Dynamic MRA Research Articles

Contrast Dose, Temporal Footprint, and Spatial Resolution Tradeoffs in Dynamic Contrast-Enhanced MRA Performed in a Porcine Model of a Carotid Aneurysm

To evaluate the tradeoffs between temporal and spatial resolution and contrast dosing in dynamic contrast-enhanced magnetic resonance angiography (CE-MRA). Bilateral carotid artery aneurysms were created in a swine model. Dynamic CE-MRA using 1 mol/L gadobutrol was performed at 3 T, with high temporal (high-temp), middle temporal (mid-temp), and low temporal (low-temp) resolutions. High temporal CE-MRA was performed twice using 1 mL and 2 mL gadobutrol (2 mL/s). Middle temporal and low-temp sequences were performed once with 2 mL gadobutrol (2 mL/s). The signal-to-noise ratio (SNR) was quantitatively assessed. Blinded reads were used to qualitatively evaluate contrast dose and image quality. The mean SNRs of high-temp, mid-temp, and low-temp resolutions were 56.7, 47.5, and 48.1. There was no significant difference between the 3 sequences with 2 mL gadobutrol. The mean SNR of the high-temp resolution with 2 mL was significantly higher than that with 1 mL (56.7 vs 39.9). In qualitative analysis, the 3 temporal sequences with 2 mL gadobutrol showed no significant differences regarding overall image quality and diagnostic value. High temporal resolution with 2 mL consistently showed the superiority of image quality than that with 1 mL. High temporal dynamic CE-MRA with 2 mL (0.04 mmol/kg body weight) gadobutrol can produce consistently superior image quality over that with 1 mL (0.02 mmol/kg body weight). For a given contrast dose, the tradeoffs between temporal and spatial resolution will not result in significant differences in image quality in TWIST (time-resolved angiography with interleaved stochastic trajectories).

Schuster L, Schenk E, Giesel F. Changes in AVM angio-architecture and hemodynamics after stereotactic radiosurgery assessed by dynamic MRA and phase contrast flow assessments. Eur Radiol 2011; 21: 1267 – 1276

Schuster L, Schenk E, Giesel F. Changes in AVM angio-architecture and hemodynamics after stereotactic radiosurgery assessed by dynamic MRA and phase contrast flow assessments. Eur Radiol 2011; 21: 1267 – 1276

Pseudostenosis at the Origin of the Vertebral Artery on Contrast-enhanced MRA: Correlation with Aortic Motion on Dynamic 3D Time-Resolved Contrast-Enhanced MRA

Purpose : The origin of the vertebral artery (VA) is a frequent site of pseudostenosis on contrast-enhanced MRA (CEMRA). The purpose of this study is to evaluate the relationship between the motion of the aortic arch and pseudostenosis at the origin of the VA. Materials and Methods: Our study had approval of our institutional review board. 47 patients underwent CT angiography (CTA), CE-MRA, and 3D time-resolved contrast-enhanced MRA (TR-CEMRA) within 6.87±9.89 days (mean±SD). Percent stenosis using the NASCET criteria was measured on CTA and CE-MRA. CTA was used as a reference standard to classify the CE-MRA into pseudostenosis and control group. Pseudostenosis was determined as 50%99% stenosis observed on CE-MRA but normal to less than 50% stenosis on CTA. Aortic motion (distance between the highest position and lowest position of aortic arch) was measured on TR-CEMRA. Age, route of intravenous contrast media, motion of aortic arch, and normal distal diameter of VA were compared between the two groups. Results: There were 17 patients and 23 vertebral arteries of pseudostenosis. Patients with pseudostenosis showed more aortic motion (3.61±1.88 vs. 2.05±1.97 mm) and older age (71.29±8.88 vs. 62.32±13.19 year-old). Route of intravenous contrast media and normal distal diameter of VA were not associated with pseudostenosis. Conclusion: VA origin is a frequent site of pseudostenosis. Older age and more motion of aortic arch are associated with pseudostenosis on CE-MRA.

Dynamic CT and MRA findings of a case of portopulmonary venous anastomosis (PPVA) in a patient with portal hypertension: a case report and review of the literature

Portopulmonary venous anastomosis (PPVA), which has been rarely reported in conventional CT and MR studies, is an unusual collateral pathway in patients with portal hypertension. It has clinical implications related to right-to-left shunt that are different from the clinical implications related to other more usual portosystemic shunts in portal hypertensive patients. Here, we report the dynamic CT and MRA findings of a case of PPVA in a patient with portal hypertension, directly demonstrating the shunt flow from the paraesophageal varix to the left atrium via the right inferior pulmonary vein.

Changes in AVM angio-architecture and hemodynamics after stereotactic radiosurgery assessed by dynamic MRA and phase contrast flow assessments

Assessment of changes in the hemodynamics of Arteriovenous malformations (AVM) induced by radiosurgery by MR Phase contrast (PC) measurements of the internal carotid arteries (ICA). 65 patients shortly after or before stereotactic radiosurgery underwent MRI including morphological series, MR-Angiography (Time-of-flight, dynamic MRA) and bilateral ECG triggered MR phase contrast (PC) measurements of the ICA. Follow-up was performed in 34 patients. The observation period was up to 4 years. Over all subjects, a significant relationship between mean arterial blood flow in the ICA on the side of the lesion and AVM volume was revealed (p = 0,0002). In large (>10 ccm) and medium-sized AVMs, (>3, 5 ≤ 10 ccm) the blood flow was significantly increased on the side of the AVM (p = 0,0004; p = 0,047), whereas in lesions <3, 5 ccm, no significant rise of the mean blood flow was detectable. At follow-up, the mean blood flow in the ipsilateral artery was not increased anymore compared to the contralateral ICA (p = 0,11). These changes correlated with a significant reduction of the average AVM volume (p = 0, 0026). The AVM angioarchitecture has significant impact on the blood flow in feeding arteries. A significant reduction of the shunt volume by successful radiotherapy leads to normalization of the hemodynamics.

Dynamic Contrast-Enhanced Magnetic Resonance Angiography of the Thoracic Vessels

The combination of parallel acquisition (generalized autocalibrating partially parallel acquisitions) and time-resolved three-dimensional (3D) view-sharing techniques is a promising tool for dynamic contrast-enhanced 3D-magnetic resonance angiography (MRA). We evaluated the influence of different k-space acquisition strategies on image quality for a recently developed time-resolved echo-shared angiographic technique during a contrast-enhanced 3D-MRA of the thoracic vessels. In 20 patients (16 men, 4 women; range, 28-75 years), 2 dynamic MRA protocols with different k-space acquisition strategies were performed on a 1.5-T whole-body scanner (MAGNETOM Avanto, Siemens AG, Erlangen, Germany) during injection of 5 mL (flow-rate, 3 mL/s) gadobutrol. For protocol 1, the central-region which was updated with every cycle included 20% of the entire k-space (protocol 2: 10%), the peripheral-region was undersampled by a factor of 10 (protocol 2: 5%). Image quality and details were compared visually. Signal-to-noise ratio and sharpness of vessel borders were estimated. Morphologic and functional assessment of the pulmonary arteries and the aorta was significantly improved for protocol 1. The sharpness of vessel borders (3.3 mm vs. 4.1 mm; P = 0.001), image quality, and the visibility of image details were significantly improved for protocol 1 compared with protocol 2. The size of the central region that is updated for every frame seems to be more crucial for image quality of echo-shared angiographic techniques than the sampling density in the periphery of the k-space.

Contrast enhanced MR angiography: evolving towards whole-body real time acquisition [in French

MRA includes all techniques used to depict vessels with MR. Gadolinium contrast injection combined with gradient echo sequences is the technique of choice for vascular imaging. Technical advances now allow faster acquisitions. The purpose of this article is to present two main advances with MRA: whole-body MRA and dynamic 3D MRA. Technical considerations, acquisition techniques, advantages and pitfalls based on our experience with a 1.5T MR unit will be discussed in order to promote their use in routine clinical practice.

Dynamic MRA With Four-Dimensional Time-Resolved Angiography Using Keyhole at 3 Tesla in Head and Neck Vascular Lesions

Conventional MRA provides inadequate visualization of the dynamic features of blood flow in vascular lesions of the head and neck. Four-dimensional time-resolved angiography using keyhole (4D-TRAK) is a new technique of performing contrast-enhanced MRA. By combining parallel imaging with sensitivity encoding (SENSE) with the keyhole imaging technique and a high field strength (3 T) magnet, we have been able to obtain detailed hemodynamic information similar to that obtained via catheter angiography with digital subtraction (DSA), but without the risks associated with ionizing radiation exposure, iodizing contrast agents, or catheterization itself.

CE‐MRA of the lower extremities using HYPR stack‐of‐stars

To investigate the properties of HYPR (HighlY constrained back PRojection) processing-the temporal fidelity and the improvements of spatial/temporal resolution-for contrast-enhanced MR angiography in a pilot study of the lower extremities in healthy volunteers. HYPR processing with a radial three-dimensional (3D) stack-of-stars acquisition was investigated for contrast-enhanced MR angiography of the lower extremities in 15 healthy volunteers. HYPR images were compared with control images acquired using a fast, multiphase, 2D Cartesian method to verify the temporal fidelity of HYPR. HYPR protocols were developed for achieving either a high frame update rate or a minimal slice thickness by adjusting the acquisition parameters. HYPR images were compared with images obtained using 3D TRICKS, a widely used protocol in dynamic 3D MRA. HYPR images showed good temporal agreement with 2D control images. In comparison with TRICKS, HYPR stack-of-stars demonstrated higher spatial and temporal resolution. High radial undersampling factors for each time frame were permitted, typically approximately 50 to 100 compared with fully sampled radial imaging. In this feasibility study, HYPR processing has been demonstrated to improve the spatial or temporal resolution in peripheral CE-MRA.

Angiographie par résonance magnétique avec injection de produit de contraste : évolution vers le corps entier et le temps réel

MRA includes all techniques used to depict vessels with MR. Gadolinium contrast injection combined with gradient echo sequences is the technique of choice for vascular imaging. Technical advances now allow faster acquisitions. The purpose of this article is to present two main advances with MRA: whole-body MRA and dynamic 3D MRA. Technical considerations, acquisition techniques, advantages and pitfalls based on our experience with a 1.5T MR unit will be discussed in order to promote their use in routine clinical practice.

Three‐dimensional dynamic time‐resolved contrast‐enhanced MRA using parallel imaging and a variable rate k‐space sampling strategy in intracranial arteriovenous malformations

To evaluate the effectiveness of three-dimensional (3D) dynamic time-resolved contrast-enhanced MRA (TR-CE-MRA) using a combination of a parallel imaging technique (ASSET: array spatial sensitivity encoding technique) and a time-resolved method (TRICKS: time-resolved imaging of contrast kinetics) and to compare it with 3D dynamic TR-CE-MRA using ASSET alone in the assessment of intracranial arteriovenous malformations (AVMs). Twenty consecutive patients with angiographically confirmed AVMs were investigated using both 3D dynamic TR-CE-MRA techniques. Examinations were compared with respect to image quality, spatial resolution, number and type of feeders and drainers, nidus size, presence of early venous filling and temporal resolution. Digital subtraction angiography was used as standard of reference. The higher temporal and spatial resolution of 3D dynamic TR-CE-MRA TRICKS ASSET allowed a better assessment of intracranial vascular malformations, namely better depiction of feeders, drainers and better detection of early venous drainage. There was no significant difference between them in terms of nidus size. 3D dynamic TR-CE-MRA combining parallel imaging and a time-resolved method with subsecond and submillimeter resolution could become the first-line investigation technique in both diagnosis and follow-up of intracranial AVMs.

Assessment of Intracranial Collateral Flow by Using Dynamic Arterial Spin Labeling MRA and Transcranial Color-Coded Duplex Ultrasound

To evaluate the potential of a new dynamic MRA sequence (DynAngio) based on arterial spin labeling for the assessment of intracranial collateral flow. Twelve patients with unilateral internal carotid artery obstruction were investigated. Different patterns of collateral flow were compared between DynAngio, transcranial color-coded duplex ultrasound, and time-of-flight MRA. There was a good agreement between the methods, with sensitivities between 80% and 90%. Small collateral vessels were detected more frequently with DynAngio compared to time-of-flight MRA. DynAngio provides anatomic and similar to transcranial color-coded duplex ultrasound functional information on collateral flow for the assessment of intracranial hemodynamics.

An evaluation of parsimony for microbial risk assessment models

AbstractMicrobial risk assessment (MRA) is a process that evaluates the likelihood of adverse human health effects following exposure to a medium in which pathogens are present. Several different classes of models are available to quantitatively characterize risks to human health from exposure to pathogens. Herein, we consider the question of parsimony for specific realizations of representative static and dynamic MRA models and identify conditions under which the more complex dynamic model provides sufficient additional insight to justify the added modeling complexity. To address this question, a standard static individual‐level risk model is compared to a deterministic dynamic population‐level model that explicitly includes secondary transmission and immunity processes. Exposure parameters are based on a scenario defined by human exposure to pathogens in reclaimed water. A sensitivity analysis is implemented to identify conditions under which static and dynamic models yield substantially different results. Under low risk conditions, defined by a combination of exposure levels and infectivity of the pathogen, the simpler static model provides satisfactory risk estimates. The approach presented here provides a basis for model selection for a broad range of MRA applications. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Dynamic CE-MRA for Endoleak Classification after Endovascular Aneurysm Repair

AimTo evaluate the value of dynamic contrast enhanced magnetic resonance angiography (CE-MRA) for classification of endoleaks after endovascular aneurysm repair (EVAR). Materials and methodsTwenty-eight patients, between 2 days and 54 months after EVAR, were evaluated with CTA, MRI and dynamic CE-MRA. The additional diagnostic value of the dynamic 3D CE-MRA was evaluated by determining the ability of the dynamic series in pinpointing the site of inflow of an endoleak. ResultsAn endoleak was detected in 23 patients. Seventeen of the 23 dynamic series were technically successful (no disturbing artifacts limiting the diagnostic value). Using MRI our findings were: 2 type I, 6 type II, 1 type III, no type IV endoleaks and in 14 cases classification could not be made. The classification results for MRI plus the dynamic CE-MRA were: 2 type I, 12 type II, 1 type III, no type IV endoleaks and in eight cases classification could not be made. In six cases the dynamic MRA allowed classification of the endoleak, which was not possible with the non-dynamic images alone (p=0.091, Fisher exact). ConclusionThis pilot study shows that dynamic CE-MRA can have additional value in the classification of endoleaks. Dynamic CE-MRA might obviate the need for diagnostic digital subtraction angiography and aid planning for intervention.

Non-invasive visualization of collateral blood flow patterns of the circle of Willis by dynamic MR angiography

The circle of Willis plays an important role in the distribution of blood flow in the brain. To obtain dynamic information of the blood flow through the circle of Willis, a dynamic MRA technique based on arterial spin labeling (ASL) is introduced as a non-invasive technique. When the ASL labeling slab is restricted to a single artery, it is possible to visualize selectively the flow distribution of that specific artery. However, because of the decay of the label and the presence of noise it is difficult to extract functional information from these images. In the present study we propose three visualization and post-processing methods for the interpretation of these images. Firstly, the passage of labeled blood was corrected for decay of the label and hereafter shown as a movie. Secondly, by calculating the time of arrival at every location in the arteries of the circle of Willis, a 2D image was reconstructed summarizing the information of the movie. Finally, quantitative flow values were obtained by relating the arterial input function to the passage of labeled blood through a region of interest encompassing the vessel under investigation. Experiments in a circle of Willis phantom showed a high linear relation between measured flow and true flow, although the measured values were 10–15% lower than the true flow values. Measurements in healthy volunteers showed the potential to quantify the flow in all major arteries of the circle of Willis.

Applications de l’arm dynamique dans la pathologie vasculaire du système nerveux central

Conventional catheter angiography (CCA) remains the gold standard for the evaluation of most intracranial vascular malformations. MRA techniques such as Time of Flight, Phase Contrast or 3D contrast-enhanced MRA, provide anatomic evaluation but without hemodynamic information. Recently developed, dynamic MRA is based on dynamic acquisition of images and image subtraction; these two principal characteristics produce images comparable to those obtained by CCA. The purpose of this review is to explain the principles, advantages and drawbacks of this technique in the evaluation of arteriovenous malformations, arteriovenous fistulas, aneurysms and venous thrombosis.

Assessment of the anomalous pulmonary circulation by dynamic contrast-enhanced MR angiography in under four seconds

The purpose of this study was to demonstrate the initial results of the dynamic contrast-enhanced MRA in under four seconds in the assessment of anomalous pulmonary circulation. We performed dynamic contrast enhanced MRA on ten patients with a temporal resolution of 2–3 sec for each phase. Five patients had pulmonary vascular anomaly and five patients had reconstructed pulmonary circulation. On nine patients catheter angiography was performed for the correlation. Dynamic contrast-enhanced MRA successfully demonstrated congenital pulmonary vascular anomalies and the pathway of anomalous pulmonary circulation in our series. With the improved temporal and spatial resolution, the dynamic contrast-enhanced MRA can be used in children and infants for the assessment of congenital vascular disease.

Editorial: The Radiology Fellowship as a Pre-Doctoral Training Equivalent

Editorial: The Radiology Fellowship as a Pre-Doctoral Training Equivalent

Contrast-enhanced 3D-MRA of the upper abdomen with a bolus-injectable SPIO (SH U 555 A).

The purpose of this study was to study temporal changes in signal intensity of liver, spleen, abdominal vessels, and focal liver lesions following iv bolus injection of a superparamagnetic iron oxide (SPIO) using a breath-held three-dimensional magnetic resonance angiography (3D-MRA) sequence. Dynamic SH U 555 A-enhanced 3D-MRA studies were performed in 20 patients with focal liver lesions. Sequential coronal 3D-MRA-FISP scans were acquired (TR 5.0 msec, TE 2.0 msec, flip angle 25 degrees, 140 x 256 matrix, and 80 mm slab) within 15 seconds. Scanning was started immediately after bolus injection of 10 micromol Fe/kg bodyweight and was repeated at multiple time points (baseline and 30, 60, 90, 120, 180, 240, 300, 360, and 420 seconds). Signal intensity values of liver, focal liver lesions, spleen, the portal venous system, the abdominal aorta, and the inferior vena cava were obtained to calculate relative enhancement (ENH = [SI post - SI pre]/SI pre x 100). Visibility of vessels was assessed by consensus of two readers. Signal enhancement within abdominal vessels peaked during the first pass; however, significant signal enhancement was still present 420 seconds following injection. The liver and the spleen also demonstrated a biphasic enhancement pattern with prolonged parenchymal enhancement. Dynamic MRA with bolus injectable SH U 555 A is clinically feasible, and significant vessel enhancement can be achieved even at the dose of 10 micromol Fe/kg bodyweight. However, further refinements are required to improve contrast effects.

Renal MR angiography: a comprehensive approach.

Renal artery MR angiography has now emerged as a safe, accurate approach to renal arteriography. A comprehensive examination, including both three-dimensional (3D) dynamic gadolinium-enhanced and 3D phase contrast MRA techniques, allows evaluation of both the aorta-renal and splanchnic arterial anatomy as well as the hemodynamic significance of any stenoses identified. The 3D gadolinium-enhanced MRA technique produces a contrast arteriogram but without risks of iodinated contrast or ionizing radiation. The 3D phase contrast technique is a flow-based technique, which may show dephasing in the presence of hemodynamically significant stenoses. A comprehensive examination should also include T1- and T2-weighted imaging for the assessment of potential neoplastic masses and the ubiquitous renal cysts. Through trial and error over the course of over a thousand examinations, this comprehensive approach to the MR evaluation of renal vascular pathology has emerged.