MRI of the head and neck vessels: with and without contrast, indications

Magnetic resonance angiography is a type of magnetic resonance imaging that creates detailed, three-dimensional images of arteries and veins without ionizing radiation. This method is used to evaluate blood flow and the structure of blood vessels in the brain and neck, helping to detect stenosis, aneurysms, congenital anomalies, and vascular malformations. In most clinical situations, the examination can be performed without contrast, and when necessary, gadolinium contrast is used to improve diagnostic accuracy. [1]

Current guidelines emphasize that early vascular imaging in suspected ischemic stroke or transient ischemic attack improves patient selection for reperfusion therapy. Computed tomography angiography or magnetic resonance angiography are used for this purpose, the choice depending on availability and the clinical situation. [2]

Compared to computed tomography angiography, magnetic resonance angiography does not use X-rays or iodine-containing contrast agents, which is important for patients with iodine allergies or high cumulative radiation risk. Furthermore, contrast-enhanced magnetic resonance angiography often outperforms non-contrast techniques in terms of resistance to flow artifacts and dynamic analysis of shunt conditions. [3]

The method is constantly evolving: non-contrast high-tech sequences, deep learning for noise suppression, and high-definition vessel wall imaging are being introduced. This expands the indications, including the assessment of unstable plaques, vasculitis, and dissections. [4]

When is the test prescribed?

Main indications include acute and subacute cerebrovascular accidents, transient ischemic attacks, evaluation of carotid and vertebral artery stenoses, suspected dissection, follow-up after stenting and endarterectomy, and screening for aneurysms in high-risk patients.[5]

Magnetic resonance angiography is referred when arteriovenous malformations and dural arteriovenous fistulas are suspected, since dynamic contrast sequences allow one to see the arterial phase without venous “overlap” and to evaluate the hemodynamics of the shunt. [6]

A separate set of indications relates to the venous system: suspected cerebral vein and venous sinus thrombosis, intracranial hypertension, and assessment of venous outflow prior to neurosurgery. Magnetic resonance venography with and without contrast is used for this purpose. [7]

In everyday practice, the method is also used for headaches of unclear origin, tinnitus, dizziness, syncopal states, when it is necessary to exclude vascular causes, as well as as part of a comprehensive examination before interventions on the carotid arteries. [8]

Table 1. Typical clinical tasks and what magnetic resonance angiography provides

Clinical situation	Purpose of the study	Preferred modes
Suspected ischemic stroke or transient attack	Rapid screening for large artery occlusion, assessment of collaterals	Non-contrast magnetic resonance angiography based on the entrance effect, contrast magnetic resonance angiography when dynamics are needed
Suspected dissection	Search for intramural hematoma and false lumen	High-definition vessel wall imaging, non-contrast and contrast modes
Screening and monitoring of aneurysms	Identification of the neck and dome, assessment of residual filling after clipping or coiling	Non-contrast modes, contrast dynamic series in complex hemodynamics
Suspected venous thrombosis	Evaluation of patency of sinuses and veins, collateral pathways	Magnetic resonance venography without and with contrast
Arteriovenous malformations, dural fistulas	Mapping of feeding arteries, nidus, drainage veins, time phases	High frame rate time series

Safety and contraindications

Magnetic resonance angiography (MRA) is performed in a magnetic field and does not involve radiation, so it is suitable for a wide range of patients if safety standards are met. Absolute and relative contraindications are primarily related to ferromagnetic implants, their compatibility with MRA, and the risk of displacement or overheating. The decision is made by an MRA safety specialist based on the current 2024 guidelines of the American College of Radiology. [9]

Pregnancy is not a contraindication to magnetic resonance imaging (MRI) itself; however, the use of gadolinium contrast agents during pregnancy is limited and considered only when significant clinical benefit is expected. This is reflected in the guidelines of the American College of Obstetricians and Gynecologists and is consistent with the position on MRI safety. [10]

In chronic kidney disease, the choice of contrast agent is critical. The consensus of the American College of Radiology and the National Kidney Foundation notes an extremely low risk of nephrogenic systemic fibrosis when using modern macrocyclic contrast agents in low-risk groups, including in patients with an estimated glomerular filtration rate (GFR) below 30 ml per minute per 1.73 m² with justified clinical benefit. Discussion is conducted with the treating physician, with an individual benefit-risk assessment. [11]

For patients with severe claustrophobia, pre-sedation or selection of a device with a wide gantry is possible, and for patients with implanted devices, protocols for conditionally compatible systems are used after checking the manufacturer and compliance with scanning modes. [12]

Table 2. Contraindications and precautions

Situation	Approach
Presence of implants and devices	Compatibility check against the manufacturer's database and the 2024 Magnetic Resonance Imaging Safety Guidelines
Pregnancy	Preferably without contrast; gadolinium only if there is significant clinical benefit
Chronic kidney disease	Low-risk macrocyclic contrasts; individual consensus-based approval
Severe claustrophobia	Preparation with sedation, selection of a device with a wide opening
History of allergic-like reactions	Selection of low-risk contrast, surveillance plan, discussion of alternatives

How the study is performed

Non-contrast magnetic resonance angiography (NCA) relies on the effects of fresh blood entry and phase contrast. The most common technique visualizes arteries using the signal from incoming blood, making it suitable for screening the arterial bed without contrast injection. The method is sensitive to flow parameters, so localized signal loss is possible during turbulence. [13]

Contrast-enhanced magnetic resonance angiography uses gadolinium to shorten relaxation times and enhance blood signals, improving image quality in complex areas, reducing saturation artifacts, and allowing for larger volumes to be imaged in less time. This approach is particularly useful for high-grade stenoses, shunt conditions, and for detailed neck evaluation. [14]

High-frame-rate time-contrast series provide a dynamic map of bolus flow through vessels, helping to isolate the arterial phase, minimize venous overlay, and assess arteriovenous shunts. These sequences are applicable to malformations and fistulas, as well as to the complex hemodynamics of aneurysms. [15]

Separately, non-contrast, so-called "silent" magnetic resonance angiography with noise suppression and high flow sensitivity for stent-associated changes is being developed. Publications demonstrate advantages in assessing stents and residual aneurysm necks compared to classical non-contrast techniques. [16]

Table 3. Comparison of magnetic resonance angiography techniques

Technique	What is useful?	Restrictions
Contrast-free based on the input effect	Injection-free artery screening, highly accessible	Signal loss in slow or turbulent flow
Non-contrast phase-contrast	Quantitative assessment of flow velocity and direction	Sensitivity to settings and motion artifacts
Contrast static	High signal-to-noise ratio, large coverage areas	Need for contrast, consideration of renal function and pregnancy
Contrast temporary	Phase separation, shunt evaluation	Requires a clear synchronized protocol

Magnetic resonance venography

Magnetic resonance venography is used to assess the patency of venous sinuses and cerebral veins, primarily when thrombosis is suspected. Non-contrast modes and contrast-enhanced 3D sequences are available, which reduce errors in the presence of slow venous flow and vascular variations. [17]

Updated clinical statements on cerebral venous thrombosis emphasize the role of magnetic resonance imaging with venography in the initial diagnosis and subsequent monitoring, especially when computed tomography is uninformative. Contrast-enhanced 3D series increase sensitivity for acute thrombi and small collaterals. [18]

Contrast-enhanced 3D gradient series have been historically shown to be superior to 2D non-contrast modes for excluding acute venous sinus thrombosis, particularly in complex anatomy. This is important for early initiation of anticoagulant therapy. [19]

In venous pathology, the study is often supplemented by an assessment of the parenchyma and perfusion, which allows for the detection of venous infarctions and edema. The result is a comprehensive picture of venous hemodynamics and its impact on brain tissue. [20]

Table 4. When to choose magnetic resonance venography

Clinical task	Recommended modes
Acute sinus thrombosis	Contrast 3D series, additionally non-contrast venography
Intracranial hypertension	Venography and assessment of lumen stenosis, possible quantitative flow assessment
Preoperative planning	Mapping of the major sinuses and cortical veins
Monitoring therapy	Comparison of permeability and collaterals in dynamics

What exactly is visible in typical diseases?

In carotid atherosclerosis, magnetic resonance angiography reveals the degree of narrowing and plaque characteristics, including a lipid core and intraplaque hemorrhage. These features are associated with the risk of embolism and influence treatment decisions. Magnetic resonance imaging of the vessel wall and multi-contrast protocols improve the accuracy of risk stratification. [21]

Dissection of the carotid or vertebral arteries presents with a linear filling defect, a false lumen, and a "hematoma" in the wall. High-definition wall imaging helps confirm the diagnosis, especially in the early days when lumen changes may be minimal. [22]

Aneurysms appear as saccular or fusiform arterial bulges. Contrast-enhanced dynamic series improve visualization of inflow and drainage when combined with arteriovenous shunts and aid in treatment planning. For monitoring after endovascular occlusion, non-contrast "silent" modes demonstrate promising results. [23]

In venous thrombosis, venography reveals filling defects and lack of sinus tracing, while conventional sequences show changes in the thrombus signal depending on age. The current guidelines for cerebral venous thrombosis support the use of magnetic resonance venography in the initial diagnosis. [24]

Table 5. Key features in the images

Pathology	Findings
Atherosclerosis	Lumen narrowing, uneven contours, signs of unstable plaque
Dissection	Double lumen, intramural hematoma, intimal "visor"
Aneurysm	Protrusion of the wall, assessment of the neck and relationship to the branches
Venous thrombosis	Sinus filling defect, collaterals, white matter edema
Arteriovenous shunts	Early venous filling, visualization of feeding arteries and drainage veins

Comparison with alternatives

Computed tomography angiography remains the standard for assessing calcifications and accurately measuring the degree of stenosis, especially in severe turbulence. However, magnetic resonance angiography better characterizes plaque composition and wall characteristics, while eliminating radiation exposure and iodine contrast. Clinically, these methods often complement each other. [25]

To stratify the degree of stenosis, standardized measurement methods are used, as outlined in the European Vascular Guidelines for 2023. These guidelines also highlight differences in the methods, which is important for the comparability of results between studies and the choice of treatment tactics. [26]

Digital subtraction angiography remains the invasive "gold standard" for planning endovascular interventions and in ambiguous cases. In the absence of a need for immediate intervention, noninvasive methods have high sensitivity and specificity for severe stenoses. [27]

When venous thrombosis is suspected, magnetic resonance venography is often preferred because it allows assessment of both tissue changes and venous outflow without ionizing radiation, and the dynamic contrast series improves accuracy. [28]

Table 6. How to choose a visualization method for a task

Task	Preference	Comment
Confirm high carotid artery stenosis	Computed tomography angiography or magnetic resonance angiography	For measurements, it is important to have a consistent methodology according to guidelines
Assess plaque instability	Magnetic resonance angiography and wall imaging	The lipid core and intraplaque hemorrhage are assessed.
Exclude dissection	Magnetic resonance angiography with wall assessment	High definition of soft tissue walls
Venous thrombosis	Magnetic resonance venography	Contrasting 3D series increase sensitivity
Arteriovenous shunts	Temporal contrast series	Phase scanning and high frame rate are important

Patient preparation and procedure

A special diet is usually not required. It is recommended to remove metal objects, bring documentation regarding implants, and inform the patient in advance about any chronic illnesses or allergies. Mild sedation may be prescribed by a doctor for anxiety, as also outlined in the patient information leaflets. [29]

The duration depends on the protocol and can range from 15 to 40 minutes, longer if dynamic series and wall imaging are added. It is important to remain still during the scan, as movement degrades the quality. After a non-contrast examination, you can immediately return to your normal activities. [30]

If contrast is required, an intravenous catheter is inserted. Most modern gadolinium-based medications have a low risk of severe reactions. A brief warmth may sometimes be felt after the injection. In patients with chronic kidney disease or pregnancy, the use of contrast is decided on an individual basis. [31]

In venography, contrast-enhanced 3D series are launched at the optimal phase of venous filling, and non-contrast modes are selected taking into account the flow rate in order to reduce false-positive signal loss. [32]

Contrast agents: choice and risks

Macrocyclic gadolinium agents are preferred due to their high stability and extremely low risk of nephrogenic systemic fibrosis. The 2024 guidelines recommend avoiding routine use of gadolinium during pregnancy, making decisions only when significant benefit is expected. [33]

In patients with chronic kidney disease, decisions are made by consensus, noting that the risk of nephrogenic systemic fibrosis with modern drugs is minimal, even at low glomerular filtration rates. Dialysis is not required solely because of contrast administration. [34]

As an alternative to gadolinium, some centers are using an iron-based preparation with a long blood "pool." Publications demonstrate good vascular imaging quality and a low rate of serious reactions when administered slowly, but off-label use requires separate approval and safety protocols. [35]

After breastfeeding, there is usually no need to stop breastfeeding, as the amount of contrast that enters the milk is extremely small. This issue is also discussed in contrast media guidelines. [36]

Table 7. Contrasting strategies and security

Scenario	Recommendations
A normal patient without risk factors	Macrocyclic gadolinium in standard dose as needed
Pregnancy	Avoid contrast, consider only if expected benefit is high
Chronic kidney disease	Modern low-risk macrocyclic agents, tailored to individual needs
Allergic-like reactions previously	Selection of a low-risk drug, observation, discussion of alternatives
Special cases	Consideration of iron-based preparations based on experience and indications

Limitations and artifacts

Non-contrast modes are sensitive to flow velocity reduction and turbulence, which can simulate stenosis. Contrast-enhanced sequences reduce such artifacts but require precise timing of the scan. The choice of protocol depends on the clinical task, anatomy, and available equipment. [37]

Metal clips and stents can cause distortions. "Quiet" non-contrast sequences and wall imaging with blood signal suppression improve diagnostic yield in this patient population. [38]

For dynamic series, it is important to ensure a sufficient frame rate to separate the arterial from the venous phases and accurately assess bypass. Incorrect timing will lead to venous overlap and reduced specificity. [39]

In the venous system, slow flow, variations in anatomy, and partial volume averaging can create the appearance of defects. Contrast 3D series and comparison with conventional sequences help avoid errors. [40]

Table 8. When to repeat the survey or change the protocol

Problem	What to do
Signal loss in turbulence zones	Add a contrast series or change the parameters of a non-contrast series
Venous overlay in the arterial phase	Use time sequences with higher frame rates
Metal-induced distortion	Apply field suppression modes and "silent" sequences
Doubts about the degree of stenosis	Agree on the measurement method and, if necessary, supplement it with an alternative method
Patient immobility	Repeat short section with head restraint or light sedation

Interpretation of results and next steps

The conclusion should include the anatomical segments, the degree of stenosis according to the agreed-upon method, and signs of plaque instability. To ensure consistency in measurements, the 2023 vascular surgery guidelines detail how to correlate methods and convert percentages between approaches. This facilitates comparison with studies using other modalities and dynamic follow-up. [41]

If significant stenosis and associated symptoms are detected, the patient is referred for vascular consultation to determine drug therapy or intervention. If signs of unstable plaque are pronounced, visualization of the wall becomes crucial for risk stratification. [42]

During dissection, the decision on tactics depends on the extent of the hematoma, the patency of the true lumen, and the neurological status. Magnetic resonance angiography with wall assessment allows monitoring the dynamics of reparation and the risk of ischemia. [43]

In venous thrombosis, imaging serves as the basis for timely initiation of anticoagulant therapy and monitoring of recanalization. Repeated studies are performed as clinically indicated. [44]

Table 9. Standardized Report: Key Fields

Chapter	Content
Anatomy	Segments of the carotid and vertebral arteries, variations of the circle of Willis
Measurements	Percentage of stenosis with indication of the adopted technique
Plaque	Signs of instability based on wall imaging
Venous system	Patency of sinuses and presence of collaterals
Recommendations	Need for consultations and possible additional research

Frequently asked questions

Do all patients require contrast? No. In many cases, non-contrast modes are sufficient. Contrast improves accuracy when flow dynamics, complex hemodynamics, or significant artifacts without contrast are important. The decision is individual. [45]

Is gadolinium dangerous during breastfeeding? Stopping breastfeeding is usually not necessary, as very little of the drug enters milk. This issue is addressed in the 2024 contrast media guidelines. [46]

What should be done in chronic kidney disease? Modern macrocyclic drugs have an extremely low risk of nephrogenic systemic fibrosis. The decision is made by the physician, taking into account the clinical benefit. Dialysis is usually not required due to the administration itself. [47]

How does magnetic resonance angiography differ from computed tomography angiography? Magnetic resonance angiography (MRA) does not involve radiation or iodine and is better at characterizing soft-tissue plaque components and the wall, while MRA is superior for calcifications and precise lumen measurements. These methods are often used in combination. [48]