Diagnostic Performance of a Lower-dose Contrast-Enhanced 4D Dynamic MR Angiography of the Lower Extremities at 3 T Using Multisegmental Time-Resolved Maximum Intensity Projections

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.

Magnetic Resonance Angiography of the Arteries of the Upper and Lower Extremities

Magnetic resonance angiography (MRA) is a powerful tool for assessing upper and lower extremity artery pathologies. In addition to the classic advantages of MRA, such as the absence of radiation and iodinated contrast exposure, it can provide high temporal resolution/dynamic images of the arteries with high soft tissue contrast. Although it has a relatively lower spatial resolution than computed tomography angiography, MRA does not cause blooming artifacts in heavily calcified vessels, which is crucial in small vessel assessment. Although contrast-enhanced MRA is the most preferred technique to assess extremity vascular pathologies, recent advances in non-contrast MRA protocols provide an alternative imaging technique for patients with chronic kidney disease.

Quantitative Assessment of Regional Pulmonary Transit Times in Pulmonary Hypertension

BACKGROUND

Pulmonary hypertension (PH) contributes to restricted flow through the pulmonary circulation characterized by elevated mean pulmonary artery pressure acquired from invasive right heart catheterization (RHC). MRI may provide a noninvasive alternative for diagnosis and characterization of PH.

PURPOSE

To characterize PH via quantification of regional pulmonary transit times (rPTT).

STUDY TYPE

Retrospective.

POPULATION

A total of 43 patients (58% female); 24 controls (33% female). RHC-confirmed patients classified as World Health Organization (WHO) subgroups 1-4.

FIELD STRENGTH/SEQUENCE

A 1.5 T/time-resolved contrast-enhanced MR Angiography (CE-MRA).

ASSESSMENT

CE-MRA data volumes were combined into a 4D matrix (3D resolution + time). Contrast agent arrival time was defined as the peak in the signal-intensity curve generated for each voxel. Average arrival times within a vessel region of interest (ROI) were normalized to the main pulmonary artery ROI (t₀ ) for eight regions to define rPTT for all subjects. Subgroup analysis included grouping the four arterial and four venous regions. Intraclass correlation analysis completed for reproducibility.

STATISTICAL TESTS

Analysis of covariance with age as covariate. A priori Student's t-tests or Wilcoxon rank-sum test; α = 0.05. Results compared to controls unless noted. Significant without listing P value. ICC ran as two-way absolute agreement model with two observers.

RESULTS

PH patients demonstrated elevated rPTT in all vascular regions; average rPTT increase in arterial and venous branches was 0.85 ± 0.15 seconds (47.7%) and 1.0 ± 0.18 seconds (16.9%), respectively. Arterial rPTT was increased for all WHO subgroups; venous regions were elevated for subgroups 2 and 4 (group 1, P = 0.86; group 3, P = 0.32). No significant rPTT differences were found between subgroups (P = 0.094-0.94). Individual vessel ICC values ranged from 0.58 to 0.97.

DATA CONCLUSION

Noninvasive assessment of PH using standard-of-care time-resolved CE-MRA can detect increased rPTT in PH patients of varying phenotypes compared to controls.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY: Stage 3.

Effect of Contrast Agent Dose Reduction on Vascular Enhancement and Image Quality in Thoracoabdominal Dynamic 3-Dimensional Magnetic Resonance Angiography: A Systematic Intraindividual Analysis in Pigs

OBJECTIVE

High spatial and temporal resolution contrast-enhanced magnetic resonance angiography (MRA) with gadolinium-based contrast agents (GBCAs) at standard dose offers both detailed anatomic information on both arterial and venous vessels and hemodynamic characteristics. Several preclinical and clinical dynamic 3-dimensional (3D) MRA studies that focused on arterial vessels only proposed that high image quality may also be achieved with significantly reduced GBCA doses, calling into question the need to use standard doses. A systematic analysis of GBCA doses and resulting image quality for both arteries and veins has not yet been performed. The purpose of this study was therefore to systematically analyze dose-dependent vascular enhancements in dynamic 3D-MRA of the thoracoabdominal vasculature at 1.5 T in an animal model to determine the optimal contrast agent protocol for optimized vascular assessment.

MATERIALS AND METHODS

The vascular enhancement in thoracoabdominal dynamic 3D-MRA (time-resolved angiography with interleaved stochastic trajectories, TWIST at 1.5 T) was interindividually and intraindividually compared in 5 anesthetized Göttingen minipigs using gadobutrol at the standard dose (0.1 mmol/kg body weight, ie, 0.1 mL/kg) and at reduced doses (0.08, 0.06, 0.04, 0.02 mmol/kg) in a randomized order. All injections were performed at 2 mL/s followed by 20 mL saline. Images were quantitatively analyzed, measuring signal intensities in 5 regions that covered the passage of the GBCA through the body at different representative stages of circulation (pulmonary, arterial, and venous system). The evaluation of GBCA dose-dependent signal intensity changes in the different vascular regions was performed by linear regression analysis.The qualitative image analysis of dynamic 3D-MRA by 3 independent radiologists included the visibility of 25 arterial and venous vessel segments at different stages of GBCA passage. Possible quality losses were statistically tested by comparing image quality ratings at the reduced dose with that of the standard dose using Friedman test followed by Dunn post hoc test for multiple comparison. Significance was stated at P < 0.05.

RESULTS

Quantitative analysis revealed shorter time-to-peak intervals and bolus durations in line with decreasing GBCA dose and volume in all vessels. Although the peak signal was almost independent of the administered GBCA dose at the level of the pulmonary trunk, a linear signal decrease in the abdominal aorta ( r2 = 0.96), the renal arteries ( r2 = 0.99), the inferior vena cava ( r2 = 0.99), and the portal vein ( r2 = 0.97) was observed. Cumulative analysis of arterial segments revealed significantly lower image quality at doses below 40% of the standard dose, whereas in venous segments, significantly lower image quality was observed at doses below 60% of the standard dose.

CONCLUSIONS

In dynamic 3D-MRA at 1.5 T, dose reduction leads to a signal loss that is most pronounced in the venous system and results in significantly lower image quality according to the dose and vessels of interest. Careful dose reduction is thus required according to the specific diagnostic needs. For dynamic 3D-MRA of the arterial and venous system, GBCA doses of at least 60% of the standard dose up to the full dose are preferable, whereas 40% of the standard dose seems feasible if only the arterial system is to be imaged.

Low-dose contrast-enhanced time-resolved angiography with stochastic trajectories with iterative reconstruction (IT-TWIST-MRA) in brain arteriovenous shunt

OBJECTIVES

To assess the feasibility of low-dose contrast-enhanced four-dimensional (4D) time-resolved angiography with stochastic trajectories (TWIST) with iterative reconstruction (hereafter IT-TWIST-MRA) covering the whole brain and to compare IT-TWIST-MRA and TWIST-MRA with reference to digital subtraction angiography (DSA) in the evaluation of arteriovenous shunts (AVS).

METHODS

Institutional Review Board approval was obtained for this observational study, and the requirement for written informed consent was waived. Twenty-nine patients with known AVS underwent TWIST-MRA on a 3-T MRI scanner, using low-dose injection (0.02 mmol/kg) of gadolinium-based contrast agent (GBCA) with each of Fourier and iterative reconstruction between September 2016 and October 2019. Visual evaluation of image quality was conducted for delineation of (a) the normal cerebral arteries and veins and (b) AVS feeder, shunt, and drainer vessels. Region-of-interest evaluation was conducted to evaluate bolus sharpness and baseline signal fluctuation in the signal intensity of the cerebral vessels. We compared the detection of AVS between TWIST-MRA and IT-TWIST-MRA. The paired-samples Wilcoxon test was used to test the differences between TWIST-MRA and IT-TWIST-MRA.

RESULTS

Visualization scores for normal vasculature and AVS angioarchitecture were significantly better for images produced using IT-TWIST-MRA than those using TWIST-MRA. Peak signal and the enhancement slope of the time-intensity curve were significantly higher for IT-TWIST-MRA than for TWIST-MRA, except for the superior sagittal sinus (SSS). Baseline intensity fluctuation was significantly lower for IT-TWIST-MRA than for TWIST, except for SSS.

CONCLUSIONS

IT-TWIST-MRA yields clinically feasible 4D MR-DSA images and delineates AVS even with low-dose GBCA.

KEY POINTS

• Iterative reconstruction significantly improves the image quality of TWIST-MRA covering the whole brain. • The short temporal footprint and denoising effect of iterative reconstruction enhances the quality of 4D-MRA. • IT-TWIST-MRA yields clinically feasible images of AVS with low-dose GBCA.