Experiences with an intraoperative magnetic resonance imaging system in neurosurgery

After reading and studying the article on intraoperative magnetic resonance imaging (MRI), nurses will be able to

1. explain the basic concept of MRI,

2. discuss MRI system hardware components,

3. describe working in an intraoperative MRI environment, and

4. identify nursing responsibilities in the intraoperative MRI environment.

This program meets criteria for CNOR and CRNFA recertification, as well as other continuing education requirements.

A minimum score of 70% on the multiple-choice examination is necessary to earn 3.9 contact hours for this independent study.

Purpose/Goal: To educate perioperative nurses about using portable intraoperative magnetic resonance imaging during neurosurgery.

Dianne Carter-Gentry, RN, MSN, FNP-BC, is a part-time instructor at the University of Louisville School of Nursing, Louisville, Ky, and a family nurse practitioner.

Peter M. Black, MD, PhD, pioneered the use of magnetic resonance imaging (MRI) equipment for surgical intervention in January 1994 at Brigham and Women's Hospital, Boston. (1) Several problems had to be resolved before MRI technology could be used successfully in the OR. For example, standard surgical instruments distorted the magnetic field created by the MRI machine, so nonmagnetic (eg, titanium, plastic, glass) instruments had to be developed. Another problem encountered during these pioneering surgical procedures was that movement was inhibited around the two large magnets on either side of the patient. (2) In spite of these significant obstacles, the use of intraoperative MRI in surgery has resulted in more precise neurosurgical interventions. (3)

ACQUIRING INTRAOPERATIVE MRI CAPABILITIES AT UNIVERSITY HOSPITAL

University Hospital, Zurich, Switzerland, was the third hospital in the world to acquire an open interventional MRI system (Figure 1). This prototype had a vertical gap in its magnet that provided physical space in which surgeons performed surgical procedures. Surgeons began using this unit in mid 1996. (1) By the end of 2000, 142 stereotactic procedures had been performed, of which 114 were brain biopsy procedures and 28 were craniotomies for tumor excision and other related neurosurgical procedures.

[FIGURE 1 OMITTED]

In July 2000, an improved model was installed at University Hospital. After the machine was installed, a third operating theatre was opened in the neurosurgery department at University Hospital.

How DOES MRI WORK?

An intraoperative MRI system is not limited to electronics or machinery; it also includes the surgical environment in which it functions. This surgical environment consists of the physical nature of the OR, the surgical procedures performed, and training of personnel required to operate the system.

It is vital that all surgical team members understand how an MRI machine works.

Human tissue is made up of atoms. Hydrogen, the most common atom in the human body, is found in both water and fat. A magnetic resonance (MR) image is based almost exclusively on the study of hydrogen protons. An MRI machine is a sophisticated radio transmitter and receiver that creates radiowave energy, which is absorbed by body tissue. When radio waves (ie, electromagnetic waves at a particular radio frequency [RF]) are applied to hydrogen protons, the protons gain energy and spiral out of steady-state orientation. The frequency at which this occurs is called resonance. (3)

When the radio-wave frequency causing proton excitation is removed, the protons relax and return to their steady-state orientation. This relaxation process takes time and is dependent on the magnitude of the tissue molecules and the surrounding biological composition. The sharp image contrasts obtained by an MRI machine are the result of accurately measuring different tissue types with different relaxation times. More specifically, protons and hydrogen nuclei in the body are like small magnets that are oriented in random directions under normal conditions. During neurosurgical MRI, the patient's head is placed in a strong magnetic field, and a small portion of the patient's protons will align in the same direction as the magnetic field. This small population of protons absorbs and subsequently releases radio-wave energy, which produces the MR image. (4)