI (ρ = -0.300; P = .034). No correlations were found between relative SI and concentration of matrix metalloproteinase 9, NE/ELA, collagen type III, or proteoglycan 4 in the aneurysm wall.

CONCLUSIONS

These findings indicate a potential novel use of MRI in prediction of thrombus proteolytic enzyme concentrations and the extracellular matrix content of the aneurysm wall, thus providing additional information for the risk of potential aneurysm rupture.

Intraluminal Thrombus Predicts Rapid Growth of Abdominal Aortic Aneurysms

Background Intraluminal thrombus (ILT) within abdominal aortic aneurysms (AAAs) may be a potential marker for subsequent aneurysm growth. Purpose To investigate the role of ILT in AAA progression as assessed with CT and MRI. Materials and Methods This was a retrospective study, with patient data included from January 2004 to December 2018 at a Veteran Affairs medical center. Male patients with AAA who underwent contrast material-enhanced CT at baseline and CT or black-blood MRI at follow-up (minimal follow-up duration of 6 months) were included. The maximal AAA diameter was measured with multiplanar reconstruction, and the annual growth rate of aneurysms was calculated. Uni- and multivariable linear regression analyses were used to determine the relationship between demographic and imaging factors and aneurysm growth. Results A total of 225 patients (mean age, 72 years ± 9 [standard deviation]) were followed for a mean of 3.3 years ± 2.5. A total of 207 patients were followed up with CT, and 18 were followed up with MRI. At baseline, the median size of the AAA was 3.8 cm (interquartile range [IQR], 3.3-4.3 cm); 127 of 225 patients (54.7%) had ILT. When compared with AAAs without ILT, AAAs with ILT had larger baseline diameters (median, 4.1 cm [IQR, 3.6-4.8 cm] vs 3.4 cm [IQR, 3.2-3.9 cm]; P < .001) and faster growth rates (median, 2.0 mm/y [IQR, 1.3-3.2 mm/y] vs 1.0 mm/y [IQR, 0.4-1.8 mm/y]; P < .001). Small AAAs (size range, 3-4 cm) with ILT grew 1.9-fold faster than did those without ILT (median, 1.5 mm/y [IQR, 0.9-2.7 mm/y] vs 0.8 mm/y [IQR, 0.3-1.5 mm/y]; P < .001). Medium AAAs (size range, 4-5 cm) with ILT had 1.2-fold faster growth than did those without ILT (median growth, 2.1 mm/y [IQR, 1.4, 3.7 mm/y] vs 1.8 mm/y [IQR, 0.9, 2.0 mm/y]; P = .06). In multivariable analysis, baseline diameter and ILT were independently positively related to aneurysm growth rate (standardized regression coefficient, 0.43 [P < .001] and 0.15 [P = .02], respectively). Conclusion Both maximal cross-sectional aneurysm diameter and the presence of intraluminal thrombus are independent predictors of abdominal aortic aneurysm growth. © RSNA, 2020 Online supplemental material is available for this article.

On the Relative Impact of Intraluminal Thrombus Heterogeneity on Abdominal Aortic Aneurysm Mechanics

Intraluminal thrombus (ILT) is present in the majority of abdominal aortic aneurysms (AAA) of a size warranting consideration for surgical or endovascular intervention. The rupture risk of AAAs is thought to be related to the balance of vessel wall strength and the mechanical stress caused by systemic blood pressure. Previous finite element analyses of AAAs have shown that ILT can reduce and homogenize aneurysm wall stress. These works have largely considered ILT to be homogeneous in mechanical character or have idealized a stiffness distribution through the thrombus thickness. In this work, we use magnetic resonance imaging (MRI) to delineate the heterogeneous composition of ILT in 7 AAAs and perform patient-specific finite element analysis under multiple conditions of ILT layer stiffness disparity. We find that explicit incorporation of ILT heterogeneity in the finite element analysis is unlikely to substantially alter major stress analysis predictions regarding aneurysm rupture risk in comparison to models assuming a homogenous thrombus, provided that the maximal ILT stiffness is the same between models. Our results also show that under a homogeneous ILT assumption, the choice of ILT stiffness from values common in the literature can result in significantly larger variations in stress predictions compared to the effects of thrombus heterogeneity.

Surveillance of abdominal aortic aneurysm using accelerated 3D non-contrast black-blood cardiovascular magnetic resonance with compressed sensing (CS-DANTE-SPACE)

BACKGROUND

3D non-contrast high-resolution black-blood cardiovascular magnetic resonance (CMR) (DANTE-SPACE) has been used for surveillance of abdominal aortic aneurysm (AAA) and validated against computed tomography (CT) angiography. However, it requires a long scan time of more than 7 min. We sought to develop an accelerated sequence applying compressed sensing (CS-DANTE-SPACE) and validate it in AAA patients undergoing surveillance.

METHODS

Thirty-eight AAA patients (all males, 73 ± 6 years) under clinical surveillance were recruited for this study. All patients were scanned with DANTE-SPACE (scan time 7:10 min) and CS-DANTE-SPACE (scan time 4:12 min, a reduction of 41.4%). Nine 9 patients were scanned more than 2 times. In total, 50 pairs of images were available for comparison. Two radiologists independently evaluated the image quality on a 1-4 scale, and measured the maximal diameter of AAA, the intra-luminal thrombus (ILT) and lumen area, ILT-to-muscle signal intensity ratio, and the ILT-to-lumen contrast ratio. The sharpness of the aneurysm inner/outer boundaries was quantified.

RESULTS

CS-DANTE-SPACE achieved comparable image quality compared with DANTE-SPACE (3.15 ± 0.67 vs. 3.03 ± 0.64, p = 0.06). There was excellent agreement between results from the two sequences for diameter/area and ILT ratio measurements (ICCs> 0.85), and for quantifying growth rate (3.3 ± 3.1 vs. 3.3 ± 3.4 mm/year, ICC = 0.95.) CS-DANTE-SPACE showed a higher ILT-to-lumen contrast ratio (p = 0.01) and higher sharpness than DANTE-SPACE (p = 0.002). Both sequences had excellent inter-reader reproducibility for quantitative measurements (ICC > 0.88).

CONCLUSION

CS-DANTE-SPACE can reduce scan time while maintaining image quality for AAA imaging. It is a promising tool for the surveillance of patients with AAA disease in the clinical setting.

COMPARISON OF TWO METHODS FOR ESTIMATING THE UNLOADED STATE FOR ABDOMINAL AORTIC ANEURYSM STRESS CALCULATIONS

Biomechanical analyses can be used to better understand the rupture risk of abdominal aortic aneurysms (AAAs) on a patient-specific basis using vascular geometries obtained from medical imaging. Methodologies of varying complexity are used to estimate the unloaded state of the imaged vessel to provide a reference configuration for finite element simulations. In this work, we compare the implementation and results of two of these methods, one based on geometric scaling and the other using an iterative determination of unloaded vessel geometry. We find that the two methods result in significantly different stress predictions, and that the iterative method offers superior geometric accuracy. Our findings lend context to the variation in finite element results presented in the AAA stress analysis literature.

Intracranial Aneurysm Wall Enhancement Associated with Aneurysm Rupture: A Systematic Review and Meta-analysis

RATIONALE AND OBJECTIVES

Aneurysm wall enhancement (AWE) on magnetic resonance vessel wall imaging has been proposed as an imaging marker of aneurysm wall inflammation and instability. We performed a systematic review and meta-analysis to summarize the association between AWE and aneurysm rupture.

MATERIALS AND METHODS

We performed a comprehensive literature search of studies evaluating the association between AWE and aneurysm rupture. We abstracted the following study data: study design, patient demographics, aneurysm characteristics, MRI protocols, and AWE assessment. We performed meta-analysis using a random-effects model. Study heterogeneity was assessed by using the Cochrane Q and I² statistic, and publication bias was examined by using the Begg-Mazumdar test.

RESULTS

Five studies with 492 subjects met eligibility for systematic review. We found a significant positive overall association between AWE and aneurysm rupture, with an odds ratio (OR) of 34.26 (95% confidence interval [CI] 10.20-115.07, p < 0.001). No significant heterogeneity (Q = 5.38, p = 0.25; I² = 26%) or publication bias (p = 1.000) was present. In the separate analysis of circumferential AWE and aneurysm rupture, we identified marked heterogeneity across studies (Q = 21.23, p < 0.001; I² = 86%). Further subgroup analysis considering the effect of aneurysm size showed that the strength of association between circumferential AWE and aneurysm rupture was significant in small aneurysms (<7 mm), with an OR of 26.12 (95% CI 6.11-111.75, p < 0.001), but limited in large aneurysms (OR = 0.56, 95% CI [0.21, 1.44], p = 0.23).

CONCLUSION

AWE on magnetic resonance vessel wall imaging is significantly and independently associated with aneurysm rupture and may become a promising imaging marker to predict aneurysm behavior and identify high-risk aneurysms.

Evaluation of the distribution and progression of intraluminal thrombus in abdominal aortic aneurysms using high-resolution MRI

BACKGROUND

Intraluminal thrombus (ILT) signal intensity on MRI has been studied as a potential marker of abdominal aortic aneurysm (AAA) progression.

PURPOSE

1) To characterize the relationship between ILT signal intensity and AAA diameter; 2) to evaluate ILT change over time; and 3) to assess the relationship between ILT features and AAA growth.

STUDY TYPE

Prospective.

SUBJECTS

Eighty AAA patients were imaged, and a subset (n = 41) were followed with repeated MRI for 16 ± 9 months.

FIELD STRENGTH/SEQUENCE

3D black-blood fast-spin-echo sequence at 3 T.

ASSESSMENT

ILT was designated as "bright" if the signal was greater than 1.2 times that of adjacent psoas muscle. AAAs were divided into three groups based on ILT: Type 1: bright ILT; Type 2: isointense ILT; Type 3: no ILT. During follow-up, an active ILT change was defined as new ILT formation or an increase in ILT signal intensity to bright; stable ILT was defined as no change in ILT type or ILT became isointense from bright previously.

STATISTICAL TESTS

Shapiro-Wilk test; Mann-Whitney U-test; Fisher's exact test; Kruskal-Wallis test; Spearman's r; intraclass correlation coefficient (ICC), Cohen's kappa.

RESULTS

AAAs with Type 1 ILT were larger than those with Types 2 and 3 ILT (5.1 ± 1.1 cm, 4.4 ± 0.9 cm, 4.2 ± 0.8 cm, P = 0.008). The growth rate of AAAs with Type 1 ILT was significantly greater than that of AAAs with Types 2 and 3 ILT (2.6 ± 2.5, 0.6 ± 1.3, 1.5 ± 0.6 mm/year, P = 0.01). During follow-up, AAAs with active ILT changes had a 3-fold increased growth rate compared with AAAs with stable ILT (3.6 ± 3.0 mm/year vs. 1.2 ± 1.5 mm/year, P = 0.008).

DATA CONCLUSION

AAAs with bright ILT are larger in diameter and grow faster. Active ILT change is associated with faster AAA growth. Black-blood MRI can characterize ILT features and monitor their change over time, which may provide new insights into AAA risk assessment.

LEVEL OF EVIDENCE

2 Technical Efficacy Stage: 5 J. Magn. Reson. Imaging 2019;50:994-1001.

Ruptured intranidal aneurysm of an arteriovenous malformation diagnosed by delay alternating with nutation for tailored excitation (DANTE)-prepared contrast-enhanced magnetic resonance imaging

This case report describes the usefulness of delay alternating with nutation for tailored excitation (DANTE)-prepared, contrast-enhanced magnetic resonance imaging (CE-MRI) for detecting the rupture site of an arteriovenous malformation (AVM). A ruptured intranidal aneurysm was confirmed histopathologically. Accurate non-invasive information about the possible rupture site of an AVM is critical for optimal treatment and evaluation. Vessel wall enhancement visualized by DANTE-prepared CE-MRI may be a useful tool for providing information about changes in inflammatory status and vulnerability to further developments.

Usefulness of Vessel Wall MR Imaging for Follow-Up after Stent-Assisted Coil Embolization of Intracranial Aneurysms

BACKGROUND AND PURPOSE

Follow-up with MRA for intracranial aneurysms after stent-assisted coiling is complicated by imaging artifacts. We evaluated the usefulness of an alternative method: vessel wall MR imaging.

MATERIALS AND METHODS

We conducted a single-center, retrospective review of medical records of 47 patients who underwent 3D TOF-MRA, vessel wall MRI, and DSA after stent-assisted coiling between March 2016 and January 2018. We evaluated the mean value of the signal intensity in the stented artery and the contralateral normal artery on vessel wall MRI. The quality of visualization was further compared between TOF-MRA and vessel wall MRI. Furthermore, we evaluated the diagnostic accuracy and concordance rate of TOF-MRA and vessel wall MRI for assessing the patency of the stented parent artery. DSA was used as a reference test.

RESULTS

The mean signal intensities of the stented and normal arteries on vessel wall MRI were not significantly different (P = .133). The mean scores for the visualization of the stented parent artery on vessel wall MRI were significantly superior to those of TOF-MRA images (P < .001). Vessel wall MRI reached an excellent positive predictive value (100%). However, TOF-MRA had a poor positive predictive value (11%; 95% CI, 9%-12%). The likelihood ratios of vessel wall MRI and TOF-MRA were 27.36 (P < .001) and 2.98 (P = .225), respectively. The concordance rate of vessel wall MRI and TOF-MRA with DSA for evaluating the state of the stented artery was 100% (κ = 1) and 28% (κ = 0.038), respectively.

CONCLUSIONS

Vessel wall MRI may be useful in evaluating the patency of stented arteries after stent-assisted coil embolization for intracranial aneurysms.

Wall enhancement of intracranial unruptured aneurysm is associated with increased rupture risk and traditional risk factors

OBJECTIVE

Aneurysm wall enhancement (AWE) on MRI has been considered an imaging marker to indicate active aneurysm inflammation, but no prospective studies have assessed the ability of AWE to predict rupture risk or growth. We aim to study the association of AWE with traditional risk factors and the estimated rupture risk.

METHODS

Seventy-seven patients (mean age, 58.4 ± 10.8 years; 57% female) with 88 asymptomatic intracranial saccular aneurysms underwent both 3-T high-resolution MRI and three-dimensional (3D) rotational digital subtraction angiography (DSA). Geometric and morphologic parameters were measured on DSA, and the degree of AWE on MRI was graded. One- and 5-year rupture risks of aneurysms were estimated using the UCAS and PHASES calculator. Parameters associated with AWE were analyzed using uni- and multivariate logistic regression.

RESULTS

Non-internal carotid artery location (OR 3.4, 95% CI 1.6-7.1) and aneurysm size (OR 1.9, 95% CI 1.3-2.7) were independently associated with AWE (p < 0.05). Aneurysms with AWE had significantly higher estimated rupture risk (1 and 5 year, 1.9% and 5.8%) than aneurysms without AWE (0.5% and 2.1%) (p < 0.001). Stronger and larger areas of AWE were correlated with the aneurysm size, size ratio and estimated rupture risk (R² ≥ 0.30) (p < 0.01).

CONCLUSIONS

Prospective assessment of asymptomatic intracranial aneurysms with MRI suggests that AWE is associated with traditional risk factors and estimated short- and medium-term rupture risk.

KEY POINTS

• AWE independently associates with aneurysm location and size. • Aneurysms with AWE have higher rupture risk than aneurysms without AWE. • Stronger and larger areas of AWE correlated with the aneurysm size, size ratio and rupture risk.

Magnetic resonance imaging of the intraluminal thrombus in abdominal aortic aneurysms: a quantitative and qualitative evaluation and correlation with growth rate

BACKGROUND

The role of the intraluminal thrombus (ILT) in abdominal aortic aneurysm (AAA) growth remains incompletely understood. MRI is superior to other methods in depicting the morphology of the ILT. This study brings preliminary, but novel information on the presence and morphological characteristics of the ILT and AAA growth rates in a screening cohort.

METHODS

Cohort study with 46 patients from the Viborg Vascular Trial. All underwent one non-contrast-enhanced magnetic resonance imaging (MRI) at the end of follow-up. ILT presence was noted and, if present, it was allocated to one of four morphological categories based on visual appearance and signal intensity on T2 weighted images.

RESULTS

The mean growth rate was 1.95 mm/year ±0.87 (SD). The observation time was 5.59±0.63 (SD) years. ILT was present in AAA size groups as follows: 30-34.9 mm 20.00%, 35-39.9 mm 88.89%, 40-44.9 mm 81.25%, 45-49.9 mm 100% and 50-54.9 mm 100%. Out of 46, 8 had no ILT at the time of MRI. The presence of any sort of ILT yielded a significantly increased unadjusted and an adjusted growth rate of 1.09 mm/year (95% CI: 0.48; 1.70) and 1.24 mm/year (95% CI: 0.64; 1.83), respectively. All four thrombus types were retrospectively associated with an increased recorded growth rate compared with "no thrombus". Presence of a thin circumferential thrombus was retrospectively associated with the highest increase in growth rate, viz. 2.09 mm/year (95% CI: 1.23; 2.95).

CONCLUSIONS

We observed faster growth rate in those AAA that had developed an ILT. Even faster growth was observed amongst those AAA containing a thin ILT located along the inner circumference.

Segmentation of lumen and outer wall of abdominal aortic aneurysms from 3D black-blood MRI with a registration based geodesic active contour model

Segmentation of the geometric morphology of abdominal aortic aneurysm is important for interventional planning. However, the segmentation of both the lumen and the outer wall of aneurysm in magnetic resonance (MR) image remains challenging. This study proposes a registration based segmentation methodology for efficiently segmenting MR images of abdominal aortic aneurysms. The proposed methodology first registers the contrast enhanced MR angiography (CE-MRA) and black-blood MR images, and then uses the Hough transform and geometric active contours to extract the vessel lumen by delineating the inner vessel wall directly from the CE-MRA. The proposed registration based geometric active contour is applied to black-blood MR images to generate the outer wall contour. The inner and outer vessel wall are then fused presenting the complete vessel lumen and wall segmentation. The results obtained from 19 cases showed that the proposed registration based geometric active contour model was efficient and comparable to manual segmentation and provided a high segmentation accuracy with an average Dice value reaching 89.79%.

Non-contrast 3D black blood MRI for abdominal aortic aneurysm surveillance: comparison with CT angiography

OBJECTIVES

Management of abdominal aortic aneurysms (AAAs) is based on diameter. CT angiography (CTA) is commonly used, but requires radiation and iodinated contrast. Non-contrast MRI is an appealing alternative that may allow better characterization of intraluminal thrombus (ILT). This study aims to 1) validate non-contrast MRI for measuring AAA diameter, and 2) to assess ILT with CTA and MRI.

METHOD

28 patients with AAAs (diameter 50.7 ± 12.3 mm) underwent CTA and non-contrast MRI. MRI was acquired at 3 T using 1) a conventional 3D gradient echo (GRE) sequence and 2) a 3D T1-weighted black blood fast-spin-echo sequence. Two radiologists independently measured the AAA diameter. The ratio of signal of ILT and adjacent psoas muscle (ILTr = signalILT/signalMuscle) was quantified.

RESULTS

Strong agreement between CTA and non-contrast MRI was shown for AAA diameter (intra-class coefficient > 0.99). Both approaches had excellent inter-observer reproducibility (ICC > 0.99). ILT appeared homogenous on CTA, whereas MRI revealed compositional variations. Patients with AAAs ≥5.5 cm and <5.5 cm had a variety of distributions of old/fresh ILT types.

CONCLUSIONS

Non-contrast 3D black blood MRI provides accurate and reproducible AAA diameter measurements as validated by CTA. It also provides unique information about ILT composition, which may be linked with elevated risk for disease progression.

KEY POINTS

• Non-contrast MRI is an appealing alternative to CTA for AAA management. • Non-contrast MRI can accurately measure AAA diameters compared to CTA. • MRI affords unique characterization of intraluminal thrombus composition.

Black-blood thrombus imaging (BTI): a contrast-free cardiovascular magnetic resonance approach for the diagnosis of non-acute deep vein thrombosis

BACKGROUND

Deep vein thrombosis (DVT) is a common but elusive illness that can result in long-term disability or death. Accurate detection of thrombosis and assessment of its size and distribution are critical for treatment decision-making. In the present study, we sought to develop and evaluate a cardiovascular magnetic resonance (CMR) black-blood thrombus imaging (BTI) technique, based on delay alternating with nutation for tailored excitation black-blood preparation and variable flip angle turbo-spin-echo readout, for the diagnosis of non-acute DVT. METHODS: This prospective study was approved by institutional review board and informed consent obtained from all subjects. BTI was first conducted in 11 healthy subjects for parameter optimization and then conducted in 18 non-acute DVT patients to evaluate its diagnostic performance. Two clinically used CMR techniques, contrast-enhanced CMR venography (CE-MRV) and three dimensional magnetization prepared rapid acquisition gradient echo (MPRAGE), were also conducted in all patients for comparison. All images obtained from patients were analyzed on a per-segment basis. Using the consensus diagnosis of CE-MRV as the reference, the sensitivity (SE), specificity (SP), positive and negative predictive values (PPV and NPV), and accuracy (ACC) of BTI and MPRAGE as well as their diagnostic agreement with CE-MRV were calculated. Besides, diagnostic confidence and interreader diagnostic agreement were evaluated for all three techniques.

RESULTS

BTI with optimized parameters effectively nulled the venous blood flow signal and allowed directly visualizing the thrombus within the black-blood lumen. Higher SE (90.4% vs 67.6%), SP (99.0% vs. 97.4%), PPV (95.4% vs. 85.6%), NPV (97.8% vs 92.9%) and ACC (97.4% vs. 91.8%) were obtained by BTI in comparison with MPRAGE. Good diagnostic confidence and excellent diagnostic and interreader agreements were achieved by BTI, which were superior to MPRAGE on detecting the chronic thrombus.

CONCLUSION

BTI allows direct visualization of non-acute DVT within the dark venous lumen and has the potential to be a reliable diagnostic tool without the use of contrast medium.

Upper Extremity Runoff: Pearls and Pitfalls in Computed Tomography Angiography and Magnetic Resonance Angiography

Upper extremity vasculature can be affected by various traumatic and nontraumatic pathologies; however, the evaluation of these arteries can be challenging for the radiologists as well as for the clinicians. After an accurate history and clinical examination, imaging plays a vital role in the diagnosis and treatment planning of these patients. Depending on the urgency and the indication, upper extremity arteries may be evaluated by ultrasonography with color Doppler, computed tomography (CT), magnetic resonance imaging (MRI), or digital subtraction angiography. This review article discusses relevant imaging anatomy of the upper extremity arteries, presents CT and MRI protocols, briefly describes the state-of-the-art CT and MRI of various pathologies affecting the upper extremity arteries, and summarizes the important pearls needed for busy practicing radiologist.