Comparison of a novel Compressed SENSE accelerated 3D modified relaxation-enhanced angiography without contrast and triggering with CE-MRA in imaging of the thoracic aorta

Imaging of the renal allograft vasculature without gadolinium contrast: Intraindividual comparison between relaxation-enhanced angiography without contrast and triggering (REACT) and 4D contrast-enhanced MR-angiography

BACKGROUND

Complications after kidney transplantation include transplant renal artery stenosis (TRAS), which can be assessed using Doppler ultrasonography, computed tomography angiography, and magnetic resonance angiography (MRA). Contrast-enhanced MRA (CE-MRA) has limitations, including potential allergic reactions, limited use in kidney failure, and uncertain long-term effects of gadolinium retention.

PURPOSE

To evaluate Relaxation-Enhanced Angiography without Contrast and Triggering (REACT), a novel 3D isotropic flow-independent non-CE-MRA pulse sequence, for imaging of the renal allograft vasculature by performing an intraindividual comparison to 4D CE-MRA at 3Tesla.

METHODS

Forty studies of 39 patients were included in this retrospective, single-centre study. Two board-certified radiologists independently evaluated MRA datasets for TRAS and rated their diagnostic confidence and the image quality of pelvic vessels using 5-point Likert scales (5 = excellent). Apparent signal- and contrast-to-noise ratios (aSNR/aCNR) were measured for arterial and venous graft vessels.

RESULTS

REACT (median acquisition time 04:33 min [IQR 3:58-5:20 min]) showed 90.0 % sensitivity and 100.0 % specificity for TRAS in almost perfect agreement (r = 0.97) with 4D CE-MRA (03:41 min [3:38-4:46 min], p = 0.001) and similar diagnostic confidence (REACT: 4.0 [4.0-4.0] vs. 4D CE-MRA: 4.0 [3.0-4.0], p = 0.54). Arterial image quality was comparable (4.0 [3.7-4.4] vs. 4.0 [4.0-4.4], p = 0.49) whereas veins yielded higher scores in REACT (3.2 [3.0-3.5] vs. 2.4 [2.0-3.0], p < 0.001). Transplant renal artery (mean ± SD; 44.5 ± 18.2 vs. 45.9 ± 21.0, p = 0.71; 36.3 ± 15.0 vs. 41.0 ± 20.0, p = 0.16) and vein (37.1 ± 19.8 vs. 30.3 ± 15.2, p = 0.06; 29.4 ± 17.1 vs. 25.0 ± 14.7, p = 0.17) showed no difference in aSNR and aCNR.

CONCLUSION

REACT provides accurate detection of TRAS with image quality comparable to 4D CE-MRA, offering a risk-free alternative for imaging after renal transplantation.

Expert Panel on Vascular Imaging and Interventional Radiology, Ripley B, Scheidt MJ, Aghayev A, Kim CY, Hedgire SS, Ahmed O, Ahmad S, Clough RE, DeMartino RR, Ferencik M, Hughes GC, Klitzke AK, Steenburg SD, Thomas R, Wells BJ, Wolf SJ, Pinchot JW, Majdalany BS. ACR Appropriateness Criteria® Thoracic Aortic Aneurysm or Dissection-Treatment Planning and Follow-Up: 2024 Update

Diseases of the thoracic aorta include two broad categories: aneurysmal dilation involving all three layers of the intact aortic wall, and acute aortic syndromes, wherein at least one layer of the aortic wall is disrupted, such as in aortic dissection. These diseases carry a variable risk of subsequent aortic rupture, which is associated with high morbidity and mortality. Imaging is critical in the diagnosis, surveillance, and treatment of this constellation of diseases. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision process support the systematic analysis of the medical literature from peer reviewed journals. Established methodology principles such as Grading of Recommendations Assessment, Development, and Evaluation or GRADE are adapted to evaluate the evidence. The RAND/UCLA Appropriateness Method User Manual provides the methodology to determine the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where peer reviewed literature is lacking or equivocal, experts may be the primary evidentiary source available to formulate a recommendation.

Isotropic, high-resolution, whole-chest inversion recovery contrast-enhanced magnetic resonance angiography in under 4.5 min using image-based navigator fluoro trigger

Background

Serial assessment of the thoracic aorta with magnetic resonance angiography (MRA) is desirable due to 3D volumetric dataset, high spatial resolution, and lack of ionizing radiation. Electrocardiogram (ECG) gated, contrast-enhanced (CE), inversion recovery gradient echo MRA is efficient and historically provides low artifact burden, but the window for imaging with weak albumin binding extracellular gadolinium based contrast agents is small. Our purpose was to acquire whole-chest gated CE-MRA with 1.2 mm3 resolution using image-based navigator (iNAV) for motion correction/contrast monitoring, and variable density sampling in 4-5 min. Image quality and vessel diameter reproducibility are assessed against time resolved MRA (TR-MRA).

Methods

iNAV CE-MRA and TR-MRA were obtained prospectively in 40 patients and reviewed by 3 blinded cardiologists for vessel diameter and image quality rated on a four point scale: (1) non-diagnostic; (2) poor-significant blurring; (3) good-mild blurring; and (4) excellent. Reproducibility and image quality were evaluated using the concordance correlation statistic and Cohen's kappa with mean differences evaluated using paired t-tests and repeat-measures ANOVA.

Results

iNAV CE-MRA scan time was 4.2 ± 0.7 min. iNAV CE-MRA quality score was higher (p < .001); average difference was 1.4 ± .08 at the sinus of Valsalva (SOV), 1.3 ± .08 at the sinotubular junction (STJ), and .87 ± .10 at the ascending aorta (AAO). Major/minor diameter interobserver agreement was better for iNAV CE-MRA (SOV ICC = .87-.93; STJ ICC = .95-.96; AAO ICC = .96-.97) vs. TR-MRA (SOV ICC = .69-.82; STJ ICC = .78-.83; AAO ICC = .89), as was intraobserver agreement (SOV ICC = .93-.95; STJ ICC = .94-.96; AAO ICC = .96-.97) vs. TR-MRA (SOV ICC = .81-.88; STJ ICC = .72-.73; AAO ICC = .87-.93).

Conclusion

iNAV CE-MRA is feasible within a clinically reasonable scan time, provides superior image quality, and measurement reproducibility vs. TR-MRA.

Feasibility of magnetization-transfer-contrast relaxation-enhanced angiography without contrast and triggering (REACT) imaging at 1.5 T combined with deep learning-based reconstruction for cardiovascular visualization

Background

Relaxation-enhanced angiography without contrast and triggering (REACT) is a flow-independent three-dimensional (3D) magnetic resonance angiography sequence designed to minimize artifacts using the Dixon method and an inversion recovery pre-pulse. A magnetization transfer contrast (MTC) pre-pulse (MTC-REACT) may further enhance image quality. This study evaluates the feasibility of MTC-REACT and examines deep learning-based reconstruction to improve image quality for pulmonary veins.

Methods

This study was approved by the institutional review board. Twenty participants were prospectively recruited. Ten-fold undersampling was applied for REACT and MTC-REACT data acquisition. The inline compressed sense (CS) reconstruction algorithm, and an off-line Adaptive-CS-Net algorithm, were used for MTC-REACT and REACT image reconstruction. Commercially available analysis software was used for multi-planar reformatting, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) measurements, and image quality analysis. Categorical data were compared with a Wilcoxon signed ranks test and normally distributed variables with a t-test.

Results

The Adaptive CS-Net reconstructed MTC-REACT images provided significantly higher SNR and CNR for right pulmonary veins (SNR 33.9±4.1, 30.3±3.4; CNR 33.3±3.4, 29.6±4.3), and left pulmonary veins (SNR 35.0±3.6, 31.2±4.3; CNR 34.6±4.2, 30.6±4.4) with all P values <0.05 compared to the CS-reconstructed MTC-REACT sequence. When Adaptive CS-Net reconstruction is used for both techniques, MTC-REACT images displayed significantly higher SNR and CNR compared to the REACT sequence for only left pulmonary veins (SNR 35±3.3, 32.4±4.6; CNR 34.6±3.4, 31.8±4.6). The Adaptive-CS-Net reconstructed MTC-REACT sequence consistently outperforms the CS-reconstructed MTC-REACT for pulmonary artery and vein imaging.

Conclusions

The Adaptive-CS-Net reconstructed MTC-REACT images consistently deliver superior CNR, and SNR compared to the CS reconstructed images for pulmonary veins. Notably, the MTC-REACT technique enhances image quality for pulmonary veins compared to the REACT sequence, irrespective of the deep-learning reconstruction method's impact.

Non-contrast-enhanced MR-angiography of the abdominal arteries: intraindividual comparison between relaxation-enhanced angiography without contrast and triggering (REACT) and 4D contrast-enhanced MR-angiography

PURPOSE

To evaluate Relaxation-Enhanced Angiography without Contrast and Triggering (REACT), a novel 3D isotropic flow-independent non-contrast-enhanced magnetic resonance angiography (non-CE-MRA) for imaging of the abdominal arteries, by comparing image quality and assessment of vessel stenosis intraindidually with 4D CE-MRA.

METHODS

Thirty patients (mean age 35.7 ± 16.8 years; 20 females) referred for the assessment of the arterial abdominal vasculature at 3 T were included in this retrospective, single-centre study. The protocol comprised both 4D CE-MRA and REACT (navigator-triggering, Compressed SENSE factor 10, nominal scan time 02:54 min, and reconstructed voxel size 0.78 × 0.78 × 0.85  mm3). Two radiologists independently evaluated 14 abdominal artery segments for stenoses, anatomical variants, and vascular findings (aortic dissection, abdominal aorta aneurysms and its branches). Subjective image quality was assessed using a 4-point Likert scale (1 = non-diagnostic, 4 = excellent).

RESULTS

REACT had a total acquisition time of 5:36 ± 00:40 min, while 4D CE-MRA showed a total acquisition time (including the native scan and bolus tracking sequence) of 3:45 ± 00:59 min (p = 0.001). Considering 4D CE-MRA as the reference standard, REACT achieved a sensitivity of 87.5% and specificity of 100.0% for relevant (≥ 50%) stenosis while detecting 89.5% of all vascular findings other than stenosis. For all vessels combined, subjective vessel quality was slightly higher in 4D CE-MRA (3.0 [IQR: 2.0; 4.0.]; P = 0.040), although comparable to REACT (3.0 [IQR: 2.0; 3.5]).

CONCLUSION

In a short scan time of about 5 min, REACT provides good diagnostic performance for detection of relevant stenoses, variants, and vascular findings of the abdominal arteries, while yielding to 4D CE-MRA comparable image quality.

Assessment of the thoracic aorta after aortic root replacement and/or ascending aortic surgery using 3D relaxation-enhanced angiography without contrast and triggering

Objective

Relaxation-Enhanced Angiography without Contrast and Triggering (REACT) is a novel 3D isotropic flow-independent non-contrast-enhanced MRA (non-CE-MRA) and has shown promising results in imaging of the thoracic aorta, primarily in patients without prior aortic surgery. The purpose of this study was to evaluate the performance of REACT after surgery of the aortic root and/or ascending aorta by performing an intraindividual comparison to CE-MRA.

Material and methods

This retrospective single center study included 58 MRI studies of 34 patients [mean age at first examination 45.64 ± 11.13 years, 31 (53.44%) female] after ascending aortic surgery. MRI was performed at 1.5T using REACT (ECG- and respiratory-triggering, Compressed SENSE factor 9, acquired spatial resolution 1.69 × 1.70 × 1.70 mm3) and untriggered 3D CE-MRA. Independently, two radiologists measured maximum and minimum vessel diameters (inner-edge) and evaluated image quality and motion artifacts on 5-point scales (5 = excellent) for the following levels: mid-graft, distal anastomosis, ascending aorta, aortic arch, and descending aorta. Additionally, readers evaluated MRAs for the presence of aortic dissection (AD) and graded the quality of depiction as well as their diagnostic confidence using 5-point scales (5 = excellent).

Results

Vessel diameters were comparable between CE-MRA and REACT (total acquisition time: 05:42 ± 00:38 min) with good to excellent intersequence agreement (ICC = 0.86-0.96). At the distal anastomosis (minimum/maximum, p < .001/p = .002) and at the ascending aorta (minimum/maximum, p = .002/p = .06), CE-MRA yielded slightly larger diameters. Image quality for all levels combined was higher in REACT [median (IQR); 3.6 (3.2-3.93) vs. 3.9 (3.6-4.13), p = .002], with statistically significant differences at mid-graft [3.0 (2.5-3.63) vs. 4.0 (4.0-4.0), p < .001] and ascending aorta [3.25 (3.0-4.0) vs. 4.0 (3.5-4.0), p < .001]. Motion artifacts were more present in CE-MRA at all levels (p < .001). Using CE-MRA as the standard of reference, readers detected all 25 cases of residual AD [Stanford type A: 21 (84.0%); Stanford type B: 4 (16.0%)] in REACT with equal quality of depiction [4.0 (3.0-4.5) vs. 4.0 (3.0-4.0), p = .41] and diagnostic confidence [4.0 (3.0-4.0) vs. 4.0 (3.0-4.0), p = .81) in both sequences.

Conclusions

This study indicates the feasibility of REACT for assessment of the thoracic aorta after ascending aortic surgery and expands its clinical use for gadolinium-free MRA to these patients.

Non-contrast-enhanced MR-angiography of Extracranial Arteries in Acute Ischemic Stroke at 1.5 Tesla Using Relaxation-Enhanced Angiography Without Contrast and Triggering (REACT)

PURPOSE

To evaluate a novel flow-independent sequence (Relaxation-Enhanced Angiography without Contrast and Triggering (REACT)) for imaging of the extracranial arteries in acute ischemic stroke (AIS) at 1.5 T.

METHODS

This retrospective single-center study included 47 AIS patients who received REACT (scan time: 3:01 min) and contrast-enhanced MRA (CE-MRA) of the extracranial arteries at 1.5 T in clinical routine. Two radiologists assessed scans for proximal internal carotid artery (ICA) stenosis, stated their diagnostic confidence and rated the image quality of cervical arteries, impact of artifacts and image noise. Apparent signal- and contrast-to-noise ratios (aSNR/aCNR) were measured for the common carotid artery and ICA.

RESULTS

REACT achieved a sensitivity of 95.0% and a specificity of 97.3% for ICA stenoses in high agreement with CE-MRA (κ = 0.83) with equal diagnostic confidence (p = 0.22). Image quality was rated higher for CE-MRA at the aortic arch (p = 0.002) and vertebral arteries (p < 0.001), whereas REACT provided superior results for the extracranial ICA (p = 0.008). Both sequences were only slightly affected by artifacts (p = 0.60), while image noise was more pronounced in CE-MRA (p < 0.001) in line with higher aSNR (p < 0.001) and aCNR (p < 0.001) values in REACT for all vessels.

CONCLUSION

Given its good diagnostic performance while yielding comparable image quality and scan time to CE-MRA, REACT may be suitable for the imaging of the extracranial arteries in acute ischemic stroke at 1.5 T.

Accuracy of 3D CE-MRA combined with ultrasound microbubble angiography for the diagnosis of lower extremity atherosclerotic occlusion

OBJECTIVES

To evaluate the diagnostic performance of 3D contrast-enhanced magnetic resonance angiography (3D CE-MRA) and ultrasound microbubble angiography, individually and combined, using digital subtraction angiography (DSA) as the gold standard.

METHODS

This retrospective study included 60 patients diagnosed with lower extremity arterial stenosis occlusion (LEASO) from October 2019 to July 2022. All patients underwent 3D CE-MRA and ultrasound microbubble angiography, collectively assessing 470 arterial segments. The diagnostic accuracy, sensitivity, and specificity of 3D CE-MRA, ultrasound microbubble angiography, and their combination were evaluated compared to DSA findings. Kappa statistics were used to analyze the consistency of combined diagnostic efficacy.

RESULTS

The cohort included subjects aged 56 to 85 years, with a mean age of 65.42 ± 12.65 years. The diagnostic accuracy of 3D CE-MRA was 91.70%, with sensitivity and specificity of 99.72% and 65.49%, respectively. Ultrasound microbubble angiography revealed an 87.66% accuracy with sensitivity and specificity of 99.13% and 56.35%, respectively. When combined, the diagnostic accuracy was improved to 96.17%, maintaining a sensitivity of 100%, although specificity decreased to 50.44%. The Youden index improved to 96.17%, and the Kappa value of 0.951 indicated excellent agreement, demonstrating superior performance over individual modalities.

CONCLUSION

The combination of 3D CE-MRA and ultrasound microbubble angiography exhibits enhanced diagnostic precision for detecting and grading LEASO compared to either modality alone. Despite reduced specificity, the combined approach increases overall diagnostic efficacy, advocating its potential for more comprehensive clinical evaluations. Further studies are warranted to confirm these findings and assess their clinical implications.

A novel non-contrast agent-enhanced 3D whole-heart magnetic resonance sequence for congenital heart disease patients: the REACT Study

BACKGROUND

The three-dimensional balanced-steady-state-free-precession (3D bSSFP) whole-heart (WH) technique has long been used to depict cardiac morphology in congenital heart disease (CHD) but is prone to banding artifacts. The Relaxation Enhanced Angiography without Contrast and Triggering (REACT) sequence is an alternative method that is resistant to off-resonance effects.

OBJECTIVE

To evaluate cardiac structures and great vessels in CHD patients using 3D WH REACT sequence and compare it to 3D WH bSSFP sequence.

MATERIALS AND METHODS

This study was approved by the Institutional Review Board. Thirty CHD patients were prospectively enrolled. Contrast-to-noise ratio (CNR), image quality, and cross-sectional area (CSA) were analyzed. Categorical data were compared with a Wilcoxon signed-rank test and normally distributed variables with a t-test.

RESULTS

Thirty patients (16 females) participated in this study (median age 17, range 5 months to 52 years). REACT showed higher CNR in all pulmonary veins (all P<0.05), while 3D bSSFP had higher CNR in the right ventricle (P<0.001) and right pulmonary artery, (P=0.04). Image quality favored 3D bSSFP in the right atrium and ventricle (both P<0.001), main pulmonary artery (P=0.02), and coronary arteries (left: P<0.001, right: P=0.01). REACT outperformed 3D bSSFP for the pulmonary veins (all P<0.05) from image quality perspective. CSA measurements were not significantly different between REACT and 3D bSSFP (all P≥0.05).

CONCLUSION

The REACT method is associated with improved image quality and CNR for pulmonary veins, with CSA measurements concordant with 3D bSSFP in CHD patients, while bSSFP shows better performance for imaging cardiac chambers and coronary arteries.

Flow independent black blood imaging with a large FOV from the neck to the aortic arch: A feasibility study at 3 tesla

PURPOSE

To investigate the feasibility of obtaining black-blood imaging with a large FOV from the neck to the aortic arch at 3 T using a newly modified Relaxation-Enhanced Angiography without Contrast and Triggering for Black-Blood Imaging (REACT-BB).

MATERIALS AND METHODS

REACT-BB provides black-blood images by adjusting the inversion time (TI) in REACT to the null point of blood. The optimal TI for REACT-BB was investigated in 10 healthy volunteers with TI varied from 200 ms to 1400 ms. Contrast ratios were calculated between muscle and three branch arteries of the aortic arch. Additionally, a comparison between REACT-BB and MPRAGE involved evaluating the depiction of high-intensity plaques in 222 patients with stroke or transient ischemic attack. Measurements included plaque-to-muscle signal intensity ratios (PMR), plaque volumes, and carotid artery stenosis rates in 60 patients with high-intensity plaques in carotid arteries.

RESULTS

REACT-BB with TI = 850 ms produced the black-blood image with the best contrast between blood and background tissues. REACT-BB outperformed MPRAGE in depicting high-intensity plaques in the aortic arch (55.4% vs 45.5%) and exhibited superior overall image quality in visual assessment (3.31 ± 0.70 vs 2.89 ± 0.73; p < 0.05). Although the PMR of REACT-BB was significantly lower than MPRAGE (2.227 ± 0.601 vs 2.285 ± 0.662; P < 0.05), a strong positive correlation existed between REACT-BB and MPRAGE (ρ = 0.935; P < 0.05), and all high-intensity plaques that MPRAGE detected were clearly detected by REACT-BB.

CONCLUSION

REACT-BB provides black-blood images with uniformly suppressed fat and blood signals over a large FOV from the neck to the aortic arch with comparable or better high-signal plaque depiction than MPRAGE.

Review of strategies to reduce the contamination of the water environment by gadolinium-based contrast agents

Gadolinium-based contrast agents (GBCA) are essential for diagnostic MRI examinations. GBCA are only used in small quantities on a per-patient basis; however, the acquisition of contrast-enhanced MRI examinations worldwide results in the use of many thousands of litres of GBCA per year. Data shows that these GBCA are present in sewage water, surface water, and drinking water in many regions of the world. Therefore, there is growing concern regarding the environmental impact of GBCA because of their ubiquitous presence in the aquatic environment. To address the problem of GBCA in the water system as a whole, collaboration is necessary between all stakeholders, including the producers of GBCA, medical professionals and importantly, the consumers of drinking water, i.e. the patients. This paper aims to make healthcare professionals aware of the opportunity to take the lead in making informed decisions about the use of GBCA and provides an overview of the different options for action.In this paper, we first provide a summary on the metabolism and clinical use of GBCA, then the environmental fate and observations of GBCA, followed by measures to reduce the use of GBCA. The environmental impact of GBCA can be reduced by (1) measures focusing on the application of GBCA by means of weight-based contrast volume reduction, GBCA with higher relaxivity per mmol of Gd, contrast-enhancing sequences, and post-processing; and (2) measures that reduce the waste of GBCA, including the use of bulk packaging and collecting residues of GBCA at the point of application.Critical relevance statement This review aims to make healthcare professionals aware of the environmental impact of GBCA and the opportunity for them to take the lead in making informed decisions about GBCA use and the different options to reduce its environmental burden.Key points• Gadolinium-based contrast agents are found in sources of drinking water and constitute an environmental risk.• Radiologists have a wide spectrum of options to reduce GBCA use without compromising diagnostic quality.• Radiology can become more sustainable by adopting such measures in clinical practice.

Highly accelerated, Dixon-based non-contrast MR angiography versus high-pitch CT angiography

OBJECTIVES

To compare a novel, non-contrast, flow-independent, 3D isotropic magnetic resonance angiography (MRA) sequence that combines respiration compensation, electrocardiogram (ECG)-triggering, undersampling, and Dixon water-fat separation with an ECG-triggered aortic high-pitch computed tomography angiography (CTA) of the aorta.

MATERIALS AND METHODS

Twenty-five patients with recent CTA were scheduled for non-contrast MRA on a 3 T MRI. Aortic diameters and cross-sectional areas were measured on MRA and CTA using semiautomatic measurement tools at 11 aortic levels. Image quality was assessed independently by two radiologists on predefined aortic levels, including myocardium, proximal aortic branches, pulmonary veins and arteries, and the inferior (IVC) and superior vena cava (SVC). Image quality was assessed on a 5-point Likert scale.

RESULTS

All datasets showed diagnostic image quality. Visual grading was similar for MRA and CTA regarding overall image quality (0.71), systemic arterial image quality (p = 0.07-0.91) and pulmonary artery image quality (p = 0.05). Both readers favored MRA for SVC and IVC, while CTA was preferred for pulmonary veins (all p < 0.05). No significant difference was observed in aortic diameters or cross-sectional areas between native MRA and contrast-enhanced CTA (p = 0.08-0.94).

CONCLUSION

The proposed non-contrast MRA enables robust imaging of the aorta, its proximal branches and the pulmonary arteries and great veins with image quality and aortic diameters and cross-sectional areas comparable to that of CTA. Moreover, this technique represents a suitable free-breathing alternative, without the use of contrast agents or ionizing radiation. Therefore, it is especially suitable for patients requiring repetitive imaging.

Three-dimensional aortic geometry mapping via registration of non-gated contrast-enhanced or gated and respiratory-navigated MR angiographies

BACKGROUND

The measurement of aortic dimensions and their evolution are key in the management of patients with aortic diseases. Manual assessment, the current guideline-recommended method and clinical standard, is subjective, poorly reproducible, and time-consuming, limiting the capacity to track aortic growth in everyday practice. Aortic geometry mapping (AGM) via image registration of serial computed tomography angiograms outperforms manual assessment, providing accurate and reproducible 3D maps of aortic diameter and growth rate. This observational study aimed to evaluate the accuracy and reproducibility of AGM on non-gated contrast-enhanced (CE-) and cardiac- and respiratory-gated (GN-) magnetic resonance angiographies (MRA).

METHODS

Patients with thoracic aortic disease followed with serial CE-MRA (n = 30) or GN-MRA (n = 15) acquired at least 1 year apart were retrospectively and consecutively identified. Two independent observers measured aortic diameters and growth rates (GR) manually at several thoracic aorta reference levels and with AGM. Agreement between manual and AGM measurements and their inter-observer reproducibility were compared. Reproducibility for aortic diameter and GR maps assessed with AGM was obtained.

RESULTS

Mean follow-up was 3.8 ± 2.3 years for CE- and 2.7 ± 1.6 years for GN-MRA. AGM was feasible in the 93% of CE-MRA pairs and in the 100% of GN-MRA pairs. Manual and AGM diameters showed excellent agreement and inter-observer reproducibility (ICC>0.9) at all anatomical levels. Agreement between manual and AGM GR was more limited, both in the aortic root by GN-MRA (ICC=0.47) and in the thoracic aorta, where higher accuracy was obtained with GN- than with CE-MRA (ICC=0.55 vs 0.43). The inter-observer reproducibility of GR by AGM was superior compared to manual assessment, both with CE- (thoracic: ICC= 0.91 vs 0.51) and GN-MRA (root: ICC=0.84 vs 0.52; thoracic: ICC=0.93 vs 0.60). AGM-based 3D aortic size and growth maps were highly reproducible (median ICC >0.9 for diameters and >0.80 for GR).

CONCLUSION

Mapping aortic diameter and growth on MRA via 3D image registration is feasible, accurate and outperforms the current manual clinical standard. This technique could broaden the possibilities of clinical and research evaluation of patients with aortic thoracic diseases.

The feasibility of relaxation-enhanced angiography without contrast and triggering for preprocedural planning of transcatheter aortic valve implantation

Background

Cardiovascular MRI is advantageous in transcatheter aortic valve implantation (TAVI) planning. This study aimed to evaluate the feasibility of comprehensive non-contrast MRI [relaxation-enhanced angiography without contrast and triggering (REACT)] combined with a three-dimensional whole-heart MRI protocol for preprocedural planning of TAVI vs. computed tomography angiography (CTA).

Methods

Thirty patients with severe aortic stenosis were prospectively enrolled. The anatomical properties of the aortic root anatomy, including the perimeter and area of the virtual aortic valve annulus and coronary heights, were determined from 3D whole-heart MRI and cardiac CTA (CCTA) images, respectively. The diameters of the aorta (thoracic and abdominal aorta) and iliofemoral arteries were measured from REACT and aortic CTA (ACTA) images, respectively. A paired t-test was used to compare these two modalities. Bland-Altman plots were used to assess cardiovascular MRI and CTA measurements. Transcatheter heart valve (THV) sizing was performed based on CCTA measurements and compared with 3D whole-heart MRI measurements. The extent of annular calcification on 3D whole-heart MRI images was evaluated by a four-point grading scale and compared with CCTA data.

Results

All 30 patients completed CTA and cardiovascular MRI examinations, with the TAVI procedure being administered in 25 patients. The mean acquisition time of the comprehensive MRI protocol was 18 ± 3.2 min. There were no significant differences between ACTA and REACT data in regard to the diameters of aortic and iliofemoral arteries, including the ascending thoracic aorta (37 ± 4.6 mm vs. 37.7 ± 5.2 mm, p = 0.085), descending thoracic aorta (24.3 ± 2.8 mm vs. 24.3 ± 2.8 mm, p = 0.832), abdominal aorta (20.9 ± 2.5 mm vs. 20.8 ± 2.5 mm, p = 0.602), bilateral common iliac arteries (right: 8.36 ± 1.44 mm vs. 8.42 ± 1.27 mm, p = 0.590; left: 8.61 ± 1.71 mm vs. 8.86 ± 1.46 mm, p = 0.050), and bilateral femoral arteries (right: 6.77 ± 1.06 mm vs. 6.87 ± 1.00 mm, p = 0.157; left: 6.75 ± 1.02 mm vs. 6.90 ± 0.80 mm, p = 0.142). Both modalities showed similar aortic valve morphology and semi-quantitative valve calcification (all, p's > 0.05). Overall agreement for implanted THV was found in all 25 (100%) patients assessed with both modalities.

Conclusion

REACT combined with 3D whole-heart MRI enables reliable measurements of aortic root anatomy, annular calcification, and aorta and iliofemoral access in patients under evaluation for TAVI.

Thoracic aorta diameters in Marfan patients: Intraindividual comparison of 3D modified relaxation-enhanced angiography without contrast and triggering (REACT) with transthoracic echocardiography

OBJECTIVE

To compare the measurement of aortic diameters using a novel flow-independent MR-Angiography (3D modified Relaxation-Enhanced Angiography without Contrast and Triggering (modified REACT)) and transthoracic echocardiography (TTE) in Marfan syndrome (MFS) patients.

MATERIAL AND METHODS

This retrospective, single-center analysis included 46 examinations of 32 MFS patients (mean age 37.5 ± 11.3 years, 17 women, no prior aortic surgery) who received TTE and 3D modified REACT (ECG- and respiratory-triggering, Compressed SENSE factor 9 for acceleration of image acquisition) of the thoracic aorta. Aortic diameters (sinus of Valsalva (SV), sinotubular junction (STJ), and ascending aorta (AoA)) were independently measured by two cardiologists in TTE (leading-edge) and two radiologists in modified REACT (inner-edge, using multiplanar reconstruction). Intraclass correlation coefficient, Bland-Altman analyses, and Pearson's correlation (r) were used to assess agreement between observers and methods.

RESULTS

Interobserver correlation at the SV, STJ, and AoA were excellent for both, TTE (ICC = 0.95-0.98) and modified REACT (ICC = 0.99-1.00). There was no significant difference between TTE and modified REACT for diameters measured at the SV (39.24 ± 3.24 mm vs. 39.63 ± 3.76 mm; p = 0.26; r = 0.78) and the STJ (35.16 ± 4.47 mm vs. 35.37 ± 4.74 mm; p = 0.552; r = 0.87). AoA diameters determined by TTE were larger than in modified REACT (34.29 ± 5.31 mm vs. 30.65 ± 5.64 mm; p < 0.01; r = 0.74). The mean scan time of modified REACT was 05:06 min ± 02:47 min, depending on the patient's breathing frequency and heart rate.

CONCLUSIONS

Both TTE and modified REACT showed a strong correlation for all aortic levels; however, at the AoA, diameters were larger using TTE, mostly due to the limited field of view of the latter with measurements being closer to the aortic valve. Given the excellent interobserver correlation and the strong agreement with TTE, modified REACT represents an attractive method to depict the thoracic aorta in MFS patients.

Respiratory-Triggered Flow-Independent Noncontrast Non-ECG-Gated MRV (REACT) Versus CE-MRV for Central Venous Evaluation in Children and Young Adults: A Six-Reader Study

BACKGROUND. Contrast-enhanced MRI is commonly used to evaluate thoracic central venous patency in children and young adults. A flow-independent noncontrast non-ECG-gated 3D MRA-MR venography (MRV) technique described in 2019 as "relaxation-enhanced angiography without contrast and triggering (REACT)" may facilitate such evaluation. OBJECTIVE. The purpose of our study was to compare image quality, diagnostic confidence, and interreader agreement between respiratory-triggered REACT and 3D Dixon-based contrast-enhanced MRV (CE-MRV) for evaluating thoracic central venous patency in children and young adults. METHODS. This retrospective study included 42 consecutive children and young adults who underwent MRI of the neck and chest to evaluate central venous patency between August 2019 and January 2021 (median age, 5.2 years; IQR, 1.4-15.1 years; 22 female patients and 20 male patients). Examinations included respiratory-triggered REACT and navigator-gated CE-MRV sequences based on the institution's standard-of-care protocol. Six pediatric radiologists from four different institutions independently reviewed REACT and CE-MRV sequences; they assessed overall image quality (scale, 1-5; 5 = excellent), diagnostic confidence (scale, 1-5; 5 = extremely confident), and presence of clinically relevant artifact(s). Readers classified seven major central vessels as normal or abnormal (e.g., narrowing, thrombosis, or occlusion). Analysis used Wilcoxon signed rank and McNemar tests and Fleiss kappa coefficients. RESULTS. The distribution of overall image quality scores was higher (p = .02) for REACT than for CE-MRV for one reader (both sequences: median score, 5). Image quality scores were not significantly different between the sequences for the remaining five readers (all p > .05). Diagnostic confidence scores and frequency of clinically relevant artifact(s) were not significantly different between sequences for any reader (all p > .05). Interreader agreement for vessel classification as normal or abnormal was similar between sequences for all seven vessels (REACT: κ = 0.37-0.81; CE-MRV: κ = 0.34-0.81). Pooling readers and vessels, 65.4% of vessels were normal by both sequences; 18.7%, abnormal by both sequences; 9.8%, abnormal by REACT only; and 6.1%, abnormal by CE-MRV only. CONCLUSION. Respiratory-triggered REACT, in comparison with CE-MRV, showed no significant difference in image quality (aside from for one of six readers), diagnostic confidence, or frequency of artifact(s), with similar interreader agreement for vessel classification as normal or abnormal. CLINICAL IMPACT. High-resolution 3D MRV performed without IV contrast material can be used to assess central venous patency in children and young adults.

Recent advances in highly accelerated 3D MRI

Three-dimensional MRI has gained increasing popularity in various clinical applications due to its improved through-plane spatial resolution, which enhances the detection of subtle abnormalities and provides valuable clinical information. However, the long data acquisition time and high computational cost pose significant challenges for 3D MRI. In this comprehensive review article, we aim to summarize the latest advancements in accelerated 3D MR techniques. Covering over 200 remarkable research studies conducted over the past 20 years, we explore the development of MR signal excitation and encoding, advancements in reconstruction algorithms, and potential clinical applications. We hope that this survey serves as a valuable resource, providing insights into the current state of the field and serving as a guide for future research in accelerated 3D MRI.

Non-contrast free-breathing 3D cardiovascular magnetic resonance angiography using REACT (relaxation-enhanced angiography without contrast) compared to contrast-enhanced steady-state magnetic resonance angiography in complex pediatric congenital heart disease at 3T

BACKGROUND

To evaluate the great vessels in young children with complex congenital heart disease (CHD) using non-contrast cardiovascular magnetic resonance angiography (CMRA) based on three-dimensional relaxation-enhanced angiography without contrast (REACT) in comparison to contrast-enhanced steady-state CMRA.

METHODS

In this retrospective study from April to July 2021, respiratory- and electrocardiogram-gated native REACT CMRA was compared to contrast-enhanced single-phase steady-state CMRA in children with CHD who underwent CMRA at 3T under deep sedation. Vascular assessment included image quality (1 = non-diagnostic, 5 = excellent), vessel diameter, and diagnostic findings. For statistical analysis, paired t-test, Pearson correlation, Bland-Altman analysis, Wilcoxon test, and intraclass correlation coefficients (ICC) were applied.

RESULTS

Thirty-six young children with complex CHD (median 4 years, interquartile range, 2-5; 20 males) were included. Native REACT CMRA was obtained successfully in all patients (mean scan time: 4:22 ± 1:44 min). For all vessels assessed, diameters correlated strongly between both methods (Pearson r = 0.99; bias = 0.04 ± 0.61 mm) with high interobserver reproducibility (ICC: 0.99 for both CMRAs). Native REACT CMRA demonstrated comparable overall image quality to contrast-enhanced CMRA (3.9 ± 1.0 vs. 3.8 ± 0.9, P = 0.018). With REACT CMRA, better image quality was obtained at the ascending aorta (4.8 ± 0.5 vs. 4.3 ± 0.8, P < 0.001), coronary roots (e.g., left: 4.1 ± 1.0 vs. 3.3 ± 1.1, P = 0.001), and inferior vena cava (4.6 ± 0.5 vs. 3.2 ± 0.8, P < 0.001). In all patients, additional vascular findings were assessed equally with native REACT CMRA and the contrast-enhanced reference standard (n = 6).

CONCLUSION

In young children with complex CHD, REACT CMRA can provide gadolinium-free high image quality, accurate vascular measurements, and equivalent diagnostic quality compared to standard contrast-enhanced CMRA.

Role of Cardiovascular Magnetic Resonance to Assess Cardiovascular Inflammation

Cardiovascular inflammatory diseases still represent a challenge for physicians. Inflammatory cardiomyopathy, pericarditis, and large vessels vasculitis can clinically mimic a wide spectrum of diseases. While the underlying etiologies are varied, the common physio-pathological process is characterized by vasodilation, exudation, leukocytes infiltration, cell damage, and fibrosis. Cardiovascular magnetic resonance (CMR) allows the visualization of some of these diagnostic targets. CMR provides not only morphological and functional assessment but also tissue catheterization revealing edema, hyperemia, tissue injury, and reparative fibrosis through T2 weighted images, early and late gadolinium enhancement, and parametric mapping techniques. Recent developments showed the role of CMR in the identification of ongoing inflammation also in other CV diseases like myocardial infarction, atherosclerosis, arrhythmogenic and hypertrophic cardiomyopathy. Future developments of CMR, aiming at the specific assessment of immune cell infiltration, will give deeper insight into cardiovascular inflammatory diseases.

Imaging of the extracranial internal carotid artery in acute ischemic stroke: assessment of stenosis, plaques, and image quality using relaxation-enhanced angiography without contrast and triggering (REACT)

BACKGROUND

In stroke magnetic resonance imaging (MRI), contrast-enhanced magnetic resonance angiography (CE-MRA) is the clinical standard to depict extracranial arteries but native MRA techniques are of increased interest to facilitate clinical practice. The purpose of this study was to assess the detection of extracranial internal carotid artery (ICA) stenosis and plaques as well as the image quality of cervical carotid arteries between a novel flow-independent relaxation-enhanced angiography without contrast and triggering (REACT) sequence and CE-MRA in acute ischemic stroke (AIS).

METHODS

In this retrospective, single-center study, 105 consecutive patients (65.27±18.74 years, 63 males) were included, who received a standard stroke protocol at 3T in clinical routine including Compressed SENSE (CS) accelerated (factor 4) 3D isotropic REACT (fixed scan time: 02:46 min) and CS accelerated (factor 6) 3D isotropic CE-MRA. Three radiologists independently assessed scans for the presence of extracranial ICA stenosis and plaques (including hyper-/hypointense signal) with concomitant diagnostic confidence using 3-point scales (3= excellent). Vessel quality, artifacts, and image noise of extracranial carotid arteries were subjectively scored on 5-point scales (5= excellent/none). Wilcoxon tests were used for statistical comparison.

RESULTS

Considering CE-MRA as the standard of reference, REACT provided a sensitivity of 89.8% and specificity of 95.2% for any and of 93.5% and 95.8% for clinically relevant (≥50%) extracranial ICA stenosis and yielded a to CE-MRA comparable diagnostic confidence [mean ± standard deviation (SD), median (interquartile range): 2.8±0.5, 3 (3-3) vs. 2.7±0.5, 3 (2-3), P=0.03]. Using REACT, readers detected more plaques overall (n=57.3 vs. 47.7, P<0.001) and plaques of hyperintense signal (n=12.3 vs. 5.7, P=0.02) with higher diagnostic confidence [2.8±0.5, 3 (3-3) vs. 2.6±0.7, 3 (2-3), P<0.001] than CE-MRA. After analyzing a total of 1,260 segments, the vessel quality of all segments combined [4.61±0.66 vs. 4.58±0.68, 5 (4-5) vs. 5 (4-5), P=0.0299] and artifacts [4.51±0.70 vs. 4.44±0.73, 5 (4-5) vs. 5 (4-5), P>0.05] were comparable between the sequences with REACT showing a lower image noise [4.43±0.67 vs. 4.25±0.71, 5 (4-5) vs. 4 (4-5), P<0.001].

CONCLUSIONS

Without the use of gadolinium-based contrast agents or triggering, REACT provides a high sensitivity and specificity for extracranial ICA stenosis and a potential improved depiction of adjacent plaques while yielding to CE-MRA comparable vessel quality in a large patient cohort with AIS.

Deep Learning-Based Magnetic Resonance Imaging in Diagnosis and Treatment of Intracranial Aneurysm

This study was focused on the positioning of the intracranial aneurysm in the magnetic resonance imaging (MRI) images using the deep learning-based U-Net model, to realize the computer-aided diagnosis of the intracranial aneurysm. First, a network was established based on the three-dimensional (3D) U-Net model, and the collected image data were input into the network to realize the automatic location and segmentation of the aneurysm. The 3D convolutional neural network (CNN) network can extract the aneurysm blood vessels to locate and identify the areas of possible aneurysms. Next, 40 patients highly suspected of intracranial aneurysm were selected as research subjects, and they were subjected to magnetic resonance angiography (MRA) and digital subtraction angiography (DSA) examinations. The results showed that based on the U-Net algorithm model, 40 patients' hemangiomas were completely contained in the labeling bounding box, one patient's hemangioma was at the edge of the labeling bounding box, and 4 patients' hemangiomas were outside the labeling box. The final accuracy coefficient was 88.9%, and it was in good agreement with the doctor's manual labelling results. Under the 3D CNN network test, the sensitivity, specificity, and accuracy of DSA for intracranial aneurysm were 91.46%, 86.01%, and 90.2%, respectively; the sensitivity, specificity, and accuracy of MRA for intracranial aneurysm were 95.87%, 100%, and 97.19%, respectively. In conclusion, the 3D CNN can successfully realize the positioning of intracranial aneurysm in MRA images, providing a certain theoretical basis for subsequent imaging diagnosis of aneurysm.

Free-breathing non-contrast flow-independent cardiovascular magnetic resonance angiography using cardiac gated, magnetization-prepared 3D Dixon method: assessment of thoracic vasculature in congenital heart disease

BACKGROUND

To evaluate a non-contrast respiratory- and electrocardiogram-gated 3D cardiovascular magnetic resonance angiography (CMRA) based on magnetization-prepared Dixon method (relaxation-enhanced angiography without contrast and triggering, REACT) for the assessment of the thoracic vasculature in congenital heart disease (CHD) patients.

METHODS

70 patients with CHD (mean 28 years, range: 10-65 years) were retrospectively identified in this single-center study. REACT-CMRA was applied with respiratory- and cardiac-gating. Image quality (IQ) of REACT-CMRA was compared to standard non-gated multi-phase first-pass-CMRA and respiratory- and electrocardiogram-gated steady-state-CMRA. IQ of different vessels of interest (ascending aorta, left pulmonary artery, left superior pulmonary vein, right coronary ostium, coronary sinus) was independently assessed by two readers on a five-point Likert scale. Measurements of vessel diameters were performed in predefined anatomic landmarks (ascending aorta, left pulmonary artery, left superior pulmonary vein). Both readers assessed artifacts and vascular abnormalities. Friedman test, chi-squared test, and Bland-Altman method were used for statistical analysis.

RESULTS

Overall IQ score of REACT-CMRA was higher compared to first-pass-CMRA (3.5 ± 0.4 vs. 2.7 ± 0.4, P < 0.001) and did not differ from steady-state-CMRA (3.5 ± 0.4 vs. 3.5 ± 0.6, P = 0.99). Non-diagnostic IQ of the defined vessels of interest was observed less frequently on REACT-CMRA (1.7 %) compared to steady-state- (4.3 %, P = 0.046) or first-pass-CMRA (20.9 %, P < 0.001). Close agreements in vessel diameter measurements were observed between REACT-CMRA and steady-state-CMRA (e.g. ascending aorta, bias: 0.38 ± 1.0 mm, 95 % limits of agreement (LOA): - 1.62-2.38 mm). REACT-CMRA showed high intra- (bias: 0.04 ± 1.0 mm, 95 % LOA: - 1.9-2.0 mm) and interobserver (bias: 0.20 ± 1.1 mm, 95 % LOA: - 2.0-2.4 mm) agreements regarding vessel diameter measurements. Fat-water separation artifacts were observed in 11/70 (16 %) patients on REACT-CMRA but did not limit diagnostic utility. Six vascular abnormalities were detected on REACT-CMRA that were not seen on standard contrast-enhanced CMRA.

CONCLUSIONS

Non-contrast-enhanced cardiac-gated REACT-CMRA offers a high diagnostic quality for assessment of the thoracic vasculature in CHD patients.

Clinical application of free-breathing 3D whole heart late gadolinium enhancement cardiovascular magnetic resonance with high isotropic spatial resolution using Compressed SENSE

BACKGROUND

Late gadolinium enhancement (LGE) cardiovascular magnetic resonance (CMR) represents the gold standard for assessment of myocardial viability. The purpose of this study was to investigate the clinical potential of Compressed SENSE (factor 5) accelerated free-breathing three-dimensional (3D) whole heart LGE with high isotropic spatial resolution (1.4 mm3 acquired voxel size) compared to standard breath-hold LGE imaging.

METHODS

This was a retrospective, single-center study of 70 consecutive patients (45.8 ± 18.1 years, 27 females; February-November 2019), who were referred for assessment of left ventricular myocardial viability and received free-breathing and breath-hold LGE sequences at 1.5 T in clinical routine. Two radiologists independently evaluated global and segmental LGE in terms of localization and transmural extent. Readers scored scans regarding image quality (IQ), artifacts, and diagnostic confidence (DC) using 5-point scales (1 non-diagnostic-5 excellent/none). Effects of heart rate and body mass index (BMI) on IQ, artifacts, and DC were evaluated with ordinal logistic regression analysis.

RESULTS

Global LGE (n = 33) was identical for both techniques. Using free-breathing LGE (average scan time: 04:33 ± 01:17 min), readers detected more hyperenhanced lesions (28.2% vs. 23.5%, P < .05) compared to breath-hold LGE (05:15 ± 01:23 min, P = .0104), pronounced at subepicardial localization and for 1-50% of transmural extent. For free-breathing LGE, readers graded scans with good/excellent IQ in 80.0%, with low-impact/no artifacts in 78.6%, and with good/high DC in 82.1% of cases. Elevated BMI was associated with increased artifacts (P = .0012) and decreased IQ (P = .0237). Increased heart rate negatively influenced artifacts (P = .0013) and DC (P = .0479) whereas IQ (P = .3025) was unimpaired.

CONCLUSIONS

In a clinical setting, free-breathing Compressed SENSE accelerated 3D high isotropic spatial resolution whole heart LGE provides good to excellent image quality in 80% of scans independent of heart rate while enabling improved depiction of small and particularly non-ischemic hyperenhanced lesions in a shorter scan time than standard breath-hold LGE.

Relaxation-Enhanced Angiography Without Contrast and Triggering (REACT) for Fast Imaging of Extracranial Arteries in Acute Ischemic Stroke at 3 T

Purpose

To evaluate a novel flow-independent 3D isotropic REACT sequence compared with CE-MRA for the imaging of extracranial arteries in acute ischemic stroke (AIS).

Methods

This was a retrospective study of 35 patients who underwent a stroke protocol at 3 T including REACT (fixed scan time: 2:46 min) and CE-MRA of the extracranial arteries. Three radiologists evaluated scans regarding vessel delineation, signal, and contrast and assessed overall image noise and artifacts using 5-point scales (5: excellent delineation/no artifacts). Apparent signal- and contrast-to-noise ratios (aSNR/aCNR) were measured for the common carotid artery (CCA), internal carotid artery (ICA, C1 segment), and vertebral artery (V2 segment). Two radiologists graded the degree of proximal ICA stenosis.

Results

Compared to REACT, CE-MRA showed better delineation for the CCA and ICA (C1 and C2 segments) (median 5, range 2–5 vs. 4, range 3–5; P < 0.05). For the ICA (C1 and C2 segments), REACT provided a higher signal (5, range 3–5; P < 0.05/4.5, range 3–5; P > 0.05 vs. 4, range 2–5) and contrast (5, range 3–5 vs. 4, range 2–5; P > 0.05) than CE-MRA. The remaining segments of the blood-supplying vessels showed equal medians. There was no significant difference regarding artifacts, whereas REACT provided significantly lower image noise (4, range 3–5 vs. 4 range 2–5; P < 0.05) with a higher aSNR (P < 0.05) and aCNR (P < 0.05) for all vessels combined. For clinically relevant (≥50%) ICA stenosis, REACT achieved a detection sensitivity of 93.75% and a specificity of 100%.

Conclusion

Given its fast acquisition, comparable image quality to CE-MRA and high sensitivity and specificity for the detection of ICA stenosis, REACT was proven to be a clinically applicable method to assess extracranial arteries in AIS.

Electronic supplementary material

The online version of this article (10.1007/s00062-020-00963-6) contains supplementary material, which is available to authorized users.