In anxious patients, the MRI environment -- confinement, acoustic noise, immobility, and diagnostic uncertainty -- can sustain or amplify activation of the sympathetic nervous system. Anxiety, therefore, should not be regarded solely as a subjective experience, but as a physiological condition associated with increased noradrenergic tone. Peripheral veins of the upper limb, commonly used for intravenous access in MRI, are sympathetically innervated and respond to this activation with an increase in venous smooth muscle tone.
Giuseppe Scappatura
The result is a functional reduction in venous compliance: The vessel remains patent but becomes less distensible. This distinction is critical in MRI practice. Venous access is generally assessed under static, low-pressure conditions before the patient enters the scanner. These checks confirm patency, but they do not provide information on how the vein will behave under dynamic conditions -- namely, during automated, high-flow contrast administration. During the interval between cannulation and injection, particularly in anxious patients, effective venous compliance may therefore decrease to a clinically relevant extent.
This leads to what can be described as a "static-dynamic dissociation." An access that appears stable and reliable during initial assessment may become mechanically unstable at the time of injection because venous compliance has changed. Even modest functional narrowing of the venous lumen can have significant mechanical consequences. Because the pressure required to sustain a given flow increases nonlinearly as vessel radius decreases, small reductions in effective diameter can result in disproportionate increases in injection pressure.
This phenomenon concentrates mechanical stress at the catheter-vein interface: Reduced venous compliance limits the vessel’s ability to accommodate the pressure rise induced by high-flow injection, causing localized stress to be transferred to the point of contact between catheter and vessel wall. The consequence is an increased risk of microdislodgement of the catheter tip or focal leakage, even when technique is formally correct.
This physiological model helps explain why contrast extravasation in MRI can occur despite conservative flow rates and proximal access sites. It also provides an interpretive framework for understanding why such events may be less evident or recognized later than in other imaging contexts. Gadolinium-based contrast agents are often administered in relatively small volumes and have favorable rheological properties, which may attenuate early pain and edema. In addition, during MRI, the injection site is frequently not directly visible, making recognition based solely on local symptoms less reliable.
Viewing anxiety as a procedural variable, therefore, allows certain extravasation events to be reinterpreted not as unpredictable occurrences or the result of a single technical shortcoming, but as the outcome of a combination of dynamic physiological factors that develop over the course of the examination. In anxious patients, sympathetic activation may persist over time and may even intensify during prolonged time spent in the MRI bore. This state of arousal is not a point event related to venipuncture, but a process that evolves throughout the scan.
Progressive reduction in vagal tone and sympathetic predominance produces a form of intra-examination autonomic drift, altering peripheral vascular behavior without generating immediately apparent clinical signs. Additional anxiety-related factors may contribute: Increased peripheral muscle tone, even in the absence of voluntary movement, can raise extravascular pressure on the limb; altered respiratory patterns, such as shallow or irregular breathing, can influence intrathoracic pressure and venous return; and reduced autonomic self-regulation, reflected by decreased heart rate variability, limits the patient’s ability to return to a more physiologically relaxed state during the examination.
Taken together, these considerations support interpreting contrast extravasation in MRI as a dynamic phenomenon influenced by time, patient physiology, and the examination environment. In increasingly automated and AI-supported MRI workflows, this perspective does not diminish the value of technology but clarifies its limits. AI can standardize processes and reduce technical variability, but the patient remains a biologically open system that evolves over time and responds to context. When technique and technology are appropriate, yet outcomes still vary, it is this human variability that becomes evident -- reinforcing the central role of clinical observation and understanding of the patient in ensuring safety during contrast-enhanced MRI.
Giuseppe Scappatura is a radiology technician at the Grande Ospedale Metropolitano Bianchi Melacrino Morelli in Reggio Calabria, Italy.
The comments and observations expressed are those of the author and do not necessarily reflect the opinions of AuntMinnie.com.
