“The need for patient monitoring in MRI will continue to grow”

Madhu Nair

As MRI technology continues to evolve, MR systems of high magnetic field strengths, faster gradient fields, and large amounts of radio frequency (RF) energy will become commonplace. The evolution of MRI technologies and applications in neuro-imaging, MR guided surgery, and cardiovascular MRI has increased and will continue to increase the level of patient acuity in MRI. Therefore, the need for patient monitoring in MRI will continue to grow.

This article discusses why patient monitoring systems are important in MRI, specifically during cardiovascular MRI (CVMRI) procedures.

Why is it important to have patient vital signs monitoring systems readily available in the MRI area?

Monitoring of patient vital signs during an MRI procedure should take place whenever monitoring of that patient is part of routine care or the patient is unable to alert a health care provider of either pain, cardiac, or respiratory problems. Additionally, a patient should be monitored if there is any concern that the patient’s physiologic state could change abruptly during the MRI procedure.

Because contrast agents used daily in the MRI have the potential for causing adverse effects and reactions, it is recommended that MRI vital signs monitoring systems be readily available in the MRI room for situations where a patient might experience side effects from contrast agents. Although, extremely rare, side effects related to the use of MR contrast agents can be fatal.

The Safety Committee of the Society for Magnetic Resonance Imaging has published guidelines and recommendations concerning the monitoring of patients during MR procedures. This information indicates that all patients undergoing MR procedures should be monitored with a camera or intercom system; and patients who are sedated, anaesthetised, or unable to communicate should have appropriate vital signs monitoring.

Why can’t conventional patient vital signs monitoring systems be used in MRI?

Several factors affect the safety and performance of patient monitoring during MRI procedures. Ferromagnetic components such as transformers, chassis components, and accessories can be strongly attracted by the large static magnetic field associated with the MRI system. This poses a serious missile’ hazard to patients, clinicians, and the MR System. Only patient monitoring systems designed with a minimal amount of ferrous metal should be placed in the MRI room.

Radio frequency (RF) energy emitted from the MRI system can adversely affect the operation of standard vital signs monitors. In addition, the monitor may emit RF interference that will cause artifact to be present on the MR images. Therefore, MRI patient monitoring systems must not only be designed with shielding to protect them from RF inferences but must also be designed to not emit RF interference.

The electromagnetic fields generated during MRI sequences cause electrical interference (gradient artifact) on patient vital signs. Consequently, all patient vital signs parameters must contain filters that remove gradient artifact from the vital signs before processing, analysis and display.

What is the relationship between cardiac gating and patient monitoring in MRI?

The use of MRI of imaging of the cardiovascular system, cardiovascular MRI (CVMRI), has recently evolved and with it the need for cardiac gating. MRI systems are configured with cardiac gating modules that acquire patients’ cardiac (ECG) single sthrough cardiac(ECG) electrodes and lead wires. MRI systems manufacturers are quick to point out the aeh ECG signal obtained from cardiac gating systems cannot be used for physical monitoring of a patient’s vital signs. Therefore, if patient monitoring is a requirement, then a patient monitoring system must be used in conjunction with the cardiac gating module. This situation poses a problem with MRI systems manufacturers who discourage placing two sets of leads and electrodes on a patient. Patient monitoring systems designed specifically for use in th MRI, such as the Magnitude MRI Patient Vital Signs Monitoring System from INvivo research, are designed with cardiac gating interfaces that utilise the ECG signal generated at the patient vital signs monitoring system for cardiac gating of the MRI system. This interface allow apatient monitoring and cardiac gat to tale place simultaneously and eliminates the need to place two sets of cardiac electrodes on the patient. The Magnitude also provides the MRI cardiac gating module with a dital representation of the cardiac signal. This is advantageous because, unlike analog signals, the digital signal does not contain the exaggerated T-wave brought about by haemo-dynamic flow artifact. As a result, the gating performance through the Magnitude is improved due to the reduction in the number of mis triggers during a procedure. Digital gating becomes even more advantageous on 3.0 and 4.0 Tesla MRI systems.

The writer is director with Summit Healthcare Pvt Ltd. Email:summit3@vsnl.com, (M)98201 01821